PubMed · 10098056
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S F Conti. 1999. Total contact casting.. https://pubmed.ncbi.nlm.nih.gov/10098056/
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The poor results of total ankle replacement have been attributed to the inability of designers to restore adequately the critical mutual function of the ligaments and the articular surfaces. The purpose of this study was to design sagittal shapes of the articular surfaces for a new ankle prosthesis to be compatible with the geometry of the retained ligamentous structures. Several ligament-compatible pairs of articular surfaces were tested using a computerised version of a four-bar linkage model. The kinematics of the ankle when replaced by non-conforming two-component and by fully conforming three-component designs with either flat, concave or convex tibial surfaces were assessed by the model. A ligament-compatible convex-tibia fully-congruent three-component prosthesis showed the best features. The three-component prosthesis allows complete congruence over the entire range of flexion. A convex shape for the tibial arc was preferred because of the better degree of entrapment of the meniscal bearing. A 5 cm convex-tibia arc radius gave 2 mm entrapment together with 9.8 mm of tibial bone cut. Ligament elongation imposed by full congruence of the articular surfaces was less than 0.03% of the original length. The original patterns of joint kinematics and ligament tensioning are closely restored in the joint replaced by the proposed prosthesis.
The ankle joint as a component within the construction of the foot must be seen as a compromise between the static and dynamic demands made upon it. In this article the structure and function of the ankle joint are described with special reference to the formation of morphological parameters such as the distribution of subchondral mineralization, cartilage thickness, subarticular cancellous bone and mechanical properties. These parameters could be seen as a biological reflection of the individual mechanical conditions.
OBJECTIVE: Reliable evaluation of joint space width and subchondral sclerosis of osteoarthritic joints is difficult. The present study describes a new digital method to analyse standard radiographs of the ankle. DESIGN: Standardized radiographs were taken of the ankle of 12 patients with severe osteoarthritis (OA) under full weight-bearing conditions, before treatment and 1 year after initiation of treatment. Treatment consisted of 3 months distraction of the tibio-talar joint, for which clinical benefit has been shown previously. The width of the joint space was measured on digitized images of the radiographs by means of the newly developed semi-automatic digital technique called AIDA (Ankle Images Digital Analysis) and by means of the most widely used conventional analogue measurements. In addition, AIDA was used to assess subchondral sclerosis by measuring the intensity of the radiograph at fixed positions at the bone-cartilage interface. RESULTS: AIDA appeared to be a reliable method for measuring small changes in joint space width and subchondral sclerosis because the intra- and interobserver variation was small. Mean JSW for two observers was 1.96 and 2.00 mm, with mean differences between two observations of 0.05 and -0.01, respectively. Mean subchondral sclerosis in the tibia was 1.52 and 1.61 with mean differences between two observations of, respectively, 0.00 and 0.03. In addition to conventional measurements, AIDA could demonstrate a decrease in subchondral sclerosis as a result of joint distraction of 71% and 69% after 1 year for talus and tibia, respectively. CONCLUSION: The use of AIDA is preferable to the conventional analogue method for evaluating the severity of ankle OA, because the method provides quantitative data not only for the joint space width but also for subchondral sclerosis.