The Effect of Retrograde Intramedullary Nail Entry at the Metacarpal Head on Metacarpophalangeal Joint Contact Mechanics

Purpose: Intramedullary (IM) screw fixation is widely used for metacarpal fractures, but retrograde entry through the metacarpal head can violate articular cartilage and theoretically alter metacarpophalangeal (MCP) joint contact mechanics, with potential implications for posttraumatic osteoarthritis. Prior work has largely quantified surface damage, but direct effects on MCP contact pressure and area remain less defined. The purpose of the study is to evaluate the effect of a dorsal retrograde IM nail entry hole at the metacarpal head on contact area, average contact pressure, peak contact pressure, and percent surface area of the distal articular cartilage of the first, second, third, fourth, and fifth metacarpals. Methods: Five fresh-frozen cadaveric hands (digits 1-5, age range: 35-64 years; three women and two men) underwent repeated-measures testing in full extension under 100 N of axial compression. Pressure sensors recorded MCP contact mechanics. Metacarpal head articular surfaces were laser scanned to determine surface area. Measurements were obtained in the native state and after creation of a dorsal metacarpal head entry hole simulating retrograde IM screw placement. Results: Across all digits, there were no differences between native and hole states in MCP contact area, average contact pressure, or peak contact pressure. Metacarpal head articular surface area also did not differ between states. Conclusions: A dorsal retrograde entry hole at the metacarpal head did not change MCP contact area, mean pressure, or peak pressure in load in full extension across all five digits. These findings suggest that when the entry corridor is dorsal, retrograde IM fixation may be unlikely to elevate articular contact stresses in extension. Clinical relevance: These findings suggest that dorsal retrograde IM fixation for metacarpal fractures is unlikely to increase MCP joint contact stresses in extension, supporting its safe use without elevating the risk of mechanically driven posttraumatic osteoarthritis.