Clinical And Biomechanical Study Of Cervical Spondylosis And Cervical Artificial Disc Replacement

Study background and objectiveCervical spondylisis has become one of the common and frequently occurring illness in clinic and brought great hazardous to sufferers ,their families and society,along with the development of society,population aging ,and alteration of people's work and life styles especially.The cervical spondylosis is a chronic disease,most of which can be cured by proper expectant treament or natural relief.However there are about 3 %(15/516) of them could not recover by long-term expectant treatment.What's more serious is that it can result in great damage of functions of nerve root and spinal cord.In that case,it must turn to operation trearment in time.Fortunatly, the surgical treatment level of cervical spondylosis has been improved greatly since the announcement of anterior cervical decompression and bone-graft fusion by Robison-Smith(1955) and Cloward(1958).A large number of cervical spondylosis patients's condition have been relieved or cured. However,concerns for the possibility of acceleration of adjacent-segment disease after fusion have been growing in long-term follow up.There are other drawbacks of fusion,such as the alteration of spinal biomechanics,graft and hardware complications.and harvest site chronic pain,etc.In addition,it must be realized that decompression,not fusion,remains the primary indication and goal of anterior cervicalsurgery.The artificial cervical disc replacement provides the opportunity to preserve motion after neural decompression while providing stability.This paper summarizes the research progress and history in this field and aims to comment on the current development and future prospects of cervical arthroplasty.The studies were designed to evaluate the clinical value after treatment of degenerative disc disease with the Bryan cervical disc prosthesis, determine whether the new device can provide relief from objective neurologic symptoms and signs,and maintain the biomechanical stability and segmental motion.Meanwhile,some interrated clinical and biomechanical questions were investigated in this paper. Methods(1) The epidemiological investigation and biomechanical analysis of the cervical spondylosis: 4785 staffs and their family numbers (between 20 and 89 years old,mean 47.8,male 2655,female 2130) were studied with general surveying method in a university. 516 staffs were diagnosed by criteria of special conference summary of cervical spondylosis( 1992 China). Analyzed the nosogenesis and biomechanical mechanism.3-year follow-up,to observe the treatment outcome and the natural history of cervical spondylosis.(2) Magnetic resonance imaging analysis of accelerated degenerative changesadjacent to the fused segment after anterior cervical fusion: Preoperative and short-term follow-up (mean duration 26 months, range 1 to 5years) cervical MR images obtained in 28 patients who had undergone one- or two-level corpectomy for cervical spondylotic myelopathy were evaluated qualitatively and quantitatively. The motion segment adjacent to the fused segment and a segment remote from the fused segment were evaluated for indentation of the thecal sac, disc height, and sagittal functional diameter of the spinal canal on midsagittal T2-weighted MR images. Thecal sac indentations were classified as mild, moderate, and severe.(3) Biomechanical study of artificial nucleus pulposus replacement and bone-graft implantation in cervical disc: six fresh human cadaveric specimens (C1-T1) were used to establish normal nucleotomy,artificial nucleus pulposus replacement and bone graft implantationmodels.Mechanical stability were determined by testing cervical spinal range of motion(ROM)in flexion,extension,lateral bending and torsion combined with axial compressive loading. Meanwhile,the dynamic radiographys were taken and analysed in the operative disc with or without artificial nucleus pulposus and bone graft implantation.(4) Bryan disc prosthesis replacement: 16 Patients(20 discs) with symptomatic cervical radiculopathy and/or myelopathy underwent implantation with the Bryan prosthesis after a standard anterior cervical discectomy.At scheduled follow-up periods, the effectiveness of the device was characterized by evaluating each patient's pain, neurologic function, and radiographically measured range of motion at the implanted level. Results(1) The prevalence of the cervical spondylosis was 10.78%,in which male 9.38%,female 12.54%.The local type(neck and shoulder pain) and cervical radiculopathy was 58% and 37% respectively, cervical spondylotic myelopathy and other types were 5% totally. Surgical treatment was required in 3 %(15/516) patients for 3-year follow-up.(2) New indentations of the thecal sac of varying severity (mild in 7 patients [25%], moderate in 6[21%], and severe in 3 [10.71%]) had developed at the adjacent segments in 16 (57%) of 28 patients. The degenerative changes were seen at the superior level in 8 patients, inferior level in 3 patients, and at both levels in 5 patients and resulted from both anterior and posterior element degeneration in the majority (10 [62.5%]) of patients. The remote segments showed mild thecal sac indentations in 2 patients and moderate indentations in one patient(3 [10.71%] of 28). Compared with the preopration, the canal size was significantly decreased at the superior adjacent segment by 1.93 mm (p < 0.001)and 1.35mm(p=0.O02) at the inferior adjacent segment. Three patients sustained new neurological deficit due to adjacent-segment changes.(3) The ROM in nucleotomy group increased significantly compared with the intact segment(P<0.01).Placement of artificial nucleus pulposus or bone graft decreasd the ROM of cervical spine compared with the nucleotomygroup(P<0.01).The motion decrease was statistically significant. (4) Clinical success rate was 93% that exceeded the study acceptance criteria of 85%.JOA improved from average 12 grades preoperatively to 15.5 postoperatively.At follow-up, the flexion-extension range of motion per level averaged 10.2+5.4 degrees. No devices have been explanted. Conclusion(1) The cervical spondylosis was one of common diseases in clinic ,in which operation was required for some severe patients. Long-term flexion posture to blow one's head or fixation posture of neck is one of the important factors which induce cervical spondylosis.The cervical spondylotic nosogenesis is relationship to stress increasing in intervertebral disc.(2) On follow-up MR imaging, levels adjacent to the fused segment exhibited more pronounced degenerative changes in 57% of patients who had undergone one- or two-level central corpectomy. Reopration treatment was required to relief the new neurological symptoms and signs in about 10.71% patients.(3) The present results demonstrate that artificial nucleus pulposus replacementhas better biomechanial properties,increase the segment stability,and restores the normal lordosis of the cervical spine.(4) Discectomy and implantation of the device alleviates neurologic symptoms and signs similar to anterior cervical discectomy and fusion.lt is more consistent with the biomechanical feature of cervical spine motion.Radiographic evidence supports maintenance of motion. The procedure is safe and the patients recover quickly.Longer time of follow-up and further systemic research will be needed to assess the long-term functionality of the prosthesis and protective influence on adjacent levels.