Nerve injuries after reverse total shoulder arthroplasty.

Persistent and Profound Peripheral Nerve Injuries Following Reverse Total Shoulder Arthroplasty

These authors point out that peripheral nerve injuries associated with reverse total shoulder arthroplasty (rTSA) are uncommonly recognized and are often dismissed as neuropraxias, particularly in the setting of perioperative nerve blocks. 

They conducted a retrospective review of 22 patients referred to a nerve injury service who had undergone rTSA and had a concomitant major nerve injury. The average time from surgery to referral to a nerve injury practice was 9.0 months.

 

Injury patterns were variable and involved diffuse pan-plexopathies with severity localized to the posterior and medial cords (11), the upper trunk (5), lateral cord (2) and axillary nerve (4). 

The average postoperative acromiohumeral distance (AHD) was 3.7 cm with an average change of 2.9 cm. 

17 patients were confirmed to have undergone preoperative nerve blocks, which were initially attributed as the etiology of nerve injury. 

18 patients were initially treated with observation: 11 experienced residual debilitating neuropathic pain and/or disability and 7 had substantial improvement. 

Complete axillary nerve injury was seen in 4 patients, of which none resolved spontaneously. Patients with upper trunk or lateral cord injuries spontaneously resolved over the course of their 18.8 month follow-up.  There were 13 cord level injuries of which 11 were medial/posterior cord combined injuries. These were the most serious, especially the medial cord injuries which severely affected hand function via ulnar nerve injury. Of these 11 posterior/medial cord injuries, all had altered ulnar nerve function with loss of intrinsic function, thumb adduction and digital flexion with altered ulnar nerve sensation. Four of the 11 required reconstructive hand surgery to improve their pattern of grasp. All 11 had disabilities consistent with permanent ulnar nerve dysfunction as evidenced by their high Quick DASH scores and need for neuropathic medications.

The authors concluded that these nerve injuries were secondary to traction at the time of arthroplasty, and/or substantial distalization and lateralization of the implants.

Comment: One of the important lessons from this study is that the use of nerve block anesthesia may prevent the surgeon from promptly recognizing a postoperative nerve injury and eliminate the possibility of prompt intervention. A second lesson is that these nerve injuries can be long lasting and disabling in terms of pain and loss of function.  A third lesson is that the average distalization of the humerus in these cases was 2.9 cm. While there is not a comparison group of measurements in reverses without nerve injuries, it seems likely that distalization can result in a traction injury to the nerves of the plexus as explained nicely in this link.

The nerve injuries reported in this article were major. It seems likely that many less severe injuries occur in association with reverse total shoulder arthroplasty and that these injuries might account for compromised deltoid function as well as postoperative pain.

While some surgeons prefer substantial distalization (below left), our technique (see this link) strives for a more anatomic reconstruction with only a small amount of distalizalization and less tension on the nerves (below right). We also avoid brachial plexus blocks on our patients having shoulder arthroplasty so that a complete examination can be documented in the recovery room.

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Here are some videos that are of shoulder interest

Shoulder arthritis - what you need to know (see this link).

How to x-ray the shoulder (see this link).

The ream and run procedure (see this link).

The total shoulder arthroplasty (see this link).

The cuff tear arthropathy arthroplasty (see this link).

The reverse total shoulder arthroplasty (see this link).

The smooth and move procedure for irreparable rotator cuff tears (see this link).

Shoulder rehabilitation exercises (see this link).

 

Nerve injuries are not uncommon after shoulder joint replacement.

 Neurologic complications in primary anatomic and reverse total shoulder arthroplasty: A review

This article presents a comprehensive review of nerve injuries after shoulder arthroplasty. Published rates of nerve injuries range as high as 47% for reverse total shoulders in contrast to 4% with anatomic arthroplasty.

The causes of neurologic injury in shoulder arthroplasty include transection during surgical dissection, compression secondary to retractors, traction, excessive lengthening of the arm, thermal injury from cement, cervical radiculopathy aggravated by positioning at surgery or damage due to interscalene nerve blocks.

The authors review the anatomy of each nerve in relation to its risk for injury at arthroplasty.

 How you can support research in shoulder surgery Click on this link.

Here are some videos that are of shoulder interest

Shoulder arthritis - what you need to know (see this link).

How to x-ray the shoulder (see this link).

The total shoulder arthroplasty (see this link).

The ream and run technique is shown in this link.

The cuff tear arthropathy arthroplasty (see this link).

The reverse total shoulder arthroplasty (see this link).

The smooth and move procedure for irreparable rotator cuff tears (see this link).

Shoulder rehabilitation exercises (see this link).

Revision shoulder arthroplasty - risk of nerve injury

Incidence of Peripheral Nerve Injury in Revision Total Shoulder Arthroplasty: An Intraoperative Nerve Monitoring Study

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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Use the "Search" box to the right to find other topics of interest to you.

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Nerve injuries in shoulder joint replacement

Incidence of clinically evident isolated axillary nerve injury in 869 primary anatomic and reverse total shoulder arthroplasties without routine identification of the axillary nerve

These authors presented their experience in 869 cases of primary anatomic and reverse total shoulder arthroplasties performed without specific attempts to identify the axillary nerve by visualization or the "tug test". 

Six cases (0.7%) were found to have axillary nerve injury recognized within 3 months of arthroplasty.
All of these injuries were neuropraxias and all patients had experienced complete neurologic recovery.

These authors point out that positioning the arm in extension and external rotation (what we call the "danger position") places the nerves running anterior to the humerus - the musculocutaneous and median - under tension. This is especially the case if retractors have been placed anterior to the glenoid, in which position they can increase the tension in these nerves. We avoid holding the arm in this position for more than a minute at the time and then return the arm to a neutral position to "give the nerves a drink".

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We have a new set of shoulder youtubes about the shoulder, check them out at this link.

Be sure to visit "Ream and Run - the state of the art" regarding this radically conservative approach to shoulder arthritis at this link and this link

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How you can support progress in shoulder surgery

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Nerve injuries and the Latarjet procedure

A reduction in the rate of nerve injury after Latarjet: a before-after study after neuromonitoring

These authors reviewed the Latarjet practice of a highly experienced shoulder surgeon, including 38 patients (group 1) who underwent surgery before neuromonitoring study and 48 patients (group 2) who underwent surgery with neuromonitoring. 

In group 1, there were 7 nerve injuries, of which all but 2 recovered. In group 2, there were 3 nerve injuries, of which all but 1 recovered. The overall incidence of nerve injury was 18.4% (group 1) vs. 6.3% (group 2); however, the incidence of permanent motor dysfunction was 5.3% (group 1) vs. 2.1% (group 2).

Thus overall 12% of patients experienced nerve injuries and 3.5% of these did not recover. 

The supra scapular nerve was injured in 2, the axillary in 6, the musculocutaneous (MCN) in 3 and the radial in one. For the nerve injuries that were not permanent, recovery took from 2 to 9 months.

In one patient the EMG demonstrated severe axillary nerve dysfunction and MCN dysfunction. Required open nerve release of his axillary and MCNs MCN resolved, axillary permanent (mild deltoid weakness at 11 months).

In another with EMG confirmation, resection of axillary nerve neuroma was performed with end-to-end motor nerve transfer of radial nerve medial triceps to axillary motor nerve (12.6 months post-op). Moderate recovery with mild deltoid weakness at 12 months after nerve transfer.

In another with EMG confirmation, revision reconstruction was performed with iliac crest bone graft and suprascapular nerve decompression (28 months).

In another with EMG confirmation, there was mild permanent deltoid weakness and numbness (lost to follow-up at 15 months).

The authors identified certain risk factors for nerve injury:

Comment: This report clearly documents the risk of serious nerve injury with the Latarjet procedure, even when it is performed by expert hands. Recovery, if it occurred, required many months. When recovery did not occur,  major reconstructive procedures were considered.

This information is useful in surgical decision making and in preoperative discussions with patients considering this procedure.

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We have a new set of shoulder youtubes about the shoulder, check them out at this link.

Be sure to visit "Ream and Run - the state of the art" regarding this radically conservative approach to shoulder arthritis at this link and this link

Use the "Search" box to the right to find other topics of interest to you.

How you can support progress in shoulder surgery

You may be interested in some of our most visited web pages arthritis, total shoulder, ream and run, reverse total shoulder, CTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'

Avoiding nerve injury in shoulder joint replacement

Preventing brachial plexus injury during shoulder surgery: a real-time cadaveric study

These authors aimed to identify arm positions and maneuvers that may risk causing nerve injury during shoulder joint replacement arthroplasty.

They measured the tensions in the cords of the brachial plexuses of 6 human cadavers while the limb was placed in different arm positions during shoulder arthroplasty.

The four key findings were:

1. Strain in the cords of the brachial plexus sufficient to cause neurologic injury (10%) occurs during shoulder abduction greater than 70°, the combination of 70° shoulder abduction with external rotation, and the combination of shoulder external rotation greater than 60° with extension greater than 50°.

2. During shoulder hemiarthroplasty, tensions in the medial cord of the brachial plexus increased compared with baseline tension during sounder insertion to size the medullary canal, humeral head prosthesis implantation and impaction, and retractor removal and humeral head reduction.

3. Supporting the upper limb from under the elbow reduced medial cord tensions during these surgical steps.

Comment: There is no question that the nerves of the upper extremity experience major and unaccustomed tension during shoulder arthroplasty - tension sufficient to disrupt their function either briefly or for a long time.  This is especially the case for shoulders that have been stiff for a protracted period before surgery. Retractors, extreme positions while removing osteophytes or seeking to optimize glenoid exposure can further increase the tension on the nerves. Medications, such as methotrexate, or diagnoses, such as diabetes, or additional interventions, such a brachial plexus block injections, can increase the risk of nerve injury.

In all cases, but especially in those with increased risk, we seek to minimize the amount of time the shoulder is held in positions other than the neutral position, in which position tension on the nerves is minimized.
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The reader may also be interested in these posts:

Healing through joint replacement

Supporting progress in shoulder surgery

Consultation for those who live a distance away from Seattle.

Click here to see the new Shoulder Arthritis Book.

Click here to see the new Rotator Cuff Book

Information about shoulder exercises can be found at this link.

Use the "Search" box to the right to find other topics of interest to you.

You may be interested in some of our most visited web pages including:shoulder arthritis, total shoulder, ream and run, reverse total shoulder, CTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'

See from which cities our patients come.

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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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The reader may also be interested in these posts:

Healing through joint replacement

Supporting progress in shoulder surgery

Consultation for those who live a distance away from Seattle.

Click here to see the new Shoulder Arthritis Book.

Click here to see the new Rotator Cuff Book

Information about shoulder exercises can be found at this link.

Use the "Search" box to the right to find other topics of interest to you.

You may be interested in some of our most visited web pages including:shoulder arthritis, total shoulder, ream and run, reverse total shoulder, CTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'

See from which cities our patients come.

See the countries from which our readers come on this post.

Nerve injury after shoulder joint replacement

Neurologic complications of shoulder joint replacement

This author conducted a retrospective review of 211 shoulder arthroplasties in 202 patients. All patients received interscalene regional anesthesia. In 56 patients, this involved the use of a continuous ambulatory interscalene catheter; in the remainder, a singleshot nerve block was administered.

44 patients were identified as having sustained a nerve complication. Reverse shoulder arthroplasty was associated with the highest number of nerve complications. The median nerve (25 patients) and musculocutaneous nerve (8 patients) were most commonly involved. 

Most nerve complications were transient and resolved within 6 months. 

Comment: It is not clear how each patient was examined for a nerve injury or when the examination was carried out: "In all patients, a comprehensive analysis of all postoperative neurologic complications had been undertaken, including onset, duration, investigation, treatment, and resolution of neurologic symptoms. The diagnosis was established at the time by subjective complaints of the patient and careful clinical assessment of the upper extremity. " "In many of these cases, the patient was not aware of biceps weakness in the postoperative period and tended to complain only of altered sensation in the distribution of the lateral antebrachial cutaneous nerve. " Thus, it is possible that the rate of neurologic complications may be substantially higher than reported here.

This report highlights the difficulty in establishing the etiology of a nerve deficit after surgery: related to the interscalene block, to carpal tunnel syndrome, to compression of the ulnar were at the elbow, to cervical radiculopathy, or to retraction or positioning at the time of shoulder arthroplasty.  This differential diagnosis may be quite difficult to sort out.

To minimize the risk of neurologic problems, we are careful in positioning of the neck, avoiding traction on the arm, limiting the number of minutes the coracoid muscles are retracted during glenoid exposure, and limiting the number of minutes during which the arm is held in extension and external rotation for humeral preparation. We also avoid any form of brachial plexus block. 

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The reader may also be interested in these posts:

Healing through joint replacement

Supporting progress in shoulder surgery

Consultation for those who live a distance away from Seattle.

Click here to see the new Shoulder Arthritis Book.

Click here to see the new Rotator Cuff Book

Information about shoulder exercises can be found at this link.

Use the "Search" box to the right to find other topics of interest to you.

You may be interested in some of our most visited web pages including:shoulder arthritis, total shoulder, ream and run, reverse total shoulder, CTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'

See from which cities our patients come.

See the countries from which our readers come on this post.

Nerve injury in shoulder arthroplasty

The risk of nerve injury during anatomical and reverse total shoulder arthroplasty: an intraoperative neuromonitoring study

These authors reviewed 36 consecutive patients who underwent reverse (RSA) (n = 12) or anatomic (TSA) (n = 24) shoulder arthroplasties with intraoperative neuromonitoring.

They found nearly 5 times as many postreduction nerve alerts per patient in the RSA cohort compared with the TSA cohort (2.17 vs. 0.46). 

Most of the nerve alerts for both groups in this study occurred during humeral (43% for TSA vs. 23% for RSA) and glenoid preparation (29% for TSA vs. 34% for RSA) while the arm is in external rotation, accounting for 65% of all nerve alerts in both groups.

There were 17 unresolved nerve alerts postoperatively, with only 2 clinically detectable nerve injuries, which fully resolved by 6 months postoperatively. 

A preoperative decrease in active forward flexion and the diagnosis of rotator cuff arthropathy were independent predictors of intraoperative nerve alerts.

The authors attributed the higher incidence of intraoperative nerve alerts in the post reduction stage in RSA  to the resultant arm lengthening which they state is "inherent in the Grammont-design RSA".

Comment: In their discussion the authors provide evidence that traction nerve injury is related to strain (6 to 12%) and the duration of application of the strain. They suggest that external rotation is the position placing greatest strain on the brachial plexus.  We agree that the 'danger position' is external rotation and extension. For this reason we limit the time the arm is in this position to under one minute at the time. 

Their findings also support the direct relationship between arm lengthening after reduction and neurologic injury. There is evidence that lengthening of 2 cm increases the risk of plexus injury. They raise the question of whether a non-Grammont design that lateralizes the glenosphere (or the humerus) has less brachial stretch and fewer nerve injuries.  We agree and for that reason we use a RSA technique that avoids excessive lengthening.

They observe that nerve injury may present without obvious sensory or motor dysfunction but as pain. We have seen instances of palm pain after shoulder arthroplasty that cannot be otherwise explained.

With respect to factors that may predispose to nerve injury, preoperative stiffness and methotrexate therapy can be added to the list.

Interested readers are directed to this related post:

Shoulder arthroplasty can be/is hard on the nerves around the shoulder

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Consultation for those who live a distance away from Seattle.

Click here to see the new Shoulder Arthritis Book.

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Information about shoulder exercises can be found at this link.

Use the "Search" box to the right to find other topics of interest to you.

You may be interested in some of our most visited web pages including:shoulder arthritis, total shoulder, ream and run, reverse total shoulder, CTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'

See from which cities our patients come.

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Shoulder arthroplasty can be/is hard on the nerves around the shoulder

Nerve stress during reverse total shoulder arthroplasty: a cadaveric study

These authors point out that neurologic lesions are relatively common after total shoulder arthroplasty.  Most are apparently related to traction applied to the nerves when the arm is placed in unaccustomed positions during the procedure. 

They used a tensiometer to measure tension in the individual nerves of 10 shoulders of 5 cadavers while the arm was placed in different positions during the surgical steps of reverse total shoulder arthroplasty (RTSA)

Tensiometer

Internal rotation increased stress on the radial and axillary nerves.

External rotation increased stress on the musculocutaneous, median, and ulnar nerves. 

Extension was correlated with increase in stress on all nerves. 

Abduction was correlated with increase in stress for the radial nerve. 

They identified 2 high-risk steps during RTSA: 

(1) humeral exposure, particularly when the shoulder was in a position of more extension (Step 3 below), and 

(2)glenoid exposure (Step 4 below)

The thickness of polyethylene humeral cups used was associated with increased nerve stress in all but the ulnar nerve.

Comment: This is an important study, indicating that shoulder arthroplasty (both anatomic and reverse) requires putting the arm in unphysiologic positions that apply tension to the nerves of the brachial plexus. The risk to the nerves is heightened in shoulders with preoperative stiffness and prior surgery because the nerves may be adherent to surrounding tissues. Prior studies have shown that certain medications, such as methotrexate, can raise the risk even more. Finally, brachial plexus block anesthesia can increase the risk even more.

Rather than using intraoperative nerve monitoring, we assume that the nerves are always at risk in these positions (which we refer to as the 'danger positions'). We minimize the time in these positions, returning the arm to a neutral positions to 'give the nerves a drink'.

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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Shoulder arthroplasty and nerve monitoring

Intraoperative nerve monitoring during total shoulder arthroplasty surgery

The authors quote a published incidence of postoperative neurological deficit after shoulder arthroplasty between 1% and 16%. They conducted a prospective study of nerve conduction in 21 patients who underwent primary or revision total shoulders using intraoperative sensory evoked potentials.

Seven (33%) patients had a signal change. The only significant risk factor identified for signal change was male sex.The median nerve was the most affected nerve in the operated arm. All but one signal change returned to normal before completion of the operation and no patient had a persisting postoperative clinical neurological deficit.

Changes in the neurophysiological signal could not be attributed to a particular position of the limb, stage during surgery or physiological parameter (e.g. blood pressure).

Comment: It is our experience that the median and the musculocutaneous nerves are at greatest risk for traction injury and that the position of greatest risk is when the arm is externally rotated and extended (positions it which these nerves are wrapped around the humerus). The injury most commonly presents as dysethesia in the hand (median nerve) or lateral forearm (musculocutaneous nerve) or as weakness of the biceps. Traction injuries are best avoided by minimizing the amount of time the arm is held in this 'danger position'.
Nerves are at increased risk if (1) the arm lacks external rotation preoperatively and (2) if the patient is on Methotrexate.

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Consultation for those who live a distance away from Seattle.

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