Posterior screw-rod fixation for thoracic spine trauma usually involves fusion across long segments. Biomechanical data on screw-based short-segment fixation for thoracic fusion are lacking. The authors compared the effects of spanning short and long segments in the thoracic spine.
Seven human spine segments (5 segments from T-2 to T-8; 2 segments from T-3 to T-9) were prepared. Pure-moment loading of 6 Nm was applied to induce flexion, extension, lateral bending, and axial rotation while 3D motion was measured optoelectronically. Normal specimens were tested, and then a wedge fracture was created on the middle vertebra after cutting the posterior ligaments. Five conditions of instrumentation were tested, as follows: Step A, 4-level fixation plus cross-link; Step B, 2-level fixation; Step C, 2-level fixation plus cross-link; Step D, 2-level fixation plus screws at fracture site (index); and Step E, 2-level fixation plus index screws plus cross-link.
Long-segment fixation restricted 2-level range of motion (ROM) during extension and lateral bending significantly better than the most rigid short-segment construct. Adding index screws in short-segment constructs significantly reduced ROM during flexion, lateral bending, and axial rotation (p < 0.03). A cross-link reduced axial rotation ROM (p = 0.001), not affecting other loading directions (p > 0.4).
Thoracic short-segment fixation provides significantly less stability than long-segment fixation for the injury studied. Adding a cross-link to short fixation improved stability only during axial rotation. Adding a screw at the fracture site improved short-segment stability by an average of 25%.
Abbreviations used in this paper: BMD = bone mineral density; LZ = lax zone; ROM = range of motion; SZ = stiff zone; VB = vertebral body.
SassoRCCotlerHB: Posterior instrumentation and fusion for unstable fractures and fracture-dislocations of the thoracic and lumbar spine. A comparative study of three fixation devices in 70 patients. Spine18:450–4601993
SukSIKimWJKimJHLeeSM: Restoration of thoracic kyphosis in the hypokyphotic spine: a comparison between multiple-hook and segmental pedicle screw fixation in adolescent idiopathic scoliosis. J Spinal Disord12:489–4951999
VerlaanJJDiekerhofCHBuskensEvandT IVerboutAJDhertWJOnerFC: Surgical treatment of traumatic fractures of the thoracic and lumbar spine: a systematic review of the literature on techniques, complications, and outcome. Spine29:803–8142004
YueJJSossanASelgrathCDeutschLSWilkensKTestaiutiMGabrielJP: The treatment of unstable thoracic spine fractures with transpedicular screw instrumentation: a 3-year consecutive series. Spine27:2782–27872002