Abstract
Sublaminar wiring with posterior instrumentation is one of the methods used when long fusions involving 10 to 12 thoracolumbar levels are required. Classically wires are used at every consecutive level to make the construct as rigid as possible although complications like dural tears, CSF leak, and neurological deficiet have been reported during their passage.
We compared the mechanical stability of five specimens of each of the three construct designs by static and fatigue testing to torsional strain on Electro-servo-hydraulic testing machine. In construct A, a contoured Hartshill rectangle was used from T2 to L2, with sub-laminar wires passed at every level. In construct B, every alternate level was wired. In construct C, every alternate level was wired except at the proximal end two consecutive levels were wired. Industrially fabricated spine models were used to prepare these constructs. The intervertebral motion within the construct was measured using FASTRAK magnetic field sensor device.
On static testing, no statistically significant difference was found in the rotational displacement of the three construct designs. On fatigue testing, all samples of construct B consistently failed with breakage of the wire at the most proximal level on the left side. But on adding additional wires to the next level (Construct C), all five samples withstood fatigue testing at 300 Newton load to 3 million cycles.
Wiring alternate levels instead of every level, does not compromise the stability of the construct provided the most proximal two levels are consecutively wired. This practise would minimise the risk of dural tears and cord damage during wire passage and reduce surgical time, not to mention the economical benefit.
The abstracts were prepared by Mr Richard Buxton. Correspondence should be addressed to him at Bankton Cottage, 21 Bankton Park, Kingskettle, Cupar, Fife KY15 7PY, United Kingdom
