Morphologic changes in the injured anterior cruciate ligament (ACL) correlated with the expressions of protein S100 AND NFAP: Major therapeutic implications or a wrong gateway towards improving ACL reconstruction ?

Objectives: We examined the histoarchitecture of the anterior cruciate ligament [ACL] stumps in different stages of evolution after injury and we analyzed the correlation with the expressions of protein S100 and neurofilament associated protein [NFAP]. Materials and Methods: A total number of 102 cases of ruptured ACL was included in our study. Immunohistochemistry was performed for protein S100 [56 cases] and NFAP [46 cases] in order to evaluate the nervous structures located in the ligament and in the synovial tissue. Results: Protein S100 and NFAP were identified in the quasi-normal ligament, in the disrupted ligament and in the synovial tissue. Protein S100 was positive in the nervous structures of the synovial tissue. The nervous fibers from the ligament also reacted to protein S100. The synovial tissue reacted to NFAP at the level of the small nervous fibers and free nerve endings. In the ligament, NFAP expression was predominantly found in the small nervous fibers and in the free nerve endings. The quasi-normal ligament showed a greater number of NFAP positive free nerve endings. Conclusions: We found significant differences between the quasi-normal and the disrupted ligament regarding the expressions of protein S100 and NFAP. The low number of nervous structures identified using the two markers may suggest a time- and injury-dependent loss of nervous fibers following post-rupture ligament remodeling. The persistence of nervous fibers in the remnant stumps of the ruptured ACL is not ‘absolute’ and may not always ensure a successful recovery of the patient after ACL reconstructio