Association of knee extension deficit and lumbar kyphosis with functional impairments in patients with knee osteoarthritis: The Nagahama study

The knee extension deficit is known to occur with an increase in lumbar kyphosis. This study aimed to determine the association of knee extension deficit and lumbar kyphosis with knee symptoms and functional activities in patients with Knee Osteoarthritis (KOA). Four hundred forty-eight participants aged 60 or over with radiographic KOA, all local community residents, were included in the analysis. The Knee Scoring System (KSS) was used to assess the functional abilities and symptoms. The knee extension angle was measured using a goniometer, and the lumbar spine angle was measured using Spinal Mouse, which is a noninvasive skin surface device. The associations between KSS symptoms or function scores with the presence or absence of knee extension deficit and lumbar kyphosis was evaluated using the multiple regression analysis. Another multiple regression analysis was conducted to clarify the effect of the coexisting knee extension deficit and lumbar kyphosis on KSS scores. The presence of knee extension deficit (β = -2.67; 95 % confidence interval [95 % CI]: -5.08, -0.27; p = 0.03) and lumbar kyphosis (β = -6.15; 95 % CI: -9.44, -2.86; p < 0.01) were associated with the KSS function score. Furthermore, the coexisting knee extension deficit and lumbar kyphosis significantly decreased the KSS function score (β = -10.24; 95 % CI: -15.1, -5.37; p < 0.01). However, the interaction between knee extension deficit and lumbar kyphosis was not statistically significant (p = 0.25). The KSS symptom score was not associated with knee extension deficit or lumbar kyphosis in either analysis. Our findings indicate that the coexisting knee extension deficit and lumbar kyphosis are an adverse clinical indicator associated with functional impairments in patients with KOA. Retrospective clinical study.