B-27 Free Communication/Poster - Motor Control: MAY 27, 2009 1:00 PM - 6:00 PM ROOM: Hall 4F
Deficits in muscle strength that compromise functional performance persist years after total knee arthroplasty (TKA). Unweighting or unloading of the involved limb both before and after TKA is a common adaptation to avoid knee pain and instability, but may exacerbate quadriceps strength loss.
PURPOSE: To quantify the relationship between changes in involved limb unloading and the amount of quadriceps strength loss after TKA.
Subjects: Twenty-four patients with end-stage osteoarthritis were studied (68.3±8.4 years; 15 women, 9 men). Patients were excluded if they had uncontrolled hypertension, uncontrolled diabetes, body mass index > 35, or significant neurologic impairments. All subjects underwent a primary, unilateral TKA.
METHODS: Maximal voluntary isometric strength (MVIC) of the quadriceps muscle was assessed preoperatively and again 4 weeks after TKA using an isokinetic dynamometer. Static limb unloading was quantified by having patients place each limb on one of 2 electronic scales. Weight on each scale was recorded continuously and averaged over a total of 90 seconds. Patients were asked questions to distract them and encourage habitual stance patterns. All patients participated in a standardized rehabilitation program for 9 weeks following surgery.
RESULTS: Average quadriceps strength loss 1 month following TKA was 37.9+27.9% (range: 85.5% loss to 30% gain). The average amount of unloading did not change significantly before and after surgery (5.7 ± 6.1% vs 7.0 ± 4.4% respectively) (p>0.05), although the changes in unloading by individual were more variable and ranged from a 35.9% decrease to a 29.9% increase in unloading of the involved limb. The change in quadriceps strength was significantly correlated with the change in limb unloading (r=0.47, p<0.05).
CONCLUSION: Quadriceps strength loss following TKA was associated with an increase in involved limb unloading. Additionally, limb unloading did not improve following TKA and one month of standard rehabilitation, suggesting that habitual unloading patterns may persist. Further research is required to determine if targeted quadriceps strengthening after TKA would attenuate limb unloading and if other causal factors exist for limb unloading.
Funding: Foundation for Physical Therapy, American College of Rheumatology, NIH 1 UL1 RR025780