Variability in the Spectrum of Reporting on the Schenck KD I Classification in the Orthopaedic Literature: A Systematic Review and Meta-analysis.

Background: There has been a marked increase in the number of Schenck knee dislocation (KD) I injuries reported in the multiligament knee (MLK) injury (MLKI) and KD literature. Purpose: To examine the heterogeneity of the Schenck KD I classification in the MLKI and KD literature. Study Design: Systematic review; Level of evidence, 4. Methods: A systematic literature search of PubMed, CINAHL, Scopus, Web of Science, EMBASE, and Cochrane Library was conducted for all studies that investigated KDs and/or MLKIs, utilized the Schenck or an MLKI classification system, and included patients with KD I or MLK 1 injuries. Pooled analysis determined the total number of KD I or MLK 1 injuries and the specific ligamentous tear patterns. Binary meta-analyses of the studies that reported neurovascular injury within each Schenck KD class compared the pooled odds ratio (OR) of vascular and neurological injury in unicruciate (KD I) and bicruciate (KD II-IV) injuries. Results: Included were 50 studies in which 3460 KD I injuries were reported out of 7872 KDs and MLKIs (43.9%). Of the 2912 patients reported to have had a Schenck KD I injury, 26 patients (0.9%) had a clinically and/or radiographically confirmed tibiofemoral KD. The overall prevalence of Schenck KD I injury with documented tibiofemoral KD was 26 of 7872 (0.3%). A total of 22 studies (n = 1702 patients) reported the specific ligamentous tear patterns; the most common patterns were posterior cruciate ligament (PCL)/lateral collateral ligament (LCL) (n = 526; 30.9%), anterior cruciate ligament (ACL)/LCL (n = 488; 28.7%), ACL/medial collateral ligament (MCL) (n = 408; 24.0%), and PCL/MCL (n = 198; 11.6%). Meta-analyses demonstrated that when compared with bicruciate KD or MLKI, unicruciate KD or MLKI was significantly less likely to have concomitant vascular injury (OR, 0.28; 95% CI, 0.15-0.51; Conclusion: The number of true, clinically and/or radiographically confirmed unicruciate KDs was extremely rare, representing <1% of all reported Schenck KD I injuries. A misappropriation of these injury patterns as true KDs may be taking place, affecting outcome studies and potentially biasing published clinical results. An MLKI classification system must document whether a confirmed KD has occurred.