Finite-element analysis for lumbar interbody fusion under axial loading.

A parametric study was conducted to evaluate axial stiffness of the interbody fusion, compressive stress, and bulging in the endplate due to changes in the spacer position with/without fusion bone using an anatomically accurate and validated L2-L3 finite-element model exercised under physiological axial compression. The results show that the spacer plays an important role in initial stability for fusion, and high compressive force is predicted at the ventral endplate for the models with the spacer and fusion bone together. By varying the positioning of the spacer anteriorly along anteroposterior axis, no significant change in terms of axial stiffness, compressive stress, and bulging of the endplate are predicted for the implant model. The findings suggest that varying the spacer position in surgical situations does not affect the mechanical behavior of the lumbar spine after interbody fusion.

[In vitro stability study of an improved implant system for minimally invasive transforaminal approach]. / In-vitro-Stabilitätsuntersuchung eines neuartigen Implantatsystems für den minimal-invasiven transforaminalen Zugang.

Calf specimens from the L3-4 and L5-6 levels were used for in vitro stability testing of a new transforaminal lumbar interbody fusion (TLIF) implant. Results were compared with those of the conventional posterior lumbar interbody fusion (PLIF) technique using two cuboid spacers. The specimens were loaded with pure moments of 10 Nm in flexion, extension, lateral bending, and axial rotation without any axial preload. They were allowed to move freely and unconstrained in all directions. In extension the PLIF implants showed slightly higher degrees of stiffness than the TLIF implant. While the conventional PLIF technique results in an increased range of motion by a factor of 2.5 after implant insertion, the TLIF approach prevents segmental destabilization in axial rotation. The facet joint arthrodesis using resorbable pins reveals biomechanically interesting results and will therefore be investigated in further studies.

[Acute symptom transverse laminectomy for a benign osteoclastoma of thethoracic spine--case report and review of the literature]. / Akute Querschnittsymptomatik durch benignes Osteoklastom der Brustwirbelsäule--Falldarstellung und Literaturübersicht.

Benign osteoclastomas of the spine above the sacrum are uncommon lesions. Acute paraparesis as the presenting sign of disease is unusual and rarely described in the literature. We report on the case of a 41 yrs old male who underwent acute T3-5 laminectomy for spinal cord decompression from a T4 expansive mass lesion with locally destructive growth. Although a malignant lesion was suspected, definitive histologic examination disclosed a benign osteoclastoma. Therefore, elective trans-thoracic total vertebrectomy T4 with ventral stabilization was performed to allow for marginal total resection of the tumor and reconstruction of the spine. Twenty-four months after the procedure the patient has made a good neurologic recovery with no evidence of tumor recurrence.