The structure of the coracoacromial ligament: fibrocartilage differentiation does not necessarily mean pathology

Abstract

The coracoacromial ligament forms part of the coracoacromial arch and is implicated in impingement syndrome and acromial spur formation. Here, we describe its structure and the composition of its extracellular matrix. Ligaments were obtained from 15 cadavers, nine from older people (average age 74.7 years) and six from younger individuals (average age 24.2 years). Cryosections of methanol-fixed tissue were cut and sections were immunolabelled with monoclonal antibodies against collagens, glycosaminoglycans, proteoglycans, matrix proteins and neurofilament proteins. Both ligament entheses were highly fibrocartilaginous and immunolabelled strongly for type II collagen, aggrecan and link protein. The area of labelling was more extensive in older people. However, fibrocartilage also characterized the ligament midsubstance, particularly with increased age. Signs of fibrocartilage degeneration were more common in older people. Ligament fat (containing blood vessels and nerve fibers) was conspicuous in both age groups, especially between fiber bundles at the entheses. We conclude that fibrocartilage is a normal feature but becomes more pronounced with age. It is not necessarily pathological, for it simply indicates that the ligament is subject to compression and/or shear. Nevertheless, the prominence of fibrocartilage at the acromial enthesis may relate to the frequency with which enthesophytes develop.

The Coracoacromial Ligament: Anatomy, Function, and Clinical Significance

“…(C) Demonstrates the neurovascular bundle (BV) and nerve fibers (arrows) within the ligament. B, bony acromion (Reprinted with permission from Milz et al 38 )…”

“…Investigation into alterations of “normal” CAL histology has revealed a number of consistent changes associated with age and shoulder pathology. Milz et al 38 found that the distribution of fibrocartilage varied with age, as older (mean age, 74.7 years) specimens had increased concentrations of type II collagen and aggrecan along the CAL midsubstance when compared with younger (mean age, 24.2 years) specimens. Degenerative changes in fibrocartilage, including extracellular matrix degeneration, calcification, and ossification, were also associated with increasing age.…”

“…In addition to potential roles in degenerative rotator cuff pathology, CAL enthesopathy, independent of acromial angle, has been associated with impingement syndrome. 37,38,40,47,65 A recent retrospective review evaluated the grade of CAL degeneration in patients with subacromial impingement. 29 In this level 4 study, grades 1 and 2 CAL degeneration were strongly correlated with impingement syndrome, and partial CAL release was advocated by the authors particularly in the setting of bursal-sided partial rotator cuff tears.…”

Discrimination of meniscal cell phenotypes using gene expression profiles

“…The placement in this spectrum is dependent on the extent of the fi brocartilage cell differentiation, which is infl uenced by the mechanical forces it experiences. While the majority of tendons and ligaments are composed of fi brous tissues, some regions such as the enthesis or contact region of wrap-around tendons, which are exposed to compression, have been found to naturally develop cartilage-like properties of avascularity and high contents of proteoglycan and collagen II (Milz et al, 2008). The degree of this differentiation within the tendon varies according to the distance from the wrap-around surface against which the tissue is compressed, indicating that such transformation of tissue properties is in fact an adaptation to the mechanical response (Wren et al, 2000).…”

Reliability of Determining and Measuring Acromial Enthesophytes

“…Acromial enthesophytes are thought to be an ossification of the insertion of the coracoacromial ligament where it attaches to the anterior acromial surface [5, 7, 12, 27] (Fig. 1).…”