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Diagnostic Values of Tests for Acromioclavicular Joint Pain

Authors: Walton J et al.

References: J Bone Joint Surg Am. 2004;86A(4):807–12.

Purpose.
Disorders that produce shoulder pain often have similar clinical symptoms, thus challenging the differential diagnosis. This prospective study was conducted to determine which clinical tests and imaging studies were most helpful for diagnosing acromioclavicular joint (ACJ) pain.

Methods.
Of 1,037 patients with shoulder pain, 113 who mapped pain about the ACJ (within an area bounded by the midpart of the clavicle and the deltoid insertion) were eligible for inclusion in the study. This area was chosen because it represents the site map for pain after provocative injection into the ACJ. Of 113 subjects, 38 agreed to participate in and completed the study. Twenty clinical tests, three imaging modalities, and ACJ diagnostic injection tests were performed on all subjects.
The physical examination included inspection of the supraspinatus, infraspinatus and deltoid muscles for atrophy; tenderness at
the sternoclavicular, acromioclavicular, subacromial and biceps regions; passive range of motion of the neck; passive range of motion of the shoulder in flexion, abduction, internal and external rotation; the Paxinos sign; the O'Brien sign; testing for impingement in internal and external rotation; strength testing in external rotation (supraspinatus resisted external rotation); and strength testing of internal rotation (lift off test for subscapularis).
The Paxinos sign was performed with the patient seated and the affected arm dependent. The examiner placed his hand over the affected shoulder with his thumb under the posterolateral aspect of the acromion and the index and long fingers of the
same or contralateral hand superior to the midpart of the ipsilateral clavicle. The examiner then applied pressure to the acromion with the thumb, in an anterosuperior direction, and inferiorly to the midpart of the clavicular shaft with the index
and long fingers. The response was considered positive if pain was felt or increased in the region of the acromioclavicular
joint and negative if there was no change in the pain level.
The test for the O'Brien sign was designed primarily to detect labral tears, but it can also reproduce ACJ pain. The patient is asked to forward flex the affected arm 90 degrees with the elbowin full extension. The arm is then adducted 10 to 15 degrees medial to the sagittal plane and internally rotated so that the thumb points downward. The examiner applies uniform downward force to the arm. The maneuver is repeated in external rotation (palm up). The test result is positive if the first maneuver causes pain on top of the shoulder or at the ACJ, and the pain is less intense or is absent with the second maneuver.
The reference test standard was the patient's response to the ACJ injection, which consisted of lidocaine and methylprednisolone. The injection was performed under imaging control, by an experienced musculoskeletal radiologist who was masked to the patients' clinical data. The initial examiner then evaluated patients.
The test result was considered positive if the patient reported alleviation of the superior shoulder pain by at least 50% within 10 minutes after the injection (i.e., they were considered to have pain at the ACJ).
Results of imaging studies (radiographs, magnetic resonance, and bone scans) of the ACJ were classified as abnormal or normal by an experienced musculoskeletal radiologist who examined them for joint space narrowing, osteophytes, or
subchondral cysts.

Results and Discussion.
Of the 48 patients who indicated pain about the ACJ on the body diagram, 38 (74%) were confirmed to have ACJ pathology based on their positive response to the injection. This suggests that the patient's pain diagram is a good screening tool for ACJ pain. The clinical tests and imaging modalities were highly sensitive or highly specific, but not both. Each test was, by itself, relatively poor at predicting the ACJ as the cause of shoulder pain. The most sensitive tests were examination for acromioclavicular tenderness (96% sensitivity), the Paxinos test (79%), magnetic resonance imaging (85%), and bone
scanning (82%), but these studies had low specificity. The tests that best identified patients without an ACJ abnormality as such were the O'Brien test and radiographs; each had a specificity of 90%. However, the Paxinos test and bone scan in combination was highly predictive for ACJ abnormality (likelihood ratio 55:1; p , 0.001).
Thus, if a new patient who had mapped pain at the ACJ and radiating to the marked area had both a positive Paxinos test result and a positive bone scan result, the odds that that patient had ACJ pain as opposed to another type of shoulder pain would be 55:1. Similarly, if the patient had a negative result on both the Paxinos test and the bone scan, ACJ joint damage could be ruled out as the source of the pain.

Other investigators have reported that radiographs and magnetic resonance imaging have poor specificity (i.e., degenerative changes of the ACJ do not correlate well with ACJ pain). These authors found that bone scans had relatively high sensitivity and
specificity and therefore were more accurate in the diagnosis of ACJ pain. The O'Brien sign and the cross-arm adduction test may compress the ACJ indirectly and elicit pain by horizontal adduction of the arm or internal rotation of the shoulder. However, these test results can be positive in other shoulder disorders, such as posterior capsular tightness, or rotator cuff pathology. In contrast, the Paxinos test involves direct manual compression of the ACJ. It was found to be more sensitive than the O'Brien test for ACJ pain.

The authors conclude that ''direct compression of the ACJ (the Paxinos test) is a good clinical diagnostic tool, and bone-scanning is the best imaging modality for the diagnosis of ACJ pain. When both of these tests are positive in a patient with shoulder pain, the diagnosis of ACJ pain is virtually certain.''


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