A mechanical comparison of veterinary linear external fixation systems

To compare the fixation rigidity of recently developed external fixation systems (EFSs) to that of the traditional Kirschner-Ehmer (KE) system.

In vitro biomechanical study.

Five different EFSs (KE, Secur-U, small SK carbon fiber, small SK titanium, large SK carbon fiber) were assembled into 7 frame geometries to stabilize Delrin plastic rods with a 1-cm gap.

External skeletal fixation (ESF) constructs were tested in axial compression, torsion, medial-lateral bending, and cranial-caudal bending. Testing was conducted within the elastic range of each fixator. Mean stiffness in each mode was determined from the slope of the linear portion of the load-deformation curve. Comparison of stiffness values of each EFS within each loading mode and frame type was performed with 1-way analysis of variance (P <.05).

Mean stiffness values were significantly higher for the large SK EFS in all frame types compared with KE but were equal in torsional stiffness in the double-bar type 1a frame. The small SK EFS with titanium connecting bar had greater stiffness than the KE in all modes for frame types Ia, Ia-accessory bar, and II-modified. No overall difference was detected between the KE EFS and the small SK with carbon fiber rod. The stiffness of the Secur-U type Ia frame with augmentation plate was significantly greater than the KE type Ia with accessory bar.

The newer external fixation systems evaluated in this study provided fixation rigidity equal to or greater than that of the KE system.

EFSs with increased frame rigidity should permit the use of less complex frame designs while providing fracture stability.