Piso-hamate coalition may displace the deep motor branch of the ulnar nerve superficially over the osseous bridge. We report a 25-year-old man with a retained glass fragment and a posttraumatic neuroma one year after a penetrating hand injury. At surgery, the branch lay directly within the trajectory of the foreign body. After neuroma excision, the resulting nerve gap of 8 mm precluded tension-free repair. A longitudinal groove was created in the superficial aspect of the osseous bridge, shortening and protecting the nerve course and enabling direct tension-free neurorrhaphy. Qualitative dynamic radiographs showed hamato-triquetral widening in radial deviation, which contributed to the decision to preserve most of the coalition. Piso-hamate coalition may predispose the deep motor branch to penetrating injury. This case demonstrates the technical feasibility of selective osseous grooving to facilitate direct repair of the deep motor branch.