Finite element stress analysis of the wrist joint without and with an endoprosthesis

The finite element analysis method was used to obtain the lateral deformation profile and values of the von Mises stress in the cortical and cancellous regions of the various bones in models of a selected space in the coronal plane of a human wrist joint, without and with a prosthesis. The prosthesis was the metacarpal component of the Trispherical design of the total wrist joint arthroplasty. The models included all the bones, the associated network of ligaments, and the intervening soft muscle tissue. Each type of model was completely constrained along its entire proximal surface and subjected to either a static point force (in the axial compressive or anteroposterior tensile direction) acting at the center of the distal tip of the third metacarpal cortical bone. For the models containing the prosthesis, a parametric study was conducted involving the method of anchorage of the prosthesis to the contiguous bones and the material of fabrication of the prosthesis. It was found that: (1) the axial force produces lower stresses in the bones compared with the anteroposterior one; (2) no clear-cut case can be advanced, from the stress viewpoint, for press-fitting the prosthesis to the contiguous bones rather than using bone cement for such anchorage; and (3) any alloy with modulus of elasticity in the 79 to 196 GPa range and Poisson's ratio of about 0.3 may be used to fabricate the prosthesis. The approximations used and the associated limitations of the work are fully discussed, as are the design implications and clinical significance of the results.     

Possibilities of individual one-pole endoprosthesis of the joints

Experimental studies and an analysis of 72 organ-preserving operations fulfilled with individual endoprosthesis have shown that for each patient an individual one-pole endoprosthesis should be created.     

The wrist joint

The wrist joint is involved in a great majority of cases of rheumatoid arthritis. Tenosynovitis and synovitis can lead to severe destruction of the joint and to spontaneous ruptures of the tendons. Therefore, early tenosynovectomy and wrist-joint synovectomy are required. At the advanced stage of the disease, arthroplasty is necessary. Arthrodesis is rarely indicated in the treatment of severe wrist destruction in rheumatoid arthritis.     

The instability of wrist joint and total wrist replacement

Total wrist arthroplasty are not used as widely as total knee and hip replacement. The functional hands are requiring surgeons to design a durable and functional satisfying prosthesis. This article will list the main reasons that cause the failure of the prosthesis. Some remarkable and representative prostheses are listed to show the devolvement of total wrist prosthesis and their individual special innovations to fix the problems. And the second part we will discuss the part that biomechanical elements act in the total wrist replacement (TWA). Summarize and find out what the real problem is and how we can find a way to fix it.     

Total hip joint endoprosthesis in osteopetrosis]

Albers-Sch?nberg disease (osteopetrosis) is a rare condition, and it very seldom occurs that a patient requiring a hip endoprosthesis is also suffering from this disease. The report describes the difficulties which may confront a surgeon unprepared for such a case and the author illustrates the problem taking the case history of a 46-year-old patient with X-rays and histological tests as an example. The reasons for implantation of either a cemented or cementless endoprosthesis are discussed.