Abstract
BACKGROUND: Valgus bracing may be particularly effective for the management of varus malaligned medial knee osteoarthritis (OA). Among several potential mechanisms, valgus bracing may impart clinical benefit by reducing medial tibiofemoral joint contact force. However, prior research shows a tenuous effect of valgus bracing on medial tibiofemoral joint contact force. Tissue-level knee mechanics, such as the magnitude and location of cartilage pressure, may provide important insights into potential mechanisms but remain underinvestigated. QUESTIONS/PURPOSES: (1) Does valgus bracing reduce estimates of medial tibial, medial femoral, and patella cartilage contact pressure during walking compared with unbraced walking in patients with varus malaligned medial knee OA? (2) Are there changes in the region of cartilage pressure upon the medial tibia, medial femoral condyle, and patella between braced and unbraced walking? METHODS: Baseline data from 28 clinical trial participants with varus malalignment and knee OA walking braced and unbraced were used. Volunteers were recruited from the community in Melbourne, Australia between April 2019 and November 2019. Major inclusion criteria included having radiographic tibiofemoral joint OA and varus malalignment, age ≥ 50 years, and current and > 3-month history of knee pain. Because of incomplete MRI data (n = 3), 25 of the original 28 participants were included in this secondary analysis. The cohort had a mean ± SD age of 64 ± 5 years, BMI of 29.4 ± 3.1 kg/m 2 , and more males (n = 14) than females (n = 11). A validated 12 degrees of freedom knee model with MRI-derived cartilage morphology and ligament insertion points was combined with a calibrated EMG-informed neuromusculoskeletal model to simulate knee contact mechanics. Tibiofemoral and patellofemoral cartilage contact simulations were performed across the stance phase of walking for four braced and unbraced trials using a nonlinear elastic foundation contact model. Outcomes addressing our first study question were estimates of maximum and mean medial tibial, medial femoral, and patella cartilage contact pressure (in megapascals [MPa]). Outcomes addressing our second study question were change in center of pressure from heel strike in the anatomic medial-lateral direction (normalized to % of cartilage width) and AP direction (normalized to % of cartilage length). Primary statistical analysis was statistical parametric mapping using one-way repeated-measures ANOVA models, which evaluate time-varying differences across stance. The point in stance with the largest differences was reported as mean difference and 95% confidence interval (CI). RESULTS: Braced walking had a lower maximum medial tibial cartilage contact pressure compared with unbraced walking during 7% to 15%, 26% to 40%, and 65% to 90% of stance, with the largest difference at 87% of stance (mean ± SD unbraced 16.0 ± 4.3 MPa, braced 14.0 ± 3.6 MPa, mean difference -2.0 MPa [95% CI -3.5 to -0.6]; p < 0.001) (12.5% change). Reductions in cartilage pressures during braced walking were of similar magnitudes and occurred at similar regions of stance for mean tibial and maximum/mean femoral cartilage contact pressure, with no differences in patella cartilage contact pressure. Compared with unbraced, braced walking had a center of pressure located more lateral on the medial tibia cartilage during 0% to 54% of stance and more posterior during 0% to 12% of stance, with the largest difference occurring at 4% of stance (unbraced -0.8% ± 2.1%, braced 3.6% ± 3.8%, mean difference 4.4% [95% CI 1.9% to 6.8%]; p < 0.001) and 5% of stance (unbraced -5.0% ± 2.9%, braced -3.0% ± 3.5%, mean difference 2.0% [95% CI 0.2% to 3.8%]; p < 0.003), respectively. Upon the medial femur cartilage, center of pressure was more laterally located during braced walking compared with unbraced, but showed no differences in the AP direction. No differences in center of pressure were found upon the patella cartilage. CONCLUSION: Valgus bracing reduced the magnitude of medial tibiofemoral cartilage contact pressure in patients with varus malaligned knee OA, which may be a mechanism underpinning the reported clinical benefit of valgus bracing. Further investigation is needed to explore whether shifting the location of loading away from potential sources of pain has clinical relevance. CLINICAL RELEVANCE: Our study found valgus bracing to reduce knee cartilage pressure during certain stance regions, which may help to improve brace design and thus patient care in knee OA. Future clinical trials should examine whether brace-induced changes to cartilage pressure create meaningful benefit to the patient. Such knowledge will help clinicians make informed decisions about which patients may benefit most from a valgus bracing intervention.