Control of frontal plane knee laxity during gait in patients with medial compartment knee osteoarthritis

Abstract

Objective: Patients with medial compartment knee osteoarthritis (OA) adopt an abnormal gait pattern, and often develop frontal plane laxity at the knee. The purpose of this study was to quantify the extent of frontal plane knee joint laxity in patients with medial knee OA and genu varum and to assess the effect of joint laxity on knee joint kinetics, kinematics and muscle activity during gait.

Design: Twelve subjects with genu varum and medial compartment knee osteoarthritis (OA group) and 12 age-matched uninjured subjects underwent stress radiography to determine the presence and magnitude of frontal plane laxity. All subjects also went through gait analysis with surface electromyography of the medial and lateral quadriceps, hamstrings, and gastrocnemius to calculate knee joint kinematics and kinetics and co-contraction levels during gait.

Results: The OA group showed significantly greater knee instability (P = 0.002), medial joint laxity (P = 0.001), greater medial quadriceps-medial gastrocnemius (VMMG) co-contraction (P = 0.043), and greater knee adduction moments (P = 0.019) than the control group. Medial joint laxity contributed significantly to the variance in both VMMG and the knee adduction moment during early stance.

Conclusion: The presence of medial laxity in patients with knee OA is likely contributing to the altered gait patterns observed in those with medial knee OA. Greater medial co-contraction and knee adduction moments bodes poorly for the long-term integrity of the articular cartilage, suggesting that medial joint laxity should be a focus of interventions aimed at slowing the progression of disease in individuals with medial compartment knee OA.

Figure 1

Diagram of the proposed influence of varus alignment on joint laxity. Both medial and lateral joint laxity are thought to develop leading to lateral “condylar liftoff”, increasing joint stress on the medial compartment exacerbating the degenerative process and continuing the cycle. Figure modified, with permission, from an original published by the Arthritis Research Campaign, www.arc.org.uk

Figure 2

Setup for a stress radiograph. The knee is flexed to 20°, and placed in the TELOS device. For the valgus stress (shown), a consistent 15dN force is applied to the lateral aspect of the knee at the joint line. For the varus stress (not shown), the force is applied to the medial aspect of the joint.

Figure 3. Knee flexion angle during stance phase of gait

Positive values indicate flexion. The black solid line is the mean and the shaded region is ∀ 1SD of the control group. The dotted line represents the mean of the OA group. The OA subjects demonstrated a reduced knee flexion excursion from initial contact to peak knee flexion, during weight acceptance.

Figure 4. External knee adduction moment during stance phase of gait

The black solid line is the mean and the shaded region is ∀ 1SD of the control group. The dotted line represents the mean of the OA group. The OA group had a greater peak external knee adduction moment compared to the control group.

Figure 5. Muscle co-contraction during gait

Co-contraction values calculated from 100msec prior to initial contact through peak knee adduction moment for VMMH (vastus medialis-medial hamstrings), VMMG (vastus medialis-medial gastrocnemius), VLLH (vastus lateralis-lateral hamstrings), and VLLG (vastus lateralis-lateral gastrocnemius). Values represent mean and standard deviation. The OA group is in gray and the control group is in black.

Figure 6

Revised theory of the influence of genu varum on joint laxity. Frontal plane laxity is located on the medial side. Greater co-contraction and medial joint load exacerbate medial compartment degeneration, increasing joint laxity, and propagating a cycle of medial articular cartilage destruction. Figure modified, with permission, from an original published by the Arthritis Research Campaign, www.arc.org.uk