Background  Extension loss caused by anterior cruciate ligament (ACL) remnants nodule was usually reported by case reports. There is no systematic report analyzing ACL remnants nodule. The purpose of this study was to investigate the characteristics of extension loss caused by remnants of ACL after injury.

Methods  From June 2008 to December 2011, ACL remnants were observed by arthroscopy in 1012 cases with ACL injuries at the time of primary reconstruction. ACL remnants nodules were recorded. The time of extension loss occurrence caused by ACL remnants nodule, associated symptom and sign, magnetic resonance imaging (MRI), and arthroscopic findings were observed. Histological examination was performed on the lesion resected.

Results  Twenty-four cases with ACL remnants nodules were found by arthroscopy. Among them extension loss caused by remnants of ACL happened in 19 cases (male 13; female 6). The average extension loss were 9.1° (range, 5°-20°). The average time from injury to operation was 8.9 weeks (range, 3-26 weeks). The remnants of ACL depressed in the inter-condylar notch were found on MRI in 15 cases with extension loss. The rupture locations of ACL were all close to the upper insertion of ACL. The microscopic examination of the resected remnants of ACL revealed disorganized fibrous connective tissue and tissue of ACL ligament.

Conclusions  Among 1012 ACL injury cases, 24 ACL remnants nodules were found with arthroscopy and 19 nodules could cause knee extension loss. ACL remnants nodule should be paid attention to as a potential cause of extension loss.