Joints Replacement

HDPE by itself is a safe plastic material on account of its chemical inertness and lack of toxicity. Consequently, film and containers made from HDPE are used on a large scale in food and dmg packaging. Moreover, HDPE has been used in prosthetic devices including hip and knee joint replacements (122). 

Fig. 11. Three views of a hip implant for joint replacement (a) insertion of the implant into the femur (b) implant in place and (c) femur and implant...

The materials used in a total joint replacement ate designed to enable the joint to function normally. The artificial components ate generally composed of a metal piece that fits closely into bone tissue. The metals ate varied and include stainless steel or alloys of cobalt, chrome, and titanium. The plastic material used in implants is a polyethylene that is extremely durable and wear-resistant. Also, a bone cement, a methacrylate, is often used to anchor the artificial joint materials into the bone. Cementiess joint replacements have mote tecentiy been developed. In these replacements, the prosthesis and the bone ate made to fit together without the need for bone cement. The implants ate press-fit into the bone. 

The main benefits to the patient after total joint replacement ate pain tehef, which often is quite dramatic, and increased muscle power, which was lost because the painhil arthritic joint was not used and usually returns with exercise once pain is teheved. Motion of the joint generally improves as well. The extent of movement depends on how stiff the joint was before the joint was replaced. An extremely stiff joint continues to be stiff for some period of... 

The principal complication for total joint replacement is infection, which may occur just in the area of the incision or more seriously deep around the prosthesis. Infections in the wound area, which may even occur years after the procedure has been performed, are usually treated with antibiotics (qv). 

Breakage of an implanted joint is rare. Breakage occurs when the bone flexes and the metal implant does not flex as much, thereby exceeding its mechanical fatigue point causing the implant to break or crack. A revision joint replacement operation is necessary if breakage occurs. 

Nerves are rarely damaged during the total joint replacement surgery. However, nerve damage can occur if considerable joint deformity must be corrected in order to implant the prosthesis. With time these nerves sometimes return to normal function. 

The next advance in total hip arthroplasty came with the development of various porous surface treatments which allow bone tissue to grow into the metal porous coating on the femoral stem of the hip implant and on the acetabular component of the total joint replacement. These developments arose because of patients who were not able to tolerate cemented implants because of allergies to the cement, methylmethacrylate. More youthflil patients are better served by a press-fit implant as well. Figure 12 shows the difference between textured and beaded surface-treated orthopedic prostheses. 

Resorption of bone tissue occurs in total hip joint replacement patients if sufficient stresses are not adequately transmitted to the remaining bone in exactiy the same way that the bone transmitted those stresses originally. Therefore, the design and proper placement of the neck coUar and hip stem must be effective in recreating anatomical stmcture. 

As a last example we turn to the world of medicine. Osteo-arthritis is an illness that affects many people as they get older. The disease affects the joints between different bones in the body and makes it hard - and painful - to move them. The problem is caused by small lumps of bone which grow on the rubbing surfaces of the joints and which prevent them sliding properly. The problem can only be cured by removing the bad joints and putting artificial joints in their place. The first recorded hip-joint replacement was done as far back as 1897 - when it must have been a pretty hazardous business - but the operation is now a routine piece of orthopaedic surgery. In fact 30,000 hip joints are replaced in the UK every year world-wide the number must approach half a million. 

In 1998, the FDA approved fibrin sealant for three specific indications. These include hemostasis at the time of cardiac surgical operations [8] (Fig. 2) as well as at the time of operative procedures to treat splenic trauma. The application of the fibrin sealant which consists of normal biologic components in the body s clotting cascade creates a localized clot which further enhances inherent clotting ability. Although approved for these specific hemostatic indications only, fibrin sealant is useful as a hemostat in a wide variety of off-label clinical situations as well [9,10]. These include such applications as hemostasis for liver trauma or resection [11], vascular anastomoses [12], tonsillectomy [13], peripheral joint replacement [14], dental extractions [15], and bum debridement [16]. 

Table 2.23 Selected mechanical properties of materials used in total joint replacement ...

One of the main problems of corrosion testing in-vivo and the interpretation of the mechanisms of corrosion which have taken place in-vivo after the implant has been removed from a patient is well illustrated in Figure 2.35 used by Semlitsch and Willet to illustrate the types of corrosion which are associated with a total hip joint replacement. This figure shows that many corrosion mechanisms could be taking place simultaneously in a system of this nature. 

As the surgical techniques advance, the average age of the patient subjected to total joint replacement is decreasing and therefore the life expectancy of the implant is increasing. This obviously places more emphasis on the fatigue and corrosion resistant properties of the materials which are used in orthopaedic surgery. 

Total joint replacement The replacement of a joint by an endoprosthesis. 

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. 

Electrolysis of solutions containing Au(CN)2 is widely used to recover gold from solution (electrowinning) [17]. The process is also used to deposit gold coverings for electrons (e.g. printed circuit boards, electrical connectors) and most recently for hip and shoulder joint replacement surgery. 

EC Reclassifies hip, knee and shoulder joint replacements as Class 111 devices by way of derogation from the general classification rules... 

Jonck, L. M., Grobbelaar, C. J. Strafing, H. (1989). The biocompatibility of glass-ionomer cement in joint replacement bulk testing. Clinical Materials, 4, 85-107. 

Successful applications of materials in medicine have been experienced in the area of joint replacements, particularly artificial hips. As a joint replacement, an artificial hip must provide structural support as well as smooth functioning. Furthermore, the biomaterial used for such an orthopedic application must be inert, have long-term mechanical and biostability, exhibit biocompatibility with nearby tissue, and have comparable mechanical strength to the attached bone to minimize stress. Modem artificial hips are complex devices to ensure these features. 

Patients with severe disease may benefit from surgical procedures such as tenosynovectomy, tendon repair, and joint replacements. 

Joint replacement S. aureus, S. epidermidis Cefazolin 1 gx 1 preoperatively, then every 8 hours x 2 more doses Vancomycin reserved for penicillin-allergic patients or where institutional prevalence of methicillin-resistant Staphylococcus aureus warrants use IA... 

Cefazolin is the best-studied antibiotic and is thus the drug of choice. For hip fracture repairs and joint replacements, it should be administered for 24 hours. Vancomycin is not recommended unless a patient has a history of /3-lactam hypersensitivity or the propensity for MRSA infection at the institution necessitates its use. 

Orthopedic devices, 3 721-735 joint replacement, 3 727-735 Orthopedic marrow needles, 3 743-744 Orthophosphate (PO4), in soil, 11 112 Orthophosphates, 18 830-841 20 637 magnesium, 18 839 manufacture of, 18 853-855 Orthophosphate salts, 18 836 Orthophosphoric acid, 18 815, 817-826 condensation of, 18 826 properties of, 18 817-819 solubility of boron halides in, 4 140t orf/zo-phthalic resins, 20 101, 113 formulation of, 20 102 Orthorhombic crystal system, 8 114t Orthorhombic phosphorus pentoxide, 19 49 Orthorhombic structure, of ferroelectric crystals, 11 95, 96 Orthorhombic symmetry, 8 114t Orthosilicate monomers, in silicate glasses, 22 453... 

---