Why it's better to believe in a larger definition of the diametaphyseal junction zone in pediatric distal radius fractures.

INTRODUCTION: Diametaphyseal radius fractures (DMRF) in children are characterized by special biomechanical behavior. They present with a stereotypical loss of reduction (radial translation and ulnar tilt) of the distal fragment when stabilized with elastic stable intramedullary nailing (ESIN), the standard osteosynthesis for pediatric diaphyseal forearm fractures. No consensus has been found on the definition of the diametaphyseal junction zone (DMJZ). Some authors claim that diaphyseal fractures immediately proximal to the metaphysis, as defined by the AO Pediatric Comprehensive Classification of Long Bone Fractures (AO-PCCF), can safely be stabilized with ESIN. They confine the DMJZ to a small part within the metaphysis. Other definitions of the DMJZ extend slightly more proximally, including a small part of the distal diaphysis. The forearm fracture index (FFI) calculates the ratio of the fracture's distance to the radius' growth plate over its width and defines DMRF to have an FFI between 1 and 2. The aim of this case series was to demonstrate that these particular fractures, which can be considered diaphyseal according to the AO-PCCF, still exhibit biomechanical characteristics typical of DMRF.

MATERIALS AND METHODS: Radiologic and clinical outcomes of 11 DMRF, that would be considered diaphyseal by the AO-PCCF classification but fall into the DMJZ when using the FFI, are being reported.

RESULTS: 7 fractures were treated with ESIN and 4 with transepiphyseal percutaneous intramedullary Kirschner-wire (TEPIK) fixation. ESIN osteosynthesis led to only a small reduction in angulation but a notable increase in translational dislocation in the a.p. radiograph, both typical dislocation patterns seen in DMRF. Fractures stabilized with TEPIK, an osteosynthesis technique obeying the biomechanical demands of DMRF, did not present with these stereotypical dislocation patterns.

CONCLUSIONS: The biomechanical demands typical of DMRF also apply to very distal diaphyseal forearm fractures. Hence, a larger definition of the DMJZ might include all fractures with the characteristic biomechanical behavior.