Saturday, December 6, 2008

Peripheral nerve function during shoulder arthroplasty
The incidence of peripheral nerve injury during shoulder arthroplasty is reported between one and four percent. However as these numbers are based on retrospective chart review, the actual incidence of intraoperative nerve dysfunction has not been clearly revealed.

The present study utilized intraoperative nerve monitoring to identify the frequency, type, and predisposing factors for peripheral nerve injury during shoulder arthroplasty. Thirty consecutive patients undergoing shoulder arthroplasty participated in this study. Continuous intraoperative nerve monitoring of the brachial plexus was performed by a neurophysiologist. Brachial plexus functioning was monitored by both EMG activity and transcranial electrical motor evoked potentials (MEPs) from six extremity muscles. A significant intraoperative nerve event was defined as a sustained neurotonic EMG activity or a 50 percent reduction in transcranial MEPs from one or more muscles. Both arm and retractor positions were recorded and modified to relieve stress on the brachial plexus when an event took place. If the patient had an intraoperative “nerve alert”, he/she had a follow-up EMG at least four weeks following the surgery.

Seventeen patients had a total of 30 intraoperative nerve alerts. Of the 30 alerts, none returned to baseline with retractor repositioning. However 23 did return to baseline with repositioning of the extremity to a neutral position. Four of the seven patients who did not experience an intraoperative return to baseline MEPs had positive postoperative EMG results. The incidence of nerve dysfunction was associated with a history of prior shoulder surgery and passive external rotation of less than 10° with the arm at the side (P < .05). The authors conclude that intraoperative nerve injury during shoulder arthroplasty is likely greater than reported and certain patients with prior history of shoulder surgery or limited external rotation may be candidates for routine nerve monitoring.
A Great Study

The present study won the 2005 Neer Award from the American Shoulder and Elbow Surgeons. It is a very elegant example of the intersection of neuroscience with orthopedics. Shoulder arthroplasty represents the classic mechanical approach to orthopedic dysfunction. Yet without understanding the neurologic implications of these procedures, we may not fully appreciate the patients’ postoperative courses.

Although the sample size is not overwhelming, 16.7 % of the patients in the study had postoperative EMG changes resulting from an intraoperative neuropraxic event. Interestingly the authors noted that almost half of the nerve alerts occurred within the brachial plexus and not the peripheral nerves themselves. Mechanical strain data indicate the greatest tensile load on the brachial plexus with the arm in 90° of abduction, external rotation, and extension. Intuitively, this makes sense as this is a common intraoperative position for this procedure.

Implications for Physical Therapists

The results of the present study could have implications for the practicing therapist as well. It may be reasonable to assert preoperative improvement of passive ER could reduce the intraoperative traction placed on the brachial plexus. Additionally, the therapists should be aware that in the absence of intraoperative nerve monitoring, there is a possibility that an intraoperative neuropraxic event took place during the procedure. While certainly not something to speculate openly to the patient, it does make a reasonable case for early neural mobilization of the brachial plexus following shoulder arthroplasty in addition to the standard ROM progression.

S NAGDA, K ROGERS, A SESTOKAS, C GETZ, M RAMSEY, D GLASER, G WILLIAMSJR (2007). Neer Award 2005: Peripheral nerve function during shoulder arthroplasty using intraoperative nerve monitoring Journal of Shoulder and Elbow Surgery, 16 (3) DOI: 10.1016/j.jse.2006.01.016

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