| 1. ObjectivePosterior lumbar interbody fusion (PLIF) with autogenous iliac bone is the standard surgery for treating lumbar degenerative disease. Problems with PLIF have included postoperative collapse and migration of the donor bone and pseudarthrosis. The need for iliac bone adds graft harvest site morbidity. Pedicle fixation systems appear to improve fusion rates. However, their use may generate new and occasionally serious complications. As a key to reduce or eliminate these complications, interbody fusion cages have recently been gaining acceptance as a method of ensuring lumbar interbody arthrodesis. Despite the growing clinical interest in intervertebral cages, complications occur because of its design deficiency. Threaded cylindrical cages cannot be narrower than their height, thereby taking up more space transversely and increasing facet excision during insertion into the disc. Rectangular cage cannot be used singly because its insufficient stability. With the developing of minimal invasive surgery, the need for a new type of cage that could be inserted with smaller diameter as well as gain more stability is obviously. The current study is to design a new cage using memory shape alloy, and perform biomechanical test in human cadaver specimens and animal fusion study in the Chinese minimal pig. The purpose of the present investigation was to determine the biomechanical behavior of the newly designed shape memory alloy cage (SMAcage) and whether it increased the success rate for bony fusion compared with identical procedures done with autogenous iliac bone graft.2. Materials and Methods2.1 Seventy sets of lumbar and sacra vertebrae of L3-S1 for anatomic measurements were obtained from the Department of Anatomy of the First Military Medical University. The following parameters were evaluated including: transverse diameter, mid-sagittal diameter and para-sagittal diameter of the vertebrae on axial plane. The upper interfacetal distance, interpar distance and lower interfacetal distance on coronal plane.-7-2.2 Seventy MRI scans of the lumbosacral spine of patients between the age of 18 and 55 years undergoing investigation for low back pain or routine healthy check were used for morphometric study of the human lumbar spine. The interfacetal distances and intervertebral disc heights were measured from transverse and sagittal images, respectively, at L3/4,L4/5 and L5/S1. The inner, mid, and outer interfacetal distances(IFDin, IFDmid, IFDout) were recorded and compared with the dimensions of paired cylindrical cages of 12mm> 14mm 16mm in diameter to obtain the number of lumbar segments that would accommodate paired cages.2.3 To design a new type of special construct for the purpose of minimal invasive surgery which can be shaped into small contour outside body in 0癈 ice water and come back to its original structure after inserted into interbody interval.2.4 Eight human cadaver lumbar spine specimens (L3/4) were designed to compare the range of motion of three differential cages with one another. They were cylindrical threaded cages (Interfix, SOFAMOR DANEK), solid rectangle cages (Prospace, AESCULAP), and hollow rectangle cages (Syncage, SYNTHES). The three type cages were divided into seven groups: (Dcontrol (intact),(2)Interfix,(3)Prospace, and (4)Syncage. All cage groups were fixed again with posterior transpedicular screw plate system (Variable Steffee Plate, VSP, DEPUY-ACROMED). Differential cages were inserted randomly. All groups were tested for range of motion using a spinal three dimensional movement analysis system.2.5 To evaluate the biomechanical stability of lumbar functional segment unit after insertion with a newly designed shape memory alloy cage (SMAcage) and compare with three different lumbar interbody fusion cages (Interfix, Prospace, Syncage). Eight young male cadavers' lumbar spine specimens(L3/4) was used to detect the range of motion(ROM) of SMAcage as well as three differential cages .They were divided into five groups: (1) control (intact),(2)SMAcage, (3)Inter...
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