These authors sought to determine whether preoperative shoulder strength is predictive of postoperative outcomes and improvement after primary anatomic total shoulder arthroplasty (aTSA) in 160 shoulders with minimum 2-year follow-up.
External rotation (ER) and supraspinatus strength were assessed using a hand-held dynamometer. ER strength was measured with the involved shoulder in 0° external rotation, 0° abduction, and the elbow in 90° flexion. Supraspinatus strength was assessed with the involved shoulder in 30 degrees of flexion and 30 degrees of abduction.
Abduction strength was assessed as the maximum amount of weight that a patient could elevate vertically with the involved shoulder in 90° abduction and the arm in pronation in 5 pound intervals. Abduction strength was scored as follows: not capable of 90° abduction, 0; 0 lbs., 1; 5 lbs., 2; 10 lbs., 3; 15 lbs., 4; 20 lbs., 5.
The authors found that preoperative ER strength, supraspinatus strength, and abduction strength were each correlated positively with their respective postoperative values and negatively with improvement.
On multivariate analysis, baseline abduction strength was a significant positive predictor of postoperative values and a negative predictor of
improvement.
Comment: Once again we see that shoulders that are more functional prior to TSA are likely to be more functional after surgery, but are less likely to show improvement. Conversely, shoulders that are less functional before surgery are more likely to show improvement but tend to have lower postoperative scores.
The measurement of abduction strength as described (
the maximum amount of weight that a patient could elevate vertically with the involved shoulder in 90° abduction) actually reflects several aspects of the shoulder: strength, passive range of motion, and pain. A shoulder that can actively abduct 20 pounds to 90° must not only be strong, but also flexible and relatively painless.How you can support research in shoulder surgery Click on this link.
