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Early Quadriceps Strength Loss After Total Knee ArthroplastyThe 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; 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@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
View Disclosures and Other Information
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.
Investigation performed at the University of Delaware, Newark, Delaware, and the University of Florida, Gainesville, Florida

The Journal of Bone and Joint Surgery, Incorporated
J Bone Joint Surg Am, 2005 May 01;87(5):1047-1053. doi: 10.2106/JBJS.D.01992
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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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    Accreditation Statement
    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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    Jerrold Gorski
    Posted on May 05, 2005
    Activating the Quadriceps after Total Knee Replacement
    Winthrop University Hospital

    To the Editor:

    I read “Early Quadriceps Strength Loss After Total Knee Arthroplasty”, (JBJS,87A,1047-1053), hoping to find relevent clinical application. Identifying failure of voluntary muscle activation, the authors may have inadvertently provided a scientific rationale for an empirically effective post op technique that my patients describe as cruel, albeit while laughing.

    It is my routine to tickle the ipsilateral foot post op TKR, usually eliciting a robust quadriceps contraction, some pain and usually a laugh. If done artfully, patients accept this treatment, as it literally “jumpstarts” recovery of the quadriceps. It works well but only in those who are ticklish. Many family members eagerly take part with this treatment. Patients are motivated to avoid the tickle technique by doing the quad contraction on their own, and moving the leg to avoid the noxious irritant. Counterintuitively, pain avoidance and “very rapid mobilization” can be beneficially combined to improve voluntary and involuntary quadriceps muscle activation.

    Might I suggest study of this technique as a clinical application suitable for the authors continuing research?

    Respectfully, Jerrold Gorski MD

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