Immunohistochemical analysis of mechanoreceptors in transverse acetabular ligament and labrum: a prospective analysis of 35 cases

Objective: The labrum and transverse acetabular ligament (TAL) are classically described as distinct anatomical structures with abundant mechanoreceptors and free nerve fibers. They deepen the joint and act as natural barriers against dislocation, thus providing additional stability. We hypothesized that severe coxarthrosis leads to elimination of labrum and TAL mechanoreceptors. This study evaluated the microscopic anatomy of the labrum and TAL and specifically investigated the neurological status of these structures. Methods: Labral and TAL specimens from 35 consecutive patients with coxarthrosis undergoing total hip arthroplasty were dissected into a total of 4 specimens per hip. Formaldehyde-fixed specimens were evaluated for the presence of mechanoreceptors and free nerve endings by neurofilament protein and S-100 protein immunohistochemistry and microscopy. Results: Mechanoreceptors were identified in the labral (2.3/high power field) but not TAL specimens, with a sharp delineation between the tissues. In contrast, both labrum and TAL showed good vascularity with abundant free nerve fibers within fibrous connective tissue (mean, 2.6 sensory fibers/ high power field vs 3.1/high power field, respectively). Conclusion: This study demonstrated that the TAL lacks mechanoreceptors. However, TAL and labrum free nerve fibers suggest potential roles as hip pain generators.