The contralateral knee of those with unilateral endstage hip OA is known to be at greater risk for endstage knee OA compared to the ipsilateral, same side knee. Likewise, in endstage hip OA, this contralateral knee is known to have increased dynamic joint loads compared to the ipsilateral knee. Here, we study a population with unilateral hip OA, who are asymptomatic at the knees, for early asymmetries in knee loading.
Data from 62 subjects with unilateral hip OA were evaluated. Subjects underwent gait analyses for evaluation of dynamic knee loads as well as dual energy X-ray absorptiometry for evaluation of bone mineral density (BMD) at both knees. Differences between knees were compared.
Peak dynamic knee loads were significantly higher at the contralateral knee compared to the ipsilateral knee (2.46±0.71 vs 2.23±0.81 %BW*ht, p=0.029). Similarly, medial compartment tibial BMD was significantly higher at the contralateral knee compared to the ipsilateral knee (0.897±0.208 vs 0.854±0.206 gm/c2, p=0.033). Interestingly, there was a direct correlation between contralteral:ipsilateral dynamic knee load and contralateral:ipsilateral medial compartment tibial BMD (Spearman’s rho= 0.287, p=0.036).
This study demonstrates that at the contralateral knees of patients with unilateral hip OA, which are at higher risk of developing progressive symptomatic OA compared to the ipsilateral knees, loading and structural asymmetries appear early in the disease course, while the knees are still asymptomatic. These early biomechanical asymmetries may have corresponding long term consequences, providing further support for the potential role of loading in OA onset and progression.