Causes / typical injury mechanism: Glenoid fractures result from dislocation of the glenohumeral joint or blunt, high-energy trauma to the shoulder. Glenoid rim fractures most commonly occur with anterior or posterior shoulder dislocation from sports injuries or seizures. They can also occur following a direct blow or iatrogenically through suture anchor holes. Glenoid fossa fractures usually occur from high-energy trauma, with common causes including motor vehicle or motorcycle accidents and falls.

Classic history and presentation: Patients usually present with shoulder pain following an acute trauma or shoulder dislocation as described above. The affected arm may be held in adduction and internal rotation with pain limiting movement in all directions. The patient may report swelling, ecchymosis, and/or instability at the site of injury.

Incidence / prevalence: Glenoid fractures are uncommon. Scapular fractures comprise approximately 0.5% of all fractures, and glenoid fractures account for 10%-29% of these. Anterior glenoid rim or avulsion fractures occur in 5%-75% of anterior shoulder dislocations, while posterior glenoid rim fractures occur in 4%-11% of patients with an acute posterior dislocation.

• Age – Mostly younger patients (average age of 35 years).
• Sex / gender – Men are more frequently affected than women (4:1).

Risk factors:

• Shoulder instability
• Seizure disorder
• Trauma (humeral head driven against the glenoid fossa)

Pathophysiology: The glenoid process extends laterally from the body of the scapula and is comprised of the glenoid neck and glenoid cavity, which in turn is made up of the glenoid rim and glenoid fossa. It forms the socket of the glenohumeral joint, articulating with the humeral head.

• Glenoid neck: See scapula fracture.
• Glenoid fossa: Fractures occur when the humeral head is forcefully driven into the center of the glenoid, creating a transverse disruption that can propagate in various directions, depending on the direction of the force.
• Glenoid rim: True glenoid rim fractures occur when the humeral head strikes the rim with considerable force. Avulsion fractures occur when a dislocating humeral head applies a tensile force to the periarticular soft tissues of the shoulder.

Grade / classification system: Several classification systems exist for glenoid fractures. One widely used scheme is the Ideberg classification, which includes 6 general fracture types:

• Type Ia: Anterior glenoid rim fracture
• Type Ib: Posterior glenoid rim fracture
• Type II: Fracture line through glenoid fossa exiting glenoid neck inferiorly
• Type III: Fracture line through glenoid fossa exiting glenoid neck superiorly
• Type IV: Fracture line through glenoid fossa exiting scapula body medially (trans-scapular)
• Type Va: Combination of types II and IV
• Type Vb: Combination of types III and IV
• Type Vc: Combination of types II, III, and IV
• Type VI: Severe comminution (more than 2 articular fragments)

Although often used, this system does not predict morbidity or guide intervention, has low-to-moderate interobserver and intraobserver reliabilities, and approximately 25% of glenoid fractures cannot be classified.

A more recent AO Foundation and Orthopaedic Trauma Association classification system for scapula fractures has been demonstrated to be more reliable. It includes 3 general categories of glenoid fractures, with subclassifications based on fracture location within the fossa:

• F0: Fracture of the articular segment, not involving the glenoid fossa (glenoid neck)
• F1: Simple glenoid fossa fractures
  • 1.1: Anterior glenoid rim
  • 1.2: Posterior glenoid rim
  • 1.3: Transverse / short oblique
• F2: Multi-fragmentary glenoid fossa fractures:
  • 2.1: 3 or more articular fragments
  • 2.2: Central fracture-dislocation