Bone ingrowth into dynamically loaded porous-coated intramedullary nails

Abstract

Research to determine whether porous-coated Vitallium intramedullary rods could be used to bridge segmental defects in long bones was performed using rabbit tibias as a suitable model for human bone growth. One-centimeter segments of the midshaft of tibias of mature rabbits were removed surgically and replaced with equal-sized segments of Silastic tubing to maintain leg length. A coated rod was inserted through the proximal tibial segment, through the tubing, and into the distal bone segment. The legs were taken out of plaster at 3 weeks, and x-rays were taken periodically until sacrifice. At sacrifice, 30 weeks postoperatively, the mechanical properties of both tibias from each rabbit were measured destructively in a torsional testing machine. The load at failure of the tibia with the segmental defect averaged 90% of the contralateral control tibia. Rod pullout data and electron-probe x-ray microanalysis indicated that a substantial rod–endosteal bone bond existed due to ingrowth into the porous coating. The torsional data may have been somewhat obscured by the presence of a bony callus which grew over the Silastic tubing and bridged the segmental defect exosteally in every case.