eMedicine Specialties > Sports Medicine > Neurological

Suprascapular Neuropathy

Jonathan C Reeser, MD, PhD, Department of Physical Medicine and Rehabilitation, Marshfield Clinic
Contributor Information and Disclosures

Updated: Apr 16, 2008

Introduction

Background

Athletes who participate regularly in overhead sports frequently report shoulder pain. Sports such as baseball, volleyball, and tennis demand skills that place substantial load on the athlete’s shoulder when the upper limb is in an overhead or abducted and externally rotated position.^{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21} Epidemiologic studies have demonstrated that athletes who participate in these and other overhead sports are at higher risk for overuse injuries of the upper limb in general and overuse injuries of the shoulder in particular, including rotator cuff tendinopathy and attritional injury to the glenoid labrum.^{6, 22, 23, 24, 25, 26} One often overlooked cause of shoulder pain among such athletes is infraspinatus syndrome.

Infraspinatus syndrome is defined as a condition of frequently painless atrophy of the infraspinatus muscle caused by suprascapular neuropathy. The syndrome typically causes symptoms that mimic those of rotator cuff tendinopathy, and the diagnosis may be overlooked until the symptomatic athlete fails to have a therapeutic response to a traditional rotator cuff treatment program.

For excellent patient education resources, visit eMedicine's Osteoporosis and Bone Health Center. Also, see eMedicine's patient education article Shoulder and Neck Pain.

Related eMedicine topics:
Nerve Entrapment Syndromes
Overuse Injury
Rotator Cuff Injury
Shoulder Impingement Syndrome

Related Medscape topics:
Resource Center Arthritis
Resource Center Exercise and Sports Medicine

Frequency

United States

Although the true incidence is unknown, several authors believe that infraspinatus syndrome is underreported. Although the condition has been described in a variety of athletes, including weight lifters and baseball players (and has been reported as an occupational injury among newsreel cameramen), the prevalence of infraspinatus syndrome appears to be highest among volleyball players.^{1, 4, 7, 9, 11, 12, 13, 15, 18, 19, 21, 22, 27, 28, 29} Studies have reported that 13-45% of elite volleyball athletes have signs of suprascapular neuropathy.^{7, 9, 11, 12, 13, 15, 18, 19, 21, 29} This observation lends credence to the term “volleyball shoulder.”

Functional Anatomy

The suprascapular nerve (SSN) is a mixed nerve that provides the motor innervation of the supraspinatus and infraspinatus muscles and the sensory and proprioceptive innervation of the posterior aspect of the glenohumeral joint, as well as the acromioclavicular joint, subacromial bursa, and scapula.^{30, 31, 32, 33} This nerve carries afferents from approximately 70% of the shoulder joint. The nerve arises from the upper trunk of the brachial plexus and is composed predominantly of C5-C6 level fibers. Some authors suggest that the nerve may also receive contributions from the fourth cervical nerve root in as many as 25% of people. Although the suprascapular nerve is a mixed nerve, it typically carries no cutaneous afferent fibers. The SSN is thought to carry cutaneous afferent fibers in only 15-25% of the general population.

In its initial course, the SSN courses posterior and parallel to the inferior belly of the omohyoid muscle and anterior to the trapezius muscle in the posterior triangle of the neck. The nerve then passes dorsally through the suprascapular notch, where it is retained by the transverse scapular ligament, into the suprascapular fossa, where 2 motor branches to the supraspinatus muscle originate. Just proximal to the suprascapular notch, the SSN gives off the superior articular branch, which travels with its fellow nerve through the notch before proceeding laterally to innervate the acromioclavicular joint and its associated bursa and the coracoclavicular and coracohumeral ligaments (see Image 1).

Cadaveric studies reveal that the suprascapular notch may be either U -shaped or V -shaped, and some physicians believe that this anatomic variation may be related to an individual’s predisposition to SSN entrapment at this level. After supplying the supraspinatus, the nerve subsequently travels inferolaterally to wrap around the spine of the scapula at the spinoglenoid notch.

Sport-Specific Biomechanics

Anatomic considerations suggest that at least 2 sites of potential SSN entrapment exist: the suprascapular notch and the spinoglenoid notch. Although the distribution of injury at these 2 sites varies in published case series, findings in the available literature suggest that the most common site of entrapment among volleyball athletes is the spinoglenoid notch.^{12, 34} Selective involvement of the SSN at this level results in the isolated atrophy and weakness of the infraspinatus muscle that characterizes infraspinatus syndrome. Interestingly, no consensus about the precise mechanism of suprascapular neuropathy exists. There is, however, general agreement that the SSN (like other peripheral nerves) may be vulnerable to injury due to compressive forces or repetitive distraction.

The importance of the scapula in the throwing motion and other overhead sport-specific skills is now well appreciated. As the scapula protracts and retracts with functional use of the upper limb, some traction of the SSN can be expected to occur at 1 or both notches through which it traverses. This concept forms the basis of the “sling effect," which proposes that, in certain functional positions of the upper limb, the SSN is exposed to damaging sheer stress in the suprascapular notch. Similar reasoning leads to the prediction that the nerve is vulnerable to traction injury as it bends around the spine of the scapula at the spinoglenoid notch.
 
Some authors have proposed that individuals in whom the SSN angles sharply around the spinoglenoid notch may be particularly prone to this mechanism of injury. The so-called "SICK scapula" (defined by Burkhart et al as scapular protraction, inferior border prominence, coracoid tightness, and scapular dyskinesis) that occurs in adaptive response to chronic shoulder overuse and functional instability may also theoretically contribute to the increased tension on the SSN via the sling effect.⁶

Demirhan et al reported that the spinoglenoid ligament, when present, inserts into the posterior glenohumeral capsule.³⁵ They also observed that the ligament becomes taut when the ipsilateral upper limb is adducted across the body or internally rotated; this motion results in traction of the SSN at the spinoglenoid notch. Other possible mechanisms in which the SSN may be compromised include Sandow and Ilic’s proposal that the SSN nerve is vulnerable to direct compression by the medial border of the spinatus tendons at the spinoglenoid notch when the upper limb is abducted and externally rotated.¹⁸ This mechanism would appear to be a further manifestation of posterior (or internal) impingement.

Ferretti, who has written extensively about volleyball shoulder, hypothesized that the mechanism of selective injury to the terminal portion of the SSN in volleyball players is traction on the nerve due to repetitive, sudden, eccentric activation of the infraspinatus during the deceleration phase of the floater serve.^{12, 15, 21}

Several studies have reported that the SSN may be compressed in the vicinity of the spinoglenoid notch by ganglion cysts arising from the glenohumeral joint.^{25, 34, 36, 37, 38} These ganglion cysts, like Baker cysts that occur in the popliteal fossa after meniscal degeneration or injury, are likely to be the consequence of an injury to the posterior glenoid labrum with resultant leakage of synovial fluid. Finally, some investigators have also proposed that suprascapular neuropathy can result from ischemia caused by migration of posttraumatic microemboli from the suprascapular artery (which generally follows a course parallel to the companion nerve) to the vasa nervorum.

The shoulder joint, or glenohumeral joint, is the most mobile joint in the human body.³ Unfortunately, this mobility comes at the cost of stability, of which the bony components in the joint provide little. Ligamentous structures and the fibrocartilaginous glenoid labrum provide additional static stability, particularly at the extremes of glenohumeral motion. The supraspinatus and infraspinatus muscles are part of the rotator cuff, which dynamically stabilizes the shoulder joint through a precise system of force couples and agonist-antagonist coactivation, keeping the humeral head centered in the glenoid socket. SSN dysfunction disturbs this mechanism and could potentially result in proximal migration and elevation of the humeral head, with consequent secondary impingement of the supraspinatus tendon beneath the coracoacromial ligament.

Related eMedicine topics:
Multidirectional Glenohumeral Instability
Nerve Entrapment Syndromes
Shoulder Impingement Syndrome

Related Medscape topics:
Resource Center Arthritis
Resource Center Exercise and Sports Medicine

Clinical

History

• Although knowledge of the clinical symptom complex has improved since Kopell and Thompson first reported shoulder pain as the result of SSN injury in 1959, from a practical standpoint, the diagnosis of infraspinatus syndrome remains largely a diagnosis of exclusion unless the clinician remains alert to the diagnostic possibility when the affected athlete initially presents for treatment.
• The typical patient is a young overhead athlete who reports vague posterior shoulder pain.
• Although case reports of bilateral involvement exist, symptoms are typically unilateral and involve the dominant side.
• Male athletes account for most of the cases reported in the literature, but Ferretti et al reported one series of 38 athletes in which the incidence was approximately equal among males and females.¹²
• More often that not, the pain (when present) is described as a deep, dull, aching discomfort.
• Activities that involve overhead motions or sport-specific skills may exacerbate symptoms. Diagnostic signs may include weakness and compromised endurance in performing overhead, sport-specific skills.
• Because of the anatomy (see Functional Anatomy), more distal nerve injuries are often relatively painless.
  • In particular, nerve injuries at the spinoglenoid notch that result in selective denervation of the infraspinatus muscle may be insidious in their onset due to the relative lack of pain.
  • In Ferretti et al's series, elite volleyball players with isolated atrophy of the infraspinatus generally did not report any pain or sports-related functional disability.¹² 
• Based upon anatomic considerations, it is reasonable to predict that athletes with more proximal lesions of the SSN that affect both the supraspinatus and infraspinatus muscles are more likely to have pain and symptom-limited function than are individuals with distal nerve lesions that affect only the infraspinatus.
• Genetic factors undoubtedly play a role in the predisposition and susceptibility of individual athletes to suprascapular neuropathy, but the specific factors that are involved have yet to be elucidated.

Physical

• Atrophy of the supraspinatus and/or infraspinatus muscles may be present on the physical examination, depending on the site of the nerve entrapment (see Image 1).
• Note that supraspinatus involvement may be frequently overlooked because of the bulk of the overlying trapezius.
• Manual muscle testing may reveal relative weakness of ipsilateral shoulder abduction (a function of the supraspinatus muscle in addition to the deltoid muscle) and/or weakness of external rotation (a function of the infraspinatus muscle in addition to the teres minor muscle).
• The athlete may report worsening pain with cross-body adduction of the ipsilateral upper limb.
• Pressure applied over the suprascapular or spinoglenoid notches may elicit pain.
• Muscle stretch reflexes are unaffected by this condition.
• Rarely, cutaneous appreciation of sensory modalities may be affected in an approximate axillary nerve distribution.

Causes

• Sports that place a substantial load on the athlete’s shoulder when the upper limb is in an overhead or abducted and externally rotated position may precipitate this condition.
  • Suprascapular neuropathy causes infraspinatus syndrome.
  • The site of suprascapular neural entrapment determines whether the infraspinatus muscle alone or both the supraspinatus and infraspinatus muscles are affected.
• Although sports-related overuse mechanisms of SSN injury are the most common causes, the SSN can also be damaged as a result of direct trauma as well as iatrogenic factors.
• The relationship of the nerve to the clavicle makes it vulnerable to injury after a clavicular fracture occurs.
• Surgical procedures involving the shoulder (eg, Bankhart repair) can place the nerve at risk for either direct injury or indirect injury. Interestingly, SSN neuropathy has also been reported to occur after positioning patients for spinal surgery.
• Other diagnoses should be considered.
  • Most commonly, the clinician diagnoses rotator cuff tendinopathy and prescribes a conservative treatment program. Because the rehabilitation programs for rotator cuff tendinopathy and infraspinatus syndrome are similar, in many (perhaps most) instances, the patient's condition improves, and the correct diagnosis goes unrecognized.
  • Delayed-onset muscular soreness may be present, but this soreness is not expected to progress over 3 weeks. Rather, symptoms of delayed-onset muscular soreness tend to spontaneously resolve over 7-10 days.

Related eMedicine topics:
Clavicle Fractures
Clavicular Injuries
Rotator Cuff Injury

Related Medscape topics:
Resource Center Exercise and Sports Medicine
Resource Center Fracture

References

• Cervical Disc Injuries
• Cervical Radiculopathy
• Rotator Cuff Injury
• Shoulder Impingement Syndrome
• Superior Labrum Lesions

• Bone Health Center
• Shoulder and Neck Pain Overview
• Shoulder and Neck Pain Causes
• Shoulder and Neck Pain Symptoms
• Shoulder and Neck Pain Treatment