More on nerve injuries in shoulder joint replacement

Incidence of peripheral nerve injury during shoulder arthroplasty when motor evoked potentials are monitored

Previous studies using intraoperative nerve monitoring during shoulder arthroplasty found a 56.7% incidence of intraoperative nerve dysfunction, including both clinically relevant nerve injuries and subclinical abnormalities demonstrated on post-operative EMG. Patients with a history of prior open shoulder surgery and pre-operative external rotation of < 10° had a statistically significant higher incidence of nerve injury

These authors utilized transcranial electrical motor evoked potentials (MEPs) during shoulder arthroplasty to detect nerve alerts during 284 shoulder arthroplasties. While there were no permanent post-operative nerve injuries and only two transient nerve injuries (0.7%), nerve alerts occurred in 102 cases (36.2%). 72% of these involved the axillary nerve, 28% the radial, 34% the musculocutaneous, 14% the median and 10% the ulnar.

The surgeon was notified of any changes during intraoperative compromise nerve monitoring. If an alert meeting threshold criteria occurred, retractors were removed and the arm was placed back into a neutral position briefly (3–5 min). Typically, the surgeon proceeds only after alerts had partially resolved however, there were instances where the reported change did not resolve with manipulation and the surgeon proceeded judiciously.  Invariably, the decision to proceed despite a sustained alert status involved deltoid MEPs. If multiple nerves repeatedly met alert criteria after proper repositioning precautions were performed with the arm, then the surgeon modified the surgical plan to a hemiarthroplasty if appropriate. Given the frequency of axillary nerve alerts and location of the recording electrodes in the surgical field (i.e. retractors relative to the electrodes), if the alert was isolated to just a portion of the three heads of the deltoid muscle and not all the three heads, a clinical decision was sometimes made to proceed despite the alert.

Nineteen (6.7%) cases did not have signals return above alert threshold at closure. Two of these cases had postoperative nerve injuries, one involving the radial nerve and one the radial, musculocutaneous, median, and ulnar nerves. Both patients had cervical spine degeneration.

Comment: It is apparent that nerves can sustain injury during shoulder arthroplasty. Many surgeons will not be using intraoperative nerve monitoring. In this case, the surgeon may be able to minimize the risk of nerve injury by avoiding periods of extreme shoulder positions or vigorous retraction for more than several minutes, then returning the arm to a neutral position to 'let the nerves have a drink'. A careful neurologic examination after the patient has recovered from the anesthetic is important, in that patients themselves may only recognize deficits after discharge. 

See prior relevant post at this link.
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