Causes / typical injury mechanism: Glenohumeral arthritis is a degenerative joint disease that involves damage to the articular cartilage surface of the humeral head and glenoid. The typical cause is primary osteoarthritis, which often does not have a discrete injury but instead results from long-term wear and tear of the joint surfaces. Secondary causes include rotator cuff tear arthropathy (degeneration of the glenohumeral joint after untreated rotator cuff tears), posttraumatic arthritis, postsurgical arthritis, chronic dislocation arthropathy, inflammatory arthritis (such as rheumatoid arthritis), septic arthritis, avascular necrosis, and neuropathic causes (eg, Charcot arthropathy).

Classic history and presentation: Patients with classic primary osteoarthritis present with pain with shoulder motion and limited range of motion. Symptoms are often insidious and not related to a specific injury or event, although a recent injury may aggravate these symptoms. Patients will often describe limitations in daily activities or hobbies / sports.

Prevalence:

• Age – Glenohumeral arthritis incidence increases with age. It is uncommon in patients younger than 40 years and more common in patients 60 years and older.
• Sex / gender – Overall, men and women are equally affected by glenohumeral arthritis.

Risk factors:

• Older age
• Prior trauma / dislocation / surgery to the shoulder
• Rheumatoid arthritis
• Heavy manual labor
• Heavy weightlifting

Pathophysiology: Regardless of the underlying cause, glenohumeral arthritis occurs due to loss of the smooth articular cartilage surfaces of the humeral head and glenoid articulation. Commonly, there is destruction of the joint space with large osteophytes on the humeral head and glenoid.

Grade / classification system: The most widely used classification for glenohumeral arthritis is the Walch classification, which describes the degenerative wear pattern of the glenoid (concentric, posterior erosion, or dysplastic). This classification system is most relevant for surgical planning.

• Type A: centered humeral head, concentric wear, no subluxation of the humeral head
  • A1: minor central erosion
  • A2: major central erosion, humeral head protruding into the glenoid cavity
• Type B: humeral head subluxated posteriorly, biconcave glenoid with asymmetric wear
  • B1: narrowing of the posterior joint space, subchondral sclerosis, osteophytes
  • B2: biconcave aspect of the glenoid with posterior rim erosion and retroverted glenoid
  • B3: monoconcave and posterior wear with more than 15 degrees retroversion or more than 70% posterior humeral head subluxation, or both
• Type C
  • C1: dysplastic glenoid with more than 25 degrees retroversion regardless of the erosion
  • C2: biconcave, posterior bone loss, posterior translation of the humeral head
• Type D
  • Glenoid anteversion or anterior humeral head subluxation less than 40 degrees