BackgroundThe objective of the study was to depict the pathoanatomy of traumatic valgus instability of the elbow and to report clinical outcomes of primary operation.MethodsThirty-one patients presented with traumatic valgus instability of the elbow without dislocation. Thirty-one patients underwent surgical intervention of radial head fractures (28 open reduction and internal fixation and 3 radial head resection) and anatomical repair of the anterior bundle of medial collateral ligament (AMCL) with suture anchors. Twenty patients with disruption of the flexor-pronator tendon (FPT) and 14 patients with tears of the anterior capsule had primary repair of the FPT and anterior capsule simultaneously. Clinical outcomes were evaluated with the Mayo Elbow Performance Score (MEPS), modified hospital for special surgery assessment scale (HSS), and Disabilities of the Arm, Shoulder, and Hand (DASH) score.ResultsThe median follow-up was 37.3 months (range, 15–53 months). Radial head fractures and complete avulsion of the medial collateral ligament (MCL) from its humeral footprint were confirmed in all patients intraoperatively. Intraoperative findings indicated disruption of the FPT in 20 patients and tears of the anterior capsule in 14 patients. Twenty-nine of 31 patients returned to previous activity and work levels within 6 months after surgery. The MEPS, modified HSS, and DASH score were 94 ± 4, 91 ± 5, and 8 ± 2 at the latest follow-up.ConclusionsRadial head fractures with avulsion of the MCL can lead to severe valgus instability of the elbow. Primary operation to repair these disrupted structures, especially repair of the AMCL, can effectively restore valgus stability.