Anatomic variations of the hook of hamate and the relationship to carpal tunnel syndrome

Purpose: To determine the incidence of anatomic variations of the hook of hamate and to evaluate its association with the development of carpal tunnel syndrome (CTS). Methods: Radiographs of 3,218 hands (2,070 patients) were evaluated. This group included 2,866 hands diagnosed with CTS and 352 hands without the diagnosis of CTS. Using the carpal tunnel view variations of the hook of hamate were identified. Variants were classified based on appearance and measurements. Patients having variant hooks of hamate who were diagnosed with CTS then were compared with patients with variant hooks of hamate who had no evidence of CTS. Endoscopic carpal tunnel release using the Chow technique was performed on all patients with CTS who had a known variation of the hook of hamate without difficulty or complication. Results: Variations of the hook of hamate were found in 96 hands: 42, bipartite hook; 50, hypoplastic hook; and 4, aplastic hook. Ninety-three hands with variant hooks of hamate were diagnosed with CTS. The remaining 3 hands identified with variants had no evidence of CTS. After comparing the 2 groups, we found that the incidence of a variant hook of hamate in the group with CTS was significantly greater than the incidence of variations in the group without CTS. Conclusions: Three variations of the hook of hamate were identified with radiographic evaluation using the carpal tunnel view. Variations are more prevalent than once thought. There was a significant increase in the incidence of variation in the hook of hamate in the group with CTS compared with the group without CTS.