Thrower's Exostosis of the Shoulder: A Systematic Review With a Novel Classification

Background: A variety of thrower’s exostoses are grouped under the term Bennett lesion, which makes understanding diagnosis and treatment difficult. Purpose: To identify all types of reported thrower’s and overhead athlete’s exostoses and categorize them into a classification system to allow a morphology-based classification. Study Design: Systematic review; Level of evidence, 4. Methods: A systematic review of all articles pertaining to Bennett lesions and thrower’s exostosis was performed. The classification and treatments were evaluated to describe the types, proposed causes, diagnosis, and treatment options. Results: A total of 27 studies were included in the systematic review. The anatomic locations referenced in the study demonstrated posteroinferior, posterior, and posterosuperior glenoid lesions. Aggregate radiographic data demonstrated 158 of 306 patients (52%) with a thrower’s exostosis of any type and location. Of these 158 patients with a radiographic lesion, 119 (75%) patients were symptomatic. The locations were posteroinferior in 110 patients (70%), directly posterior in 2 patients (1.3%), posterosuperior in 44 patients (28%), and unknown in 2 patients (1.3%). Avulsed lesions were present in 9 (5.7%) posteroinferior lesions, 0 direct posterior lesions, and 2 (1.3%) posterosuperior lesions. Treatment plans included both nonoperative and operative strategies, but operative intervention was more commonly reported for detached lesions. After operative intervention, only 61% of reported athletes returned to preinjury performance. Conclusion: Based on a comprehensive review of the literature, we identified several anatomic locations for a thrower’s exostosis beyond the classic Bennett lesion. We categorized the reported exostoses into a new classification system for description of location and type (subperiosteal or free fragment) of the thrower’s exostosis, which may be used to study future treatments. Current treatment strategies recommend that surgical treatment of thrower’s exostosis is considered only after exhausting nonoperative management because reported return to sport is variable after surgery. The effectiveness of excision or repair for both subperiosteal and detached lesions has not been established.