European spine journal : official publication of the European Spine Society, the European Spinal Deformity Society, and the European Section of the Cervical Spine Research Society
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The aim of the current study is twofold: first, to compare load sharing in compression between an intact and a surgically repaired lumbar spine motion segment L3/4 using a biomechanically validated finite element approach; second, to analyse the influence of bone mineral density on load sharing. Six cadaveric human lumbar spine segments (three segments L2/3 and three segments L4/5) were taken from fresh human cadavers. The intact segments were tested under axial compression of 600 N, first without preload and then following instrumented stabilisation. ⋯ Using 10 MPa--representing soft, osteoporotic bone--this percentage decreased, but it increased using 100 MPa in both the intact and the altered segment. Thus, it is concluded that reconstruction of both the disc and the posterior elements with the implants used in the study recreates the ability of the spine to act as a load-sharing construction in compression. The similarity in load sharing between normal and instrumented spines appears to depend on assumed bone density, and it may also depend on applied load and loading history.
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Giant cell tumours involving vertebral bodies are still difficult to treat, though results are gradually improving. The object of this study was to assess the results of "complete excision", both of previously untreated giant cell tumours and of recurrences, and to consider the possible effects of any tumour contamination during operation. Nine consecutive patients with giant cell tumours of the thoracic and lumbar spine were treated surgically between 1986 and 1995. ⋯ Where an intralesional component is unavoidable, total removal of the (pseudo)capsule should be ensured by preliminary extralesional dissection. Any tumour spill should be meticulously removed. The use of frozen sections to check resection margins is advisable.
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Harvesting autogenous bone grafts of the iliac crest carries complications and lengthens operative times. Allografts are preferred to avoid these problems. Fusion after using allogenic bone grafts has been well studied, by examining trabeculations and remodelling on anteroposterior and lateral radiographs. ⋯ Fresh-frozen femoral or tibial allografts worked effectively to maintain correction after trauma when combined with anterior instrumentation. CT examinations with sagittal and coronal reconstructions were more effective for evaluation of fusion compared with anteroposterior and lateral radiographs. The high fusion rate and the low morbidity achieved using allografts in this way supports the exclusive use of allografts in the anterior thoracic and lumbar spine in the future.
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Some patients with scoliosis have a relatively short vertebral canal. This poses the question of whether a short spinal cord may sometimes cause scoliosis. The present paper presents two observations that may support this concept. ⋯ The study confirms that the vertebral canal and the intervertebral foraminae retain their original orientation. The spinal cord is eccentric in the canal towards the concavity of the curve; the major component of rotation occurs anterior to the vertebral canal and the axis of this rotation seems to be at the site of the spinal cord. These observations do not establish that a short spinal cord will result in scoliosis, but the results are compatible with this hypothesis, and that impairment of spinal cord growth factors may sometimes be responsible for scoliosis.
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Comparative Study
Biomechanical compression tests with a new implant for thoracolumbar vertebral body replacement.
The authors present an investigation into the biomechanical functioning of a new titanium implant for vertebral body replacement (Synex). Possible indications are fractures and/or dislocations with damage of the anterior column, posttraumatic kyphosis and tumors of the thoracolumbar spine. The construction must be supplemented by a stabilizing posterior or anterior implant. ⋯ A significant (P < 0.001) correlation (R = 0.89) between Fmax and BMD was found. Synex was found to be at least comparable to MOSS concerning the compressive performance at the vertebral end-plate. A possible consequence of the significantly higher mean compression forces between 1 and 2 mm displacement might be decreased collapse of the implant into the vertebral body in vivo.