Friday, November 28, 2014

Nerve and brachial plexus injuries during shoulder arthroplasty - causes and prevention

Brachial Plexus Injuries During Shoulder Arthroplasty: What Causes Them and How to Prevent Them

This very nice review points out that neurological complications have been reported to occur in 3% of hemiarthroplasties, 0.1% to 4% of anatomic total shoulder arthroplasties, and 2% to 4% of reverse total shoulder arthroplasties. The brachial plexus is most commonly involved. Observations in cadaver studies have suggested that the most likely etiology of these neuropathies is stretch of the brachial plexus secondary to patient arm positioning.

Nerves appear to be able to tolerate stretching of up to 10% of their length for short periods, but more stretching and longer periods can disrupt the blood supply or the anatomic integrity of the nerve. Cadaver and intraoperative nerve monitoring studies have identified shoulder abduction of >90 degrees; combinations of abduction, external rotation, and either flexion or extension; and combinations of adduction, extension, and either internal or external rotation as positions which cause nerve dysfunction.

While it is suggested that many of these injuries are transient, it is estimated that one in 100 shoulder arthroplasties are complicated by long lasting or permanent nerve injury.

Comment: While published data may suggest that one in 25 shoulder arthroplasties is complicated by a neurologic injury, we can suspect that the actual incidence is higher - both because such injuries may go unnoticed and because they are likely to be underreported. This article points out that at arthroplasty the nerves can be exposed to extraordinary stretching because the protective effects of pain and muscle tightness are removed by anesthesia, the protective effects of soft tissue contracture are removed by surgical releases, and the humerus is put in unnatural positions as the surgeon resects humeral osteophytes and exposes the glenoid for arthroplasty. 

While some surgeons rely on nerve monitoring to prevent clinical neurological injury, our approach is to recognize the 'positions of risk' and to assure that the surgical time spent in these positions is short, allowing for periods of 'nerve rest' with the arm back in a neutral position and with the retractors relaxed. We are particularly concerned about shoulders that have been very stiff prior to arthroplasty as well as shoulders of patients with diabetes or those on medications such as methotrexate. Positions of particular concern include (1) humeral external rotation and extension which stretches the median nerve, (2) coracoid muscle retraction to expose the glenoid which stretches the musculocutaneous nerve, and (3) traction on the arm which stretches the upper trunk of the brachial plexus (especially if the head is turned and inclined to the contralateral side). Overlengthening of the arm in reverse total shoulder is also known to be a risk factor for plexus injury. And, of course, brachial plexus block anesthetic carries a risk of neurologic injury.

Addition posts of interest can be found here.


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