The Biomechanical Evidence for Valgus Knee Bracing in Medial Compartment Osteoarthritis

Author: Jim Richards, Professor of Biomechanics, School of Public Health & Clinical Sciences, University of Central Lancashire

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° was dialed in.

This was to first take up the slack in the brace, and then to try to correct by a further 5°. The greatest effect in the varus angle is during loading response from 0 to 20% of the gait cycle (Figure 1). At approximately 10% of the gait cycle, the point of greatest loading, the difference between the braced and unbraced conditions was 4°, indicating that actual correction is in a similar order to the dial in correction, which in turn will reduce the moment arm of the ground reaction force in the coronal plane.

Figure 1: Varus angle from 0 to 50% of the gait cycle

Knee adduction moments
Kim et al (2004) looked at the adduction moment in individuals with and without medial compartment knee osteoarthritis. They found a significant difference in the adduction moment between the osteoarthritis group and an age and gender matched normal group; the osteoarthritis group having on average a 50% increase in their adduction moments. Kim also found a correlation between knee adduction moments with the WOMAC Score. This supports the comments by Goh et al (1993), who suggested that the adduction moment and the increased loads are a causation factor for the incidence of medial compartment osteoarthritis. The reduction in the varus deformity during loading, should in turn lead to a reduction in the adduction moment about the knee joint. Figure 2 shows that this is indeed the case, with the braced condition reducing the adduction moment by 13%.

Figure 2: Adduction moments normalized to body mass

Ground reaction forces
Ground reaction forces give useful information about the loading and propulsion during walking. For both the vertical and anterior posterior forces, increases in the loading and propulsive forces are seen (Figure 3) when wearing the valgus brace. But isn’t an increase in force bad? The ground reaction forces do not tell us much about the loading patterns within the knee; however, they are useful in determining how well an individual can load and push off during walking, the larger vertical loading and propulsive forces indicating an improved weight acceptance and propulsion.

Figure 3: Vertical and anterior posterior forces with and without bracing normalized to body weight

Summary and Conclusion
Overall, these findings show that valgus bracing can give a degree of correction to the varus deformity of the medial compartment osteoarthritic knee and a reduced adduction moment, which gives the subject substantial functional improvements during gait. Although this appears to be very clear evidence for the mechanical effect of valgus bracing, further research is needed on the effect of different designs and different amounts of correction. Can we, for instance, get the same amount of correction using a smaller brace, and what is the limit of correction we can achieve either by building the correction into the brace or by dialing the correction into the brace?

References

* Goh JC, Bose K, Khoo BC. Gait analysis study on patients with varus osteoarthrosis of the knee. Clinical Orthopaedics and Related Research 1993;(294):223–231.
* Hewett TE, Noyes FR, Barber-Westin SD, Heckmann T. Decrease in knee joint pain and increase in function in patients with medial compartment arthrosis: a prospective analysis of valgus bracing. Orthopedics 1998;21:131–138.
* Johnson F, Leitl S, Waugh W. The distribution of load across the knee. A comparison of static and dynamic measurements. British Journal of Bone and Joint Surgery 1980;62(3):346–349.
* Jones RK, Nester CJ, Kim WY, Tyson S, Laxton P, Jari S, Johnson D, Richards JD. Direct and indirect orthotic management of medial compartment osteoarthritis of the knee, ESMAC & GCMAS meeting, Amsterdam, 25–30 September, 2006.
* Kim WY, Richards JD, Jones RK, Hegab A. Single limb stance adduction moment in medial compartment osteoarthritis of the knee. The Knee 2004;11:225–231.
* Kirkley A, Webster-Bogaert S, Litchfi eld R, Amendola A, MacDonald S, McCalden R, Fowler P. The effect of bracing on varus gonarthrosis. American Journal of Bone and Joint Surgery 1999;81–A:539–548.
* Lindenfeld TN, Hewett TE, Andriacchi TP. Joint loading with valgus bracing in patients with varus gonarthrosis. Clinical Orthopaedics 1997; 344:290–297.
* Maly MR, Culham EG, Costigan PA. Static and dynamic biomechanics of foot orthoses in people with medial compartment knee osteoarthritis. Clinical Biomechanics (Bristol, Avon) 2002;17(8):603–610.
* Matsumo H, Kadowaki K, Tsuji H. Generation II knee bracing for severe medial compartment osteoarthritis of the knee. Archives of Physical Medicine and Rehabilitation 1997;78:745–749.
* Noyes FR, Schipplein OD, Andriacchi TP, Saddemi SR, Weise M. The anterior cruciate ligament-deficient knee with varus alignment. An analysis of gait adaptations and dynamic joint loadings. American Journal of Sports Medicine 1992;20(6):707–716.
* Pollo FE, Otis JC, Backus SI, Warren RF, Wickiewicz TL. Reduction of medial compartment loads with valgus bracing of the osteoarthritis knee. American Journal of Sports Medicine 2002;30:414–421.
* Pollo FE. Bracing and heel wedging for unicompartmental osteoarthritis of the knee. American Journal of Knee Surgery 1998;11:47–50.
* Prodromos CC, Andriacchi TP, Galante JO. A relationship between gait and clinical changes following high tibial osteotomy. American Journal of Bone and Joint Surgery 1985;67(8):1188–1194.
* Richards J, Sanchez-Ballester J, Jones RK, Darke N. A comparison of the effectiveness of two knee braces in the treatment of subjects with medial compartment osteoarthritis of the knee during walking. Journal of Bone and Joint Surgery, 7: 937-939, 2005.
* Wang JW, Kuo KN, Andriacchi TP, Galante JO. The influence of walking mechanics and time on the results of proximal tibial osteotomy. American Journal of Bone and Joint Surgery 1990;72(6):905–909.