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Biomedical subjects

W Plitz

Publications and source records attributed to W Plitz.

At least 55 records · Page 3Linked to original sources
PubMed1993

Investigations on mechanism of Salter-1-fractures of the greater trochanter.

This study aims at clarifying why the apophysis of the greater trochanter very rarely separates, in contrast to other apophyses of the hip region. The inclination and area measurement of the greater trochanteric growth plate and the mode of insertion of the muscles on the apophysis were analyzed on the basis of 16 anatomic femoral specimens from newborn to children of 14 years of age. The physiological muscle cross section Q of the muscles inserting at the greater trochanter was determined on 6 specimens. In a cross-sectional radiological study, carried out on 1350 hip joints of healthy children, the inclination of the greater trochanter growth plate was measured. The anatomical and radiological findings show that the nearly plane-shaped greater trochanter growth plate remains inclined at a 50 degree angle to the horizontal body line and is loaded from a diagonally craniolateral direction throughout the total growth period. The lateral surface of the apophysis is covered by a fibrous connection which joins the insertion areas of the gluteus medius, minimus and vastus lateralis muscles. The vastus lateralis muscle is intimately bound to the vastus intermedius muscle by fibrous tissue. According to the results of the physiological muscle cross sections these four muscle groups can form a counteracting muscle sling, which transforms the traction forces at the surface of the greater trochanter into pressure forces in line with a tension band effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1993

Characterization of the different prosthesis models.

Polyethylene is always exposed to wear. The more punctual and asymmetric the force on the surfaces, the stronger the wear. Thus, fatigue wear is more often found in unconstrained prostheses. In regard to wear problems, a prosthesis should have an axis that avoids fatigue wear and two polyethylene parts on the tibial plateau.

Biomechanical Phenomena↗
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

[Effectiveness of epicondylitis bandages from the biomechanical viewpoint--an experimental study].

QUESTIONS: During extension of the elbow joint (test measurement) and extension of the wrist (control measurement), maximal bandage pressure is desired on the extensor group of the forearm, especially of the M. extensor carpl radialis brevis (ECRB). Do the various commercial epicondylitis bandages produce a mechanical effect on the extensor group of the forearm and how do the maximal pressures of these bandages behave in direct comparison? Are the pressures produced clinically relevant? METHODS: Eleven different epicondylitis bandage constructions were examined for their biomechanical effects. The exerted pressure was measured continously during the above-mentioned movements. A fist-closing strength of ca. 30 N was maintained for the necessary pre-stressing of the forearm muscles. RESULTS: Strap-type bandages were the only bandages to produce adequately high pressures. Bands applied at pressures which approach those of the straps led to obstruction in bloodflow. Stocking designs showed no effect in respect to our study. CONCLUSION: Bandages which apply pressure to relieve the tendon insertion of the extensor muscles must, from a technical standpoint, be of a strap construction in order to build up adequate pressures to be effective.

Adult↗
PubMedDate not supplied

[The primary stability between manual and robot assisted implantation of hip prostheses: A biomechanical study on synthetic femurs].

AIM: We investigated the initial stability of cementless stems implanted with robotic milling and conventional manual broaching. METHODS: Proximally porous structured stems (G2, ESKA-Implants, Luebeck, Germany) were implanted into synthetic femora. In one group, the femoral cavity was prepared by a CT-based robot (CASPAR, URS-Ortho, Germany) with a high-speed milling head. In the other group, femora were rasped manually with broaches. The broaches had 1 mm proximal press-fit, the robotic cavities 1.5 mm. The implants were exposed to 15 000 loading cycles with 1 000 +/- 500 N. The direction of forces on the implant head were chosen to simulate stair climbing. Internal rotation and translation (caudal, dorsal and lateral) of the implants were measured by linear transducers. RESULTS: The robotic group showed significantly less reversible motion regarding translation in caudal, dorsal and lateral directions. The standard deviations of implant motions were smaller in the robotic group. CONCLUSION: Using robotic preparation of the femur, initial stability was higher and more consistent than with manual broaching, but differences in undersizing of the cavities created in the femur in relation to the implant may have contributed to these differences for the most part. In-vitro-loading experiments focusing on femoral cavities with varying press-fits are recommended before the introduction of new implants or operating procedures.

Arthroplasty, Replacement, Hip↗
PubMedDate not supplied

[Cervical collars: a clinical and biomechanical study].

AIM: Cervical collars have been used for years in the non-operative and postoperative management of cervical spine problems. They offer considerable differences in design, stability, bearing comfort and costs. In the background of controversies about the indication and in view of the limited number of scientific publications on the topic we have conceived this paper as a biomechanical and clinical investigation. METHODS: During the biomechanical investigations a defined load was exerted on 10 cervical collars of 4 producers. The clinical part was the measurement of the limitation of movement due to the 10 cervical collars in 30 healthy subjects aged 20 to 60 years. RESULTS: The biomechanical investigations showed differences of stiffness which were obvious during axial load, sideward and backward bending and less obvious in forward bending. The clinical study in 30 subjects indicated, on the other hand, only small differences in the limitation of movement. Softer cervical collars were slightly better accepted in the subjective judgment. CONCLUSION: For the aimed limitation of movement, a minimum of stiffness is obviously necessary, which is common with every tested collar. Higher degrees of stiffness do not result in further limitation of movement but only in a reduction of bearing comfort.

Adult↗
PubMedDate not supplied

[Extracorporeal single dose and radiographic dosage in image-controlled and fluoroscopic navigated pedicle screw implantation].

AIM: Goal of the current study was to compare radiation dose and fluoroscopy time of fluoroscopic computer assisted pedicle screw implantation versus the conventional technique. METHOD: For each of 10 specimens two pedicle screws were placed using conventional technique (group 1) and two screws were inserted with fluoroscopic navigation system (group 2) contralateraly. RESULTS: For implantation of two pedicle screws the mean radiation dose was 0.041 mSv in group 1 and 0.029 mSv in group 2. Fluoroscopy time was 34 seconds in group 1 and 25 seconds in group 2. The differences of radiation dose and fluoroscopy time for group 1 and 2 were statistically significant (radiation dose p = 0.00044, fluoroscopy time p = 0.00039). CONCLUSION: We achieved significantly lower radiation dose and fluoroscopy time with fluoroscopic computer assisted pedicle screw implantation compared with the conventional technique. Concerning exposure to radiation for patients and personnel fluoroscopic navigated screw insertion is to favour.

Body Burden↗