INTRODUCTION: To improve bony fusion with cages, additional stabilization is recommended. For a minimal invasive approach a new biodegradable facet fusion implant has been developed that can be inserted directly into the facet joint space and then melted and anchored in this position using an ultrasonic welding process (BoneWelding® technology). The implant inhibits segmental movement directly at the joint and should make an additional internal fixator dispensable. The aim of this in vitro study was to determine the biomechanical behavior of the new method during flexibility testing in comparison to posterior fixation.
METHODS: A biodegradable polymer (PLDAL 70/30) is inserted percutaneously into the facet joint space. The material melts at the contact area between bone and implant using ultrasonic energy and yields into the trabecular structures of the facet joints. The new method by SpineWelding AG (Schlieren, CH) was compared to an internal fixator using three L2‐3 and three L4‐5 segments (median: 75 years). After implanting an anterior cage (Syncage, Synthes CH) the segments were additionally stabilized with an internal fixator (CD Horizon® Legacy, Medtronic), which was later replaced by the new facet fusion implant. Flexibility of both methods was measured in all three motion planes at ±7.5 Nm in a spine tester.
RESULTS: Both, the fixator and the new facet fusion showed a significant reduction of the range of motion (median ROM after facet fusion: 23% flexion/extension, 25% lateral bending, 60% axial rotation). The differences between fixator and facet fusion, however, were not significant.
DISCUSSION: BoneWelding® technology provides an interesting alternative for minimal invasive stabilization of spinal motion segments and seems to achieve similar primary stability compared to an internal fixator. Exemplary histological investigations showed that the melted polymer anchored into the trabecular structures of the bone and achieve a bonding of the facet joints.