according to the procedure defined by the manufacturer. A constant deflection rate of 5 mm/min was used. All tests were performed dry at room temperature.
To determine the ultimate torque load, the implants were placed in between two blocks made of Rohacell RC 300WL with mechanical properties comparable to cancellous bone. Prior to testing, an axial preload of 1,000 N was applied to enable settlement of the contact area. The upper as well as the lower block were fixed versus the torsion measurement system. A constant axial preload of 100 N was applied during the test. Torsion was applied at a constant rate of about 100°/min.
All static tests were performed dry at room temperature. The dynamic tests were performed under Ringer solution at 37°C temperature and all specimens were preconditioned.
The fusion devices to be assessed at the postoperative evaluation were the CORNER-STONE-SR C (lordotically shaped anterior cervical interbody fusion device, Medtronic Sofamor Danek) and UNION or UNION-L (lordotically shaped anterior or lateral lumbar interbody fusion device, Medtronic Sofamor Danek) spinal fusion cages.
The implant system CORNERSTONE-SR C consists of a basic body (12 X 13mm), various heights of 4-8 mm (10-16 mm) and two lines of fins (see fig. 2). The anterior retroperitoneal implant system UNION or UNION-L consists of a basic body (24 X 26 or 26 X 31 mm, respectively) with two chambers, various heights of 10-16 mm and three lines of fins (see fig. 2). For both types of implants x-ray contrasts are layers of BaSO4 embedded into the CFRP material. Prior insertion of the implant the fins must be prepared in the bone with a special instrument.
Fig. 2. CFRP implants: cervical interbody fusion cage (CORNERSTONE-SR C, a) and anterior lumbar interbody fusion cage (UNION, b).
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