Diagnosing suprascapular neuropathy in patients with shoulder dysfunction: a report of 5 cases.

Suprascapular neuropathy (SSN) may be overlooked of mistaken for other conditions such as subacromial impingement syndrome (SAIS), rotator cuff injury, cervical radiculopathy, or brachial plexopathy. (1-6) The signs and symptoms of SSN include shoulder weakness, atrophy, and diffuse aching or burning pain at the shoulder, which often includes the posterolateral aspect of the shoulder in the region of the scapula. (1-5,7) However, painless cases, which involved denervation of the infraspinatus muscle only, also have been reported. (8)

Although SSN is uncommon, it should be considered in the differential diagnosis of patients with shoulder pain and weakness. (1-5,7) Suprascapular neuropathy has been reported in 10 patients (0.4%) in a series of 2,520 patients with shoulder pain, (6) but some authors (7) have speculated that this condition is so frequently misdiagnosed that it is probably the cause in 1% to 2% of patients with shoulder pain. Of 10 patients with SSN reported by Post and Mayer, (6) 8 patients were initially misdiagnosed, leading to inappropriate intervention. Two patients were managed surgically for SAIS with acromioplasty, 1 patient was managed surgically with C4-5 diskectomy, 3 patients were managed with cervical traction, 1 patient was managed with a cervical soft collar, and 1 patient was managed for acromioclavicular joint sprain. Six of the 10 patients were managed with unspecified physical therapy interventions. In a later case series of 39 patients with SSN, 18 patients were managed with 30 inappropriate surgical procedures for SAIS, the cervical spine, and thoracic outlet syndrome. (5) In another series of 27 patients, 6 patients underwent surgical procedures for thoracic outlet syndrome and 3 patients underwent cervical diskectomies without relief prior to their diagnosis of SSN. (3)

The suprascapular nerve is a mixed motor and sensory nerve arising from the upper trunk of the brachial plexus with contributions primarily from the anterior primary rami of the C5 and C6 nerve roots. It then courses posteroinferiorly beneath the superior transverse scapular ligament in the suprascapular notch to supply the supraspinatus muscle. It then passes inferolaterally around the lateral border of the scapular spine and beneath the inferior transverse scapular ligament in the spinoglenoid notch to innervate the infraspinatus muscle as depicted in Figure 1. (4,9) Sensory fibers of this nerve supply the acromioclavicular and glenohumeral joint capsules as well as the scapula. (4,10) Although the suprascapular nerve usually has no cutaneous sensory innervation, a cutaneous branch to the lateral shoulder has been reported in 3% to 15% of cadavers. (11,12)

[FIGURE 1 OMITTED]

Suprascapular neuropathy can be caused by compression or traction of the nerve at the suprascapular notch or spinoglenoid region. Injury to the nerve at the suprascapular notch causes weakness of both the supraspinatus and infraspinatus muscles, whereas injury at the spinoglenoid region affects only the infraspinatus muscle. Compression or traction of the suprascapular nerve in these regions can result from space-occupying lesions, traumatic injury, viral syndrome, repetitive use, or perioperative injury, or it can occur idiopathically. (8,13-20) Repetitive scapular movements may cause traction or tethering of the nerve, because the suprascapular nerve is fixed proximally at the cervical spine and distally at the scapula as it passes through the suprascapular notch and around the spinoglenoid notch. For this reason, athletic of work activities involving forceful contractions of shoulder musculature of repetitive overhead movements such as those involved in weight lifting, tennis, throwing, swimming, and volleyball have been implicated in the development of this neuropathy. (8,21-25)

Signs and symptoms of other injuries of the upper extremity overlap with signs and symptoms of SSN. Patients with SAIS or another rotator cuff injury can have a history of repetitive overhead activities as well as distribution of pain and muscle weakness similar to patients with SSN. (26-28) Cervical radiculopathy and upper trunk brachial plexopathy also can cause signs and symptoms similar to those of SSN, with weakness of the C5 and C6 innervated muscles, including the infraspinatus and supraspinatus muscles, as well as a similar pain distribution in the shoulder region. Differential diagnosis must rule out these other pathologies before diagnosing a patient with SSN.

The purpose of this case report is to describe the process for the differential diagnosis of SSN. The primary differential diagnoses include SAIS, rotator cuff pathology, C5-6 radiculopathy, and upper trunk brachial plexopathy.

Case Description

History

A summary of the patient history information is presented in Table 1. All patients were referred for physical therapy with a diagnosis of SAIS. The patients (1 female, 4 male) ranged in age from 19 to 36 years ([bar.X]=29.6, SD=6.8). The duration of symptoms ranged from 1 week to 6 months. Four of the patients had symptoms in the nondominant shoulder. All patients had at least one suspected neural traction of compression mechanism of injury. All 5 patients had pain patterns that included, but were not all limited to, the posterior aspect of the shoulder.

Examination

Given the patients' histories, the examiners considered the primary potential diagnoses to be SAIS or other rotator cuff disorders such as tendinopathy of partial-thickness tear. Alternative diagnoses, such as cervical radiculopathy, brachial plexopathy, or proximal mono-neuropathy (eg, SSN) could not be ruled out based on the histories.

The key physical examination data are summarized in Table 2. Shoulder flexion and abduction active range of motion (AROM) was limited in patient 1 only. The patient had full passive range of motion of the shoulder. Intraclass correlation coefficients (ICCs) for test-retest reliability of goniometric AROM measurements of the shoulder have been estimated to be .64 to .69. (29) Despite the limitations of the measurement tool, we considered abduction AROM impairment of 40 degrees to be clinically meaningful.

Manual muscle testing (MMT) was performed and graded on a 5-point scale, (30) with particular attention initially given to the rotator cuff muscles. Weakness was noted in the infraspinatus muscle in all patients and in the supraspinatus muscle in 4 of the patients. The infraspinatus muscle was tested by having the patients apply a shoulder lateral (external) rotation force with the arm at the side and the shoulder in 45 degrees of medial (internal) rotation. (31) The supraspinatus muscle was tested using the "empty can" technique, resisting shoulder elevation in the scapular plane. (30,31) A kinesiologic electromyographic (EMG) study (31) has demonstrated the construct validity of data obtained with these techniques. Interrater kappa coefficients for identification of muscle weakness without using a muscle test grade have been estimated to be 0.62 to 0.69 for the muscles of the rotator cuff and C5-6 innervated muscles. (32) When a formal muscle test grade was applied, these tests had ICCs that ranged from .79 to 1.00 for intrarater reliability and from .55 to .72 for interrater reliability. (33) Although examiner agreement to detect weakness in the shoulder region and C5-6 myotomes is variable, we believed that the results of our tests of the supraspinatus and infraspinatus muscles were clinically meaningful.

We also observed atrophy of the supraspinatus muscle of the infraspinatus muscle in 4 of the 5 patients during the initial evaluation. Patient 3 developed atrophy 2 weeks after the initial examination. Atrophy of the supraspinatus and infraspinatus muscles of patient 1 is depicted in Figure 2. The reliability or diagnostic accuracy of observations of atrophy in these muscles has not been investigated.

[FIGURE 2 OMITTED]

For differential diagnosis of cervical radiculopathy and brachial plexopathy, we performed myotomal strength, dermatomal sensation, and muscle stretch reflex testing. We found MMT grades of 5/5 for other C5-T1 innervated muscles. These tests have variable agreement (kappa=0.23-0.69) and variable sensitivity (0.03-0.73), but fair to good specificity (0.61-0.94) using the reference standard of the results from electrophysiologic testing for confirmation of cervical radiculopathy. (32,34) Results of reflex testing of the biceps brachii, brachioradalis, and triceps brachii muscles were normal and bilaterally symmetrical in all patients. Interrater reliability (kappa) for muscle stretch reflexes has been estimated to be 0.73, and specificity values ranged from 0.95 to 0.98. (32,34) Stretch reflex testing, however, has low sensitivity (0.03-0.24) for patients with cervical radiculopathy. (32,34) Cutaneous sensory testing was performed of the C5-T1 dermatomes, and the results were determined to be normal and bilaterally symmetrical in all patients. Interrater reliability (kappa) for dermatomal sensory testing of the C5 distribution has been estimated to be 0.67, but examination of other dermatomes has not been as reproducible (kappa=0.16-0.46). These tests also have demonstrated low sensitivity (0.12-0.38) and moderate to high specificity (0.46-0.86) in patients with cervical radiculopathy. (32,34) Although dermatome, myotome, and reflex tests have low sensitivity when considered individually, the sensitivity for diagnosing cervical radiculopathy, if any of the 3 tests is abnormal, is 0.84. The specificity for diagnosing cervical radiculopathy in the presence of 2 or 3 abnormalities with these tests ranges from 0.74 to 0.98. (34)

We also used the Spurling test to test for cervical radiculopathy. (32) The test was negative in all patients. This test has estimated interrater reliability (kappa) of 0.60 and specificity of 0.86, but sensitivity for diagnosing cervical radiculopathy is only 0.50. (32) Thus, this test also may have little utility as a screening tool.

Special tests for SAIS were performed as described by Hawkins and Kennedy (27) and Neer and Welsh (28) and in Magee's Orthopedic Physical Assessment. (35) These 2 tests are referred to as impingement "signs." All patients had at least one positive SAIS sign, and 3 patients had positive results for both signs. Although no estimates of reliability for these signs exist, both signs have sensitivity of 0.75 to 0.92 and specificity of 0.25 to 0.51 for diagnosing SAIS. (36) Thus, positive findings for these signs do not confidently rule in SAIS. Four of the 5 patients also had a painful are during shoulder elevation. This examination finding had specificity of 0.80, but sensitivity of only 0.32. Thus, it is useful for ruling in SAIS when a painful arc is present. (37) Evidence of the reliability of data obtained with the painful are test is lacking.

All patients underwent radiographic examination of the cervical spine, shoulder, and scapula in an attempt to screen for relevant bone or other dense tissue abnormalities. These findings were normal. Patient 5 also had a magnetic resonance imaging (MRI) study of his shoulder, which demonstrated a posterior glenoid cyst, acromioclavicular joint degeneration, and supraspinatus tendonosis.

Evaluation

The clinical examination findings suggested diagnoses of both SSN and SAIS in all patients. The diagnosis of SSN was based on the presence of posterior shoulder pain in conjunction with weakness and atrophy isolated to the suprascapular nerve field. Negative cervical provocation tests, no other myotomal weakness, normal reflexes, and normal sensation suggested that C5-6 radiculopathy and upper trunk brachial plexopathy were less likely diagnoses. Patients with full thickness rotator cuff tears often have weakness and atrophy similar to that of patients with SSN; thus, differentiating a full-thickness tear from SSN can be difficult. (38) Incidence of full-thickness tear increases after the age of 50 years and is most common in patients over 60 years of age, (39,40) whereas SSN is most common in patients under 40 years of age. (41) Therefore, SSN was considered a more likely diagnosis than full-thickness rotator cuff tear in these patients.

The patients also demonstrated many clinical signs and symptoms of the referral diagnosis of SAIS. All of the patients described worsening pain with shoulder elevation, which is a common finding in both SSN and SAIS. All patients had at least one positive impingement sign (Hawkins or Neer test), and all patients had a painful arc except patient 5. Because the Neer and Hawkins tests have low specificity for the diagnosis of SAIS, but the painful arc test has high specificity, we thought the evidence for a diagnosis of SAIS was strong for patients 1 to 4 and was weaker for patient 5. Patient 5, however, did have an MRI demonstrating supraspinatus tendon degeneration and acromioclavicular joint degeneration, which are suggestive of SAIS. Magnetic resonance imaging has demonstrated high sensitivity (0.93) and specificity (0.87) for imaging signs of SAIS. (42) Thus, we thought that evidence for diagnosing SAIS in all 5 patients was compelling.

Suprascapular neuropathy is rare; thus, a definitive diagnosis of SSN requires the exclusion of alternative diagnoses. Many of the clinical examination techniques used to diagnosis SSN and many of those used to rule out alternative diagnoses have imperfect reproducibility and diagnostic accuracy. In particular, the tests performed for cervical radiculopathy and brachial plexopathy are generally not sensitive; thus, false negative findings are possible. In addition, pain with muscle testing interfered with identifying any true weakness in patients 1 and 2.

In light of the examination findings and the associated diagnostic accuracy and reliability of the examination procedures used, the diagnoses of SSN and SAIS were considered to be likely in all 5 patients. The alternative diagnoses of cervical radiculopathy, other rotator cuff pathology, and upper brachial plexopathy were considered less likely, but still possible. Thus, electrophysiologic evaluation was necessary to rule out these alternative diagnoses, confirm the diagnosis of SSN, and determine the severity of the neuropathy.

Electrophysiologic Evaluation: Electromyography and Nerve Conduction Studies

Abnormal spontaneous potentials (fibrillation potentials and positive sharp waves), indicating axonal injury, were observed in the involved muscle(s) of the suprascapular nerve field in all patients. (43) Electromyographic interference patterns were estimated based on the percentage of a normal, full interference pattern of motor unit action potentials present. (43) Particular attention was given to EMG examination of other C5-6 and upper trunk innervated muscles, which demonstrated normal electrophysiologic function. Nerve conduction studies (NCS) were performed with electrical stimulation at the supraclavicular fossa while using needle recording electrodes in the supraspinatus or infraspinatus muscle.

These NCS techniques have been demonstrated to be reproducible and to have established accepted normal value ranges. (44,45) Although EMG and NCS are often considered the criterion validity standard for correlating clinical findings in diagnosing nerve injuries, (5,7,32,34,43) the interrater agreement of detecting abnormal EMG potentials has not been investigated. Electromyography and NCS have demonstrated a high level of accuracy (91%), however, in clarifying the diagnosis of patients with weakness. (46) Table 3 gives a summary of the suprascapular nerve field EMG and NCS findings.

Diagnosis

In all patients, the examination findings were consistent with both SSN and SAIS. Electrophysiologic findings confirmed the presence of SSN at the area of the suprascapular notch in patients 1 to 4 and in the region of the spinoglenoid notch in patient 5.

Intervention and Outcomes

The interventions and outcomes are summarized in Table 4. All patients were instructed to protect the suprascapular nerve and minimize their risk of aggravating SAIS symptoms by avoiding carrying backpacks or bags with straps over their shoulders, repeated overhead actions, nerve traction maneuvers such as horizontal adduction, and any other aggravating activities. All 5 patients were referred to orthopedic surgeons. The surgeon tot patient 4 chose to operate because her symptoms had been present for 9 months and she had not improved with 3 months of nonsurgical intervention.

Discussion

Compression or traction of the suprascapular nerve can result in signs and symptoms that are similar to those of other upper-extremity disorders. Several key clinical findings may indicate the possibility of SSN. These findings include pain in the posterior shoulder, a history of direct trauma of repetitive traction to the suprascapular nerve, and weakness and atrophy of the muscles innervated by the suprascapular nerve.

Posterior shoulder pain is common with SSN; however, this pain is often diffuse and not limited to that region. (1-5,7,47,48) Four of our 5 patients noted posterior shoulder pain, which is consistent with a previously reported case series in which 34 of 35 patients with SSN described posterior shoulder pain. (48)

Injury to the suprascapular nerve may occur in a variety of ways. The mechanism of injury may include a single traumatic event, such as a glenohumeral dislocation or scapular fracture, or a repetitive microtrauma, such as athletes performing repetitive overhead activity. (4,8,12,19-23,25,38,49) A history of repetitive overhead activity may suggest the possibility of SAIS or rotator cuff pathology as well as SSN. A history of surgery, recent viral illness, glenoid cyst, of metastatic disease also may be the cause of SSN; however, in many cases, the cause remains undetermined. (1-5,7,47,48,50)

In 4 of our 5 patients, we could not determine the cause of SSN with certainty. All patients were military service members and engaged in regular physical exercise. Patient 1 first noted symptoms after awakening from sleep with his shoulder fully abducted. Patient 2 first noted his symptoms the day after abdominal surgery; however, he was also a serious weight lifter and routinely carried an equipment bag over the involved shoulder. Patient 3 first noted symptoms after repetitive digging and lifting, but he also routinely wore a military backpack over his shoulders for several hours per day. Patient 4 first noted her symptoms after carrying luggage; however, she was also 3 days postpartum. Patient 5 was active in martial arts. Therefore, it is possible that compression or traction of the suprascapular nerve could have occurred from any of these potential mechanisms of injury.

Patients with SSN may have weakness of both the supraspinatus and infraspinatus muscles or of the infraspinatus alone because the suprascapular nerve innervates these muscles. In distal lesions of the suprascapular nerve in the spinoglenoid region, shoulder lateral rotation may be the only detectable weakness due to loss of infraspinatus muscle function. However, this weakness may be difficult to discern because shoulder lateral rotation force is produced by the infraspinatus, teres minor, and posterior deltoid muscles. In more proximal lesions, such as at the suprascapular notch, shoulder elevation in the scapular plane ("empty-can" test) also may be weak due to supraspinatus muscle involvement. (1-5,7) All of our patients demonstrated weakness of the infraspinatus muscle, and 4 patients demonstrated supraspinatus muscle weakness. Patient 5, who did not have weakness of the supraspinatus muscle, had evidence of spinoglenoid cyst visible on MRI. Observation of atrophy in the involved muscle(s) can frequently be associated with findings of weakness within 2 to 3 weeks of the onset of symptoms (Fig. 2). (1-5,7)

Differential diagnosis of SSN can be difficult due to overlap in the clinical presentation with other pathologies of the shoulder and cervical spine region. To aid in differential diagnosis, key diagnostic findings of SSN, SAIS, rotator cuff pathology, cervical radiculopathy, and upper trunk brachial plexopathy are presented in Table 5. This table is based on an integration of the evidence and our clinical experience.

Radiculopathy at the C5 and C6 levels can cause shoulder pain and weakness of the supraspinatus and infraspinatus muscles; however, several clinical features may distinguish SSN from cervical radiculopathy. Symptom reproduction with cervical spine maneuvers, a dermatomal pattern of impaired sensation, impaired muscle stretch reflexes, and myotomal weakness that is more extensive than the suprascapular nerve field may be present in patients with cervical radiculopathy. (32,34,43) Symptom reproduction that occurs with the Spurling test is indicative of cervical spine dysfunction, rather than SSN. Dermatomal testing should typically reveal no sensory deficits with SSN. A close overlap exists, however, between the C5 dermatome and the suprascapular nerve's cutaneous sensory field in the small percentage of people with a cutaneous branch of the suprascapular nerve. Thus, sensory impairment alone should be used with caution for differential diagnosis. Reflex testing for the C5-6 innervation pathways of the biceps brachii and brachioradialis muscles may be abnormal with radiculopathy, but not with SSN. Weakness of the infraspinatus and supraspinatus muscles should be the only strength impairment present in patients with SSN. Testing of other C5-6 innervated muscles may aid in the differential diagnosis of a cervical radiculopathy. As discussed previously, the Spurling test, MMT, reflex testing, and cutaneous sensory tests are highly specific, but generally are not sensitive for diagnosing cervical radiculopathy. Therefore, although positive findings are strongly suggestive of radiculopathy, negative tests do not rule out cervical radiculopathy with a high level of confidence. (32)

The upper-limb tension test (ULTT) is a sensitive (0.97) clinical screening tool for cervical radiculopathy. (32) The ULTT is not specific, however, so a positive ULTT still requires further clinical correlation before diagnosing cervical radiculopathy. Additional positive findings with 2 tests of provocation of symptoms with the Spurling test and limited cervical rotation increased the positive likelihood of cervical radiculopathy to 65%. (32) When a third positive finding was added, relief of symptoms with cervical traction, the positive likelihood increased to 90%. (32) Because this evidence was not published at the time we saw our patients, we did not use the ULTT.

Brachial plexopathies of the upper trunk can be affected by idiopathic lesions, viral illness, or compression or traction injuries such as "burners," "stingers," and "rucksack palsies. This region also ca be affected perioperatively after scalene anesthetic block of due to surgical positioning. (43) In idiopathic lesions or cases of viral illness, the onset of symptoms is usually marked by severe shoulder and brachial pain. Patients with upper trunk brachial plexopathies may have clinical examination findings of sensory impairments following the C5-6 dermatomes, biceps brachii and brachioradialis muscle stretch reflex abnormalities, and weakness of C5-6 innervated muscles with sparing of the serratus anterior, rhomboid, and paraspinal muscles. We are unaware of any highly sensitive screening tests for upper trunk brachial plexopathy. Muscle and reflex testing, therefore, are most likely the best clinical tools for ruling out this condition. Due to the low sensitivity of muscle and reflex testing, electrophysiologic examination may be particularly useful in differentiating brachial plexopathies from SSN or cervical radiculopathy. (43,51)

Patients with full-thickness tearing of the rotator cuff typically have weakness of shoulder elevation and lateral rotation, secondary to trauma or insidious onset. The patient's age may be particularly useful in determining whether SSN or a full-thickness rotator cuff tear is more probable, as the incidence of full-thickness rotator cuff tear increases after the age of 50 years. (39,40) A cluster of 3 positive findings of supraspinatus muscle weakness, infraspinatus muscle weakness, and a positive impingement sign have demonstrated high probability (98%) for predicting whether a patient will develop a rotator cuff tear. (37) This cluster, however, would have yielded false positive diagnoses in 4 of our 5 patients. Evidence also suggests that the drop arm test may be helpful in discriminating between full-thickness rotator cuff tear and SSN, because this test is highly specific (0.98) for full-thickness rotator cuff tear. (37) The drop arm test, however, is not sensitive (0.10). (2,52) We did not perform this test with our patients. Magnetic resonance imaging (42,50,53-55) and electrophysiologic testing (5,6,43) also may be helpful in differentiating full-thickness rotator cuff tears and SSN.

Inflammation, degeneration, and partial-thickness tearing of the rotator cuff may occur in isolation, but they are commonly associated with SAIS. Subacromial impingement syndrome involves abnormal contact between the coracoacromial arch and subacromial soft tissues (rotator cuff tendons, long biceps tendon, and bursae). Symptoms of this disorder often include anterior, superior, or deep shoulder pain that is worsened with shoulder elevation. (26,27,56,57) As with SSN, patients with SAIS may have weak shoulder abduction and lateral rotation, (26,58,59) Moreover, SAIS often occurs in patients who perform repetitive overhead activity, but it also can occur insidiously of can result from trauma. (26,27,56,57) The Hawkins and Neer impingement signs may not be helpful in differentiating SSN from SAIS because these tests have been demonstrated to have low specificity. Thus, false positive results are likely. (37,57) The painful arc test, which has higher specificity, may be more useful in ruling in SAIS. (37) Lateral rotation weakness and atrophy may be useful in differentiating SSN from SAIS because, in our experience, these symptoms are typically more severe in patients with SSN. However, interrater reliability for grading weakness with MMT is not high. (33) Posterior shoulder pain also may be a discriminator because patients with SAIS do not typically have pain in this region. (26,27,56,57)

Subacromial impingement syndrome and SSN may occur simultaneously in patients. Evidence suggests that SAIS may be caused by altered neuromuscular control of the shoulder girdle. (60-62) Suprascapular neuropathy can diminish neuromuscular control through weakness of rotator cuff muscles, thus disrupting normal shoulder mechanics and increasing the likelihood of the occurrence of SAIS. The supraspinatus and infraspinatus muscles stabilize the glenohumeral joint, while the infraspinatus muscle also depresses the humeral head and laterally rotates the shoulder. With a reduction of muscle performance of one of both of these suprascapular innervated muscles, impingement of subacromial structures against the coracoacromial arch during shoulder elevation could result. (61-67) Simulated SSN in cadaver models has demonstrated excessive humeral head translation during shoulder elevation, indicating theoretical support for the increased risk of development of SAIS in patients with SSN. (65) Thus, patient education to avoid repetitive overhead activities in order to minimize the risk for developing SAIS is appropriate for patients with SSN. We hypothesize that our patients developed SAIS as a result of weakness caused by the SSN. However, it also was possible that both the suprascapular nerve and the subacromial soft tissue structures were injured concomitantly due to repetitive shoulder activities or positioning during sleep of surgery.

Electrophysiologic abnormalities are generally considered necessary to confirm a diagnosis of SSN. (5,6,43) Electrophysiologic studies are particularly useful in differentiating SSN from brachial plexopathy, cervical radiculopathy, of nonneurologic disorders. Findings from EMG and NCS also may be useful in directing imaging studies to the appropriate anatomic location by localizing a neurologic lesion. Electromyographic abnormalities that occur in resting muscle, such as fibrillation potentials and positive sharp waves, suggest axonal injury to motoneuron fibers. Absent or decreased motor unit action potential interference patterns with attempts to contract the muscle suggest that the number of functioning motor units is decreased. (43) Nerve conduction studies for the suprascapular nerve typically measure latency to the infraspinatus of supraspinatus muscle. Conduction abnormalities can include delayed latency of an absent response. (44)

Electrophysiologic studies also may yield some prognostic value. In a series of 53 patients with SSN with 1-year follow-up, (2) EMG findings were useful in predicting functional outcome. More severe EMG findings were more predictive than mild EMG findings of greater improvement with either surgical or nonsurgical intervention.

Imaging studies may be helpful in defining the source of SSN because they may provide evidence of an anatomic source of compression. (2,47) Plain radiographs of the cervical spine, scapula, and shoulder ate considered an inexpensive screening tool. Their results, however, are typically negative. Ultrasonography, MRI, and computed tomography all have some utility in identifying ganglion cysts, other masses, bone abnormalities, muscle atrophy, and fatty infiltration. However, MRI is considered the best imaging modality for most lesions in the shoulder region and is useful in detecting sources of nerve compression such as glenoid cysts or malignancy. (4,12,47,50,53,68) The reported accuracy for using MRI to detect changes suggestive of denervation in the infraspinatus or supraspinatus muscle in patients with SSN ranges from poor to excellent and is generally not considered as good as that of EMG and NCS. (50,53) Thus, electrophysiologic examination is a particularly useful diagnostic tool for augmenting the clinical examination when a diagnosis of SSN is being considered, whereas MRI is most useful in determining the presence of space-occupying lesions as the source of SSN. In this manner, electrophysiologic studies and MRI are complementary procedures in the examination of patients with SSN. Only one of the patients discussed in this case report received an MRI. Retrospectively, we would have ordered MRI for the other 4 patients in an effort to rule out the presence of space-occupying lesions.

Evidence for the optimal management of SSN is conflicting and primarily is in the form of case series and "expert" opinions. Although glenoid cysts may resolve spontaneously, (12,68) these cysts and other sources of nerve compression generally respond best to surgical management. (2) Patients with other sources of SSN seem to respond equally well to both surgical and nonsurgical intervention. (2) Thus, imaging studies to determine the location and source of the lesion, if possible, may be useful in guiding intervention. (2,47) Several authors (16,38) have reported good or excellent results in a majority of patients managed with a conservative (nonsurgical) approach. Other authors (1,3,5,7,48) have reported good or excellent results in a majority of patients managed surgically. Of patients who receive surgery, those operated on within 6 months after developing symptoms tended to have better results. (48) In the absence of an identifiable anatomic source of nerve compression, a trial of nonoperative intervention as outlined in Table 4 is probably most appropriate. (16,38,47,48)

Three of the patients presented in this case report were managed nonsurgically and had complete or nearly complete return of strength and resolution of pain in the time that they were followed. The patient who was managed surgically had only minimal improvement in symptoms and function. We speculate that the poor outcome was due to severe nerve entrapment for a prolonged period. One patient was lost to follow-up soon after the initial evaluation, so his outcome is unknown.

Conclusion

Patients who have a mechanism of possible injury to the suprascapular nerve, posterior shoulder pain, or weakness or atrophy of the infraspinatus muscle with of without involvement of the supraspinatus muscles should be considered for a diagnosis of SSN. Before diagnosing SSN, other disorders such as C5-6 radiculopathy, upper trunk brachial plexopathy, rotator cuff pathology, and SAIS should be ruled out. Further research is needed to determine the diagnostic accuracy of various tests and measures for SSN, the optimal management of patients with SSN, and whether a relationship exists between SSN and SAIS.

Table 1.
History and Interview Findings

                      Patient 1             Patient 2

Age (y)               34                    36
Sex                   Male                  Male
Occupation            Military computer     Military
                        specialist            helicopter
                                              pilot
Shoulder pain         Diffuse, mostly       Anterior and
  location              anterior              posterior
Referral diagnosis    Subacromial           Subacromial
                        impingement           impingement
Dominant arm          Right                 Right
Affected shoulder     Left                  Left
Duration of           5 wk                  4 mo
  symptoms
Suspected mechanism   Prolonged shoulder    Perioperative
  of injury             abduction             onset of
                        during sleep          symptoms
                                            Carrying bag
                                              over shoulder
Aggravating           Push-ups              Bench press
  activities          Overhead activities   Carrying bag
                      Driving               Overhead
                                              activities
Medications           Nonsteroidal anti-    Subacrominal
                        inflammatory          steroid
                                              injection
                                              (self-report
                                              80% pain
                                              improvement)
Past medical          None significant      Abdominal
  history                                     surgery for
                                              diverticulosis
                                              1 d prior to
                                              onset of symptoms

                      Patient 3        Patient 4        Patient 5

Age (y)               19               29               30
Sex                   Male             Female           Male
Occupation            Military         Military         Army recruiter
                        mechanic-in-     intelligence
                        training         specialist
Shoulder pain         Anterior and     Superior and     Anterior and
  location              posterior        posterior        posterior
Referral diagnosis    Subacromial      Subacromial      Subacrominal
                        impingement      impingement      impingement
Dominant arm          Right            Right            Right
Affected shoulder     Right            Left             Left
Duration of           1 wk             6 mo             6 mo
  symptoms
Suspected mechanism   Lifting and      Initial          Involved in
  of injury             digging          symptoms 3 d     martial arts
                      Wearing            postpartum
                        backpack       Carrying
                                         luggage
Aggravating           Overhead         Overhead         Overhead
  activities            activities       activities       activities
                                                        Reaching
                                                          behind back
Medications           Nonsteroidal     Nonsteroidal     None
                        anti-infla-      anti-infla-
                        mmatory          mmatory
Past medical          None             Postpartum       None
  history               significant      3 d prior        significant
                                         to onset
                                         of symptoms

Table 2.
Initial Examination Findings (a)

Test and Measures      Patient 1                  Patient 2

Observation            Marked supraspinatus and   Marked supraspinatus
                         infraspinatus muscle       and infraspinatus
                         atrophy                    muscle atrophy
AROM: flexion          170[degrees] (uninvolved   Full
                         was 180[degrees])
AROM: abduction        140[degrees] (uninvolved   Full
                         was 180[degrees])
Painful arc (painful   Present                    Present
  from 80[degrees]-
  120[degrees] of
  abduction)
MMT: infraspinatus     3/5 with pain              3/5 with pain
  muscle
MMT: supraspinatus     3+/5 with pain             3+/5 with pain
  muscle ("empty-
  can" technique)
Hawkins and            Positive                   Positive
  Kennedy test
  (impingement sign)
Neer test              Positive                   Postitive
  (impingement
  sign)
Tenderness to          Long tendon of biceps      Long tendon of biceps
  palpation              brachii muscle and         brachii muscle
                         greater tubercle
MRI                    Not performed              Not performed
Etiology               Unknown                    Unknown

Test and Measures      Patient 3                 Patient 4

Observation            No atrophy initially      Marked supraspinatus
                         (moderate atrophy of      and infraspinatus
                         supraspinatus and         muscle atrophy
                         infraspinatus muscles
                         2 wk later)
AROM: flexion          Full                      Full
AROM: abduction        Full                      Full
Painful arc (painful   Present                   Present
  from 80[degrees]-
  120[degrees] of
  abduction)
MMT: infraspinatus     2/5                       2/5
  muscle
MMT: supraspinatus     3/5                       3/5
  muscle ("empty-
  can" technique)
Hawkins and            Positive                  Positive
  Kennedy test
  (impingement sign)
Neer test              Negative                  Positive
  (impingement
  sign)
Tenderness to          Long tendon of biceps     None noted
  palpation              brachii muscle

MRI                    Not performed             Not performed

Etiology               Unknown                   Compression by
                                                   superior
                                                   transverse
                                                   scapular
                                                   ligament
                                                   (determined by
                                                   surgical
                                                   observation

Test and Measures      Patient 5

Observation            Moderate
                         infraspinatus muscle
                         atrophy only
AROM: flexion          Full
AROM: abduction        Full
Painful arc (painful   Not present
  from 80[degrees]-
  120[degrees] of
  abduction)
MMT: infraspinatus     3/5
  muscle
MMT: supraspinatus     5/5
  muscle ("empty-
  can" technique)
Hawkins and            Positive
  Kennedy test
  (impingement sign)
Neer test              Negative
  (impingement
  sign)
Tenderness to          None noted
  palpation
MRI                    Posterior glenoid cyst
                       Acromioclavicular
                         joint degenerative
                         changes
                       Supraspinatus
                         tendinosis
Etiology               Glenoid cyst

(a) MMT=manual muscle testing, MRI=magnetic resonance imaging,
AROM=active range of motion.

Table 3.
Electrophysiologic Findings (a)

                         Patient 1               Patient 2

NCS                      Not performed           Not performed

EMG: supraspinatus       Increased               Increased
  muscle (insertional
  activity)
EMG: supraspinatus       3+ fibs                 3+ fibs
  muscle (test)          3+ PSWs                 3- PSWs
EMG: supraspinatus       No MUAPs                No MUAPs
  muscle (interference
  pattern)
EMG: infraspinatus       Increased               Increased
  muscle (insertional
  activity
EMG: infraspinatus       3+ fibs                 3+ fibs
  muscle (rest)          3+ PSWs                 3+ PSWs
EMG: infraspinatus       No MUAPs                No MUAPs
  muscle (interference
  pattern)
Location of lesion       Proximal to             Proximal to
  based on EMG/            supraspinatus           supraspinatus
  NCS                      muscle: region of       muscle: region of
                           suprascapular notch     suprascapular notch

                         Patient 3               Patient 4

NCS                      No response:            No response:
                           infraspinatus           infraspinatus and
                           muscle                  supraspinatus
                                                   muscles
EMG: supraspinatus       Increased               Increased
  muscle (insertional
  activity)
EMG: supraspinatus       2+ fibs                 2+ fibs
  muscle (test)          3+ PSWs                 2+ PSWs
EMG: supraspinatus       No MUAPs                No MUAPs
  muscle (interference
  pattern)
EMG: infraspinatus       Increased               Increased
  muscle (insertional
  activity
EMG: infraspinatus       2+ fibs                 2+ fibs
  muscle (rest)          3+ PSWs                 2+ PSWs
EMG: infraspinatus       No MUAPs                No MUAPs
  muscle (interference
  pattern)
Location of lesion       Proximal to             Proximal to
  based on EMG/            supraspinatus           supraspinatus
  NCS                      muscle: region of       muscle: region of
                           suprascapular notch     suprascapular notch

                         Patient 5

NCS                      No response:
                           infraspinatus
                           muscle

EMG: supraspinatus       Normal
  muscle (insertional
  activity)
EMG: supraspinatus       Normal
  muscle (test)
EMG: supraspinatus       Normal
  muscle (interference
  pattern)
EMG: infraspinatus       Increased
  muscle (insertional
  activity
EMG: infraspinatus       2+ fibs
  muscle (rest)          4+ PSWs
EMG: infraspinatus       25% interference
  muscle (interference     pattern
  pattern)
Location of lesion       Distal to
  based on EMG/            supraspinatus
  NCS                      muscle, proximal
                           to infraspinatus
                           muscle: region of
                           spinoglenoid notch

(a) NCS=nerve conduction study, EMG=electromyogtaphy,
Fibs=fibrillation potentials, PSWs=positive sharp waves,
MUAPs=motor unit action potentials.

Table 4.
Summary of Patient Data and Outcomes

               Patient 1              Patient 2

Intervention   Rotator cuff           Subacromial injection
                 strengthening        Rotator cuff
               Patient education        strengthening
                                      Posterior glenohumeral
                                        capsular
                                        mobilization
                                      Patient education

Outcomes       Full AROM              Resolved pain
               Resolved pain          Negative impingement
               Negative impingement     signs
                 signs                Strength improved:
               Strength unchanged       4/5 in abduction,
                                        "empty-can"
                                        technique, and
                                        lateral rotation
                                      Returned to weight
                                        lifting without pain

Length of      2 mo                   9 mo
follow-up      Moved from             Moved from
                 geographic region      geographic region

               Patient 3           Patient 4          Patient 5

Intervention   Rotator cuff        Preoperative and   Rotator cuff
                 strengthening       postoperative      strengthening
               Patient education     rotator cuff     Patient
                                     strengthening      education

                                   Surgical release
                                     of superior
                                     transverse
                                     scapular
                                     ligament
                                   Patient
                                     education

Outcomes       No change           Minimal decrease   Resolved pain
                                     in pain          Strength
                                   Strength             improved:
                                     improved:          5/5 in lateral
                                     3/5 in lateral     rotation
                                     rotation, 4/5    Returned to
                                     in "empty-can"     athletics
                                     technique          without pain
                                   Unable to return
                                     to full
                                     athletics due
                                     to weakness
                                     and pain

Length of      16 d                14 mo              2 mo
follow-up      Moved from
                 geographic
                 region

Table 5.
Comparison of Key Findings in Suprascapular Neuropothy (SSN)
Compared With Subacromial Impingement Syndrome (SAIS), Rotator
Cuff Pathology, Cervical Radiculopathy, and Upper Trunk
Brachial Plexopathy (a)

               SSN                         SAIS

Weakness       Infraspinatus muscle        Possible infraspinatus
                 weakness                    muscle weakness
               Possible supraspinatus      Possible supraspinatus
                 muscle weakness             muscle weakness
                 (1-7,41,47)                 (26,58,59)

Pain           Diffuse shoulder pain       Shoulder pain anterior,
               Typically includes            superior, or deep
                 posterior shoulders       Typically does not include
                 (1-7,41,47)                 posterior shoulder
                                             (26,56)

Atrophy        Infraspinatus muscle        Atrophy not typical
                 atrophy typical
               Suprospinatus muscle
                 atrophy possible
                 (1,4,5,41,47)

Reflexes       Normal (35)                 Normal (35)

Cutaneous      Typically normal            Normal (35)
sensation      Rarely decreased at
                 lateral shoulders
                 (11,12)

Age            Most common <40 y (41)      Varies (26)

History        Possible repetitive         Possible repetitive
                 overhead use                overhead use
               Possible shoulder trauma    Usually not trauma
               Possibly insidious          Often insidious (26-28,56)
               Possible viral exposure
               Possible traction or
                 compression (5,6,13-25)

EMG/NCS        Abnormalities in            Normal (43)
                 infraspinatus muscle
               Possible abnormalities in
                 supraspinatus muscle
                 (43-47)

Shoulder MRI   Possible glenoid cyst or    Possible bursitis
                 other source of           Possible rotator cuff or
                 compression                 biceps tendon
               Possible muscle               degeneration or tearing
                 edema (2,47,50,53,68)     Possible acromial
                                             changes (42)

                                                     Upper
               Rotator            C5-6               Trunk Brachial
               Cuff Tear          Radiculopathy      Plexopathy

Weakness       Possible           C5-6 myotomal      C5-6 myotomal
                 infraspinatus      pattern            pattern
                 muscle             weakness           weakness
                 weakness           (32,34,43)       Sparing of
               Possible                                rhomboid,
                 supraspinatus                         serratus
                 muscle                                anterior, and
                 weakness                              paraspinal
               Possible                                muscles (43)
                 subscopularis
                 muscle
                 weakness (52)

Pain           Diffuse shoulder   Diffuse neck,      Diffuse shoulder
                 pain               shoulder, and      and brachial
               May include          brachial pain      pain (43)
                 posterior          (32,43)
                 shoulder

Atrophy        Infraspinatus      Myotomal pattern   Expect more
                 and supras-        if present         extensive
                 pinatus muscle   May include          myotomal
                 atrophy            infraspinatus      pattern with
                 possible           and supras-        sparing of
                                    pinatus muscle     rhomboid,
                                    atrophy            serratus
                                                       anterior, and
                                                       paraspinal
                                                       muscles
                                                     May include
                                                       infraspinatus
                                                       and supras-
                                                       pinatus muscle
                                                       atrophy (43)

Reflexes       Normal (35)        Possible de-       Possible de-
                                    creased biceps     creased biceps
                                    and brachiora-     and brachiora-
                                    dialis muscles     dialis muscles
                                    (32,34)            (43)

Cutaneous      Normal (35)        Likely decreased   Likely decreased
sensation                           at lateral         at lateral
                                    shoulder, arm,     shoulder, arm,
                                    and forearm        and forearm
                                    (32,34,43)         (43,51)

Age            Most common >55    Varies (35,43)     Most common
                 y (39,40,52)                          20-30 y (43)

History        Athlete with       Possible           Possible
                 possible           cervical           compression or
                 repetitive         trauma             traction to
                 overhead         Often insidious      brachial
                 activity           (35,43)            plexus
               Possible trauma                       If insidious,
               Often insidious                         usually
                                                       preceded by
                                                       severe shoulder
                                                       and brachial
                                                       pain
                                                     Possible viral
                                                       exposure
                                                       (43,51)

EMG/NCS        Normal (43)        Abnormalities in   Abnormalities in
                                    C5-6 myotomal      C5-6 myotomal
                                    distribution       distribution
                                    (32,34,43)       Sparing of
                                                       rhomboid,
                                                       serratus
                                                       anterior, and
                                                       paraspinal
                                                       muscles (43)

Shoulder MRI   Rotator cuff       Normal unless      Possible source
                 degeneration,      concomitant        of brachial
                 partial or         shoulder           plexus com-
                 complete           pathology          pression (43)
                 treating
                 (42,54)

(a) EMG=electromyography, NCS=nerve conduction study, MRI=magnetic
resonance imaging.

References

(1) Antoniadis G, Richter HP, Rath S, et al. Suprascapular nerve entrapment: experience with 28 cases. J Neurosurg. 1996;85:1020-1025.

(2) Antoniou J, Tae SK, Williams GR, et al. Suprascapular neuropathy: variability in the diagnosis, treatment, and outcome. Clin Orthop. 2001;(386):131-138.

(3) Callahan JD, Scully TB, Shapiro SA, Worth RM. Suprascapular nerve entrapment: a series of 27 cases. J Neurosurg. 1991;74:893-896.

(4) Cummins CA, Messer TM, Nuber GW. Suprascapular nerve entrapment. J Bone Joint Surg Am. 2000;82:415-424.

(5) Post M. Diagnosis and treatment of suprascapular nerve entrapment. Clin Orthop. 1999;(368):92-100.

(6) Post M, Mayer J. Suprascapular nerve entrapment: diagnosis and treatment. Clin Orthop. 1987;(223):126-136.

(7) Vastamaki M, Goransson H. Suprascapular nerve entrapment. Clin Orthop. 1993;(297):135-143.

(8) Ferretti A, Cerullo G, Russo G. Suprascapular neuropathy in volley-ball players. J Bone Joint Surg Am. 1987;69:260-263.

(9) Moore KL. Clinically Oriented Anatomy. 3rd ed. Baltimore, Md: Williams & Wilkins; 1992.

(10) Colachis SC, Strohm BR. Effect of suprascapular and axillary nerve blocks on muscle force in the upper extremity. Arch Phys Med Rehabil. 1971;52:22-29.

(11) Harbaugh KS, Swenson R, Saunders RL. Shoulder numbness in a patient with suprascapular nerve entrapment syndrome: cutaneous branch of the suprascapular nerve--case report. Neurosurgery. 2000;47: 1452-1455.

(12) Horiguchi M. The cutaneous branch of some human suprascapular nerves. J Anat. 1980;130:191-195.

(13) Aiello I, Serra G, Traina GC, Tugnoli V. Entrapment of the suprascapular nerve at the spinoglenoid notch. Ann Neurol. 1982;12: 314-316.

(14) Cohen SB, Dines DM, Moorman CT. Familiar calcification of the superior transverse scapular ligament causing neuropathy. Clin Orthop. 1997;(334):131-135.

(15) Mallon WJ, Bronec PR, Spinner RJ, Levin LS. Suprascapular neuropathy after distal clavicle excision. Clin Orthop. 1996;(329):207-211.

(16) Martin SD, Warren RF, Martin TL, et al. Suprascapular neuropathy: results of non-operative treatment. J Bone Joint Surg Am. 1997;79: 1159-1165.

(17) Mittal S, Turcinovic M, Gould ES, Vishnubhakat SM. Acute isolated suprascapular nerve palsy limited to the infraspinatus muscle: a case report. Arch Phys Med Rehabil. 2002;83:565-567.

(18) Ogino T, Minami A, Kato H, et al. Entrapment neuropathy of the suprascapular nerve by a ganglion: a report of three cases. J Bone Joint Surg Am. 1991;73:141-147.

(19) Ringel SP, Treihaft M, Carry M, et al. Suprascapular neuropathy in pitchers. Am J Sports Med. 1990;18:80-86.

(20) Zoltan JD. Injury to the suprascapular nerve associated with anterior dislocation of the shoulder: case report and review of the literature. J Trauma. 1979;19:203-206.

(21) Agre JC, Ash N, Cameron MC, House J. Suprascapular neuropathy after intensive progressive resistive exercise: case report. Arch Phys Med Rehabil. 1986;68:236-238.

(22) Mondelli M, Cioni R, Federico A. Rare mononeuropathies of the upper limb in bodybuilders. Muscle Nerve. 1998;21:809-812.

(23) Montagna P, Colonna S. Suprascapular neuropathy restricted to the infraspinatus muscle in volleyball players. Acta Neurol Stand. 1993;87: 248-250.

(24) Montagna P. Suprascapular neuropathy after muscular effort. Electromyogr Clin Neurophysiol. 1983;23:553-557.

(25) Kukowski B. Suprascapular nerve lesion as an occupational neuropathy in a semiprofessional dancer. Arch Phys Med Rehabil. 1993;74: 768-769.

(26) Bigliani LU, Levine WN. Subacromial impingement syndrome. J Bone Joint Surg Am. 1997;79:1854-1868.

(27) Hawkins RJ, Kennedy JC. Impingement syndrome in athletes. Am J Sports Med. 1980;8:151-158.

(28) Neer CS, Welsh RP. The shoulder in sports. Orthop Clin North Am. 1977;8:583-591.

(29) Hayes K, Walton JR, Szomor ZR, Murrell GA. Reliability of five methods for assessing shoulder range of motion. Aust J Physiother. 2001;47:289-294.

(30) Kendall F, McCreary EK, Provance PG. Muscles: Testing and Function. Baltimore, Md: Williams & Wilkins; 1993.

(31) Kelly BT, Kadrmas WR, Speer KP. The manual muscle examination for rotator cuff strength: an electromyographic investigation. Am J Sports Med. 1996;24:581-588.

(32) Wainner RS, Fritz JM, Irrgang JJ, et al. Reliability and diagnostic accuracy of the clinical examination and patient self-report measures for cervical radiculopathy. Spine. 2003;28:52-62.

(33) Hayes K, Walton JR, Szomor ZL, Murrell GA. Reliability of 3 methods for assessing shoulder strength. J Shoulder Elbow Surg. 2002; 11:33-39.

(34) Lauder TD, Dillingham TR, Andary M, et al. Predicting electrodiagnostic outcome in patients with upper limb symptoms: are the history and physical examination helpful? Arch Phys Med Rehabil. 2000;81:436-441.

(35) Magee DJ. Orthopedic Physical Assessment. 3rd ed. Philadelphia, Pa: WB Saunders Co; 1997.

(36) MacDonald PB, Clark P, Sutherland K. An analysis of the diagnostic accuracy of the Hawkins and Neer subacromial impingement signs. J Shoulder Elbow Surg. 2000;9:299-301.

(37) Calis M, Akgun K, Birtane M, et al. Diagnostic values of clinical diagnostic tests in subacromial impingement syndrome. Ann Rheum Dis. 2000;59:44-47.

(38) Drez D Jr. Suprascapular neuropathy in the differential diagnosis of rotator cuff injuries. Am J Sports Med. 1976;4:43-45.

(39) Tempelhof S, Rupp S, Seil R. Age-related prevalence of rotator cuff tears in asymptomatic shoulders. J Shoulder Elbow Surg. 1999;8:296-299.

(40) Milgrom C, Schaffler M, Gilbert S, van Holsbeeck M. Rotator-cuff changes in asymptomatic adults: the effect of age, hand dominance and gender. J Bone Joint Surg Br. 1995;77:296-298.

(41) Zehetgruber H, Noske H, Lang T, Wurnig C. Suprascapular nerve entrapment: a meta-analysis. Int Orthop. 2002;26:339-343.

(42) Iannotti JP, Zlatkin MB, Esterhai JL, et al. Magnetic resonance imaging of the shoulder: sensitivity, specificity, and predictive value. J Bone Joint Surg Am. 1991;73:17-29.

(43) Dumitru D. Electrodiagnostic Medicine. Philadelphia, Pa: Hanley and Belfus; 1995.

(44) Liveson JA, Ma DM. Laboratory Reference for Clinical Neurophysiology. Philadelphia, Pa: FA Davis Co; 1992.

(45) Casazza BA, Young JL, Press JP, Heinemann AW. Suprascapular nerve conduction: a comparative analysis in normal subjects. Electromyogr Clin Neurophysiol. 1998;38:153-160.

(46) Nardin RA, Rutkove SB, Raynor EM. Diagnostic accuracy of electrodiagnostic testing in the evaluation of weakness. Muscle Nerve. 2002;26:201-205.

(47) Romeo AA, Rotenberg DD, Bach BR Jr. Suprascapular neuropathy. J Am Acad Orthop Surg. 1999;7:358-367.

(48) Fabre T, Piton C, Leclouerec G, et al. Entrapment of the suprascapular nerve. J Bone Joint Surg Br. 1999;81:414-419.

(49) Skurja M, Monlux J. Case studies: the suprascapular nerve and shoulder dysfunction. J Orthop Sports Phys Ther. 1985;6:254-258.

(50) Ludig T, Walter F, Chapuis D, et al. MR imaging evaluation of suprascapular nerve entrapment. Eur Radiol. 2001;11:2161-2169.

(51) Ferrante MA, Wilbourn AJ. The utility of various sensory nerve conduction responses in assessing brachial plexopathies. Muscle Nerve. 1995;18:879-889.

(52) Murrell CA, Walton JR. Diagnosis of rotator cuff tears. Lancet. 2001;357(9258):769-770.

(53) Inokuchi W, Ogawa K, Horiuchi Y. Magnetic resonance imaging of suprascapular nerve palsy. J Shoulder Elbow Surg. 1998;7:223-227.

(54) Quinn SF, Sheley RC, Demlow TA, Szumowski J. Rotator cuff tendon tears: evaluation with fat-suppressed MR imaging with arthroscopic correlation in 100 patients. Radiology. 1995;195:497-500.

(55) Evancho AM, Stiles RG, Fajman WA, et al. MR imaging diagnosis of rotator cuff tears. AJR Am J Roentgenol. 1988;151:751-754.

(56) Neer CS. Impingement lesions. Clin Orthop. 1983;(173):70-77.

(57) Leroux JL, Thomas E, Bonnel F, Blotman F. Diagnostic value of clinical tests for shoulder impingement syndrome. Rev Rhum Engl Ed. 1995;62:423-428.

(58) Warner JJ, Micheli LJ, Arslanian LE, et al. Patterns of flexibility, laxity, and strength in normal shoulders and shoulders with instability and impingement. Am J Sports Med. 1990;18:366-375.

(59) Leroux JL, Codine P, Thomas E, et al. Isokinetic evaluation of rotational strength in normal shoulders and shoulders with impingement syndrome. Clin Orthop. 1994;(304):108-115.

(60) Babyar SR. Excessive scapular motion in individuals recovering from painful and stiff shoulders: causes and treatment strategies. Phys Ther. 1996;76:226-238.

(61) Belling Sorensen AK, Jorgensen U. Secondary impingement in the shoulder: an improved terminology in impingement. Scand J Med Sci Sports. 2000;10:266-278.

(62) Michener LA, McClure PW, Karduna AR. Anatomical and biomechanical mechanisms of subacromial impingement syndrome. Clin Biomech (Bristol, Avon). 2003;18:369-379.

(63) Perry J. Anatomy and biomechanics of the shoulder in throwing, swimming, gymnastics, and tennis. Clin Sports Med. 1983;2:247-270.

(64) Norkin C, Levangie PK. Joint Structure and Function. 2nd ed. Philadelphia, Pa: FA Davis Co; 1992.

(65) Luo ZP, Hsu HC, An KN. An in vitro study of glenohumeral performance after suprascapular nerve entrapment. Med Sci Sports Exerc. 2002;34:581-586.

(66) Sharkey NA, Marder RA. The rotator cuff opposes superior translation of the humeral head. Am J Sports Med. 1995;23:270-275.

(67) Thompson WO, Debski RE, Boardman ND III, et al. A biomechanical analysis of rotator cuff deficiency in a cadaveric model. Am J Sports Med. 1996;24:286-292.

(68) Fritz RC. Magnetic resonance imaging of sports-related injuries to the shoulder: impingement and rotator cuff. Radiol Clin North Am. 2002;40:217-234.

MK Walsworth, PT, MPT, ECS, OCS, is Staff Physical Therapist, Walter Reed Army Medical Center, Washington, DC.

JT Mills III, PT, MS, ECS, OCS, is Chief, Physical Therapy Service, McDonald Army Community Hospital, Ft Eustis, Va.

LA Michener, PT, PhD, ATC, SCS, is Assistant Professor, Department of Physical Therapy, Room 100, West Hospital Basement, Virginia Commonwealth University-Medical College of Virginia Campus, Richmond, VA 23298 (USA) ([e-mail]). Address all correspondence to Dr Michener.

All content of this article represents the shared work and responsibility of the authors. Mr Walsworth and Mi Mills provided concept/idea/project design, data collection, subjects, and facilities/equipment. Mr Walsworth provided project management and institutional liaisons. All authors provided writing, data analysis, and consultation (including review of manuscript before submission). The authors thank Venetia Valiga for providing the illustration of the suprascapular nerve.

The material in this manuscript was presented in part as the Expert Clinical Benchmarks Annual Robert M Kellogg Honorary Lecture for Excellence in Clinical Electrophysiology, 2003.

The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense.

This article was received October 18, 2002, and was accepted October 12, 2003.