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. 2023 Mar;143(3):1523-1529.
doi: 10.1007/s00402-022-04407-3. Epub 2022 Apr 5.

Morphology of the acromioclavicular-joint score (MAC)

Milad Farkhondeh Fal  1 , Marius Junker  2 , Konrad Mader  3 , Karl Heinz Frosch  3 , Jörn Kircher  4   5
Affiliations

Morphology of the acromioclavicular-joint score (MAC)

Milad Farkhondeh Fal et al. Arch Orthop Trauma Surg. 2023 Mar.

Abstract

Introduction: To date there is no generally accepted specific definition or classification of acromioclavicular (AC) joint osteoarthritis. The aim of this study is to analyze morphological parameters using magnetic resonance imaging (MRI) and to develop a scoring system as a basis for decision making to perform an AC-joint resection.

Materials and methods: In a retrospective-monocentric matched pair study, healthy and affected subjects were investigated using T2 MRI scans in the transverse plane. There were two groups, group 1 (n = 151) included healthy asymptomatic adults with no history of trauma. In group 2, we included n = 99 patients with symptomatic AC joints, who underwent arthroscopic AC-joint resection. The central and posterior joint space width and the AC angle were measured. Morphological changes such as cartilage degeneration, cysts and bone edema were noted. Malalignment of the joint was defined as: posterior joint space width < 2 mm in conjunction with an AC angle > 12°. A scoring system consisting of the measured morphologic factors was developed.

Results: Symptomatic and asymptomatic patients showed significant differences in all measured items. We observed a significant difference in the MAC score for symptomatic and asymptomatic patients (mean 10.4 vs. 20.6, p = 0.0001). The ROC (receiver operator characteristic) analysis showed an excellent AUC of 0.899 (p = 0.001). The sensitivity of the MAC score was 0.81 and the specificity 0.86. The MAC score shows a significant moderate correlation with age (r = 0.358; p = 0.001). The correlation of age and the development of symptoms was only weak (r = 0.22, p = 0.001). Symptomatic patients showed significantly more frequent malalignment compared to asymptomatic patients (p = 0.001), but the positive predictive value that a patient with malalignment is also symptomatic is only 55%.

Conclusion: Patients with symptomatic AC joints showed a typical pattern of morphological changes on axial MRI scans with early posterior contact of the joint surfaces, reduction of joint space and malalignment as the basis for the development of a scoring system. The MAC score shows excellent test characteristics, and therefore, proved to be both an appropriate guidance for clinical practice as well as an excellent tool for comparative studies and is superior to the assessment of malalignment alone.

Level of evidence: Level IV, retrospective diagnostic study.

Keywords: Acromioclavicular joint; Degenerative joint disease; MRI; Morphology; Osteoarthritis; Score; Shoulder.

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Conflict of interest statement

Farkhondeh Fal M., Junker M., Konrad M., Frosch K.H, and Kircher J. declare that they have no conflict of interest.

Figures

Fig. 1
Fig. 1
a On MRI scans in the transverse plane with fluid-sensitive sequences (T2-weighted images, T1-weighted images with contrast medium or comparable sequences), the central and posterior joint space width of the AC joints was measured. The distance between both perpendicular bars on line C represents the central joint space width and the distance between both perpendicular bars on line P represents the posterior joint space width. b The AC angle was measured between two lines that are aligned with the joint surface of the acromion (line A) and the lateral clavicle (line B), respectively (an anteriorly open angle defined with positive values)
Fig. 2
Fig. 2
a Significant difference in the MAC score for asymptomatic (left) and symptomatic (right) patients. b MAC score: seven items (left column) are assessed and given points according to the defined criteria (column 2–4). The right column lists the maximum points achievable, the highest possible score is 30 points. AC angle: the angle between a line parallel to the joint surface of the acromion and the lateral clavicle, anteriorly open angles are positive (Fig. 2). Joint space central: the joint space width at the center of the AC joint in the anterior–posterior direction (Fig. 1). Joint space posterior: the joint space width at the most posterior part of the AC joint in the anterior–posterior direction (Fig. 1). Cartilage grading acromion and clavicle: the hyaline cartilage at the acromial part or the clavicle part of the AC joint, respectively, is graded according to Petersson et al. Grade I: superficial degenerative signs with blister formation and some fragmentation; Grade II: deep degeneration with cartilage fragmentation, blister formation and penetrating ulceration of the joint surface in irregularly shaped areas; Grade III: full-thickness cartilage degeneration denuding the subchondral bone of more than 50% of the joint surface. Bone marrow edema acromion and clavicle: the presence of a bone marrow edema at the acromial part or the clavicle part of the AC joint, respectively, is assessed
Fig. 3
Fig. 3
ROC-curve (receiver operator characteristics curve) for the MAC score. The area under the curve (AUC) is 0.899, the standard error 0.019
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