Early Changes In Quadriceps Strength Associate With Knee Cartilage Composition Following Anterior Cruciate Ligament Reconstruction

Purpose: Quadriceps weakness following anterior cruciate ligament reconstruction (ACLR) has been associated with knee joint tissue changes consistent with knee osteoarthritis. Evidence that early quadriceps weakness is associated with early deleterious changes in cartilage is limited. The purpose of our study was to evaluate associations between changes in quadriceps strength pre-operatively (pre-op) to 4, 6 and 12 months post ACLR with tibio- and patellofemoral articular cartilage compositional changes from pre-op to 12 months post ACLR. Methods: We included 34 patients with primary, unilateral ACLR via bone-patellar-tendon bone autograft (54% female, 21 ± 4 years; 75 ± 14 kg; 173 ± 10 cm). Maximal voluntary isometric (MVIC) quadriceps contractions were collected at 90° knee flexion for each limb at each timepoint and were normalized to body mass. Strength changes were calculated as the change in ACLR limb MVIC at each time post-op compared to the pre-op uninjured limb MVIC. Articular cartilage proteoglycan density was assessed via magnetic resonance imaging T1ρ relaxation times of the lateral (LFC) and medial femoral condyles and tibial plateaus, patella (PAT) and trochlea (TRO) pre-op and 12 months post-op for each limb. Cartilage changes were calculated as T1ρ relaxation time changes from pre-op to 12-months post-op in which increases were interpreted as decreased proteoglycan density (or worse cartilage composition). Pearson Product Moment correlations assessed associations. Results: Greater strength retention from pre-op to 4 months associated with increased T1ρ relaxation times in the LFC (r = .39, p = .01) and TRO (r = .31, p = .03). Greater strength retention from pre-op to 6 months associated with increased T1ρ relaxation times in the TRO (r = .28, p = .049) and PAT (r = .33, p = .03). Greater strength retention from pre-op to 12 months associated with increased T1ρ relaxation times in the LFC (r = .34, p = .03) and TRO (r = .36, p = .02). Conclusion: Mechanisms linking strength retention to early deleterious changes in cartilage composition are unclear. While speculative, it can be hypothesized that more aggressive rehabilitation designed to limit quadriceps weakness and allow for more early weight bearing activity may contribute to early deleterious cartilage changes. Supported by: Arthritis Foundation