Wednesday, June 8, 2016

Subscapularis function after total shoulder arthroplasty

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

These authors studied 30 patients who were at least 1 year (average, 2.1 years) from total shoulder arthroplasty with a subscapularis tenotomy. Patients returned for a physical examination, ultrasound evaluation, and EMG evaluation. Patients also completed postoperative surveys: the American Shoulder and Elbow Surgeons questionnaire, the Simple Shoulder Test, and the 12-Item Short Form Health Survey.

After surgery all 30 patients had what was thought to be a normal 'belly press' test. Six patients had an abnormal lift-off test.

Two patients had a subscapularis rupture on ultrasound, both had normal belly press and lift off tests. One patient reported the inability to tuck in the shirt on the SST.

The postoperative EMG finding was 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.

Comment: This article attempts to correlate patient self assessed shoulder function (SST), with two physical examination tests (lift off and belly press), ultrasound and EMG.  The results above show very poor correlation among these methods of assessment. 

The authors also state: "We believe that soft tissue releases or retraction at the time of TSA could be a risk but also acknowledge that the use of regional anesthesia in the majority of these cases would also be a possible risk factor for neurologic injury. " However we do not know the relationship of the use of blocks to any of the other parameters. 

While the authors opine that "that physical examination alone as a measure of the integrity of subscapularis repair is not reliable," we have found three physical findings to be of use in detecting if the patient has functionally important subscapularis dysfunction:

(1) increased passive external rotation (shown below for the left shoulder)
(2) weakness on belly press (see figure below)
and (3) a palpable defect in the tissues over the proximal humerus when the arm is internally and externally rotated.

In our practice, careful surgical surgical technique and careful rehabilitation seem to be the keys to good subscapularis function as described in this post. We also avoid interscalene blocks in that they have not proved important in improving the quality of the postoperative course and in that they impose additional risk as suggested in this article and in this post.

When we are referred someone with functionally important subscapularis deficiency, we use the reconstruction method described in this link.

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