Comparison of the Strength and Holding Power of 4 Pin Designs for Use with Half Pin (Type I) External Skeletal Fixation

Abstract

The strength and holding power of four pin designs for use with half pin (type I) external skeletal fixation were evaluated. Pins that were tested were fully threaded, nonthreaded, two cortices partially threaded, and one cortex partially threaded. The study involved three parts: (1) resistance of the pins to axial extraction immediately after insertion; (2) resistance of the pins to axial extraction 8 weeks after being inserted into the tibiae of live dogs; and (3) resistance of the pins to bending load. Pins with threads engaging two cortices were more resistant to axial extraction than nonthreaded pins in both the acute (p less than 0.0001) and chronic (p less than 0.0001) studies. Nonthreaded pins were more resistant to bending than fully threaded and two cortices partially threaded pins (p less than 0.0005). One cortex partially threaded pins possessed similar bending strength to nonthreaded pins (p = 0.21) and had 5.3 times more resistance to axial extraction in the acute study (p less than 0.0001) and 6.9 times more in the chronic study (p less than 0.0001). Though one cortex partially threaded pins were not as resistant to axial extraction as pins with threads engaging two cortices (p less than 0.0001), they were more resistant to bending loads (p less than 0.0005). Loss of holding power and pin failure are two of the most serious problems associated with fracture stabilization using external skeletal fixation. The results of this study suggest that one cortex partially threaded pins are better at maintaining holding power and resisting bending and breaking than nonthreaded pins.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of Holding Power of Three Different Pin Designs for External Skeletal Fixation in Avian Bone: A Study in Common Buzzard (Buteo buteo)

“…We evaluated the force required for axial extraction of pins from avian bone immediately after insertion (acute study). Our results, which are consistent with other studies, 13–15,17 showed that smooth pins had relatively little resistance to axial extraction whereas threaded pins had significantly more holding power in all bone locations. For a specific pin type, we did not observe differences in pullout strength between humerus and tibiotarsus in spite of differences in osseous structure and the thicker cortex in the tibiotarsus.…”

“…Commercial orthopedic pins have been mostly designed for mammals not birds. Previous reports of the influence of pin design on bone holding power in mammals and birds suggest that threaded pins have greater holding power in axial extraction than smooth pins 13,15,17 . Reportedly, thread pitch has little effect on pullout forces of fixation pins and screws 18,19 …”

“…Some of the most challenging problems with fracture stabilization using ESF are loss of bone holding power and failure of fixation pins 13–16 . Thus, it is essential to maintain pin holding power.…”

“…[9][10][11][12] Some of the most challenging problems with fracture stabilization using ESF are loss of bone holding power and failure of fixation pins. [13][14][15][16] Thus, it is essential to maintain pin holding power. Commercial orthopedic pins have been mostly designed for mammals not birds.…”

Mechanical Evaluation of External Skeletal Fixator–Intramedullary Pin Tie-in Configurations Applied to Cadaveral Humeri From Red-tailed Hawks (Buteo jamaicensis)

“…In addition, using an increased number of pins per segment in clinical situations dispersed weight-bearing loads that are concentrated at the pin-bone interface over a larger area, thus theoretically decreasing the incidence of pin loosening. 18,26,28 In contrast, the use of additional fixation pins requires penetration of large-muscle masses (eg, involving the proximal humerus, femur, or tibiotarsus). From the clinical experience at The Raptor Center, pin-tract drainage is rarely encountered with adequate postoperative care.…”