An assessment of the fixin tplo jig to generate effective compression using a transverse fracture model

Abstract

The objective of this study was to determine compressive loads that could be generated using a tibial plateau leveling osteotomy (TPLO) jig with a tensioned strand of 18-gauge stainless steel orthopedic wire in a simulated transverse fracture model. The wire was sequentially tensioned using heavy needle holders or an AO wire tightener. Recorded loads were subsequently compared to loads generated by applying a 3.5 mm limited contact-dynamic compression plate (LC-DCP) as a compression plate. Two segments of 2 cm diameter Delrin rod were placed in a testing apparatus and used to simulate a transverse fracture. A load cell was interposed between the two segments to measure the compressive loads generated during the application of the TPLO jig or the LC-DCP. Compression was generated by sequential tensioning a strand of 18-gauge wire secured through the base of the arms of the TPLO jig or by placing one or two load screws in the LC-DCP. Wires were tensioned using heavy needle holders or an AO wire tightener. Eight replicates of each construct were tested. Recorded loads were compared using a one-way repeated measures ANOVA and Tukey Honestly Significant Difference test. The wire being tensioned broke while attempting a second quarter rotation of the needle holders and when the crank handle of the AO wire tightener was advanced beyond two rotations. The mean + SD peak compressive loads recorded when tensioning the wire using the heavy needle holders and AO wire tightener was 148 ± 7 N and 217 ± 16 N, respectfully. The mean ± SD load recorded after placement of the first and second load screw in the LC-DCP was 131 ± 39 N and 296 ± 49 N, respectively. The compression generated by placing two load screws in the LC-DCP was superior to the compression generated using the jig. The maximum load recorded by tensioning the wire secured through the TPLO jig using the AO wire tightener was superior to the compression generated by placing a single load screw and tensioning the wire using needle holders. Our results demonstrate that the TPLO jig allows surgeons to compress transverse fractures or osteotomies effectively. Tensioning the AO wire tightener allows for sequential tensioning and generates superior compressive loads than tensioning wires with heavy needle holders.

Fig 1. Rendering of the testing jig.

A load cell was positioned between the two segments of the Delrin rod, which were secured within the testing apparatus’ cylinder.

Fig 2. Photographs of the experimental setup.

Top compression is being generated between the two Delrin rod segments by tensioning the wire secured through the TPLO jig using (A) heavy needle holders, (B) an AO wire tightener, or (C) application of a compression plate.

Fig 3. Graphic showing the compression load (N) for each experimental group.

Mean ± SD loads measured for each of the seven conditions evaluated. Compression was generated by tensioning the wire secured in the TPLO jig using heavy needle holders and performing a quarter rotation (“blue”, N 0.25), or an AO wire tightener and performing a half, one, one and a half, and two full rotations (“red”, W 0.5, W 1.0, W 1.5, W 2.0), or by applying a LC-DCP with one or two screws placed in the load position (“green”, P 1, P 2).