Sensory Innervation of the Subregions of the Scapholunate Interosseous Ligament in Relation to Their Structural Composition

PurposeTo investigate the different types of innervation and the presence of mechanoreceptors in relation to the structural composition of the scapholunate interosseous ligament and to correlate the findings with the known mechanical properties of the ligament subregions.MethodsSix fresh cadaveric scapholunate interosseous ligaments were divided into their 3 subregions: dorsal, palmar, and proximal. The microscopic features were investigated with use of a standard hematoxylin-eosin stain and immunostains for S-100, neurofilaments, neuron-specific enolase, protein gene product 9.5, CD31, and smooth muscle actin. The connective tissue structural composition and the presence of blood vessels and neural structures (myelinated and unmyelinated nerve fibers and mechanoreceptors) were investigated. The macroscopic anatomic details were also noted.ResultsThe palmar subregion consists of structured, densely collagenized tissue at the core, surrounded by looser connective tissue. Myelinated nerve fibers forming fascicles accompany the interspersed blood vessels inside the ligament substance. Their concentration is greater in the proximal part of the palmar subregion, reaching a distance of approximately 150 μm from the ligament free surface. The dorsal subregion has similar structure to the palmar one, but the fibrous tissue ratio and density are higher. The proximal subregion consists of chondroid matrix and of loose connective tissue at its core. The radio-scapholunate ligament insertion is noted at the palmar aspect of the proximal subregion. Pacinian and other sensory corpuscles were found mostly at the palmar and proximal subregions.ConclusionsThe scapholunate interosseous ligament is a richly innervated ligament that contributes to carpal proprioception, a fundamental element of dynamic wrist stability. The palmar subregion, apart from its major mechanical role, contains the greatest amount of the neural structures and mechanoreceptors. The dorsal subregion, with densely packed collagen fibers and limited innervation, functions mainly to constrain the scaphoid-lunate relative motion.