Posterior systems with transpedicular screws for stabilising the spinal column have become the gold standard in surgical treatment of spinal deformities and are used in the majority of cases where correction of scoliosis or segmental fixation is required.
In cases of severe kyphotic or scoliotic spinal deformities, however, developmental anomalies such as hyperplasia or aplasia of the pedicles can make it more difficult to introduce a screw, often leading to longer surgery times and increased X-ray exposure time.
A recent biomechanical in-vitro study published in European Spine Journal has shown that infralaminar hooks (LSZ) from SIGNUS Medizintechnik can provide a useful alternative to pedicle screws in specific sections of the spinal column, with stability comparable with that of pedicle screws.
Researchers compared the different stabilisation principles in two comparable groups – with respect to age and bone mineral density – using fresh-frozen human, bi-segmental thoracolumbar spine specimens (T11–L1). Antero-posterior and lateral radiographs were taken to assess the spinal status, then the intact specimens were biomechanically characterised in three anatomical planes in different states in terms of range of motion and neutral zone. After implantation of either a pedicle screw or lamina hook system, the primary stability was determined under the same conditions. Subsequently the specimens were cyclically loaded under complex loading, until either 100,000 cycles or one of three pre-defined ‘failure’ criteria was reached.
Results showed that the range of motion (ROM) was strongly reduced after instrumentation similar for both implant systems in all motion planes. The highest stabilisation was found in flexion/extension. During cyclic loading with increasing moments, the ROM increased continuously for both systems. The number of load cycles until one of the failure criteria was reached varied only slightly between the two groups. There was a slight trend to indicate that the pedicle screw system is influenced more by bone mineral density.
The authors concluded that both implant systems provide similar primary and long-term stability.
Wilke HJ, Kaiser D, Volkheimer D, et al. (2016) A pedicle screw system and a lamina hook system provide similar primary and long-term stability. EurSpine J. doi: 10.1007/s00586-016-4679-x.
©image rights: SIGNUS Medizintechnik