Preliminary investigation of rate of torque development deficits following total knee arthroplasty

Background: To assess changes in maximal strength and rate of torque development (RTD) following TKA, and examine the relationships between these measures and physical function. Methods: Thirty-five TKA patients and 23 controls completed isometric knee extensor torque testing preoperatively, 1, and 6months after surgery. Maximal strength was calculated as the peak torque during a maximal voluntary isometric contraction (MVIC) of the knee extensor muscles, peak RTD (RTD_peak) was calculated as the maximum value from the 1st derivative of the isometric knee extension torque data, RTD_25% and RTD _50% were calculated as the change in force over the change in time from force onset to 25% and 50% MVIC. Physical function was measured using a timed-up-and-go (TUG) and stair climbing test (SCT). Results: RTD was significantly lower in the TKA group, at all-time points, compared to the Controls. MVIC and RTD significantly decreased 1-month following surgery (p=0.000 for all measures). RTD_peak measures added to linear regressions with strength improved the prediction of TUG scores (p=0.006) and the SCT scores (p=0.015) 1-month post-surgery. Adding RTD_50% to the regression model, following MVIC, improved predicting both TUG (p=0.033) and SCT (p=0.024). At 6-months, the addition of RTD_25% to the regression model, following MVIC, improved the prediction of TUG (p=0.037) and SCT (p=0.036). Conclusion: Following TKA, physical function is influenced by both the maximal strength and the rate of torque development of the knee extensors, and the prediction of function is improved with the addition of RTD compared to that of maximal strength alone.