Bone-Fixation Devices

PLLA bone fixation devices are gradually absorbed in the human body and are used for osteotomy and osteosynthesis, thus providing efficient for use in bodily regions in which surgical removal is difficult. 

Small-diameter vascular prostheses with incorporated matrices can be absorbed into a growing anastomotic neointima. It was pointed out that a gelatin-heparin complex when adequately cross-linked, could simultaneously function as a temporary antithrombogenic surface and as an exceptional substructure for an anastomotic 

Although metal fixation is an efficient method for undisturbed bone treatment, bone and metal have completely different mechanical properties. The elasticity constant of bone is only a tenth that of implanted steel, whereas its tensile strength is 10 times lower. Because of this, removal of metal implants can bring about bone weakness and refractures. 

In contrast, biodegradable implants can adapt to the dynamic processes of bone healing through decreasing amounts of weight-bearing material Over a few months the introduced material disappears and there is no need to operate on a patient to remove it In this field, PGA, PLA, PHD, and polydioxanone can poten- 

Biodegradable polymers are also helpful in other applications. A marrow spacer can help to save autologous bone material. Plugs to close bone marrow are applied in the case of endoprosthetic joint replacement To fill large bone defects, polymer fibers are used in order to avoid mechanical load [49]. 

the use of degradable materials for this purpose is ideal. Since materials for bone fixation require high strength, 

FIGURE 27.4 Diagram of mandibular reconstruction using a PLLA mesh and bone marrow (reprinted from Ref. 34 with permission from Prof. Kinoshita). 

FIGURE 27.5 Tissue engineered chondral plug composed of a PLLA mesh cage filled with collagen sponge with cultured chondrocyte gel (reprinted from Ref. 35 with permission from Wiley-Blackwell). 

Interestingly, PLLA can exhibit a similar degree of piezoelectricity as PVDF by increasing the drawing process. Since 

CONMED (Bionx Implants) United States Pin, screw Meniscus arrow SR-PLLA Drawn PLLA 

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The concept of using biodegradable materials for implants which serve a temporary function is a relatively new one. This concept has gained acceptance as it has been realized that an implanted material does not have to be inert, but can be degraded and/or metabolized in vivo once its function has been accompHshed (12). Resorbable polymers have been utilized successfully in the manufacture of sutures, small bone fixation devices (13), and dmg dehvery systems (qv) (14). 

Poly(Dat-Tyr-Hex carbonate) is a slowly degrading, strong and ductile material. This material may be applicable in situations where a mechanical support function is needed for an extended period of time such as in small bone fixation devices (bone pins or screws). The reproducible fabrication of such devices by injection molding is particularly easy due to the amorphous character of poly(Dat-Try-Hex carbonate). 

Figure 8.28 PIA based bone fixation devices with courtesy of Gunze Ltd [T3] (Reproduced with permission from Gunze Ltd, Japan.)...

The first use of PGA was as a degradable suture, DEXON , approved by FDA in 1969. It was also marketed as an internal bone fixation device. Biofix , till 1996 [11]. PGA has been extensively used for fabricating tissue engineered scaffolds and often with other degradable polymers, it has found its application in regeneration of bone [12, 13], cartilage [14, 15], tooth [16], tendon [17], nerve [18, 19] and spine [20]. Figure 1.1 shows a nerve tube (Neurotube from Synovis Micro Companies Alliance) fabricated from absorbable woven PGA mesh. 

PDS demonstrated no acute or toxic effects on implantation, and thus has been used in a number of clinical applications ranging from suture materials to bone fixation devices. Johnson and Johnson Orthopedics provides an absorbable pin for fracture fixation, and bone pins have been introduced into the market under the names OrthoSorb and Ethipin, respectively, in the USA and Europe. In craniofacial applications, the structure of PDS has been examined clinically in cranial vault procedures with promising results. Advantages include the absence of observed intracranial translocation, acceptable aesthetic outcomes and low complication rates. Nevertheless,... 

Appiications adhesives, coatings, foams, laminates, medical (bone fixation devices, cardiovascular, drug delivery, orthopedics, plastic surgery, sutures, tissue engineering) ... 

Although there are many medical applications for polymers which require materials to be stable over a long time period, there are also devices such as sutures, small bone fixation devices, skin grafts, and drug delivery systems where polymers that break down in a controlled fashion are required. Materials that can be tailored to break down either unaided or by enzyme-assisted pathways under the conditions inherent in the location where the implant is found are desired. 

Tunc, D. C. (1984) Absorbable bone fixation device containing poly(L-lactide), Eur. Pat. Appl. EP 108, 635. 

Bone fixation devices The metal fixation in fractured bone is the most popular and successful painless treatment. Mechanical properties are very different for critical bone and steel. The elasticity constant of the steel and the bone differ completely. The elasticity of bone is 110 whereas for the steel it was 10 times lesser. Thus, removal of metal implants can lead to weakened bones with the danger of re-fracture. 

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