The association between knee joint biomechanics and neuromuscular control and moderate knee osteoarthritis radiographic and pain severity.

Astephen Wilson JL, Deluzio KJ, Dunbar MJ, Caldwell GE, Hubley-Kozey CL. Osteoarthritis and Cartilage 2010;19:186-193

It is well-known that radiographic severity of knee osteoarthritis is not strongly related to symptomatic presentation of the disease. In other words, the amount of cartilage deterioration is not associated with the magnitude of functional impairments or pain levels. To help understand what factors are related to structural changes in the knee joint and what factors are related to pain experienced by persons with osteoarthritis, the authors evaluated a set of biomechanical and neuromuscular variables in 40 patients with moderate knee osteoarthritis. The authors used a statistical technique known as Principal Component Analysis to examine the relationship between the predictor variables (knee joint moments, knee flexion angles, walking speed, electromyographic activity from lower extremity muscles and anthropometric/demographic data) and knee joint pain and structural changes in the knee separately. The most interesting finding in this paper was that different factors predict joint pain and structural changes. A greater knee adduction moment, which is a surrogate biomechanical variable of medial knee compartment joint loading, and lower knee flexion angles during gait were predictive of greater radiographic joint severity (r2 = 0.21 and 0.11, respectively). Lower gait speed, lower gastrocnemius activation and greater hamstring muscle activation were associated with more knee pain (r2 = 0.28, 0.16 and 0.10, respectively). Multiple linear regressions revealed that a combination of greater knee adduction moment and greater body mass index was associated with greater radiographic disease severity.

This study highlights an important aspect of osteoarthritis: although the severity of osteoarthritis is frequently graded using radiographs, clinical decisions related to treatment of the disease come as a result of both symptomatic presentation AND structural changes within the joint. An orthopaedic surgeon would never perform a total knee arthroplasty on a patient with radiographic evidence of knee OA, but who had no pain. This paper adds evidence to the fact that structural changes may be the result (or consequence) of biomechanical alterations, but pain drives changes in muscle control patterns and gait speed. The biomechanical variables that were predictive of structural changes are not a novel finding; the knee adduction moment is strongly related to disease progression and each pound of weight gained results in a four-fold increase in joint compression forces. However, it does suggest that if we want to affect the structural changes associated with the disease, we should encourage patients to lose weight and to use a device to reduce the adduction moment (either bracing or gait retraining). It also suggests that in order to improve gait speed and decrease abnormal hamstring activity, we need to modify pain. Future longitudinal and interventional studies are needed to support these conclusions, but these findings suggest that pain and disease severity need to be considered when interpreting biomechanical and neuromuscular changes in persons with knee osteoarthritis.

Written by:  Joseph Zeni, Jr
Reviewed by:  Stephen Thomas