BIOMECHANICAL COMPARISON OF ANTEGRADE AND RETROGRADE NAILING OF HUMERAL SHAFT FRACTURE

A pair controlled study was conducted to compare biomechanical propert ies of antegrade and retrograde nailing of humeral fractures, First, s ix paired fresh anatomic specimen humeri were used to compare the prop erties of humeri fractured at the middle to distal diaphyses junction that were nailed from the retrograde approach with the Humeral Locked nail with those of contralateral intact humeri, An 18 additional pairs were divided into three equal groups by distal, proximal, or middiaph ysis location of a standardized 5-mm bone defect to simulate unstable fractures, The retrograde and antegrade nailings were performed in eac h pair in a random manner. Nail and bone constructs were tested for be nding stiffness by nondestructive three-point bending and for torsiona l stiffness by destructive torsional tests. Compared with intact humer i, fractured humeri fixed with nails had 28.6% posteroanterior and 31. 4% mediolateral bending stiffness, 22.5% torsional stiffness, and 43.3 % failure torque. For distal fractures, retrograde nailing showed sign ificantly more initial stability and higher bending and torsional stif fness; for proximal fractures, antegrade nailing showed similar proper ties. For middle to distal diaphyses junction fractures, retrograde an d. antegrade nailing were indistinguishable, The defect created as an entry portal for retrograde nailing reduced the bone strength only 11. 1%, These results suggest that retrograde nailing, which is less detri mental to shoulder function than is antegrade nailing, is an acceptabl e alternative treatment for humeral shaft fractures. In addition, nail ing from the short to the long bone segments can improve mechanical pr operties of the fixation construct because of better nail and bone int erface purchase.