Bone plates

The actual time required for poly-L-lactide implants to be completely absorbed is relatively long, and depends on polymer purity, processing conditions, implant site, and physical dimensions of the implant. For instance, 50—90 mg samples of radiolabeled poly-DL-lactide implanted in the abdominal walls of rats had an absorption time of 1.5 years with metaboHsm resulting primarily from respiratory excretion (24). In contrast, pure poly-L-lactide bone plates attached to sheep femora showed mechanical deterioration, but Httie evidence of significant mass loss even after four years (25). 

Transosteal and Staple Implants. This implant goes through the bone and is for the purpose of attaching dentures. The mandibular bone staple plate has replaced the transosteal pin. Since 1975 the five-pin staple bone plate has been used predominantiy, and in 1985 showed a success rate of 93% after five years (317). 

In the beginning of the twentieth century, surgical techniques were developed for the fixation of bone fractures with a plate and screw combination. Sherman-type bone plates were fabricated from the best available alloy at the time, vanadium steel. By the 1920s the use of vanadium steel became questionable because of poor tissue compatibility. At that time however, no other alloy was available with high strength and good corrosion resistant properties. 

One of the most serious corrosion problems associated with type 316 stainless steel is its susceptibility to crevice corrosion. The incidence and extent of this type of corrosion in surgical implants was stressed by Scales eta/. who reported the presence of crevice corrosion in 24% of type 316L bone plates and screws examined after removal from patients. This record however compared favourably with the presence of crevice corrosion in 51 % of 18-8 stainless plates, demonstrating the superiority of the molybdenum-containing grade. 

A rapidly growing use in the medical field is for surgical implants as either bone plates and screws, joint replacements, or for the repair of cranial injuries. Here, titanium and its alloys have the advantages of complete compatibility with body fluids, low density, and low modulus. Applications also exist in dentistry. 

Christei, P., Chabot, F., and Vert, M., In vivo fate of bioresorbable bone plates of long-lasting poly(L-lactic acid), Proc. 2nd World Congress on Biomaterial, 279, 1984. 

While this book is focused on drug delivery, the value of biodegradable polymers is not limited to this field. Biodegradable polymers will be useful in other areas of medical therapeutics, such as sutures and bone plates and other types of prostheses. The polymers will also be useful in nonmedical fields, for disposable plastics, bottles, diapers and many other entities. 

Metallic biomaterials (metals such as Ti or its alloys and others) are used for the manufacture of orthopaedic implants due to their excellent biocompatibility with respect to electrical and thermal conductivity and their mechanical properties, e.g., for hard tissue replacement such as total hip and knee joints, for fracture healing aids such as bone plates and screws or dental implants. For example, Co-Cr-Mo alloys are employed for metal-on-metal hip bearings in total joint replacements. Problems with implants occur because of ion release in patients with metal implants. To control this ion release, the ultratrace determination of Co, Cr and Mo in the blood (or serum) and urine of patients with Co-Cr-Mo alloy hip implants is carried out routinely in the author s laboratory. The trace metal determination of Co, Cr and Mo in complex matrices such as urine and blood by ICP-MS is not trivial due to the low concentrations expected in the sub-ngmF1 range, the possible danger of contamination during sample collection, sample preparation and the... 

The mechanical properties of these materials are too weak to use them in places in the body where much pressure is exerted. It is virtually impossible to achieve 100% polymerisation during the production process. Consequently the material contains impurities which may lead to toxic, allergic or carcinogenic processes. In future so-called biodegradable plastics will be used in applications such as artificial skin, synthetic blood, bone plates and in the controlled release of medication. 

Around 1900 bone plates to secure broken bones were introduced. Many of these plates broke due to design flaws, i.e. they were too thin and / or had angles with tension concentrations. Scientists also experimented with vanadium steel, this material has good mechanical... 

Probably the first successful and widespread clinical use of biomaterials occurred in the early 1900s, when a number of metals and alloys were developed to stabilize bones that had been fractured. These materials were used to form bone plates that held the broken ends of bones in place until they grew back together. After healing, the plates were removed, if possible, or, if not, left in the patient s body. 

The first metal alloy developed specifically for use in bone plates was vanadium steel, invented in about 1905. Over the next two decades, a number of other alloys and metals were tried as bone plate materials. In 1926, another alloy designed especially for bone plates was invented. It was a type of stainless steel consisting of 18 percent chromium and 8 percent nickel. Later the same year, a slightly modified form of the alloy was introduced, called I8-8SM0, containing a small amount of molybdenum. 

The problems experienced with these early types of bone plates foreshadowed the types of problems medical researchers could... 

Orthopedic Joint replacements (hip, knee) Bone plate for fracture fixation Bone cement Bony defect repair Artificial tendon and ligament Titanium, Ti-Al-V alloy, stainless steel, polyethylene Stainless steel, cobalt-chromium alloy Poly(methyl methacrylate) Hydroxyapatite Teflon, Dacron ... 

Coskun, S. Korkusuz, F. and Hasirci, V. Hydroxyapatite reinforced poly(3-hydroxy-butyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvaleiate) based degradable composite bone plate. J. Biomater. Sci. Polym. Edn. 2005,16(12), 1485-1502. 

Zimmerman M.C., Alexander H., Parsons I.R., and Bajpai P.K. 1991. The design and analysis of laminated degradable composite bone plates for fracture fixation. In High-Tech Textiles, T.L. Vigo and A.F. Turbak (Eds.), pp. 132-148. ACS Symposium Series 457, American Chemical Society, Washington, D.C. 

Flexible composite bone plates are effective in promoting healing [lockish, 1992], but particulate debris from composite bone plates gives rise to a foreign body reaction similar to that caused by ultra high molecular weight polyethylene. 

FIGURE 45.1 Radiographs of (a) tibial fracture fixed with four pins and an external bar (b) a total hip joint replacement in a patient who sustained a femoral fracture and was treated with double bone plates, screws, and surgical wire (arrows) (c) application of wires, screws, and plates in the spine. 

---