Biomedical subjects

W Plitz

Publications and source records attributed to W Plitz.

70 records · Page 4Linked to original sources

PubMedDate not supplied

[Macerated human hip bone preparation as a substitute for fresh frozen preparations for testing the primary stability and frictional torques of cementless hip cups].

AIM: The aim of the study was to validate macerated human acetabuli as replacement for fresh frozen preparations for testing primary stability and the screwing in moments of cementless threaded hip cups. METHOD: Three fresh frozen human pelvis were tested. One half of each pelvis was macerated whereas the other half was preserved as fresh frozen preparation. In the side of every pelvis the moments of screwing-in, the micromotions, the maximum expressing force and the maximum pull-out torque were determined. RESULTS: The screwing in moments, the maximum expressing forces and the maximum pull-out torques did not change. The micromotions were reduced to half. CONCLUSION: Considering the reduction of the micromotions, macerated human acetabuli are valid replacements for fresh frozen preparations for testing the primary stability and the screwing-in behaviour of screwed pans.

Cementation↗

PubMedDate not supplied

[Axial load in case of press-fit fixation of the ACL graft--a fundamental study].

AIM: The aim of this study was the determination of the axial fixation load resting on smooth press-fit dowels needed for fixation of the patellar tendon graft (BTB) in order to reach the same fixation properties compared to the interference screw on anterior cruciate ligament (ACL) plasty. METHOD: Bovine test specimens with 27 BTB grafts fixed in tibial drill holes were used and divided in 3 groups: interference screw, and press-fit cylinder (Ø 7 mm) with 150 N and 100 N axial loads. Prior to fixation, impactation of the transplant into bone was carried out. Failure testing was done in a tensiometer at a cross-head speed of 50 mm/min. Determinations of peak load and stiffness were also made. RESULTS: Similar peak loads and stiffness were reached on introducing a press-fit dowel (slashed circle 7 mm) with 100 N and 150 N axial load compared to interference screw fixation of the BTB graft. Peak load: 988.1 N +/- 365.1 (screw) versus 1 210.4 N +/- 292.4 (dowel 150 N) and 1 109.8 N +/- 505.4 (dowel 100 N). Stiffness: 86.4 N/mm +/- 20.5 (screw) versus 102.4 N/mm +/- 15.2 (dowel 150 N) and 77.1 N/mm +/- 11.0 (dowel 100 N). There was no significant difference. CONCLUSION: When introducing a press-fit dowel (slashed circle 7 mm) with 100 N axial load into a preformed bone bed, the same fixation properties are reached as in the case of an interference screw on BTB-ACL plasty.

Animals↗

PubMedDate not supplied

[Stability of pedicle screws in comparison to anterior vertebral body screws after kyphoplasty augmentation].

AIM: Aim of the study was to compare stability of pedicle screws and ventral implanted screws after insertion in soft or cured kyphoplasty cement. METHODS: Pedicle screws were inserted in a total of 40 thoracolumbar vertebrae of 10 different formalin-fixed human specimens: each 10 pedicle screws were implanted in soft (group 1) and cured cement (group 2), each 10 ventral screws were placed in soft (group 3) and cured (group 4) cement. Pedicle screws were then evaluated for biomechanical axial pullout resistance. RESULTS: Mean pull-out force was 452 N (range 60-1 125 N) in group 1, 367 N (range 112-840 N) in group 2, 364 N (range 65-875 N) in group 3 and 271 N (range 35-625 N) in group 4. CONCLUSION: Implantation of pedicle screws and ventral implanted screws in soft and cured kyphoplasty cement is a sufficient method. We achieved more stability with pedicle screws compared with ventral implanted screws in soft and cured cement. No significant difference was seen.

Bone Cements↗

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↗

PubMedDate not supplied

[Material-specific wear of ceramic/ceramic sliding surfaces in revised hip endoprostheses--clinical and technological considerations].

After more than 8 years of "in-vivo"-experience with ceramic bearing surfaces in hip endoprostheses clinical and tribological aspects of damage-analysis in 29 cases of retrieved Al2O3 prostheses are performed. The balls and sockets are investigated in view of wear-quantification by relative metric determination and wear-quantification by SCAN-microscopy. In 2/3 of all cases the microstructure average grain standard was superelevated. As hypothesis of the destruction mechanism an avalanche-like acceleration of grain-excavations is discussed.

Adult↗

PubMedDate not supplied

[Operative therapy in patellar chondropathy].

A critical appraisal of the results of conservative and surgical treatment of chondropathia patellae revealed that it has not yet proved possible to achieve a good surgical result in excess of 75%. Findings with a new direct method of measuring retropatellar pressure distribution on human specimens, and the knowledge thus obtained, are discussed in connection with clinical results. They show that more detailed knowledge of the cause of the chondropathy is required if surgical treatment is to be successful.

Cartilage Diseases↗

PubMedDate not supplied

Forces acting on the juvenile hip joint in the one-legged stance.

A two-dimensional biomechanical model of the juvenile hip joint was developed to describe the forces acting on the capital epiphysis and the greater trochanter apophysis in the one-legged stance. Based on anatomic femur specimens of 16 children, ranging from toddlers to teenagers, and radiographic studies of 1,350 hip joints of healthy children, we showed that the apophysis of the greater trochanter is a pressure apophysis. If the muscular forces acting on the apophysis of the greater trochanter are added, the unit sum may be considered a resultant force acting from a craniolateral direction. The trochanteric resultant force near the end of the growth period is equivalent to approximately 1.7 times body weight. The trochanteric resultant force stimulates craniolateral growth of the greater trochanteric apophysis. This mechanism is responsible for the direction of the forces exerted by the hip abductors and thus the direction and magnitude of Pauwels' hip-joint resultant, and finally influences the neck-shaft angle.

Adolescent↗

PubMedDate not supplied

[Effect of surface energy on wear characteristics of material combinations for the artificial hip joint].

One of the factors determining the wear of UHMWPE used as acetabular cup material is the lubricating properties of the head materials. In order to determine the lubricating properties, the wettability of Al2O3, ZrO2, CoCrMo and N-coated TiAl6V4 was established. Wettability is determined by the surface energy of the head material (solid-state material), which was measured via the contact angle of drops of fluid. As head material, appropriate rings from the Ring-on-Disc Test as per International Standard 6474 were used. The poorest wettability was associated with CoCrMo. The wettability of Al2O3 and ZrO2 was comparable. Worthy of note is the tendentially good wettability of N-coated TiAl6V4.

Biomechanical Phenomena↗

PubMedDate not supplied

Strain measurement at the knee ligament insertion sites.

We describe the modification of an existing method of ligament strain measurement at the knee joint in detail. At ten fresh joint specimens we used that technique where strain gauges are attached to the ligamentous insertions and origins. We both improved the preparation of the attachment site and the application of the strain gauges. In a special apparatus the specimens were moved from 0 degree extension to 100 degrees flexion while simulating muscle strength and axial force. Testing was performed at the posterior cruciate ligament with both intact and transsected anterior cruciate ligament. In contrast to other existing techniques it does not affect the motion of the joint or the integrity and the function of the ligaments. Unlike the original description of that method we could register a loading behaviour of the posterior cruciate ligament that is similar to those reported in the literature.

Compliance↗

PubMedDate not supplied

[Stability of pedicle screws. 1: Maximum pullout force in healthy bony spine trunks with reference to drilling technique].

Pullout direction was axial and oblique to screw axis. Two different techniques of preparing the screw bed are matched: 1) 3.2 mm AO drill and 6.0 mm screws for D7-S1 and 4.5 mm screws for D11-D6, 2) resection of cancellous bone of the pedicle tube and 6.0 mm, 7.0 mm, 8.0 mm screws, which were inserted after measuring each level. With the better technique 1 (saving the cancellous bone) 620N-161N were reached from D1-S1, even if bigger screws could be used with technique 2.

Adult↗

PubMedDate not supplied

[Stability of pedicle screws. 2: Maximum pullout force with reference to bone density].

Maximum pullout strength of pedicle screws in osteoporotic cadaver spines are tested. Bone mineral density was measured before by two noninvasive methods (QCT, DRA). Pullout direction was axial to screw axis. 210 N to 920 N were reached from D1-S1. There is a high correlation between bone mineral density and pullout strength (r = 0, 8-0.9). Augmentation of osteoporotic pedicles with bone cement increases screw stability nearly to that one of non-osteoporotic spines.

Adult↗