Innervation pattern of the anterolateral ligament (ALL) of the knee: Indication of an active role in proprioception and autonomic modulation

Abstract

Background: The anterolateral ligament (ALL) of the knee is increasingly recognized as a key structure in rotational stability, yet its anatomical and functional properties remain incompletely understood. This study investigates the innervation of the ALL using immunohistochemistry and electron microscopy to characterize its neurochemical profile and structural organization.

Methods: Seventeen ALL samples from adult human body donors were analyzed. Thirteen were examined using immunohistochemical staining for PGP9.5 (ubiquitin carboxyl-terminal hydrolase L1 (UCH-L1)), VAChT (Vesicular acetylcholine transporter), TH (tyrosine hydroxylase), CGRP (calcitonin gene-related peptide), and NOS (nitric oxide synthase). Four additional samples underwent transmission electron microscopy to assess ultrastructural features. Six Fibular collateral ligaments (FCL) were used as controls.

Results: All ALL specimens displayed positive immunoreactivity for the markers evaluated, confirming the presence of neurochemically diverse peripheral nerve fibers. Both myelinated and unmyelinated fibers were identified, though no encapsulated mechanoreceptors were observed. The innervation pattern was comparable to that of the (FCL), used as a control.

Conclusion: The ALL is a richly innervated structure with sensory, autonomic, and potential for neuromodulation, suggesting an active role in proprioception and homeostasis. These findings challenge previous views of the ALL as a passive capsular thickening and underscore its functional relevance in knee joint physiology.