Relation between radiological assessment and biomechanical stability of lumbar interbody fusion in a large animal model
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To relate the progress of vertebral segmental stability after interbody fusion surgery with radiological assessment of spinal fusion.
Twenty goats received double-level interbody fusion and were followed for a period of 3, 6 and 12 months. After killing, interbody fusion was assessed radiographically by two independent observers. Subsequently, the lumbar spines were subjected to four-point bending and rotational deformation, assessed with an optoelectronic 3D movement registration system. In addition, four caprine lumbar spines were analysed in both the native situation and after the insertion of a cage device, as to mimic the direct post-surgical situation. The range of motion (ROM) in flexion/extension, lateral bending and axial rotation was analysed ex vivo using a multi-segment testing system.
Significant reduction in ROM in the operated segments was already achieved with moderate bone ingrowth in flexion/extension (71 % reduction in ROM) and with only limited bone ingrowth in lateral bending (71 % reduction in ROM) compared to the post-surgical situation. The presence of a sentinel sign always resulted in a stable vertebral segment in both flexion/extension and lateral bending. For axial rotation, the ROM was already limited in both native and cage inserted situations, resulting in non-significant differences for all radiographic scores.
In vivo vertebral segment stability, defined as a significant reduction in ROM, is achieved in an early stage of spinal fusion, well before a radiological bony fusion between the vertebrae can be observed. Therefore, plain radiography underestimates vertebral segment stability.
KeywordsLumbar spinal fusion Animal model Motion-segment stability Mechanical testing Radiography
This study was supported by the Dutch Program for Tissue Engineering (DPTE; #BGT 6734). The authors thank Klaas Walter Meijer, Paul Sinnige, Jerry Middelberg and Ger Vink from the animal facilities and Pieter Paul Vergroesen from the orthopaedic surgery department for their assistance during animal surgery and autopsy and Suzanne van Engelen from the Faculty of Human Movement Sciences for her assistance with mechanical testing of the spines.
Conflict of interest
Supplementary material 1 (MPG 29936 kb)
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