Journal of Applied Biomechanics, 2015, 31, 229 -236 http://dx.doi.org/10.1123/jab.2014-0166 © 2015 Human Kinetics, Inc.
ORIGINAL RESEARCH
Greater Step Widths Reduce Internal Knee Abduction Moments in Medial Compartment Knee Osteoarthritis Patients During Stair Ascent Max R. Paquette,1 Gary Klipple,2 and Songning Zhang3 1University
of Memphis; 2University of Tennessee Medical Center; 3University of Tennessee
Increased step widths have been shown to reduce peak internal knee abduction moments in healthy individuals but not in knee osteoarthritis patients during stair descent. This study aimed to assess effects of increased step widths on peak knee abduction moments and associated variables in adults with medial knee osteoarthritis and healthy older adults during stair ascent. Thirteen healthy older adults and 13 medial knee osteoarthritis patients performed stair ascent using preferred, wide, and wider step widths. Three-dimensional kinematics and ground reaction forces (GRFs) using an instrumented staircase were collected. Increased step width reduced first and second peak knee abduction moments, and knee abduction moment impulse. In addition, frontal plane GRF at time of first and second peak knee abduction moment and lateral trunk lean at time of first peak knee abduction moment were reduced with increased step width during stair ascent in both groups. Knee abduction moment variables were not different between knee osteoarthritis patients and healthy controls. Our findings suggest that increasing step width may be an effective simple gait alteration to reduce knee abduction moment variables in both knee osteoarthritis and healthy adults during stair ascent. However, long term effects of increasing step width during stair ascent in knee osteoarthritis and healthy adults remain unknown. Keywords: stairs, knee osteoarthritis, load, gait alteration, step width Knee osteoarthritis is the most common type of arthritis1 and is highly prevalent in individuals over the age of 60 in the United States.2 Research shows that peak internal knee abduction moment in early stance, a commonly used surrogate variable for medial knee joint loading,3,4 is greater in medial knee osteoarthritis patients compared with healthy individuals.5,6 Many researchers have investigated the effectiveness of noninvasive therapeutic strategies to reduce peak knee abduction moments and pain in knee osteoarthritis patients during daily activities.7–9 Peak knee abduction moment and its angular impulse correlates with severity and progression of medial knee osteoarthritis.10 Stair walking has been shown to yield greater peak knee abduction moments compared with level walking in medial knee osteoarthritis patients.11 Several gait modification strategies to reduce peak knee abduction moments in knee osteoarthritis patients during level walking have been studied.7,12–17 Even though one of the first complaints from knee osteoarthritis patients during daily activities is difficulty in stair walking,18 only a few studies have examined the effects of gait modifications on reducing the knee abduction moment during stair walking. These gait modifications aim to provide early noninvasive intervention options that are simple and safe to implement. During stair ascent, greater toe-out angle (ie, external rotation of the feet) reduced the second peak knee abduction moment (late stance) but did not change the first peak knee abduction moment Max R. Paquette is with the Department of Health & Sport Sciences, University of Memphis, Memphis, TN. Gary Klipple is with the Division of Rheumatology, University of Tennessee Medical Center, Knoxville, TN. Songning Zhang is with the Department of Kinesiology, Recreation and Sport Studies, The University of Tennessee, Knoxville, TN. Address author correspondence to Songning Zhang at [email protected].
(early stance) in medial knee osteoarthritis patients.11 Our previous work shows that increasing step width reduced first and second peak knee abduction moments in healthy individuals,19 but not in medial knee osteoarthritis patients during stair descent.20 Certain gait modification strategies can reduce peak knee abduction moment during stair walking in healthy and medial knee osteoarthritis patients, but it is currently unknown whether increased step width would have similar effects on knee abduction moment in stair ascent. A number of biomechanical variables have been associated with peak abduction moments during gait tasks. The frontal plane GRF and its moment arm are components of the knee abduction moment and can explain changes in abduction moment, especially in medial knee osteoarthritis patients.21 Furthermore, lateral trunk lean toward the stance limb has been negatively correlated to first peak knee abduction moment in medial knee osteoarthritis patients during gait.8,15 These findings suggest that, along with toe-out angle, frontal plane GRF and lateral trunk lean are important variables to explain changes in knee abduction moment. Thus, these variables could provide important information to understand mechanisms responsible for changes in knee abduction moment caused by gait modifications during gait tasks. The purpose of this study was to assess the effects of increased step width on peak knee abduction moments, abduction moment impulse, and on variables associated with knee abduction moment between medial knee osteoarthritis patients and healthy older adults during stair ascent. We hypothesized that increased step width would reduce peak knee abduction moments and abduction moment impulse, reduce frontal plane GRF, and increase lateral trunk lean. We also hypothesized that peak knee abduction moments, abduction moment impulse, frontal plane GRF, and lateral trunk lean would be greater in medial knee osteoarthritis patients compared with healthy controls during stair ascent. 229
230 Paquette, Klipple, and Zhang
Downloaded by University of Iowa Libraries on 09/16/16, Volume 31, Article Number 4
Methods Thirteen (7 women) healthy adults were recruited to participate in the study (58.9 ± 8.3 y, 67.9 ± 8.1 kg, 1.68 ± 0.16 m). The exclusion criteria for the healthy adult group included: knee pain in the past 6 months, diagnosis of any lower limb joint osteoarthritis, knee replacement, or surgery or intra-articular injection during the past 3 months. Twenty-one older adults who qualified for the knee osteoarthritis group were asked to attend a radiography session. A posterior view radiograph including both knees was performed for each participant with knees slightly flexed. A sagittal plane radiograph for each knee in slight flexion was performed one at a time during standing. A rheumatologist evaluated the radiographs for knee osteoarthritis severity using the Kellgren-Lawrence (K/L) scale.22 After radiographic screening, 13 participants (8 women) qualified for the knee osteoarthritis group (62.5 ± 9.0 y, 83.5 ± 24.0 kg, 1.71 ± 0.12 m) based on inclusion/exclusion criteria (Table 1). An a priori power analysis was conducted using first peak knee abduction moments of healthy adults during stair descent with 3 different step widths,19 and showed that a minimum of 12 subjects per group were needed to obtain a power of 0.8 at an alpha level of .05 (G*Power, 3.1). Before participating in data collection, all participants signed an informed consent document approved by the institutional review board. A 9-camera motion analysis system (240 Hz, Vicon Motion Analysis Inc., Oxford, UK) was used to obtain three-dimensional (3D) kinematics during testing. Reflective anatomical markers were placed bilaterally on the second toes, first and fifth metatarsal heads, medial and lateral malleoli, medial and lateral femoral epicondyles, greater trochanters, iliac crests, and acromion processes. The markers on the malleoli and first and fifth metatarsal heads were used to define the proximal and distal joint centers of the foot, respectively. The hip joint center positions were defined by two virtual markers located at 25% of the line between the greater trochanter markers as per the Visual3D pelvis model.23 The same researcher placed the markers on all participants. Clusters of 4 reflective markers on semirigid thermoplastic shells were used as tracking markers and placed on the trunk, pelvis, thigh, and shank. Four discrete tracking markers were placed on the medial, posterior, lateral, and dorsal–lateral aspects of the heel counter of a standard laboratory running shoe (Noveto, Adidas, Germany). An instrumented 3-step staircase (Force Plate-Stairs, American Mechanical Technology Inc., Watertown, MA) with 2 additional customized wooden steps (fourth and fifth steps) was used in the study (Figure 1). The stairs
bolted onto 2 force platforms (1200 Hz, BP600600 and OR-6–7, American Mechanical Technology Inc., Watertown, MA) and were used to measure GRF and moments. After installation of the staircase onto the 2 force platforms, the force platforms were zeroed first on the amplifiers of the force platforms and then in the Vicon Nexus software. All participants completed the Knee Injury and Osteoarthritis Outcome Score (KOOS) survey to obtain self-reported knee pain, knee functions, and functions of daily activities including stair walking.24 Healthy adults filled out the KOOS survey for their dominant limb while knee osteoarthritis participants assessed their most
Figure 1 — Illustration of the instrumented staircase used during testing, with the step of interest.
Table 1 Exclusion and inclusion criteria for medial compartment knee osteoarthritis group Exclusion
Inclusion
Diagnosed with lateral compartment knee osteoarthritis (joint space narrowing)
Radiographically diagnosed with medial compartment knee osteoarthritis (joint space narrowing score of at least 1), with or without patellofemoral knee osteoarthritis, with a grade 1–4 on the Kellgren-Lawrence scale
Osteoarthritis symptoms at the ankle or hip joint Any lower extremity joint replacement Any lower extremity joint arthroscopic surgery or intraarticular injection within past 3 months
Knee pain for at least 6 months during daily activities, including stair negotiation, on most days of the week
Systemic inflammatory arthritis Body mass index greater than 35 Inability to ascend or descend stairs without use of handrails Neurologic disease Lower back pain referred to the lower limbs JAB Vol. 31, No. 4, 2015
Downloaded by University of Iowa Libraries on 09/16/16, Volume 31, Article Number 4
Step Width and Knee Osteoarthritis in Stair Ascent 231
affected limb based on the K/L grade. Before the testing trials, all participants performed 3 stair ascent practice trials using the wider step width to establish mean preferred ascent speed. Two pairs of photo cells (63501 IR, Lafayette Instrument Inc., Lafayette, IN) and 2 electronic timers (54035A, Lafayette Instrument Inc., Lafayette, IN) were used to monitor walking speed. A range (mean ± 5%) of self-selected speed was then used to control each participant’s stair ascent speed during testing. Participants performed 5 trials in each of the following conditions: preferred step width, wide step width, and wider step width. Based on the preferred step width of healthy adults during level walking of 13% of leg length,25 the wide and wider step width conditions were set at 26% and 39% of leg length, respectively. The leg length was measured as the vertical distance between the anterior superior iliac spine and the medial malleolus of the tested limb measured in a standing position. Step width was measured as the medial–lateral distance between the centers of mass of both feet. Center of mass of the feet was defined by the mathematical anthropometric model of Hanavan26 in Visual3D. All testing conditions were randomized. Before each new condition, participants were given 2 or 3 practice trials to become familiar with the new step width condition. Black ink was marked on a strip of masking tape, which was placed on each step to control step width. For the wide and wider step width conditions, participants were instructed to cover the ink mark with their foot. Participants were not allowed to use the handrail unless they needed support to prevent a fall, and any trials in which a subject used the handrail were repeated. Healthy adults climbed the stairs with the self-reported dominant limb on the step of interest (third step from the ground, Figure 1) and knee osteoarthritis participants climbed with the most affected limb (based on the K/L grade, which also corresponded to the most symptomatic limb) on the step of interest. Participants reported their knee pain for both limbs using a 0 mm to 100 mm visual analog scale (VAS; 100 mm indicating worst possible pain). Visual3D software suite (C-Motion, Inc., Germantown, MD) was used to compute biomechanical variables. A right-hand rule
with a Cardan rotational sequence (X-y-z) was used for the 3D angular computations (X: mediolateral axis; y: anteroposterior axis; z: vertical axis). Knee joint moments were computed as internal moment and were expressed in the thigh coordinate system. Kinematic and GRF data were filtered using a fourth-order Butterworth zero-lag low-pass filter with a cut-off frequency of 8 Hz.27 The GRF data were normalized to body weight (BW) and joint moments to body mass (N∙m/kg). The knee abduction moment angular impulse was calculated with the integration of the negative portions of the abduction moment and time in the first and second halves of stance. The lateral trunk lean angle was measured as the frontal plane trunk angle at times of first (KAM1) and second (KAM2) peak knee abduction moment and was expressed in the pelvis coordinate system. Foot progression angle was measured as the transverse plane foot deviation angle from the anteroposterior axis of the laboratory coordinate system at midstance. A one-way analysis of variance (ANOVA) was performed for all participant characteristics. A nonparametric Mann–Whitney U test was used to assess the 5 KOOS subscale scores between groups. A separate Mann–Whitney U test was used to compare knee pain between groups and between the 3 step width conditions. A 2 × 3 (group × step width) repeated-measures ANOVA was performed to compare knee abduction moments and other selected variables between step width conditions and groups (SPSS v. 19.0, IBM, Chicago, IL). When an ANOVA revealed a main effect of step width, post hoc comparisons with least significant difference (LSD) were used to compare means between step width conditions. The alpha level was set a priori to .05.
Results Body mass and body mass index (BMI) were significantly higher in the knee osteoarthritis group compared with the healthy group (Table 2). The scores for all KOOS subscales were significantly
Table 2 Participant characteristics and KOOS results, mean ± SD (95% confidence interval) Variables Number of participants Age (y) Mass (kg) Height (m) Body mass index (kg/m2) Leg length (m) Kellgren-Lawrence grade of participants
KOOS—symptoms (%) KOOS—pain (%) KOOS—activities of daily living (%) KOOS—sport/recreation (%) KOOS—quality of life (%)
Healthy
Knee Osteoarthritis
P values
13 58.9 ± 8.3 (53.9–64.0) 67.9 ± 8.1 (62.9–72.8) 1.68 ± 0.16 (1.65–1.72) 23.9 ± 2.6 (22.5–25.3) 0.86 ± 0.04 (0.83–0.88) –– –– –– –– 94.8 ± 5.6 (91.4–98.2) 98.7 ± 3.1 (96.8–100.6) 98.6 ± 2.6 (97.1–100.2) 94.6 ± 13.1 (86.7–102.6) 94.7 ± 8.4 (89.7–99.8)
13 62.5 ± 9.0 (57.1–68.0) 83.5 ± 24.0 (69.0–98.0) 1.71 ± 0.12 (1.64–1.79) 28.3 ± 6.5 (24.3–32.2) 0.87 ± 0.09 (0.82–0.92) 2 (Grade 1) 5 (Grade 2) 5 (Grade 3) 1 (Grade 4) 72.0 ± 11.1 (65.3–78.7) 71.1 ± 11.5 (64.2–78.1) 75.8 ± 15.2 (66.6–85.0) 54.6 ± 23.9 (40.2–69.0) 57.7 ± 15.8 (48.2–67.2)
–– .298 .037 .494 .032 .601 –– –– –– –– < .001 < .001 < .001 < .001 < .001
Abbreviation: KOOS = Knee Injury and Osteoarthritis Outcome Score. Note. P-value for group difference: differences between groups in KOOS scores were assessed using Mann–Whitney U test. Bold values indicate significance at p < .05. JAB Vol. 31, No. 4, 2015
Downloaded by University of Iowa Libraries on 09/16/16, Volume 31, Article Number 4
232 Paquette, Klipple, and Zhang
greater in knee osteoarthritis subjects compared with healthy subjects (Table 2). Healthy adults had no pain for all 3 step width conditions, while knee osteoarthritis patients had VAS pain scores of 13.5 ± 15.0 mm for preferred step width, 12.9 ± 16.9 mm for wide step width, and 10.7 ± 11.6 mm for wider step width. VAS pain scores were significantly greater in knee osteoarthritis patients compared with healthy adults (P < .001) but not different between step width conditions. The average self-selected stair ascent walking speed was slightly slower in knee osteoarthritis patients (0.52 ± 0.09 m/s) compared with healthy adults (0.60 ± 0.06 m/s, P = .044). In general, increased step width reduced KAM1 and KAM2 and the knee abduction moment angular impulse in both healthy adults and medial compartment knee osteoarthritis patients, but no differences in abduction moment variables were observed between groups. Specifically, KAM1 was reduced in wide (P = .011) and wider step width (P < .001) conditions compared with the preferred step width condition, and in the wider condition compared with the wide step width condition (P = .002; Table 3). KAM2 was reduced in the wide (P < .001) and wider step width (P < .001) conditions compared with preferred step width, and in the wider condition compared with the wide step width condition (P < .001). Knee abduction moment angular impulse was reduced in wide (P < .001) and wider step width (P < .001) conditions compared with preferred step width, and in the wider condition compared with the wide step width condition (P < .001). Absolute step width and normalized step width (percent leg length) were both significantly greater in wide (P < .001) and wider step width (P < .001) conditions compared with preferred step width, and in the wider condition compared with the wide step width condition (P < .001; Table 4). Finally, lateral trunk lean at the time of KAM1 was greater in knee osteoarthritis patients compared with healthy adults, and smaller in the wider step width condition compared with the preferred step width condition (P = .010; Table 4). First peak vertical GRF was greater in knee osteoarthritis subjects compared with healthy subjects (P = .001; Table 4). Peak frontal plane GRF at the time of KAM1 was smaller in wide (P = .001) and wider step width (P < .001) conditions compared with preferred step width. Peak frontal plane GRF at the time of KAM2 was greater in healthy subjects compared with knee osteoarthritis patients (P = .016), and was smaller in the wider step width condition compared with the wide (P = .020) and preferred step width (P = .001) conditions.
Discussion The purpose of this study was to assess the effects of increased step width on peak knee abduction moments, abduction moment impulse, and associated variables between medial knee osteoarthritis patients and healthy older adults during stair ascent. Our main finding was that KAM1, KAM2, and abduction moment impulse were all significantly reduced with increased step width. These results support our hypothesis and are in agreement of our earlier work that noted increased step width led to reductions in peak abduction moments in healthy older adults,19 but the results are not in agreement with previous findings of knee abduction moment with increased step width in knee osteoarthritis patients during stair descent.20 Stair descent requires primarily negative joint work (ie, eccentric muscle action) to counteract the downward center of mass acceleration, whereas stair ascent requires mostly positive joint work (ie, concentric muscle action) to pull the body up onto the next step.28
These task differences between descent and ascent may be linked to the different effects of increased step width on knee abduction moments. Guo et al11 have shown that increasing toe-out angle (ie, externally rotated foot progression angle) reduced KAM2 in pain free medial compartment knee osteoarthritis patients during stair ascent compared with preferred foot progression angle. In the current study, foot progression angle did not change with increased step width. Guo et al11 suggest that a lateral displacement in the center of pressure location in late stance might be responsible for moving the GRF vector closer to the knee joint center to shorten the moment arm and, in turn, reduce the abduction moment with an increased foot progression angle. Hunt et al21 showed significant positive correlations between peak stance phase knee abduction moment and frontal plane knee moment arm in knee osteoarthritis patients during gait. In the current study, the reductions in peak knee abduction moments and frontal plane GRF at times of KAM1 and KAM2 suggest reduced moment arms of the frontal plane GRF with increased step width. Thus, it appears that step width may be successful in altering frontal plane mechanics to elicit reductions in knee-abduction-moment-related variables during both level and stair walking. Mundermann et al29 have shown that increased lateral trunk sway significantly reduces peak KAM1 during level walking in healthy adults from the same mechanism suggested with toe-out angle (ie, lateral shift of the center of pressure11). In the current study, increased step width reduced lateral trunk lean during stair ascent. Therefore, lateral trunk lean is likely not responsible for reductions in abduction moments. Similar to what has been previously suggested with toe-out angle and lateral trunk sway,11,15,29 step width alterations may not only lead to a lateral shift in the center of pressure, but also to changes in lower extremity limb alignment in the frontal plane and, as a result, alter peak knee abduction moment during gait. Specifically, an increase in step width may result in an inward motion of the knee (ie, medial thrust gait pattern30) which could decrease the GRF vector moment arm to the knee joint center and thus explain the reductions in peak knee abduction moment and abduction moment angular impulse during gait tasks. Our results strongly suggest that the reduced KAM1 and KAM2 are due to reduced moment arms to knee joint center (ie, no changes in frontal GRF vector), and that increased step width may have similar implications as increased toe-out angle for reducing abduction moment. However, in comparison with a reduction of only the second peak abduction moment with greater toe-out angle in stair ascent,11 increased step width reduces both abduction peaks along with the abduction impulse and may prove to be a more effective gait modification to reduce peak knee abduction moments during stair ascent. Although there are currently no cross-sectional studies investigating the effects of increased step width on knee joint kinetics, case studies by Zhao et al31 and Fregly30 present peak knee abduction moments during walking using wide step width. While peak stance abduction moment does not appear to be different in the study by Zhao et al,31 the estimated values from knee abduction moment curves reported by Fregly et al32 show distinct reductions in KAM1 and KAM2 during a wide step width compared with normal gait. Contrary to our third hypothesis, our findings failed to show differences in abduction moment variables between medial compartment knee osteoarthritis patients and healthy older adults during stair ascent. Previous studies show that knee osteoarthritis patients tend to ambulate over level ground with lower peak knee abduction
JAB Vol. 31, No. 4, 2015
JAB Vol. 31, No. 4, 2015
233
–0.24 ± 0.12
–0.30 ± 0.11 –0.15 ± 0.04
Knee abduction impulse (N∙m/kg·s)a,b,c –0.10 ± 0.04
–0.19 ± 0.10
–0.29 ± 0.08
Wider
–0.17 ± 0.07
–0.26 ± 0.14 –0.15 ± 0.07
–0.22 ± 0.11
–0.36 ± 0.11
Wide
Wider
–0.13 ± 0.07
–0.18 ± 0.11
–0.33 ± 0.10
Knee Osteoarthritis –0.37 ± 0.12
Preferred
Abbreviations: KAM1 = internal knee abduction moment, first peak; KAM2 = internal knee abduction moment, second peak. Note. A negative value indicates knee abduction moment or angular impulse. Bold values indicate significance at p < .05. a Wide step width significantly different from preferred step width. b Wider step width different from preferred step width. c Wider step width different from wide step width.
–0.12 ± 0.04
–0.32 ± 0.08
–0.36 ± 0.08
KAM1
KAM2 (N∙m/kg)a,b,c
Wide
Healthy
(N∙m/kg)a,b,c
Preferred
.65
< .001
.28
.42
< .001
< .001
Group
Step Width
P values
.47
.13
.34
Interaction
Table 3 Frontal plane knee moment variables for all three step width conditions (mean ± SD) in healthy and knee osteoarthritis groups
Downloaded by University of Iowa Libraries on 09/16/16, Volume 31, Article Number 4
234
JAB Vol. 31, No. 4, 2015
Absolute step width
(°)b,c,# –2.8 ± 2.5
–2.9 ± 2.6
1.9 ± 2.6
2.1 ± 2.5 –3.2 ± 2.6
1.7 ± 2.6
12.9 ± 3.3
1.05 ± 0.16
0.90 ± 0.10
1.13 ± 0.14
37.1 ± 2.8
0.32 ± 0.03
Wider
–1.3 ± 2.1
4.2 ± 2.6
13.0 ± 4.0
0.98 ± 0.10
0.92 ± 0.05
1.52 ± 0.44
17.1 ± 4.6
0.15 ± 0.04
–1.4 ± 2.5
4.3 ± 3.0
12.5 ± 4.3
0.99 ± 0.09
0.91 ± 0.07
1.50 ± 0.43
24.1 ± 2.2
0.21 ± 0.02
Wide
Wider
–1.6 ± 2.4
3.7 ± 2.7
12.7 ± 4.6
0.92 ± 0.12
0.90 ± 0.10
1.51 ± 0.43
35.9 ±3.1
0.31 ± 0.03
Knee Osteoarthritis Preferred
.14
.12
.044
.005
.012
.002
.82
.72 .28
.007
.83
< .001 .10
.64
< .001
< .001
Group
P values Step Width
.83
.52
.40
.15
.12
.61
.20
.37
Interaction
Abbreviations: GRF = ground reaction force; BW = body weight; KAM1 = internal knee abduction moment, first peak; KAM2 = internal knee abduction moment, second peak. Note. Normalized step width is normalized to leg length; foot progression angle was measured at midstance; a positive foot progression angle value indicates a toe-out angle relative to the anteroposterior axis of the laboratory coordinate system; negative lateral trunk lean value indicates a trunk lean toward the stance limb in frontal plane. Bold values indicate significance at p < .05. a Wide step width significantly different from preferred step width. b Wider step width different from preferred step width. c Wider step width different from wide step width. # Different between groups.
Lateral trunk lean at time of KAM2 (°)
Lateral trunk lean at time of KAM1
Foot progression angle (°)
12.2 ± 4.3
1.07 ± 0.13
1.10 ± 0.11
(BW)b,c,# 12.2 ± 3.5
0.91 ± 0.08
0.94 ± 0.08
Frontal GRF at time of KAM2
1.13 ± 0.15
1.15 ± 0.15
24.1 ± 2.4
15.4 ± 3.1
Frontal GRF at time of KAM1 (BW)a,b
0.21 ± 0.02
0.13 ± 0.03
Wide
Healthy
First peak vertical GRF (BW)
Normalized step width (%)a,b,c
(m)a,b,c
Preferred
Table 4 Additional kinematic and kinetic variables for all three step width conditions (mean ± SD) in healthy and knee osteoarthritis groups
Downloaded by University of Iowa Libraries on 09/16/16, Volume 31, Article Number 4
Downloaded by University of Iowa Libraries on 09/16/16, Volume 31, Article Number 4
Step Width and Knee Osteoarthritis in Stair Ascent 235
moments compared with healthy individuals.5,6 Our finding is not surprising, as frontal plane GRF at times of KAM1 and KAM2 were also not different between groups. One possible explanation for this finding may be attributed to the slower stair ascent speed in knee osteoarthritis subjects compared with older healthy adults. The slower walking speed in knee osteoarthritis patients would be expected to yield a smaller first peak vertical GRF and, in turn, at least a smaller KAM1. However, first peak vertical GRF was greater in knee osteoarthritis patients compared with healthy adults. The participants ascended the stairs at a self-selected walking speed which represented their daily stair ascent gait behavior. Furthermore, although the K/L grades of our knee osteoarthritis patients were mostly moderate, the initial low levels of knee pain and high scores on the KOOS for activities of daily living reported by the knee osteoarthritis group may be another explanation for similar abduction moments between groups. Patients with lower levels of pain may not require significant gait alterations that may otherwise be observed in individuals with high levels of knee pain. Although the current findings suggest that acute increases in step width can reduce abduction moments, our results cannot imply long-term effects of reducing medial knee loads during stair ascent. Gait modifications over a prolonged period of time can be uncomfortable7 and thus, such changes to gait patterns should be considered carefully. In the current study, before each stair ascent practice trial, a number of participants mentioned that the wider step width condition felt “strange” or “awkward”. However, after a few trials participants had no further complaints regarding wider step width conditions. Thus, a gait intervention in knee osteoarthritis patients could be useful to understand the chronic effects of increased step width. This study has a number of limitations. Marker placement on the skin of obese patients could have introduced errors in building the models and in increasing skin motion artifact. However, the same researcher placed the markers on all participants, and tracking markers attached to a rigid plastic shell were secured and taped to Velcro neoprene bands to prevent excessive skin motion. In the current study, our knee osteoarthritis participants had low levels of knee pain and high scores on the KOOS for activities of daily living. Thus, our findings can only be generalizable to high-functioning medial compartment knee osteoarthritis patients. This is the first study to assess the effects of increased step width on frontal plane knee mechanics in knee osteoarthritis patients during stair ascent. Our findings of reduced peak abduction moments and abduction moment impulse with increased step width suggest that increasing step width may be an effective and acute strategy to reduce medial knee loads. In addition, it appears that reductions in frontal plane GRF and its moment arm to the knee joint center may be responsible for reductions in abduction moment variables with increased step width. Future studies should investigate the chronic effects of increased step width on knee joint loading variables and should also consider knee osteoarthritis patients with higher levels of knee pain. Acknowledgments The study was in part supported by funding from the Opportunity Fund of Office of Research, College of Education, Health and Sport Sciences at the University of Tennessee, and the University of Tennessee Medical Center. The authors would like to thank Joseph Hoekstra for his help with data collection and Ann Holden for her help with radiographic patient screening at the University of Tennessee Medical Center.
References 1. Felson DT, Lawrence RC, Dieppe PA, et al. Osteoarthritis: new insights. Part 1: the disease and its risk factors. Ann Intern Med. 2000;133(8):635–646. PubMed doi:10.7326/0003-4819-133-8200010170-00016 2. Jordan JM, Helmick CG, Renner JB, et al. Prevalence of knee symptoms and radiographic and symptomatic knee osteoarthritis in African Americans and Caucasians: the Johnston County Osteoarthritis Project. J Rheumatol. 2007;34(1):172–180. PubMed 3. Andriacchi TP, Koo S, Scanlan SF. Gait mechanics influence healthy cartilage morphology and osteoarthritis of the knee. J Bone Joint Surg Am. 2009;91(Suppl 1):95–101. PubMed doi:10.2106/JBJS.H.01408 4. Schipplein OD, Andriacchi TP. Interaction between active and passive knee stabilizers during level walking. J Orthop Res. 1991;9(1):113– 119. PubMed doi:10.1002/jor.1100090114 5. Kaufman KR, Hughes C, Morrey BF, Morrey M, An KN. Gait characteristics of patients with knee osteoarthritis. J Biomech. 2001;34(7):907–915. PubMed doi:10.1016/S0021-9290(01)00036-7 6. Mundermann A, Dyrby CO, Andriacchi TP. Secondary gait changes in patients with medial compartment knee osteoarthritis: increased load at the ankle, knee, and hip during walking. Arthritis Rheum. 2005;52(9):2835–2844. PubMed doi:10.1002/art.21262 7. Shull PB, Silder A, Shultz R, et al. Six-week gait retraining program reduces knee adduction moment, reduces pain, and improves function for individuals with medial compartment knee osteoarthritis. J Orthop Res. 2013;31(7):1020–1025. PubMed doi:10.1002/jor.22340 8. Simic M, Hunt MA, Bennell KL, Hinman RS, Wrigley TV. Trunk lean gait modification and knee joint load in people with medial knee osteoarthritis: the effect of varying trunk lean angles. Arthritis Care Res. 2012;64(10):1545–1553. PubMed doi:10.1002/acr.21724 9. Bechard DJ, Birmingham TB, Zecevic AA, Jones IC, Giffin JR, Jenkyn TR. Toe-out, lateral trunk lean, and pelvic obliquity during prolonged walking in patients with medial compartment knee osteoarthritis and healthy controls. Arthritis Care Res. 2012;64(4):525–532. PubMed doi:10.1002/acr.21584 10. Mundermann A, Dyrby CO, Hurwitz DE, Sharma L, Andriacchi TP. Potential strategies to reduce medial compartment loading in patients with knee osteoarthritis of varying severity: reduced walking speed. Arthritis Rheum. 2004;50(4):1172–1178. PubMed doi:10.1002/ art.20132 11. Guo M, Axe MJ, Manal K. The influence of foot progression angle on the knee adduction moment during walking and stair climbing in pain free individuals with knee osteoarthritis. Gait Posture. 2007;26(3):436–441. PubMed doi:10.1016/j.gaitpost.2006.10.008 12. Fregly BJ, Reinbolt JA, Rooney KL, Mitchell KH, Chmielewski TL. Design of patient-specific gait modifications for knee osteoarthritis rehabilitation. IEEE Trans Biomed Eng. 2007;54(9):1687–1695. PubMed doi:10.1109/TBME.2007.891934 13. Simic M, Hinman RS, Wrigley TV, Bennell KL, Hunt MA. Gait modification strategies for altering medial knee joint load: a systematic review. Arthritis Care Res. 2011;63(3):405–426. PubMed 14. Jenkyn TR, Hunt MA, Jones IC, Giffin JR, Birmingham TB. Toe-out gait in patients with knee osteoarthritis partially transforms external knee adduction moment into flexion moment during early stance phase of gait: a tri-planar kinetic mechanism. J Biomech. 2008;41(2):276– 283. PubMed doi:10.1016/j.jbiomech.2007.09.015 15. Hunt MA, Birmingham TB, Bryant D, et al. Lateral trunk lean explains variation in dynamic knee joint load in patients with medial compartment knee osteoarthritis. Osteoarthritis Cartilage. 2008;16(5):591– 599. PubMed doi:10.1016/j.joca.2007.10.017
JAB Vol. 31, No. 4, 2015
Downloaded by University of Iowa Libraries on 09/16/16, Volume 31, Article Number 4
236 Paquette, Klipple, and Zhang 16. Rutherford DJ, Hubley-Kozey CL, Deluzio KJ, Stanish WD, Dunbar M. Foot progression angle and the knee adduction moment: a crosssectional investigation in knee osteoarthritis. Osteoarthritis Cartilage. 2008;16(8):883–889. PubMed doi:10.1016/j.joca.2007.11.012 17. van den Noort JC, Schaffers I, Snijders J, Harlaar J. The effectiveness of voluntary modifications of gait pattern to reduce the knee adduction moment. Hum Mov Sci. 2013;32(3):412–424. PubMed doi:10.1016/j. humov.2012.02.009 18. Costigan PA, Deluzio KJ, Wyss UP. Knee and hip kinetics during normal stair climbing. Gait Posture. 2002;16(1):31–37. PubMed doi:10.1016/S0966-6362(01)00201-6 19. Paquette MR, Zhang S, Milner CE, Fairbrother JT, Reinbolt JA. Effects of increased step width on frontal plane knee biomechanics in healthy older adults during stair descent. Knee. 2014;21(4):821–826. PubMed doi:10.1016/j.knee.2014.03.006 20. Paquette MR, Zhang S, Milner CE, Klipple G. Does increasing step width alter knee biomechanics in medial compartment knee osteoarthritis patients during stair descent? Knee. 2014;21(3):676–682. PubMed doi:10.1016/j.knee.2014.02.020 21. Hunt MA, Birmingham TB, Giffin JR, Jenkyn TR. Associations among knee adduction moment, frontal plane ground reaction force, and lever arm during walking in patients with knee osteoarthritis. J Biomech. 2006;39(12):2213–2220. PubMed doi:10.1016/j.jbiomech.2005.07.002 22. Kellgren JH, Lawrence JS. Radiographic assessment of osteoarthritis. Ann Rheum Dis. 1957;16:494–502. PubMed doi:10.1136/ard.16.4.494 23. Weinhandl JT, O’Connor KM. Assessment of a greater trochanter-based method of locating the hip joint center. J Biomech. 2010;43(13):2633– 2636. PubMed doi:10.1016/j.jbiomech.2010.05.023 24. Roos EM, Toksvig-Larsen S. Knee injury and Osteoarthritis Outcome Score (KOOS) - validation and comparison to the WOMAC in total
knee replacement. Health Qual Life Outcomes. 2003;1:17. PubMed doi:10.1186/1477-7525-1-17 25. Donelan JM, Kram R, Kuo AD. Mechanical and metabolic determinants of the preferred step width in human walking. Proc Biol Sci. 2001;268(1480):1985–1992. PubMed doi:10.1098/rspb.2001.1761 26. Hanavan EP. A Mathematical Model of the Human Body. WrightPatterson Air Force Base; Oct 1964. 27. Kristianslund E, Krosshaug T, van den Bogert AJ. Effect of low pass filtering on joint moments from inverse dynamics: implications for injury prevention. J Biomech. 2012;45(4):666–671. PubMed doi:10.1016/j.jbiomech.2011.12.011 28. DeVita P, Helseth J, Hortobagyi T. Muscles do more positive than negative work in human locomotion. J Exp Biol. 2007;210(Pt 19):3361–3373. PubMed doi:10.1242/jeb.003970 29. Mundermann A, Asay JL, Mundermann L, Andriacchi TP. Implications of increased medio-lateral trunk sway for ambulatory mechanics. J Biomech. 2008;41(1):165–170. PubMed doi:10.1016/j.jbiomech.2007.07.001 30. Fregly BJ. Computational assessment of combinations of gait modifications for knee osteoarthritis rehabilitation. IEEE Trans Biomed Eng. 2008;55(8):2104–2106. PubMed doi:10.1109/ TBME.2008.921171 31. Zhao D, Banks SA, Mitchell KH, D’Lima DD, Colwell CW, Jr, Fregly BJ. Correlation between the knee adduction torque and medial contact force for a variety of gait patterns. J Orthop Res. 2007;25(6):789–797. PubMed doi:10.1002/jor.20379 32. Fregly BJ, Reinbolt JA, Chmielewski TL. Evaluation of a patientspecific cost function to predict the influence of foot path on the knee adduction torque during gait. Comput Methods Biomech Biomed Engin. 2008;11(1):63–71. PubMed doi:10.1080/10255840701552036
JAB Vol. 31, No. 4, 2015
ORIGINAL RESEARCH
Greater Step Widths Reduce Internal Knee Abduction Moments in Medial Compartment Knee Osteoarthritis Patients During Stair Ascent Max R. Paquette,1 Gary Klipple,2 and Songning Zhang3 1University
of Memphis; 2University of Tennessee Medical Center; 3University of Tennessee
Increased step widths have been shown to reduce peak internal knee abduction moments in healthy individuals but not in knee osteoarthritis patients during stair descent. This study aimed to assess effects of increased step widths on peak knee abduction moments and associated variables in adults with medial knee osteoarthritis and healthy older adults during stair ascent. Thirteen healthy older adults and 13 medial knee osteoarthritis patients performed stair ascent using preferred, wide, and wider step widths. Three-dimensional kinematics and ground reaction forces (GRFs) using an instrumented staircase were collected. Increased step width reduced first and second peak knee abduction moments, and knee abduction moment impulse. In addition, frontal plane GRF at time of first and second peak knee abduction moment and lateral trunk lean at time of first peak knee abduction moment were reduced with increased step width during stair ascent in both groups. Knee abduction moment variables were not different between knee osteoarthritis patients and healthy controls. Our findings suggest that increasing step width may be an effective simple gait alteration to reduce knee abduction moment variables in both knee osteoarthritis and healthy adults during stair ascent. However, long term effects of increasing step width during stair ascent in knee osteoarthritis and healthy adults remain unknown. Keywords: stairs, knee osteoarthritis, load, gait alteration, step width Knee osteoarthritis is the most common type of arthritis1 and is highly prevalent in individuals over the age of 60 in the United States.2 Research shows that peak internal knee abduction moment in early stance, a commonly used surrogate variable for medial knee joint loading,3,4 is greater in medial knee osteoarthritis patients compared with healthy individuals.5,6 Many researchers have investigated the effectiveness of noninvasive therapeutic strategies to reduce peak knee abduction moments and pain in knee osteoarthritis patients during daily activities.7–9 Peak knee abduction moment and its angular impulse correlates with severity and progression of medial knee osteoarthritis.10 Stair walking has been shown to yield greater peak knee abduction moments compared with level walking in medial knee osteoarthritis patients.11 Several gait modification strategies to reduce peak knee abduction moments in knee osteoarthritis patients during level walking have been studied.7,12–17 Even though one of the first complaints from knee osteoarthritis patients during daily activities is difficulty in stair walking,18 only a few studies have examined the effects of gait modifications on reducing the knee abduction moment during stair walking. These gait modifications aim to provide early noninvasive intervention options that are simple and safe to implement. During stair ascent, greater toe-out angle (ie, external rotation of the feet) reduced the second peak knee abduction moment (late stance) but did not change the first peak knee abduction moment Max R. Paquette is with the Department of Health & Sport Sciences, University of Memphis, Memphis, TN. Gary Klipple is with the Division of Rheumatology, University of Tennessee Medical Center, Knoxville, TN. Songning Zhang is with the Department of Kinesiology, Recreation and Sport Studies, The University of Tennessee, Knoxville, TN. Address author correspondence to Songning Zhang at [email protected].
(early stance) in medial knee osteoarthritis patients.11 Our previous work shows that increasing step width reduced first and second peak knee abduction moments in healthy individuals,19 but not in medial knee osteoarthritis patients during stair descent.20 Certain gait modification strategies can reduce peak knee abduction moment during stair walking in healthy and medial knee osteoarthritis patients, but it is currently unknown whether increased step width would have similar effects on knee abduction moment in stair ascent. A number of biomechanical variables have been associated with peak abduction moments during gait tasks. The frontal plane GRF and its moment arm are components of the knee abduction moment and can explain changes in abduction moment, especially in medial knee osteoarthritis patients.21 Furthermore, lateral trunk lean toward the stance limb has been negatively correlated to first peak knee abduction moment in medial knee osteoarthritis patients during gait.8,15 These findings suggest that, along with toe-out angle, frontal plane GRF and lateral trunk lean are important variables to explain changes in knee abduction moment. Thus, these variables could provide important information to understand mechanisms responsible for changes in knee abduction moment caused by gait modifications during gait tasks. The purpose of this study was to assess the effects of increased step width on peak knee abduction moments, abduction moment impulse, and on variables associated with knee abduction moment between medial knee osteoarthritis patients and healthy older adults during stair ascent. We hypothesized that increased step width would reduce peak knee abduction moments and abduction moment impulse, reduce frontal plane GRF, and increase lateral trunk lean. We also hypothesized that peak knee abduction moments, abduction moment impulse, frontal plane GRF, and lateral trunk lean would be greater in medial knee osteoarthritis patients compared with healthy controls during stair ascent. 229
230 Paquette, Klipple, and Zhang
Downloaded by University of Iowa Libraries on 09/16/16, Volume 31, Article Number 4
Methods Thirteen (7 women) healthy adults were recruited to participate in the study (58.9 ± 8.3 y, 67.9 ± 8.1 kg, 1.68 ± 0.16 m). The exclusion criteria for the healthy adult group included: knee pain in the past 6 months, diagnosis of any lower limb joint osteoarthritis, knee replacement, or surgery or intra-articular injection during the past 3 months. Twenty-one older adults who qualified for the knee osteoarthritis group were asked to attend a radiography session. A posterior view radiograph including both knees was performed for each participant with knees slightly flexed. A sagittal plane radiograph for each knee in slight flexion was performed one at a time during standing. A rheumatologist evaluated the radiographs for knee osteoarthritis severity using the Kellgren-Lawrence (K/L) scale.22 After radiographic screening, 13 participants (8 women) qualified for the knee osteoarthritis group (62.5 ± 9.0 y, 83.5 ± 24.0 kg, 1.71 ± 0.12 m) based on inclusion/exclusion criteria (Table 1). An a priori power analysis was conducted using first peak knee abduction moments of healthy adults during stair descent with 3 different step widths,19 and showed that a minimum of 12 subjects per group were needed to obtain a power of 0.8 at an alpha level of .05 (G*Power, 3.1). Before participating in data collection, all participants signed an informed consent document approved by the institutional review board. A 9-camera motion analysis system (240 Hz, Vicon Motion Analysis Inc., Oxford, UK) was used to obtain three-dimensional (3D) kinematics during testing. Reflective anatomical markers were placed bilaterally on the second toes, first and fifth metatarsal heads, medial and lateral malleoli, medial and lateral femoral epicondyles, greater trochanters, iliac crests, and acromion processes. The markers on the malleoli and first and fifth metatarsal heads were used to define the proximal and distal joint centers of the foot, respectively. The hip joint center positions were defined by two virtual markers located at 25% of the line between the greater trochanter markers as per the Visual3D pelvis model.23 The same researcher placed the markers on all participants. Clusters of 4 reflective markers on semirigid thermoplastic shells were used as tracking markers and placed on the trunk, pelvis, thigh, and shank. Four discrete tracking markers were placed on the medial, posterior, lateral, and dorsal–lateral aspects of the heel counter of a standard laboratory running shoe (Noveto, Adidas, Germany). An instrumented 3-step staircase (Force Plate-Stairs, American Mechanical Technology Inc., Watertown, MA) with 2 additional customized wooden steps (fourth and fifth steps) was used in the study (Figure 1). The stairs
bolted onto 2 force platforms (1200 Hz, BP600600 and OR-6–7, American Mechanical Technology Inc., Watertown, MA) and were used to measure GRF and moments. After installation of the staircase onto the 2 force platforms, the force platforms were zeroed first on the amplifiers of the force platforms and then in the Vicon Nexus software. All participants completed the Knee Injury and Osteoarthritis Outcome Score (KOOS) survey to obtain self-reported knee pain, knee functions, and functions of daily activities including stair walking.24 Healthy adults filled out the KOOS survey for their dominant limb while knee osteoarthritis participants assessed their most
Figure 1 — Illustration of the instrumented staircase used during testing, with the step of interest.
Table 1 Exclusion and inclusion criteria for medial compartment knee osteoarthritis group Exclusion
Inclusion
Diagnosed with lateral compartment knee osteoarthritis (joint space narrowing)
Radiographically diagnosed with medial compartment knee osteoarthritis (joint space narrowing score of at least 1), with or without patellofemoral knee osteoarthritis, with a grade 1–4 on the Kellgren-Lawrence scale
Osteoarthritis symptoms at the ankle or hip joint Any lower extremity joint replacement Any lower extremity joint arthroscopic surgery or intraarticular injection within past 3 months
Knee pain for at least 6 months during daily activities, including stair negotiation, on most days of the week
Systemic inflammatory arthritis Body mass index greater than 35 Inability to ascend or descend stairs without use of handrails Neurologic disease Lower back pain referred to the lower limbs JAB Vol. 31, No. 4, 2015
Downloaded by University of Iowa Libraries on 09/16/16, Volume 31, Article Number 4
Step Width and Knee Osteoarthritis in Stair Ascent 231
affected limb based on the K/L grade. Before the testing trials, all participants performed 3 stair ascent practice trials using the wider step width to establish mean preferred ascent speed. Two pairs of photo cells (63501 IR, Lafayette Instrument Inc., Lafayette, IN) and 2 electronic timers (54035A, Lafayette Instrument Inc., Lafayette, IN) were used to monitor walking speed. A range (mean ± 5%) of self-selected speed was then used to control each participant’s stair ascent speed during testing. Participants performed 5 trials in each of the following conditions: preferred step width, wide step width, and wider step width. Based on the preferred step width of healthy adults during level walking of 13% of leg length,25 the wide and wider step width conditions were set at 26% and 39% of leg length, respectively. The leg length was measured as the vertical distance between the anterior superior iliac spine and the medial malleolus of the tested limb measured in a standing position. Step width was measured as the medial–lateral distance between the centers of mass of both feet. Center of mass of the feet was defined by the mathematical anthropometric model of Hanavan26 in Visual3D. All testing conditions were randomized. Before each new condition, participants were given 2 or 3 practice trials to become familiar with the new step width condition. Black ink was marked on a strip of masking tape, which was placed on each step to control step width. For the wide and wider step width conditions, participants were instructed to cover the ink mark with their foot. Participants were not allowed to use the handrail unless they needed support to prevent a fall, and any trials in which a subject used the handrail were repeated. Healthy adults climbed the stairs with the self-reported dominant limb on the step of interest (third step from the ground, Figure 1) and knee osteoarthritis participants climbed with the most affected limb (based on the K/L grade, which also corresponded to the most symptomatic limb) on the step of interest. Participants reported their knee pain for both limbs using a 0 mm to 100 mm visual analog scale (VAS; 100 mm indicating worst possible pain). Visual3D software suite (C-Motion, Inc., Germantown, MD) was used to compute biomechanical variables. A right-hand rule
with a Cardan rotational sequence (X-y-z) was used for the 3D angular computations (X: mediolateral axis; y: anteroposterior axis; z: vertical axis). Knee joint moments were computed as internal moment and were expressed in the thigh coordinate system. Kinematic and GRF data were filtered using a fourth-order Butterworth zero-lag low-pass filter with a cut-off frequency of 8 Hz.27 The GRF data were normalized to body weight (BW) and joint moments to body mass (N∙m/kg). The knee abduction moment angular impulse was calculated with the integration of the negative portions of the abduction moment and time in the first and second halves of stance. The lateral trunk lean angle was measured as the frontal plane trunk angle at times of first (KAM1) and second (KAM2) peak knee abduction moment and was expressed in the pelvis coordinate system. Foot progression angle was measured as the transverse plane foot deviation angle from the anteroposterior axis of the laboratory coordinate system at midstance. A one-way analysis of variance (ANOVA) was performed for all participant characteristics. A nonparametric Mann–Whitney U test was used to assess the 5 KOOS subscale scores between groups. A separate Mann–Whitney U test was used to compare knee pain between groups and between the 3 step width conditions. A 2 × 3 (group × step width) repeated-measures ANOVA was performed to compare knee abduction moments and other selected variables between step width conditions and groups (SPSS v. 19.0, IBM, Chicago, IL). When an ANOVA revealed a main effect of step width, post hoc comparisons with least significant difference (LSD) were used to compare means between step width conditions. The alpha level was set a priori to .05.
Results Body mass and body mass index (BMI) were significantly higher in the knee osteoarthritis group compared with the healthy group (Table 2). The scores for all KOOS subscales were significantly
Table 2 Participant characteristics and KOOS results, mean ± SD (95% confidence interval) Variables Number of participants Age (y) Mass (kg) Height (m) Body mass index (kg/m2) Leg length (m) Kellgren-Lawrence grade of participants
KOOS—symptoms (%) KOOS—pain (%) KOOS—activities of daily living (%) KOOS—sport/recreation (%) KOOS—quality of life (%)
Healthy
Knee Osteoarthritis
P values
13 58.9 ± 8.3 (53.9–64.0) 67.9 ± 8.1 (62.9–72.8) 1.68 ± 0.16 (1.65–1.72) 23.9 ± 2.6 (22.5–25.3) 0.86 ± 0.04 (0.83–0.88) –– –– –– –– 94.8 ± 5.6 (91.4–98.2) 98.7 ± 3.1 (96.8–100.6) 98.6 ± 2.6 (97.1–100.2) 94.6 ± 13.1 (86.7–102.6) 94.7 ± 8.4 (89.7–99.8)
13 62.5 ± 9.0 (57.1–68.0) 83.5 ± 24.0 (69.0–98.0) 1.71 ± 0.12 (1.64–1.79) 28.3 ± 6.5 (24.3–32.2) 0.87 ± 0.09 (0.82–0.92) 2 (Grade 1) 5 (Grade 2) 5 (Grade 3) 1 (Grade 4) 72.0 ± 11.1 (65.3–78.7) 71.1 ± 11.5 (64.2–78.1) 75.8 ± 15.2 (66.6–85.0) 54.6 ± 23.9 (40.2–69.0) 57.7 ± 15.8 (48.2–67.2)
–– .298 .037 .494 .032 .601 –– –– –– –– < .001 < .001 < .001 < .001 < .001
Abbreviation: KOOS = Knee Injury and Osteoarthritis Outcome Score. Note. P-value for group difference: differences between groups in KOOS scores were assessed using Mann–Whitney U test. Bold values indicate significance at p < .05. JAB Vol. 31, No. 4, 2015
Downloaded by University of Iowa Libraries on 09/16/16, Volume 31, Article Number 4
232 Paquette, Klipple, and Zhang
greater in knee osteoarthritis subjects compared with healthy subjects (Table 2). Healthy adults had no pain for all 3 step width conditions, while knee osteoarthritis patients had VAS pain scores of 13.5 ± 15.0 mm for preferred step width, 12.9 ± 16.9 mm for wide step width, and 10.7 ± 11.6 mm for wider step width. VAS pain scores were significantly greater in knee osteoarthritis patients compared with healthy adults (P < .001) but not different between step width conditions. The average self-selected stair ascent walking speed was slightly slower in knee osteoarthritis patients (0.52 ± 0.09 m/s) compared with healthy adults (0.60 ± 0.06 m/s, P = .044). In general, increased step width reduced KAM1 and KAM2 and the knee abduction moment angular impulse in both healthy adults and medial compartment knee osteoarthritis patients, but no differences in abduction moment variables were observed between groups. Specifically, KAM1 was reduced in wide (P = .011) and wider step width (P < .001) conditions compared with the preferred step width condition, and in the wider condition compared with the wide step width condition (P = .002; Table 3). KAM2 was reduced in the wide (P < .001) and wider step width (P < .001) conditions compared with preferred step width, and in the wider condition compared with the wide step width condition (P < .001). Knee abduction moment angular impulse was reduced in wide (P < .001) and wider step width (P < .001) conditions compared with preferred step width, and in the wider condition compared with the wide step width condition (P < .001). Absolute step width and normalized step width (percent leg length) were both significantly greater in wide (P < .001) and wider step width (P < .001) conditions compared with preferred step width, and in the wider condition compared with the wide step width condition (P < .001; Table 4). Finally, lateral trunk lean at the time of KAM1 was greater in knee osteoarthritis patients compared with healthy adults, and smaller in the wider step width condition compared with the preferred step width condition (P = .010; Table 4). First peak vertical GRF was greater in knee osteoarthritis subjects compared with healthy subjects (P = .001; Table 4). Peak frontal plane GRF at the time of KAM1 was smaller in wide (P = .001) and wider step width (P < .001) conditions compared with preferred step width. Peak frontal plane GRF at the time of KAM2 was greater in healthy subjects compared with knee osteoarthritis patients (P = .016), and was smaller in the wider step width condition compared with the wide (P = .020) and preferred step width (P = .001) conditions.
Discussion The purpose of this study was to assess the effects of increased step width on peak knee abduction moments, abduction moment impulse, and associated variables between medial knee osteoarthritis patients and healthy older adults during stair ascent. Our main finding was that KAM1, KAM2, and abduction moment impulse were all significantly reduced with increased step width. These results support our hypothesis and are in agreement of our earlier work that noted increased step width led to reductions in peak abduction moments in healthy older adults,19 but the results are not in agreement with previous findings of knee abduction moment with increased step width in knee osteoarthritis patients during stair descent.20 Stair descent requires primarily negative joint work (ie, eccentric muscle action) to counteract the downward center of mass acceleration, whereas stair ascent requires mostly positive joint work (ie, concentric muscle action) to pull the body up onto the next step.28
These task differences between descent and ascent may be linked to the different effects of increased step width on knee abduction moments. Guo et al11 have shown that increasing toe-out angle (ie, externally rotated foot progression angle) reduced KAM2 in pain free medial compartment knee osteoarthritis patients during stair ascent compared with preferred foot progression angle. In the current study, foot progression angle did not change with increased step width. Guo et al11 suggest that a lateral displacement in the center of pressure location in late stance might be responsible for moving the GRF vector closer to the knee joint center to shorten the moment arm and, in turn, reduce the abduction moment with an increased foot progression angle. Hunt et al21 showed significant positive correlations between peak stance phase knee abduction moment and frontal plane knee moment arm in knee osteoarthritis patients during gait. In the current study, the reductions in peak knee abduction moments and frontal plane GRF at times of KAM1 and KAM2 suggest reduced moment arms of the frontal plane GRF with increased step width. Thus, it appears that step width may be successful in altering frontal plane mechanics to elicit reductions in knee-abduction-moment-related variables during both level and stair walking. Mundermann et al29 have shown that increased lateral trunk sway significantly reduces peak KAM1 during level walking in healthy adults from the same mechanism suggested with toe-out angle (ie, lateral shift of the center of pressure11). In the current study, increased step width reduced lateral trunk lean during stair ascent. Therefore, lateral trunk lean is likely not responsible for reductions in abduction moments. Similar to what has been previously suggested with toe-out angle and lateral trunk sway,11,15,29 step width alterations may not only lead to a lateral shift in the center of pressure, but also to changes in lower extremity limb alignment in the frontal plane and, as a result, alter peak knee abduction moment during gait. Specifically, an increase in step width may result in an inward motion of the knee (ie, medial thrust gait pattern30) which could decrease the GRF vector moment arm to the knee joint center and thus explain the reductions in peak knee abduction moment and abduction moment angular impulse during gait tasks. Our results strongly suggest that the reduced KAM1 and KAM2 are due to reduced moment arms to knee joint center (ie, no changes in frontal GRF vector), and that increased step width may have similar implications as increased toe-out angle for reducing abduction moment. However, in comparison with a reduction of only the second peak abduction moment with greater toe-out angle in stair ascent,11 increased step width reduces both abduction peaks along with the abduction impulse and may prove to be a more effective gait modification to reduce peak knee abduction moments during stair ascent. Although there are currently no cross-sectional studies investigating the effects of increased step width on knee joint kinetics, case studies by Zhao et al31 and Fregly30 present peak knee abduction moments during walking using wide step width. While peak stance abduction moment does not appear to be different in the study by Zhao et al,31 the estimated values from knee abduction moment curves reported by Fregly et al32 show distinct reductions in KAM1 and KAM2 during a wide step width compared with normal gait. Contrary to our third hypothesis, our findings failed to show differences in abduction moment variables between medial compartment knee osteoarthritis patients and healthy older adults during stair ascent. Previous studies show that knee osteoarthritis patients tend to ambulate over level ground with lower peak knee abduction
JAB Vol. 31, No. 4, 2015
JAB Vol. 31, No. 4, 2015
233
–0.24 ± 0.12
–0.30 ± 0.11 –0.15 ± 0.04
Knee abduction impulse (N∙m/kg·s)a,b,c –0.10 ± 0.04
–0.19 ± 0.10
–0.29 ± 0.08
Wider
–0.17 ± 0.07
–0.26 ± 0.14 –0.15 ± 0.07
–0.22 ± 0.11
–0.36 ± 0.11
Wide
Wider
–0.13 ± 0.07
–0.18 ± 0.11
–0.33 ± 0.10
Knee Osteoarthritis –0.37 ± 0.12
Preferred
Abbreviations: KAM1 = internal knee abduction moment, first peak; KAM2 = internal knee abduction moment, second peak. Note. A negative value indicates knee abduction moment or angular impulse. Bold values indicate significance at p < .05. a Wide step width significantly different from preferred step width. b Wider step width different from preferred step width. c Wider step width different from wide step width.
–0.12 ± 0.04
–0.32 ± 0.08
–0.36 ± 0.08
KAM1
KAM2 (N∙m/kg)a,b,c
Wide
Healthy
(N∙m/kg)a,b,c
Preferred
.65
< .001
.28
.42
< .001
< .001
Group
Step Width
P values
.47
.13
.34
Interaction
Table 3 Frontal plane knee moment variables for all three step width conditions (mean ± SD) in healthy and knee osteoarthritis groups
Downloaded by University of Iowa Libraries on 09/16/16, Volume 31, Article Number 4
234
JAB Vol. 31, No. 4, 2015
Absolute step width
(°)b,c,# –2.8 ± 2.5
–2.9 ± 2.6
1.9 ± 2.6
2.1 ± 2.5 –3.2 ± 2.6
1.7 ± 2.6
12.9 ± 3.3
1.05 ± 0.16
0.90 ± 0.10
1.13 ± 0.14
37.1 ± 2.8
0.32 ± 0.03
Wider
–1.3 ± 2.1
4.2 ± 2.6
13.0 ± 4.0
0.98 ± 0.10
0.92 ± 0.05
1.52 ± 0.44
17.1 ± 4.6
0.15 ± 0.04
–1.4 ± 2.5
4.3 ± 3.0
12.5 ± 4.3
0.99 ± 0.09
0.91 ± 0.07
1.50 ± 0.43
24.1 ± 2.2
0.21 ± 0.02
Wide
Wider
–1.6 ± 2.4
3.7 ± 2.7
12.7 ± 4.6
0.92 ± 0.12
0.90 ± 0.10
1.51 ± 0.43
35.9 ±3.1
0.31 ± 0.03
Knee Osteoarthritis Preferred
.14
.12
.044
.005
.012
.002
.82
.72 .28
.007
.83
< .001 .10
.64
< .001
< .001
Group
P values Step Width
.83
.52
.40
.15
.12
.61
.20
.37
Interaction
Abbreviations: GRF = ground reaction force; BW = body weight; KAM1 = internal knee abduction moment, first peak; KAM2 = internal knee abduction moment, second peak. Note. Normalized step width is normalized to leg length; foot progression angle was measured at midstance; a positive foot progression angle value indicates a toe-out angle relative to the anteroposterior axis of the laboratory coordinate system; negative lateral trunk lean value indicates a trunk lean toward the stance limb in frontal plane. Bold values indicate significance at p < .05. a Wide step width significantly different from preferred step width. b Wider step width different from preferred step width. c Wider step width different from wide step width. # Different between groups.
Lateral trunk lean at time of KAM2 (°)
Lateral trunk lean at time of KAM1
Foot progression angle (°)
12.2 ± 4.3
1.07 ± 0.13
1.10 ± 0.11
(BW)b,c,# 12.2 ± 3.5
0.91 ± 0.08
0.94 ± 0.08
Frontal GRF at time of KAM2
1.13 ± 0.15
1.15 ± 0.15
24.1 ± 2.4
15.4 ± 3.1
Frontal GRF at time of KAM1 (BW)a,b
0.21 ± 0.02
0.13 ± 0.03
Wide
Healthy
First peak vertical GRF (BW)
Normalized step width (%)a,b,c
(m)a,b,c
Preferred
Table 4 Additional kinematic and kinetic variables for all three step width conditions (mean ± SD) in healthy and knee osteoarthritis groups
Downloaded by University of Iowa Libraries on 09/16/16, Volume 31, Article Number 4
Downloaded by University of Iowa Libraries on 09/16/16, Volume 31, Article Number 4
Step Width and Knee Osteoarthritis in Stair Ascent 235
moments compared with healthy individuals.5,6 Our finding is not surprising, as frontal plane GRF at times of KAM1 and KAM2 were also not different between groups. One possible explanation for this finding may be attributed to the slower stair ascent speed in knee osteoarthritis subjects compared with older healthy adults. The slower walking speed in knee osteoarthritis patients would be expected to yield a smaller first peak vertical GRF and, in turn, at least a smaller KAM1. However, first peak vertical GRF was greater in knee osteoarthritis patients compared with healthy adults. The participants ascended the stairs at a self-selected walking speed which represented their daily stair ascent gait behavior. Furthermore, although the K/L grades of our knee osteoarthritis patients were mostly moderate, the initial low levels of knee pain and high scores on the KOOS for activities of daily living reported by the knee osteoarthritis group may be another explanation for similar abduction moments between groups. Patients with lower levels of pain may not require significant gait alterations that may otherwise be observed in individuals with high levels of knee pain. Although the current findings suggest that acute increases in step width can reduce abduction moments, our results cannot imply long-term effects of reducing medial knee loads during stair ascent. Gait modifications over a prolonged period of time can be uncomfortable7 and thus, such changes to gait patterns should be considered carefully. In the current study, before each stair ascent practice trial, a number of participants mentioned that the wider step width condition felt “strange” or “awkward”. However, after a few trials participants had no further complaints regarding wider step width conditions. Thus, a gait intervention in knee osteoarthritis patients could be useful to understand the chronic effects of increased step width. This study has a number of limitations. Marker placement on the skin of obese patients could have introduced errors in building the models and in increasing skin motion artifact. However, the same researcher placed the markers on all participants, and tracking markers attached to a rigid plastic shell were secured and taped to Velcro neoprene bands to prevent excessive skin motion. In the current study, our knee osteoarthritis participants had low levels of knee pain and high scores on the KOOS for activities of daily living. Thus, our findings can only be generalizable to high-functioning medial compartment knee osteoarthritis patients. This is the first study to assess the effects of increased step width on frontal plane knee mechanics in knee osteoarthritis patients during stair ascent. Our findings of reduced peak abduction moments and abduction moment impulse with increased step width suggest that increasing step width may be an effective and acute strategy to reduce medial knee loads. In addition, it appears that reductions in frontal plane GRF and its moment arm to the knee joint center may be responsible for reductions in abduction moment variables with increased step width. Future studies should investigate the chronic effects of increased step width on knee joint loading variables and should also consider knee osteoarthritis patients with higher levels of knee pain. Acknowledgments The study was in part supported by funding from the Opportunity Fund of Office of Research, College of Education, Health and Sport Sciences at the University of Tennessee, and the University of Tennessee Medical Center. The authors would like to thank Joseph Hoekstra for his help with data collection and Ann Holden for her help with radiographic patient screening at the University of Tennessee Medical Center.
References 1. Felson DT, Lawrence RC, Dieppe PA, et al. Osteoarthritis: new insights. Part 1: the disease and its risk factors. Ann Intern Med. 2000;133(8):635–646. PubMed doi:10.7326/0003-4819-133-8200010170-00016 2. Jordan JM, Helmick CG, Renner JB, et al. Prevalence of knee symptoms and radiographic and symptomatic knee osteoarthritis in African Americans and Caucasians: the Johnston County Osteoarthritis Project. J Rheumatol. 2007;34(1):172–180. PubMed 3. Andriacchi TP, Koo S, Scanlan SF. Gait mechanics influence healthy cartilage morphology and osteoarthritis of the knee. J Bone Joint Surg Am. 2009;91(Suppl 1):95–101. PubMed doi:10.2106/JBJS.H.01408 4. Schipplein OD, Andriacchi TP. Interaction between active and passive knee stabilizers during level walking. J Orthop Res. 1991;9(1):113– 119. PubMed doi:10.1002/jor.1100090114 5. Kaufman KR, Hughes C, Morrey BF, Morrey M, An KN. Gait characteristics of patients with knee osteoarthritis. J Biomech. 2001;34(7):907–915. PubMed doi:10.1016/S0021-9290(01)00036-7 6. Mundermann A, Dyrby CO, Andriacchi TP. Secondary gait changes in patients with medial compartment knee osteoarthritis: increased load at the ankle, knee, and hip during walking. Arthritis Rheum. 2005;52(9):2835–2844. PubMed doi:10.1002/art.21262 7. Shull PB, Silder A, Shultz R, et al. Six-week gait retraining program reduces knee adduction moment, reduces pain, and improves function for individuals with medial compartment knee osteoarthritis. J Orthop Res. 2013;31(7):1020–1025. PubMed doi:10.1002/jor.22340 8. Simic M, Hunt MA, Bennell KL, Hinman RS, Wrigley TV. Trunk lean gait modification and knee joint load in people with medial knee osteoarthritis: the effect of varying trunk lean angles. Arthritis Care Res. 2012;64(10):1545–1553. PubMed doi:10.1002/acr.21724 9. Bechard DJ, Birmingham TB, Zecevic AA, Jones IC, Giffin JR, Jenkyn TR. Toe-out, lateral trunk lean, and pelvic obliquity during prolonged walking in patients with medial compartment knee osteoarthritis and healthy controls. Arthritis Care Res. 2012;64(4):525–532. PubMed doi:10.1002/acr.21584 10. Mundermann A, Dyrby CO, Hurwitz DE, Sharma L, Andriacchi TP. Potential strategies to reduce medial compartment loading in patients with knee osteoarthritis of varying severity: reduced walking speed. Arthritis Rheum. 2004;50(4):1172–1178. PubMed doi:10.1002/ art.20132 11. Guo M, Axe MJ, Manal K. The influence of foot progression angle on the knee adduction moment during walking and stair climbing in pain free individuals with knee osteoarthritis. Gait Posture. 2007;26(3):436–441. PubMed doi:10.1016/j.gaitpost.2006.10.008 12. Fregly BJ, Reinbolt JA, Rooney KL, Mitchell KH, Chmielewski TL. Design of patient-specific gait modifications for knee osteoarthritis rehabilitation. IEEE Trans Biomed Eng. 2007;54(9):1687–1695. PubMed doi:10.1109/TBME.2007.891934 13. Simic M, Hinman RS, Wrigley TV, Bennell KL, Hunt MA. Gait modification strategies for altering medial knee joint load: a systematic review. Arthritis Care Res. 2011;63(3):405–426. PubMed 14. Jenkyn TR, Hunt MA, Jones IC, Giffin JR, Birmingham TB. Toe-out gait in patients with knee osteoarthritis partially transforms external knee adduction moment into flexion moment during early stance phase of gait: a tri-planar kinetic mechanism. J Biomech. 2008;41(2):276– 283. PubMed doi:10.1016/j.jbiomech.2007.09.015 15. Hunt MA, Birmingham TB, Bryant D, et al. Lateral trunk lean explains variation in dynamic knee joint load in patients with medial compartment knee osteoarthritis. Osteoarthritis Cartilage. 2008;16(5):591– 599. PubMed doi:10.1016/j.joca.2007.10.017
JAB Vol. 31, No. 4, 2015
Downloaded by University of Iowa Libraries on 09/16/16, Volume 31, Article Number 4
236 Paquette, Klipple, and Zhang 16. Rutherford DJ, Hubley-Kozey CL, Deluzio KJ, Stanish WD, Dunbar M. Foot progression angle and the knee adduction moment: a crosssectional investigation in knee osteoarthritis. Osteoarthritis Cartilage. 2008;16(8):883–889. PubMed doi:10.1016/j.joca.2007.11.012 17. van den Noort JC, Schaffers I, Snijders J, Harlaar J. The effectiveness of voluntary modifications of gait pattern to reduce the knee adduction moment. Hum Mov Sci. 2013;32(3):412–424. PubMed doi:10.1016/j. humov.2012.02.009 18. Costigan PA, Deluzio KJ, Wyss UP. Knee and hip kinetics during normal stair climbing. Gait Posture. 2002;16(1):31–37. PubMed doi:10.1016/S0966-6362(01)00201-6 19. Paquette MR, Zhang S, Milner CE, Fairbrother JT, Reinbolt JA. Effects of increased step width on frontal plane knee biomechanics in healthy older adults during stair descent. Knee. 2014;21(4):821–826. PubMed doi:10.1016/j.knee.2014.03.006 20. Paquette MR, Zhang S, Milner CE, Klipple G. Does increasing step width alter knee biomechanics in medial compartment knee osteoarthritis patients during stair descent? Knee. 2014;21(3):676–682. PubMed doi:10.1016/j.knee.2014.02.020 21. Hunt MA, Birmingham TB, Giffin JR, Jenkyn TR. Associations among knee adduction moment, frontal plane ground reaction force, and lever arm during walking in patients with knee osteoarthritis. J Biomech. 2006;39(12):2213–2220. PubMed doi:10.1016/j.jbiomech.2005.07.002 22. Kellgren JH, Lawrence JS. Radiographic assessment of osteoarthritis. Ann Rheum Dis. 1957;16:494–502. PubMed doi:10.1136/ard.16.4.494 23. Weinhandl JT, O’Connor KM. Assessment of a greater trochanter-based method of locating the hip joint center. J Biomech. 2010;43(13):2633– 2636. PubMed doi:10.1016/j.jbiomech.2010.05.023 24. Roos EM, Toksvig-Larsen S. Knee injury and Osteoarthritis Outcome Score (KOOS) - validation and comparison to the WOMAC in total
knee replacement. Health Qual Life Outcomes. 2003;1:17. PubMed doi:10.1186/1477-7525-1-17 25. Donelan JM, Kram R, Kuo AD. Mechanical and metabolic determinants of the preferred step width in human walking. Proc Biol Sci. 2001;268(1480):1985–1992. PubMed doi:10.1098/rspb.2001.1761 26. Hanavan EP. A Mathematical Model of the Human Body. WrightPatterson Air Force Base; Oct 1964. 27. Kristianslund E, Krosshaug T, van den Bogert AJ. Effect of low pass filtering on joint moments from inverse dynamics: implications for injury prevention. J Biomech. 2012;45(4):666–671. PubMed doi:10.1016/j.jbiomech.2011.12.011 28. DeVita P, Helseth J, Hortobagyi T. Muscles do more positive than negative work in human locomotion. J Exp Biol. 2007;210(Pt 19):3361–3373. PubMed doi:10.1242/jeb.003970 29. Mundermann A, Asay JL, Mundermann L, Andriacchi TP. Implications of increased medio-lateral trunk sway for ambulatory mechanics. J Biomech. 2008;41(1):165–170. PubMed doi:10.1016/j.jbiomech.2007.07.001 30. Fregly BJ. Computational assessment of combinations of gait modifications for knee osteoarthritis rehabilitation. IEEE Trans Biomed Eng. 2008;55(8):2104–2106. PubMed doi:10.1109/ TBME.2008.921171 31. Zhao D, Banks SA, Mitchell KH, D’Lima DD, Colwell CW, Jr, Fregly BJ. Correlation between the knee adduction torque and medial contact force for a variety of gait patterns. J Orthop Res. 2007;25(6):789–797. PubMed doi:10.1002/jor.20379 32. Fregly BJ, Reinbolt JA, Chmielewski TL. Evaluation of a patientspecific cost function to predict the influence of foot path on the knee adduction torque during gait. Comput Methods Biomech Biomed Engin. 2008;11(1):63–71. PubMed doi:10.1080/10255840701552036
JAB Vol. 31, No. 4, 2015
