Is a Partial Anterior Cruciate Ligament Tear Truly Partial? A Clinical, Arthroscopic, and Histologic Investigation.

PURPOSE: (1) To determine whether examination under anesthesia (EUA) and/or magnetic resonance imaging (MRI) is an accurate means for determining patient selection for a selective-bundle reconstruction, (2) to determine whether the preoperative clinical assessment correlates with the arthroscopic examination, and (3) to examine histologically whether a partial anterior cruciate ligament (ACL) tear is truly partial in terms of vascular insult. METHODS: This prospective, nonrandomized cohort study included 95 patients who underwent primary ACL reconstruction from January 2013 through May 2014. All patients underwent an EUA, MRI, and arthroscopic evaluation. In patients with partial ACL tears, the intact bundle was resected and underwent histologic examination. The χ2 test was used to compare EUA and MRI in the detection of partial tears. RESULTS: Of the 95 patients included, 40 (42%) had EUA findings consistent with a partial ACL tear whereas 22 (23%) had MRI findings interpreted as showing a partial ACL tear. Arthroscopic examination confirmed a partial ACL tear in only 11 patients (12%). The sensitivity of EUA and MRI in the detection of partial ACL tears was 100% and 90.9%, and the specificity was 65% and 85.7%, respectively. The χ2 test suggested statistically significant associations between the method of evaluation and diagnostic outcome [χ2(1) = 7.83, P = .005]. MRI was 1.24 times more likely to correctly identify a partial tear (95% confidence interval, 1.06-1.45). EUA was 2.23 times as likely to incorrectly identify a partial tear (95% confidence interval, 1.24-4.02). The histologic analysis showed increased numbers of lymphocytes, absent polymorphonuclear leukocytes, predominant fibroblasts, neovascularization, and variable collagen orientation. CONCLUSIONS: There is a disparity between EUA, MRI, and arthroscopic findings in the evaluation of partial ACL tears. Arthroscopy remains the gold standard for diagnosing the macroscopic integrity of the intact bundle. Microscopic analysis reveals that the integrity of the remaining intact ligament material is altered and may show a histologic response similar to a complete ACL rupture. LEVEL OF EVIDENCE: Level III, prospective, nonrandomized cohort study.