The Journal of Bone and Joint Surgery (American). 2005;87:1047-1053.
doi:10.2106/JBJS.D.01992
© 2005 The Journal of Bone and Joint Surgery, Inc.
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Early Quadriceps Strength Loss After Total Knee Arthroplasty

The Contributions of Muscle Atrophy and Failure of Voluntary Muscle Activation

Ryan L. Mizner, MPT, PhD1, Stephanie C. Petterson, MPT1, Jennifer E. Stevens, MPT, PhD2, Krista Vandenborne, PT, PhD2 and Lynn Snyder-Mackler, PT, ScD1

1 Department of Physical Therapy, 301 McKinly Laboratory, University of Delaware, Newark, DE 19716. E-mail address for L. Snyder-Mackler: smack{at}udel.edu
2 Department of Physical Therapy, P.O. Box 100154, UFHSC, University of Florida, College of Public Health and Health Professions, Gainesville, FL 32610

Investigation performed at the University of Delaware, Newark, Delaware, and the University of Florida, Gainesville, Florida

In support of their research or preparation of this manuscript, one or more of the authors received grants or outside funding from the National Institutes of Health (R01HD041055-01, T32 HD07490) and the Foundation for Physical Therapy through the Promotion of Doctoral Studies program. None of the authors received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

Background: While total knee arthroplasty reduces pain and provides a functional range of motion of the knee, quadriceps weakness and reduced functional capacity typically are still present one year after surgery. The purpose of the present investigation was to determine the role of failure of voluntary muscle activation and muscle atrophy in the early loss of quadriceps strength after surgery.

Methods: Twenty patients with unilateral knee osteoarthritis were tested an average of ten days before and twenty-seven days after primary total knee arthroplasty. Quadriceps strength and voluntary muscle activation were measured with use of a burst-superimposition technique in which a supramaximal burst of electrical stimulation is superimposed on a maximum voluntary isometric contraction. Maximal quadriceps cross-sectional area was assessed with use of magnetic resonance imaging.

Results: Postoperatively, quadriceps strength was decreased by 62%, voluntary activation was decreased by 17%, and maximal cross-sectional area was decreased by 10% in comparison with the preoperative values; these differences were significant (p < 0.01). Collectively, failure of voluntary muscle activation and atrophy explained 85% of the loss of quadriceps strength (p < 0.001). Multiple linear regression analysis revealed that failure of voluntary activation contributed nearly twice as much as atrophy did to the loss of quadriceps strength. The severity of knee pain with muscle contraction did not change significantly compared with the preoperative level (p = 0.31). Changes in knee pain during strength-testing did not account for a significant amount of the change in voluntary activation (p = 0.14).

Conclusions: Patients who are managed with total knee arthroplasty have profound impairment of quadriceps strength one month after surgery. This impairment is predominantly due to failure of voluntary muscle activation, and it is also influenced, to a lesser degree, by muscle atrophy. Knee pain with muscle contraction played a surprisingly small role in the reduction of muscle activation.

Level of Evidence: Prognostic Level I. See Instructions to Authors for a complete description of levels of evidence.


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Letters to the Editor:

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Activating the Quadriceps after Total Knee Replacement
Jerrold Gorski
JBJS Online, 24 May 2005 [Full text]