Joints, total replacement

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... 

Total hip replacement is an operation where the surgeon removes the rough surfaces of bone at the joint and replaces them with new smooth surfaces of the implant used. The modern hip replacement implant is complex and made of several components that the surgeon carefully fits together during surgery. Some of the components are made of metal and others of a special hard medical plastic. 

The major factors limiting the effective life of a total replacement synovial joint are loosening of one or more of the prosthetic components, a variety of medical problems (e g. infection) and wear. Most internal prostheses now consist of metallic and polymeric components and it is the penetration of the former into the latter which is the subject of this paper. 

A knee joint simulator designed to evaluate the mechanical and tribological characteristics of total replacement knee joints will be described. Measurements of penetrations of metallic femoral components into the polymeric tibial components by means of dual index holographic contouring will be presented and the findings compared with observations from detailed studies of wear in well-controlled laboratory machines and the limited evidence of in-vivo performance of replacement knee joints. 

The development of satisfactory total replacement synovial joints is sometimes described as the major advance in orthopaedic surgery in recent times. The hip joint was the first major load bearing joint to respond to the efforts of surgeons, engineers and materials scientists in the past two decades to develop satisfactory replacements, but attention is now focussed upon the more complex knee joint. 

Most total replacement joints consist of a metallic and a polymeric component, although alternative materials such as ceramics and carbon reinforced materials are currently being examined for this role. The life of a prosthesis is thus directly affected by the rate of penetration of the metallic component into the polymeric component and this has prompted considerable Interest in the subject of wear of polymers in the hostile environment of the body. 

When polytetrafluoroethylene (PTFE) was Introduced in the early 1960 s the life of total replacement hip joints was limited to about three years by the poor wear characteristics of the polymer. When ultra-high molecular weight polyethylene (UHMWPE) replaced PTFE, the rate of penetration of the metallic component into the polymeric component was reduced to such an extent that loosening emerged as a major aspect of prosthetic life. There is, nevertheless, a need to pursue studies of the wear of prosthetic materials to facilitate the development of satisfactory materials which can be used with confidence in long-life prostheses. 

A knee joint simulator was designed and built in the bioengineering laboratory at Leeds in the late 1970 s to enable the mechanical and tribological characteristics of current and projected knee joint replacements tp.he assessed. The simulator has been described by Dowson et al and it is shown in Figure 1. Realistic load and motion cycles are applied to the knee joints to simulate any desired activity, but usually walking, and the penetration of the metallic femoral components into the polymeric tibial components after a large number of cycles can then be used to assess the life of the joints. Furthermore, the penetrations recorded, which include both wear and creep, can be related to results of laboratory wear studies of the behaviour of UHMWPE and to the in-vivo performance of total replacement knee joints. The simulator is therefore an Important machine in both the pragmatic and fundamental aspects of total replacement knee join development. 

The derived wear factor (k) for the Freeman-Swansog and Leeds knee joints tested in the simulator for about 10 cycles are both interesting and similar. The ln-vlvo Freeman-Swanson joint was kindly made available by Professor S.A.V. Swanson and the conditions of service were not known with any certainty. The joint had functioned in an elderly patient for some four years, with a light to medium level of walking activity. It was therefore assumed that /PdX remained constant at 47.7 Nm/cycle and that the patient achieved 6000 strides or 3000 loading cycles per day. These assumptions are consistent with a subsequent study of the walking activity of patients fitted with total replacement joints reported by Wallbrldge and Dowson, but considerable scope for errors... 

The experimental findings confirm the merit of joint simulators in furthering the development of total replacement joints. 

There is an urgent need for further careful analysis of the wear characteristics of total replacement joints after service in the body. Such studies would enhance the understanding of the long term performance of prostheses and would indicate the merit of versatile laboratory wear testing machines and joint simulators. 

Dowson, D., New Joints for the Millennium Wear Control in Total Replacement Hip Joints, Proc. I. Mech. Eng. Part H, 215, 225-357, 2001. 

The Smith-Petersen implant is an early example of a hemiarthroplasty, in which only the femoral side of the hip joint is replaced. By contrast, in a total hip joint replacement, both the femoral and acetabular surfaces are replaced. The radiograph, shown in Figure 6.1, was obtained at the Chamley Museum at Wrightington Hospital (Wigan, England) and illustrates this early design. 

Leitner, F., et al., Computer-assisted knee surgical total replacement, in Proc. First Joint Cottference of CVRMed and MRCAS, 1997, Grenoble, France, Springer. 

Dowson, D. (1995) A comparative study of the performance of metallic and ceramic femoral head components in total replacement hip joints. Wear, 190, 171-183. 

Dowson, D.B. and Jobbins, B. (1988) Design and development of a Versatile hip joint simulator and a preliminary assessment of wear and creep in Charnley total replacement hip joints, Engineering in Medicine, 17, 111-117. 

Dowson, D. and Wallbridge N.C. (1985) Laboratory wear tests and clinical observations of the penetration of femoral heads into acetabular cups in total replacement hip joints I Charnley prosthesis with polytetrafluoroethylene acetabular cups. Wear, 104, 203-215. 

Saikko, V. (1992) Simulator study of friction in total replacement hip joints. Proceedings of the Institution of Mechanical Engineers Part H Journal of Engineering in Medicine, 206, 201-211. 

Wallbridge, H., Dowson, D. and Roberts, E.W. (1983) A study of the wear characteristics of sliding pairs of high density polycrystalline aluminum oxide with particular reference to their use in total replacement in human joints. Engg in Med., 12(1), 23-28. 

Dowson D (2001), New joints for the Millennium wear control in total replacement hip joints , Proc Inst Mech Eng H, 215, 335-358. 

In general, weld repair of any cracked metallic bellow is not recommended, as it is not possible to restore the original bellow functionality after repair. That will further jeopardize its operational integrity. Therefore it is always considered safe to replace the entire expansion joint bellow assembly from the reliability point of view. Procuring a new bellow joint for replacement normally takes a minimum of 10 to 14 weeks subject to the supplier / manufacturer constraints. Shutting down SRU totally and flaring Acid gas for extended periods imtil the replacement of bellow is not permitted as it is anti-environmental. 

Saikko VO. Tribology of total replacement hip joints studied with new hip joint simulators and a materials-screening apparatus. 

It is known from recent investigations (2, 3, 4) that the transient elastohydrodynamic film formation and supplemental lubrication mechanism such as micro-elastohydrodynamic lubrication, weeping, blphasic, boosted or boundary lubrication are capable of providing sufficient protection to the articular cartilages in natural joints. On the contrary, there is just a little information on the actual lubricating film formation in total replacement joints. 

Dee R. Total replacement arthroplasty of the elbow for rheumatoid arthritis. J Bone Joint Surg Br 1972 February 54(l) 88—95. 

Kudo H, Iwano K, Watanabe S. Total replacement of the rheumatoid elbow with a hingeless prosthesis. J Bone Joint Surg Am 1980 March 62(2) 277-85. 

The Relationship Between Steady-state Wear Rate and Theoretical Film Thickness in Metal-on-Metal Total Replacement Hip Joints... 

The relationship between steady-state wear rate and theoretical film thickness in metal-on-metal total replacement hip joints... 

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