Diffuse idiopathic skeletal hyperostosis (DISH) predisposes the spine to highly unstable fractures because of long lever-arm biomechanics. Unstable injuries, including AO Spine Osteoporotic Fracture (OF) type 5, are typically treated with long-segment posterior instrumentation; however, pedicle-screw fixation may be infeasible in very elderly patients with severe osteoporosis, critically narrow pedicles, and/or significant comorbidities. A 93-year-old Japanese woman presented with severe back pain without apparent trauma. Computed tomography (CT) revealed a T12 fracture with DISH, classified as OF5. The pedicles were critically narrow (3.7-4.1 mm), and dual-energy X-ray absorptiometry confirmed severe osteoporosis. Because conventional pedicle-screw fixation was considered technically unsafe and excessively invasive, limited posterior stabilization was performed using a single spinous process plate spanning T10-L1. The operative time was 48 min and the estimated blood loss was 10 ml. Immediate postoperative CT confirmed appropriate implant positioning and maintained alignment. At the 1-year follow-up, CT demonstrated solid bony union with preserved alignment and no implant failure; the patient had remained pain-free and ambulatory. This case demonstrates that spinous process-plate fixation can be a minimally invasive salvage option for carefully selected very-elderly patients with DISH when pedicle-screw instrumentation is not feasible.