A winged scapula, or scapula alata, is a condition where the shoulder blade protrudes from the upper back instead of lying flat against the rib cage. This abnormal prominence gives the shoulder blade a wing-like appearance, often visible when the arm is moved or when pushing against a surface. The condition arises because the muscles stabilizing the scapula against the posterior chest wall have become weak or paralyzed. This loss of muscle control disrupts the coordinated motion between the shoulder blade and the upper arm, leading to limited function, pain, and deformity.
Key Muscles and Nerves Responsible for Scapular Stability
The scapula relies entirely on a complex network of muscles to keep it anchored and moving correctly, as it is not connected to the thoracic cage by a joint. Dysfunction in this system leads to instability. The primary stabilizers involved in preventing a winged scapula are the Serratus Anterior, the Rhomboids, and the Trapezius muscles.
The Serratus Anterior muscle pulls the shoulder blade forward and wraps it around the rib cage to maintain close contact with the chest wall. This muscle is controlled exclusively by the Long Thoracic Nerve, which travels a long, superficial course along the rib cage, making it vulnerable to injury.
The Rhomboid muscles (major and minor) pull the scapula toward the spine and stabilize the medial border, receiving signals from the Dorsal Scapular Nerve. The Trapezius muscle is responsible for elevating, retracting, and rotating the scapula, and it is innervated by the Spinal Accessory Nerve.
Primary Causes: Neurological Damage
Damage to one of the three main stabilizing nerves is the most common cause of scapular winging. The specific nerve injured dictates the pattern of winging and the resulting functional deficit. This nerve-related paralysis is often categorized by the type of winging it produces, with the Long Thoracic Nerve being involved in the most frequent presentation.
Long Thoracic Nerve Injury
Injury to the Long Thoracic Nerve (LTN) paralyzes the Serratus Anterior muscle, causing the most common form known as medial scapular winging. This paralysis prevents the muscle from holding the scapula against the rib cage, causing the medial border and inferior angle to protrude significantly. The LTN is susceptible to damage due to its long course.
Injuries often occur from blunt trauma, sudden shoulder depression, or iatrogenic injury during surgeries like mastectomies or axillary lymph node dissection. Non-traumatic causes include inflammatory conditions like Parsonage-Turner Syndrome or repetitive strain from overhead activities.
Spinal Accessory Nerve Injury
Damage to the Spinal Accessory Nerve (SAN) paralyzes the Trapezius muscle, leading to lateral scapular winging. This weakness causes the shoulder to droop and the scapula to rotate downward and displace laterally. The superficial course of the SAN in the posterior triangle of the neck makes it highly vulnerable to iatrogenic injury.
Surgical procedures, such as lymph node biopsies or neck dissections, are the most frequent mechanism of injury. Trauma, including wrenching injuries to the neck or arm, can also cause damage.
Dorsal Scapular Nerve Injury
The Dorsal Scapular Nerve (DSN) controls the Rhomboid muscles, and its injury leads to a more subtle form of winging that is sometimes overlooked. Rhomboid weakness causes the scapula to drift away from the midline, resulting in slight lateral winging or instability during arm movements.
The DSN can be compressed as it passes through the middle scalene muscle in the neck, often linked to muscle hypertrophy from heavy weightlifting. Traction injury to the C5 nerve root, from which the DSN originates, can also cause rhomboid paralysis following motor vehicle accidents or heavy lifting.
Secondary Causes: Structural and Muscular Strain
While nerve lesions cause the most dramatic presentation of a winged scapula, secondary causes involve non-neurological factors that disrupt the shoulder blade’s mechanics, resulting from muscular imbalance or structural problems.
Muscular strain and overuse injuries, especially in athletes performing repetitive overhead motions, can lead to fatigue and weakness in the scapular stabilizers. This fatigue disrupts the coordinated scapulohumeral rhythm, resulting in apparent winging, sometimes called scapular dyskinesis. Direct muscle tears or avulsions can also eliminate the stabilizing function of the Serratus Anterior or Rhomboids.
Structural issues in the shoulder or surrounding area also contribute to abnormal scapular positioning. Conditions like rotator cuff pathology or shoulder instability force the body to compensate, overloading and fatiguing the stabilizing muscles. Rare causes include bony abnormalities of the scapula, such as osteochondromas, or deformities of the ribs or spine.
Pinpointing the Specific Cause Through Diagnosis
Determining the exact cause of scapular winging is essential for dictating the appropriate treatment path. Diagnosis begins with a detailed physical examination to visually observe the winging and its pattern. The location of the protrusion is key; for instance, medial winging is accentuated during a wall push-up test, suggesting Long Thoracic Nerve involvement and Serratus Anterior weakness.
Lateral winging is often assessed during arm abduction against resistance to test the Trapezius muscle, or during arm extension to check the Rhomboids. Physicians use electrodiagnostic tests, specifically Electromyography (EMG) and Nerve Conduction Studies (NCS), to confirm the diagnosis. These tests evaluate the electrical activity of the muscles and nerves, helping to differentiate between a primary muscle disorder and a neurological lesion.
Imaging studies are used to rule out structural or bony abnormalities contributing to the winging. X-rays can help identify cervical spine disease or a fracture, while Magnetic Resonance Imaging (MRI) is useful for visualizing soft tissues. MRI can show signs of acute denervation, such as muscle edema or atrophy in the affected muscles, which helps confirm the diagnosis and localize the site of nerve injury.