Effect of a tri compartment unloader knee brace on knee moments and quadriceps activity during a chair rise and lower and stair descent in individuals with knee osteoarthritis

      Purpose: Osteoarthritis (OA) is the most common joint disease in adults. Cartilage loss in OA afflicted joints causes pain, disability and reduced quality of life. The knee is the most common location of OA, with the majority of cases being bi- and tri- compartment knee OA. Knee pain associated with OA has a mechanical component and excessive joint loading induces knee pain. The Levitation “Tri-Compartment Unloader” (TCU) knee brace (Spring Loaded Technology) was designed to reduce pain in individuals suffering from multi-compartment knee OA. A silicone “liquid spring” provides knee extension assist, aiming to reduce forces in all three knee compartments. Theoretical simulation results support the intended reduction in quadriceps forces and multi-compartment joint contact forces. Preliminary survey data indicate reduced pain with TCU brace use, predicted to result from biomechanical unloading. However, there is a knowledge gap regarding the mechanism by which such an energy-return system influences knee biomechanics in individuals with multicompartment knee OA. The objective of the current study was to determine the effect of the TCU knee brace on resultant knee joint moments and quadriceps activity during weight bearing knee flexion activities.
      Methods: Three male participants with multi-compartment knee OA were recruited and tested (age 63 ± 8.7 yrs; BMI 29.8 ± 5.4 kg/m2) following informed consent. Participants had Kellgren-Lawrence grades 2-4 bi- or tri-compartment knee OA diagnosed by an orthopaedic surgeon. Joint kinetics and muscle activity were evaluated for a chair rise-and-lower (Chair) and stair descent (Stair) to determine differences between 3 bracing conditions: 1) without brace (OFF); 2) brace in low power (LOW); and 3) brace in high power (HIGH). In low power the brace spring engages at 35° knee flexion, while the spring engages throughout the entire range of motion (0° to 120°) in high power. Each chair trial consisted of 5 repetitions from sitting with 90° knee flexion to full extension (standing) and back. Each stair trial consisted of step-over-step stair descent without handrail use. Participants performed 1 chair trial and 3 stair trials for each bracing condition. Six-degree-of-freedom kinematics were acquired using an 8-camera motion capture system (Motion Analysis Corp., 240Hz). Forty-one spherical reflective markers were attached to the skin (on each leg and pelvis segment) and an additional 8 markers on the brace. Ground reaction forces (OR6-6 force plate, AMTI, 2400Hz) and EMG from the vastus medialis (VM) and vastus lateralis (VL) (surface electrodes, Noraxon, 2400Hz) were collected for the brace leg. Resultant knee moments and forces at the tibiofemoral (TF) joint were calculated using inverse dynamics (Visual3D). TCU brace torque was described using piecewise linear functions for each brace condition. The timewise TCU brace moment was calculated for each trial and applied to the calculated knee extension moment (KEM). Maximum KEMs were calculated for the chair task rise and lower phases and during brace leg foot contact for stair descent. EMG signals were analysed using a wavelet analysis approach, which allows the EMG signal to be analysed simultaneously in both the time and frequency domains. Signal intensities were summed across wavelets and time to determine muscle power. Muscle power for LOW and HIGH conditions were normalized to the OFF condition. Results were averaged across 3 repetitions for each participant. Alterations associated with bracing condition were analysed statistically using the Friedman test (α=0.05, SPSS).
      Results: Internal KEM was significantly different between bracing conditions during chair rise (p=0.028) and lower (p=0.028) but was not significant for stair descent (p=0.194) (Figure 1). VM and VL muscle power were significantly different between bracing conditions during chair rise (p=0.028) and lower (p=0.028) but were not significant for stair descent (VM: p=0.361, VL: p=0.194) (Figure 2). Participants showed trends of decreased KEM and quadriceps muscle power with brace use in low and high power compared to the OFF condition during all tasks.
      Conclusions: These data suggest that TCU brace use lowers internal KEM and quadriceps muscle effort in individuals with knee OA during two activities of daily living. Internal KEM and quadriceps contraction are known contributors to patellofemoral (PF) and TF joint loads. Therefore, use of the TCU brace is predicted to reduce knee joint loading, associated with knee OA pain, during these tasks. Quadriceps EMG activity was highly variable during stair descent, and further study with a larger sample size will determine whether these findings are generalizable to the knee OA population. These preliminary results are promising and highlight the need for musculoskeletal modelling to investigate alterations in internal TF and PF contact forces with TCU brace use. Evaluating the effectiveness of the TCU brace with respect to its intended benefits will generate evidence for use of an energy-return system to manage the symptoms of multicompartment knee OA. A future clinical trial will assess clinical outcomes associated with TCU brace use.