Design of a movable artificial lumbar complex and its preliminary biomechanical analysis in goats

English Keywords:Artificial vertebral body  Lumbar spine  Subtotal resection  Non-fusion  Goat

English Abstract:

  【Abstract】 Objectives: To design a movable artificial lumbar complex to reconstruct the height of lumbar vertebra and preserve the motion of inter-vertebral discs, and to perform the biomechanical tests in vitro. Methods: 26 fresh specimens of goat lumbar spines were used, and those with spinal deformity or fracture by the examination of thin slice CT scan were ruled out. Two specimens were finally excluded for vertebral fracture and twenty-four specimens were included in this research. The specimens were randomly divided into normal, fusion and non-fusion group, with eight specimens in each group, and bone mineral density was tested before operation. The anatomical data of goat lumbar spine dissected in operation were acquired and the design of movable prosthesis model was optimized with the computer-aided software, while the size of prosthesis was designed into five specifications according to the average anatomical parameters of 24 specimens, and the prosthesis was produced with the technique of 3D printing and machining. Image examination was performed for specimens in fusion and non-fusion groups(implants in L4) after operation to determine the position of implants and condition of spinal cord, and then bio-mechanical tests with the load of 4Nm were added to assess the activity and stability of movable prosthesis. Results: Bone mineral density showed no statistical difference among three groups(P>0.05). The anterior height, middle height and posterior height of L4 vertebra were 38.8±2.7mm, 39.7±2.1mm, and 40.9±1.1mm respectively; the upper, middle, lower sagittal diameters and horizontal diameters were 16.5±0.8mm, 12.5±2.0mm, 16.6±0.5mm and 22.9±2.6mm, 14.3±1.3mm, 23.6±2.9mm respectively; the anterior, middle and posterior heights of L3/4 and L4/5 vertebral discs were 4.9±1.0mm, 3.0±0.5mm, 1.9±1.0mm and 5.0±0.4mm, 3.6±0.9mm, 2.4±0.9mm respectively. The movable artificial complex of goat lumbar was formed by the vertebral body part and disc part and both were jointed together by ball-and-socket joints resisting dislocation. Postoperative imaging found no abnormal position of prosthesis and spinal cord compression. Compared with the fusion group, the non-fusion group could retain motion of L3/4 and L4/5 range of motion and reduce the range of motion of L2/3(P＜0.05); compared with the normal group, non-fusion group had no significant difference in the range of motion of inter-vertebral discs(P>0.05). Conclusions: The movable artificial lumbar complex designed according to the anatomical structure of goat lumbar, not only can reconstruct the height and stability of operative segments but also retain the activity of inter-vertebral discs.