Biomedical subjects
Publications and source records attributed to Helmut D Link.
Explore the source record for details and available documents.
STUDY: Knowledge gained through the clinical history of total joint replacement materials combined with the current promise of new biomaterials provides improved guidelines for biomaterial selection in total disc arthroplasty. OBJECTIVES: The following will detail: 1) current biomaterials technology; 2) how current designs of total disc arthroplasty seek to optimize implant performance through judicious biomaterial selection; and 3) what technical obstacles and clinical concerns remain. METHODS: Metals and polymers remain the central material components of state-of-the-art total joint arthroplasties. Polymers provide low friction surfaces for articulating bearings and some degree of shock absorption. Metals provide appropriate material properties such as high strength, ductility, fracture toughness, hardness, corrosion resistance, formability, and biocompatibility necessary for use in load-bearing roles required total disc replacement. There are three principal metal alloys used in orthopaedics and particularly in total joint replacement: 1) titanium based alloys; 2) cobalt based alloys; and 3) stainless steel alloys. Alloy specific differences in strength, ductility, and hardness generally determine which of these three alloys is used for a particular application or implant component. RESULTS: Current designs. Two examples of current lumbar (Charitè and Prodisc) and cervical (Bryan and Prestige) disc replacements are compared. The similarities and differences in the biomaterials used for each demonstrate prevailing consensus and some idea of how to best optimize implant performance through biomaterial selection. CONCLUSION: The primary factors governing total disc arthroplasty biomaterials are similar to those of all total joint arthroplasties: generation of wear debris is the primary source of implant degradation, and the subsequent tissue reaction to such debris is the primary factor limiting the longevity of joint replacement prostheses. Particulate debris generated by wear, fretting, or fragmentation induces the formation of an inflammatory reaction, which at a certain point promotes a foreign-body granulation tissue response that has the ability to invade the bone-implant interface. This commonly results in progressive, local bone loss that threatens the fixation of both cemented and cementless devices alike. All metal alloy implants corrode in vivo. When severe, the degradative process may reduce structural integrity of the implant, and the release of corrosion products is potentially toxic to the host. The corrosion resistance of implant alloys is primarily due to the formation of passive oxide films to prevent significant electrochemical dissolution from taking place. The result of this knowledge is a consensus of opinion as to which materials are best suited for use in current total disc arthroplasty designs, where most total disc replacement designs incorporate cobalt-chromium-molybdenum alloy endplates articulating internally on a relatively soft polymeric core and externally coated with titanium or titanium alloy for enhanced bone fixation.
The SB Charité I artificial disc was developed in 1982 by Schellnack and Büttner-Janz and modified as the Mark II version in 1984. Both types were manufactured in the former German Democratic Republic (GDR). Today's design, the SB Charité III, was first produced by LINK in 1987. Five sizes of the artificial disc in various angulations are available today, with a double coating of titanium/calciumphosphate. Designed with a three-component set-up, the SB Charité mimics the physiological segmental motion. The possibility of translation in the SB Charité provides proper biomechanical function and protects the zygapophysial joints. Results of biomechanical testing showed a sufficient cold-flow resistance of the UHMWPE (Ultra High Molecular Weight Polyethylene) sliding core and confirmed the negligible abrasion rate. The LINK SB Charité disc is a safe and effective operative treatment for discogenic low back pain. Long-term results (10 years and more) have been published.
BACKGROUND CONTENT: Three important basic scientific studies are presented that measured the volumetric density of longitudinal bony columns within the cervical vertebra. The most solid bone is lateral, adjacent to the uncovertebral joints in a radial pattern. PURPOSE: To characterize the best footprint, profile and biomaterials to construct a cervical disc replacement. STUDY DESIGN: A compilation of biomechanical and anatomical basic scientific studies. METHODS: Microcomputed tomographic imaging, trabecular density and mineral distribution were quantitated from human cervical vertebra. RESULTS: The lateral portions of the cervical vertebra are subjected to higher bending loads than the lumbar vertebral bodies. Therefore, the optimal prosthesis needs to be anchored in the lateral uncovertebral bone. To reduce the incidence of cervical subsidence, the prosthesis needs to be more rectangular than round to take advantage of the radially oriented lateral trabeculae. TiCaP (titanium/calcium phosphate) (Cervitech, Inc., Rockaway, NJ) bony ingrowth coating leads to 10% to 15% greater bony integration than plasma-sprayed titanium. TiCaP causes a supersaturated solution of CaP at the metal-bone interface, which enables reprecipitation of hydroxyapatite and superior bony integration. The optimum pore size of the ingrowth coating of the lumbar spine is 75 to 300 microns, whereas in the cervical spine the optimal ingrowth coating is 20 to 30 microns. This is an order of magnitude lower in pore size to match the smaller cervical trabecular architecture. CONCLUSIONS: Kinematic considerations for the cervical spine show the load is 1/9th the load carried by the lumbar spine or 50 N per segment. Knowing the sliding distance and wear characteristics of conventional biomaterials (ultrahigh molecular weight polyethylene and cobalt chrome) demonstrates that the generation of particulate debris should be a very minor consideration with cervical arthroplasty.
The results of a pilot study performed between December 2002 and October 2003 in which 82 cervical disc arthroplasties were implanted in 53 patients are reviewed in detail. Visual Analog Scale (VAS) pain scale, Neck Disability Index (NDI), and Treatment Intensity Gradient Test (TIGT) scales were evaluated as were static and dynamic radiographs. Significant improvents in all scales were seen postoperatively. One device migration of 4 millimeters was seen at 3 months and observed. Eighty percent of patients had a good or excellent result at one week, improving to ninety percent of patients being judged to have a good or excellent result by one month (Odom's criteria), which then remained at ninety percent at 3 months.