Persistence of mechanoreceptors in ACL remnants: a histological and immunohistochemical analysis of 128 patients

BACKGROUND: Anterior cruciate ligament (ACL) remnants may retain sensory neural elements after rupture, potentially contributing to proprioceptive function and graft reinnervation following reconstruction. However, the persistence of mechanoreceptors in remnant tissues and the factors influencing their preservation remain incompletely understood. This study aimed to evaluate the presence of neural structures in ACL remnants using histological and immunohistochemical methods and to determine the association between mechanoreceptor preservation, injury duration, and remnant attachment pattern. METHODS: ACL remnant tissues were obtained from 128 patients undergoing arthroscopic ACL reconstruction. Specimens were examined using hematoxylin-eosin (H&E) staining and immunohistochemistry with S100, myelin basic protein (MBP), and β-III-tubulin antibodies to identify neural elements. Patients were classified according to injury duration as subacute (≤ 3 months), chronic (3-12 months), and late chronic (> 12 months). Remnants were also categorized based on arthroscopic appearance as PCL-femur attachment or tibial stump. Mechanoreceptor presence and distribution were analyzed, and multivariate logistic regression was performed to evaluate factors associated with mechanoreceptor preservation. RESULTS: Mechanoreceptors or neural structures were identified in 81 of 128 specimens (63.3%). Free nerve endings were the most frequently observed neural elements, whereas structured receptors such as Ruffini or Golgi-like endings were less common and Pacinian corpuscles were rare. Mechanoreceptor prevalence differed significantly according to injury duration, being highest in the subacute group (84.8%) and lower in the chronic (58.7%) and late chronic (53.1%) groups (p = 0.01). The remnant attachment pattern did not show a significant association with mechanoreceptor presence (p = 0.23). Logistic regression analysis demonstrated that longer injury duration was independently associated with reduced odds of mechanoreceptor detection. CONCLUSIONS: ACL remnants frequently retain neural structures, particularly during the early post-injury period, but the prevalence of mechanoreceptors decreases with increasing injury duration. Remnant attachment pattern appears to have a limited influence on neural preservation. These findings support the biological rationale for remnant-preserving reconstruction strategies when technically feasible and highlight the potential importance of early surgical intervention for maintaining proprioceptive tissue integrity.