THEKNE-01874; No of Pages 7 The Knee xxx (2014) xxx–xxx

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The Knee

Does increasing step width alter knee biomechanics in medial compartment knee osteoarthritis patients during stair descent? Max R. Paquette a,⁎, Songning Zhang b, Clare E. Milner c, Gary Klipple d a

Health & Sport Science, University of Memphis, Memphis, TN, USA Kinesiology, Recreation and Sport Studies, University of Tennessee, Knoxville, TN, USA Department of Physical Therapy and Rehabilitation Sciences, Drexel University, Philadelphia, PA, USA d Rheumatology Division, University of Tennessee Medical Center, Knoxville, TN, USA b c

a r t i c l e

i n f o

Article history: Received 19 July 2013 Received in revised form 7 December 2013 Accepted 14 February 2014 Available online xxxx Keywords: Knee load Osteoarthritis Abduction moment Adduction angle Stair walking

a b s t r a c t Background: Research shows that one of the first complaints from knee osteoarthritis (OA) patients is difficulty in stair ambulation due to knee pain. Increased step width (SW) has been shown to reduce first and second peak internal knee abduction moments, a surrogate variable for medial compartment knee joint loading, during stair descent in healthy older adults. This study investigates the effects of increased step width (SW) on knee biomechanics and knee pain in medial compartment knee OA patients during stair descent. Methods: Thirteen medial compartment knee OA patients were recruited for the study. A motion analysis system was used to obtain three-dimensional joint kinematics. An instrumented staircase was used to collect ground reaction forces (GRF). Participants performed stair descent trials at their self-selected speed using preferred, wide, and wider SW. Participants rated their knee pain levels after each SW condition. Results: Increased SW had no effect on peak knee abduction moments and knee pain. Patients reported low levels of knee pain during all stair descent trials. The 2nd peak knee adduction angle and frontal plane GRF at time of 2nd peak abduction moment were reduced with increasing SW. Conclusions: The findings suggest that increases in SW may not influence knee loads in medial compartment knee OA patients afflicted with low levels of knee pain during stair descent. © 2014 Elsevier B.V. All rights reserved.

1. Introduction Osteoarthritis (OA) is the most common type of arthritis and millions of Americans are affected by the disease [1]. Arthritis is more prevalent in older adults but it can also affect younger populations with nearly 30% of adults between the ages 45 and 64 diagnosed with arthritis between 2003 and 2005 [2]. About 11% of arthritis patients between the ages of 45 and 64 and 20% of patients over the age of 65 years have limitations in daily activities [2]. In addition, one of the first complaints from older adults suffering from knee OA is difficulty in stair ambulation [3]. Previous research has extensively studied lower extremity biomechanical variables during daily gait tasks such as level-walking and stair ambulation in individuals afflicted with knee OA [4–14]. During stair descent, biomechanical data of knee OA patients compared to healthy adults show greater impact ground reaction force

⁎ Corresponding author at: 313 Elma Roane Field House, University of Memphis, Memphis, TN 38152, USA. Tel.: +1 901 678 5025; fax: +1 901 678 4316. E-mail address: [email protected] (M.R. Paquette).

(GRF), higher loading rate of impact GRF [15], smaller peak knee flexion [5], and greater peak knee adduction angle [10]. In level-walking, knee OA patients generally yield greater internal knee abduction moment compared to healthy adults [14]. Peak knee abduction moment is often used as a surrogate variable for medial compartment knee loading [16,17]. Thus, reductions in the peak knee abduction moments may have implications in reducing medial compartment loads in knee OA patients. The internal knee abduction moment is a net reactive moment created by muscles, ligaments and internal structures of the knee joint in response to the external knee adduction moment (i.e., the product of the frontal plane GRF vector and its moment arm to the knee joint center). Thus, it is important to consider both the frontal plane GRF vector and its moment arm to the knee joint center to better understand the mechanisms associated with changes in abduction moments during gait tasks [18]. Limited studies have reported frontal plane knee moments in knee OA patients during stair walking. Guo et al. [19] reported greater peak knee abduction moments in stair descent compared to stair ascent and level-walking in knee OA patients. A recent study reported similar 1st and 2nd internal peak knee abduction moments in medial compartment knee OA patients compared to healthy controls during stair descent [20]. More studies investigating knee abduction moments in knee OA patients during stair descent are needed.

http://dx.doi.org/10.1016/j.knee.2014.02.020 0968-0160/© 2014 Elsevier B.V. All rights reserved.

Please cite this article as: Paquette MR, et al, Does increasing step width alter knee biomechanics in medial compartment knee osteoarthritis patients during stair descent?, Knee (2014), http://dx.doi.org/10.1016/j.knee.2014.02.020

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M.R. Paquette et al. / The Knee xxx (2014) xxx–xxx

Several non-pharmaceutical interventions which aim to reduce knee joint load and pain such as in-shoe lateral wedges [21,22], use of unstable footwear [23], minimal shoes and barefoot [20,24], valgus knee braces [25,26] and various types of training interventions [27–31] have been implemented for medial compartment knee OA patients during level- and stair walking. These interventions for knee OA during level and stair walking all require patients to either adhere to a training regime for a period of time or wear different footwear and braces. During level-walking, studies have suggested several factors that can alter the peak knee abduction moments such as foot progression angle (i.e., toeing out) [32–34] and lateral trunk lean towards the stance limb [32,35–37] in knee OA patients. Limited research has been conducted on simple gait strategies to alter knee loading of knee OA patients in stair walking. One study found that greater foot progression angle during stair ascent led to reductions in the 2nd peak knee abduction moment in medial compartment knee OA patients [19]. Step width (SW) alterations could potentially be another simple gait strategy to reduce peak values of frontal plane knee kinematics and kinetics and, knee pain during stair descent. Hicks-Little et al. [38] found that individuals with knee OA negotiate stairs with greater SW compared to healthy controls at a self-selected speed. In healthy older adults, increased SW significantly reduces the 1st and 2nd peak knee adduction angles and peak knee abduction moments compared to preferred SW during stair descent [39]. Thus, increased SW may lead to reductions in peak knee abduction moments in knee OA patients. To date, no studies have investigated the effects of SW changes on knee joint motion and pain in knee OA patients during stair descent. The purpose of this study was to examine the effects of increased SW on knee biomechanics in patients with medial compartment knee OA during stair descent. We hypothesized that increased SW during stair descent would reduce the peak knee adduction angles and peak knee abduction moments. The primary dependent variables (e.g. knee abduction moments and adduction angles) were chosen as surrogate medial knee loading estimates.

Based on the inclusion/exclusion criteria (Table 1), thirteen participants qualified for the study (Table 2). A priori power analysis (Sample Power 3.0, IBM SPSS, Chicago, IL) indicated that a minimum of 12 participants were needed to obtain an alpha level of 0.05 and a beta of 0.80 based on the previously reported peak internal knee abduction moment values of healthy older adults between preferred, wide and wider SW during stair descent [39]. The K/L grades of the participants ranged between 1 and 4 (grade 1 = 1, grade 2 = 5, grade 3 = 5 & grade 4 = 1). Medial joint space narrowing K/L grades ranged between 1 and 3 (grade 1 = 9, grade 2 = 3 & grade 3 = 1). Twelve of the thirteen participants had bilateral medial compartment knee OA. The contra-lateral knee K/L grades ranged between 1 and 4 (grade 1 = 8, grade 2 = 3 & grade 4 = 1). 2.2. Instrumentation A nine-camera motion analysis system (240 Hz, Vicon Motion Analysis Inc., Oxford, UK) was used to obtain three-dimensional (3D) kinematics during testing. Participants wore a standardized laboratory running shoe (Adidas, USA) during the experiment. Reflective anatomical markers were placed on toes (i.e., anterior most aspect of the shoes), 1st and 5th metatarsal heads, medial and lateral malleoli, medial and lateral femoral epicondyles, greater trochanters, iliac crests and acromion processes. Clusters of four reflective markers on semi-rigid thermoplastic shells were used as tracking markers and placed on lateral shank, lateral thigh, lateral pelvis and posterior-inferior trunk. Four individual tracking markers were placed on medial, posterior, lateral and dorsal– lateral aspects of the shoe. An instrumented 3-step staircase (FP-stairs, American Mechanical Technology Inc., Watertown, MA, USA) with two additional customized wooden steps was used in the study (Fig. 1a). The FP-Stairs bolted independently to two force platforms (1200 Hz, BP600600 and OR-6-7, American Mechanical Technology Inc., Watertown, MA, USA) were used to measure the GRF during stair walking. 2.3. Experimental procedures

2. Methods 2.1. Participants Twenty-one adults who reported knee osteoarthritis were initially recruited via flyers, online forums and from a database of knee OA patients that participated in a previous study conducted in the Biomechanics/Sports Medicine Laboratory. All participants signed an informed consent document approved by the local Institutional Review Board or. Three X-rays were obtained for each participant. A posterior-view radiograph including both knees was taken while the patient stood with the knees slightly flexed at approximately 30°. A sagittal-plane (side-view) radiograph was also obtained for each knee during standing. Medial compartment knee OA and knee OA severity using the Kellgren–Lawrence (K/L) scale [40] were assessed by a rheumatologist.

The thirteen qualified participants attended a laboratory biomechanical test session. They were administered with the Knee injury and Osteoarthritis Outcome Score (KOOS) survey to obtain their opinion on knee pain, knee functions, and associated problems during common daily activities including stair walking [41]. Knee OA participants filled out the KOOS for their most affected limb based on the K/L grade (Table 2). All participants performed three practice trials of stair descent before the experimental trials using the wider SW in order to establish their average self-selected descent speed (mean ± 5%) to be used during testing trials. Two pairs of photo cells (63501 IR, Lafayette Instrument Inc., IN, USA) set at shoulder height in line with the 1st and 4th steps and two electronic timers (54035A, Lafayette Instrument Inc., IN, USA) were used to monitor descent speed. The average self-selected stair descent speed was 0.45 ± 0.08 m/s. Participants were asked to

Table 1 Participant exclusion and inclusion criteria. Exclusion -

Diagnosed with lateral compartment knee OA (joint space narrowing only), OA symptoms at the ankle or hip joint, Any lower extremity joint replacement, Any lower extremity joint arthroscopic surgery or intra-articular injection within past 3 months, Systemic inflammatory arthritis, BMI greater than 35, Inability to ascend or descend stairs without use of handrails, Neurologic disease, Lower back pain referred to the lower limbs.

Inclusion - Radiographically diagnosed with medial compartment knee OA (joint space narrowing), with or without patella-femoral knee OA, with a grade 1 to 4 on the Kellgren–Lawrence scale, - Knee pain for at least 6 months during daily activities including stair negotiation on most days of the week.

Please cite this article as: Paquette MR, et al, Does increasing step width alter knee biomechanics in medial compartment knee osteoarthritis patients during stair descent?, Knee (2014), http://dx.doi.org/10.1016/j.knee.2014.02.020

M.R. Paquette et al. / The Knee xxx (2014) xxx–xxx Table 2 Participant characteristics and KOOS results: mean ± standard deviation (95% confidence interval). Variables

Knee OA

Age (years) Gender: male/female Mass (kg) Height (cm) BMI (kg/m2) Leg length (m) KOOS — symptoms (%) KOOS — pain (%) KOOS — ADL (%) KOOS — sport/recreation (%) KOOS — QOL (%)

62.5 ± 9.0 (57.1–68.0) 5/8 83.5 ± 24.0 (69.0–98.0) 171 ± 12.0 (164.0–179.0) 28.3 ± 6.5 (24.3–32.2) 0.87 ± 0.09 (0.82–0.92) 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)

KOOS, Knee Osteoarthritis Outcome Score; ADL, Activities of Daily Living; QOL, Quality of Life.

perform five trials of stair descent in each of three testing conditions at their self-selected speed: preferred SW, wide SW, and stair descent at wider SW. The wide and wider SW were standardized as 26% and 39% of each participant's leg length, respectively, based on a reported preferred SW of 13% of leg length during level-walking (i.e., wide and wider SW are double and triple of previously reported preferred SW) [42]. Leg length was measured as the vertical distance between the anterior superior iliac spine (ASIS) and the medial malleolus of the tested limb during standing. The testing order of the SW conditions was randomized. At the start of each descent trial, participants stood on the top platform, took one step on the platform before initiating stair descent, contacted the 2nd step (step of interest, Fig. 1a) with the tested foot, and continued to walk for at least two steps after stepping onto the laboratory floor. Before each new condition, participants were given practice trials to become familiar with the new SW condition. Black ink marks on a strip of masking tape were placed on each step to control SW during the trials (Fig. 1b). For the wide and wider SW conditions, participants were instructed to step over the ink marks with their foot on each step but no other instructions on foot placement were given to avoid changes in their normal stair walking gait pattern. Participants

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were also instructed to not use the handrail unless needed. If participants used the handrail, a new trial was collected. Each participant was instructed to descend the stairs one foot at a time without having both feet on a step at the same time. Following each test condition, all participants were given a rest period of at least two minutes, or more if requested, to avoid fatigue. During this rest period, all participants rated their right and left knee levels using a visual analogue scale (VAS: 0 indicating no pain and 10 indicating most possible pain). 2.4. Data analyses Visual3D biomechanical analysis software suite (C-Motion, Inc., Germantown, MD, USA) was used to compute the 3D kinematic and kinetic variables. A Cardan rotational sequence (x-y-z) was used for the 3D angular computations and a right hand rule was used to define the conventions of angular kinematic and kinetic variables. Kinematic and GRF data were both filtered using a fourth-order Butterworth lowpass filter with the same cut-off frequency of 8 Hz [43,44]. Customized computer programs (VB_V3D and VB_Tables, Visual Basics, Microsoft) were used to determine critical events of the kinematic and kinetic variables of interest from the outputs of Visual3D and organize these for statistical analyses. The medial and vertical GRF components were normalized to body weight (BW) and internal frontal and sagittal plane joint moments computed in the thigh coordinate system were normalized to body mass (Nm/kg). The loading rate of the early stance vertical GRF was calculated as the ratio of peak vertical GRF and time from contact (10 N threshold) to the peak. SW was measured as the medial– lateral distance between the center of mass (COM) positions of both feet at the time of testing limb foot contact on the step of interest. Based on the previous findings that foot progression angle [19,32–34], lateral trunk lean [32,35,37] and both frontal plane GRF and its knee joint center moment arm [18] can alter knee abduction moments in knee OA patients during gait tasks, these variables were also analyzed to better understand mechanisms related to changes in the peak knee abduction moments. Foot progression angle (FPA) was measured as the transverse plane foot deviation angle in the laboratory coordinate system at mid-stance. Lateral trunk lean and frontal plane moment arm values were measured at the instants of 1st and 2nd peak knee abduction

Fig. 1. Illustration of staircase (A) and black ink marks on steps to control step width during the wide and wider step width conditions (B).

Please cite this article as: Paquette MR, et al, Does increasing step width alter knee biomechanics in medial compartment knee osteoarthritis patients during stair descent?, Knee (2014), http://dx.doi.org/10.1016/j.knee.2014.02.020

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M.R. Paquette et al. / The Knee xxx (2014) xxx–xxx

Table 3 Ground reaction force variables for all three step width conditions (mean ± standard deviation) with 95% confidence intervals. Variables

Preferred SW

Wide SW

Wider SW

pc

Fx1 (BW) Fz1 (BW) LR (BW/s) Fz2 (BW) FF1 (BW) FF2 (BW)

−0.11 ± 0.03a,b (0.09–0.12) 1.35 ± 0.15 (1.26–1.44) 9.6 ± 2.0 (8.3–10.8) 0.95 ± 0.05 (0.82–0.98) 1.21 ± 0.11 (1.15–1.28) 0.89 ± 0.05b (0.86–0.92)

−0.12 ± 0.2b (0.11–0.14) 1.34 ± 0.16 (1.25–1.44) 9.7 ± 2.3 (8.3–11.1) 0.94 ± 0.05 (0.91–0.96) 1.21 ± 0.12 (1.14–1.29) 0.88 ± 0.06b (0.84–0.91)

−0.17 ± 0.02 (0.16–0.18) 1.34 ± 0.17 (1.24–1.44) 10.0 ± 2.4 (8.6–11.5) 0.92 ± 0.06 (0.89–0.96) 1.19 ± 0.13 (1.12–1.27) 0.85 ± 0.06 (0.82–0.89)

0.001 0.736 0.182 0.155 0.406 0.021

Peak medial GRF (Fx1), 1st peak vertical GRF (Fz1), loading rate to Fz1 (LR), 2nd peak vertical GRF (Fz2), peak frontal plane GRF at KAM1 (FF1) and peak frontal plane GRF at KAM2 (FF2). a Significantly different from wide SW. b Significantly different from wider SW. p: Step width main effect p-value. c p-Value for ANOVA test.

moment. Frontal plane moment arm was computed using the following equation:

Moment Arm ¼

KAM Frontal GRF

3.2. Ground reaction force variables The peak medial GRF was greater in wide (p = 0.007) and wider SW (p = 0.001) compared to preferred SW and greater in wider compared to wide SW (p = 0.001; Table 3). The frontal plane peak GRF at the time of 2nd peak knee abduction moment was smaller in wider SW compared to preferred (p = 0.020) and wide SW (p = 0.001; Table 3). 3.3. Step width and kinematic variables

where Moment Arm is the frontal plane moment arm of the Frontal GRF vector to the knee joint center; KAM is the peak knee abduction moment and Frontal GRF is the resultant vector of the vertical and medial GRF vectors transformed in the thigh coordinate system. All variables were analyzed during stance phase on the step of interest. The most affected knee OA limb, based on the medial compartment K/L grade, was analyzed.

Absolute SW was smaller in preferred compared to wide (p = 0.007) and wider SW (p = 0.001) and smaller in wide compared to wider SW (p = 0.001, Table 3). Normalized SW was also smaller in preferred compared to wide (p = 0.009) and wider SW (p = 0.001) and smaller in wide compared to wider SW (p = 0.001). Moment arms and lateral trunk lean at the instants of 1st and 2nd peak abduction moments were not different between SW conditions (Table 4). 3.4. Knee angles and moments

2.5. Statistical analyses A repeated measures analysis of variance (ANOVA) was performed on selected variables to detect any differences between SW conditions (19.0, IBM SPSS, Chicago, IL). Mauchly's Test of Sphericity was used in order to test the assumption of equal variance of the difference between pairs of means. When the assumption of sphericity was not met (i.e., p b 0.05), the Greenhouse–Geisser adjustment was used to assess within subject differences. When the ANOVA revealed a main SW effect, a least significant difference method was used to detect differences between SW conditions in post-hoc comparisons. The alpha level was set at 0.05.

Knee flexion range of motion (ROM) and peak extension moment were both unchanged with increasing SW (Table 4). The 2nd peak knee adduction angle was greater in preferred compared to wide (p = 0.016) and wider SW (p = 0.001) and greater in wide compared to wider SW (p = 0.008, Table 4). It occurred significantly earlier in wide (p = 0.006) and wider SW (p = 0.001) compared to preferred SW, and earlier in wider (p = 0.009) compared to wide SW. No significant differences were found in 1st and 2nd peak internal knee abduction moments between SW conditions. The 2nd peak knee abduction moment occurred significantly earlier in wide (p = 0.007) and wider SW (p = 0.007) compared to preferred SW, and earlier in wider (p = 0.038) compared to wide SW. The ensemble knee adduction angle and knee abduction moment curves across SW conditions are provided to illustrate the timing differences in peak adduction angles and abduction moments (Fig. 2).

4. Discussion 3. Results 3.1. Knee pain The VAS knee pain scores were 1.45 ± 1.77 cm (CI: 0.38–2.52), 1.40 ± 1.77 cm (CI: 0.33–2.47) and 1.32 ± 1.36 cm (CI: 0.49–2.14) for preferred, wide and wider SW, respectively, and were not different between SW conditions (p = 0.806).

The purpose of this study was to examine the effects of increased SW on knee biomechanics in medial compartment knee OA patients during stair descent. Our results indicate that increased SW did not alter peak abduction moments, 1st peak adduction angle, sagittal plane ROM and peak extension moment, vertical GRF variables, and knee pain. Our

Table 4 Step width, moment arm, foot progression angle, lateral trunk lean and sagittal plane knee variables for all three step width conditions (mean ± standard deviation) with 95% confidence intervals. Variables

Preferred SW

Wide SW

Wider SW

pc

SW (m) NormSW (%) MA1 (cm) MA2 (cm) FPA (°) LTL1 (°) LTL2 (°) FL_ROM (°) Ext_M (Nm/kg)

0.11 ± 0.03a,b (0.09–0.12) 20.4 ± 5.0 a,b (0.17–0.23) 5.47 ± 1.73 (4.40–6.50) 5.63 ± 1.87 (4.50–6.80) −13.5 ± 4.2 (−11.0 to −16.0) 1.07 ± 2.89 (−0.67–2.81) 3.35 ± 2.60 (1.79–4.92) −79.1 ± 9.0 (−73.6 to −84.5) 0.71 ± 0.24 (0.57–0.85)

0.12 ± 0.02b (0.11–0.14) 24.0 ± 2.2b (0.23–0.25) 5.49 ± 1.90 (4.30–6.60) 5.59 ± 1.78 (4.50–6.70) −12.7 ± 4.2 (−10.2 to −15.2) 0.92 ± 2.53 (−0.61–2.45) 3.26 ± 2.53 (1.73–4.79) −80.0 ± 6.9 (−75.8 to −84.1) 0.71 ± 0.24 (0.57–0.86)

0.17 ± 0.02 (0.16–0.18) 34.0 ± 3.0 (0.32–0.36) 5.52 ± 1.84 (4.40–6.60) 5.41 ± 1.84 (4.30–6.50) −12.9 ± 4.9 (−10.0 to −16.0) 0.50 ± 2.63 (−1.08–2.10) 2.89 ± 2.53 (1.36–4.42) −79.8 ± 5.9 (−76.2 to −83.3) 0.77 ± 0.18 (0.66–0.89)

0.001 0.001 0.918 0.406 0.474 0.107 0.072 0.646 0.160

Step width (SW), SW normalized to leg length (NormSW), frontal plane GRF vector moment arm to knee center at KAM1 (MA1) and KAM2 (MA2), foot progression angle (FPA), lateral trunk lean at KAM1 (LTL1) and KAM2 (LTL2), stance phase knee flexion range of motion (FL_ROM) and peak knee extensor moment (Ext_M). a Significantly different from wide SW. b Significantly different from wider SW. p: Step width main effect p-value. c p-Value for ANOVA test.

Please cite this article as: Paquette MR, et al, Does increasing step width alter knee biomechanics in medial compartment knee osteoarthritis patients during stair descent?, Knee (2014), http://dx.doi.org/10.1016/j.knee.2014.02.020

M.R. Paquette et al. / The Knee xxx (2014) xxx–xxx

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Fig. 2. Ensemble curves of knee adduction angle (A) and abduction moment (B) for knee OA patients in all three step width conditions. Solid line: preferred, dashed line: wide SW, dotted line: wider SW.

subjects reported low levels of knee pain (i.e., less than 1.45 cm on a 10.0 cm scale) during all stair descent trials. The increase in SW reduced the 2nd peak knee adduction angle. The frontal plane GRF vector was also reduced in wider SW compared to preferred and wide SW at the time of 2nd peak abduction moment. Factors that have been shown to influence the peak knee abduction moments such as moment arm, lateral trunk lean and foot progression angle were all unaltered between SW conditions. Our results confirm that absolute and normalized SWs were increased from preferred to wider SW conditions. The results indicate that preferred SW in knee OA adults during stair descent was 20.4% of leg length which is similar to the preferred SW of 19.8% found in healthy adults during stair descent [39]. Contrary to our primary hypothesis, the 1st peak knee adduction angle and the 1st and 2nd peak knee abduction moments were not changed with increased SW. Hunt et al. [18] found significant positive correlations between frontal plane GRF and the peak knee abduction moment, and between frontal plane GRF moment arm and the peak knee abduction moment in medial compartment knee OA patients during level-walking. Our results show that both the moment arm and the frontal plane GRF vector at the time of 1st peak abduction moment were unchanged between SW conditions. This would explain the unaltered

1st peak knee abduction moments with increased SW. The moment arm at the time of 2nd peak abduction moment was also unchanged between SW conditions. The peak frontal plane GRF at the time of 2nd peak abduction moment was smaller in wider SW compared to preferred and wide SW. This would yield a smaller 2nd peak abduction moment in wider SW compared to the other conditions considering the unchanged moment arm at that time. It is important to note that the 2nd peak abduction moment, although not significantly different, was slightly smaller in wider SW compared to preferred and wide SW (Table 5). This slight reduction in the 2nd peak abduction moment appears to be related to the smaller frontal plane GRF at the time of 2nd peak abduction moment. However, the difference is likely too small to be clinically relevant. Differences in timing of the 2nd peak adduction angle and 2nd peak abduction moment may offer additional insights on why the 2nd peak abduction moment and the related moment arm were not different between SW, despite a smaller adduction angle. For all SW conditions, the 2nd peak adduction angle occurs later than the 2nd peak knee abduction moment (Table 4). At the time of 2nd peak abduction moment, the knee adduction angle between SW conditions does not appear to be much different (Fig. 2). The knee adduction angle is an important

Table 5 Frontal plane knee variables for all three step width conditions: mean ± standard deviation (95% confidence interval). Variables

Preferred SW

Wide SW

Wider SW

pc

KADD1 (°) Time_KADD1 (s) KADD2 (°) Time_KADD2 (s) KAM1 (N m/kg) Time_KAM1 (s) KAM2 (N m/kg) Time_KAM2 (s)

3.8 ± 3.5 (1.8–5.9) 0.19 ± 0.03 (0.17–0.22) 7.8 ± 4.4a,b (5.2–10.5) 0.66 ± 0.13a,b (0.58–0.74) −0.65 ± 0.23 (−0.51 to −0.79) 0.19 ± 0.03 (0.17–0.21) −0.49 ± 0.17 (−0.38 to −0.59) 0.59 ± 0.07a,b (0.54–0.63)

3.5 ± 3.5 (1.4–5.6) 0.17 ± 0.06 (0.14–0.21) 6.7 ± 4.7b (3.9–9.6) 0.62 ± 0.15b (0.54–0.71) −0.65 ± 0.24 (−0.51 to −0.80) 0.19 ± 0.03 (0.17–0.20) −0.48 ± 0.17 (−0.38 to −0.59) 0.56 ± 0.08b (0.51–0.61)

3.1 ± 4.1 (0.6–5.5) 0.17 ± 0.05 (0.14–0.20) 5.1 ± 4.9 (2.2–8.1) 0.56 ± 0.13 (0.48–0.64) −0.65 ± 0.24 (−0.50 to −0.79) 0.18 ± 0.03 (0.17–0.20) −0.46 ± 0.17 (−0.35 to −0.56) 0.53 ± 0.10 (0.47–0.59)

0.083 0.162 0.001 0.001 0.912 0.488 0.139 0.006

First peak knee adduction (KADD1), time to KADD1 (Time_KADD1), 2nd peak knee adduction (KADD2), time to KADD2 (Time_KADD2), 1st peak knee abduction moment (KAM1), time to KAM1 (Time_KAM1), 2nd peak knee abduction moment (KAM2), and time to KAM2 (Time_KAM2). a Significantly different from wide SW. b Significantly different from wider SW; p: Step width main effect p-value. c p-Value for ANOVA test.

Please cite this article as: Paquette MR, et al, Does increasing step width alter knee biomechanics in medial compartment knee osteoarthritis patients during stair descent?, Knee (2014), http://dx.doi.org/10.1016/j.knee.2014.02.020

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variable related to the medial knee loads as varus knee alignment increases the medial bone contact in the knee [4]. However, in late stance the knee adduction angle may not create clinically relevant medial knee bone loads as the stance limb is unloaded when the weight is shifted to the contralateral limb. To date, the implications of the 2nd peak knee adduction angle on the medial knee loads are unknown. Furthermore, foot progression angle has been shown to reduce the 2nd peak knee abduction moment during stair ascent in medial compartment knee OA patients [19]. However, since both foot progression angle and abduction moment were not different between conditions in the current study, no insight can be gained. In addition, Hunt et al. [37] reported that lateral trunk lean was significantly but negatively correlated to the 1st and 2nd peak knee abduction moments in medial compartment knee OA patients during level-walking. An increased lateral trunk lean shifts the trunk over the stance limb and causes a lateral shift of the frontal plane GRF vector. This reduces its moment arm to the knee joint center and, in turn, reduces the knee abduction moment [37]. However, our results indicated that lateral trunk lean at 1st and 2nd peak abduction moments was not significantly different between SW conditions. Knee pain also remained unchanged between SW conditions. One of the first complaints due to pain in older adults suffering from knee OA is difficulty in stair ambulation [3]. In the current study, the preferred SW pain values fell in the lower range of previously reported VAS knee pain values during level-walking and stair negotiation combined in knee OA patients [45]. The low initial levels of reported knee pain in our knee OA patients may explain the lack of pain reduction with increased SW. It is difficult to interpret this finding as we did not document or control for pain medications which could explain low pain levels. Further, it is possible that knee OA patients with more severe knee pain would show reductions in pain when SW increased. Although our knee OA group reported low KOOS quality of life (QOL) scores, they reported higher KOOS activities of daily living (ADL; which includes stair negotiation) scores suggesting that, along with the low knee pain, our knee OA participants had relatively high levels of daily knee function. Future stair negotiation studies should not only account for knee OA severity (i.e., K/L grade) but should also consider studying groups of knee OA patients with greater levels of knee pain to further understand potential factors related to knee joint loads during stair walking. Finally, the peak knee abduction moments have been shown to decrease with increased SW in healthy adults at an average descending speed of 0.57 m/s [39]. The 1st peak knee abduction moment ranged between − 0.73 and − 0.77 Nm/kg while the 2nd peak abduction moment −0.38 and −0.48 Nm/kg in healthy adults [39]. In the current study, the stair descent speed was slower and peak abduction moments were smaller compared to the previously reported findings in the healthy older adults during stair descent with increasing SW [39]. Given the slower speed and smaller peak abduction moments, it appears that knee OA patients tend to adopt a safer or more comfortable gait pattern in stair descent. The current study reported only acute effects of increased SW on knee abduction moment, a variable often used as a surrogate for medial compartment knee loading in the literature. However, it does not accurately depict actual tibial and femoral contact forces that could only be measured in vivo or estimated through musculoskeletal modeling. Further, it is unknown whether or not individuals could adapt to negotiating stairs with increased SW without visual targets. In addition the smaller number of participants (13) may have limited statistical power and may reduce the generalizability of the findings. However, a priori statistical power analysis showed that a minimum of 12 participants was required to obtain sufficient statistical power (i.e., α = 0.05, β = 0.80). Difficulty in marker placement on obese individuals may have introduced errors in calculating knee and hip joint centers. The same experienced researcher placed the markers on all participants and markers remained in place on the participant for all three conditions in order to minimize such errors during testing.

5. Conclusion In summary, the findings of the current study indicate that increased SW during stair descent did not reduce peak internal knee abduction moments or knee pain in medial compartment knee OA patients. The low initial knee pain in our patients may explain the unaltered pain levels. This is the first study to report changes in GRF and knee joint variables when SW is increased in knee OA patients during stair descent. The unchanged abduction moments with increased SW may suggest that medial compartment knee loads are not related to changes in SW in knee OA patients during stair descent. Future studies are needed to assess the long term effects of increased SW on knee loads and function. Conflict of interest statement The authors have no conflicts of interest to declare. Acknowledgments No funding was provided for this study. 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 Medical Center. References [1] Felson DT, Lawrence RC, Dieppe PA, Hirsch R, Helmick CG, Jordan JM, et al. Osteoarthritis: new insights. Part 1: the disease and its risk factors. Ann Intern Med 2000;133:635–46. [2] Hootman J, Bolen J, Helmick C, Langmaid G. Prevalence of doctor-diagnosed arthritis and arthritis-attributable activity limitation — United States, 2003–2005. Centers for Disease Control and Prevention MMWR, 55; 2006. p. 1089–92. [3] Costigan PA, Deluzio KJ, Wyss UP. Knee and hip kinetics during normal stair climbing. Gait Posture 2002;16:31–7. [4] Andriacchi TP, Mundermann A, Smith RL, Alexander EJ, Dyrby CO, Koo S. A framework for the in vivo pathomechanics of osteoarthritis at the knee. Ann Biomed Eng 2004;32:447–57. [5] Hinman RS, Bennell KL, Metcalf BR, Crossley KM. Delayed onset of quadriceps activity and altered knee joint kinematics during stair stepping in individuals with knee osteoarthritis. Arch Phys Med Rehabil 2002;83:1080–6. [6] Hinman RS, Cowan SM, Crossley KM, Bennell KL. Age-related changes in electromyographic quadriceps activity during stair descent. J Orthop Res 2005;23:322–6. [7] Asay JL, Mundermann A, Andriacchi TP. Adaptive patterns of movement during stair climbing in patients with knee osteoarthritis. J Orthop Res 2009;27:325–9. [8] Hicks-Little CA, Peindl RD, Fehring TK, Odum SM, Hubbard TJ, Cordova ML. Temporal-spatial gait adaptations during stair ascent and descent in patients with knee osteoarthritis. J Arthroplasty 2012 (2012/03/06 ed). [9] Hicks-Little CA, Peindl RD, Hubbard TJ, Scannell BP, Springer BD, Odum SM, et al. Lower extremity joint kinematics during stair climbing in knee osteoarthritis. Med Sci Sports Exerc 2010. [10] Hicks-Little CA, Peindl RD, Hubbard TJ, Scannell BP, Springer BD, Odum SM, et al. Lower extremity joint kinematics during stair climbing in knee osteoarthritis. Med Sci Sports Exerc 2011;43:516–24. [11] Baliunas AJ, Hurwitz DE, Ryals AB, Karrar A, Case JP, Block JA, et al. Increased knee joint loads during walking are present in subjects with knee osteoarthritis. Osteoarthritis Cartilage 2002;10:573–9. [12] Kaufman KR, Hughes C, Morrey BF, Morrey M, An KN. Gait characteristics of patients with knee osteoarthritis. J Biomech 2001;34:907–15. [13] Messier SP, Loeser RF, Hoover JL, Semble EL, Wise CM. Osteoarthritis of the knee: effects on gait, strength, and flexibility. Arch Phys Med Rehabil 1992;73:29–36. [14] 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;52:2835–44. [15] Liikavainio T, Isolehto J, Helminen HJ, Perttunen J, Lepola V, Kiviranta I, et al. Loading and gait symmetry during level and stair walking in asymptomatic subjects with knee osteoarthritis: importance of quadriceps femoris in reducing impact force during heel strike? Knee 2007;14:231–8. [16] Schipplein OD, Andriacchi TP. Interaction between active and passive knee stabilizers during level walking. J Orthop Res 1991;9:113–9. [17] 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. [18] 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;39:2213–20. [19] 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;26:436–41.

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Please cite this article as: Paquette MR, et al, Does increasing step width alter knee biomechanics in medial compartment knee osteoarthritis patients during stair descent?, Knee (2014), http://dx.doi.org/10.1016/j.knee.2014.02.020