Heterotrophic Ossification of the Flexor Retinaculum in a Patient with Ankylosing Spondylitis

Carpal tunnel syndrome (CTS) is the most common peripheral neuropathy. This syndrome has various etiologies of which heterotopic ossification of the flexor retinaculum is a rare cause. Ankylosing spondylitis (AS) is a systemic, progressive inflammatory disease of unknown etiology that mainly affects the axial skeleton and rarely causes peripheral neurological symptoms. A 48-year-old woman presented with numbness and pain in her right hand. Ten years earlier, she was diagnosed with AS. Electrodiagnostic evaluation revealed severe median nerve compression at the right wrist. The patient underwent surgery for severe CTS. During the operation, the flexor retinaculum could not be incised due to marked stiffness. Ossification of the flexor retinaculum was seen, and the retinaculum was partially excised with an osteotome and Kerrison rongeur. The patient's complaints resolved almost totally after the operation. AS is a common systemic inflammatory disease that can produce heterotopic ossification of the flexor retinaculum. Preoperative wrist computed tomography should be obtained in patients with CTS and AS.