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Biomedical subjects

W Plitz

Publications and source records attributed to W Plitz.

At least 37 records · Page 2Linked to original sources
PubMed1992

Medial meniscus replacement by a tendon autograft. Experiments in sheep.

In 20 skeletally mature female merino sheep, divided into four groups, we performed total medial meniscectomy, removal of the middle third of the patellar tendon, and tenotomy of the calcaneal tendon of the right hind leg. Group I (control) had no additional procedures. In the other three groups the medial meniscus was replaced by the middle third of the patellar tendon from the ipsilateral knee. The animals were killed at three (group II), six (group III), or 12 months (group IV) and the tendon-meniscus examined macroscopically, by light and scanning electron microscopy, and biomechanically. Remodelling of the tissue had taken place by 12 months but the failure stress and tensile modulus for the tendon-meniscus were lower than for the normal meniscus. Our evidence suggests that, in sheep, replacement of a meniscus by a tendon autograft may decrease the severity of the degenerative changes that occur after meniscectomy.

Animals↗
PubMed1992

[Method for in vivo measurement of intraosseous pressure of the patella].

During the development of degenerative joint disease (osteoarthritis, chondropathy), a diagnostic or even pathogenetic role is attributed to the phenomenon of intraosseous pressure (IOP). Owing to technical problems and a lack of systematic experimental or clinical studies on the control mechanisms of the IOP, the actual importance of this factor is still not known with certainty. Now, a measuring method that enables correct recording of the IOP and standardized on-line processing of the measured signal minimize artefact-related problems. The technique is evaluated for reliability in an in vitro model of the human patella and in a limited clinical study of the IOP in patients undergoing knee surgery for various reasons. Factors such as intra-articular effusion, joint position or changes in intra-articular soft tissue are examined for their influence of the primary signal.

Female↗
PubMed1991

[Endoprosthesis of the knee joint: current status and trends].

Knee joint endoprosthetics has proved to be at least as successful as hip joint endoprosthetics, although the total implantation rate has risen to only about 15%, which ignores its widespread unpopularity. There is a great variety of artificial knee joints, although according to ISO standards all models can be reduced to four basic ones. Deciding to use a stabilized, semi-constrained or unconstrained artificial knee prosthesis requires careful consideration especially if the possibility of its removal is taken into account. The main reason for unsatisfactory clinical results is still retropatellar pain. Intensive basic research is necessary in this area as well as in the development of new materials that might be used for new prosthetic designs. Designers as well as surgeons should aim at regaining the natural function level with no pain for the patient.

Humans↗
PubMed1990

A theoretical and numerical approach to optimal positioning of the patellar surface replacement in a total knee endoprosthesis.

The clinical results of total knee joint arthroplasty with patellar replacement have shown that postoperative problems arise, especially under unfavourable biomechanical conditions. The findings concerning retropatellar contact forces have been obtained by means of different methods, partly through experimental investigations and partly through theoretical considerations. But so far patellar replacement criteria and the resulting changes of the retropatellar contact force were not taken into consideration in other studies. Our mathematical model is based on a mechanical one and the parameter study considers the influence of the height of the patellar surface replacement upon different biomechanical parameters at varying positions. The results suggest that the patellar replacement should therefore be kept as low as possible, thus reducing the retropatellar contact force to a minimum, especially in the extremely stressed flexion areas of up to about 90 degrees.

Biomechanical Phenomena↗
PubMed1989

[Biomechanical aspects of loosening of hip prostheses].

The central problem of endoprosthetics that still needs to be solved is aseptic loosening of a prosthesis. The various efforts toward solving this problem have also included optimization of design so as to minimize remodelling and to include adaptation to the performance of the bone-supporting tissue. In this respect, special kinds of surface structures using biomaterials similar to the bone matrix have also been developed. These materials are optimized by means of the latest morphometric analytical devices. Another goal in this respect is to analyze the reactions of the bone implant to mechanical stimuli. Finally, prospective multicentric studies should be carried out to evaluate the various anchoring methods such as cement, cementless or custom-made methods.

Biomechanical Phenomena↗
PubMed1983

Mechanical properties of temporary ligament replacement.

The mechanical properties of possible polymer ligament replacement materials are established by static and dynamic testing of about 50 specimens. In accordance to approximate physiological conditions the examinations demonstrate only one entangled polyester-flat-ligament to be satisfying the requirements.

Biocompatible Materials↗
PubMed1979

Unhooking of GSB total knee during dislocation of the patella.

This is a case report of a special and undoubtedly rare complication occurring in a hinge joint with a moving instant center such as the GSB total knee joint. The preoperative situation, the history of the incident and the operative report are being described as well as a radiological follow-up. The mechanism of unhooking of the tibial shaft from its junction with the femoral stem during dislocation of the patella is being reconstructed.

Aged↗
PubMed1979

Damage analysis of the Harrington rod fracture after scoliosis operation.

Fracture of the distraction rod is one of the complications following operative treatment of scoliosis by the device of Harrington. It is reported to occur in about 7% of cases. We found this complication twice in our own number of 41 patients during a follow up period of 1 to 4 years. The rods had broken 18 and 23 months after operation, but we never saw a breakage in the 1st postoperative year during the time of cast fixation. The fracture surfaces of each rod were examined under the scanning electron microscope. In one case a fatigue fracture with two beginnings at the opposite sides of the rod was found in combination with a forced fracture in the middle. The number of alterations of load from the beginning of the fracture to the complete breakage was about 10,000. The X-ray showed a loss of correction in the curve of 20 degrees with a pseudoarthrosis visible in the fusion. In the other case a typical pure fatigue fracture was seen 23 months after the operation with 18,000 alterations of load. The X-ray showed only a slight loss of correction of less than 5 degrees and no pseudoarthrosis was visable, neither in the X-ray nor in the operative exploration of the fusion. The breakage of the distraction rod results not only from a pseudoarthrosis but also from other explained facts of the procedure. Further treatment depends on a proven pseudoarthrosis.

Adolescent↗
PubMedDate not supplied

[Biomechanic results in impingement syndrome of the shoulder].

Forces underneath the coraco-acromial vault during elevation of the arm were evaluated with a dynamic shoulder model. The deltoid muscle and the rotator cuff muscles were simulated with a hydrodynamic device, in ten autopsy specimens. Controlled cycles of glenohumeral joint motion were initiated with computerised regulation. An ultrasonic device measured the position of the arm in all spatial orientations. Capacitive sensors recorded forces underneath the coraco-acromial vault. The mean force during one cycle of elevation averaged 13.9 Newton +/- 12.5 Newton underneath the coraco-acromial ligament and 3.44 Newton +/- 4.37 Newton underneath the coracoid process. The peak force averaged 37.8 Newton +/- 33.2 Newton underneath the acromion, 3.03 Newton +/- 2.62 Newton underneath the coraco-acromial ligament and 6.93 Newton +/- 7.38 Newton underneath the coracoid process. The force markedly increased at the final stage of arm elevation and during early reverse-elevation in most specimens, corresponding to the painful arc sign. In some specimens, the force under the coracoid process exceeded the force under the acromion. Osteophytes protruding into the subacromial space may lead to a concentration of force and to high regional pressures.

Adult↗
PubMedDate not supplied

[Age-related force distribution at the proximal end of the femur in normally growing children].

In a group of normally developed children and adolescents the age dependent distribution of forces at the proximal end of the femur was to be described. The results should explain why the shape of the proximal end of the femur changes significantly during the time of growth and why the neck shaft angle decreases. The method applied was the biomechanical computation analyzing in the coronal plane according to Pauwels' biomechanical hip model. The necessary age relevant data was derived from 675 anteroposterior pelvis radiographs of healthy children of both sexes and of varying age. The following can be put down as a result: 1. The proximal end of the femur is stressed by two resultant forces: the hip resultant force R controls the growth of the capital growth plate, the trochanteric resultant force RT regulates the growth of the greater trochanter growth plate. 2. During the growing period the hip resultant force R adjusts itself less vertically: during the second year of life it inclines at an average of 11,6 degrees towards the vertical, towards the end of the growing period it is incident with an inclination angle of 20 degrees. With the older child the magnitude of the hip resultant force R decreases in relation to the exerting body weight. 3. During the time of growth the trochanteric resultant force RT maintains its direction stability with inclination angles of 50-52 degrees towards the vertical. Its magnitude increases significantly (in relation to the exerting body weight). 4. From age 2 to 10 the projected neck shaft angle decreases from an average of 148.2 degrees to 133.7 degrees and usually remains stable. It can be concluded that the shape of the proximal end of the femur is determined by the muscle forces stimulating the greater trochanter apophysis and by gravity. With increasing age the growth of the greater trochanter apophysis shifts the insertions of abductor muscles laterally. As a result the directions of the hip abductors and the hip resultant force R incline. The neck shaft angle decreases consecutively.

Adolescent↗
PubMedDate not supplied

[Biomechanics of the hip joint in children].

Based on the data derived from the examination of 16 infantile and juvenile anatomical hip specimens as well as the radiological examination of 1350 hip joints of healthy children, a biomechanical model of the developing hip was computed. This two-dimensional vector model describes the forces acting on the growth plates of the head and the greater trochanter during the one-legged stance. It could be proven that the apophysis of the greater trochanter is subject to compressive stress by lateral-cranial traction bands and therefore corresponds with a "pressure apophysis". The muscle forces acting on the trochanter apophysis can be combined as a trochanteric resultant RT. This stimulates a lateral-cranial growth of the trochanter apophysis. The direction of the hip abductors and, as a result, also the direction and the length of Pauwels' hip resultant R are influenced by this mechanism.

Adolescent↗
PubMedDate not supplied

[Thermo-elastic stress analysis of human bones].

The Thermoelastic Stress Analysis (THESA) is a widely used procedure in motorcar- and airplane engineering. This study investigated the reliability of THESA for stress analysis of human bone. A human femur was cyclic stressed and the resulting stress pattern was scanned from the surface of the bone by means of the thermoelastic stress measuring instrument SPATE 9000. To proof whether the scan of SPATE 9000 is equivalent to the stress distribution of human femur surface, strain gauges are used to control the results at two different regions of the femur diaphysis under equal but static conditions. It could be shown, that both measuring methods lead to corresponding results of stress pattern on human femur surface.

Adult↗
PubMedDate not supplied

[Material properties of meniscus tissue and the effect of the menisci on the compression behavior of the knee joint].

Specimens of meniscus tissue were taken from different locations of the medial and lateral meniscus. They were tested to failure in the tensometer and force elongation diagrams were recorded. 28 meniscus specimens (14 medial, 14 lateral) gained at autopsy were available for testing. The posterior third of the medial meniscus and the middle third of the lateral meniscus were the strongest and stiffest parts of the meniscus. Yet local differences within one meniscus were only subtle. One clinical significance of these data is, that for replacement of the medial and lateral meniscus the same homogeneous material can be employed. Six tests under compression were carried out using six knee specimens gained at autopsy. Knee compression tests yielded different results after radial cutting of the meniscus, whereas partial meniscectomy had no effect on deformation and hysteresis. These biomechanical results support the concept of partial meniscectomy and preservation of the meniscal periphery. But they cannot be related to the problem of possible degenerative arthritis after partial meniscectomy.

Adult↗
PubMedDate not supplied

[Biomechanics of cement-free endoprostheses].

At present only about 20 per cent of endoprosthetic stems and 30 per cent cups are implanted without cement. Nevertheless, the number of modifications and new developments in cementless endoprosthetics is continuously growing. Years ago bone cement was made responsible for all failures, but meanwhile the approach to it got more differentiated. The advantages of cement fixation in case of elderly patients as well as those of cementless implantation for patients where revision operation could be expected were recognized. Whereas sufficient primary stability can be generally achieved without any problem in case of cement implantation, the cementless one needs more intensified planning as well as a different surgical technique. Today not only torsional stability and stiffness of stem and bone implant are discussed more intensively than before but also new anchorage concepts as for example tubular stems or custom made systems. Obviously, the existing screw cups and clamp/clip systems are more in demand than cementless stem systems. The results of different coatings and surface modifications are rather inhomogeneous and there is a need of more basic research in this respect.

Acetabulum↗