Validity and Responsiveness of Forearm Strength Measurements in the Evaluation of Distal Radioulnar Joint Implant Arthroplasty

Abstract

To assess the responsiveness of forearm strength tests and to correlate the change to grip strength and a patient-reported outcome measure used for evaluation of distal radioulnar joint (DRUJ) implant arthroplasty. We performed a retrospective review of 18 patients treated with Herbert (n= 12) and Scheker (n= 6) DRUJ implants. Patients who had undergone the various measurements of arm and grip strength both before surgery and after a minimum follow-up of 1 year were included. Our primary aim was to compare the responsiveness of grip strength with our new methods for measuring forearm torque and lifting strength. The secondary aim was to correlate observed changes in strength measurements to change in a patient-reported outcome measure with use of the patient-reported wrist evaluation (PRWE). Measurements of grip strength, forearm torque, and lifting strength were performed with the Jamar dynamometer and the Kern and Baseline instruments. Preoperative values were compared with 1-year values. Standardized response mean and effect size values were higher for forearm torque than for grip strength. Change in forearm torque and lifting strength had a moderate to strong correlation with change in PRWE. The correlation between grip strength and PRWE was weak. Forearm torque measurements were better than grip strength in detecting changes after DRUJ arthroplasty. It also had a stronger correlation to patient-reported outcome, measured with the PRWE. Forearm torque testing may add further information to the evaluation of DRUJ disorders and their treatments. These tests can provide quantifiable data on the patient's ability to perform various tasks requiring physical strength.