EX-VIVO BIOMECHANICAL COMPARISON OF PIN FIXATION TECHNIQUES FOR CANINE DISTAL FEMORAL PHYSEAL FRACTURES

Objective-To compare the biomechanical properties of five intramedulla ry (IM) pin fixation techniques for Salter-Harris type I fractures of the distal femur in dogs. Study Design-Randomized, one-way factorial d esign composed of five treatment groups: (1) single IM pin, (2) dynami c IM crossed pins, (3) paired convergent pins, (4) crossed pins, and ( 5) crossed polyglycolic acid (PGA) rods. Sample Population-Forty pairs of cadaver canine femurs. Materials-One femur of each pair was manual ly fractured and subsequently repaired; the contralateral intact femur served as its control. Each femur was loaded in torsion until failure occurred and load-deformation curves were generated. Results-The cros sed-pin technique sustained the greatest load to failure (116.8%) foll owed by the paired convergent pins (104.8%), dynamic IM pins (90.6%), single IM pin (72.1%), and crossed PGA rods (71.9%). Statistically sig nificant differences in strength at failure were detected between the crossed-pin and single IM pin and the crossed-pin and crossed PGA rod techniques. All fixation techniques underwent greater deformation (1.5 times as much) and had a lower stiffness (66% to 75%) compared with t he intact controls; however, there was no significant difference betwe en techniques. Failure in the paired convergent and crossed-pin techni ques occurred by fracture of the bone; failure in the other techniques occurred by distraction at the fracture site. Conclusion-The rotation al stability of any of the fixation techniques appears to be primarily determined by the ability to prevent distraction and maintain interdi gitation of the physis. Clinical Relevance-When choosing a particular fixation technique for repair of a distal femoral physeal fracture, co nsideration should be given to the technique's relative biomechanical merits. (C) Copyright 1997 by The American College of Veterinary Surge ons.