Knee malalignment and the progression of osteoarthritis.

摘要

Knee osteoarthritis (OA) predominantly affects the medial tibiofemoral compartment and can produce substantial pain and disability. Medial knee OA is often associated with genu varum, a frontal plane malalignment of the lower extremity. Genu varum alters the forces across the joint, increasing joint stress in the medial compartment. As the increased stress gradually erodes the medial articular cartilage, varus alignment progresses and propagates a continued degenerative cycle. In addition, the presence of a number of impairments can contribute to this cycle. Specifically, alterations in quadriceps strength, joint laxity, muscle activity and movement patterns during gait, and neuromuscular reflexive responses may contribute to the progressive nature of medial knee OA. The purpose of this series of studies was to examine these impairments and determine whether evidence exists that they contribute to the deterioration of articular cartilage in medial knee OA. Twelve subjects with symptomatic medial compartment knee OA and genu varum were tested along with 12 age- and gender-matched uninjured subjects. The subjects with knee OA had quadriceps strength deficits compared to the control subjects despite minimal activation failure. Excessive medial joint laxity was also present in the OA subjects, and likely led to the development of dynamic knee instability (observed in 75% of OA subjects). During walking it appeared that the OA group attempted to minimize laxity and instability through greater medial muscle co-contraction, a reduced knee flexion excursion, and greater relative medial joint loading. The OA subjects also use less variable frontal plane knee movement patterns compared to the uninvolved side which was associated with greater co-contraction and more joint laxity. Finally, a delayed reflexive response from the medial gastrocnemius, and greater reflexive medial than lateral co-contraction compared to the controls, suggested a dysfunctional muscle activity pattern yielding greater medial joint loads through less selective recruitment patterns. In summary, the findings in this series of studies indicate that the altered movement patterns and muscle dysfunction are consistent with forces and actions that would foster progressive deterioration of the medial aspect of the varus joint through increased medial joint loading.