When knee osteoarthritis causes pain, many people instinctively buy a knee brace in the hope of easing the discomfort. Another worry follows: does wearing a brace make the leg weaker the longer it is worn, create dependence, or even make the muscles waste faster? These two questions need to be answered separately. The most common misunderstanding is to treat “works biomechanically” as “certainly reduces pain clinically”, and to blame the brace for the muscle weakness that comes from stopping exercise. This article focuses on the valgus unloader brace, and sets out what it can help with and where it is limited.
First, what this article covers: the unloader brace. It is a rigid brace that uses three-point force to change the alignment of the knee and move load away from the affected compartment. It is generally used for patients with one-sided (inner or outer) degeneration. It works in a very different way from the soft elastic knee supports commonly sold in shops, and the two should not be confused.
How an unloader brace changes the load on the knee
Start with the part that has evidence behind it. From a biomechanical point of view, an unloader brace does have an effect. It significantly reduces the knee adduction moment (KAM) during walking, which means it reduces the pressure on the inner compartment of the knee.
KAM is an important mechanical measure for inner-compartment knee osteoarthritis. A larger adduction moment means a heavier load on the inner compartment. The systematic review and pooled analysis by Moyer 2015 showed that valgus unloader braces significantly reduce KAM, with an effect size of about 0.61, which is a medium to large effect. In other words, the principle of using a brace to take load off the knee is backed by firm mechanical data.
Note that this study is a biomechanical pooled analysis and does not analyse clinical pain or daily function. It can only be said that an unloader brace reduces the knee adduction moment (KAM). The data of Moyer 2015 alone cannot be used to say that a brace moderately improves pain and function clinically. Less load mechanically does not mean the knee will certainly be pain-free once the brace is on, and the two points must be kept apart.
Pain-relieving effect in clinical practice
After the mechanical data, look at the clinical results. Once the question becomes whether pain is actually reduced and walking improved after putting the brace on, the scientific evidence is not as strong.
The Cochrane systematic review (Duivenvoorden 2015) examined the clinical effect of braces and orthoses for knee osteoarthritis and concluded that the evidence is of low quality and the benefit is uncertain. It also pointed to a practical difficulty: poor tolerance and adherence. In real life many patients stop wearing the brace after a few days because it feels bulky, is awkward to put on or gets in the way of walking. A brace that cannot be tolerated or used in the long term will have little effect, however good its mechanical design.
Mechanically effective does not mean clinically effective. Moyer 2015 tested biomechanics (reduced KAM, a medium to large effect), whereas Duivenvoorden 2015 looked at clinical outcomes (low-quality evidence, uncertain benefit). The two findings do not contradict each other. The mechanical principle of the brace makes sense and some people benefit clinically, but there is no guarantee that everyone will get pain relief from wearing it. An unloader brace is therefore an option worth trying and not a cure that is certain to work.
Does wearing a knee brace make the leg weaker?
This is the question patients ask most often in the consulting room. The direct answer is that with regular strength training, the leg does not get weaker the longer the brace is worn. Weakness does not come from the brace itself. It comes from a wrong attitude to using it: believing that the brace gives enough protection and so stopping even daily exercise. Lack of exercise is what causes the muscles around the knee to decline, and the brace should not be blamed.
- The brace is a support and strength training continues
- ACR 2019 strongly recommends a tibiofemoral brace, positioned as support alongside exercise
- Better alignment and maintained strength, so the leg does not get weaker the longer the brace is worn
- Stopping exercise once the brace is on, as if the brace replaced the muscles
- Muscles weaken because training has stopped, so the cause is stopping exercise and not the brace
- Blaming the brace for the result of stopping exercise
The key is to be clear about what a brace is: it is a support and does not replace exercise. Clinical guidelines (such as ACR 2019) have always positioned a brace as something used alongside exercise, and have never advised using a brace in place of strength training. As long as the patient keeps training the thigh and buttock muscles, with the brace sharing part of the load on the joint and making training more comfortable, the two work together and do not cancel each other out.
What international guidelines say: ACR strongly recommends tibiofemoral braces
Next, the position of international guidelines. The 2019 American College of Rheumatology (ACR) guideline for osteoarthritis of the knee, hip and hand gives a “strong recommendation” for tibiofemoral (TF) braces for knee osteoarthritis, and the unloader brace discussed here belongs to this category. Note, however, that the same guideline “conditionally recommends against” patellofemoral (PF) braces, and the two types of brace must not be confused.
In everyday clinical use, an unloader brace is not suited to everyone and is not a necessity. It helps most in patients with one-sided degeneration and an obvious alignment deviation, and the effect in other types of patient may not be significant. Whether to buy one should therefore not be decided from advertising alone, and should be left to professional assessment.
How to use an unloader brace correctly
Putting the evidence above together gives a practical set of steps. The process below is practical consensus in physiotherapy.
- The first step is for a physiotherapist to assess lower limb alignment, the site of degeneration (one side or both) and gait, to judge whether an unloader brace suits the patient, and not to buy one as soon as the knee hurts.
- If it is used, the brace must be treated as a support: it reduces the load on the affected side so that exercise is smoother and more comfortable, while strength and alignment training continue.
- Strength training must carry on as usual. Strengthening the thigh and buttock muscles remains the core of treatment for knee osteoarthritis, and a brace cannot replace it.
- Check whether the brace fits well and is comfortable. If it feels too tight, painful or slips, adjust it promptly. A brace that cannot be worn is useless, and this is the main reason many people give up wearing one.
- Do not stop all exercise once the brace is on. The real reason the leg gets weaker is giving up exercise and not the brace itself.
Carrying out this checklist has a practical precondition: the first step can be completed only if the therapist has watched the patient walk. For a patient troubled by knee pain, though, the hardest stretch is often the journey to the clinic, with stairs, waiting for transport and then walking to the treatment room, so the legs have already done the walking they least want to do before the assessment begins. A physiotherapist’s home assessment moves this step into the home, so that the treatment plan that follows is not held up by difficulty getting out.
Among the braces and aids for knee osteoarthritis, a knee brace is only one tool. Insoles, a walking stick and alignment adjustment are also options, and which to use depends on the individual patient. For the general principles of choice, or to go back and browse the main topics, see the overview of physiotherapy for knee osteoarthritis.