Is There a Critical Dorsal Lunate Facet Size in Distal Radius Fractures That Leads to Dorsal Carpal Subluxation? A Biomechanical Study of the Dorsal Critical Corner

Purpose Intra-articular distal radius fractures are common and can be associated with carpal instability. Failure to address articular fragments linked to maintaining carpal stability can lead to radiocarpal subluxation or dislocation. The purpose of this study was to evaluate the size of a dorsal osteotomy in the dorsal/ volar plane of the lunate facet that leads to dorsal carpal subluxation. Methods Dorsal lunate facet fractures were simulated twice in each of nine fresh-frozen cadavers. After completing a partial dorsal osteotomy in the radial/ulnar plane between the scaphoid and lunate facets, an osteotomy in the dorsal/volar plane was completed. Using a cutting jig, first an estimated 5-mm osteotomy, and then a 10-mm osteotomy (from the dorsal rim of the distal radius) were completed. The wrist was mounted in a custom jig and loaded with 100 N. Displacement of the lunate in the dorsal/volar plane compared with displacement in an intact specimen was evaluated and used to assess carpal subluxation. Results Lunate translation was 0 mm +/- 0 mm in the intact state. The 5-mm osteotomy averaged 29% of the distal radius dorsal lunate facet in the dorsal/volar plane, and lunate translation was 0.7 mm +/- 1.7 mm. The 10-mm osteotomy averaged 54% of the dorsal lunate facet in the dorsal/volar plane, and lunate translation was 2.8 mm +/- 2.6 mm. Assuming a linear relationship from the osteotomies created, an osteotomy of an estimated >40% of the distal radius in the dorsal to volar plane resulted in substantial dorsal subluxation, although this specific osteotomy was not assessed in our study. Conclusions Sequentially increased dorsal osteotomies of the dorsal lunate facet result in increased dorsal carpal subluxation. Clinical relevance Distal radius fractures that include >40% of the "dorsal critical corner" are at risk for dorsal carpal subluxation and may require supplementary fixation.