H R Sukhiani1, D L Holmberg. 1. Department of Clinical Studies, Ontario Veterinary College, University of Guelph, Canada.
Abstract
OBJECTIVE: To compare the biomechanical properties of five intramedullary (IM) pin fixation techniques for Salter-Harris type I fractures of the distal femur in dogs. STUDY DESIGN: Randomized, one-way factorial design composed of five treatment groups: (1) single IM pin, (2) dynamic 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 manually 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 crossed-pin technique sustained the greatest load to failure (116.8%) followed by the paired convergent pins (104.8%), dynamic IM pins (90.6%), single IM pin (72.1%), and crossed PGA rods (71.9%). Statistically significant 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 the intact controls; however, there was no significant difference between techniques. Failure in the paired convergent and crossed-pin techniques occurred by fracture of the bone; failure in the other techniques occurred by distraction at the fracture site. CONCLUSION: The rotational stability of any of the fixation techniques appears to be primarily determined by the ability to prevent distraction and maintain interdigitation of the physis. CLINICAL RELEVANCE: When choosing a particular fixation technique for repair of a distal femoral physeal fracture, consideration should be given to the technique's relative biomechanical merits.
OBJECTIVE: To compare the biomechanical properties of five intramedullary (IM) pin fixation techniques for Salter-Harris type I fractures of the distal femur in dogs. STUDY DESIGN: Randomized, one-way factorial design composed of five treatment groups: (1) single IM pin, (2) dynamic 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 manually 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 crossed-pin technique sustained the greatest load to failure (116.8%) followed by the paired convergent pins (104.8%), dynamic IM pins (90.6%), single IM pin (72.1%), and crossed PGA rods (71.9%). Statistically significant 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 the intact controls; however, there was no significant difference between techniques. Failure in the paired convergent and crossed-pin techniques occurred by fracture of the bone; failure in the other techniques occurred by distraction at the fracture site. CONCLUSION: The rotational stability of any of the fixation techniques appears to be primarily determined by the ability to prevent distraction and maintain interdigitation of the physis. CLINICAL RELEVANCE: When choosing a particular fixation technique for repair of a distal femoral physeal fracture, consideration should be given to the technique's relative biomechanical merits.