Localization of degenerative changes of the acromioclavicular joint: a cadaveric study

It has not been fully clarified yet how degenerative changes occur within the acromioclavicular (AC) joint, including their localizations. The aim of this study was to clarify the localization of degenerative changes in the AC joint using cadaveric specimens.

Thirty-eight cadaveric AC joints with the sections were cut in the coronal plane. For both the acromion and the clavicle, the joint surface was divided into upper and lower halves. Histological features including the mean thickness of cartilage, reduction of proteoglycan staining and the extent of damaged tidemark were evaluated. The shapes of intraarticular discs as well as their histological structures were also assessed, which were compared between the upper and lower halves.

Articular cartilage in the lower half was significantly thinner than that in the upper half for both the acromion and the clavicle (p < 0.01). Similarly, the lower half of cartilage was more degenerated than the upper half. Intraarticular discs were absent in nine joints and the meniscoid-like type in 29, which contained rich fibrocartilaginous tissues in the upper half, whereas it mainly consisted of the fibrous tissues with granulation in the lower half.

The lower half of the AC joint demonstrated more advanced degeneration than the upper half, which might reflect the greater repetitive mechanical stress. The present study revealed both the localization and the extent of degenerative changes in AC joint, which might be useful information for surgeons to determine the proper amount of bony resection in the surgical treatment for osteoarthritis of this joint.