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

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.

Comparative histomorphological analysis of elbow ligaments and capsule.

This study aimed to compare the histomorphology of the elbow capsule and its ligaments to gain a better understanding of the clinically relevant biomechanical stabilization. Eleven human elbows were dissected including the joint capsule with its anterior (AJC) and posterior (PJC) parts, the annular ligament (AL), the radial collateral ligament (RCL) and the ulnar collateral ligament with its anterior (AUCL), posterior (PUCL) and transverse (TUCL) parts. Hematoxylin-Eosin and Elastica van Gieson as conventional histology stainings were applied to determine collagenous and elastic fiber arrangements in transmission and polarization light microscopy. The radial collateral ligament and the anterior part of the ulnar collateral ligament showed significantly more densely packed parallel fiber arrangement than the anterior joint capsule, the posterior joint capsule, and the posterior part of the ulnar collateral ligament (p < 0.02, respectively). The PUCL had significantly more mixed tight and loose parallel arrangements than the PJC, the annular ligament, the RCL, the AUCL and the transverse part of the ulnar collateral ligamentp < 0.02, respectively), while the PJC showed significantly more interlaced mixed tight and loose fiber arrangement than the AL, the RCL and the AUCL (p < 0.003, respectively). The AJC had a significantly higher amount of elastic fibers as compared to the AL, the RCL, the AUCL and the TUCL in fascicular regions (p < 0.04, respectively), while the AUCL had significantly lesser elastic fibers than the AJC and the PJC (p < 0.004, respectively). The densely packed parallel fiber arrangement and few elastic fibers of the AUCL, RCL, and AL indicate a strong biomechanically stabilizing function. The fiber arrangement of the PUCL and the TUCL with few elastic fibers support the medial elbow stabilization. Crimping and elastic fibers provide the viscoelasticity of the joint capsule.