The Scandinavian total ankle replacement (STAR)

Ankle joint arthritis is a condition that affects many people. Initial conservative treatment includes nonsteroidal antiinflammatory drugs, soft bracing, and ankle foot orthosis. When conservative management fails, surgical intervention is often considered. Previously an ankle joint fusion has been considered the "gold standard" to treat disabling ankle joint arthritis because early total ankle joint replacements had unacceptably high complication rates. However, early and midterm data have demonstrated that the Scandinavian Total Ankle Replacement (STAR) or Agility Total Ankle may be a reasonable alternative to an ankle joint fusion.

[Longevity factors in total trapezometacarpal prostheses]

We report the long term outcome of the trapeziometacarpal prosthesis in a personal series of 13 cases with a follow-up ranging from 12 to 17 years. This ball and socket prosthesis with a metal on polyethylene pairing is cemented. Several modifications were performed along the years: such as increased range of motion, better fit between the metacarpal medullary canal and the proximal part of the stem and addition of a versatile, intermediate component in order to re-establish length of the first ray. The status of the metacarpo-phalangeal joint is critical. Natural hyperextension of this joint has been seen in about two-third of th normal individuals. If the metacarpal component become loose, the thumb column become shorter and hyperextension of the metacarpophalangeal joint is followed by an adduction contracture of the metacarpal which produces a shear force component on the cup and finally the loosening of the cup (sequential loosening). Keeping or re-establishing the length of the first ray is the major principle in the trapeziometacarpal prosthesis. On the other hand, metacarpophalangeal arthrodesis is a contraindication for a trapeziometacarpal prosthesis. Trapeziometacarpal prosthesis should only be used as a last resort when there is severe pain. If the dominant hand is involved, intensive use is a contraindication. The trapezium must be large enough to accommodate the cup. The author recommends a posterior approach which preserve the anterior ligaments and allows a proper bone resection and a good positioning of the cup.

[Metacarpophalangeal prosthesis modeling. Comparison of stress factors in a normal and a prosthetic metacarpophalangeal joint using finite element analysis]

INTRODUCTION

Prosthetic replacement of the metacarpophalangeal joints of long fingers is a problematical technique for the surgeon. The aim of the present study was to examine and compare, by means of finite element analysis, stress distribution in a normal metacarpophalangeal joint and to compare this with the findings in a similar joint with a prosthesis in order to better determine the risk of aseptic loosening, and also to examine possible solutions to limit these risks.

METHOD

Finite element modelling was carried out using Abaqus software. Various criteria were taken into account including anatomical data, stress distribution, mechanical characteristics of the materials used, and different positions of the phalanx.

RESULTS

A comparison of the results showed two significant stress distribution factors, i.e., a reduction of normal stress in the cortical bone of the finger fitted with a prosthesis; and the appearance of a flexion moment which completely modified the stress distribution throughout the metacarpal and therefore also in the opposite phalanx.

DISCUSSION

To reduce the risk of aseptic loosening, two solutions were proposed: a) to reduce Young's module. The problem which arises, as in the case of total hip prosthesis, is that of finding a material with a Young's module which is closer to that of cortical bone, and which at the same time has a high elastic limit and breakage point and good biocompatibility; b) to reduce the inertia of the prosthesis, which seems the more likely of the two propositions, as it is based on the results of the modelling. The inertia of the prosthesis on stress distribution can be reduced by modifying two parameters, namely by producing a hollow section and shortening the structure of the prosthesis.

The ethical allocation of scarce resources in surgery: implants and cost

This paper is a discussion of the factors involved in instituting a bulk purchasing program for surgical supplies. An improved understanding of the surgical procedure of joint arthroplasty must relate to the variability in surgical methods that achieve patient outcomes. An understanding of the outcomes in relation to the expected duration of the success of an implant and the high costs associated with a revision earlier than expected must be factored into the budget and costs of implants. The ethical implications of choosing one implant over another are considered. A more uniform outcome assessment with respect to surgical activities is needed and potential savings related to other operating-room costs must be examined. Optimizing the implant to patient requirements is the goal within the framework of current fiscal constraints.