Primary osteoarthritis of the glenohumeral joint is uncommon relative to other major joints, has the highest average
age of onset, and presents more frequently in females.²³,⁸⁴,⁹⁸ When it occurs in men and younger individuals, it is often related to acute or repetitive trauma, and is often associated with a posterior glenoid bone loss and on occasion osteochondral fracture (Fig. 22-1).⁵⁶ Posttraumatic osteoarthritis and posterior subluxation of the humeral head may develop and is associated with posterior glenoid bone loss. Glenoid dysplasia, glenoid hypoplasia, and static subluxation of the humeral head may increase the risk of developing osteoarthritis.¹¹⁵,¹²⁰ Secondary osteoarthritis may be related to a previous fracture, chronic dislocation, or instability, or may be the result of failed surgical attempts to correct glenohumeral instability. Whether it is the result of an age-related inability to accommodate to normal forces or a failure to respond to excess loading, the process is an imbalance between reparative and degradative factors. The disorder is mechanically driven and biomechanically mediated.²⁹

Articular changes are characterized by asymmetric joint space narrowing, subchondral sclerosis, cyst formation, and development of large osteophytes. Early articular thinning, surface fibrillation, and fissuring may remain subclinical for years.¹³,²⁸ These changes usually begin on the glenoid and then progress to the humeral head. Hypertrophic osteophyte formation occurs circumferentially around the neck of the humerus and glenoid rim. These osteophytes occupy intra-articular volume and restrict capsular excursion. Asymmetric contracture of the anterior capsule and subscapularis progressively limits external rotation of the arm and causes obligate posterior translation of the humeral head relative to the glenoid. Preferential posterior glenoid erosion occurs, and a crista may develop between the intact anterior glenoid cartilage and the posteriorly eburnated bone. Osteochondral loose bodies may float within the recesses of the joint or may attach to adjacent bone or synovium.

Patients with primary osteoarthritis frequently present with complaints of shoulder pain and restricted motion. Although there exists a global loss of motion, the most profound losses usually develop in forward elevation and external rotation of the arm. Patients often complain of difficulty sleeping at night, especially on the affected side.⁷⁴ They may also describe a sense of weakness and atrophy. In contrast with rheumatoid arthritis, rotator cuff defects do not commonly occur in association with osteoarthritis.

Severe secondary or posttraumatic osteoarthritis may result from identifiable insults such as fracture, chronic dislocation, or surgery.⁵,⁵²,¹¹⁰ Alterations in the joint anatomy, biology, or mechanics will contribute to the development of arthritis or osteonecrosis. The reported rate of osteonecrosis associated with proximal humerus fractures varies according to the severity of injury, personality of the fracture, and method of treatment.⁴²,⁴⁷,⁵⁸,⁶²,¹⁰⁶ Traumatic and iatrogenic intra-articular fractures may result in some degree of arthropathy because of intra-articular incongruity or the development of osteonecrosis.³⁸,⁴⁸ Chronic unreduced dislocations will develop softening and fragmentation of the cartilage and subchondral bone in the absence of normal physiologic joint forces. Large articular impression fractures will further contribute to the joint destruction. Osteoarthritis in the setting of fracture or chronic dislocation may result from a combination of intra-articular injury, malunion, instability, vascular disruption, and capsular contracture. Treatment of these problems can be very complex.

Iatrogenic causes of osteoarthritis may follow the treatment of instability. Periarticular implants that have been improperly placed or have dislodged may abrade the articular surfaces.⁹⁰,¹¹⁰,¹²⁸ Intra-articular or extra-articular bone augmentation may lead to impingement, articular abrasion, and abnormal contact forces.⁵² Procedures that are associated with excessive scarring (Bristow) may result in secondary osteoarthritis through pathologic compressive and shear forces across the articular surfaces.⁷⁰ Intra-articular fractures as a result of posterior glenoid osteotomy may result in a combination of osteonecrosis and osteoarthritis.⁴⁸

Capsulorrhaphy arthropathy describes the arthritic condition that follows excessive surgical tightening of one side of the joint in the treatment of instability.⁴⁵ This complication occurs more commonly after nonanatomic repairs such as the Putti-Platt, Bristow, or Magnuson-Stack reconstruction.⁴⁰,⁴⁶,⁵³,⁷⁰ However, it may also occur after a unidirectional repair in the treatment of multidirectional instability or excessive tightening of an “anatomic” repair.⁷¹ Excessive anterior tightening after an anterior repair will restrict
external rotation of the arm and push the humeral head posteriorly. Attempts to externally rotate the arm will lead to further obligate posterior translation of the humeral head relative to the glenoid. This constant eccentric loading of the glenoid results in posterior glenoid erosion and rapid destruction of the joint over a 10- to 15-year time period.

Rheumatoid arthritis is the most common form of inflammatory arthritis and is representative of the pathologic and clinical manifestations seen in the glenohumeral joint. Shoulder pain develops in up to 90% of patients with rheumatoid arthritis, with 30% to 60% of patients experiencing significant pain or functional impairment.⁹⁹,¹¹² Symptomatic shoulder involvement typically occurs in early middle-aged females who test positive for rheumatoid factor and variably involves the acromioclavicular joint, subacromial bursa, rotator cuff, and glenohumeral joint. Although the shoulder is commonly affected, rarely is it the primary manifestation of the disease or the only involved joint. The clinical course is one of insidious onset and gradual progression of pain and dysfunction.²² Morning stiffness, weakness, and fatigue are common complaints. Shoulder pain, especially nocturnal pain, is the most common complaint of patients with glenohumeral rheumatoid arthritis. However, the actual source of pain in these patients may be difficult to locate. Cervical radiculopathy or myelopathy may produce shoulder pain and weakness. In addition, pain from the acromioclavicular joint, subacromial bursa, or rotator cuff may mimic or coexist with glenohumeral arthritis. A thorough history and physical examination, combined with radiographs and selective local anesthetic injections, will assist in accurately identifying the sources of pain and determining the appropriate treatment.

The destructive inflammatory process initially affects the periarticular soft tissues. Proliferation of the inflamed synovium and pannus, and the resulting reactive effusion, will distend the capsule and lead to an intensely painful joint that is exacerbated by motion. Clinically, the patient will try to limit this pain by avoiding the end ranges of motion. The proliferative pannus not only causes indirect damage through the release of destructive inflammatory mediators such as proteases and collagenase but also directly invades the adjacent cartilage, bone, tendon, and ligaments. The rotator cuff and biceps tendon are affected early in the disease process, leading to progressive attenuation and dysfunction. The incidence of rotator cuff defects and biceps tendon ruptures at the time of arthroplasty is approximately 40% and 60%, respectively.⁸,⁹ Superior migration of the humeral head occurs in 20% of patients even in the presence of an intact rotator cuff. This is thought to occur through a muscular imbalance between a dysfunctional rotator cuff incapable of centering the head within the glenoid concavity in the presence of a properly functioning deltoid muscle. Degradative enzymes from the inflammatory synovium, combined with direct invasion of pannus and altered cartilage nutrition from decreased joint motion, contribute to the destruction of the articular cartilage surfaces.⁷³,⁷⁵ Synovial infiltration of the marginal bone characteristically begins along the superomedial aspect of the greater tuberosity, adjacent to the concomitant rotator cuff disease. Periarticular erosions and cysts become evident at the margins of the joint. Central and medial glenoid erosion progresses toward the base of the coracoid. The final result is severe glenohumeral incongruity and bone loss, symmetric capsular contracture, and an incompetent rotator cuff, which manifests as a very painful, poorly functioning shoulder.¹⁰¹ Most shoulder surgeons advocate early intervention before the loss of bone stock and rotator cuff tissue.

Osteonecrosis is often referred to as avascular necrosis, or aseptic necrosis. Occurring through a variety of traumatic or atraumatic means, osteonecrosis’ common denominator is vascular embarrassment and bone death.²¹ The ascending branch of the anterior humeral circumflex artery is the primary blood supply to the proximal humerus. Traumatic vascular disruption of the articular segment of the humeral head may occur after trauma or surgical intervention, variably resulting in osteonecrosis. Atraumatic osteonecrosis is associated with a variety of conditions such as steroid use, alcohol use, smoking, vascular disorders, coagulopathies, infiltrative marrow disorders, sickle cell disease, and Caisson’s disease.¹⁴,²⁰,²⁵,⁶¹,¹¹⁶ The disease process is believed to occur through a disturbance of the microcirculation, which results in ischemia and infarction of the marrow elements. The reparative response to remove and repair the necrotic bone leaves the subchondral bone weakened and vulnerable to compressive forces. Microfracturing and trabecular incompetence lead to collapse of the subchondral bone. Articular incongruity of the humeral head eventually leads to arthritic changes involving both the humeral head and glenoid.

Pain develops insidiously and is the primary complaint of patients with osteonecrosis. Pain may be related to bone infarction, elevated intraosseous pressure, or microfracturing of the subchondral cancellous trabeculae. Progressive subchondral collapse may produce painful mechanical symptoms such as catching or locking. Although the development of arthritis may be associated with weakness and atrophy, the rotator cuff and deltoid are generally intact.

Imaging studies are obtained to confirm the pathologic process and determine its extent. Plain radiographs are the initial studies of the shoulder and include three orthogonal views: an anteroposterior (AP) view in the scapular plane, a
scapular lateral (Y) view, and an axillary view.³⁹ Except in the earliest stages, glenohumeral arthritis is usually easily detected on plain radiographs. External and internal rotation AP views of the humerus (35 degrees) or weight-bearing abduction views may facilitate the detection of early joint narrowing. Important radiographic features include joint space narrowing, proximal humeral migration, and amount and direction of bone loss. Other pathologic features may include postsurgical changes, periarticular erosions, hypertrophic marginal osteophytes, and the presence of calcifications or loose bodies.

Particular radiographic features are disease specific and offer important information regarding treatment options. Progressive osteoarthritic changes include joint space narrowing, subchondral sclerosis, subchondral cystic changes, and humeral head and glenoid flattening.⁸⁴ The classic inferomedial humeral osteophyte becomes prominent on the AP view. Although posterior subluxation of the humeral head and posterior erosion of the glenoid will be evident on the axillary view, it may not reveal the actual extent of osseous erosion.

Radiographic characteristics of rheumatoid arthritis are related to the duration and severity of the disease and include periarticular osteopenia, marginal erosions, joint space narrowing, and medial migration of the humeral head into the glenoid.³⁹,⁶⁴ The axillary view reveals symmetric central erosion of the glenoid. End-stage disease is often accompanied by rotator cuff insufficiency and superior humeral head migration. Narrowing of the acromiohumeral interval and superior glenoid bone loss are seen on the AP view.⁶⁷ Resorption and collapse of the humeral head may allow the medial humeral metaphysis to articulate with the inferior aspect of the glenoid.

The radiographic features of osteonecrosis have been described by Cruess and are based on the Ficat staging system.¹⁹, ²⁰ and ²¹ Focal sclerosis without collapse (stage II) may be apparent on the AP film with the humerus in external rotation. Stage III represents mild collapse of subchondral bone (1-2 mm) as depicted by a “crescent sign” on the AP view in external rotation. The articular cartilage is soft and bollotable but has not collapsed. Collapse of the humeral head articular surface and secondary degenerative changes of the glenoid (stages V and VI) may follow.

Advanced imaging studies should not replace a series of high-quality plain radiographs. When indicated, computed tomography (CT) scanning and magnetic resonance imaging (MRI) are useful adjunctive tests in determining the extent of the disease and in surgical planning. Computed tomography scanning allows an accurate assessment of bony architecture, whereas MRI offers exceptional noninvasive visualization of the articular cartilage and soft tissues.

Rarely, CT scanning may be performed as a primary study when it is not possible to obtain an adequate axillary view. Stiffness, severe pain, or obesity may prevent proper patient positioning for a quality study. In most cases, CT scanning is obtained to assess alterations in bony anatomy, especially in determining glenoid version and the extent and pattern of glenoid erosion.⁷,³⁶,⁸³ Although the accuracy may vary slightly depending on scapular rotation, it is more accurate than plain radiographs, which will frequently underestimate the degree of osteoarticular destruction. Glenoid erosion is variable among the arthritides, occurring posteriorly in cases of osteoarthritis and capsulorrhaphy arthropathy, superior and central in patients with cuff-tear arthropathy or rheumatoid arthritis, and either anteriorly or posteriorly in association with a chronic dislocation of the shoulder. The degree of erosion will influence the available surgical options. Computed tomography scanning is also particularly useful in assessing proximal humeral bone stock, tuberosity malunion, and deformity of the proximal humerus and shaft, which occurs in cases of posttraumatic arthritis and in the revision setting.³¹

The role of MRI in the evaluation of the painful shoulder continues to expand.⁵⁰,⁸⁷ Recent advances in magnetic resonance sequencing have improved the ability to detect early osteochondral abnormalities, which were previously underestimated by MRI and plain radiographs.⁹⁷,¹⁰³ Currently, MRI is the best imaging study for detecting early osteoarthritis.¹⁰² The loose bodies associated with synovial chondromatosis may only be evident by MRI. The ability to identify the presence of inflammatory synovitis and joint effusions may represent a clinical application in the early detection and treatment of patients with inflammatory arthropathies of the shoulder.¹⁰⁴,¹¹¹,¹²⁴ The high accuracy afforded by MRI provides valuable information regarding rotator cuff retraction and muscular atrophy.⁵⁷ In the setting of concomitant rotator cuff disease and glenohumeral arthritis, MRI is useful in assessing both the integrity of the rotator cuff and the degree of osteoarticular destruction.