Shoulder Injury Essentials: Deformities, Fractures, Sprains

Shoulder Anatomy and Injury Mechanisms

Step Deformity

The distal end of the clavicle lies superior relative to the acromion process. This is a typical sign of an AC (acromioclavicular) sprain or dislocation.

Scapulohumeral Rhythm Explained

This refers to the movement of the scapula relative to the movement of the humerus throughout the full range of abduction. It occurs in distinct phases:

• 0-30 degrees of humeral abduction: No scapular movement (setting phase).
• 30-90 degrees of abduction: 2 degrees of humeral elevation = scapular abduction and upward rotation of 1 degree (2:1 ratio).
• 90-180 degrees of abduction: 1 degree of humeral elevation = scapular abduction and upward rotation of 1 degree (1:1 ratio).

Static Scapular Winging

The medial border of the scapula moves away from the posterior chest wall. Potential causes include:

• Structural deformity of the scapula, clavicle, spine, or ribs.
• Serratus anterior weakness.
• Scoliosis.
• Injury to the long thoracic nerve.

Rotary Winging

The inferior angle of one scapula is rotated farther from the spine when compared to the inferior angle of the other scapula. This can be caused by:

• A lesion of the long thoracic nerve affecting the serratus anterior.
• Rhomboid weakness.

Dynamic Winging (Scapular Dyskinesia)

Also known as “scapular dyskinesia,” this occurs when the medial border of the scapula moves away from the posterior chest during movement. Possible causes include:

• A lesion of the long thoracic nerve affecting the serratus anterior.
• Trapezius palsy (spinal accessory nerve).
• Rhomboid weakness.
• Multidirectional instability.
• Painful shoulder conditions.

Clavicle Fracture

These fractures usually occur in the middle one-third of the clavicle, often as a greenstick type in young athletes. The common mechanism of injury (MOI) is:

• A fall on an outstretched hand/arm (FOOSH).
• A fall directly on the tip of the shoulder.

Scapular Fracture

A partial or complete interruption in the continuity of the scapula.

Humerus Fracture Types

• Shaft Fracture: Typically caused by a direct blow.
• Proximal Fracture: Resulting from a direct blow, dislocation, or a FOOSH injury.
• Epiphyseal Fracture: Caused by a direct or indirect blow that travels along the long axis of the bone.

Sternoclavicular (SC) Sprain

The medial end of the clavicle is usually displaced upward and anterior. If the clavicle is displaced posteriorly, pressure may be placed on blood vessels, the esophagus, or the trachea, potentially causing a life-threatening situation.

SC Sprain Grades:

• Grade 1: Little pain and disability, point tenderness, no visible deformity.
• Grade 2: Subluxation of the SC joint, visible deformity, pain, swelling, point tenderness, inability to abduct the shoulder or bring the arm across the chest.
• Grade 3: Complete dislocation with clavicle displacement, severe pain, swelling, and significant disability.

Acromioclavicular (AC) Sprain

Commonly known as a “separated shoulder.” Common mechanisms of injury (MOIs) include:

• Direct impact to the tip of the shoulder.
• A fall on an outstretched hand/arm (FOOSH).

Glenohumeral Joint Sprain

Common mechanisms of injury (MOIs) include:

• Forced abduction and/or external rotation.
• Direct blow to the shoulder.
• FOOSH with the arm in an upward position.

Symptoms often involve a stretch to the joint capsule, pain during arm movement (especially when re-creating the MOI), decreased range of motion (ROM), and pain with palpation.