Summary

The molecular profile of a repaired ACL is very similar to that of a healthy ACL cadaver knee

Abstract

Background

The healing process of an anterior cruciate ligament (ACL) injury is not yet fully understood. Unlike extra-articular ligaments, whose repair occurs early, the intra-articular environment of the cruciate often prevents this process.

Purpose

To assess and compare the healing process and eventual tissue formation in ACL repair and ACL reconstruction.

Methods

Three different groups were included in this study. In 15 patients, who previously underwent ACL repair (ACL REP), an outpatient needle arthroscopic second look was performed between 8 and 12 months postoperatively and a biopsy specimen of the repaired ACL was performed. The second group involved 10 patients, who had previously undergone ACL reconstruction (ACL REC) with hamstrings. A biopsy specimen was also taken in these patients, who underwent subsequent knee arthroscopy for reasons other than graft failure. The third control group (CTRL) consisted of 15 specimens taken from healthy ACL cadaver knees. A gene expression analysis of Collagen I (Coll I), Collagen III (Coll III), Collagen I-III ratio, alpha smooth muscle actine (a-SMA) and p16 in the three groups was performed.

Results

Gene expression analysis of Coll I showed a statistically significant difference between both the CTRL group and ACL REC group and between ACL REP group and ACL REC group (p = 0.0027). A statistically significant difference in both the Coll I/III ratio (p= 0.0003) and a-SMA expression (p = 0.001) was also found between the groups CTRL and ACL REC and between the groups ACL REP and ACL REC.

Conclusions

The molecular profile of a repaired ACL is very similar to that of a healthy ACL cadaver knee in terms of mRNA expression. This similarity was observed in collagen quality, degree of activation of the cellular differentiation process (a-SMA), and degree of cellular senescence (p16) in the tissue samples examined. In contrast, the reconstructed ACL exhibits a completely different molecular profile than a healthy ligament.