Purpose: The goal of this study was to arthroscopically identify and assess the progressive changes in isolated ruptures of the posterolateral bundle of the anterior cruciate ligament (ACL) over time.
Methods: This prospective study investigated 174 patients for isolated posterolateral bundle tears during arthroscopic ACL reconstruction. The preoperative side-to-side anterior laxity was measured in all patients. The torn ACLs were inspected and analyzed arthroscopically to determine the tear pattern.
Results: Complete ACL tears were identified in 78.7% of patients and partial ACL tears in 21.3%. Isolated anteromedial bundle tears were identified in 22 patients and posterolateral bundle tears in 15 patients. Statistical analysis showed a significant difference in preoperative differential knee laxity between the group with complete ACL rupture and the group with partial ACL rupture. On arthroscopic evaluation, the posterolateral bundle had retracted distally toward the tibial surface over time. The amount of retraction was correlated to the time period from injury to reconstruction.
Conclusions: In this study the exact diagnosis of an ACL partial tear was made at arthroscopy in all cases. Our observations confirm the evolution of the ruptured posterolateral bundle, which shows a retraction toward the tibia over time.
Level of evidence: Level II, development of diagnostic criteria based on consecutive patients with a universally applied gold standard.