A biomechanical analysis of sublaminar and subtransverse process fixation using metal wires and polyethylene cables.
METHODS
An in vitro biomechanical calf thoracic spine study.


OBJECTIVE
To evaluate the biomechanical stability of sublaminar and subtransverse process fixation using stainless steel wires and ultra-high molecular weight polyethylene (UHMWPE) cables.


BACKGROUND
It is commonly held that transverse process fixation provides less stability than sublaminar fixation. To our knowledge, this is the first biomechanical study to compare the stability afforded by sublaminar fixation and subtransverse process fixation using metal wire and UHMWPE cable before and after cyclic loading.


METHODS
There were 6 fresh-frozen calf thoracic spines (T4-T9) used to determine the sublaminar fixation stiffness and subtransverse process fixation stiffness in each group. Double strands of 18-gauge stainless steel wire, 3 and 5 mm-width UHMWPE cable (Nesplon; Alfresa, Inc., Osaka, Japan) were applied to each spine. Cyclic pure flexion-extension moment loading (2 Nm, 0.5 Hz, 5000 cycles) was applied after the initial stability was analyzed by measuring the range of motion. Statistical analyses were used to delineate differences between the various experimental groups.


RESULTS
Subtransverse process wiring was more stable than sublaminar wiring after cyclic loading in flexion-extension (P < 0.05). There were no significant differences between each group in lateral bending and axial rotation after cyclic loading. Sublaminar stainless steel wiring was more stable than sublaminar 3 and 5-mm cable before and after cyclic loading in axial rotation (P < 0.01). Acute subtransverse process fixation using 3-mm cable was less stable after cyclic loading in axial rotation (P < 0.05). All other groups did not produce statistically significant differences.


CONCLUSIONS
Subtransverse process fixation provides at least as much stability as sublaminar fixation. A 5-mm UHMWPE cable and stainless steel wire result in equivalent sublaminar and subtransverse process stability.
Fujita
Masaru
M
Department of Orthopaedic Surgery, University of California at San Francisco, USA.
Diab
Mohammad
M
Xu
Zheng
Z
Puttlitz
Christian M
CM
D000818:Animals; D001672:Biocompatible Materials; D001696:Biomechanical Phenomena; D001864:Bone Wires; D002417:Cattle; D016268:Internal Fixators; D007593:Joint Instability / Q000517:prevention & control; D020959:Polyethylene; D013123:Spinal Fusion / Q000295:instrumentation*; D013193:Stainless Steel; D013904:Thoracic Vertebrae / Q000601:surgery*
D001672:Biocompatible Materials; D013193:Stainless Steel; D020959:Polyethylene