By linking the upper extremity to the axial skeleton, the scapula plays an important role in the function of the arm. Fractures of the scapula are somewhat uncommon, comprising less than 1% of all fractures. The low incidence may be due to its shape or position between muscle layers on the chest wall. Most scapula fracture are secondary to shoulder instability or high energy trauma imparted to the chest wall. High energy fractures have a 35-98% rate of associated injury including: ipsilateral chest wall injuries, pneumothorax, pulmonary contusion, brachial plexus injury, spine injury and skull fracture.
The scapula is a flat triangular bone that links the upper extremity to the axial skeleton and provides a surface for the origin or insertion of 17 muscles. The anterior surface is composed of the subscapular fossa, which is the site of the origin of the subscapularis muscle. The posterior surface is divided by the transverse projection known as the scapular spine which ascends to form an anteriorly projecting hook known as the acromion. The acromion forms an articulation with the clavicle. The surface superior to the scapular spine is the suprasinatus fossa and is the origin of the supraspinatus muscle. Inferior to the scapular spine is the infraspinatus fossa which is the site of origin for the infraspinatus and tere muscles. Another hook-like projection comes off of the scapula anteriorly and is the origin of the short head of the biceps, coracobrachialis and the coraco-humeral and coraco-acromial ligaments. This is an important anatomical landmark in anterior approaches to the shoulder as it aids in identifying the axillary and musculocutaneuous nerves.
The glenoid is the oval saucer shaped portion of the scapula that articulates with the humeral head. The glenoid is lined by a circular fibrocartilage called the labrum that deepens the glenoid surface to increase the stability of the glenohumeral articulation. In shoulder instability, damage to the labrum by avulse a piece of the glenoid articular surface and this is known as a boney Bankart lesion.
There are numerous classification systems and they are usually divided by the anatomic area of the scapula.
Zdravkovic and Damholt divided the scapula anatomicially into:
Type I - scapula body
Type II- apophyseal fractures including the acromion and coracoid
Type III - superolateral angle fractures including the glenoid and scapular neck
Ideberg classified just glenoid fractures into five types:
Type I - avulsion fracture of the anterior margin
Type II - transverse or oblique fracture exiting inferiorly
Type III - oblique fracture exiting superiorly, often associates with acrmioclavicular joint injury
Type IV - transverse fracture exiting the medial border
Type V - combination of type II and type IV
Kuhn classified acromial fractures:
Type I - minimally displaced
Type II - displaced, but no reduction in subacromial space
Type III - displaced fracture with reduction of the subacromial space.
Ogawa classified coracoid fractures based on the fractures relationship to the coraco-clavicular ligament.
The OTA classification:
Type A: scapula, extraarticular
A1: scapular processes
A1.1 acromion, simple
A1.2 acromion, comminuted
A2: scapular body
A2.3 glenoid neck
A3: extraarticular, complex
A3.1 glenoid neck plus body
A3.2 glenoid neck plus clavicle, simple
A3.3 glenoid neck plus clavicle, comminuted
Type B: scapula, intraarticular glenoid
B1: glenoid impacted
B1.1 anterior rim
B1.2 posterior rim
B1.3 inferior rim
B2: glenoid, nonimpacted
B2.1 anterior rim, free
B2.2 posterior rim, free
B2.3 antior/posterior rim with glenoid neck
B3: glenoid complex
B3.1 comminuted, intraarticular
B3.2 comminuted with glenoid neck
B3.3 comminuted with clavicle fracture
Patients typically present with the arm adducted against the body and reluctance to move the arm. If no ipsilateral upper extremity fracture is present, there may be no deformity of the arm, however, scapular neck fractures may present with a depressed shoulder. There is typically tenderness to palpation over the site of the facture posteiroly and variable amount of edema and ecchymosis. Pulmonary distress should raise suspicion or pulmonary contusion or pneumothorax. Non-acute injuries may present with pain and weakness upon testing the rotator cuff.
The physical exam will typically reveal varying edema and ecchymosis over the shoulder and scapula. There will be tenderness to palpation and pain with range of motion of the shoulder. A full trauma evaluation should ensue with special attention to the chest wall, spine and neurovascular exam of the upper extremity. The chest wall and clavicle should be palpated or associated rib or clavicle fractures and subcutaneous crepitus that may be a sign of pneumothorax.
Radiographic evaluation should begin with an AP chest radiograph. This will give an assessment of the ribs, lungs and clavicles, but often scapula fractures are difficult to observe. A dedicated AP, axillary lateral and Y-view of the scapula should be obtained. For fractures that appear to involve the glenoid or coracoid, CT scan with reconstructions are often quite useful for operative decision making and planning.
Most non-articular fractures of the scapula are treated non-operatively with brief sling immobilization for comfort and early shoulder range of motion. Nonunion is believed to be rare.
Operative treatment is controversial, but relative indications include: displaced intra-articular glenoid fractures involving >25% of the articular surface, scapular neck fractures with >40 degrees of angulation, scapular neck fracture with associated clavicle fracture (floating shoulder), articular step off greater than 2mm and coracoid fractures resulting in AC joint dysfunction.
Displaced glenoid fractures are usually treated with open reduction and internal fixation with screws. Arthroscopic reduction and internal fixation has also been successful for some fracture patterns. Os acromiale should be ruled out prior to treating a acromial fracture. Tension banding or dorsal plating may stabilize these fratures. Coracoid fractures resulting a functional grade III AC separation should be treated with open reduction and internal fixation with transclavicular screw and suturing.
Post traumatic arthiritis
Neurovascular damage - suprascapular nerve injury has been reported for scapular spine fractures
Compartment syndrome- of the supraspinatus and infraspinatus fossa have been reported.
Red Flags and controversies
Indications for operative treatment
It appears that most non-articular fractures treated non-operatively achieve acceptable function and minimal residua. Pain althought results among studies have varied. Results of non-operatively treated intraarticular glenoid fractures are sparse, but appear to fare worse than non-articular fractures resulting in restricted painful movement. Results of open reduction and internal fixation of intra-articular glenoid fractures have been reported to be good in the few small series in the literature.