Introduction
The use of knee orthoses to correct and to support moments about joints is one of the most common uses of direct orthotic management. In the case of knee valgus braces the aims are to unload the painful compartment through bending moments applied proximally and distally to the knee joint and to reduce the varus deformity (Pollo, 1998). Several studies have been conducted into the use of valgus knee braces for medial compartment osteoarthritis and have reported that patients experience significant pain relief and an improvement in physical function (Hewett et al, 1998; Kirkley et al, 1999; Lindenfeld et al, 1997; Matsumo et al, 1997; Richards et al 2005) and also a reduction in medial compartment load (Pollo et al, 2002; Jones et al, 2006).
But how can a valgus brace reduce the load on the medial compartment of the knee? The answer is that this is a very hard thing to measure directly; however, measures that give an indirect indication of the loading on the medial compartment are a reduction in the knee adduction moments and the varus angle of the knee.
It is widely known that knee osteoarthritis is more prevalent in the medial compartment of the knee joint than the lateral compartment and it has been estimated that during normal gait approximately 60-80% of the load across the knee joint is transmitted to the medial compartment (Prodromos et al, 1985).
During walking, individuals have an almost continuous large, external varus moment about their knees throughout stance phase, with the exception of a small valgus moment at initial contact (Johnson et al, 1980, Matsumo et al, 1997). It has been suggested that this varus or adduction moment and the increased loads are a causation factor for the incidence of medial compartment osteoarthritis (Goh et al, 1993). These increasing loads have a degenerative effect on the cartilage in the medial compartment with a narrowing in the joint space between the medial femur and medial tibial plateau. This causes a moment arm increased over that of the unaffected side in a control population (Wang et al, 1990). Increasing disability will therefore arise from the increased moment arm with pain and functional impairment being the principal complaints of knee osteoarthritis sufferers (Kim et al, 2004), ultimately leading to a reduced quality of life.
Treatment options available to the sufferer are aimed at minimizing these forces at the medial compartment of the knee (Pollo, 1998). Surgical options such as high tibial osteotomy (HTO) and unicompartmental arthroplasty attempt to unload the medial compartment by realigning the tibia, and decrease the loading at the medial compartment by transferring the load to the less affected lateral compartment (Maly et al, 2002; Noyes et al, 1992).
However, these types of surgery may not be appropriate for many individuals, therefore conservative treatment modalities have been introduced in an attempt to reduce this excessive compartmental loading without the need for surgical intervention. One form of conservative treatment for medial compartment osteoarthritis of the knee is valgus bracing. Valgus braces often claim more than just the ability to support and often claim to offload the painful compartment, correct the varus alignment of the knee and improve quality of life. Various studies have investigated the biomechanical effects and the pain reduction using such devices.
Biomechanical Changes seen with Valgus Bracing
Varus knee angle
The effect of valgus bracing on knee varus has been a point of debate for some time; however, recent research (Pollo et al, 2002; Jones et al, 2006) has shown that bracing can have a direct effect on the knee angulation in the coronal plane. The data below show the immediate effect of an individual with medial compartment knee OA walking with and without a valgus brace. The brace fitted in this instance was an OA Adjuster (DJO), which allows the clinician to dial in a 'correction'. In this case the brace was adjusted until contact was made with the lateral aspect of the knee joint, and then a further 5
