Early Quadriceps Strength Loss After Total Knee Arthroplasty : The Contributions of Muscle Atrophy and Failure of Voluntary Muscle Activation

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 theearly loss of quadriceps strength after surgery

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

Reliability and Validity of the Knee Injury and Osteoarthritis Outcome Score in Patients Undergoing Unicompartmental Knee Arthroplasty

BACKGROUND: The Knee Injury and Osteoarthritis Outcome Score (KOOS) was developed to document outcomes from knee injury, including the impact of osteoarthritis on knee function. The purpose of this study is to determine the reliability and validity of the KOOS subscales for evaluating outcomes following unicompartmental knee arthroplasty (UKA). METHODS: KOOS Pain, Activities of Daily Living (ADL), Sport, Symptoms, and Quality of Life (QoL) scores collected from 172 patients who underwent UKA were used in the analysis. KOOS subscales were tested for reliability and validity of scores through a Rasch model analysis. RESULTS: KOOS Sport, KOOS ADL, and KOOS QoL had good evidence of reliability with acceptable person reliability, person separation, and item reliability. For overall scale functioning, KOOS Pain, Symptoms, and ADL all had 1 question that did not have an acceptable value for infit or outfit mean square value. Questions in KOOS Sport and QoL all had acceptable values. There was a positive, linear relationship between the Short-Form 12 Physical Component Summary and the KOOS subscales which indicated good evidence of convergent validity. These associations were also seen when the cohort was separated in medial and lateral UKA. CONCLUSION: Two of the 5 KOOS subscales (KOOS Sport and KOOS QoL) were considered adequate in measuring outcomes, as well as reliability. The KOOS ADL had borderline values; however, it had adequate infit and outfit values. The KOOS Pain and Symptom score performed poorly in this analysis. For documenting outcomes following UKA, this study supports the use of KOOS ADL, Sport, and QoL