Design Evaluation of a Novel Multicompartment Unloader Knee Brace

Abstract

Knee osteoarthritis (OA) is a significant problem in the aging population, causing pain, impaired mobility, and decreased quality of life. Conservative treatment methods are necessary to reduce rapidly increasing rates of knee joint surgery. Recommended strategies include weight loss and knee bracing to unload knee joint forces. Although weight loss can be beneficial for joint unloading, knee OA patients often find it difficult to lose weight or begin exercise due to knee pain, and not all patients are overweight. Unicompartment offloader knee braces can redistribute joint forces away from one tibiofemoral (TF) compartment; however, <5% of patients have unicompartmental tibiofemoral osteoarthritis (TFOA), while patients with isolated patellofemoral or multicompartmental OA are much more common. By absorbing body weight (BW) and assisting the knee extension moment using a spring-loaded hinge, sufficiently powerful knee-extension-assist (KEA) braces could be useful for unloading the whole knee. This paper (1) describes the design of a spring-loaded tricompartment unloader (TCU) knee brace intended to provide unloading in all three compartments of the knee while weight-bearing, (2) measures and compares the force output of the TCU against the only published and commercially available KEA brace, and (3) calculates the static unloading capacity of each device. The TCU and KEA braces delivered maximum assistive moments equivalent to reducing BW by approximately 45 and 6 lbs, respectively. The paper concludes that sufficiently powerful spring-loaded knee braces show promise in a new class of multicompartment unloader knee orthoses, capable of providing a clinically meaningful unloading effect across all three knee compartments.

Biomechanical Study of a Tricompartmental Unloader Brace for Patellofemoral or Multicompartment Knee Osteoarthritis

“…When the knee joint is flexed (e.g., during a squat), the spring-powered lateral hinge applies an assistive extension moment to reduce the user's quadriceps muscle effort. This assistive moment is transferred to the back of the user's leg via reaction forces at the proximal strap (Strap 3) and lower shell and cuff as an anteriorly directed force, ∼20 cm above-and below-knee center (Budarick et al, 2020).…”

“…The design of the TCU brace is detailed elsewhere (Budarick et al, 2020). Briefly, the brace is coupled to the upper and lower leg in a similar manner to traditional rigid frame knee braces.…”

“…A new brace concept was recently introduced to provide simultaneous unloading (rather than off-loading) benefits to multiple knee compartments (i.e., TF and PF compartments) by reducing sagittal plane muscle effort (Budarick et al, 2020), with the goal of reducing pain and improving joint function for individuals with multicompartmental knee OA (Waller et al, 2011). The Levitation R Tri-Compartment Unloader (Spring Loaded Technology Inc., Halifax, Nova Scotia, Canada), herein referred to as the tricompartment unloader (TCU) (Figure 1), is a passive mechanical brace capable of energy storage and body weight (BW) support during gravity assisted knee flexion (such as lowering to a squat).…”

“…These brace models are designed for different therapeutic purposes or to meet varying user requirements. As muscles are the primary contributors to PF and TF joint contact loads that increase during weightbearing flexion (Kuster, 2002;Winby et al, 2009;Sasaki and Neptune, 2010;Trepczynski et al, 2012), reduction in muscle effort should reduce the forces transmitted through the joint structures (Budarick et al, 2020). As in vivo measurements are generally infeasible, a model is required to quantify these effects.…”

“…On one end of the spectrum, finite element models provide high-resolution estimates of tissuelevel stress and strain but at high computational cost (Kazemi et al, 2013;Shriram et al, 2019). Conversely, reductionist models (Morrison, 1968;Wismans et al, 1980;Yamaguchi and Zajac, 1989) rely on simplifying assumptions to lump or omit some tissues, but may still be of sufficient quality to reveal the net action of load-bearing structures of the knee (Dumas et al, 2019) and to estimate the unloading effect of a knee brace (Pollo et al, 2002;Budarick et al, 2020). Regardless of the modeling approach, validation is both crucial and challenging (Hicks et al, 2015).…”