The Journal of Bone & Joint Surgery

The Journal of Bone & Joint Surgery, Volume 93, Issue 14

Scientific Articles | July 20, 2011

Prevalence of Neurologic Lesions After Total Shoulder Arthroplasty

A. Lädermann, MD¹; A. Lübbeke, MD, DSc¹; B. Mélis, MD²; R. Stern, MD¹; P. Christofilopoulos, MD¹; G. Bacle, MD²; G. Walch, MD²

¹ Division of Orthopaedics and Trauma Surgery, Department of Surgery, Geneva University Hospitals, Rue Gabrielle-Perret-Gentil 4, CH-1211 Geneva 14, Switzerland. E-mail address for A. Lädermann: alexandre.laedermann@hcuge.ch. E-mail address for A. Lübbeke: Anne.LubbekeWolff@hcuge.ch. E-mail address for R. Stern: Richard.Stern@hcuge.ch. E-mail address for P. Christofilopoulos: Panayiotis.Christofilopoulos@hcuge.ch
² Department of Orthopaedic Surgery, Centre Orthopédique Santy, 24 Avenue Paul Santy, 69008 Lyon, France. E-mail address: brbmelis@gmail.com. E-mail address for G. Bacle: bacle.guillaume@wanadoo.fr. E-mail address G. Walch: walch.gilles@wanadoo.fr

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Investigation performed at the Division of Orthopaedics and Trauma Surgery, Department of Surgery, Geneva University Hospitals, Geneva, Switzerland, and the Department of Orthopaedic Surgery, Centre Orthopédique Santy, Lyon, France

J Bone Joint Surg Am, 2011 Jul 20;93(14):1288-1293. doi: 10.2106/JBJS.J.00369

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Abstract

Background:

Clinically evident neurologic injury of the involved limb after total shoulder arthroplasty is not uncommon, but the subclinical prevalence is unknown. The purposes of this prospective study were to determine the subclinical prevalence of neurologic lesions after reverse shoulder arthroplasty and anatomic shoulder arthroplasty, and to evaluate the correlation of neurologic injury to postoperative lengthening of the arm.

Methods:

All patients undergoing either a reverse or an anatomic shoulder arthroplasty were included during the period studied. This study focused on the clinical, radiographic, and preoperative and postoperative electromyographic evaluation, with measurement of arm lengthening in patients who had reverse shoulder arthroplasty according to a previously validated protocol.

Results:

Between November 2007 and February 2009, forty-one patients (forty-two shoulders) underwent reverse shoulder arthroplasty (nineteen shoulders) or anatomic primary shoulder arthroplasty (twenty-three shoulders). The two groups were similar with respect to sex distribution, preoperative neurologic lesions, and Constant score. Electromyography performed at a mean of 3.6 weeks postoperatively in the reverse shoulder arthroplasty group showed subclinical electromyographic changes in nine shoulders, involving mainly the axillary nerve; eight resolved in less than six months. In the anatomic shoulder arthroplasty group, a brachial plexus lesion was evident in one shoulder. The prevalence of acute postoperative nerve injury was significantly more frequent in the reverse shoulder arthroplasty group (p = 0.002), with a 10.9 times higher risk (95% confidence interval, 1.5 to 78.5). Mean lengthening (and standard deviation) of the arm after reverse shoulder arthroplasty was 2.7 ± 1.8 cm (range, 0 to 5.9 cm) compared with the normal, contralateral side.

Conclusions:

The occurrence of peripheral neurologic lesions following reverse shoulder arthroplasty is relatively common, but usually transient. Arm lengthening with a reverse shoulder arthroplasty may be responsible for these nerve injuries.

Figures in this Article

Introduction

Introduction | Materials and Methods | Results | Discussion

The goal of total shoulder arthroplasty is to relieve pain and improve function in patients with glenohumeral joint disease. However, both a reverse and an anatomic shoulder arthroplasty are associated with several different complications, including postoperative hematoma formation, glenohumeral instability, periprosthetic fracture, rotator cuff tears, infection, deltoid muscle dysfunction, prosthetic loosening, and nerve injury. Nerve injury makes up a small percentage of these complications¹. The causes of nerve injury are multifactorial, including direct nerve damage during surgical dissection, compression secondary to retractors or postoperative hematoma, excessive mobilization of the limb, vascular injury, humeral shaft fractures, cement extrusion, and possibly interscalene block^2-4. All of these factors are similar whether a reverse or an anatomic shoulder replacement is implanted.

The prevalence of clinically evident neural impairment of the involved limb has been reported to be 2% in patients after reverse shoulder arthroplasty⁵ and 1% to 4.3%^1,6-8 following anatomic shoulder arthroplasty. Nagda et al. documented episodes of nerve disturbance in up to 57% of patients undergoing intraoperative nerve monitoring during anatomic shoulder arthroplasty and hemiarthroplasty³. No study, to our knowledge, has prospectively investigated the postoperative prevalence of neural impairment in patients undergoing reverse shoulder arthroplasty.

Although reverse shoulder arthroplasty is a powerful tool in reconstructive surgery, it may be associated with a higher prevalence of nerve complications because of its nonanatomic design. Moving the center of rotation more medially and distally is necessary to provide space for unrestricted range of motion of the proximal part of the humerus and to retension the deltoid muscle. This creates a consequent lengthening of the involved arm^5,9 and elongation of the brachial plexus¹⁰. Our hypothesis was that a higher prevalence of nerve injury occurred during reverse shoulder arthroplasty compared with anatomic shoulder arthroplasty, and the purpose of this prospective study was to assess the prevalence of neurologic lesions detected with electromyography after both of these types of total shoulder arthroplasty.

Materials and Methods

Introduction | Materials and Methods | Results | Discussion

Patient Selection

Between November 2007 and February 2009, all patients who had a primary total shoulder arthroplasty performed by the senior author (G.W.) were considered potentially eligible for inclusion in this prospective study. We excluded patients with (1) incomplete documentation, (2) follow-up of less than ten months, (3) any comorbidity that might result in a neuropathy (such as diabetes mellitus or alcoholism), and (4) an abnormality of the ipsilateral or contralateral side that could influence the measurement of humeral length and side-to-side differences in the reverse arthroplasty group. Eighteen patients (nineteen shoulders) who had a reverse shoulder arthroplasty and twenty-three patients (twenty-three shoulders) who had an anatomic shoulder arthroplasty met the entry criteria and were enrolled in the study. The study protocol was approved by the hospital ethics committee, and all patients gave informed written consent.

Surgical Technique

The Aequalis shoulder prosthesis system (Tornier, Montbonnot, France) was used for both reverse and anatomic shoulder arthroplasty. Insertion of both implant designs was through a standard deltopectoral approach^11,12. Other than the arthroplasty components, the only differences between the two procedures were the section of the coracoacromial ligament during reverse shoulder arthroplasty, the level of the cut of the humeral head, and the method of glenohumeral reduction. All humeral stems were cemented following insertion of a cement restrictor plug. Postoperative immobilization and rehabilitation programs were standardized according to validated protocols¹³.

Study Variables

The outcome of interest was the prevalence of neurologic lesions following reverse and anatomic shoulder arthroplasty confirmed by electromyography performed three weeks after the operation. Furthermore, the prevalence of neurologic lesions in the reverse shoulder arthroplasty group was evaluated in relationship to postoperative arm lengthening and the presence or absence of preexisting neurologic lesions.

The following baseline characteristics were assessed: age, sex, diagnosis (primary osteoarthritis or cuff tear arthropathy compared with secondary osteoarthritis), previous surgery, preoperative neurologic lesion, shoulder side, and limb dominance.

Clinical Evaluation

Patient demographics collected at the initial presentation included any history of diabetes mellitus, alcoholism, neurotoxic medication, previous trauma to the upper limbs, cervical spine disease, nerve entrapment syndrome, or pain in the upper limbs. Although we relied primarily on electromyographic examination to determine neurologic lesions¹⁴, careful clinical assessment was performed and included range of motion, muscle strength, sensation, and the Constant score in both upper extremities. We defined subclinical changes as postoperative electromyographic changes without obvious neurologic impairment on postoperative clinical assessment. Usual clinical postoperative findings such as a decrease in active range of motion or pain were not considered potential neurologic lesions. Follow-up evaluations were at three weeks, six weeks, three months, six months, and ten months and up to eighteen months for patients with persistent neurologic symptoms. The Constant score was recorded at the latest follow-up examination. The medical records, operative reports, and radiographs for each patient were analyzed by an orthopaedic surgeon (A. Lädermann) who had not been involved in the surgical procedures.

Electromyographic Evaluation

Each patient included in the study underwent electromyographic evaluation one week prior to surgery and was scheduled for a second electromyographic evaluation three to four weeks postoperatively. Only two senior physicians, blinded to the type of surgery, performed the preoperative and postoperative electromyographic examinations, using the same method and protocol, for each specific patient. We allowed each patient to choose one of the two physicians. In patients with neurologic lesions, control electromyographic evaluation was performed every six months. The parameters that were used for the whole segment included (1) motor and sensory nerve examinations and nerve conduction velocity and (2) standard needle electromyographic examination¹⁵. This included a search for abnormal spontaneous activity at rest (positive sharp waves, fibrillation potentials, complex repetitive discharge, and fasciculations), qualitative evaluation of motor unit action potentials, and recording of recruitment pattern at effort. The examinations were performed at different sites to determine the level of the lesion. We defined an acute lesion as a new lesion, not a worsening of a preexisting lesion.

Radiographic Evaluation

A standard set of radiographs, consisting of true anteroposterior, lateral scapular, and axillary views, was made preoperatively and postoperatively. Additionally, we included true anteroposterior scaled radiographs of both arms according to a previously standardized and validated protocol to measure the lengthening of the arm in the patients who underwent reverse shoulder arthroplasty⁹. The radiographs were made with the arm in neutral rotation with the patient erect. The humeri were positioned flat against the cassette, and the x-ray beam was directed toward the middle third. A centimeter marker was placed on the skin adjacent to the lateral aspect of the humerus to correct for magnification. Measurements were made to determine relative arm length with use of points along the humerus as well as the acromion. No measurement was performed in the anatomic shoulder arthroplasty group because, by definition, this type of prosthesis restores anatomy and does not lead to arm lengthening. The radiographs were examined for component malposition, dislocation or subluxation, cement extrusion, or periprosthetic fracture.

Statistical Analysis

In order to estimate the association between exposure and outcome of interest, we first calculated a relative risk and its 95% confidence interval (CI). Second, we used logistic regression analysis to obtain a crude odds ratio and an age-adjusted odds ratio with 95% confidence intervals.

The post hoc power calculation revealed that the power to detect a difference in subclinical electromyographic changes in the eighteen patients (nineteen shoulders) who had a reverse shoulder arthroplasty compared with the twenty-three who had anatomic shoulder arthroplasty was 92% (alpha = 0.05).

Source of Funding

No funding was received for this study.

Results

Introduction | Materials and Methods | Results | Discussion

During the study period, thirty-four reverse and forty-three anatomic shoulder arthroplasties were performed. Ten patients were excluded from the study because of diabetes mellitus (seven patients), alcoholism (one patient), incomplete documentation (one), and fracture of the contralateral diaphysis (one). Fifteen patients declined to participate, eight lived too far away to return for a follow-up electromyographic evaluation, and three patients were excluded because they declined a postoperative electromyographic examination. Thus, there were forty-one patients (forty-two prostheses) for the final analysis at a mean follow-up (and standard deviation) of 12.2 ± 1 months (range, ten to eighteen months). The reverse shoulder arthroplasty group consisted of eighteen patients (nineteen shoulders). There were four men and fourteen women (one had a bilateral arthroplasty), with a mean age of 75.4 ± 6.6 years (range, fifty-three to eighty-three years). The anatomic shoulder arthroplasty group consisted of twenty-three patients (twenty-three shoulders), including seven men and sixteen women, with a mean age of 70.8 ± 7.2 years (range, sixty to eighty years). The indications for primary reverse shoulder arthroplasty were rotator cuff arthropathy in fourteen shoulders, posttraumatic arthritis or fracture malunion in four, and chronic anterior glenohumeral dislocation in one shoulder. Five patients had previous shoulder surgery, including open reduction and internal fixation of a fracture (four patients) and repair of a rotator cuff tear (one patient). The indications for anatomic shoulder arthroplasty were primary osteoarthritis in twenty-two patients and posttraumatic arthritis in one. Patients in both groups underwent preoperative electromyographic evaluation at a mean of 8 ± 5 days (range, one to twenty days) prior to surgery. A comparison of the baseline characteristics (Table I) demonstrated that patients in the reverse shoulder arthroplasty group were, on the average, five years older and had a higher rate of secondary osteoarthritis (four of nineteen shoulders) compared with the anatomic shoulder arthroplasty group (one of twenty-three shoulders). The two groups were otherwise similar with respect to sex distribution, side involved, and the preoperative Constant score. The prevalence of preoperative neurologic abnormalities on the basis of the electromyographic findings was also similar in the groups. The postoperative electromyographic evaluation for both groups was performed at a mean of 3.6 ± 0.7 weeks (range, three to seven weeks). There was no significant difference between the groups with regard to the time to postoperative electromyography (3.5 and 3.7 weeks for the reverse and anatomic shoulder arthroplasty groups, respectively).

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TABLE I Baseline Characteristics According to the Two Types of Shoulder Prosthesis

	Reverse Shoulder Arthroplasty (N = 19)	Anatomic Shoulder Arthroplasty (N = 23)
Sex*(no. of shoulders)
Female†	15 (79)	16 (70)
Male	4 (21)	7 (30)
Age‡(yr)	75.4 ± 6.6	70.8 ± 7.2
Side*
Right	12 (63)	15 (65)
Left	7 (37)	8 (35)
Dominant shoulder*	12 (63)	14 (61)
Diagnosis*
Primary osteoarthritis or rotator cuff arthropathy	15 (79)	22 (96)
Secondary osteoarthritis	4 (21)	1 (4)
Preop. neurologic lesion*
Yes	9 (47)	13 (57)
No	10 (53)	10 (43)
Preop. Constant score‡(points)	29.2 ± 11.1	33.9 ± 15.1

*The values are given as the number, with the percentage in parentheses.
†One woman in the reverse shoulder arthroplasty group had bilateral involvement.
‡The values are given as the mean and the standard deviation.

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TABLE I Baseline Characteristics According to the Two Types of Shoulder Prosthesis

	Reverse Shoulder Arthroplasty (N = 19)	Anatomic Shoulder Arthroplasty (N = 23)
Sex*(no. of shoulders)
Female†	15 (79)	16 (70)
Male	4 (21)	7 (30)
Age‡(yr)	75.4 ± 6.6	70.8 ± 7.2
Side*
Right	12 (63)	15 (65)
Left	7 (37)	8 (35)
Dominant shoulder*	12 (63)	14 (61)
Diagnosis*
Primary osteoarthritis or rotator cuff arthropathy	15 (79)	22 (96)
Secondary osteoarthritis	4 (21)	1 (4)
Preop. neurologic lesion*
Yes	9 (47)	13 (57)
No	10 (53)	10 (43)
Preop. Constant score‡(points)	29.2 ± 11.1	33.9 ± 15.1

Reverse Shoulder Arthroplasty Group

Preoperatively, nine of nineteen shoulders had twelve neurologic lesions noted on electromyography (Table II). Postoperatively, electromyography revealed acute lesions involving mainly the axillary nerve in nine shoulders. The lesions in eight of the nine shoulders had completely resolved by the six-month follow-up electromyographic examination. In three of the nineteen shoulders, electromyography revealed postoperative worsening of preexisting asymptomatic neurologic abnormalities. This included two shoulders in patients with carpal tunnel syndrome and one shoulder in a patient with cubital tunnel syndrome. None of these three patients developed clinical symptoms postoperatively. No postoperative neurologic lesions were detected by electromyography in the five shoulders that had previous surgery.

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TABLE II Preoperative and Postoperative Electromyographic Findings

		Postoperative Findings
	Preoperative Findings	Worsening of Preexisting Lesion	Acute Lesion (Axonotmesis)	Recovery (Latest Follow-up)
Reverse shoulder arthroplasty group
Case
1	Carpal tunnel syndrome	No	Axillary nerve	Complete (5 mo)
2	Cervical radiculopathy	No	Axillary and suprascapular nerves	Complete (6 mo)
3	–	No	Plexus	Partial (18 mo)
4	Cubital tunnel syndrome	No	Musculocutaneus nerve	Complete (6 mo)
5	Carpal tunnel syndrome	No	–
6	Cervical radiculopathy	No	–
7	Carpal tunnel syndrome	Yes	Suprascapular nerve	Complete (6 mo)
8	Carpal tunnel syndrome, suprascapular nerve	Yes	Axillary and ulnar nerves	Complete (6 mo)
9	Cubital tunnel syndrome, suprascapular nerve	Yes	Axillary and musculocutaneus nerves	Complete (6 mo)
10	Carpal and cubital tunnel syndrome	No	Axillary nerve	Complete (6 mo)
11	–	No	Axillary nerve	Complete (6 mo)
Anatomic shoulder arthroplasty group
1	Carpal tunnel syndrome	No
2	Cervical radiculopathy, Carpal tunnel syndrome	No
3	Carpal tunnel syndrome	No
4	Cervical radiculopathy	No
5	Carpal tunnel syndrome	No
6	Carpal tunnel syndrome	No
7	Cervical radiculopathy	No	Plexus	Partial (18 mo)
8	Cubital tunnel syndrome	No
9	Carpal tunnel syndrome	No
10	Cervical radiculopathy	No
11	Carpal tunnel syndrome	No
12	Cubital tunnel syndrome	No
13	Cervical radiculopathy	No

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TABLE II Preoperative and Postoperative Electromyographic Findings

		Postoperative Findings
	Preoperative Findings	Worsening of Preexisting Lesion	Acute Lesion (Axonotmesis)	Recovery (Latest Follow-up)
Reverse shoulder arthroplasty group
Case
1	Carpal tunnel syndrome	No	Axillary nerve	Complete (5 mo)
2	Cervical radiculopathy	No	Axillary and suprascapular nerves	Complete (6 mo)
3	–	No	Plexus	Partial (18 mo)
4	Cubital tunnel syndrome	No	Musculocutaneus nerve	Complete (6 mo)
5	Carpal tunnel syndrome	No	–
6	Cervical radiculopathy	No	–
7	Carpal tunnel syndrome	Yes	Suprascapular nerve	Complete (6 mo)
8	Carpal tunnel syndrome, suprascapular nerve	Yes	Axillary and ulnar nerves	Complete (6 mo)
9	Cubital tunnel syndrome, suprascapular nerve	Yes	Axillary and musculocutaneus nerves	Complete (6 mo)
10	Carpal and cubital tunnel syndrome	No	Axillary nerve	Complete (6 mo)
11	–	No	Axillary nerve	Complete (6 mo)
Anatomic shoulder arthroplasty group
1	Carpal tunnel syndrome	No
2	Cervical radiculopathy, Carpal tunnel syndrome	No
3	Carpal tunnel syndrome	No
4	Cervical radiculopathy	No
5	Carpal tunnel syndrome	No
6	Carpal tunnel syndrome	No
7	Cervical radiculopathy	No	Plexus	Partial (18 mo)
8	Cubital tunnel syndrome	No
9	Carpal tunnel syndrome	No
10	Cervical radiculopathy	No
11	Carpal tunnel syndrome	No
12	Cubital tunnel syndrome	No
13	Cervical radiculopathy	No

Anatomic Shoulder Arthroplasty Group

Preoperatively, thirteen (57%) of twenty-three patients had fourteen neurologic lesions detected by electromyography (Table II). One patient with a preoperative electromyographic examination demonstrating a cervical radiculopathy developed an acute postoperative brachial plexus lesion. In this patient, an axillary vein injury during subscapularis release necessitated an osteotomy of the coracoid for vascular repair. The patient developed a large postoperative hematoma thought to be responsible for the brachial plexus lesion. Electromyography at three weeks revealed a motor deficit in the axillary, ulnar, median, and radial nerves; absent sensory potentials; and abnormal spontaneous activity at rest with fibrillation potentials. At twelve months postoperatively, electromyography revealed incomplete recovery. Motor conduction velocity was improved for all nerves, while sensory conduction velocities were normal for the median and the radial nerves but remained abnormal for the ulnar nerve. Abnormal spontaneous activity at rest was observed in muscles innervated by roots C5 to T1.

Nine of nineteen shoulders in the reverse shoulder arthroplasty group and one of twenty-three shoulders in the anatomic shoulder arthroplasty group presented with acute postoperative neurologic lesions confirmed by electromyography. The prevalence of an acute postoperative nerve injury was significantly higher in the reverse shoulder arthroplasty group compared with the anatomic shoulder arthroplasty group (p = 0.002), with a relative risk of 10.9 (95% CI, 1.5 to 78.5) and an unadjusted odds ratio of 19.8 (95% CI, 2.2 to 178.2). After adjustment for age, the odds ratio was 17.1 (95% CI, 1.8 to 161.0). A subgroup analysis including only the twenty shoulders without a preoperative neurologic lesion (ten in each group) revealed that two such shoulders in the reverse shoulder arthroplasty group and none in the anatomic shoulder arthroplasty group developed a postoperative neurologic lesion. Among the twenty-two shoulders with a preexisting neurologic lesion (nine in the reverse shoulder arthroplasty group and thirteen in the anatomic shoulder arthroplasty group), seven of the nine shoulders in the reverse shoulder arthroplasty group and one of the thirteen in the anatomic shoulder arthroplasty group presented with subclinical electromyographic changes postoperatively.

The mean postoperative lengthening of the arm after reverse shoulder arthroplasty was 2.7 ± 1.8 cm (range, 0 to 5.9 cm) compared with the preoperative measurement on the ipsilateral side and 2.4 ± 2.1 cm (range, −0.5 to 5.8 cm) compared with that on the normal, contralateral side. Among the ten shoulders that did not have preexisting neurologic lesions in the reverse shoulder arthroplasty group, the mean arm lengthening was 4.2 cm in the three with subclinical electromyographic changes postoperatively compared with 2.6 cm in the seven that did not develop the outcome of interest. Among the nine shoulders with preexisting neurologic lesions in the reverse shoulder arthroplasty group, the mean arm lengthening was 1.9 cm in the six shoulders that had subclinical electromyographic changes postoperatively compared with 2.9 cm in the three that did not develop these electromyographic changes.

There was no radiographic evidence of dislocation, cement extrusion, periprosthetic fractures, or other factors that could predispose to neurologic damage in either group.

The mean Constant score at the time of the latest follow-up was 68.7 ± 7.6 points (range, 50.5 to 81.5 points) in the reverse shoulder arthroplasty group and 71.1 ± 10.2 points (range, 45.5 to 88.5 points) in the anatomic shoulder arthroplasty group.

Discussion

Introduction | Materials and Methods | Results | Discussion

The advent of reverse shoulder arthroplasty represents a new era in shoulder surgery. The procedure may allow for improved function in patients who were previously not amenable to any other treatment, but the complication rate is higher than that following conventional total shoulder arthroplasty. To our knowledge, there is only one prospective study in the literature concerning neurologic lesions following shoulder hemiarthroplasty and anatomic shoulder arthroplasty³. It demonstrated that the prevalence of intraoperative neurologic lesions during shoulder arthroplasty was related to arm and retractor position. Since only half of those patients underwent postoperative electromyography, the authors could not evaluate the prevalence of lesions related to hematoma, postoperative regional nerve block for pain control, and a deterioration of a previous nerve injury. Recent reports have demonstrated an increased prevalence of clinically evident peripheral nerve lesions with muscle weakness in the involved limb following reverse shoulder arthroplasty. In a study of 202 reverse shoulder arthroplasties, Bacle et al. reported that, solely on the basis of clinical evaluation, eight patients (4%) had postoperative neurologic symptoms and two (1%) remained symptomatic at the time of the two-year follow-up¹⁶. The prevalence of subclinical neurologic abnormalities following reverse shoulder arthroplasty as detected by electrodiagnostic studies may indicate an even greater occurrence of neurologic injury, although it has not as yet been reported. Injuries to the axillary, musculocutaneous, radial, and ulnar nerves have been previously described as complications of shoulder arthroplasty^1,17,18. These lesions represent a broad spectrum from neurapraxia to neurotmesis, and they may be a potentially serious complication. Reported symptoms vary from transitory pain to persistent dysesthesia and even include catastrophic loss of shoulder function, particularly in patients with lesions of the axillary nerve.

The purposes of this investigation were to assess the prevalence of subclinical neurologic lesions following reverse shoulder arthroplasty and to compare it with the prevalence after anatomic shoulder arthroplasty. Our study demonstrated a substantially higher prevalence of acute postoperative subclinical neurologic lesions in the reverse shoulder arthroplasty group (nine of nineteen shoulders) compared with that in the anatomic shoulder arthroplasty group (one of twenty-three shoulders). If one also takes into account subclinical worsening of preoperative lesions, most (twelve) of the nineteen shoulders undergoing reverse shoulder arthroplasty had postoperative deterioration. The proposed mechanisms for nerve injury during or after shoulder arthroplasty include surgical dissection, compression secondary to retractors or hematoma, vascular injury, intraoperative mobilization of the upper limb, and interscalene block anesthesia. All of these mechanisms are similar for both reverse and anatomic shoulder arthroplasties, and the only relevant differences between the two groups are lengthening of the arm and the preoperative indication for shoulder arthroplasty. For this reason, we included no revision shoulder arthroplasty, as this generally implies a different anatomic situation and difficult surgical approach. However, in five shoulders in the reverse shoulder arthroplasty group that had previous surgery (four of the five had open reduction and internal fixation) with the presence of scar tissue, there were no postoperative neurologic lesions. We hypothesized that lengthening of the arm during reverse shoulder arthroplasty, because of its nonanatomic design and/or maneuver of glenohumeral reduction, might be a factor responsible for the increased prevalence of neurologic injury. Conversely, arm lengthening and deltoid retensioning is crucial in reverse shoulder arthroplasty to achieve good stability and function^9,19. In shoulders with an anticipated risk of postoperative neurologic impairment because of excessive lengthening, the use of larger glenospheres or superolateral approaches could be an option in order to minimize lengthening without increasing the risk of instability.

We are unable to propose a lengthening threshold, compared with the preoperative measurement, beyond which the frequency of nerve damage is likely to increase because of the small sample size of our study. Effectively, it is crucial not to consider the absolute value of lengthening in centimeters but rather as a ratio that takes into consideration the total length of the upper limb of the patient, thus representing a percentage of lengthening. In a study utilizing three-dimensional computer reconstruction of the brachial plexus, Van Hoof et al.¹⁰ demonstrated that some segments of the brachial plexus sustain a large strain, as much as 19% of lengthening of the nerve, after reverse shoulder arthroplasty. Nerve damage is related to the amount of strain, and a critical level of 8% of lengthening of the nerve is known to initiate the arrest of blood flow in the sciatic nerve of rabbits and rats. A complete arrest of blood flow occurs at approximately 15% of strain^20,21. This suggests the possibility that arm lengthening with a reverse shoulder arthroplasty predisposes the entire brachial plexus to nerve injury.

Another troublesome postoperative effect is that preexisting neurologic impairment, including entrapment neuropathy and cervical radiculopathy, was frequently aggravated in the same proportion in both groups. We believe the cause is multifactorial. Patients should be informed that preoperative neurologic symptoms could become worse following either type of total shoulder arthroplasty.

Strengths and Limitations

To our knowledge, this is the first prospective comparative study evaluating the prevalence of neurologic lesions after reverse and anatomic shoulder arthroplasty. Electromyography was performed preoperatively and postoperatively in all patients. However, the sample size and the number of patients who were discovered to have neurologic lesions were small. This has limited our ability to investigate the influence of arm lengthening on the development of postoperative subclinical electromyographic changes in subgroup analyses with adequate sample sizes.

To recognize significant differences, thirty patients in each group would be necessary (a power of 80% and an alpha level of 0.05). Furthermore, this is a limiting factor in determining the exact amount of arm lengthening that might result in nerve damage, as well as with respect to the influence of preexisting neurologic lesions in this context.

In conclusion, the occurrence of peripheral nerve lesions determined by electromyographic analysis following reverse shoulder arthroplasty is common, but patients usually recover. While arm lengthening is necessary for retensioning of the deltoid muscle to achieve good stability and mobility, neurologic lesions may result. Additional prospective studies with a larger sample size are necessary to further elucidate this relationship and to determine the amount of lengthening that can be achieved without development of these neurologic complications.

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Disclosure: None of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of any aspect of this work. One or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. No author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by the authors of this work are available with the online version of this article at jbjs.org.

Topics

shoulder replacement arthroplasty ; nerve injury ; neurologic deficits ; reverse shoulder arthroplasty

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A. Lädermann, A. Lübbeke, B. Mélis, R. Stern, P. Christofilopoulos, G. Bacle, G. Walch; Prevalence of Neurologic Lesions After Total Shoulder Arthroplasty. The Journal of Bone & Joint Surgery. 2011 Jul;93(14):1288-1293.

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