The purpose of this study was to compare the stiffness of a Type II external skeletal fixator (ESF) to a 3.5 mm locking compression plate (LCP) in axial compression, mediolateral, and craniocaudal bending in a fracture gap model. The hypothesis was that the Type II ESF would demonstrate comparable stiffness to the LCP. A bone simulant consisting of short fiber reinforced epoxy cylinders and a 40 mm fracture gap was used. The LCP construct consisted of a 12 hole 3.5 mm plate with three 3.5 mm bicortical locking screws per fragment. The Type II ESF construct consisted of 3 proximal full fixation pins (Centerface®) per fragment in the mediolateral plane, and 2 carbon fiber connecting rods. Five constructs of each were tested in non-destructive mediolateral and craniocaudal bending, and axial compression. Stiffness was determined from the slope of the elastic portion of force-displacement curves. A one-way ANOVA and a Tukey-Kramer multiple comparisons test were performed, with significance defined as p < 0.05. In mediolateral bending, the stiffness of the Type II ESF (mean ± standard deviation; 1584.2 N/mm ± 202.8 N/mm) was significantly greater than that of the LCP (110.0 N/mm ± 13.4 N/mm). In axial compression, the stiffness of the Type II ESF (679.1 N/mm ± 20.1 N/mm) was significantly greater than that of the LCP (221.2 N/mm ± 19.1 N/mm). There was no significant difference between the constructs in craniocaudal bending. This information can aid in decision-making for fracture fixation, although ideal stiffness for healing remains unknown. / Master of Science / Optimum fracture stabilization requires a balance between providing a stable mechanical environment and preserving the blood supply to healing tissues. When the complexity of a fracture precludes reconstruction of the bony column, the fixation method chosen for repair must counteract the forces of weight bearing, including compression and bending. Knowledge of the relative construct stiffness is important for a clinician to determine the ability of a fixation technique to withstand all forces acting on a fracture, while supporting bone healing. The purpose of this study was to compare the stiffness of a Type II external skeletal fixator (ESF) and a locking compression plate (LCP) when non-destructive physiologic loads are applied in axial compression, mediolateral bending, and craniocaudal bending. Five constructs of each were tested in non-destructive mediolateral and craniocaudal bending, and axial compression. Stiffness was determined from the slope of the elastic portion of force-displacement curves. There was a significant difference between the stiffnesses of the Type II ESF and the LCP in all modes of loading except craniocaudal bending. The Type II ESF was significantly stiffer in mediolateral bending than the LCP, and the Type II ESF was significantly stiffer in axial compression compared to the LCP. There was no statistically significant difference in stiffness in craniocaudal bending. This information will aid a clinician in selecting an appropriate fixation method for a non-reconstructable fracture, but further studies are required to assess the importance of increased stiffness in a clinical setting.

The Clamp-Rod Internal Fixator (CRIF) is a fracture fixation implant with growing popularity among veterinarian’s for its versatility and ease of use. Although the CRIF is currently in clinical use, relatively few reports exist describing the biomechanical properties and clinical results of this system. The objective of this study was to determine the in vitro biomechanical properties of a 5mm CRIF/rod construct to a 3.5mm Limited Contact-Dynamic Compression Plate (LC-DCP/rod) construct using a canine femoral gap model. Paired canine femora were treated with 40mm mid-diaphyseal ostectomies and randomly assigned to CRIF/rod or LC-DCP/rod. Five pairs of constructs were tested in bending and five pairs were evaluated in torsion. Single ramp to failure tests were conducted to evaluate construct stiffness, yield load, and failure mode. While CRIF/rod and LC-DCP/rod were not significantly different when evaluated in bending, LC-DCP/rod constructs are significantly more rigid than CRIF/rod constructs at higher torsional loads. Below 10degrees of twist, or 4.92Nm torque, the LC-DCP/rod and CRIF/rod were not statistically different in torsion. Catastrophic injuries of the metacarpophalangeal joint resulting in the disruption of the suspensory apparatus are the most common fatal injuries in thoroughbred racehorses. Fetlock arthrodesis is a procedure designed to mitigate suffering from injury as well as degenerative diseases affecting articulation. The objective of this study is to assess the in vitro biomechanical behavior of techniques for fetlock arthrodesis. Twelve forelimb pairs were collected from adult horses euthanized for reasons unrelated to disease of the metacarpophalangeal joint (MCP). A 14-16-hole broad 4.5mm Locking Compression Plate (LCP) was compared to a 14-16 hole broad Dynamic Compression Plate (DCP). Both constructs used a two “figure-eight” 1.25mm stainless steel wire tension band. Fatigue tests and to failure tests were conducted. There were no significant differences in stiffness between groups for fatigue tests. Stiffness increased after the first fatigue cycle for the LCP/wire (80.56+/-52.22%) and DCP/wire (56.58+/-14.85%). Above 3.5mm of axial deformation there was a statistical difference between the stiffness of the LCP/wire (3824.12+/-751.84 N/mm) and the DCP/wire (3009.65+/-718.25 N/mm) (P=0.038). The LCP/wire showed increased stiffness above 3.5mm compression compared to the DCP/wire. Under fatigue testing conditions the constructs are not statistically different.

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