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 cocontractions 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 cocontraction 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
cocontraction 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 cocontraction 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 cocontraction.
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 cocontraction, and knee adduction
excursions. Pain relief may result from diminished muscle cocontractions
rather than from so-called medial compartment unloading.
Level of Evidence: Therapeutic Level II. See Instructions
to Authors for a complete description of levels of evidence.