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When Reducing Knee Pain Isn't Enough

Knee pain from arthritis is often the reason for having a knee joint replacement called total knee arthroplasty (TKA). The TKA reduces pain but at a price. The quadriceps muscle along the front of the thigh straightens the knee. Control of this muscle is reduced after TKA.

This problem can persist a year or more after surgery. Poor muscle performance has been linked with increased risk of falling, reduced walking speed, and difficulty getting up out of a chair.

Many studies have shown that a loss of knee extension is common after TKA. This study goes beyond that and looks at the cause for the decrease in muscle force after TKA. Rehab suggestions are offered.

The key problem is failure of voluntary activation. This means that the patient is trying hard to straighten the knee, but the muscle isn't contracting fully. Pain, swelling, and joint damage may be part of the cause. However, simply reducing knee pain doesn't improve muscle contraction.

This study shows the importance of special muscle training to get back full muscle force. Traditional exercises may not be enough for many patients. Electrical stimulation to the muscles and biofeedback for the patient are useful tools. The patient learns how to maximize muscle contraction.

According to these authors, decreasing knee pain with a TKA is not a good enough measure of success. Restoring full force during knee muscle contraction is important after TKA. The authors think restoring muscles to their full capacity may prevent falls and lengthen the life of the new knee implant.

References: Ryan L. Mizner, PT, MPT, et al. Voluntary Activation and Decreased Force Production of the Quadriceps Femoris Muscle After Total Knee Arthroplasty. In Physical Therapy. April 2003. Vol. 83. No. 4. Pp. 359-365.

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