Can measures of limb loading and dynamic stability during the squat maneuver provide an index of early functional recovery after unilateral total hip Arthroplasty?

Objective To investigate limb loading and dynamic stability during squatting in the early functional recovery of patients who had undergone total hip arthroplasty (THA).

Design Cohort study.

Setting Inpatient rehabilitation clinic.

Participants Of the total participants (N=99), a random sample of patients who had undergone THA (n=61; 34 men and 27 women; mean age, 62±9y; weight, 77±14kg; height, 174±9 cm) was assessed twice, 13.2±3.8 days (t1) and 26.6±3.3 days postsurgery (t2), and compared with a healthy reference group (n=38; 22 men and 16 women; mean age, 47±12y; weight, 78±20kg; height, 175±10cm).

Interventions Patients who had undergone THA received 2 weeks of standard inpatient rehabilitation.

Main Outcome Measures Interlimb vertical force distribution and dynamic stability during the squat maneuver, as defined by the root mean square of the center of pressure in anteroposterior and mediolateral directions, of operated and nonoperated limbs. Self-reported function was assessed via the Function Assessment Questionnaire Hannover for Osteoarthritis questionnaire.

Results At t1, unloading of the operated limb was 15.8% greater (P<.001; d=1.070) and anteroposterior and mediolateral center of pressure root mean square values were 30% to 34% higher in patients who had undergone THA than in the healthy reference group (P<.05). Unloading was reduced by 12.8% toward a more equal distribution from t1 to t2 (P<.001; d=.874). Although mediolateral stability improved between t1 and t2 (operated limb: 14.8%; P=.024; d=.397; nonoperated limb: 13.1%; P=.015; d=.321), anteroposterior stability was not significantly different. Self-reported physical function improved by 15.8% (P<.001; d=.965).

Conclusions Patients who had undergone THA unload the operated limb and are dynamically more unstable during squatting in the early rehabilitation phase after THA than are healthy adults. Although loading symmetry and mediolateral stability improved to the level of healthy adults with rehabilitation, anteroposterior stability remained impaired. Measures of dynamic stability and load symmetry during squatting provide quantitative information that can be used to clinically monitor early functional recovery from THA.