Valgus knee bracing for medial knee osteoarthritis and varus malalignment: a pilot study

Abstract

Purpose: Knee bracing is inconsistently recommended in clinical guidelines for the management of knee osteoarthritis (OA). Knee OA progression may be related to altered mechanical knee loads, particularly in those with varus malignment. Valgus knee bracing is thought to alleviate symptoms by reducing loads borne through the medial tibiofemoral compartment during walking. However, the effect of valgus knee bracing on medial tibiofemoral compartment mechanical loads is not well understood. Investigations on valgus knee bracing to date have largely used the external knee adduction moment as a surrogate to infer medial tibiofemoral compartment mechanical loads. This is a critical limitation, as the external knee adduction moment does not account for muscle forces that account for a considerable proportion of the medial tibiofemoral contact force (MTCF) during walking. The purposes of this study were to determine: 1) the effect of a valgus knee brace on MTCF (peak and impulse) during walking; 2) whether the effect of the valgus knee brace on MTCF (peak and impulse) is more pronounced at 8-week follow-up compared to baseline; 3) change in knee OA symptoms, quality of life and confidence; 4) adverse events, adherence and acceptability of wearing the valgus knee brace over an 8-week period.

Methods: A within-participant study design was used to test the effect of the valgus knee brace on the MTCF during walking, and an observational study design was used to determine to change in knee OA symptoms, quality of life, confidence, adverse events, adherence and acceptability. Participants with clinical and radiographic knee OA and varus malalignment were recruited from the community. Participants were fitted with an Össur Unloader One brace by a trained researcher. Participants were instructed to gradually increase their brace usage by 1-2 hours per day until they were wearing the brace “whenever you are on your feet performing daily activities” for 8 weeks. Outcome measures included: MTCF (peak and impulse) estimated via an electromyogram-driven neuromuscular model during walking with and without the knee brace (randomised assessment order) at baseline and 8-week follow-up, symptoms, including knee pain intensity during walking assessed using a numeric rating scale (NRS, score 0-10, higher scores greater pain), knee pain, function in daily living, function in sport and recreation, knee-related quality of life and patellofemoral related problems assessed using Knee injury and Osteoarthritis Outcome Score subscales (KOOS, score 0 - 100, higher scores fewer knee problems), quality of life using the Assessment of Quality of Life (AQoL, score -0.04 to 1.00, higher scores indicating better quality of life) at baseline and 8-week follow-up, and weekly confidence levels whilst performing daily tasks when wearing the brace using via NRS (score 0-10, higher greater confidence). Adverse events (number and nature), adherence (self-rated on NRS, score 0-10 [higher greater adherence], and number of hours brace worn per day) and comfort were recorded weekly. Acceptability of the brace (e.g. ease of use, likelihood of continuing to wear brace) was assessed using NRSs at the 8-week follow-up (scores 0-10, higher scores greater comfort, ease or likelihood). We aimed to detect a small to medium bracing effect size of 0.35 for peak MTCF. Assuming 80% and alpha of 0.05, and a correlation between measurement on the same individual of 0.82 a sample of at least 26 participants was required. To allow for 15% dropout we aimed to recruit 30 participants.

Results: Of the 30 (60% male) participants enrolled into the study, 28 (93%) completed 8-week outcome assessments. Biomechanical data at baseline and follow-up for the braced and unbraced conditions are presented in Table 1. There was a main effect of condition (two levels: brace and no brace, p<0.001), but no main effect for time (two levels: baseline and 8-week follow-up, p=0.10), and no interaction between brace and time (p=0.62). Wearing the brace during walking significantly reduced the peak MTCF (-0.05 BW 95%CI [-0.10, -0.01]) and MTCF impulse (-0.07 BW.s 95%CI [-0.09, -0.05]) compared to walking without the brace. No difference in change in MTCF (peak or impulse) was observed between baseline and 8-week follow-up (p = 0.62). The average change scores exceeded minimal clinically important improvements for: knee pain during walking (-3.3, 95%CI [-4.1, 2.6]), all the KOOS subscales (pain: 20.4, 95%CI [14.9, 25.8]; function: 20.5, 95%CI [14.2, 26.8]; sport and recreation: 22.9, 95%CI [14.6, 31.3]; quality of life: 18.5, 95%CI [10.9, 26.2]; and patellofemoral: 25.9, 95%CI [18.1, 33.6]) and the AQoL (mean difference 0.07, 95%CI [0.03, 0.12]). The weekly confidence levels on the 11-point NRS while performing daily tasks when wearing the brace was mean (SD), 8.7 (0.3). Thirty adverse events were reported related to the knee brace: n=11 (37%) skin irritation; n=5 (25%) increased study knee pain; contralateral knee/hip pain n=3 (10%); back pain n=1(4%); pain in other area n=1 (3%). The weekly adherence levels on the 11-point NRS to wearing the knee brace as instructed was mean (SD), 8.4 (0.2). Participants reported to wear the brace a mean (SD), [range] hours per day: 6 (3) [1 - 11]. On the 11-point NRS, participants rated the brace as easy to use, mean (SD) 7.1 (2.0); easy to put on and off, mean 8.5 (1.6), easy to wear over clothing, mean 6.9 (2.0); rated they were likely to continue to wear the brace upon completion of the study, mean 7.8 (SD) (2.6); and likely to recommend to a friend with similar knee problems, mean (SD) 8.3 (2.3). The weekly comfort levels on the 11-point NRS while wearing the brace was mean (SD), 8.0 (0.5).

Conclusions: Biomechanical interventions are a highly ranked OA research priority, that might be particularly applicable to people with medial knee OA and varus malalignment. Although significant, reductions in the peak MTCF and MTCF while wearing the knee brace were small. The immediate effect of the brace on the MTCF (peak and impulse) was no different to the 8-week effect. Further investigation into individual patient changes may reveal hypothesis-generating criteria for future exploration of responders and non-responders with respect to MTCF. Nevertheless, this study identified clinically meaningful improvements in symptoms and quality of life, with confidence levels performing daily activities with the brace reasonably high. The number of adverse of adverse events warrants consideration. Some may be preventable (e.g. skin irritation), with additional support such as regular re-fitting. Adherence and acceptability were generally high overall, with some areas to consider for improvement (i.e., wearing brace over clothing). Our findings will help further refine the knee brace intervention for more robust evaluation in a clinical trial to determine the efficacy of knee bracing for people with knee OA.