Knee Joint Biomechanics following Arthroscopic Partial Meniscectomy Daina L. Sturnieks,1 Thor F. Besier,3 Peter M. Mills,1 Tim R. Ackland,1 Ken F. Maguire,4 Gwidon W. Stachowiak,2 Pawel Podsiadlo,2 David G. Lloyd1 1 School of Sports Science, Exercise, and Health, The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia, 2School of Mechanical Engineering, The University of Western Australia, Perth, Australia, 3Department of Orthopaedics, Stanford University, Stanford, California, 4Perth Orthopaedic and Sports Medicine Centre, Perth, Australia
Received 17 May 2007; accepted 26 November 2007 Published online 7 March 2008 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jor.20610
ABSTRACT: We investigated spatiotemporal data, joint kinematics, and joint kinetics during gait in a group of subjects who had recently undergone arthroscopic partial meniscectomy and compared the results to those of healthy controls. Gait analysis was performed on 105 pain-free meniscectomy patients and 47 controls, walking at a self-selected speed. The meniscectomy population was comparable to controls in spatiotemporal parameters and knee kinematics. However, they had reduced range of motion (ROM) and lower peak moments in the sagittal plane on the operated limb compared to the nonoperated limb. Compared to controls, the meniscectomy patients had significantly larger knee adduction moments over stance, even after accounting for their greater body weight. These differences likely increase articular loads on the medial compartment of the tibiofemoral joint and may contribute to the high risk of knee osteoarthritis following arthroscopic meniscal surgery. ß 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:1075–1080, 2008 Keywords: knee; adduction moment; meniscectomy; osteoarthritis; gait
Larger-than-normal knee adduction moments during the stance phase of gait generate enlarged loads on the medial articular surface of the tibiofemoral joint and may contribute to degenerative joint changes.1,2 The presence3 and severity4,5 of knee osteoarthritis (OA) has been associated with these moments. Furthermore, these large adduction moments are the best predictor of progression of knee OA over 6 years.6 This evidence suggests that knee adduction moments influence disease advancement. However, the role of the knee adduction moments in the causality of knee OA remains uncertain. A proposed mechanism by which ambulatory joint mechanics may lead to knee cartilage degeneration involves gait patterns that increase the loading of articular surfaces, particularly the adduction moment that predominantly loads the medial tibiofemoral joint. Increased articular load may elevate subchondral bone stress and increase subchondral bone density,7 which in turn may alter the mechanical loads on the cartilage. Over time, abnormal cartilage loading may change the tissue’s mechanical properties, resulting in degeneration of cartilage matrix and initiation of OA.8 Investigating this hypothesis in the general population requires a very large cohort and considerable time. Alternatively, studying populations at high risk of knee OA may help determine whether a causative link exists between knee adduction moments and knee OA. Arthroscopic partial meniscectomy is among the most common orthopedic interventions9 and patients have 50% risk of developing OA.10 Limited information exists regarding gait patterns in this population. Durand et al.11 found reduced sagittal knee range of motion (ROM) up to 8 weeks postsurgery in meniscectomy patients, compared to healthy controls. To our knowledge, this report provides the only published gait data Correspondence to: David Lloyd (T: þ61 8 6488 3919; F: þ61 8 6488 1039; E-mail:
[email protected]) ß 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.
following meniscectomy, yet it was limited to 17 patients and no kinetic data were reported. Altered knee kinetics during gait have been reported in other populations with knee pathology.12–16 Minimizing the external knee flexion moment during weight acceptance appears to be a common strategy adopted by people with knee trauma, as reduced knee flexion moments have been found in people with ACL injury,12 knee OA,13,14 knee pain,15 and experimentally induced knee joint effusion.16 This strategy may be a generalized adaptation to reduce pain related to compressive forces during stance-phase knee flexion. Indeed, reduced flexion angles have been shown in populations with knee pain,15 knee OA,13,17 total knee arthroplasty,18 ACL deficiency,19 ACL reconstruction,12 and arthroscopic partial menisectomy.11 It appears that sagittal plane joint loading is commonly moderated in people with knee trauma. With the exception of OA patients, the effects of knee trauma on frontal plane mechanics are less clear. Analysis of lower limb kinetics, which has been unreported in meniscectomy patients, may provide important information regarding surgery outcomes and long-term joint condition. The purpose of this study was to describe knee kinematics and kinetics in a group of patients who had recently undergone meniscectomy and compare these to a healthy, age and gender-matched control group. We hypothesized that, compared with healthy controls, meniscectomy subjects would have a reduced range of flexion, reduced external flexion moments, and larger external knee adduction moments over the stance phase of gait and that these differences would be more pronounced on the operated, compared to nonoperated, limbs.
METHODS The patient group were recruited from suburban orthopedic clinics and comprised 105 subjects (88 males) with a mean age of 39.7 years (SD 7.5, range 17–51 years), who had recently undergone partial meniscectomy via arthroscope. Left knee JOURNAL OF ORTHOPAEDIC RESEARCH AUGUST 2008
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meniscectomy was performed in 44% of cases, while 56% had a right knee meniscectomy. Medial meniscectomy was performed in 83% of the subjects; lateral meniscectomy was performed on 18%, while 5% had both menisci surgically treated. The majority of subjects had sustained an injury to the posterior horn, with only four subjects having surgery performed for an anterior horn injury. Gait analysis was performed on the subjects between 1 and 3 months postsurgery when subjects were able to walk without pain (mean 11 weeks, SD 4.3). The control group consisted of 47 adults (29 males) with a mean age of 37.0 years (SD 7.5, range 23–56). All subjects were screened and excluded if they had clinical and radiographic evidence of knee OA, with surgery reports checked in meniscectomy subjects. All subjects were further screened for: previous or current back, hip, knee, or ankle joint disease, pain, or injury; any form of arthritis; diabetes; cardiac, circulatory, or neurological conditions; multiple sclerosis; stroke; lower limb fractures; bone or joint conditions; and any other disease or injury that may affect gait patterns or predispose to knee OA. All subjects gave informed, written consent prior to testing to comply with the Human Ethics Committee at the University of Western Australia. 3D gait analysis was conducted at subjects’ freely chosen walking speed. Subjects walked across an instrumented 10-m walkway, with a rest period between trials to mitigate fatigue. A minimum of four trials with successful force-plate strikes were captured from each subject. Kinematic and kinetic data were averaged across legs for the control group and within the operated and nonoperated limbs for the meniscectomy group. A six-camera VICON motion analysis system (Oxford Metrics, Oxford, UK) was used in conjunction with two AMTI force-plates (AMTI, Watertown, MA) to collect motion (50 Hz) and ground reaction force (2000 Hz) data, respectively. A custom seven-segment ‘‘cluster’’ model, constructed using BodyBuilder software (Oxford Metrics), incorporating functional methods to define hip joint centers and the knee joint flexion/extension axes,20 was used to estimate hip, knee, and ankle kinematic and kinetic data. Gait data were normalized to 51 points over stride using a cubic spline with custom software developed in MATLAB (Mathworks, Natick, MA). Gait speed (m/s) was measured from the pelvis center averaged over a 3-s data collection period. Stride length (m) and stride width (m) were measured between right and left calcaneal markers in the sagittal and frontal planes, respectively. Cadence (steps/min) was calculated from the time between consecutive heel strike events. The sagittal plane kinematics analyzed were: knee angle at heel strike; peak knee flexion during weight acceptance; peak knee extension during late stance; and knee ROM. ROM was the excursion of the knee angle from heel strike to peak flexion in the weight acceptance phase of stance. Kinetic parameters analyzed were: peak flexion moment; peak extension moment; peak adduction moment during early stance; minimum adduction moment during midstance; peak adduction moment during late stance; and average adduction moment over stance. Joint moments analyzed over stance were expressed as external moments applied to the distal segment. Within a week of the gait analyses, standard radiographs of a full lower limb in extension and in weight-bearing position (Marquet view) were taken. A specialized calibration rig was used that allowed subjects to assume the standing posture21 and for foot abduction–adduction and knee and hip flexion– extension to be standardized across subjects. The rig also had
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fudicial markers that permitted parallax correction for each X-ray. Positioning of subjects and calibration procedures were based on a QUESTOR standardized radiographic procedure.22 The X-rays were digitized using a drum scanner and subsequent images analyzed using custom software, which permitted center points of the hip, knee, and ankle to be identified. The hip joint center was determined by fitting a circle to the femoral head. Center points of the knee and ankle were defined as midpoints of five (i.e., centers of soft tissue, tibia, femoral condyles, tips of tibial spines, and femoral intercondylar notch) and three (i.e., centers of soft tissue, external surface of malleoli, and talus) center points, respectively.23 All images were digitized by the same person. The knee alignment variable was the hip–knee–ankle angle measured between mechanical axes of femur and tibia, with the femur (tibia) axis defined as a line running through center points of the hip (knee) and knee (ankle) joints. Statistical Analyses No between-group differences in body height were found, however, body weight was larger for the meniscectomy than controls. One method to control for this difference while examining kinetic data is to divide the moment variable by body weight, although this has associated problems. If one assumes the moment term (M) has some linear relationship with body weight (BW), M ¼ mBW þ c, where m and c are the constants of the linear function. Dividing by BW, the equation becomes M/BW ¼ m þ c/BW that results in the normalized moment, M/BW, having a residual correlation the c/BW, with M/BW becoming smaller as BW increases.24 The relationships between BW and each of the moment parameters were analyzed using GraphPad Prism (Windows 5.01, GraphPad Software, San Diego, CA) and showed similar regression slopes between groups ( p > 0.429) and y-intercepts that significantly deviated from zero ( p < 0.002). Therefore, we chose to control for the confounds of BW by using BW as covariate in the statistical analyses as this does not introduce the residual relationship between moment and BW. Gait data were statistically tested to determine differences between: A) APM operated limb (Op) and controls; B) APM nonoperated limb (NonOp) and controls; and C) between Op and NonOp limbs. ANCOVAs were used to test differences between meniscectomy and controls (analyses A and B) with BW entered as a covariate. Paired t-tests were used to examine betweenlimb effects in the meniscectomy group (i.e., analysis C). Pearson Product Moment Correlation Coefficients and stepwise linear regressions were used to examine influences of BW and knee alignment on the raw adduction moment over stance. All hypotheses were set a priori, and we specified the direction of the differences. These are then one-sided tests where it was acceptable to use p < 0.10 (twice the alpha for two-sided tests); however, statistical significance was maintained at p < 0.05 to help avoid the chance of type I error. Data are presented as mean standard deviation.
RESULTS Control and meniscectomy groups were of similar age and height, although the meniscectomy subjects were, on average, 7.5 kg heavier than controls (Table 1). No significant differences between the limbs of the meniscectomy subjects compared to controls were found for leg alignment, gait velocity, stride length, stride width, and cadence (Tables 1 and 2).
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Table 1. Mean (SD) Spatio-Temporal Parameters for Meniscectomy and Control Groups Parameters
Control
Age (yrs) 38.2 (7.9) Height (m) 1.74 (0.09) Body mass (kg) 75.5 (11.8) Body Mass Index 24.9 (3.6) Gait speed (m/sec) 1.41 (0.21) Cadence (steps/min) 116.2 (15.6) Stride length (m) 1.49 (0.17) Stride width (m) 0.07 (0.09) Stance time (sec) 0.67 (0.06)
Meniscectomy
p
39.7 (7.2) 1.76 (0.07) 83.2 (15.6) 26.8 (4.4) 1.41 (0.17) 117.5 (12.5) 1.51 (0.16) 0.07 (0.08) 0.68 (0.06)
0.08 0.23 0.007 0.013 0.90 0.73 0.64 0.47 0.50
Differences were found in knee kinematics between controls, Op and NonOp limbs (Table 2). The Op limb showed a slightly more flexed joint position at heel strike compared to controls and the NonOp limb, which was related to a reduced ROM over stance in the Op limb. No significant differences existed in peak flexion angle during stance. The NonOp limb showed a more extended position during late stance, compared to controls and the Op limb. Overall, the Op limb of meniscectomy patients displayed similar sagittal plane kinetics to the control group; however, the Op limb peak knee flexion moment was smaller, compared to the NonOp limb ( p < 0.05) (Fig. 1). The NonOp limb demonstrated a larger peak knee extension moment compared to controls and Op limb ( p < 0.03) (Fig. 1). The meniscectomy group experienced larger knee adduction moments over stance than controls (Fig. 2). The Op limb showed larger adduction moments during early, mid, and late stance, compared to controls ( p < 0.04). The NonOp limb also showed larger peak adduction moments during early stance ( p < 0.01), which approached significance during late stance ( p ¼ 0.08), compared to controls. Furthermore, the average knee adduction moment over stance was significantly greater on the Op limb (21.5 9.1 Nm) and the NonOp limb (21.4 11.3 Nm), compared to controls (17.9 7.4 Nm) ( p < 0.05). No significant between-limb differences existed for adduction moments in the meniscectomy group. The correlation coefficient for BW and average knee adduction moment across stance in the meniscectomy
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group was 0.396 for the Op limb and 0.256 for the NonOp limb ( p < 0.05). In controls, the coefficient was 0.417 ( p < 0.001). Leg alignment was negatively correlated with average knee adduction moment over stance. This association was significant only for NonOp limb (r ¼ 0.307, p < 0.01), with a trend seen in the controls (r ¼ 0.219, p ¼ 0.056). Stepwise regression analysis found BW to be the only significant predictor of average knee adduction moment for the Op limb ( p < 0.01), accounting for 15% of the variance (adjusted r2). Significant predictors of average knee adduction moment on the NonOp limb were knee alignment and BW ( p < 0.01), together accounting for 15% of the variance. In controls, BW was the only significant predictor of average knee adduction moment, accounting for 16% of the variance.
DISCUSSION Atypical gait patterns were previously identified in people with knee trauma/pathology12–14 and may be related to outcomes after surgery18,25 and long-term joint condition.1 Arthroscopic partial meniscectomy patients have a higher than normal risk of developing knee OA.10 However, the dynamic joint mechanics in these patients have not previously been reported. While this study found patients achieved normal gait speed and stride characteristics, the hypothesis that meniscectomy patients would have abnormal gait mechanics was supported by the findings. The knee adduction moment during gait has often been noted for its potential role in the pathogenesis of knee OA.2,3,26,27 The adduction moment, to a large extent, determines the mediolateral distribution of load across the tibial plateau, such that large adduction moments concentrate load on the medial tibiofemoral compartment. We found larger adduction moments in a group of meniscectomy subjects compared to healthy controls, while controlling for BW. The operated limb displayed significantly larger peak adduction moments during early, mid, and late stance compared to controls. The nonoperated limb also showed significantly larger peak adduction moment during early stance and increased average adduction moment across stance compared to controls. These findings suggest that meniscectomy patients walk with increased force on the medial compartment during stance phase,2 particularly on the
Table 2. Mean (SD) Leg Alignment and Kinematics for Meniscectomy and Control Groupsa Meniscectomy Variable Leg alignment (deg) Knee angle–heel strike (deg) Peak knee flexion (deg) Knee ROM (deg) Knee extension–late stance (deg)
Control 0.4 (2.2) 2.4 (4.7) 19.5 (5.1) 22.0 (5.9) 3.5 (5.7)
Op 0.7 (2.5) 0.4 (5.3)*,** 18.7 (5.1) 19.1 (5.3)*,** 4.2 (5.0)***
NonOp 0.2 (2.8) 2.2 (5.3) 19.2 (5.3) 21.9 (7.5) 1.7 (4.7)****
a
Flexion angles are positive. Compared to control: ****p < 0.050 and *p < 0.010. Compared to APM NonOp: **p < 0.050 and ***p < 0.010. JOURNAL OF ORTHOPAEDIC RESEARCH AUGUST 2008
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Figure 1. Stance-phase knee flexion and extension moment peaks in meniscectomy nonoperated (NonOp) and meniscectomy operated (Op) limbs, and control group. *p < 0.05.
operated limb. This is the first study, to our knowledge, to identify larger-than-normal knee adduction loads during gait in a population likely to develop early onset knee OA. Wu and colleagues28 found that surgically inducing extreme angulation of the tibial plateau of healthy rabbits to concentrate articular forces onto one condyle of the knee led to severe cartilage changes and increased subchondral bone density. Similarly, histological evidence of degenerative changes was identified following valgus osteotomy in rabbit knees.29 In humans, large adduction moments in gait have been positively correlated with increased bone density of the proximal medial tibia in normal subjects.7 Interestingly, significantly higher bone density exists in the proximal medial tibia 12 years post-meniscectomy,30 and faster rates of cartilage volume loss in the 2 years post-meniscectomy compared to matched controls.31 These findings raise the question as to whether larger adduction moments in meniscectomy subjects, such as those we identified, contribute to changes in knee architecture and development of OA. Body weight may also contribute to degenerative joint changes and is associated with increased incidence of knee OA.32 In this study, the meniscectomy patients were heavier than controls. BW showed a significant positive association with knee adduction moments, accounting for 15% of knee loading. One longitudinal study showed that weight loss of 5 kg over 10 years
reduced the odds for developing knee OA by more than 50%.33 Simply reducing BW might help normalize knee loading and reduce the risk of joint degeneration. However, the fact that significantly larger adduction moments exist in meniscectomy subjects while controlling for BW suggests that other factors contribute to these loads, which requires further study. In the sagittal plane, the operated limb demonstrated a slightly more flexed knee position at heel strike and a reduced ROM during early stance, compared to the nonoperated limb and the control group. This finding supports that of Durand et al.,11 who showed reduced flexion angles at 2 and 8 weeks post-meniscectomy compared to a control group. The functional significance of these small differences is unknown; differences may be a residual gait alteration from surgery, but may also be the beginning of future gait abnormalities, such as those seen in people with knee OA.13 Considering that high loads exist on the knee at heel strike, a shift in the rotational load bearing contact to adjacent regions unaccustomed to high loads may lead to degenerative cartilage changes.27 This hypothesis can only be tested with longitudinal studies. Meniscectomy subject’s peak knee flexion moment was not significantly different to controls, unlike that seen in other knee pathology populations, including knee OA,13 ACL injury,12 and in healthy subjects with simulated knee joint effusion.16 However, the meniscectomy group had increased peak flexion moments on their
Figure 2. Peak knee adduction moments at early stance, midstance, and late stance in control and meniscectomy subjects, nonoperated (NonOp) and operated (Op) limbs. *p < 0.05. JOURNAL OF ORTHOPAEDIC RESEARCH AUGUST 2008
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nonoperated limb compared to the operated limb. This difference might suggest a relative unloading of the affected limb, to reduce forces through the knee in response to pain and/or structural damage while maintaining normal walking speed by compensatory work on the unaffected limb. The increased extension angles, together with the larger extension moments on the unaffected limb suggest this compensation strategy. Although meniscectomy patients were deemed pain-free at the time of testing, unloading strategies in response to previous pain might persist, even after the adaptation stimulus is alleviated.12 Certain limitations of this cross-sectional study should be considered. The differences observed may have existed prior to the meniscal injury and indeed, contributed to the injury. Those identified in the sagittal plane in the meniscectomy group are similar to gait patterns previously shown to be adaptive to trauma and/ or pain.12,14,16 However, no such evidence exists for differences seen in the adduction moments, due to a lack of literature reporting frontal plane gait data. Here we have reported gait patterns in patients, on average, 11weeks postsurgery, and it is unknown whether their gait patterns may return to normal. One study showed rehabilitated ACL reconstruction patients regain normal knee ROM at 6 months postsurgery, yet knee flexion moments remained significantly reduced.12 Longitudinal studies are required to examine gait patterns over time in a meniscectomy population and their influence on the development of knee OA. Should the adduction moment be found to be a significant causative factor in the pathogenesis of knee OA, it might be used to screen people at high risk, so that appropriate measures can be taken to prevent or moderate development of disease. In summary, we have shown that post-meniscectomy patients achieve stride characteristics and knee motion while walking that are comparable to healthy controls. Between-limb differences were found, with a reduced knee ROM and lower peak moments in the sagittal plane on the operated compared to the nonoperated limb. This asymmetry may be a strategy to reduce compressive forces at the knee on the affected limb, while compensating with the nonaffected limb. The meniscectomy group had significantly increased adduction moments over stance compared to normal individuals, while controlling for BW. These larger loads would tend to concentrate more force on the medial compartment of the tibiofemoral joint and may contribute to the high risk of knee OA in people who have previously undergone meniscectomy.
ACKNOWLEDGMENTS We acknowledge financial support from NHMRC (Grants 991134 and 254565 to D. G. L., G. W. S., and K. F. M.) and Western Australian Medical Research Infrastructure Fund (to D. G. L.). Thanks to Alec Buttfield, Catherine Hill, Donna Ferguson, and Rob King for assistance with data collection and processing. Thanks to the following surgeons for support in
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recruiting patients: Keith Holt, Greg Witherow, Greg Janes, Peter Annear, Hari Goonatillake, Dermot Collopy, David Colvin, and Peter Campbell. Thanks to Stephen Davis and Simone Mattfield for assistance in the radiology clinic.
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