Relationship of knee adduction and flexion moments during gait with medial compartment cartilage thickness 9 years following posterior cruciate ligament reconstruction

Purpose: Posterior cruciate ligament (PCL) ruptures and concomitant posterolateral corner (PLC) injuries are associated with an increased risk of incident knee osteoarthritis (OA). As the PCL and PLC are primary knee restraints to posterior tibial translation and axial rotation, injuries to these structures can result in altered joint stability and kinematics. Accordingly, PCL-ruptured knees exhibit increased contact forces in the medial compartment, a finding that correlates with an increased incidence of arthroscopically determined cartilage lesions in this region. While PCL reconstruction aims to counteract instability and restore joint biomechanics, >50% of PCL-reconstructed knees display joint space narrowing and osteophytes on X-rays 2-9 years post-surgery. Gait mechanics, particularly the external knee adduction (KAM) and flexion (KFM) moments, have been implicated in the development of medial knee OA in older adults without history of trauma. The relationship between these gait variables and cartilage thickness following PCL reconstruction has not been studied. This study tested the hypothesis that peak KAM and peak KFM during gait are inversely associated with medial knee cartilage thickness measured at one time point after PCL reconstruction. Methods: Thirteen PCL-reconstructed patients completed MRI and gait analysis 9.2±3.2 years post-surgery. Patients underwent PCL reconstruction (isolated or combined with PLC stabilization), performed by the same surgeon using the same surgical technique (anterolateral single bundle). MRI of the knee was performed using a 1.5 Tesla scanner with the following parameters: FLASH 3D with water excitation, 0.3125x0.3125x1.5 mm resolution, 6.48 ms echo time, 14.6 ms repetition time, 20 degree flip angle. Segmentations of weight-bearing tibiofemoral cartilage plates was performed by experienced operators, and mean cartilage thickness was determined in 8 medial knee sub-regions (5 tibial, 3 femoral) (Figure 1). Gait data were acquired for 3 barefoot walking trials at a self-selected pace using a motion capture system and force plate. External knee moments (Nm/kg) were calculated using a three-dimensional floating axis coordinate system and inverse dynamics. The peak KAM and peak KFM during the stance phase were extracted from all 3 gait cycles and were then averaged. Linear regression was used to determine the association of peak KAM and peak KFM with mean cartilage thickness in the eight medial knee sub-regions using a cross-sectional study design. Potential outliers/influential observations were identified using leverage-versus-residuals-squared plots. Assumptions of linearity and normality were confirmed. Univariate models, comprising peak KAM or peak KFM as independent variable and one of eight sub-regional cartilage thickness measures as dependent variable, were tested. Significant models were further adjusted for covariates (age, sex, body mass index, gait speed) by individually adding these variables into the model. Significance was set at p<0.05. Results: The sample comprised 10 men and 3 women (age 38±10 y; body mass index 28.3±3.9 kg/m2; gait speed 1.23±0.14 m/s). The average peak KAM was 0.48±0.13 Nm/kg and the average peak KFM was 0.67±0.29 Nm/kg. Cartilage thickness for each sub-region is given in Figure 1. Two outliers, which had low cartilage thickness overall and exerted high influence across models, were identified. To enable transparent data interpretation, models were evaluated with and without these observations. Only one model was significant, in which peak KAM was positively associated with anterior medial tibial cartilage thickness, explaining 37% of its variance (n=11; p=0.046) (Table 1; Figure 2). No covariate explained additional variance in this model (p>0.05). Conclusions: This work examined the relationship between gait mechanics and cartilage thickness following PCL reconstruction. Greater cartilage thickness in only one sub-region (anterior medial tibia) was associated with greater peak KAM, with a small effect size. This finding contrasts prior evidence supporting an inverse relationship between KAM and cartilage thickness in cohorts with established knee OA. Yet, this finding may reflect under-loading of the knee after acute injury/reconstruction associated with higher risk of OA development. For instance, in patients with anterior cruciate ligament injury/reconstruction, those with radiographic OA 5 years post-surgery walked with lower KAMs than those without OA. Overall, results suggest little-to-no link between gait mechanics and medial knee cartilage thickness in PCL-reconstructed patients. Longitudinal data are needed to confirm this notion.xView Large Image Figure ViewerDownload Hi-res image Download (PPT)View Large Image Figure ViewerDownload Hi-res image Download (PPT)