The movable artificial lumbar vertebralbody: development and biomechanical study / 中华骨科杂志

ABSTRACT

Objective To develop a new type of lumbar prosthesis,movable artificial lumbar vertebral body (MALV) and evaluate the stability and activity of the prosthesis by in vitro biomechanical test.Methods Fifteen adult fresh lumbar spine specimens were randomly divided into three groups:intact group,fusion group and non-fusion group.The anatomical parameters of L2 vertebral body and adjacent intervertebral discs were collected by software (Mimics 16.0,Materialise Company,USA) and the new prosthesis was personalized by 3D printing and mechanical processing.All specimens in fusion group and in non-fusion group were implanted with titanium cage,titanium plate and MALV respectively after partial resection of L2 vertebra and adjacent intervertebral disc.No other intervention was conducted on physiological specimens.All specimens were examined by imaging to determine the position of the prosthesis and the condition of the spinal cord.Specimens in all groups were subjected to a 7.5 N · m load biomechanical test in flexion,extension,left and right lateral bending,left and right rotation aiming to evaluate the mobility of operative site and adjacent discs.Results The new prosthesis consists of three parts,vertebral body,intervertebral disc and composite material ball.All 15 cadavers were free of spinal deformity,fracture and osteoporosis.Postoperative radiographic examination indicated no prosthesis displacement and spinal compression without adverse phenomena.The results in vitro mechanical test were as followed.There was no statistical difference in ROM of the T12L1 intervertebral in non-fusion group (3.68°±0.86°,3.52°± 0.86°,2.64°±0.93°,2.58°±0.76° respectively) and in intact group (3.98°±0.90°,3.74°±0.91°,2.94°±1.10°,2.96°±0.86° respectively) in flexion,extension,left and right lateral bending (P＞0.05).The ROM of the T12L1 intervertebral in fusion group (5.28°±0.83°,5.32°±0.42°,4.72°±1.10°,4.94°±1.17° respectively) was significantly larger than that in intact group and non-fusion group (P＜0.05).There was no statistically significant difference between the ROM of L1.2 and L2.3 intervertebral in flexion,extension and left and rightlateral bending in the non-fusion group (ROM of L1.2 were 4.62°±0.51 °,4.34°±0.67°,3.16°±0.55°,3.28°±0.41 ° respectively;ROM of L2.3 were 4.54°±0.58°,4.36°±0.65°,3.26°±0.21°,3.42°±0.37° respectively) and the intact group (ROM of L1.2 were 4.10°±0.53°,3.72°±0.42°,2.74°±0.50°,3.04°±0.40° respectively;ROM of L2.3 were 4.26°±0.72°,4.08°±0.77°,3.00°±0.36°,3.20°±0.31° respectively) (P＞0.05).The ROM of L1.2 and L2.3 in intact group and in non-fusion group were significantly greater than those in the fusion group (ROM of L1.2 were 1.10°± 0.35°,1.28°±0.31°,0.84°±0.34°,0.80°± 0.43° respectively;ROM of L2.3 were 1.14°±0.30°,1.18°±0.28°,0.94°± 0.36°,1.06°±0.32°) (P＜0.05).There was no statistically significant difference in the ROM of the T12-L3 full segment in the left and right rotation of the three groups (Intact group:4.47°± 0.99°,4.40°±0.70°;Non-fusion group:4.60°±0.90°,4.50°±0.77°;Fusion group:3.85°±0.50°,3.72°±0.70°)(P＞0.05).Conclusion The MALV can retain the mobility of the operative site in flexion,extension,lateral bending and rotation.Furthermore,it can effectively avoid the increased mobility of adjacent segment intervertebral.After implantation,the prosthesis can obtain satisfied immediate stability.