We present a case that is unusual in two respects. To our knowledge, it is the first clearly documented instance in the literature of a post-traumatic, irreducible nondissociative volar intercalated carpal instability to result from a known wrist flexion force and a known dorsal capsuloligamentous tear. Second, the same wrist revealed a coalition at both intraosseous levels of the proximal carpal row: a synfibrosis at the scapholunate joint and a synostosis at the lunotriquetral joint. Treatment by open removal of an interposed capsuloligamentous flap from the radiocarpal joint, followed by alignment of carpal elements, temporary internal fixation, and repair of the damaged dorsal capsule and ligaments gave an excellent result.