Scand J Med Sci Sports 2015: ••: ••–•• doi: 10.1111/sms.12434

© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd

Anterior cruciate ligament injury about 20 years post-treatment: A kinematic analysis of one-leg hop E. Tengman1, H. Grip1, AK. Stensdotter1,2, C. K. Häger1 Department of Community Medicine and Rehabilitation, Physiotherapy, Umeå University, Umeå, Sweden, 2Faculty of Health Education and Social Work, Physiotherapy, Sør-Trøndelag University College, Trondheim, Norway Corresponding author: Eva Tengman, Umeå University, Department of Community Medicine and Rehabilitation, Physiotherapy, Umeå SE-90187, Sweden. Tel: 0046 703770680, Fax: 0046 907869267, E-mail: [email protected]

1

Accepted for publication 20 January 2015

Reduced dynamic knee stability, often evaluated with oneleg hops (OLHs), is reported after anterior cruciate ligament (ACL) injury. This may lead to long-standing altered movement patterns, which are less investigated. 3D kinematics during OLH were explored in 70 persons 23 ± 2 years after ACL injury; 33 were treated with physiotherapy in combination with ACL reconstruction (ACLR) and 37 with physiotherapy alone (ACLPT). Comparisons were made to 33 matched controls. We analyzed (a) maximal knee joint angles and range of motion (flexion, abduction, rotation); (b) medio-lateral position of the center of mass (COM) in relation to knee and ankle joint

centers, during take-off and landing phases. Unlike controls, ACL-injured displayed leg asymmetries: less knee flexion and less internal rotation at take-off and landing and more lateral COM related to knee and ankle joint of the injured leg at landing. Compared to controls, ACLR had larger external rotation of the injured leg at landing. ACLPT showed less knee flexion and larger external rotation at take-off and landing, and larger knee abduction at Landing. COM was more medial in relation to the knee at take-off and less laterally placed relative to the ankle at landing. ACL injury results in long-term kinematic alterations during OLH, which are less evident for ACLR.

An anterior cruciate ligament (ACL) injury is generally sustained in sports or leisure activities when landing from a jump or in situations involving decelerations or side-cutting maneuvers (Boden et al., 2000; Olsen et al., 2004). A movement pattern with a combination of large hip adduction, large hip internal rotation, large knee abduction, and small knee flexion is associated with an increased risk of ACL injury (Hewett et al., 2005, 2010). Risk of ACL injury is higher when the center of mass (COM) of the body is placed away from the center of the base of support (Paterno et al., 2010), especially with a more lateral COM during one-legged actions, which may particularly increase knee abduction loading (Hewett & Myer, 2011). The positioning of COM relative to the knee and ankle joint centers may therefore be crucial for knee protection. A dynamic alignment of “knee-in and toe-out” is a common injury mechanism (Kobayashi et al., 2010) and a “knee over the foot” strategy proposed to prevent injury is therefore often targeted in prevention programs and rehabilitation (Renstrom et al., 2008; Kobayashi et al., 2010; Trulsson et al., 2010). An ACL injury often leads to reduced knee function in the short as well as long term. The majority of afflicted individuals become less physically active in sports and recreation (Frobell et al., 2010; Ardern et al., 2011), and often remain less active many years later (von Porat

et al., 2004; Neuman et al., 2008; Tengman et al., 2014a). A common consequence of ACL injury is osteoarthritis (OA) in the knee, regardless of treatment (Lohmander et al., 2004; von Porat et al., 2004). One reason might be altered biomechanical properties of the knee joint post-injury. Movement pattern asymmetries between the injured and noninjured leg in daily life activities that incur both low and high loading may presumably increase the risk of OA in the injured knee over time. In the short-term perspective, the ACL injury results in kinematic asymmetries between the injured and noninjured leg even in low demanding activities such as gait (Chmielewski et al., 2001; Webster et al., 2012). These asymmetries are sometimes normalized over time (von Porat et al., 2006). For high demanding activities (regarding both load and coordination), such as different jump tasks, changed knee kinematics have been observed in the short term (Deneweth et al., 2010; Orishimo et al., 2010; Roos et al., 2014). Long-term kinematic consequences are much less investigated and so far with contradictory results. Less knee flexion and increased knee abduction in the injured knee 4.4 years post-injury were reported (Delahunt et al., 2012), while other studies show no differences in kinematics in comparison to the noninjured leg or to controls after 7–16 years (von Porat et al., 2006; Ortiz et al., 2008). Conflicting results may be explained by the fact that studies

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Tengman et al. have investigated different functional tests and not always included the same variables. The most common jump task used in rehabilitation for assessment of functional performance after ACL injury is the one-leg hop (OLH), a jump for maximal distance. The standard way to evaluate this jump capacity is by dividing the jump distance for the injured leg to that of the noninjured leg, i.e., the limb symmetry index (LSI). A performance with an LSI ≥ 90% is often classified as normal performance and less than 90% as abnormal performance (Augustsson et al., 2004). Even if a person performs a jump with high LSI, and of equal hop length as healthy controls, the kinematics are not necessarily similar between limbs or in comparison with uninjured controls. The movement quality during functional tasks may encompass aspects not reflected simply by the distance jumped. Despite the frequent use of the OLH in both clinics and in research, the kinematics have so far not been extensively analyzed after injury. No clear agreement exists on what should be measured in terms of specific kinematic variables in relation to jump length or to side asymmetry. Hence, it seems imperative to examine the movement pattern after ACL injury in more detail and especially in the long-term perspective where even less is known, and also after different types of treatment, i.e., physiotherapy with or without surgery. Further, men and women may differ in movement patterns (Hewett et al., 2010), which may need to be taken into consideration.

with physiotherapy without surgery (ACLPT) were included. Radiological OA at stage 1–4 (Kellgren & Lawrence, 1957) was detected in 90% of the participants at the time of study. The ACL groups were balanced in age and gender; therefore, we recruited 33 healthy knee controls matched to both ACL groups for age and gender. The controls reported no previous knee injuries and were clinically examined for any injury to the menisci or ligaments. Demographics, knee scores (Lysholm questionnaire, Knee injury and Osteoarthritis Outcome Score, Tegner activity scale) and hop length have been reported more in detail elsewhere (Tengman et al., 2014a). No significant differences were seen in “hop length/body height” between ACL groups and controls, while both ACLR and ACLPT had significantly lower LSI than controls (Table 1). All participants were given written and oral information and gave their written informed consent. The project was approved by the Regional Ethical Review Board. Participants in ACLR (injured 1981–1993) had reconstructive surgery in the period of 1987–1993. The participants were operated upon with conventional surgical methods for that time period. Postoperative physiotherapy included functional exercises according to a progressive design with gradually increased levels of intensity and difficulty, aiming for improved joint mobility, strength, coordination, and balance. The goal was return to sports activities approximately 22 weeks after surgery. Participants in ACLPT (injured 1983–1988) underwent individualized physiotherapy treatments with a goal-oriented six-step program of increasing difficulty focused on activity modification and progressively increased functional stability. All exercises were performed with both legs, three sessions per week. Rehabilitation was considered complete when the patient could perform the final stage of exercises safely and with good quality (Tegner, 1990). The median time to reach this level and return to sports was 22 weeks (range 12–60 weeks). Participation in high-risk sports such as soccer, floorball, and wrestling was advised against (for further details, see Tengman et al., 2014a).

Aim

Data acquisition

The aim was to examine the kinematics during OLH in the long-term perspective (on average 23 years postinjury) of persons who had suffered unilateral ACL injury and who were treated either with physiotherapy in combination with surgery, or physiotherapy alone, and to compare the kinematics (a) between the injured and noninjured leg, and (b) to age- and gender-matched controls. We further aimed to relate the kinematics to the degree of radiological knee OA in the ACL-injured persons.

The test procedure started with a 6-min warm-up on a bicycle ergometer at moderate intensity, and some practice jumps. OLHs for maximal distance were performed starting on one leg in an upright position, jumping forward as far as possible and landing on the same leg while maintaining balance. Arms were held across the chest. If the participant put the other foot down or could not hold their arms across the chest, the jump was not approved. Hops were performed until three jumps were approved on each leg, starting on the noninjured leg for the ACL-injured and on the dominant leg for the controls, alternating jumping on the contralateral leg. Dominant leg was defined as the preferred leg for kicking a ball. Participants wore a training tank top, shorts, and were barefoot. Tests were performed at the U-Motion lab, Umeå University. Movements were registered using a motion capture system (Oqus®, Qualisys AB, Gothenborg, Sweden); eight cameras (240 Hz) emitting infrared light reflected back from 42 passive spherical markers (diameter 12 and 19 mm) on the body. The markers were placed on the sternum and between the posterior superior iliac spine, as well as bilaterally on the acromion, clavicle, crista, anterior superior iliac spine, trochanters, lateral/ medial epicondyles, patellas, tuberositas tibiae, caput fibulae, lateral/medial malleoli, lateral/medial foot, and three-marker rigid clusters were placed on thighs and shanks. Rigid marker clusters may also reduce errors caused by soft tissue artifacts (Collins et al., 2009). A stationary registration trial in standing for modeling purposes was performed prior to recording of OLHs. After the stationary registration, eight markers were removed from trochanters, lateral and medial epicondyles, and medial malleoli. The participants jumped off from a force plate (custom made, Department of Biomedical Engineering and Informatics, Norrlands Uni-

Methods Participants The present study is part of the X20-follow-up, a cross-sectional research programme involving two cohorts consisting of 113 individuals from two different hospitals who suffered an ACL injury 17–28 years ago. A subset of 81 participants with ACL injury was eligible for the present study because of inclusion criteria KACL20-study (knee injury – anterior cruciate ligament after more than 20 years; Tengman et al., 20144a, b). These criteria were unilateral ACL injury, no prosthesis, and no inflammatory or rheumatic disease or neurological pathology. Eleven persons declined to participate (9 ACLR and 2 ACLPT) because of living far away, considering testing too time consuming, or for unknown reasons. Thus, 33 persons treated with physiotherapy in combination with reconstructive surgery (ACLR) and 37 treated

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Kinematic analysis of one-leg hop Table 1. Participant characteristics

Means and SD

Group ACLR

N participants 33 Male/female 21/12 Age at test 45.6 (4.5) Height (cm) 174.0 (9.1) Weight (kg) 83.0 (15.6) BMI (kg/m2) 27.2 (3.3) Years since injury 23.9 (2.8) Years between injury – surgery 3.8 (2.5) Cause of injury Soccer 24 Alpine 2 Other sports 6 Nonsporting 1 Lysholm* 78 (18) KOOS† Pain 78 (18) Symptoms 79 (20) ADL 41 (16) Sport/Rec 50 (28) QoL 49 (22) Tegner‡ median (range) 4 (3–7) IPAQ§ 1563 (480–7572) OA KL 1¶ 5 OA KL 2 12 OA KL 3 10 OA KL 4 4 One-leg hop – hop length (m)/body length (m)** Injured leg 0.64 (0.15) Noninjured leg 0.68 (0.14) Limb symmetry index (%) 94 (11)

ACLPT

Controls

ACLR – controls

ACLPT – controls

37 23/14 48.1 (5.9) 173.5 (8.0) 87.1 (14.9) 28.9 (4.6) 23.1 (1.3) –

33 21/12 46.7 (5.0) 176.4 (9.8) 77.4 (14.9) 24.6 (2.5) – –

– – NS NS NS P = 0.014 – –

– – NS NS P = 0.025 P < 0.001 – –

25 5 2 5 69 (17) 85 (16) 72 (19) 90 (15) 67 (29) 61 (25) 4 (2–7) 1217 (212–7398) 6 13 9 3

–

– – – – P < 0.001 P < 0.001 P < 0.001 P < 0.001 P < 0.001 P < 0.001 P = 0.001 NS – – – –

– – – – P < 0.001 P < 0.001 P < 0.001 P < 0.001 P < 0.001 P < 0.001 P < 0.001 NS – – – –

NS NS P = 0.024

NS NS P = 0.008

0.58 (0.15) 0.63 (0.16) 92 (13)

100 99 (1) 98 (2) 100 99 (2) 98 (3) 6 (3–7) 1893 (499–8958) – – – – 0.61 (0.13) 0.61 (0.13) 100 (9)

ACLR was treated with physiotherapy in combination with reconstructive surgery while ACLPT was treated with physiotherapy alone. Background data has been reported more in detail in Tengman et al. 2014a. *0 represents the worst knee function and 100 is maximal value (Tegner and Lysholm 1985). † Knee injury and Osteoarthritis Outcome Score (KOOS) ranging between 0 (worst) and 100 (best) (Roos et al., 1998). ‡ Tegner activity scale 0–10 (highest) (Tegner and Lysholm 1985). § The short form of the International Physical Activity Questionnaire (IPAQ) scored in MET-minutes/week. ¶ Radiographic osteoarthritis (OA) was graded according to Kellgren & Lawrence 1957 (KL). **For controls, injured leg is comparable with nondominant leg. BMI, body mass index.

versity Hospital, Umeå, Sweden) that was used to determine hop take-off and landed on the floor. The force data were sampled with 1200 Hz and were time synchronized with the motion analysis system.

Data analyses The software Qualisys Track Manager (version 2.2, Qualisys AB) was used for capturing, construction of 3D marker coordinates, and for interpolation and identification of markers. The data was then exported for further analysis (Visual3D v.4.96, C-Motion Inc. Germantown, Maryland, USA). An eight-segment rigid body model consisting of feet, shanks, thighs, pelvis, and trunk was constructed, and joint center calculations were based on a 6-dof model (Grip & Häger, 2013). The center of mass (COM) was calculated based on this model where each segment was given a mass and cylindrical geometry based on anatomical landmarks at segment end points. The calculation also included an approximation of head and arm positions, where the arms were held across the chest (cf. http://www.c-motion.com). A bidirectional secondorder low-pass 6 Hz Butterworth filter was applied before further calculations.

The following two time events were determined for extracting the kinematic variables: (a) “take-off” when the foot was lifted from the force plate, which was calculated at the point in time when the force signal reached its’ minimum; (b) “initial contact” when the foot first touched the ground after the hop, defined as the minimum velocity of the marker on the lateral side of the foot. The OLH was thus divided into three phases: (a) take-off phase (−0.7 s to take-off); (b) flight phase (take-off to initial contact); and (c) landing phase (initial contact to 0.7 s after). All events were manually inspected, and corrected if the automatic algorithm had failed because of missing markers or movement artifacts. Knee joint flexion/extension, abduction/adduction, and internal/external rotation of tibiae relative to the femurs were measured. The outcome variables were maximum angles and range of motion (ROM; values of minimum to maximum angles) during the take-off and landing phases and absolute angle at initial contact. COM relative to the calculated center of the knee and ankle joints in the mediolateral directions was also determined. The outcome variables during the take-off and landing phases were (a) maximum distance between COM and knee and ankle joints in the lateral direction and (b) ROM (minimum to maximum values), and at initial contact (c), the distance between COM and knee and ankle joints.

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Tengman et al. Hop distance was calculated by measuring the displacement of the reflective marker on the lateral malleolus from take-off to landing. The longest jump was selected for each participant for further kinematic analysis.

at initial contact compared with the noninjured leg. COM in relation to knee and ankle joints on the injured side also showed a smaller total displacement during the landing phase (Tables 2 and 3).

Statistics All kinematic data were screened for normality of distribution assumptions using Shapiro–Wilk normality tests, outliers through the use of boxplots, and Levene’s test for homogeneity of variance. A prior power analysis was performed based on pilot data (n = 10, 80% power). There were some missing values because of hidden markers; this applies especially for COM relative to knee and ankle joints where all body segments are needed for calculations (6–17% of the values were missing). For the knee angles, 0–6% of the values were missing. For within-group comparisons, linear mixed models (LMMs) were used. LMM is often used when data is hierarchical, e.g., when some variables are clustered or nested within other variables or being nested within subjects (West et al., 2007). For ACLR and ACLPT, the fixed factors considered in the models were leg (injured and noninjured), gender (men and women), and radiographic OA [no-or-low OA (no OA or Kellgren and Lawrence KL 1) and moderate-to-high OA (KL2-4)]. The kinematics for both legs was included in the analysis for all participants. In a first model, all potential factors and two-way interactions between all factors were included. Thereafter, all nonsignificant interactions and nonsignificant factors were successively removed to a final model. Bonferroni post-hoc tests were used. “Participant” was included in the model as a random effect. Outcome variables were knee angles and positions for COM. Group was not included in the LMMs because no X-ray was performed on the controls, and therefore, we had no information of OA. Further, we chose not to make a strict comparison between the ACL groups since the present study is not a randomized controlled trial. Comparisons between each ACL group and the control group were therefore made with analyses of variance including all three groups using Bonferroni post-hoc test. The significance level was set to P < 0.05. All statistics were performed using the Statistical Package for the Social Sciences (IBM SPSS Statistics, Armonk, New York, USA), version 20.

Results Comparisons between injured and noninjured leg within the ACL groups ACLR Kinematic asymmetries were found during the OLH between the injured and noninjured leg (Tables 2 and 3). The injured knee displayed reduced maximal knee flexion and ROM before take-off and reduced knee flexion ROM and maximal knee abduction in the landing phase. There was also an increased external tibial rotation of the injured knee in the landing phase. Knee joint angles did not differ between men and women or between those with no-or-low and moderate-to-high degree of radiographic OA. Regarding COM in relation to the knee and ankle joint, there were also asymmetries between the injured and noninjured leg (Tables 2 and 3). The COM relative to the injured knee had a smaller displacement during the take-off phase compared with the noninjured side for the males, while females did not show any side differences. The COM position was less medially placed relative to the injured knee joint center

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ACLPT The injured knee displayed reduced maximal flexion and ROM during take-off and landing (Tables 2 and 3). For knee abduction, those with no-or-low OA displayed greater knee abduction at initial contact than those with moderate-to-high OA. Regarding tibial rotation, the injured knee had smaller internal rotation (max values and ROM) during take-off, and a larger maximum external rotation in the landing phase. COM position differed between legs in relation to the knee joint and ankle joint (Tables 2 and 3). The COM in relation to the knee during take-off had less ROM for males in the injured leg, while females showed no side differences. COM was less laterally positioned in relation to the ankle joint for the injured leg. Males showed larger maximum knee flexion during take-off, larger external rotation, and a more laterally placed COM in relation to the ankle joint during landing than females.

Comparisons between ACL groups and controls No significant differences were seen between dominant and nondominant leg for the controls, with the exception of a slightly higher ROM of knee abduction for nondominant leg at take off. ACLR in comparison with controls had larger external tibial rotation in their injured leg at initial contact and during landing (Fig. 1(c), Table 2). For their noninjured leg, the ACLR displayed a larger knee abduction ROM during take-off and landing. For COM placement in relation to the knee and ankle joint center in the mediolateral direction, there were no differences between injured leg and controls, while the noninjured leg had a larger total displacement of COM in relation to ankle joint (Fig. 2(a–b), Table 2). ACLPT in comparison with controls showed several differences (Fig. 1(a–c), Table 2): a decreased maximum knee flexion during take-off and landing, and larger knee abduction during Initial contact were observed both for the injured and noninjured leg. In analogy with the ACLR, the ACLPT showed larger external tibial rotation in their injured leg at initial contact and during the landing phase. In addition, the ACLPT displayed less internal rotation during take-off. Compared with controls, COM was more medially placed and with a smaller total displacement relative to the injured knee joint during take-off. Relative to the ankle joint, COM was less laterally placed to the injured knee joint at initial contact and during the landing phase compared with controls. For the noninjured leg,

Max angle TO ROM TO Angle IC Max angle L ROM L Max angle TO ROM TO Angle IC Max angle L ROM L Max angle TO ROM TO Angle IC Max angle L ROM L Max lateral COM TO Max displacement TO IC Max lateral COM L Max displacement L Max lateral COM TO Max displacement TO IC Max lateral COM L Max displacement L

64.3 (8.8) 36.4 (8.6) 19.7 (6.4) 57.1 (9.8) 38.8 (9.5) 0.4 (5.7) 7.9 (2.8) −2.4 (5.3) 0.4 (5.4) 9.9 (4.2) 3.2 (5.9) 12.3 (4.1) −13.8 (8.3) −1.1 (6.2) 13.6 (5.1) −0.6 (2.1) 4.4 (1.9) 1.6 (2.1) 0.2 (2.8) 3.6 (1.6) −1.5 (0.8) 3.4 (2.1) −2.8 (2.4) −3.6 (2.4) 3.1 (1.8)

68.1 (7.6) 39.1 (6.7) 19.5 (7.0) 60.9 (10.8) 42.3 (8.5) 1.6 (4.4) 7.9 (3.0) −0.9 (5.6) 3.3 (4.9) 11.5 (4.6) 3.4 (5.4) 11.9 (3.5) −10.5 (1.3) 3.0 (6.1) 14.6 (5.1) −0.6 (2.1) 4.9 (1.9) 2.4 (1.8) 0.7 (2.1) 4.4 (1.9) −1.7 (1.7) 3.3 (1.6) −2.3 (2.7) −3.5 (3.2) 4.8 (2.6)

60.5 (9.5) 33.6 (8.4) 17.7 (5.9) 52.0 (8.6) 38.3 (11.0) 3.8 (5.5) 7.5 (3.1) 2.3 (5.3) 4.2 (6.1) 9.1 (3.6) 1.4 (4.8) 10.5 (3.5) −10.8 (4.6) −1.3 (4.2) 12.0 (4.0) 1.2 (1.8) 3.3 (1.4) 2.5 (1.3) 1.1 (2.0) 3.6 (1.9) −1.2 (1.6) 2.9 (1.8) −1.3 (2.4) −2.4 (2.2) 2.9 (1.7)

Injured leg

Injured leg

Noninjured leg

ACLPT

ACLR

62.9 (8.3) 39.2 (8.1) 17.0 (5.2) 57.2 (8.4) 43.4 (9.9) 4.7 (4.7) 7.3 (3.1) 3.0 (4.7) 5.3 (4.0) 10.3 (4.0) 3.5 (5.2) 11.7 (3.0) −9.2 (7.0) 2.1 (5.9) 13.1 (4.0) 0.5 (2.4) 3.7 (1.4) 2.1 (1.8) 0.8 (2.3) 3.5 (1.6) −1.5 (1.2) 2.5 (1.3) −2.2 (2.8) −3.9 (3.0) 3.4 (2.1)

Noninjured leg 66.3 (5.9) 36.6 (8.1) 19.5 (5.4) 60.0 (11.0) 41.8 (9.6) 2.0 (4.8) 6.7 (2.6) −1.0 (4.8) 1.5 (5.08) 8.4 (3.0) 4.6 (4.9) 11.7 (4.0) −7.6 (5.1) 3.8 (3.6) 13.0 (4.7) −0.5 (2.5) 4.4 (1.5) 2.2 (1.3) 0.7 (2.1) 3.3 (3.2) 1.7 (1.1) 3.0 (1.7) −3.1 (1.9) −3.9 (1.8) 3.2 (1.8)

Nondominant leg

Controls

67.3 (7.2) 38.4 (6.8) 18.7 (4.5) 61.6 (9.2) 43.3 (8.5) 1.6 (5.3) 6.1 (2.7) −1.2 (5.0) 1.7 (5.1) 8.1 (2.8) 3.3 (4.1) 10.4 (3.5) −9.5 (5.9) 2.6 (4.2) 12.8 (5.6) −0.4 (1.7) 4.4 (1.5) 2.1 (1.2) 0.3 (1.5) 3.6 (1.8) 1.3 (1.1) 3.4 (1.9) −2.3 (2.2) −3.7 (2.0) 2.7(1.1)

Dominant leg

NS NS NS NS NS NS NS NS NS NS NS NS P < 0.001 P = 0.026 NS NS NS NS NS NS NS NS NS NS NS

I-ND

NS NS NS NS NS NS P = 0.035 NS NS P = 0.001 NS NS NS NS NS NS NS NS NS NS NS NS NS NS P = 0.001

NI-D

ACLR – controls

P = 0.0013 NS NS P = 0.008 NS NS NS P = 0.015 NS NS P = 0.049 NS P = 0.0019 P = 0.001 NS P = 0.012 P = 0.037 NS NS NS NS NS P = 0.013 P = 0.014 NS

I-ND

P = 0.030 NS NS NS NS P = 0.030 NS P = .001 NS P = 0.034 NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS

NI-D

ACLPT – controls

For comparisons between ACL-injured and controls, analyses of variance were used and P-values are reported. I stands for injured leg, NI for noninjured leg, D for dominant, and ND for nondominant leg for controls. *Medio-lateral position; positive values indicate medial position relative to the joint center and negative values represent a lateral position. ACLR was treated with physiotherapy in combination with reconstructive surgery and ACLPT was treated with physiotherapy alone.

COM in relation to ankle M-L*, cm

COM in relation to knee joint center M-L*, cm

Knee internal rotation, angle°

Knee abduction angle°

Knee flexion angle°

Variables mean (SD)

Table 2. Variables reported for the one-leg hop: peak and range of motion (ROM) of the knee angles in degrees, maximum lateral position of center of mass (COM) relative to knee and ankle joint centers in cm, and maximal displacement (MD) of COM in medio-lateral (M-L) direction in relation to knee and ankle joint centers in cm. These variables are reported for take-off phase (TO), at initial contact at landing (IC), and during the landing phase (L)

Kinematic analysis of one-leg hop

5

6 NS P = 0.010; I −1.35 2.22; NI 1.5− 5.1 NS NS NS NS P = 0.034; I−2.2 – 2.3; NI 0.8–5.2 NS NS Leg × gender P = 0.038; F NS; M P = 0.014 P = 0.034; I 0.9–2.3; NI 1.7–3.1 NS P = 0.026; I 2.9–4.2; NI 3.8–5.1 NS NS NS NS

Max angle TO ROM TO

Angle IC

Max angle L

ROM L Max angle TO

ROM TO

Angle IC

Max angle L

Max displacement L

Max lateral COM TO Max displacement TO IC Max lateral COM L

Max lateral COM L Max displacement L

IC

ROM L Max lateral COM TO Max displacement TO

P = 0.003; I 2.3–4.0; NI 4.0–5.8

P = 0.001; I 30.9–36.4; NI 36–41.9 NS NS

ROM L

Angle IC Max angle L

ROM TO

P = 0.027; I 61.9–67.8; NI 64.9–70.8 P = 0.050; I 33.7–39.1; NI 36.4–41.8 NS NS

Max angle TO

NS

NS NS NS NS

NS NS

NS

NS NS

NS

NS

NS

NS NS

NS

NS

NS NS

NS

NS NS

NS

NS

NS

NS NS NS NS

NS NS

NS

NS NS NS

NS

NS

NS

NS NS

NS

NS

NS NS

NS

NS NS

NS

NS

NS NS NS P = 0.019; I −3.1 −1.3; NI −4.6 −2.8 NS

NS NS

P = 0.003; I −2.4 – 0.9; NI 1.0–4.3 NS NS Leg × gender P = 0.017; F NS; M P = 0.013 NS

NS P = 0.028; I 0.2–3.5; NI 2.3–5−6 P = 0.036; I 9.6–12.3; NI 11.3–14.0 NS

NS

NS

P = 0.024; I 56.6–61.9; NI 59.2–64.4 P = 0.001; I 30.9–36.4; NI 36.5–41.9 NS P = 0.021; I 49.6–55.5; NI 54.2–59.9 P = 0.028; I 34.8–41.7; NI 39.9–46.8 NS NS

NS NS NS P = 0.035; M −4.4 −2.9; F −3.3 −1.1 NS

NS NS

NS

P = 0.002; M −14.0− −9.9; F −8.95− 3.6 P = 0.017; M −2.4−0.6; F 0.7–4.8 NS NS

NS P = 0.046; M −0.2 – 3.1; F 2.1–6.6 NS

NS

NS

NS NS

NS

NS NS

P = 0.001; M 62.2–68.1; F 52.1–59.7 NS

Gender

NS

NS NS NS NS

NS NS

NS

NS NS NS

NS

NS

NS

NS NS

P = 0.04; OA 1.4 −2.5; no OA −0.9 −4.9 NS

NS NS

NS

NS NS

NS

NS

OA*

NS

NS NS NS NS

NS NS

NS

NS NS NS

NS

NS

NS

NS NS

NS

NS P = 0.041 D 5.2–7−7 ND 6.7–9.3 NS

NS

NS NS

NS

NS

Leg dominance

Controls

NS

NS NS NS NS

NS NS

NS

NS NS NS

NS

NS

NS

NS NS

NS

NS

NS NS

NS

NS NS

NS

NS

Gender

“Participant” was included in the model as a random effect and all models had a significant random effect of “participant.” The variables are reported for take-off phase (TO), at initial contact at landing (IC), and during the landing phase (L): peak and range of motion (ROM) of the knee angles in degrees, maximum lateral position of center of mass (COM) relative to knee and ankle joint centers in cm, and maximum displacement (MD) of COM in medio-lateral (M-L) direction in relation to knee and ankle joint centers in cm. Interactions are reported with a x between the factors. *Bilaterally radiographic osteoarthritis (OA) was graded according Kellgren & Lawrence (KL) and divided into participants with no-or-low (KL 0–1) or moderate-to-high (KL 2–4) degree of OA. ACLPT, anterior cruciate ligament with physiotherapy; ACLR, anterior cruciate ligament reconstruction; I stands for injured leg, NI for noninjured leg; NS, Non-significant.

COM in relation to ankle M-La, cm

COM in relation to knee joint center M-La, cm

Knee internal rotation angle°

Knee abduction angle°

Knee flexion angle°

Leg

OA*

Leg

Gender

ACLPT

ACLR

Table 3. Linear mix models were used for within-group comparisons. P values and estimated 95% CI from the model are presented

Tengman et al.

Kinematic analysis of one-leg hop

Fig. 1. Knee angles curves presented in sagittal plane (a), frontal plane (b), and transverse plane (c). The three phases (take-off, flight, and landing) for the one-leg hop are presented where the events take-off and initial contact are marked with horizontal lines. Take off phase is −0.7 s to take-off and the landing phase is +07.s after initial contact. The …. line represents ACLR injured leg, - - - line ACLPT injured leg and the ___ line the controls nondominant leg. The shaded areas represent standard deviation for the controls.

Fig. 2. The three phases (take-off, flight, and landing) for the one-leg hop are presented where the events take-off and initial contact are marked with horizontal lines. (a) Center of mass (COM) in relation to knee joint in medial (+) and lateral (−) direction. (b) COM in relation to ankle joint in medial (+) and lateral (−) direction. The - - - line represents ACLR injured leg, ___ line ACLPT injured leg and the …. line the controls nondominant leg. The shaded areas represent standard deviation for the controls.

there were no differences in COM placement relative to the knee or ankle joint compared with controls (Fig. 2(a–b), Table 2). Discussion The aim of the present study was to describe the movement pattern during OLH in individuals who had suffered a unilateral ACL injury approximately 23 years earlier, and compare with controls. The focus was on knee joint angles and position of COM during the takeoff and landing phases of the jump. Divergent movement patterns were seen in ACL-injured compared with controls despite a similar hop length in all three groups (Tengman et al., 2014a). In comparison with controls, the differences for the injured leg were greater in ACLPT than for ACLR. Although only knee joint rotation differed in ACLR, knee kinematics in ACLPT deviated from controls also for knee flexion and abduction as well as with regard to the relative position of COM in the frontal plane above the joint centers of the knee and ankle. Altered movement patterns in the injured leg were also seen compared with the noninjured leg, both regarding knee angles and COM placement. Our results are in line with earlier studies of OLH after ACL injury, showing less internal tibial rotation of

the surgically reconstructed knee at landing compared with the noninjured leg (Deneweth et al., 2010). A reduced internal tibial rotation has also been reported for the ACL-deficient knee in other tasks such as drop landing and gait (Ristanis et al., 2005; Webster et al., 2012). Both ACL groups in the present study displayed increased external rotation of the tibia at initial contact, which supports the assumption that reconstruction does not restore the rotational component (Ristanis et al., 2005), even though the translational component may have been normalized (Kothari et al., 2012). More recent surgical techniques may, however, better reestablish the rotational stability. For instance, surgical procedures known to reduce the rotational deviation include drilling the femoral tunnel through an anteromedial portal (Kothari et al., 2012; Wang et al., 2013), and the use of double-bundle reconstructions (Samuelsson et al., 2009). None of the participants in the present study were, however, operated upon with these techniques. With regard to knee flexion, our results are also in line with earlier studies showing reduced knee flexion in the ACL-injured knee when landing on two legs (Hewett et al., 2005), as well as on one leg (Deneweth et al., 2010). In our study, knee flexion at landing was reduced in the injured knee in both ACLR and ACLPT compared

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Tengman et al. with the noninjured side. In addition, ACLPT displayed less knee flexion in both knees compared with controls. Movement patterns with less knee flexion during landing after a jump is associated with an increased risk of ACL injury (Hewett et al., 2005, 2010) and proper landing techniques are recommended to be included in rehabilitation, e.g., landing softly on the forefoot and with larger knee flexion (Renstrom et al., 2008). The ACLR group displayed less abduction in the reconstructed knee compared with the noninjured knee and greater dynamic ROM in the noninjured knee in comparison with controls. Deneweth et al. (2010) demonstrated increased knee adduction in the ACLreconstructed knee during the OLH compared with controls, which is similar to our data (Fig. 1(b)). Regarding ACLPT, no side differences were observed between the injured and noninjured leg, although greater knee abduction was evident in both knees at initial contact compared with controls. In conjunction, there was a medial position of COM relative to the knee for the injured side. A medial position of COM redirects the body mass over the knee and reduces the moment across the joint. Valgus position of the knee is considered a risk factor as it increases the moment across the knee which augments ACL strain (Shin et al., 2009), Thus, the position of COM may compensate for the valgus position in the knee. In addition, there was a lateral placement of COM relative to the ankle joint in the injured side, but this was less laterally placed compared with controls (Fig. 2(a–b)). The pattern shown in ACLPT may be interpreted as a compensatory strategy for the increased valgus position. In general, ACLR showed a more similar movement parameter to controls than ACLPT. There were, however, side differences between the injured and noninjured legs in both the ACLR and ACLPT groups. The injured leg had significantly shorter hop length compared with the noninjured leg (Tengman et al., 2014a) and some of the outcome measures may be associated with hop length. A greater knee flexion and longer hop length characterized the noninjured leg in both ACL groups. Greater knee flexion extends the time that force is applied by the leg muscles, which technically results in a longer jump. However, many other factors, such as the inclination of the jump, are consequential (Wu, 2003). Although the groups were comparable with regard to gender, age, and body height, the control group had a lower body mass index (BMI). In ACLPT, females displayed less flexion and greater internal rotation at the knee. Gender had no effect in the other groups. The lack of gender kinematic differences may be due to the small sample size, and further studies regarding gender influence are warranted. In general, females display inferior jump performance compared with men (Ageberg et al., 2001). Further research is also required regarding other factors that may influence the kinematics, e.g., hop length, physical activity level, knee muscle strength,

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knee stability, OA, meniscus injuries, age, and BMI. Reduced strength (Tengman et al., 2014b), reduced physical activity level (Tengman et al., 2014a), and OA (Lohmander et al., 2004; von Porat et al., 2004) are common consequences of an ACL injury. In the present study, radiographic OA did not predict hop strategy. One reason may be that over 90% of both ACL populations had radiographic OA. Therefore, we cannot entirely distinguish between the direct effects of ACL injury and the contribution of OA. Altered biomechanical properties of the knee joint post-injury have also been suggested to increase the risk of OA. Notably, there are few kinematic studies performed in the long term. Deneweth et al. (2010) investigated the OLH just 4–5 months after reconstructive surgery, where the surgical techniques were different compared with the present study. Nevertheless, the general results with regard to both ACL groups were similar. In contrast, a long-term study of gait and crossover hop in conservatively treated individuals who suffered an ACL injury 16 years ago, did not show any kinematic differences compared with controls (von Porat et al., 2006). Von Porat’s study was, however, most likely underpowered as it was only based on six ACL-injured subjects. It should be noted that our study was not an randomized controlled trial with a follow-up aimed to evaluate conservative treatment and ACL reconstructive surgery, but a cross-sectional study of functional performance in two different cohorts with biomechanically different ACL conditions compared with matched controls without knee injury. 3D movement analysis has its limitations when it comes to the use of skin markers to detect small joint movements such as rotation around the vertical axis and ab- or adduction in the knee joint (Akbarshahi et al., 2010). However, potential soft tissue artifacts are likely to be similar in all three groups and the same examiner (E. T.) attached all markers and tested all participants. All movements involve variability, and the amount of variation in a maximum jump would be valuable to explore in a reliability study which to our knowledge has not been done. The traditional approach in kinematic analyses, which we have applied in the present study, is to compare event-related variables such as maximum joint angles at specific points in time or during certain phases. The movements during the entire time domain were therefore not considered. For instance, maximal knee angles may occur at different time points in a specific phase for different individuals. Movement curves might thus be very diverse despite common maximum or minimum values, which were not considered in our statistical analyses. Recent statistical advances allow for analyses comparing the entire movement curve during the whole jump (Godwin et al., 2010). Such expanded analyses of the jump with statistical methodological focus are under way in multiprofessional collaborative efforts (Hebert Losier et al. in manuscript).

Kinematic analysis of one-leg hop Perspectives Our findings indicate persistent altered movement patterns during an OLH in persons who have suffered an ACL injury more than 20 years earlier. For ACLR, there was a particular difference in tibial rotation during the landing phase compared with controls, as well as to the noninjured leg. Apart from tibial rotation, ACLR appears to regain a better normalized movement pattern comparable with that of controls, as studied by this set of kinematic variables, suggesting that reconstructive surgery may restore the knee biomechanics to some extent. The movement pattern for ACLPT differs in several variables compared with controls and to the noninjured leg, indicating compensatory strategies both regarding knee kinematics as well as the placement of COM. To gain further knowledge regarding movement

patterns and potential compensatory movements in persons with ACL injury, more kinematic studies are warranted of high and low knee-loading activities. Key words: Biomechanics, long-term perspective, knee, jump performance.

Acknowledgements We would like to acknowledge support from the Swedish Scientific Research Council project nr K2008-70X-20845-01-3 and nr K2011-69X-21876-01-3, Umeå University (Young Researcher Awardee C Häger), Västerbotten county council, the foundation for medical research at Umeå University, Swedish National Centre for Research in Sports and Ingabritt & Arne Lundbergs research foundation. The assistance of Lisbeth Brax Olofsson, Monica Edström and Andrew Strong are gratefully acknowledged.

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