Objective: The aims of this study were to evaluate weight bearing during standing and 30- and 60-degree squats approximately 1 wk and 2 mos after surgery and determine whether weight bearing during squatting could be a better clinical marker than standing for identifying perceived functional limitation approximately 1 wk after surgery. A further objective was to determine whether age, body mass index, and number of outpatient visits over the course of rehabilitation predicted weight bearing during a squat approximately 2 mos after surgery.
Design: The percentage of body weight placed over both limbs during stand and 30- and 60-degree squats in 38 patients (25 women and 13 men) who had primary unilateral knee arthroplasty was determined. An asymmetry index would be used as a marker that could discriminate between those who perceived at least moderate difficulty with functional tasks and those who perceived only slight or no difficulty with functional activities based on the physical function dimension of the Western Ontario McMaster Universities Osteoarthritis index approximately 1 wk after surgery. Stepwise regression was conducted to determine whether clinical characteristics predicted weight-bearing asymmetry at discharge.
Results: At initial visit (first observation), and compared with the uninvolved side, individuals placed significantly less body weight over the involved or operated limb for stand and 30- and 60-degree squats (P < 0.0001). Results were similar at last rehabilitation visit (second observation). Identifying at least moderate self-reported difficulty with functional tasks based on the receiver operator characteristic curve for the asymmetry index for the stand position was 0.64, whereas for the 30- and 60-degree squats, the area under the curve was 0.81 and 0.89, respectively. At discharge from rehabilitation, there was a moderate to good direct relationship (r = 0.70) between the number of rehabilitation visits completed and the weight-bearing asymmetry index for the 60-degree squat.
Conclusions: On the first outpatient visit, individuals who had primary unilateral knee arthroplasty placed more body weight over the uninvolved side for the three weight-bearing positions. With high probability, the asymmetry index for both squatting angles identified perceived functional difficulty. As rehabilitation visits increased, there was a direct association to improved interlimb weight-bearing symmetry when squatting to 60 degrees.