Prosthetic component malposition is not infrequent, because of technical flaws, especially without a computed navigation system. We assumed that an inclined interline of a prosthetic knee with components parallel in the coronal plane provides a better load distribution and lower contact pressure towards a varus malalignment. For that we studied, using finite element analysis, load intensity and distribution for three situations: ideal alignment of prosthetic components, tibial varus malposition of 3° and 8° leading to tibio-femoral varus malalignment (i.e. an unbalanced knee) and the same tibial varus malpositions, but with the femoral component also malpositioned in the coronal plane, so that they are parallel, and with equally tightened collateral ligaments (i.e. a balanced knee). We found that maximum contact pressure and underlying bone compression forces are higher for a balanced knee with an inclined interline than in ideal alignment, but lower than in an unbalanced knee. According to our results, 2- and 4-mm additional medial plateau resection on a proper balanced knee does not significantly affect the load distribution towards ideal alignment. Balancing is a key factor for prosthetic survival in cases when a certain degree of coronal malposition cannot be avoided.

Acrylic cement was introduced into practice by Sir John Charnley 40 years ago. The advantages of this cement are the good and durable fixation of the hip and knee prostheses ensuring the distribution of the forces from the implant to the bone. It is also used in vertebroplasties, osteoporosis and bone substitutes. One of the major problems associated with the use of bone cements is the decrease of the mechanical properties in time due to the incompatibility between the organic matrix and the inorganic phase. In this respect we propose the replacement of the inorganic radio-opacyfing agent with an iodine-based polymer that is compatible with poly(methymethacrylate). The new iodine-based polymer proved to have good chemical stability, low toxicity against cells and excellent radio-opacity, so it could be a potential candidate for the manufacture of the orthopaedic cements.

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In case of an orthopedic implant, it would be ideal that resorption to occur by biodegradation and bone remodeling. The main advantage of using resorbable orthopedic implants is eliminating the need for a new surgical procedure. The use of pure magnesium for orthopedic implants shows some drawbacks, which need to be considered and evaluated by in vitro and in vivo assays. One of the main problems encountered when pure Mg is used as biodegradable implant is represented by a high corrosion rate, faster than the rate of bone formation. The aim of this study is testing and evaluation of Mg-1Ca alloy from biocompatibility in vivo point of view. The purpose of in vivo test was to demonstrate good biocompatibility and lack of local and systemic toxicity of implants made by Mg-1Ca alloy. The study was conducted by implanting Mg-1Ca alloy parallelepiped shaped implants in the tibia of rabbits. In our tests related to Mg-1Ca alloy in vivo evaluation, there were no pathological increases in blood levels of Mg and Ca, or other elements, showing that it has no adversely affect to their metabolism. Also it shows a good bone integration, newly formed bone being adherent to the implant surface, with no tissue interposed between it and the bone. In conclusion, magnesium alloy Mg-1Ca represents a promising solution in orthopedic surgery, proving to be safe, with a high degree of biocompatibility and without toxic effects during in vivo testing.

The study was designed to assess the validity of a finite element analysis for predicting the behavior of cemented knee implant used in total knee arthroplasty (TKA), for different mechanical loads, and correlation with clinical outcomes of this procedure. We conducted computational simulations using finite element analysis of two situations: i) The ideal prosthetic component positioning; and ii) variable varus tibial malposition, but with a balanced knee. A total of 80 cemented TKAs performed on 70 patients were divided into two groups. Patients from one group required secondary asymmetric tibial recut for balancing the prosthetic knee and patients from the other group, did not. In regards to the results, we observed no differences upon analysis of the postoperative results of the Knee Society Score (KSS), the angle between the femur and tibia, the range of motion and frontal laxity between groups. The finite element analysis showed that in a 3˚ varus inclination of the joint interline, but with a balanced knee, the maximum contact stress, measured on the tibial plateau surface, increased by 11% compared to the value of mechanical alignment. In conclusion, analysis of the computational model using finite elements showed predictable results of cemented TKA for the different situations of mechanical loads.