| Retrograde degeneration and pathological changes of cervical intervertebral discs are one of the common causes resulting in cervicodynia and omalgia. In recent years, the preclinic and clinic related to cervical spine have become pop studies. The anterior cervical decompression with intervertebral bone grafting has been applied generally in clinic, but some problems such as the sliding of bone graft, narrow or anterior angulation of intervertebral space, iliac donor-site morbidity and plaster exopexy with long term are still remained to this day. With the development of medical science, new techniques continuously spring up, such as the clinical applications of TFC and BAK. These new appliances not only have the advantage of firm intervertebral immobilization and early exercise without plaster exopexy, but also have the advantage of short operative and anesthetic time without the excision of ilium. Many scholars consider that the motion segment is artificially stabilized because of the threaded design of the prostheses, which is similar to that stabilization created by pedicle screw constructs. Many researches have showed that spondylodesis inevitably lead to changes of spine biomechanical characteristic, vertebral body osteopenia, degeneration of the segment adjacent to the fusion, hypertrophy of the facet joints at adjacent levels, spinal stenosis and degenerative lumbar spondylolisthesis. The purpose of the present study was to develop a new intervertebral disc implant new active threaded intervertebral fusion cage (ATIFC) with the ability of according with the biomechanical environment of human body. 1 The design and processing of the ATIFC According to the anatomical and biomechanical data of the cervical vertebrae and intervertebral discs, the new intervertebral disc implant? ATIFC was designed and manufactured. The implant consists of two parts: cage and internal nucleus. The cage with flat olive bore is some similar to the contour of the Ray FC, and have screw thread on up and down sides and grooving spring on lateral sides. The internal nucleus approximates to flat olive in appearance and is little small than the bore. After the insertion of the internal nucleus into the bore, the analogous motion of flexion, extension and lateral bending could be achieved through the stretching of the spring and the minute sliding of the nucleus. The cage was made of titanium alloy and was processed through thread lathing, line cutting, electric spark and aftertreatment, and the internal nucleus was made of high olecular weight polyethylene and manufactured with numerical controlled machine tool. 2 Mechanical test of the ATIFC The intensity and fatigue tests were conducted on a material testing machine (model 858 Bionix, MTS Systems). With regard to the Small Size I Model (14mm in diameter, 13mm in length), the spring was reduced 0.70mm under the load of 130N; under the sinusoidal load of 40N with the frequency of 1HZ, the shell has not been destroyed for 1 X i0~ times. The results demonstrate that its mechanical nature might come up to the design demand. The fatigue test of the whole implant has not been carried out and will be continued. For the examination of function of the ATIFC, eight fresh human cervical spines (C21) were potted, and clinically relevant loads were applied through a loading frame attached to the C2 vertebra of each specimen. The specimens were tested in the intact state and following the resection of nucleus pulposus of intervertebral disc, i...
|
PDF Full Text Request