Bone ingrowth into dynamically loaded porous-coated intramedullary nails.

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 micro-analysis 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 bony callus which grew over the Silastic tubing and bridged the segmental defect exosteally in every case.