Early quadriceps strength loss after total knee arthroplasty

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 twentyseven
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.

Citation:
Mizner, R. et al. (2005) ‘Early quadriceps strength loss after total knee arthroplasty’ Journal of Bone and Joint Surgery, 87-A (5) 1047-1053..