Acromioclavicular Osteoarthritis: A Cause of Shoulder Pain
Acromioclavicular Osteoarthritis: A Cause of Shoulder Pain
Patients with AC arthritis generally present with complaints of progressively worsening shoulder pain, although minor trauma or strenuous activity may cause an acute exacerbation of this chronic degenerative condition. The pain is typically localized over the anterior aspect of the shoulder in the region of the AC joint or referred throughout the shoulder and upper arm. Radicular-type pain that radiates into the base of the neck or arm may be present and some patients may complain of associated headaches. Overhead activities, weight lifting, and cross-body movements using the affected arm often are associated with worsening symptoms. Pain at night is common when patients lay on the affected side, and difficulty sleeping can be the factor driving patients to seek treatment. In addition, patients may complain of popping, clicking, grinding, or a catching sensation with movement of their shoulder. A careful history of trauma or injuries should be elicited to raise suspicion for instability or other associated pathologies.
A thorough physical examination of both the affected and nonaffected shoulders should be performed, noting differences between the two. The shoulder is first inspected, assessing for enlargement or asymmetry of the AC joint, muscular atrophy, or evidence of prior trauma. Tenderness directly over the joint is seen with palpation, and the patient's pain exacerbated by provocative maneuvers. Stability of the clavicle in relation to the acromion is evaluated by holding the distal aspect of the clavicle with one hand and noting the amount of translation while stabilizing the acromion with the other hand.
A number of provocative tests have been described to specifically evaluate the AC joint. The cross-body adduction test is performed by passively bringing the patient's arm into 90 degrees of forward flexion and maximal adduction, thus causing compression across the joint. With the AC resisted-extension test, the patient's arm is placed in 90 degrees of forward flexion and the patient is asked to actively extend against resistance. Lastly, the O'Brien active compression test is performed with the arm placed in 90 degrees of forward flexion with 10 degrees of adduction. With the arm in maximal internal rotation (thumb pointed downward) the patient resists a uniform downward force applied by the examiner. The arm is then externally rotated (palm facing upward) and the maneuver repeated. The test is considered positive if pain is present with internal rotation but decreases or resolves with external rotation. Pain localized to the AC region during this test is indicative of AC joint pathology, whereas pain located deep inside the shoulder may indicate labral pathology. In a study of these tests, Chronopoulos et al found the cross-body adduction test to be the most sensitive (77%), although the O'Brien active compression test was found to be the most specific (95%).
Initial imaging should include a modified AP view, scapular Y-view, and Zanca view radiographs (Figs. 1–4). These x-rays help the clinician to assess the degree of AC arthropathy and any other underlying abnormalities. In contrast to a standard AP radiograph of the glenohumeral joint, the x-ray voltage should be reduced by approximately 50% to better visualize the AC joint. If full voltage is used, then the resultant image of the distal clavicle and acromion will appear dark and overexposed. In an effort to provide optimal visualization of the AC joint, Zanca described a technique in which the x-ray beam is angled with 10 degrees of cephalic tilt, commonly known as the Zanca view. This technique eliminates overlap from the scapula and other tissues seen on standard AP radiographs, thereby creating an unobstructed view of the joint. In some cases, a bilateral Zanca view also may be useful to measure the side-to-side difference in the superior displacement of the clavicle and the relative extent of degenerative changes. If a patient has experienced trauma to the affected shoulder, then an axillary lateral x-ray also should be obtained to assess for posterior displacement of the clavicle.
(Enlarge Image)
Figure 1.
Modified anteroposterior view of a right shoulder with advanced acromioclavicular osteoarthritis.
(Enlarge Image)
Figure 2.
Scapular Y-view of a right shoulder with advanced acromioclavicular osteoarthritis. Note the impingement effect of the inferior osteophyte formation on the relative space available for the rotator cuff in the outlet.
(Enlarge Image)
Figure 3.
Modified anteroposterior view of a right shoulder with advanced glenohumeral and acromioclavicular osteoarthritis. Note the spurring in both joints, including the distal clavicle, as well as the inferior humerus and glenoid.
(Enlarge Image)
Figure 4.
Zanca view of a left shoulder 2 years after rotator cuff repair (note metal anchor) and open distal clavicle excision. Note the residual gap between the lateral clavicle and the acromion, as well as postoperative calcification in the area.
Magnetic resonance imaging (MRI) can be used to further characterize the degree of arthrosis when radiographs are equivocal, and its use is increasing in prevalence in the evaluation of shoulder pain. MRI should be obtained only after a careful history and physical examination have been performed because it is sensitive in identifying pathology but has poor specificity. Shubin-Stein et al demonstrated reactive bone edema to be a more reliable predictor of symptomatic AC pathology than degenerative changes on MRI (Fig. 5). It is important to note that a patient's pain may not correlate clinically with his or her radiographic findings because it has been shown that up to 82% of patients with AC joint arthritis based on MRI are asymptomatic.
(Enlarge Image)
Figure 5.
Right shoulder with acute acromioclavicular posttraumatic osteoarthritis in a 19-year-old football player with continued severe shoulder pain 6 months after a partial acromioclavicular separation. Note the bone edema in the lateral clavicle and the medial acromion, as well as the irregularity of the joint surface.
When arthritis of the AC joint is suspected to be the cause of a patient's symptoms based on history, physical examination, and imaging, an injection into the joint may serve both diagnostic and therapeutic purposes. A combination of local anesthetic and corticosteroid commonly is preferred. The joint is located by palpation and a superior approach is recommended. Accurate needle placement into the joint may prove difficult because of variations in joint anatomy, osteophyte formation, and other degenerative changes. Radiographic evaluation in advance of injection can help delineate the local anatomy to aid in successful joint entry. Ultrasound guidance also has been shown to further improve the accuracy of proper intraarticular needle placement.
Evaluation
Patients with AC arthritis generally present with complaints of progressively worsening shoulder pain, although minor trauma or strenuous activity may cause an acute exacerbation of this chronic degenerative condition. The pain is typically localized over the anterior aspect of the shoulder in the region of the AC joint or referred throughout the shoulder and upper arm. Radicular-type pain that radiates into the base of the neck or arm may be present and some patients may complain of associated headaches. Overhead activities, weight lifting, and cross-body movements using the affected arm often are associated with worsening symptoms. Pain at night is common when patients lay on the affected side, and difficulty sleeping can be the factor driving patients to seek treatment. In addition, patients may complain of popping, clicking, grinding, or a catching sensation with movement of their shoulder. A careful history of trauma or injuries should be elicited to raise suspicion for instability or other associated pathologies.
A thorough physical examination of both the affected and nonaffected shoulders should be performed, noting differences between the two. The shoulder is first inspected, assessing for enlargement or asymmetry of the AC joint, muscular atrophy, or evidence of prior trauma. Tenderness directly over the joint is seen with palpation, and the patient's pain exacerbated by provocative maneuvers. Stability of the clavicle in relation to the acromion is evaluated by holding the distal aspect of the clavicle with one hand and noting the amount of translation while stabilizing the acromion with the other hand.
A number of provocative tests have been described to specifically evaluate the AC joint. The cross-body adduction test is performed by passively bringing the patient's arm into 90 degrees of forward flexion and maximal adduction, thus causing compression across the joint. With the AC resisted-extension test, the patient's arm is placed in 90 degrees of forward flexion and the patient is asked to actively extend against resistance. Lastly, the O'Brien active compression test is performed with the arm placed in 90 degrees of forward flexion with 10 degrees of adduction. With the arm in maximal internal rotation (thumb pointed downward) the patient resists a uniform downward force applied by the examiner. The arm is then externally rotated (palm facing upward) and the maneuver repeated. The test is considered positive if pain is present with internal rotation but decreases or resolves with external rotation. Pain localized to the AC region during this test is indicative of AC joint pathology, whereas pain located deep inside the shoulder may indicate labral pathology. In a study of these tests, Chronopoulos et al found the cross-body adduction test to be the most sensitive (77%), although the O'Brien active compression test was found to be the most specific (95%).
Initial imaging should include a modified AP view, scapular Y-view, and Zanca view radiographs (Figs. 1–4). These x-rays help the clinician to assess the degree of AC arthropathy and any other underlying abnormalities. In contrast to a standard AP radiograph of the glenohumeral joint, the x-ray voltage should be reduced by approximately 50% to better visualize the AC joint. If full voltage is used, then the resultant image of the distal clavicle and acromion will appear dark and overexposed. In an effort to provide optimal visualization of the AC joint, Zanca described a technique in which the x-ray beam is angled with 10 degrees of cephalic tilt, commonly known as the Zanca view. This technique eliminates overlap from the scapula and other tissues seen on standard AP radiographs, thereby creating an unobstructed view of the joint. In some cases, a bilateral Zanca view also may be useful to measure the side-to-side difference in the superior displacement of the clavicle and the relative extent of degenerative changes. If a patient has experienced trauma to the affected shoulder, then an axillary lateral x-ray also should be obtained to assess for posterior displacement of the clavicle.
(Enlarge Image)
Figure 1.
Modified anteroposterior view of a right shoulder with advanced acromioclavicular osteoarthritis.
(Enlarge Image)
Figure 2.
Scapular Y-view of a right shoulder with advanced acromioclavicular osteoarthritis. Note the impingement effect of the inferior osteophyte formation on the relative space available for the rotator cuff in the outlet.
(Enlarge Image)
Figure 3.
Modified anteroposterior view of a right shoulder with advanced glenohumeral and acromioclavicular osteoarthritis. Note the spurring in both joints, including the distal clavicle, as well as the inferior humerus and glenoid.
(Enlarge Image)
Figure 4.
Zanca view of a left shoulder 2 years after rotator cuff repair (note metal anchor) and open distal clavicle excision. Note the residual gap between the lateral clavicle and the acromion, as well as postoperative calcification in the area.
Magnetic resonance imaging (MRI) can be used to further characterize the degree of arthrosis when radiographs are equivocal, and its use is increasing in prevalence in the evaluation of shoulder pain. MRI should be obtained only after a careful history and physical examination have been performed because it is sensitive in identifying pathology but has poor specificity. Shubin-Stein et al demonstrated reactive bone edema to be a more reliable predictor of symptomatic AC pathology than degenerative changes on MRI (Fig. 5). It is important to note that a patient's pain may not correlate clinically with his or her radiographic findings because it has been shown that up to 82% of patients with AC joint arthritis based on MRI are asymptomatic.
(Enlarge Image)
Figure 5.
Right shoulder with acute acromioclavicular posttraumatic osteoarthritis in a 19-year-old football player with continued severe shoulder pain 6 months after a partial acromioclavicular separation. Note the bone edema in the lateral clavicle and the medial acromion, as well as the irregularity of the joint surface.
When arthritis of the AC joint is suspected to be the cause of a patient's symptoms based on history, physical examination, and imaging, an injection into the joint may serve both diagnostic and therapeutic purposes. A combination of local anesthetic and corticosteroid commonly is preferred. The joint is located by palpation and a superior approach is recommended. Accurate needle placement into the joint may prove difficult because of variations in joint anatomy, osteophyte formation, and other degenerative changes. Radiographic evaluation in advance of injection can help delineate the local anatomy to aid in successful joint entry. Ultrasound guidance also has been shown to further improve the accuracy of proper intraarticular needle placement.
