Complication rates for primary anatomic (aTSA) and reverse TSA (rTSA) have been cited to be as high as 20%. Revision following aTSA and rTSA occurs in 7.5%-16.3% cases. The complication rates for revision surgery can be as high as 50%.
The incidence of nerve injury following primary TSA has been cited at 1-18.7% and may actually be higher as suggested by studies performed utilizing electromyography in the postoperative period.
Most of these injuries are thought to be related to inadvertent traction and stretching of the brachial plexus during intra-operative positioning/manuevering. Other mechanisms include injury secondary to surgical dissection, laceration, instrumentation, interscalene block anesthesia, lengthening of the limb vascular injury and/or compression secondary to hematoma formation and/or retractor use.
These authors reported their experience with continuous intraoperative nerve monitoring in patients having revision arthroplasty for infection (N=7), failed total and hemi-arthroplasty secondary to pain, dysfunction and/or loose components (N=36), and a periprosthetic fracture (N=1).
Thirty-two patients were revised to a reverse ( rTSA), six to an anatomic (aTSA) and six had a spacer placed.
The protocol for monitoring is extensive, utilizing a neurophysiologist in the operating room and a remote neuromonitoring professional remotely. Nerve monitoring data included transcranial electrical motor evoked potentials (MEPs), somatosensory evoked potentials (SSEPs), and free-run electromyography (EMG). Subdermal electrodes for stimulation and recording were placed in the non-operative arm by the technician while the operative arm electrodes were positioned by the surgeon following draping and preparation of the surgical extremity. Two electrodes were placed in each muscle approximately 2 cm apart for differential channel recordings. The muscles recorded in the operative arm included all three heads of the deltoid, biceps brachii, extensor carpi radialis (ECR), abductor pollicis brevis (APB) and the first dorsal interosseous (FDI) or abductor digiti minimi (ADM) to assess the axillary, musculocutaneous, radial, median and ulnar nerves, respectively. The electrodes were inserted into the belly of the muscle to maximize recording the compound action potential. SSEP stimulating electrodes were placed superficially over the median and ulnar nerves in the operative arm. The distal ulnar and median nerves have relatively large afferent somatosensory components and stimulation of these nerves are known to produce large monitorable SSEPs. In contrast, reliable SSEPs cannot be obtained from axillary, musculocutaneous nerves under general anesthesia. MEP Alerts were defined as reduction in signal of ≥80% in from an individual muscle recording, except for deltoid muscle alerts which required all three heads to have a signal reduction of ≥80% to define an alert.
In the case of an alert, the operating surgeon was immediately notified. Patient extremity was returned to neutral position, retractors were removed, and a 2-3-minute surgical pause was performed.
22.4% of procedures (n=10) had a transcranial electrical motor evoked potential (MEPs) alert with eight isolated to a single nerve (seven axillary, one radial) and one isolated to the axillary and musculocutaneous nerves.
One patient experienced a major brachial plexus alert involving axillary, musculocutaneous, radial, ulnar, and median nerve MEP alerts as well as ulnar and median nerve somatosensory evoked potentials (SSEPs), alerts.
Age, gender, BMI, CCI, and preoperative ROM were not found to be significantly different between cases in which a MEP occurred compared to those with no MEP. There were zero minor or major nerve injuries found in the postoperative period, while four (9.1%) developed distal peripheral neuropathy (DPN).
Comment: The nerves around the shoulder are at increased risk for injury during revision arthroplasty. The tissues around the shoulder are scarred with obliteration of the normal planes. Dissection can be difficult, so that reference to reliable landmarks is important.
The joint is often stiff, so that during surgical mobilization the nerves may experience a stretch exceeding what they've been used to. Substantial retraction may be necessary to expose the implants. Nerves can be scarred to the surrounding tissues.
One approach, as detailed in this report, is to use intraoperative nerve monitoring (IONM). The article does not present the cost of the personnel, supplies and equipment or the time IONM adds to the procedure.
Another approach, the one we use, is to limit the time during which the shoulder is held in extreme positions (i.e. those substantially different from the preoperative range) and to limit the time during which vigorous retraction is applied. Thus we "give the nerves a drink", returning the arm to a neutral position and relieving pressure on the retractors, every ten minutes or so. Because we do not use inter scalene blocks, we can document the integrity of the brachial plexus immediately after surgery.
It is not clear that surgeons using IONM have lower rates of nerve injury than those who do not.
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