The Changes in Gross Morphology and Histologic Features of the Torn Human Anterior Cruciate Ligament over Time

Background: In recent years there is a renewed interest in remnant preservation and repair surgery of the torn anterior cruciate ligament (ACL). These techniques rely on understanding the pathophysiological processes within the injured ligament. Studies that investigate those processes on humans are scarce.

Purpose: To observe the morphological and histological appearances of the torn ACL in relation to the time length from injury.

Study Design: Case series; Level of evidence, 4.

Methods: The study included twenty eight remnant specimens of torn ACL from patients who had reconstruction surgery of the knee. The remnant pathology was evaluated by its morphology during arthroscopy and by histopathologic measurements. A correlation analysis was performed between the pathological features of the remnant and the time length from injury.

Results: At surgery there were four distinct ACL tear morphological patterns that were correlated to the time span from injury (r = 0.86, p < 0.001) and ended with scarring of the femoral remnant to the posterior cruciate ligament. The earlier two patterns were noticed within an average time of 2.3 months and were characterized by abundance of lymphocytes and blood vessels at the torn femoral end. The latter two patterns were noticed within an average time of 15.9 months and were characterized by fewer lymphocytes and blood vessels with organized collagen fibers and hyaline degeneration.

Conclusions: At a short time from injury the morphological features of the ACL remnant show no scar and its histological features have characteristics of a reparative phase. This phase is followed by a prolonged remodeling phase that ends with scarring of the femoral remnant to the posterior cruciate ligament.

Keywords: anterior cruciate ligament; tear; histology; pathology; morphology