Knee joint prostheses

BS ISO 14243-1 (2009), Implants for surgery. Wear of total knee-joint prostheses. Loading and displacement parameters for wear-testing machines with load control and corresponding environmental conditions for test, London, British Standards Institute. 

Fig. 6. Wear patterns of UHMWPE from examination of retrieved knee joint prostheses. SEM Examination.

A useful collection of symposium papers under the general title Corrosion and Degradation of Implant Materials has been published by the American Society for Testing and Materials. " In this, two separate studies of retrieved orthopaedic implants are presentedtogether with an account by Dumbleton " of the literature on the use, primarily in Scandinavia, of polyoxymethylene (Delrin) for compK>nents of total hip and total knee joint prostheses. 

Knee-joint prostheses consist of two metal components that replace the destroyed joint surfaces of the thigh bone (femur) and the shinbone (tibia) and that are usually cast from cobalt- or titanium-based alloys. The tibia part is typically extended by a short stem, anchoring the system in the marrow cavity. A UHMWPE insert is used as the articulating counterpart to optimize sliding behavior and to minimize wear see Fig. 8.6. 

Surface Characteristics and Tribological Behaviour of New Zirconia Ceramics for Cementless Knee Joint Prostheses... 

In this study, the tribological behaviour of the HTOZ-on-UHMWPE sliding pair for cementless knee joint prostheses was evaluated using unidirectional pin-on-disk tests and multidirectional pin-on-plate tests. Results were compared to the friction and wear properties of the TZP-on-UHMWPE sliding pair and the effects of the altered surface characteristics were examined. 

The tribological characteristics of new prosthetic materials have to be examined, as excessive wear of the joint surface is a major cause of the failure of current joint prostheses. It has been widely recognised that UHMWPE wear debris released firom the articulating surface of joint prostheses have an adverse effect on the surrounding tissue and can induce joint loosening [3-5]. Therefore, we evaluated in this study the friction and wear characteristics of the UHMWPE-on-HTOZ sliding pair, which was newly developed by our co-authors, to examine whether it was suitable to use in cementless knee joint prostheses. 

A different method of creating UHMWPE fibre-reinforced UHMWPE composites was presented by Mosleh et al. [179]. In this method, dry UHMWPE powder was mechanically oscillated through a funnel onto subsequent layers of short (25 mm) chopped UHMWPE fibres, or pieces of continuous UHMWPE fabric. By repeating this process with many layers of short chopped UHMWPE fibres or UHMWPE fabric, a layered stmcture was reported to have been created. These fibre assemblies were then heated under pressure to consolidate the structures. The short UHMWPE fibre-reinforced composites had a fibre volume fraction between 25 and 75%, while the continuous UHMWPE fabric-reinforced composites had a fibre volume fraction of 60%. Investigations into the potential application of these homocomposites in an articulation surface for a knee joint prosthesis were also described, as were the challenges associated with measuring the tribological performance of such fibre-reinforced materials [180]. 

Orthopaedic prosthesis Mechanism of wear of Ultra-high molecular weight polyethylene currently used in total hip and knee joint implants— see J. Mater. Set. 28 1045-1058 (1993). 

This High Intelligence Prosthesis for the knee uses an MR fluid damper to provide motion that closely duplicates the naturai movement of the knee joint. 

Experiments were carried out in the simulator on an early form of Freeman-Swanson Knee Joint and on a Leeds Knee Joint. Distilled water was allowed to drip onto the prosthesis to wet the interface, the flow rate being adjusted to maintain temperature of the tlbial component at 37 C. Contour diagrams based upon holography are recorded for the initial and worn tlbial components of each joint in Figures 3 and 4 and schematic representations of the wear scars are shown in Figures 5 and 6. 

Figure 4a. Contours of Leeds Knee Prosthesis Tibial Component prior to test in knee joint simulator (Ah = 1.75 /im).

Aeyels, B., Peeraer, L., Van der Sloten, J., and Van der Perre, G., Development of an above-knee prosthesis equipped with a microprocessor-controlled knee joint first test results, /. Biomed. Eng. 14 199-202,1992. 

The prosthesis for total knee joint replacement consists of femoral, tibial, and patellar components. Compared to the hip joint, the knee joint has a more complicated geometry and movement biomechanics, and it is not intrinsically stable. In a normal knee, the center of movement is controlled by the geometry of the ligaments. As the knee moves, the ligaments rotate on their bony attachments and the center of movement also moves. The eccentric movement of the knee helps distribute the load throughout the entire joint surface [Burstein and Wright, 1993]. 

Transtibial prosthesis Artificial leg for amputees with the amputation between the ankle and the knee joints (transtibia)... 

In the medical praxis, UHMWPE have been used successfully as one half of the bearing couple (against metallic alloys or ceramics) in total hip and total knee joint replacements crosslinked under irradiation [82]. Even y-irradiated UHMWPE at doses higher than 100 kGy presents the incipient ffacmre development [83], the alkyl macroradicals are involved in crosslinking and in a smaller proportion they promote oxidation [84, 85]. The prosthesis manufactures by the irradiation of UHMWPE have long durability, because the application of radiation treatment induces an increased crystallinity and promotes sterilization in the whole volume of material. 

Macroscopic particles found in the knee joint of explanted prosthesis following failure. 

Orhanli, T., Finite State Control of Semiactive Knee Joint with Pneumatic Damper and a Test Platform Design for Testing Knee Prosthesis. Hacettepe University, 2014. 

In the present study, a knee joint simulator is used to simulate the tibial axis load and flexion-extension motion under walking condition. The lubrication condition or fluid film formation in knee prosthesis models is evaluated by measuring the electric contact resistance between the femoral metallic component and tibial conductive polymeric or elastomeric component under the constant applied voltage in a knee joint simulator. 

Puncturing the knee joint with a lateral approach is common clinical practice. The needle is inserted blindly at the level of the upper pole of the patella to reach the suprapatellar synovial recess. In general, US guidance is not requested to direct the needle within the joint space. However, in patients presenting with small effusion or knee prosthesis or when the puncture has to be performed quickly (pediatric patients), US guidance may be helpful. Both indirect and direct techniques can be used. We prefer to recognize the site of maximal fluid accumulation within the suprapatellar pouch on transverse images. 

Affatato S, Leardini A, Leardini W, Giannini S, Viceconti M. Meniscal wear at a three-component total anMe prosthesis by a knee joint simulator. J Biomech 2007 40(8) 1871-6. 

The application of polymeric materials in medicine is a fairly specialized area with a wide range of specific applications and requirements. Although the total volume of polymers used in this application may be small compared to the annual production of polyethylene, for example, the total amount of money spent annually on prosthetic and biomedical devices exceeds 16 billion in the United States alone. These applications include over a million dentures, nearly a half billion dental fillings, about six million contact lenses, over a million replacement joints (hip, knee, finger, etc.), about a half million plastic surgery operations (breast prosthesis, facial reconstruction, etc.), over 25,000 heart valves, and 60,000 pacemaker implantations. In addition, over AO,000 patients are on hemodialysis units (artificial kidney) on a regular basis, and over 90,000 coronary bypass operations (often using synthetic polymers) are performed each year (]J. 

Preoperative (A) and [xjstoperative (B) radiographs of a Total Condylar knee prosthesis. The components are well [xjsitioned. (Reprinted with permission from Walker, RS. 1977. Human joints and their artificial replacements. Springfield, IL CC Thomas Publisher.)... 

The Polycentric knee design, as originally conceived by Gunston, did not address the patello-femoral joint. Gunston mentions in his 1971 paper that "the patella may be retained because no impingement of the patella on the prosthesis... 

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