Tuesday, October 4, 2016

How well does the subscapularis work after total shoulder arthroplasty? ?Hazards of inter scalene block?

Subscapularis function after total shoulder arthroplasty: electromyography, ultrasound, and clinical correlation

These authors correlated the EMG activity of the subscapularis after total shoulder arthroplasty (TSA) with clinical and ultrasound findings in 30 patients who were at least 1 year (average, 2.1 years) from TSA approached through a standard subscapularis tenotomy. 28 of 30 patients had an interscalene block.

The average Simple Shoulder Test (SST) score improved from 3.9 preoperatively to 9.0 postoperatively (P < .0001). Six patients reported inability to tuck in their shirt on the SST questionnaire. Of these 6 patients, decreased internal rotation range of motion was documented: 2 reached to the belt, 2 to the buttock, and 2 to the side only.

Lift-off test was documented in 21 participants preoperatively. Eight patients were unable to perform the test because of lack of internal rotation motion; the remaining patients had a negative lift-off test result. Postoperatively, the total study group showed that the lift-off test result was negative in 23
patients, positive in 6 patients, and equivocal in 1 patient. The 6 patients with a positive test result had an intact subscapularis on ultrasound examination; therefore, there were 6 false positive results for the lift-off test. Only 1 of these patients reported an inability to tuck in the shirt on the SST score. On review of the EMG data of these 6 patients, 2 of the 6 patients had chronic denervation and reinnervation pattern. The 2 patients with a documented subscapularis tendon tear on ultrasound had negative belly-press and lift-off test results, and 1 patient reported an inability to tuck in the shirt on the SST score.

The postoperative EMG findings were normal in 15 patients; in the other 15 patients, there was evidence of chronic denervation with reinnervation changes: 30% subscapularis, 27% infraspinatus, 20% supraspinatus, 20% teres minor, and 13% rhomboids.

These authors concluded that in half of the patients, there was evidence of chronic denervation and reinnervation changes across 5 different muscle groups. They theorized that surgical exposure, traction, and the use of interscalene regional anesthesia may have contributed to these unexpected EMG results.

Comment: The surprising result of this study was the 50% rate of denervation of multiple muscle groups. This result suggests that surgeons consider the possible effects of brachial plexus blocks as well as arm manipulation and traction on postoperative muscle function.

Physical examination alone was not a reliable measure of subscapularis integrity. In this study, the belly-press improved postoperatively, and it was negative in all patients, with 2 false-negative results. The liftoff test had 6 false-positive results.

Our approach to care of the subscapularis is shown in this link.