Recent Advances in Finite Element Applications in Artificial Lumbar Disc Replacement

As a new choice for the treatment of degenerative lumbar disease, artificial lumbar disc replacement has been widely used in clinical surgery. The finite element is a very effective method to predict and simulate the surgery effect. The purpose of this paper is to review the applications of finite element in artificial lumbar disc replacement, such as design of artificial lumbar disc prosthesis, risk and effect evaluation of artificial lumbar disc replacement, and assessment of operation methods. Lastly, we discuss the future development of finite element method applied in this field, including personalized design of the prosthesis, postoperative behavior guide, and artificial lumbar disc replacement combined with fusion surgery. In conclusion, as an invaluable complement to biomechanical experiments and clinical studies, the finite element method makes important contributions to our understanding of biomechanics of intervertebral disc, and plays an important role in the field of artificial lumbar disc replacement.

Application of cervical arthroplasty with Bryan cervical disc： long-term X-ray and magnetic resonance imaging follow-up results

Background Cervical disc arthroplasty is a new technique for treating degenerative cervical disease. Its goal is to avoid the degeneration of adjacent levels by preserving motion at the treated level. The aims of this study were to evaluate the radiologic outcomes of Bryan cervical disc replacement and the degenerative status of adjacent segments.Methods Twenty-two patients at a single center underwent discectomy and implantation of Bryan cervical disc. The mean follow-up period was 60 months （57-69 months）. Twenty patients underwent single-level arthroplasty and two underwent arthroplasty at two levels. The levels of surgery included C3/4 （3 levels）, C4/5 （2 levels）, C5/6 （18 levels） and C6/7 （1 level）. Radiographic evaluation included dynamic X-ray examination and magnetic resonance imaging （MRI） at baseline and at final follow-up.Results On X-ray examination, the range of motion （ROM） at the operated level was 7.2° （2.5°-13.0°） at baseline and 7.8° （1.0°-15.0°） at final follow-up （P 〉0.05）. Heterotopic ossification around the prosthesis was observed in eight levels,and two levels showed loss of motion （ROM 〈2°）. MRI showed worsening by a grade at the upper level in 2/22 patients,and worsening by a grade at the lower level in 3/22, according to Miyazaki＇s classification. No further impingement of the ligamentum flavum into the spinal canal was observed at adjacent levels, though the disc bulge was slightly increased at both the adjacent upper and lower levels at final follow-up.Conclusions Arthroplasty using Bryan cervical disc prosthesis resulted in favorable radiologic outcomes in this study.Disc degeneration at adjacent levels may be postponed by this technique.

Potential Application of Entangled Porous Titanium Alloy Metal Rubber in Artificial Lumbar Disc Prostheses

Entangled Porous Titanium Alloy Metal Rubber(EPTA-MR)was used as a nucleus pulposus material in the design of non-fusion intervertebral disc prosthesis for the first time.A novel artificial lumbar intervertebral disc prosthesis was designed by reconstructing the lumbar model with reverse engineering technology,and the biomechanical behavior of the prosthesis was simulated under varied working conditions.The nucleus pulposus size was determined by the actual size of human prosthesis.EPTA-MR samples with different densities were prepared by medical titanium alloy wire experimental studies were conducted on static stiffness,damping energy consumption,and fatigue life.The results indicated that the static stiffness of EPTA-MR could reach approximately 1500 N mm and its loss factor remained higher than 0.2,and the variation range was relatively small,with excellent vibration damping capacity and bearing capacity.Among them,the overall performance of EPTA-MR with a density of 2.5 g em 3 was closer to that of the physiologic intervertebral disc.A macro experiment of five million fatigue vibration tests combined with microstructure observation exhibited a wear rate of only 0.9396 g-MC with no noticeable change in the internal micro-morphology.Therefore,the EPTA-MR has a broad application prospect as the nucleus pulposus material of artificial intervertebral disc prosthesis.

Comparison of adjacent segment degeneration five years after single level cervical fusion and cervical arthroplasty： a retrospective controlled study

Background Cervical arthroplasty is indicated to preserve cervical motion and prevent accelerated adjacent segment degeneration. Whether accelerated adjacent segment degeneration is prevented in the long term is unclear. This trial compared adjacent segment degeneration in Bryan disc arthroplasty with that in anterior cervical decompression and fusion five years after the surgery. Methods We studied patients with single level degenerative cervical disc disease. The extent of adjacent segment degeneration was estimated from lateral X-rays. Results Twenty-six patients underwent single level Bryan disc arthroplasty and twenty-four patients underwent single level anterior cervical decompression and fusion. All patients were followed up for an average of sixty months. In the Bryan arthroplasty group, nine （17.6%） segments developed adjacent segment degeneration, which was significantly lower than that （60.4%） in the anterior cervical decompression and fusion group. Eleven segments in the Bryan arthroplasty group developed heterotopic ossification according to McAfee＇s classification and two segments had range of motion less than 2%. In the heterotopic ossification group, four （19.5%） segments developed adjacent segment degeneration, similar to the number in the non-heterotopic ossification group （16.7%）. Adjacent segment degeneration rate was 50% in grade IV group but 11.8% in grade II to III. Conclusions Adjacent segment degeneration was accelerated after anterior cervical decompression and fusion. However, Bryan disc arthroplasty avoided accelerated adjacent segment degeneration by preserving motion. Patients with grade IV heterotopic ossification lost motion, and the rate of adjacent segment degeneration was higher than that in patients without heterotopic ossification.