Abstracts & Literature Review 6

A Mechanical Theory for the Effectiveness of Bracing for Medial Compartment Osteoarthritis of the Knee

Dan K. Ramsey, PhD, Kristen Briem, PT, MHSc, Michaels J. Axe, MD
and Lynn Synder-Mackler, ScD, PT, SCS

J Bone Joint Surg AM 2007; 89:2398-407

JACO Editorial Reviewer: Raymond S Nanko, MD, DC, DAAPM

Published:
Journal of the Academy of Chiropractic Orthopedists
December 2011, Volume 8, Issue 4

The original article copyright belongs to the original publisher. This review is available from: http://www.dcorthoacademy.com
© 2011 Nanko and the Academy of Chiropractic Orthopedists. This is an Open Access article which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Authors’ Abstract:

Background

Evidence that knee braces used for the treatment of osteoarthritis mediate pain relief and improve function by unloading the joint (increasing the joint separation) remains inconclusive. Alternatively, valgus-producing braces may mediate pain relief by mechanically stabilizing the joint and reducing muscle co-contractions and joint compression. In this study, therefore, we sought to examine the degree to which so-called unloader braces control knee instability and influence muscle cocontractions during gait.

Methods

Sixteen subjects with radiographic evidence of knee malalignment and medial compartment osteoarthritis were recruited and fitted with a custom Generation II Unloader brace. Gait analysis was performed without use of the brace and with the brace in neutral alignment and in 4° of valgus alignment. A two-week washout period separated the brace conditions. Muscle co-contraction indices were derived for agonist and antagonist muscle pairings. Pain, instability, and functional status were obtained with use of self-reported questionnaires, and the results were compared.

Results

The scores for pain, function, and stability were worst when the knee was unsupported (the baseline and washout conditions). At baseline, nine of the sixteen patients reported knee instability and five of the nine complained that it affected their activities of daily living. Poor knee stability was found to be correlated with low ratings for the activities of daily living, quality of life, and global knee function and with increased pain and symptoms. Knee function and stability scored best with the brace in the neutral setting compared with the brace in the valgus setting. The co-contraction of the vastus lateralis-lateral hamstrings was significantly reduced from baseline in both the neutral (p = 0.014) and valgus conditions (p = 0.023), and the co-contraction of the vastus medialis-medial hamstrings was significantly reduced with the valgus setting (p = 0.068), as a result of bracing. Patients with greater varus alignment had greater decreases in vastus lateralis-lateral hamstring muscle co-contraction.

Conclusions

• When knees with medial compartment osteoarthritis are braced, neutral alignment performs as well as or better than valgus alignment in reducing pain, disability, muscle co-contraction, and knee adduction excursions. Pain relief may result from diminished muscle co-contractions rather than from so-called medial compartment unloading. JACO Editorial Summary
• The article was written by authors from the Department of Physical Therapy, Graduate Program in Biomechanics and Movement Science, and Center of Biomedical Engineering Research, University of Delaware, Newark, Delaware
• Osteoarthritis of the knee is the most common cause of functional disability among Americans, and the medial compartment is most often affected.
• Joint laxity and mediolateral instability necessitate increased muscle activity and coactivation of antagonistic muscles to stabilize the knee. Greater laxity raises the likelihood of episodes of knee instability.
• The purpose of this study was to evaluate the effectiveness of bracing for Medial Compartment Osteoarthritis of the knee. Additionally, the aim of this study was to examine the degree to which valgusproducing unloader knee braces control instability and influence muscle cocontraction during gait.
• Sixteen subjects who had genu varum and medial compartment osteoarthritis of the knee were referred from a local orthopedic practice. They had a mean age (and standard deviation) of 54.9 ± 8.8 years and a mean body mass index of 31.1 ± 4.2 kg/m2.
• The patients underwent three-dimensional lower-extremity gait analysis with simultaneous surface electromyographic measurement on three separate occasions (without braces, with the braces in neutral alignment, and with the braces in 4° of valgus correction).
• The individuals wore the brace in neutral alignment throughout the day for two weeks before returning for the second gait analysis. Following Test 2, no brace was worn for two weeks (the washout period). After the washout period, braces were reset to the original setting at 4° of valgus, relative to the varus alignment measured at the time of fitting. Patients then wore the brace for an additional two weeks before the final gait analysis
• At the time of the baseline assessment when the knee was unsupported, the patients demonstrated significantly greater cocontraction of the vastus medialis-medial hamstrings (p = 0.068) and vastus lateralislateral hamstrings (p = 0.014) during weight acceptance, which may be an attempt to stiffen the knee through use of increased joint compression. Both bracing conditions led to a significant overall lowering of antagonist muscle co-contractions on both the medial and lateral sides
• Pain and functional status were assessed during each of the brace conditions and the washout period with use of the Knee Injury and Osteoarthritis Outcome Score (KOOS)
• Knee adduction excursions were significantly reduced as a result of bracing (p = 0.038 for the neutral setting and p = 0.000 for the valgus setting - Fig. 4), with excursions being lowest at 4° of valgus correction.
• Self-reported knee pain and functional disability in patients with medial compartment osteoarthritis were significantly reduced when the knee was braced in both the neutral condition and with a 4° of valgus correction. Muscle co-contraction and knee adduction excursions were also lower when the knees were braced.
• Functional knee stability improved with the neutral brace setting, with only one patient reporting that instability affected daily activity. Functional knee instability worsened during the washout period, with eight patients who reported that instability affected their activities of daily living.

Summary

This was a small study. The study was limited to 16 participants and there were no randomized controls. There is inherent weakness in the study when patients serve as their own controls. Musculature co-contraction and ligamentous laxity of the unsupported or braced osteoarthritic knee results in progression of the disease process. Neutrally aligned bracing of the osteoarthritic knee may result in reduced muscle co-contractions, mediated by the brace mechanically stabilizing the knee. The authors report that when a neutrally aligned brace is worn for the treatment of medial compartment osteoarthritis of the knee, positive effects results in reduced pain and improved functional stability. Mechanical Bracing also improved functional scores with the Knee Injury and Osteoarthritis Outcome Score (KOOS) and improved activities of daily living. Additional large scale randomized controlled studies may be helpful.