Typical patterns of malalignment in the degenerative acromioclavicular joint

Abstract

Although arthroscopic acromioclavicular (AC) joint resection is a frequently performed procedure, the pathophysiology of non-traumatic AC joint degeneration is still unclear. The purpose of this study was to investigate whether non-traumatic AC joint degeneration shows a typical pattern and whether it starts at the posterior part of the joint with malalignment of the articular surfaces. In a retrospective monocentric diagnostic study, healthy and affected subjects were investigated using T2 magnet resonance imaging (MRI) scans in the transverse plane. Group 1 included 30 healthy asymptomatic adults with no history of trauma (mean age, 38.6 years). In group 2, 90 patients with symptomatic AC joints who underwent arthroscopic AC joint resection were included (mean age, 60.0 years). All patients with relevant pathologies that affect the AC joint were excluded. Malalignment was defined as posterior joint space smaller than 2\u202fmm in conjunction with an AC angle lower than 12°. The measured values were (mean group 1 in mm; mean group 2 in mm; p-value): anterior joint space (6.07; 5.63; 0.50), central joint space (2.97; 2.09; 0.001), and posterior joint space (3.97; 2.38; 0,001), AC angle (7.63; 19.2; 0.001). In group 1, n\u202f=\u200924 (80%) of subjects showed aligned AC joints, whereas in group 2, only n\u202f=\u200911 (12.2%) of joints were aligned (p\u202f<\u202f0.001). Increasing age correlated significantly with malalignment (r\u202f=\u20090.21, p\u202f=\u20090.021). Patients with symptomatic degenerative changes of the AC joint show a typical pattern of anterior opening of the joint with early contact of the posterior joint surfaces in contrast to healthy subjects. Increasing age influences this effect.