The role of proprioception in knee OA management

Photo courtesy of Ossur Americas.

Demonstrated associations between im­paired proprioception and knee osteo­arthritis suggest some interventions that help relieve painful symptoms in patients with knee osteoarthritis , such as exercise and bracing, do so by positively affecting joint position sense.

By Barbara Boughton

It’s long been known that patients with knee osteoarthritis (OA) have impaired proprioception, and research has suggested that this deficit may influence pain and functional ability. But why patients with proprioceptive deficits seem to have more painful knee OA symptoms, and whether improving joint position sense will significantly improve their pain and daily function, are open to question.

“There’s absolutely no question that knee OA patients have proprioceptive and kinesthetic deficits. But the questions that research has still not entirely answered are: What do these deficits mean, and can you intervene in a way to impact those deficits and change the patient’s symptoms?” said Lynn Snyder-Mackler, PT, ScD, alumni distinguished professor in the department of physical therapy at the University of Delaware.

For clinicians on the front lines of treating patients with knee OA, these questions are more than academic. They need to know if and how proprioception influences their patients’ pain, function, and disease progression because such knowledge is critical to designing a treatment program. Some helpful tidbits can be gleaned from recent research to inform clinical practice, but the answers to all questions about proprioception and knee OA are still incomplete.

The evidence

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The latest research papers—and some of the most influential studies—to examine the role of proprioception relative to risk of knee OA and to disease progression were published by Neil Segal, MD, MS, and colleagues at the University of Iowa in 2010 and David Felson, MD, MPH, and colleagues at Boston University School of Medicine in 2009.

In a study published in Medicine and Science in Sports and Exercise¹ in November 2010, Segal and colleagues speculated that because impaired quadriceps strength and joint position sense have been linked with knee OA cross-sectionally, better sensorimotor function might protect against the development of radiographic knee OA or symptoms of the disease. The research was part of the Multicenter Osteoarthritis (MOST) study, a longitudinal study of adults aged 50 to 79 years at high risk for knee OA, with risk factors that included previous knee injury, surgery on the knee, or obesity.

Participants underwent bilateral weight-bearing fixed-flexion radiographs, joint position sense acuity tests, and isokinetic quadriceps strength tests at baseline and at 30-month follow up. Body mass index and self-reported frequency of knee pain and/or stiffness were assessed at the same timepoints. Participants also completed medical and physical activity questionnaires at baseline.

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Results revealed that greater knee extensor strength was associated with a decreased risk of symptomatic but not radiographic knee OA, regardless of patients’ proprioceptive acuity.

Participants who were older and had more knee pain at baseline were more likely to have proprioceptive deficits at that time, according to Segal.

“That’s consistent with other research² that has shown that impaired proprioception cannot predict who’s going to get knee osteoarthritis or have worse outcomes from the disease. And although patients with proprioception seem to have more pain, these symptoms don’t seem to correlate with more disease,” said Segal, who is director of the clinical osteoarthritis research program and medical director for research at the Orthopaedic Motion Analysis Laboratory at the University of Iowa.

Proprioception and pain

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Segal noted that there are a number or theories about why patients with knee OA who have poor proprioception also seem to have painful symptoms, yet their joint position sense deficits at baseline don’t seem to correlate with development of disease over 30 months. A person experiencing pain (which is a nervous system function, as is proprioception) may not be very attuned to joint position because their nervous system is overwhelmed with the sensation of pain. Having poor proprioception could lead a patient to load the joint in an abnormal way, which might lead to more painful symptoms, Segal said.

In another recent paper on proprioception and its influence on pain and the progression of knee OA, researchers led by Felson studied 2243 subjects from the MOST study to find out if impaired joint position sense could increase the risk of developing knee OA or worsen pain or structural damage in those who already had knee OA. In Arthritis and Rheumatism in August 2009,² they noted that no longitudinal studies had yet evaluated these questions.

The researchers found that at baseline, proprioceptive acuity was associated with the presence and severity of knee pain but not with the presence of knee OA on x-ray. Yet 30 months later, the results indicated that proprioceptive deficits had no effect on long term outcomes in terms of frequency of pain, WOMAC (Western Ontario and McMaster Universities Osteoarthritis Index) scores, and radiographic findings. Proprioceptive acuity was not associated with any new onset of frequent pain. The WOMAC scores of those with the worst proprioceptive acuity also worsened more (but just slightly more) than those with better joint position sense, and physical function scores deteriorated slightly less in those with better joint position sense. Progression of disease on x-ray in subjects with knee OA was not associated with proprioceptive acuity.

The researchers concluded that “proprioceptive acuity as assessed by the accuracy of reproduction of the angle of knee flexion has modest effects on the trajectory of pain and physical limitation in knee OA.”

In search of interventions

The quandary for clinicians, when looking at these research results, is whether clinical interventions that improve proprioceptive abilities will also improve OA symptoms. And which interventions are best for their patients? Researchers have attempted to answer that question, but the results have been mixed.

A study by Da-Hon Lin, MD, of the En Chu Kong Hospital at the National Taiwan University Hospital in Taipei, Taiwan, published in the Journal of Orthopaedic & Sports Physical Therapy in June 2009,³ investigated the clinical efficacy of two different non-weight-bearing exercise regimens, one involving proprioceptive training and the other strength training, for patients with knee OA. The 108 patients in the study were randomly assigned to eight weeks of exercises to improve proprioception, a strength training regimen, or no exercise intervention. The patients’ WOMAC pain and function scores, walking time on three different terrains, knee strength, and absolute knee reposition error were assessed at baseline and after the eight-week intervention.

The researchers found that both exercise regimens significantly improved WOMAC pain and function scores compared to the control group who received no exercise intervention. The patients who had received proprioceptive training demonstrated significantly greater improvement in walking time on a spongy surface and knee reposition error than other patients in the study, yet patients who underwent a strength training program demonstrated significantly greater increases in knee extensor muscle strength.

Still, the latest research to address the question of whether exercise that addresses proprioceptive deficits is actually helpful in outcomes that matter—i.e., improving pain and function in knee OA patients—came up with a resounding negative answer.

In a study published in the April 2011 issue of Physical Therapy,⁴ G. Kelley Fitzgerald, PT, PhD, and colleagues at the University of Pittsburgh performed a single-blinded randomized controlled trial of 183 knee OA patients in which agility and perturbation exercises were added to standard exercise therapy for one group of patients, while a placebo group received only a standard exercise program intervention. Knee instability is a common complaint of patients with knee OA and perturbation training (which enhances proprioceptor signals to muscles) has been shown⁵ to reduce reported symptoms of knee instability in people with anterior cruciate ligament injury. The researchers reasoned that agility and perturbation training techniques—which require changes in direction, challenges to balance, and negotiating obstacles—might help enhance function in patients with knee OA.

However, results indicated that although both exercise groups exhibited modest improvements in outcome measures (including WOMAC physical function score, knee pain, and global rating of change) at two and six months and one year follow up, there were no significant differences between the two groups. Although the researchers measured knee alignment in each subject at baseline, they did not assess proprioception before or after the intervention, so it remains unknown whether the exercises actually improved proprioception. The percentage of patients with knee instability in each group did not change significantly from baseline. The researchers speculated that individual patient characteristics might determine who would benefit most from adding agility and perturbation training techniques to standard exercise programs for knee OA and they noted that they’re continuing to examine their data to tease out these factors.

In yet another smaller study e-published late last year by Rheumatology, researchers from the Gulhane Military Medical Academy in Turkey found that three weeks of proprioceptive exercises had some benefits for patients with severe knee OA. After the intervention, the 30 patients who received training experienced significantly improved static balance compared to the 24 patients in the control group. Patients in the intervention group showed a greater tendency toward improved proprioceptive perception after the exercise program than those in the control group, but the difference was not statistically significant.⁶

So should a clinician include exercises that improve proprio­ception in a training program for a patient with knee OA? According to Segal, clinicians should not focus on just improving strength or improving proprioception, but should emphasize “functional exercises.” That means using strength training for muscles such as the quadriceps and hip abductors that can help improve outcomes, and prescribing exercises that are simultaneously weightbearing so they strengthen muscles and improve proprioception at the same time.

“An integrated program could be helpful—that would be a combination of strength training and proprioceptive rehabilitation,” Segal said.

Benefits of bracing

Looking beyond exercise, other questions include whether interventions such as knee bracing address proprioceptive deficits in patients with knee OA. And if knee bracing does affect proprioception, does it really have an impact on symptoms or progression of disease?

In many ways the jury is still out on these questions, but the research does give us some hints on whether knee bracing may improve proprioception. Trevor Birmingham, PhD, of the University of Western Ontario in London, Ontario, and colleagues evaluated knee braces specifically for their effect on proprioception. In a study published in March 2001 in Rheumatology⁷ they assessed the effects of functional knee braces specifically designed for knee OA patients with varus gonarthrosis on measures of proprioception and postural control. The 14 knee OA patients in the study (all of whom had proprioceptive deficits at baseline) experienced significantly improved proprioception after application of the brace, but the difference from baseline was small—a mean difference of .7° in proprioceptive acuity. Postural control was not significantly affected by the use of the brace.

“Although enhanced proprioception may be partially responsible for reported improvements with the use of a brace, the present findings call into question the functional importance of the small changes observed,” the authors concluded.

In a more recent study, published in October in Knee,⁸ researchers at the University of North Carolina at Chapel Hill found that a knee sleeve significantly improved proprioception during a partial weight-bearing task in 38 patients with knee OA, whether or not the sleeve was combined with stochastic resonance electrical stimulation. Neither of the sleeve conditions significantly affected proprioception during a nonweight-bearing task.

The researchers, however, also found that patients who had better proprioceptive acuity when they did not wear a knee sleeve reported less knee pain and stiffness and greater ability to perform functional tasks (when assessed using WOMAC scores). The authors hypothesized that patients with larger proprioceptive deficits may benefit most from knee sleeve wear.

There’s no question that bracing does improve pain and sometimes function in patients with knee OA, but whether that improvement is due to proprioception is a question that’s difficult to answer, added Yatin Kirane, PhD, MBBS, DOrth, a fellow at the Hospital for Special Surgery in New York, NY.

“The reason that bracing may improve symptoms is that not only do they affect loading of the joint, but they may theoretically improve feedback regarding proprioception—helping to control the patient’s motion. But right now that’s just speculation,” Kirane said.

Kirane is involved in an ongoing study in which knee OA patients are fitted with custom-made valgus braces. Changes in pain relief, perceived function, radiographic findings, knee synovial fluid chemistry, and motion abilities in 3D motion analysis associated with bracing are being assessed over time. So far, the study has recruited 15 patients with knee OA.

“We haven’t formed a final conclusion but it looks like there’s been some relief for the patients with the braces; some patients have experienced up to 30% pain relief,” Kirane said.

Yet there are downsides to bracing. It’s sometimes difficult to fit the brace correctly so that it’s easy for the patient to wear. Many patients also find them cumbersome, preferring to opt for knee arthroplasty instead, Kirane said.

In studying proprioception and bracing, researchers often encounter two problems, Kirane said. One is that there is usually a large placebo effect associated with bracing in knee OA patients. And there are so many different kinds of braces that it’s difficult to make sweeping conclusions about their effects on the joint and muscles, not to mention joint position sense.

“We need better studies—and we need randomized controlled studies on bracing in knee OA. But randomized controlled studies would be difficult to do, because proving a cause and effect relationship with bracing is so difficult—there are so many different types of braces and so many other factors that can impact a patient’s health,” Kirane said.

Barbara Boughton is a freelance health and medical writer based in the San Francisco Bay Area.

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