Congruence angle and medial ulnar translation: a novel measurement to assess the severity of ligament injury in simple elbow dislocation

Aims: This study was to propose novel measurements to assess severity of ligament injury in simple elbow dislocation using axial imaging. This study assessed inter- and intraobserver reliability of the proposed novel measurements and compared their application as measures of severity of medial collateral ligament (MCL) and lateral collateral ligament (LCL) injuries.Methods: This retrospective study included patients diagnosed with simple elbow dislocations from January 2013 to December 2023. The degree of MCL and LCL injuries was assessed by four grades: (0 (normal); 1 (sprain); 2 (partial tear); and 3 (complete tear)) using MRI. Patients were classified into two groups according to the severity of MCL and LCL injuries (Group I (degree of MCL injury ≥ LCL injury); and Group II (degree of MCL injury < LCL injury)). The novel measurements were defined by measuring congruence angle (CA), medial ulnar translation (TRANS), and lateral ulnar tilt (TILT) as determined by axial MRI. Adjusted medial ulnar translation (ADJ-TRANS) was calculated. Two observers measured all parameters twice over four weeks.Results: A total of 21 patients were analyzed. Interobserver reliability was moderate to good for CA and good for TRANS. Both CA and TRANS showed excellent intraobserver reliability. Grade 2 MCL injury had significantly higher ADJ-TRANS than grade 1, while grade 2 LCL injury had significantly higher TRANS than grade 1. Meanwhile, grade 3 LCL injury had significantly higher CA and TRANS than grade 2, and significantly higher CA, TRANS, and ADJ-TRANS than grade 1. Group II also had significantly higher CA, TRANS, and ADJ-TRANS than Group I.Conclusion: Novel measurements using axial images of MRI scans achieved overall good inter- and intraobserver reliability. Higher grade LCL injury exhibited higher CA, TRANS, and ADJ-TRANS. Patients with LCL injury graded higher than that of MCL injury exhibited higher CA, TRANS, and ADJ-TRANS.Cite this article: Bone Jt Open 2025;6(11):1468–1474.