Immunofluorescence analysis of sensory nerve endings in the periarticular tissue of the human elbow joint.

ABSTRACT

INTRODUCTION: To investigate the dynamic aspects of elbow stability, we aimed to analyze sensory nerve endings in the ligaments and the capsule of elbow joints. MATERIALS AND METHODS: The capsule with its anterior (AJC) and posterior (PJC) parts, the radial collateral ligament (RCL), the annular ligament (AL), and the ulnar collateral ligament with its posterior (PUCL), transverse (TUCL) and anterior parts (AUCL) were dissected from eleven human cadaver elbow joints. Sensory nerve endings were analyzed in two levels per specimen as total cell amount/ cm2 after immunofluorescence staining with low-affinity neurotrophin receptor p75, protein gene product 9.5, S-100 protein and 4',6-Diamidin-2-phenylindol, Carbonic anhydrase II and choline acetyltransferase on an Apotome microscope according to Freeman and Wyke's classification. RESULTS: Free nerve endings were the predominant mechanoreceptor in all seven structures followed by Ruffini, unclassifiable, Golgi-like, and Pacini corpuscles (p ≤ 0.00001, respectively). Free nerve endings were observed significant more often in the AJC than in the RCL (p < 0.00002). A higher density of Ruffini endings than Golgi-like endings was observed in the PJC (p = 0.004). The RCL contained significant more Ruffini endings than Pacini corpuscles (p = 0.004). Carbonic anhydrase II was significantly more frequently positively immunoreactive than choline acetyltransferase in all sensory nerve endings (p < 0.05). Sensory nerve endings were significant more often epifascicular distributed in all structures (p < 0.006, respectively) except for the AJC, which had a pronounced equal distribution (p < 0.00005). CONCLUSION: The high density of free nerve endings in the joint capsule indicates that it has pronounced nociceptive functions. Joint position sense is mainly detected by the RCL, AUCL, PUCL, and the PJC. Proprioceptive control of the elbow joint is mainly monitored by the joint capsule and the UCL, respectively. However, the extreme range of motion is primarily controlled by the RCL mediated by Golgi-like endings.