Summary Statement

Spinal flexibility in bending and axial torque has been shown to exhibit very modest changes with advancing disc degeneration. This study is the first to address the possible relationship in pure anterior shear and no clear relationship was observed.

Purpose: At present there is no reported, valid and reproducible model of degenerative spondylolisthesis for biomechanical testing of spinal implants. The purpose of this study was to create a single functional spinal unit (FSU) model that could demonstrate anterolisthesis consistent with low grade degenerative spondylolisthesis under physiologic shear loads.

Method: Eight fresh-frozen human cadaveric, lumbar FSU’s were potted and secured in a custom jig for pure shear testing. The cranial segment was loaded from – 50N (posterior) to 250N (anterior) over three cycles for each of five test conditions with a 300N preload. Test conditions addressed known restraints to shear translation and were performed in the same order for all specimens, and included: intact, facet capsulectomy and bilateral two mm facet gap, bilateral four mm facet gap, nucleotomy, and annular release. Three-dimensional motion was recorded using an optoelectronic camera system.

Results: Mean anterior translation at 250N for the five test conditions was 0.7 mm (95% confidence interval 0.4 to 0.9), 1.2 mm (0.9 to 1.6), 1.5 mm (1.1 to 2.0), 1.9 mm (1.4 to 2.4) and 3.1 mm (2.2 to 4.0). The mean maximum anterior translation was significantly different for each test condition with two exceptions. The four mm facet gap did not result in a significantly different maximum anterior translation compared to the two mm facet gap or the nucleotomy. There were no differences in off-axis motion (lateral or superior-inferior translation, flexion-extension, axial rotation, lateral bending) between the five test conditions.

Conclusion: Anterior translation consistent with low grade degenerative spondylolisthesis was repeatedly demonstrated under physiologic shear loads using this model. All sequential destabilizations preserved anatomy critical for the application of pedicle screw constructs, interbody devices and interspinous spacers. As such, this model is appropriate for biomechanical testing of implants currently used in the treatment of low grade degenerative spondylolisthesis.

Desmoid tumors are rare benign but aggressive lesions. They are characterized by bland-appearing fibroblasts, indistinct margins, and the ability of local invasion and recurrence. Though they are not cancer they may metastasize and can cause significant morbidity. Treatment is primarily surgical, although radiation or systemic therapy can be beneficial if surgery is not feasible. We retrospectively reviewed our patients since 1980 in respect to treatment modalities and outcome.

Between 1980 and 2008 26 patients (16 m, 10 f) with desmoid tumours had been surgically treated. The mean age with diagnosis was 37 years (7 – 69 years). The mean age at surgery was 46 years (10 – 81 years). 17 of the patients had only one resection. In 6 patients two resections, in 2 three resections and in one patient four resections had to be performed. Only 7 patients achieved a R0-situation. In 9 patients adjuvant radiotherapy was used. Two patients had several courses of Vinblastine or MTX based chemotherapy, three patients had Sulindac or Tamoxifen, several other patients combinations of different NSARs. All patients were still alive, one patient developed metastatic disease from the initial lesion in the groin to the foot. After an average of 17 months (7 – 42 months) 11 patients showed recurrent disease. 13 patients are without recurrence after an average of more than 9 years. In 4 patient stable disease is seen without progression in 42 to 156 months (Ø 95 months).

In conclusion desmoid tumours did show an inpredictable course of disease. Due to many alterations in treatment in the 28 years since the first patient of this study and the rareness of this disease no clear predicitve factor could be established. Remarkably no patient did need an amputation. A more detailed analysis regarding the dose effect of irradiated patients is intented.