Upper Extremity Considerations: Osteoarthritis of the Shoulder

Sara L. Edwards

John-Erik Bell

William N. Levine

Louis U. Bigliani

Glenohumeral Joint

The glenohumeral joint is a synovial joint comprised of the articulation between the round humeral head and the shallow cup-shaped glenoid process of the scapula. It has the greatest range of motion of any joint in the body.¹ Many arthritic conditions can disrupt the normally smooth, congruent, and lubricated articular surfaces of the glenohumeral joint, including osteoarthritis (OA), rheumatoid arthritis (RA), avascular necrosis, post-traumatic arthritis, rotator cuff tear arthropathy, and postcapsulorrhaphy arthropathy. The most common of these is OA, a slowly progressive disease that leads to cartilage thinning and ultimately complete cartilage loss. Advanced OA affecting the glenohumeral joint typically results in unremitting, achy pain and limitation of motion. The result is a significantly decreased level of function and impairment of general health status.²^,³ Multiple surgical procedures have been described for the treatment of painful glenohumeral arthritis. Prosthetic arthroplasty has proven to be an effective and reliable procedure with a well-established record of success.

Anatomy and Pathophysiology

The glenoid process of the scapula is shaped like an inverted comma with 5° to 15° of retroversion relative to the scapular plane.⁴^,⁵^,⁶ The articular surface is concave and covered with hyaline cartilage that is thinner centrally.⁷ The articular surface area of the glenoid is only one third to one fourth that of the humeral head, and relatively little of the articulating ball is captured by the shallow glenoid cup.

Articular cartilage failure is the final common pathway of OA. It is unclear whether the cartilage failure is from the initial injury or from pathological processes due to changes in the mechanical and physical properties of the subchondral bone. As the subchondral plate stiffens, there is increased shear force in the cartilage layer. This alters the ultrastructure of the cartilage, increasing the water content and precipitating a cascade of events in the cartilage substance that results in an inability to tolerate applied forces. As the cartilage degrades, increasing friction within the affected joint induces mechanical destruction of the remaining cartilage. The adjacent bone is subjected to increased stress, which leads to subchondral sclerosis and microfissures in the bone surface. Synovial fluid is compressed through the small fissures and forms cysts. Incongruency of the joint leads to painful loss of motion.⁸

Loose bodies may be present. A large volume of clear yellow synovial fluid may be present that is high in catabolic markers of cartilage degradation.⁹ While OA is primarily an osseous disease, the soft tissues of the shoulder are also affected, although less severely. Contracted anterior capsule and subscapularis tendon limit external rotation and force the humeral head posteriorly. Posterior glenoid wear and erosion result from posterior subluxation of the humeral head, with a reported incidence as high as 45%.⁶^,¹⁰

Chronic posterior subluxation can lead to a redundant and attenuated posterior capsule. The synovium may be thickened, inflamed, and friable. Although the rotator cuff may be contracted, it is usually intact, as the incidence of full thickness rotator cuff tears in shoulders undergoing arthroplasty is exceedingly low.¹⁰ In a recent series, only 4 of 110 shoulders (3.6%) undergoing replacement for OA had full thickness rotator cuff tears.¹¹

Clinical Evaluation

History

The chief complaint is often of a constant, dull ache in the shoulder that has an insidious onset and is unremitting in quality. Stiffness and loss of function are typical. Patients with severe OA will have difficulty performing activities of daily living. Patients with less severe involvement will present with muscle fatigue and difficulty with functions at the extreme of motion, such as fastening a bra strap or reaching for shelves. Patients may complain of positional night pain that is different from that of rotator cuff disease, which typically is unremitting. While uncommon, infection and tumor must be considered in the differential diagnosis. Cervical spondylosis is frequently coexistent in patients with OA and must be ruled out, as symptomatology from cervical disease can mimic primary glenohumeral disorders.

Physical Examination

The patient should be examined with both shoulders fully exposed. Inspection is made of shoulder contour, bony prominences, muscle atrophy, and deformity. A thorough examination of the cervical spine is done by assessing range of motion and performing Spurling’s test. Neurologic sensory and motor function should be assessed. Active and passive range of motion in elevation, external rotation, and internal rotation is measured and recorded. When arthritis is advanced, capsular tightness and joint incongruity become severe. Shoulder motion may become restricted to scapulothoracic motion. Since scapular movement does not contribute significantly to glenohumeral rotation, limitation of external rotation is a very sensitive physical finding of shoulder arthritis.¹²

Imaging Studies

Radiographic views recommended include anteroposterior views in neutral, internal, and external rotations taken in the plane of the scapula, an axillary view, and a supraspinatus outlet view. Classic radiographic findings include joint space narrowing, irregular articular contours, subchondral sclerosis and cyst formation, flattening of the humeral and glenoid surfaces, and a ring of osteophytes around the humeral anatomic neck. The axillary view is most useful for evaluating posterior subluxation and glenoid wear and is the most sensitive view for detecting joint space narrowing.

Early shoulder arthritis is often clinically underappreciated because of the inability to radiographically demonstrate cartilage pathology. This is compounded by the fact that the shoulder is a nonweight-bearing joint. Weighted abduction views may be used to demonstrate cartilage loss and resultant joint space narrowing that may not be apparent on routine radiographs.¹³

Specialized studies such as computed tomography and magnetic resonance imaging are rarely necessary in routine cases. Computed tomography is useful for accurate assessment of the glenoid bone stock and version in cases of severe posterior glenohumeral subluxation and glenoid wear.⁶^,¹⁴^,¹⁵ This information is useful during preoperative planning for glenoid resurfacing. Magnetic resonance imaging may be used to evaluate for the presence of a rotator cuff tear.

Treatment Options

Conservative Treatment

The initial treatment of the patient presenting with glenohumeral OA should be symptomatic, consisting of activity modification, anti-inflammatory medications and acetaminophen, moist heat, and gentle physical therapy. Glenohumeral joint injections of corticosteroid can also be helpful in patients who wish to prolong surgical intervention. Injections of steroid may be most beneficial in patients with inflammatory disease and less effective in those with long-term pain, such as OA. Other variables affecting the outcome may be needle placement, anatomical site of inflammation, frequency and dose of injection, and type of corticosteroid delivered.⁸

Surgical Indications

The primary indication for surgical treatment of glenohumeral OA is pain and loss of function that has persisted despite nonoperative management. Shoulder arthroplasty is rarely performed solely to improve motion or function without concomitant pain. The health, activity, and motivation of the patient are important factors to consider. While patients are generally advised to delay reconstructive surgery as long as possible, the timing of shoulder arthroplasty is not always so straightforward. Absolute contraindications to arthroplasty are active infection and complete functional loss of both the rotator cuff and deltoid muscles.

While prosthetic arthroplasty has become the gold standard treatment for severe shoulder OA, other surgical options do exist and should be included in the surgeon’s armamentarium.

Open Débridement and Soft Tissue Balancing

Neer reported uniformly poor results after open release, débridement, removal of osteophytes, and soft tissue balancing for OA.¹⁶ However, MacDonald et al. successfully treated ten patients who had osteoarthritic changes following previous anterior instability surgery with an open release of the subscapularis and anterior capsule.¹⁷ Each patient had decreased pain and increased external rotation an average 3.5 years after surgery. Goals of this procedure are to normalize the biomechanics of the shoulder joint through soft tissue balancing, so that joint forces are more evenly distributed and the articulation is altered to involve less affected cartilage surfaces.

Arthroscopic Débridement

Patients with early glenohumeral OA who are not candidates for prosthetic replacement may benefit from arthroscopic irrigation and débridement. Coexistent conditions that
contribute to symptoms, such as subacromial impingement, may be addressed at the same time.¹⁸ Intermediate-term results demonstrate significant pain relief, and the procedure may delay the need for arthroplasty.¹⁹ Our experience in 49 cases of early glenohumeral OA treated arthroscopically has been 93% good to excellent results at an average 4.3 years follow-up.¹⁹ Other authors have not demonstrated such positive results, with 75% of patients worsening following arthroscopic débridement. Arthroscopy is contraindicated in cases of severe arthritis, with complete loss of the joint space, large osteophytes, or posterior glenohumeral subluxation.⁸

Resection Arthroplasty

The success of prosthetic arthroplasty has significantly limited the indications for humeral head resection. This procedure is used today only in the presence of resistant infection or failed arthroplasty with extensive bone loss in which reimplantation is contraindicated. Although pain may be relieved in some cases, range of motion and function are uniformly poor as the fulcrum of the shoulder is lost.²⁰^,²¹ According to Cofield, active forward elevation is typically limited to 40° to 90°, with minimal to no active internal or external rotation.²⁰ Resection arthroplasty has no role today in the treatment of primary OA.

Glenohumeral Arthrodesis

As with humeral head resection, the indications for glenohumeral arthrodesis have markedly diminished since the introduction of shoulder arthroplasty. Shoulder fusion is indicated in cases of combined deltoid and rotator cuff paralysis (as occurs in upper brachial plexus injuries), active chronic low-grade infection, failed reconstructive procedures, and in some cases of severe bone loss following radical shoulder girdle tumor resection. It is rarely indicated for the treatment of primary OA.

Humeral Hemiarthroplasty

Shoulder arthroplasty, either humeral hemiarthroplasty or total shoulder replacement, has become the standard treatment in most patients with painful OA.²² Pain is relieved in a high percentage of patients. Restoration of function is somewhat less predictable and depends heavily on the surgical technique, the status of the soft tissues (especially the rotator cuff and deltoid muscles), and the postoperative rehabilitation. The decision whether to replace the humeral articular surface alone, or both the glenoid and humeral articular surfaces, is determined by the extent of arthritic change of the glenoid, the available glenoid bone stock, and the integrity of the rotator cuff muscles. Shoulder arthroplasty is contraindicated in the presence of combined rotator cuff and deltoid dysfunction and when active infection is present.

Prosthetic replacement of the humeral head is a satisfactory treatment option when arthritic change is confined to the humerus.²³ Better results with hemiarthroplasty are seen when the glenoid is concentric.²⁴ Shoulders with nonconcentric glenoids from posterior wear have limited forward elevation and external rotation compared to shoulders with concentric glenoids. Patients under 50 years of age with OA are candidates for humeral hemiarthroplasty, as they are often healthy and active and may outlive the longevity of a glenoid prosthesis. Burkhead and Hutton have described biologic resurfacing of the glenoid with autogenous fascia or capsule in young patients treated with hemiarthroplasty in an effort to relieve pain and avoid the complication of glenoid component loosening.²⁵

Glenohumeral OA with a deficient rotator cuff is another fairly common indication for humeral hemiarthroplasty, as long-term studies have noted an association between glenoid component loosening and irreparable rotator cuff tears.²⁶^,²⁷^,²⁸ Franklin et al. postulated that eccentric loading of the glenoid, owing to superior migration of the humeral component as occurs when the head-depressing effect of the rotator cuff is lost, causes loosening of the glenoid component.²⁹

Total Shoulder Arthroplasty

Total shoulder arthroplasty, in which both the humeral head and glenoid are replaced, is generally indicated when arthritic change involving the glenoid is advanced, glenoid bone stock is adequate, and the rotator cuff is intact and functional.³⁰ This is frequently the case in shoulders with primary OA (Fig. 20A-1). The potential advantages of glenoid resurfacing over humeral head replacement alone include a better fulcrum for improved strength and motion, increased stability, decreased friction, and elimination of arthritic glenoid pain. The disadvantages of glenoid resurfacing include increased operative time and blood loss, increased implant cost, and a slightly higher rate of revision.³¹ A review of the literature by Rodosky and Bigliani has shown that total shoulder replacement provides more reliable pain relief and function than humeral hemiarthroplasty in patients with OA and rheumatoid arthritis.³¹ Some studies have shown 30% to 50% better results with total shoulder arthroplasty compared to humeral hemiarthroplasty.³²^,³³

Results

Results of prosthetic replacement are superior to other forms of treatment for glenohumeral OA. Shoulder arthroplasty has been shown to result in a significant improvement in health status, by consistently relieving pain, increasing motion, and improving function.³⁴ Unfortunately, most published series reporting results of shoulder arthroplasty include mixed patient populations with multiple diagnoses in addition to OA, including post-traumatic arthritis, rheumatoid arthritis, avascular necrosis, and cuff tear arthropathy.¹¹^,³⁵^,³⁶^,³⁷^,³⁸^,³⁹

Nevertheless, some important trends are apparent. Results of shoulder arthroplasty for treatment of OA with an intact rotator cuff are clearly superior to results of arthroplasty for other arthritic conditions like rheumatoid arthritis, cuff tear arthropathy, and post-traumatic arthritis (Table 20A-1).¹¹^,¹²^,¹³^,¹⁴^,¹⁵^,¹⁶^,¹⁷^,¹⁸^,¹⁹^,²⁰^,²¹^,²²^,²³^,²⁴^,²⁵^,²⁶^,²⁷^,²⁸^,²⁹^,³⁰^,³¹^,³²^,³³^,³⁴^,³⁵^,³⁶^,³⁷^,³⁸^,³⁹^,⁴⁰^,⁴¹^,⁴²^,⁴³ This is likely due to the relatively preserved soft tissues in the osteoarthritic shoulder. Overall satisfactory results following shoulder arthroplasty for OA are greater than 90% in most
series.¹¹^,²⁴^,³⁵^,³⁶^,³⁷^,³⁸^,³⁹^,⁴²^,⁴³ Pain relief is predictable, with approximately 90% of patients reporting no or slight pain. Relief of pain is generally better with total shoulder arthroplasty than hemiarthroplasty.⁴⁴^,⁴⁵ Nearly full range of motion is restored in the osteoarthritic shoulder. The results of humeral head replacement alone, although not quite as good in most series, tend to deteriorate at a faster rate than total shoulder replacement, even with the presence of glenoid lucent lines. It was found that more than 50% of a well-reviewed group of patients had pain and 26% required conversion to a total shoulder within 10 years of the initial procedure. Those requiring revision to a total shoulder did not have results as good as those patients treated with a primary total shoulder arthroplasty.⁸

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