Scapular Winging

The shoulder girdle is a remarkable and complex design that brings about the scapulohumeral rhythm, a smooth integration and coordination of several joints: scapulothoracic, acromioclavicular, sternoclavicular, and glenomhumeral joints.

The scapulothoracic articulation is one of the least congruent joints in the human body. The scapula has limited articulations and is dependent on mostly muscle activation for mobility and stability. This allows the shoulder joint to have great degree of mobility and accommodation at different arm positions.  Scapular stability is required to achieve maximal activation of all the muscles that arise from it. 

Scapular winging is classically defined as a prominence of the medial border of the scapula caused by a dynamic process secondary to neuromuscular imbalance in the scapulothoracic muscles. Two types of winged scapula have been described by Fiddian and King in 1984:

Static scapular winging is a fixed deformity in the shoulder girdle, spine, or ribs.  Dynamic scapular winging results from neuromuscular disorders. Based on anatomic etiology, there are 4 types of scapular winging:

Scapular winging is considered to a form of "scapular dyskinesia," which results from dynamic prominence of the medial border of the scapula secondary to neuromuscular imbalance in the scapulothoracic stabilizer muscles. The 2 most common causes of dynamic scapular winging are traumatic or idiopathic lesions of the long thoracic nerve (which innervates the serratus anterior muscle), and the spinal accessory nerve (which provides innervation to the trapezius).  In addition, dorsal scapular nerve injury, which affects the rhomboid muscles, may cause scapular winging. This is often underreported, as clinical examination of the rhomboids is difficulty due to its anatomical position deep to the trapezius muscles and the subtleness of scapular winging. 

Painless, asymmetrical scapular winging may be a feature of FSHD.  LGMD-2A produces symmetrical scapular winging.

Three main muscle that when weak, result in scapular winging:

Additional muscles that can result in scapular dyskinesia: 

Anatomy

Scapula

The scapula is a large, flat, triangular bone located on the dorsal aspect of the thorax, extending between the 2nd and 7th ribs.  It has 2 surfaces (anterior and posterior) and is marked by 3 bony prominences: the spine of scapula; the acromion; and the coracoid process. In addition there are 3 borders (superior, lateral, and medial) and 3 angles (superior, lateral, and inferior). The posterior surface of the scapula is subdivided into 2 unequal parts by the spine of the scapula. The portion of the scapula above the spine is called the supraspinous fossa and, below it, the infraspinous process. The scapular contains either the insertion or origin for 17 separate muscles. Scapulothoracic, scapulohumeral, and rotator cuff muscles to stabilize the scapula to the thorax, provide power to the upper limb, and synchronize glenohumeral motion. The scapulothoracic stabilizers include the serratus anterior, trapezius, rhomboid major and minor, and levator scapulae. Additional muscles with attachments to the scapula include the deltoid, supraspinatus, infraspinatus, subscapularis, teres minor, teres major, lattismus dorsi, long head of triceps, coracobrachialis, pectoralis minor, and omohyoid. The scapular can perform movements in a variety of different axes.

Arm abduction


Causes of winging of the scapulae include


Scapulo-peroneal syndrome 

Scapulo-peroneal syndrome is defined by weakness of the shoulder girdle muscles, leading to bilateral scapular winging, and peroneal muscles, leading to bilateral foot drop.

Long Thoracic Nerve Palsy

Anatomy:  Arises directly from the C5–C6–C7 roots, before the brachial plexus proper.  The nerve runs inferiorly to innervate only one muscle, the serratus anterior.  The serratus anterior muscle arises from the 1st to 10th ribs and inserts on the costal margin of the scapula.  Anatomically, the serratus anterior muscle can be thought of as having an upper portion, supplied by C5–C6 fibers, and a lower portion, supplied by C7 fibers.  The upper portion is responsible principally for scapular protraction, and the lower portion for scapular stabilization.  Protraction is the movement of the scapula forward along the chest wall.

Clinical:  Long thoracic nerve palsies may occur as part of a more widespread traumatic lesion affecting the cervical roots.  Although isolated long thoracic palsies have also been reported as a consequence of external compression and stretch, most result from neuralgic amyotrophy (NA) and is some case of NA.  amyotrophy, the long thoracic nerve is affected in isolation.  Patients describe severe pain in the shoulder region that lasts several days to weeks.  As the pain abates, patients note difficulty with shoulder movement.  

Weakness or paralysis of the serratus anterior characteristically results in “winging” of the scapula.  Winging from serratus anterior dysfunction becomes most pronounced when the arm is extended in front of the body.  As the serratus anterior normally pulls the scapula forward against the ribs, weakness of the serratus anterior results in the inferior tip of the scapula being displaced closer to the spine.  Because the serratus anterior is a shoulder stabilizer, other shoulder muscles may also appear weak (e.g., deltoid, supraspinatus, infraspinatus).  If these muscles are tested with the examiner’s hand pressed against the scapula, however, much of the “weakness” will disappear. 

Lateral winging of the scapula is characteristically caused by weakness of the trapezius or rhomboid muscles (or both). The winging is accentuated with arm abduction. 

Electrodiagnosis:  EMG is especially useful in trying to differentiate true neurogenic weakness from poor shoulder fixation and functional weakness.  As the long thoracic nerve has no cutaneous distribution, there is no area of altered sensation or numbness in isolated lesions of the long thoracic nerve.  One should look for evidence of a more widespread brachial plexus lesion, sensory nerve conduction studies should be performed, studying especially those  nerves that travel through the upper and middle trunks of the brachial plexus, and which have the same root innervation as the long thoracic nerve. These studies include the lateral antebrachial cutaneous, median, and radial sensory nerves.  

The electrodiagnosis relies on the needle EMG.  In long thoracic nerve palsy, abnormalities are limited to the serratus anterior muscle.  Unfortunately, the serratus anterior is a difficult muscle to study.  Although it can be sampled under the inferior angle of the scapula, it is most approachable with a needle where it arises from the mid-thoracic ribs in the mid-axillary line.  Caution must be taken to insert the needle over the rib proper and not into the interspace, where there is a risk of pleural puncture and pneumothorax.  Other C5–C6–C7-innervated limb muscles (e.g., biceps, deltoid, supraspinatus, infraspinatus, triceps, pronator teres) should be sampled to exclude a cervical radiculopathy, brachial plexopathy, or involvement of other proximal nerves.  In addition, the cervical paraspinal muscles should be checked to help exclude a more proximal lesion at the roots.

Spinal Accessory nerve palsy

Injury to the spinal accessory nerve can lead to dysfunction of the trapezius.  The trapezius is a major scapular stabilizer and is composed of three functional components.  It contributes to scapulothoracic rhythm by elevating, rotating, and retracting the scapula.  The superficial course of the spinal accessory nerve in the posterior cervical triangle makes it susceptible to injury.  Iatrogenic injury to the nerve after a surgical procedure (lymph node dissection) is one of the most common causes of trapezius palsy.  Dysfunction of the trapezius can be a painful and disabling condition.  The shoulder droops as the scapula is translated laterally and rotated downward.  Patients present with an asymmetric neckline, a drooping shoulder, winging of the scapula, and weakness of forward elevation. Winging of the scapula with the displacement of superior angle more laterally resulting in left shoulder droop.  The inferior angle is tilted more to the midline than the superior angle.  The anterior border of the trapezius appears cord-like due to paralysis, and reduced tone. Evaluation should include a complete electrodiagnostic examination.  If diagnosed within 1 year of the injury, microsurgical reconstruction of the nerve should be considered.  Conservative treatment of chronic trapezius paralysis is appropriate for older patients who are sedentary.  Active and healthy patients in whom 1 year of conservative treatment has failed are candidates for surgical reconstruction.  Studies have shown the Eden-Lange procedure, in which the insertions of the levator scapulae, rhomboideus minor, and rhomboideus major muscles are transferred, relieves pain, corrects deformity, and improves function in patients with irreparable injury to the spinal accessory nerve. 

Good results can be expected from a repair of the spinal accessory nerve if it is performed within twenty months after the injury, as the nerve is a purely motor nerve and the distance from the injury to the motor end plates is short.  Muscle transfer should be performed in patients with spontaneous trapezius palsy, when previous nerve surgery has failed, or when the time from the injury to treatment is over twenty months.  Treatment is less likely to succeed when the patient is older than fifty years of age or the palsy was due to a radical neck dissection, penetrating injury, or spontaneous palsy.