A Comparison of Nonthreaded, Enhanced Threaded, and Ellis Fixation Pins Used in Type I External Skeletal Fixators in Dogs

Three different pin types (Ellis, enhanced threaded, and nonthreaded) were used in type 1 external skeletal fixation after transverse osteotomy of the radius and ulna in 12 skeletally mature dogs. Dogs were placed into three groups of four dogs based on the pin type used. Axial extraction forces were determined for each of the pin types after 8 weeks of weight bearing (chronic study). Nine contralateral radii were used to determine axial extraction forces for nine of each pin type not subjected to weight bearing forces (acute study). The force required for extraction of the enhanced threaded and Ellis pins in the chronic and acute studies was not significantly different. The force required to extract the nonthreaded pins was significantly less than that required for the other two pin types. Ground reaction forces had returned to levels measured before surgery by 2 weeks after surgery in the enhanced threaded and Ellis pin groups, however, dogs in the nonthreaded pin group required 4 weeks until normal ground reaction forces were measured. Radiographic evaluations 1,2,4, 6, and 8 weeks after surgery showed no difference among groups in the number of pin tract radio-lucencies, however, the enhanced threaded pins had caused more trans-cortical chip fractures than the other two pin types. None of the pins broke during the eight-week chronic study.