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Effect of slide track shape on the wear of ultra-high molecular weight polyethylene in a pin-on-disk wear simulation of total hip prosthesis.

Prosthetic joints appear to show a strong relationship between the type of relative motion and wear, requiring careful consideration in the design of wear simulators. This relationship was studied with a 12-station pin-on-disk device, specifically adapted for the wear simulation of prosthetic hip joints. Each station had a unique motion, characterized by the so-called slide track, the track of the pin on the disk. The slide track shapes included 10 ellipses, their aspect ratio (AR) varying from 1.1 to 11.0, and a circle and a straight line as extreme cases. Hence for the first time in hip wear simulation, the motion was systematically varied over a wide range. Conventional UHMWPE pins were tested against polished CoCr disks in diluted calf serum three times for 3 million cycles. Below the AR value of 5.5, the polyethylene wear factor and wear mechanisms agreed with clinical observations. Above this value, the wear factor decreased to unrealistically low values, and the wear surface topography differed from that of retrieved acetabular cups. The wear particles, however, were similar to those isolated from periprosthetic tissues, irrespective of the AR value. In conclusion, it is recommended that the AR value be kept well below the critical point of 5.5.

Animals↗

The effect of anterior cruciate ligament resection and immediate or delayed implantation of a meniscus prosthesis on knee joint biomechanics and cartilage. An experimental study in rabbits.

In a rabbit experiment with anterior cruciate ligament (ACL) resection, immediate substitution of the medial meniscus with a prosthesis was compared with delayed prosthetic implantation after a postmeniscectomy period of three weeks. The knees with a prosthetic implant were compared with their contralateral joints as well as to joints with an intact ACL and menisci. Anterior cruciate ligament resection alone led to disturbed biomechanics and cartilage degeneration. Anterior cruciate ligament resection in combination with meniscus resection increased cartilage degeneration and led to more inferior biomechanics. Ingrowth and stable fixation was less frequent when the prosthesis was inserted three weeks after meniscus resection than when inserted immediately. Furthermore, in knees with delayed prosthetic implantation, only minor improvement in terms of cartilage protection was shown when compared with knees with resection only. In contrast, knees with immediate meniscus replacement demonstrated similar joint stiffness and stress relaxation characteristics and similar cartilage protection effects as knees with a nonresected medial meniscus.

Animals↗

[Alkaptonuria and ochronotic arthropathy. Arthroscopic and intraoperative findings in implantation of a knee joint surface replacing prosthesis].

Alcaptonuria is a rare (incidence approx. 1:10(6)), autosomal-recessive transmitted metabolic disease. The basic defect is a lack of the enzyme homogentisic acid oxidase. During metabolism of phenylalanin and tyrosin to fumaric acid and acetoacetic acid this enzymatic defect causes an accumulation of the intermediate breakdown product homogentisic acid in bradytrophic tissues resulting in pigmentation and calcification of the intervertebral disks. We present a 57 year old female patient in whom we diagnosed alcaptonuria by the appearance of the typical symptom trias homogentisic acid excretion in the urine, ochronosis and arthritis. The anamnesis and results of a knee arthroscopy, radiographic and laboratory examinations as well as the intraoperative and histological findings during implantation of a knee joint surface replacing prosthesis (Gemini-System, Link Co., Hamburg, Germany) are reported.

Alkaptonuria↗

[Bypass spanning the knee joint with synthetic prosthesis].

Synthetic tubes are the second choice for below-knee bypass materials. The ring-reinforced thin-walled Goretex-PTFE graft is an approved material which was tested in a multicenter study. The primary 3 years patency for below-knee femoral-popliteal bypass was 64%, for crural bypass 39%. A total of 195 grafts have been implanted. Long-term patency depends very much on the run-off conditions (81% in good and 43% in bad cases). The over-all limb salvage rate was 80% after 3 years.

Blood Vessel Prosthesis↗

[Prosthesis implantation in the proximal ankle joint--a real therapeutic alternative in post-traumatic arthrosis?].

The results of total ankle arthroplasty were poor in the 1970s and 1980s compared to those of the arthrodeses. Because of the good long term results this technique has been accepted as the treatment of the choice for posttraumatic arthritis of the ankle. Recently the development of an unconstrained total ankle arthroplasty with an additional mobile polyethylene inlay between the fixed tibial and the talar component which enables a three dimensional range of motion seems to improve significantly the long term results of total ankle replacement. This technique, however, is an extremely demanding procedure. The range of motion after total ankle replacement following posttraumatic arthritis is poor compared to the results of total ankle replacement for rheumatoid arthritis. Furthermore, these data are obtained yet only by a few experienced surgeons in specialized centers. Further clinical trials have to be performed to answer the question whether the total ankle arthroplasty is a reliable alternative treatment of posttraumatic arthritis of the ankle. At present, the arthrodesis should be regarded as the treatment of choice for the posttraumatic arthritis of the ankle joint.

Ankle Injuries↗

Five-year results of a new total replacement prosthesis for the finger metacarpo-phalangeal joints.

An unconstrained surface metacarpophalangeal joint replacement was developed with metal metacarpal and polyethylene phalangeal components, fixed by uncemented finned polyethylene plugs which allowed some metacarpal component motion. Clinical and radiological results in 13 joints in eight patients are presented after 5 years. One infection required revision at 3 months. There were no further complications. At final review there were no implant failures. Two of 13 joints showed lucency around the phalangeal component and one showed 2mm subsidence of the metacarpal component. No other adverse radiological features were observed. Seven patients had no pain and one had minor discomfort. Joint movement had improved from an arc of 27 degrees to 60 degrees and disability, assessed using the P.E.M. questionnaire, had improved from 77% to 9%.

Aged↗

[Surgical replacement of the thumb saddle joint with the GUEPAR prosthesis].

Primary arthritis of the thumb saddle joint is very common. Among the different treatment options, the implantation of a total joint arthroplasty is an alternative. The GUEPAR prosthesis, developed by a group of French surgeons, is mainly used in elderly patients and only in cases with preserved trapezial height. This study reports the mid-term results of the second generation of this implant. The clinical results show good pain relief and good mobility of the thumb. There were a few patients with radiological signs of implant loosening, but none of them had clinical problems. The advantage of a total replacement of the saddle joint, compared to the standard resection arthroplasty, is faster rehabilitation and preservation of the length of the thumb. The new generation of the GUEPAR prosthesis has a more anatomical metacarpal stem and a modularity which allows the fit of the implants according to the anatomical situation.

Aged↗