Evaluation of Preoperative Factors That Affect the Alpha Angle of Screw Insertion After the Open Latarjet Procedure

Background: The open Latarjet procedure yields excellent results as a treatment for anterior shoulder instability. The position of the bony fragment and the insertion angle of the screw (the alpha angle) are critical factors for a successful procedure. The alpha angle is considered overangulated at >25°, which is associated with poor bone fixation and healing. Purpose: To assess preoperative patient anatomic factors that affect the alpha angle in the Latarjet procedure for anterior shoulder instability. Study Design: Case-control study; Level of evidence, 3. Methods: In this retrospective study, 76 patients who underwent the open Latarjet procedure between October 2009 and December 2023 were included. Postoperative computed tomography scans were reviewed for the alpha angle, and patients were classified into 2 groups: group 1 (alpha angle ≥25°) and group 2 (alpha angle <25°). Preoperative patient characteristics and radiological parameters obtained from preoperative computed tomography scans were analyzed and compared between groups 1 and 2. We developed a novel method to measure the depth of the chest and the angle between the deltopectoral interval and the plane of screw insertion. We also measured the thickness of the pectoralis major and subscapularis muscles. Results: Of the 76 patients in this study, 41 and 35 patients were included in groups 1 and 2, respectively. The mean alpha angles of groups 1 and 2 were 36° and 12°, respectively, and the body mass index was significantly higher in group 1 ( P < .001). In addition, group 1 had a significantly longer distance from the anterior edge of the glenoid to the skin margin of the deltopectoral interval ( P < .001). The angle between the deltopectoral interval and the plane of screw insertion (traction angle) was significantly larger in group 1 ( P < .001), and the pectoralis major and subscapularis muscles were thicker in group 1 ( P = .017 and P = .032, respectively). Conclusion: The alpha angle after the Latarjet procedure was strongly related to the patient's weight, body mass index, depth of the chest, and the angle between the deltopectoral interval and the plane of screw insertion. To our knowledge, this is the first study in which the preoperative factors that facilitate proper screw fixation in the Latarjet procedure are reported.