Shoulder Pain Management

Diagnostic Evaluation

Laboratory studies are generally not helpful in the diagnosis of shoulder pain unless septic shoulder or rheumatoid arthritis is suspected. For suspected rheumatoid arthritis, rheumatoid factor is positive in 80% of patients within 2 years of disease onset, but may be negative at initial presentation. Anti-CCP antibodies are more sensitive in early disease and should be checked when the illness is suspected.

Acromioclavicular Arthritis

Radiographic Evaluation

Although various imaging techniques have been utilized to study the acromioclavicular (AC) joint, plain radiographs are still the most appropriate initial choice. Depending on the disease stage, AP radiographs may show degenerative changes including subchondral cysts, sclerosis, osteophytes and joint-space narrowing. However, be careful in jumping to this diagnosis based on radiographic findings alone, as many patients will have radiographic findings of AC arthritis without any objective physical exam findings to support the diagnosis. The Zanca view is particularly helpful in evaluating AC joint pathology (Fig. 1).¹

Figure 1: The Zanca view of the AC joint is obtained by angling the X-ray beam 10-15 degrees in the cephalic direction and decreasing the kilovoltage. This Zanca view better depicts the soft tissue and joint detail of the AC joint; however, the glenohumeral joint is no longer well visualized.²

If the differential diagnosis includes an os acromiale, an axial view of the shoulder should be completed. MRI, with its outstanding soft tissue resolution, can detect capsular hypertrophy, effusions, inferior osteophyte formation off of the distal clavicle, subchondral edema and an os acromiale (Fig. 2). Although ultrasound is very sensitive for detecting the presence of joint inflammation, it is an operator-dependent diagnostic procedure that is rarely utilized in the evaluation of AC joint injuries or osteoarthritis. A bone scan should be considered in the patient with equivocal MRI findings and a confusing clinical picture (Fig. 3).³

Figure 2: A bone scan usually demonstrates increased activity in the AC joint when a patient has symptomatic AC joint arthritis.⁴

Figure 3: Oblique coronal (A) and oblique sagittal (B) images of the AC joint demonstrate a large spur (white arrows) on the undersurface of the distal clavicle (C).⁵

Other Diagnostic Modalities

If, after a thorough history and physical exam, if the AC joint is thought to be the cause of the patient's symptoms, an injection of a local anesthetic with steroids could prove both diagnostic and therapeutic. Although the AC joint is superficial, it can be very difficult to localize for injection, as there is significant variability in its orientation (Fig. 4). For these reasons, many clinicians prefer fluoroscopic guidance to improve accuracy. (Fluoroscopy, however, is not a practical option for most practitioners in the office.)

Within minutes of a successful injection, most patients with a painful AC joint will experience a significant reduction in their pain. Continuation of symptoms after the injection suggests an additional diagnosis or an alternative diagnosis, the most common of which is rotator cuff impingement. In this situation, a second injection directed into the subacromial space may clarify the contribution of the rotator cuff to the patient's symptoms.¹

Figure 4: Direct injection into the AC joint through a superior approach.⁶

Glenohumeral Arthritis

Radiographic Evaluation

Plain radiographs are the initial imaging study of choice. Radiographs should include a true AP view (Fig. 5) and an axillary lateral view (Fig. 6) to best see the classic features of arthritis.

Figure 5: View of the shoulder showing glenohumeral arthritis.

Figure 6: Axillary lateral view of the shoulder showing osteoarthritis.⁷

Osteoarthritis will typically show joint-space narrowing, osteophyte formation, sclerosis and subchondral cysts, while rheumatoid arthritis will show joint-space narrowing, osteopenia, bony erosions, subchondral cysts, and occasionally osteophyte formation.^8,9 Loose bodies may also be seen, typically in the axillary pouch. The axillary lateral view is particularly important in assessing the degree of joint-space narrowing and the amount and location of glenoid erosion.⁹ Radiographs may also be helpful in identifying other shoulder abnormalities, such as osteoarthritis of the acromioclavicular joint, calcific tendonitis and os acromiale.

Other Imaging Modalities

If the history, physical examination and radiographs are consistent with glenohumeral arthritis, additional imaging studies are not needed. However, CT is useful in evaluating glenoid bone stock and wear when joint arthroplasty is being considered. Osteoarthritis, for example, typically leads to posterior glenoid erosion, while rheumatoid arthritis causes more central wear (Fig. 7).

MRI is useful in evaluating the status of the rotator cuff and other surrounding soft tissues.^9,10 Although rotator cuff tears are not commonly seen in osteoarthritis, they frequently occur in rheumatoid and inflammatory arthritis and are always present in rotator cuff arthropathy.¹¹ Advanced imaging modalities may also be useful in ruling out other causes of a painful, stiff shoulder. MRI or bone scan may confirm a diagnosis of osteonecrosis of the humeral head by detecting more subtle changes not evident on plain radiographs, while electrodiagnostic studies and cervical spine radiographs or MRI may be needed if neuropathic arthritis is suspected.⁹

Figure 7: CT scan of glenohumeral osteoarthritis showing posterior glenoid erosion and joint space narrowing, humeral head osteophyte formation and an anterior loose body.¹²

Rotator Cuff Tear

Radiographic Evaluation

Plain radiographs are used to determine the bony morphology of the acromion and to evaluate the position of the humeral head relative to the glenoid fossa and acromion. Three radiographic views of the involved shoulder are recommended in patients with suspected rotator cuff injury. The first is an AP view of the glenohumeral joint (Fig. 8). This view allows the clinician to examine the glenohumeral joint for evidence of degenerative disease. Also, the clinician can examine the acromioclavicular joint and assess the acromion for undersurface spur formation or degenerative changes.^13,14

Figure 8: AP view shows osteophytes on the lateral border of the acromion.¹⁵

Normally, the space available for the cuff tendons between the humeral head and the acromion is estimated to be between 7-14 mm. With a space < 7 mm, there is an increased likelihood of a large rotator cuff tear and a poor prognosis (Fig. 9).

Figure 9: View of the shoulder showing a rotator cuff tear.

The second view is the axillary radiograph. Not only does this particular view allow verification that the shoulder is not dislocated, but it also is used to examine the glenoid and humerus. This view is also used to make the diagnosis of glenohumeral arthritis. In addition, an os acromiale is visible on this view (Fig. 10). An unstable os acromiale can hinge through the unfused segment and cause impingement symptoms.

Figure 10: Axillary radiograph demonstrating an unfused acromial epiphysis (small black arrows).

The third view is a supraspinatus outlet view, which is used to assess the shape of the acromion, bony impingement that might be present, and the space available for the rotator cuff (Fig. 11). Of the three acromial shapes visible on these radiographic views – flat (Type I), curved (Type II) or hooked (Type III) – Type III acromions have a greater association with abnormalities of the rotator cuff.¹⁶

Figure 11: Supraspinatus outlet view shows the shape of the acromion. This patient has a type III acromion because of the osteophyte formation that impinges on the rotator cuff.¹⁷

Tendon Imaging

Arthrograms are extremely accurate for the detection of full-thickness rotator cuff tears, but are invasive procedures that do not give accurate information on tear size or the condition of the rotator cuff muscles. In addition, arthrograms do not reliably assess partial-thickness rotator cuff tears.¹³

High-resolution, real-time ultrasound has also been used to evaluate the integrity of the rotator cuff. The accuracy is operator dependent; therefore, ultrasound has not become a commonly employed method to assess the rotator cuff. However, it retains the advantages of being quick, inexpensive, safe and tolerated by claustrophobics.¹³

MRI is the cuff-imaging study of choice in many centers (Fig. 12). The accuracy in detecting full-thickness cuff tears has been reported to be between 93%-100%. Partial-thickness tears are less accurately detected and are more dependent on the technique used. The main advantage of MRI, however, is the wealth of information gained. The quality of the rotator cuff muscles, the size of the tear, involvement of the biceps tendon and partial-thickness cuff tears can be clearly determined.¹³

Figure 12: (A) Sagittal T1 image of the shoulder medial to the glenoid showing the muscle bellies of the rotator cuff. Note the atrophy of the supraspinatus muscle belly. This is highly suggestive of a chronic rotator cuff tear. (B) Coronal T1 image of the shoulder demonstrating a rotator cuff tear involving the supraspinatus tendon with retraction of the tendon to the glenoid margin.

References