Does an unloader brace reduce knee loading in normally aligned knees?

BACKGROUND

Unloading knee braces often are used after tibiofemoral articular cartilage repair. However, the experimental basis for their use in patients with normal tibiofemoral alignment such as those undergoing cartilage repair is lacking.

QUESTIONS/PURPOSES

The purpose of this study was to investigate the effect of varus and valgus adjustments to one commercially available unloader knee brace on tibiofemoral joint loading and knee muscle activation in populations with normal knee alignment.

METHODS

The gait of 20 healthy participants (mean age 28.3 years; body mass index 22.9 kg/m(2)) was analyzed with varus and valgus knee brace conditions and without a brace. Spatiotemporal variables were calculated as were knee adduction moments and muscle activation during stance. A directed cocontraction ratio was also calculated to investigate the relative change in the activation of muscles with medial (versus lateral) moment arms about the knee. Group differences were investigated using analysis of variance. The numbers available would have provided 85% power to detect a 0.05 increase or decrease in the knee adduction moment (Nm/kg*m) in the braced condition compared with the no brace condition.

RESULTS

With the numbers available, there were no differences between the braced and nonbraced conditions in kinetic or muscle activity parameters. Both varus (directed cocontraction ratio 0.29, SD 0.21, effect size 0.95, p = 0.315) and valgus (directed cocontraction ratio 0.28, SD 0.24, effect size 0.93, p = 0.315) bracing conditions increased the relative activation of muscles with lateral moment arms compared with no brace (directed cocontraction ratio 0.49, SD 0.21).

CONCLUSIONS

Results revealed inconsistencies in knee kinetics and muscle activation strategies after varus and valgus bracing conditions. Although in this pilot study the results were not statistically significant, the magnitudes of the observed effect sizes were moderate to large and represent suitable pilot data for future work. Varus bracing increased knee adduction moments as expected; however, they produced a more laterally directed muscular activation profile. Valgus bracing produced a more laterally directed muscular activation profile; however, it increased knee adduction moments.

CLINICAL RELEVANCE

When evaluating changes in knee kinetics and muscle activation together, this study demonstrated conflicting outcomes and questions the efficacy for the use of unloader bracing for people with normally aligned knees such as those after articular cartilage repair.