Biomechanical comparison of ex vivo lumbar vertebral fracture luxations stabilized with tension band or polymethylmethacrylate in cats

Authors: 
Patricia Beer, Sebastian C Knell, Antonio Pozzi, Brian H Park
Vet Surg. 2020 Sep 30. doi: 10.1111/vsu.13516.

Objective: To evaluate spinal stabilization with tension band stabilization (TS) in cats compared to screw and polymethylmethacrylate fixation (SP).

Study design: Ex vivo study.

Sample population: Sixteen feline thoracolumbar spinal specimens.

Methods: The intact specimens were mounted in a six-degree-of-freedom biaxial testing machine for nondestructive testing to obtain the neutral zones (NZ) and range of motion (ROM) in flexion and extension. Thereafter, nondestructive testing was consecutively performed after destabilization by disc fenestration and partial L1 corpectomy and after treatment with either TS or SP. Load to failure was compared after surgical treatment in flexion. Significance was assessed by Student's t test or Wilcoxon signed-rank test.

Results: Range of motion was 26.4° ± 2.2° in TS constructs and 13.4° ± 2.1° in SP constructs (P = .0005). When flexion and extension were analyzed separately, no difference was found for ROM in flexion (SP, 7.0° ± 3.7°; TS, 8.3° ± 2.1°; P = .38). In extension, the mean displacement was 6.4° ± 2.7° and 18.1° ± 5.1° in SP and TS constructs, respectively (P = .0001). Neutral zone was 2.9° ± 0.6° and 7.5° ± 0.8° for the SP and TS groups, respectively (P = .0003). Screw and polymethylmethacrylate fixation constructs were two times stiffer (P = .045).

Conclusion: Tension band stabilization provided stability comparable to SP in flexion. In extension, ROM of SP constructs was half that of TS constructs. The mode of failure of TS was related to the limited dorsal bone stock of feline lumbar vertebrae.

Clinical significance: Surgeons should be aware of the limited stability in extension provided by TS when it is used to stabilize thoracolumbar spinal injuries. Our results provide evidence to justify additional studies to clarify the type of fractures amenable to TS.

Small animal: