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Biomedical subjects

D Wolter

Publications and source records attributed to D Wolter.

At least 19 recordsLinked to original sources
PubMed2004

[Experiences in the treatment of midfacial fractures using a fixed-angle osteosynthetic system. Biomechanical results].

AIM: Fixed-angle osteosynthetic systems are characterized by mechanical "locking" of the osteosynthetic screw and plate. These systems have found increasing acceptance and use for osteosynthetic fixation and temporary reconstruction of the mandible. The aim of this study was to investigate the applicability and performance of fixed-angle systems in the treatment of midfacial fractures. MATERIAL AND METHOD: A newly developed fixed-angle osteosynthetic plate system (smart lock) was compared to a conventional system using fresh human skulls. The iatrogenically produced zygomatic fractures of the human skulls were treated by osteosynthesis and biomechanically tested. Furthermore, in a dynamic test series, an artificial bone was subjected to an alternating force of 15 N of up to 1,000,000 cycles. The new screws and plates were subjected to further biomechanical tests. RESULTS: The tests using the fixed-angle implants revealed that an increase of stability of up to 40% can be expected after osteosynthetic fixation. Furthermore, the plates resisted 1,000,000 cycles of alternating forces, whereby the conventional systems failed after 170,000 cycles on the average. CONCLUSION: Fixed-angle systems, due to their construction, provide a high degree of stability even in thin bones of the midface. They appear to be promising for the treatment of midfacial fractures.

Bite Force↗
PubMed2004

Three-dimensional load measurements in an external fixator.

On the basis of a six-degree-of-freedom adjustable fracture reduction hexapod external fixator, a system which can be used for measuring axial and shear forces as well as torsion and bending moments in the fixator in vivo was developed. In a pilot study on 9 patients (7 fresh fractures and 2 osteotomies of the tibia), the load in the fixator during the healing process was measured after 2, 4, 8 and 12 weeks and at fixator removal. The measured values enabled both the type of fracture to be determined as well as the monitoring of the healing process. In well-reduced type A3 fractures small axial (direction of the bone axis) forces were found in the fixator. A2, B2 and C3 fractures showed distinct axial forces, which decreased during the healing process, according to an increasing load transfer over the bone. Bending moments in the fixator showed good correspondence with the clinical healing process, except in the case of a C3 fracture. A combination of bending moment and axial force proved to be particularly suitable to assess fracture healing. In transverse fractures, the well-known resorption phenomenon of bone in the fracture gap at approximately 4 weeks was detected by the system. Compared with other external fixator load measurements in vivo, the hexapod offers the advantage of being able to measure all forces and moments in the fixator separately and with a relatively simple mechanical arrangement. In our opinion, it will be possible to control fracture healing using this system, thereby minimizing radiation exposure from radiographs. Furthermore, the measurement system is a step towards the development of external fixator systems that enable automatic adjustments of the callus mechanical situation ("automatic dynamization") and inform the patients about the optimal weight bearing of their extremity ("intelligent fixator").

Equipment Design↗
PubMed2004

Prevention of thromboembolism with low-molecular-weight heparin in orthopedic surgery: a 5-year experience.

A regimen of prophylaxis of thromboembolism with low molecular weight heparin (LMWH) and unfractionated heparin (UFH) in orthopedic surgery is presented. Over a 5-year period, 11,905 patients have been operated in all fields of orthopedic surgery in a big trauma center. In 498 cases, deep vein thrombosis (DVT) was clinically suspected and phlebography was performed: 122 patients had confirmed DVT (rate 0.98%); 59.8% of the DVT were limited to the calf. Nineteen pulmonary embolisms (rate 0.16%) were diagnosed (3 lethal). Heparin-induced thrombocytopenia type II was diagnosed in 12 of 122 patients. Only one of these had received LMWH. The related rates of DVT were highest for tibial head fractures (12.4%), total knee replacement (6.7%), and multiple trauma (6.4%). The extent of DVT was most severe in multiple trauma. The results proved the regimen to be of good clinical use and showed that more attention has to be paid to fractures, especially of the knee; and to patients with multiple injuries.

Adolescent↗
PubMed2001

Dimensional variability of nonstandardized greater taper finger spreaders with matching gutta-percha points.

AIM: The purpose of this research was to determine the compatibility and dimensional variability between nonstandardized gutta-percha points and matching finger spreaders. METHODOLOGY: The diameters of nonstandardized gutta-percha points (n = 15) and matching finger spreaders (n = 15) from different manufacturers (Kerr, Dentsply Maillefer, Vereignigte Dentalwerke and Roeko) were determined and statistically analysed using a profile projector under a magnification of 50 x (+/- 0.002 mm). RESULTS: The dimensions of the finger spreaders and gutta-percha cones were inconsistent. Of the 29 groups of nonstandardized gutta-percha cones evaluated, 22 had standard deviations larger than 0.020 at D1. The standard deviations at D11 were greater than at D1, with the exception of those manufactured by Roeko. Overall, nonstandardized gutta-percha cones made by VDW had the greatest dimensional consistency within each size group; the largest variations were seen in the Dentsply Maillefer gutta-percha points. The 13 sizes of nonstandardized finger spreaders were more consistent. CONCLUSIONS: The results of this study show that corresponding sizes of nonstandardized finger spreaders and gutta-percha cones have statistically significant differences. There were large dimensional variations within sizes and discrepancies between the nominal size and actual size. Thus, these discrepancies may cause problems during root canal filling.

Equipment Design↗
PubMed2000

[Corrections using the hexapod].

The hexapod is a construction that has been subjected to a great deal of investigation in robotics for use in three-dimensional positioning. One use of it is for positioning of the cockpit in flight simulators. Application of the hexapod principle in the external fixator makes it possible to realize prescribed movements of bone fragments with a simple and stable design. The precise setting of the system requires software that has been developed and optimized for clinical use. Translations, axis corrections and rotations are possible individually and also in combinations for correction of complex deformities. The system has advantages, especially in the case of rotations around the longitudinal axis of the bone and in the realization of translation movements. Because the centres of rotation are taken into account by the mathematical calculations, the planning of corrections is simplified. The hexapod system is described, and its clinical application is presented with reference to case reports.

Adult↗
PubMed1999

Fracture reduction and deformity correction with the hexapod Ilizarov fixator.

A configuration for the Ilizarov external fixator with six distractors and 12 ball joints in the form of a hexapod was developed. The system allows for six degrees of freedom bone fragment displacement by controlling the distractors. Using this assembly, universal three-dimensional corrections or reductions are possible without the need for complicated joint mechanisms. The device was used in 16 patients: five had displaced tibial fractures with severe soft tissue damage, 10 had deformities or pseudarthroses subsequent to treatment of tibial fractures, and one had an axis deviation in the course of tibial lengthening. Translational (to 40 mm) and rotational deformities (to 33 degrees) were corrected. Final radiographic examinations after the correction procedure was complete showed median residual deformities of 3.5 mm (range, 0-5 mm) and 1 degree (range, 0 degree-4 degrees) in the anteroposterior projection and of 1.5 mm (range, 0-6 mm) and less than 1 degree (range, 0 degree-9 degrees) in the lateral projection. The construction is a useful and important addition to the Ilizarov fixator system. As a bone fixation device it is unique in that its optimal use depends on the availability of computer software.

Adolescent↗
PubMed1998

Follow-up evaluation of open intra-articular fractures of the calcaneus.

The results of a follow-up evaluation of open intra-articular calcaneal fractures are presented. A modified Merle d'Aubigné functional score and Zwipp radiographic score were used. A retrospective analysis of 35 patients with 36 open intra-articular fractures represents the basis of the study. At the time of follow-up examination (on average 44 months after the injury), 5 amputations of the affected extremity and 4 ankle arthrodeses had been carried out. The 23 patients still able to bear weight on the affected hindfoot and possessing a functional ankle joint were radiographically and functionally evaluated. No excellent results were documented. Only 6 good functional and 2 good radiographic outcomes were noted. In 17 instances, a poor functional or radiographic score was given. Devastating results were seen in the course of treatment of third-degree open joint depression or comminuted intra-articular fractures (n = 15): 9 cases of osteomyelitis, 5 amputations, 1 partial calcanectomy, 1 arthrodesis. An open reduction as part of the primary treatment (n = 6) led to local complications in all instances. The most favorable results were seen after nonoperative fracture management: complication-free course of treatment in 4 of 11 patients. All workmen's injuries led to a permanent disability, and these patients received compensation. The treatment and salvage of the soft-tissue envelope should be paramount in all therapeutic decisions. The fracture treatment must not further jeopardize these tissues. An aggressive operative treatment of local complications, including arthrodesis or amputation, is recommended.

Adolescent↗
PubMed1997

[Transoral metal implant removal after ventral C2/C3 spondylodesis in pharyngo-vertebral fistula].

A 26-year-old man sustained a C2 arc fracture. Ventral spondylodesis using an H-plate was performed. The patient developed a pharyngovertebral fistula which remained undetected for 1 year. Spontaneous fusion of C3/C4 and osteolysis of the cortical block occurred. The fistula was demonstrated intraoperatively and the implant was transorally removed. No further problems occurred after this unusual method of treatment. The anatomy of the cervical spine, special problems of intensive care patients and the use of proper instrumentation are discussed.

Adult↗
PubMed1996

[Dangers and risks of thoracic drainage at the accident site].

For several years it has been argued that a chest tube should be placed at the scene of an accident if thoracic trauma is suspected. However, during emergency treatment in hospital it has been observed that a high number of such tubes have been placed incorrectly. To validate this impression, we conducted a retrospective analysis of the clinical course of 33 trauma victims who had chest tubes placed at the scene of accident. It was found that 39.4% of the chest tubes were placed completely incorrectly and 21.2% required some correction; 39.4% were placed correctly. In two cases (6.1%) life-threatening complications developed because of the chest tube, necessitating a thoracotomy in 1 patient and repeated pericardial punction in the other. Based on the results of our study we believe that a more critical attitude should be adopted to the placement of chest tubes at the scene of the accident.

Chest Tubes↗
PubMed1996

[Universal 3-dimensional correction and reposition with the ring fixator using the hexapod configuration].

A new configuration for the Ilisarov fixator with 6 distractors and 12 ball joints in the form of a hexapod is proposed. Using this assembly, a correction or reduction is possible with respect to any given point and axis in space. The primary position of the rings is not critical. The fixator system is statically determined and there is no stress between the longitudinal rods. Difficult corrections like those necessary for rotational deformities can be done without complicated joint mechanisms.

Biomechanical Phenomena↗
PubMed1996

[Significance of isthmic spondylolisthesis in expert assessment of occupational disease of the lumbar spine].

In Germany, disc-related disease of the lumbar spine is eligible for workmen's compensation if caused by long-standing work requiring heavy lifting or carrying or extreme trunk-bending (BK 2108). The appraisal of causality is particularly difficult if conditions like isthmic spondylolisthesis preexist. 250 consecutive appraisals in nurses concerning the BK 2108 were analysed, 12 applicants (4.8%) had isthmic spondylolisthesis (4.6% of females and 5.9% of males). The literature about the natural history of isthmic spondylolisthesis is reviewed. A person who has isthmic spondylolisthesis is up to 25% more likely to have significant back trouble during his life than one who does not. Back pain in adults associated with spondylolisthesis is usually heralded by back pain in the late teens or early twenties. Progression of the slip is rarely seen after maturity. Due to the loss of protection by the posterior elements the disc is prone to premature degeneration which, however, does not become clinically apparent in most cases. Longstanding vocational heavy lifting or excessive stooping can negatively influence the natural history of isthmic spondylolisthesis. It can produce symptomatic disease in a person who would otherwise have remained asymptomatic, or it can cause a deterioration in those with preexisting symptoms. Criteria for the appraisal of causality are proposed. It is stressed that the course of the disease in relation to age and vocational strains has to be analysed in each individual case.

Adolescent↗
PubMed1995

[The transparent tibia].

To keep damage to vascular and neural structure in the lower leg to a minimum when Ilizarov ring fixators are mounted, a transparent model of the lower leg has been designed and produced. In this model the course of the vascular and neural structures is shown anatomically correct relative to the bones of the lower leg. This model makes it easier to imagine the spatial relations and helps in correct placement of the Kirschner wires in the lower leg.

Arteries↗
PubMed1995

[Development and characterization of an absorbable temporary wound dressing].

Most of the temporary dressings used in the treatment of burns do not meet the objectives of a skin substitute concerning application, safety and comfort. Removal is often painful and traumatic and increases the risk of infection. Biodegradable polymers of lactic and caproic acid were developed as part of a research programme (BMFT/FRG 01 KG 8809/7), and chemical and physical properties were investigated. Films made of the copolymer material were characterized by structure, transparency, permeability, tensile strength, flexibility and degradation. The transparent films appeared increasingly opaque during hydrolysis. The water vapour permeance could be varied between 40 and 250 (40-136) ml/m2 per h (according to the method of measurement). The mechanical properties are characterized by a maximum elongation of > 2000% at 37 degrees C and a very low elastically modulus. When the results were compared with those of three established film dressings, no restriction was found in the aptitude of the material as a wound dressing.

Animals↗
PubMed1994

[Treatment concepts and results in non-infected post-traumatic pseudarthroses of the femur and tibia].

AIM OF INVESTIGATION: Different methods of internal and external fixation are used to treat aseptic posttraumatic nonunion of the femur and tibia. The advantages and disadvantages of the different methods will be demonstrated by analysing the clinical course and the outcome of our patients. Utilizing these data, a therapeutic concept tailored to the individual situation is recommended. METHODS: Depending on the form of reaction we distinguish between vital and non-vital nonunions. The classification is made according to the clinical course, x-ray-findings and in special cases the results of scintigraphy. Due to anatomic differences in vascularisation and soft tissue coverage nonunion of the femur and the tibia are discussed separately. Stabilisation is achieved by intramedullary nail, plate or external fixator. As new methods the internal plate fixator was used for the femur and the Ilizarov ring fixator for the tibia. If there has been a mistake in the choice of the method of the primary stabilisation a change of method is done. If the indication for the initial method of stabilisation was correct, the therapy of nonunions is limited to the correction of technical mistakes. Additionally, a biologic stimulation is required for the therapy of non-vital nonunion. RESULTS: The clinical data of 77 patients treated from 1985-1993 were analysed retrospectively. Vital nonunions of the femur (11) healed after 9.5 months on the average, those of the tibia (49) after 10 months. The duration of treatment of non-vital nonunions was much longer and required 20 and 16 months, respectively. The treatment of two non-vital nonunions of the tibia could not be completed. For the femur only intramedullary nail (4) and plate (8) were used, for the tibia mainly the fixator (43), of these in 18 cases the Ilizarov-apparatus. Differences in the duration of treatment due to the choice of implant could not be recognized. Complications were pin problems (14) and one lesion of the peroneal nerve in the fixator group and superficial wound infection (2), nerve irritation (1) and fracture (1) in the group treated with intramedullary nailing. CONCLUSIONS: Due to the good soft tissue coverage and vascularisation internal fixation is favored for the treatment of femoral nonunions. The fixator should only be used if distraction osteogenesis is necessary because of a bony defect. Due to the problematic soft tissue situation and poorer vascularisation on the external fixator is preferred in the treatment of tibial nonunions if a change of method is indicated. For this purpose, we currently use predominantly the Ilizarov-apparatus because of its biomechanical properties and the convincing results. Initial problems with its use could markedly be reduced with growing experience.

Adolescent↗
PubMed1993

[Mechanoreceptors in the distal aspects of the m. vastus medialis?].

Five cadavers were fixed in Jores' solution and alcohol. The distal parts of the medial vastus muscle and the medial parts of the patella ligament and of the capsule of the knee joint were prepared and histologically examined. Previous examinations had shown mechanoreceptors in the knee joint ligaments; the present study was designed to find whether mechanoreceptors could be identified in the anatomical structures mentioned, in which case an arthrotomy by the Payr access would interrupt the muscle reflexes. Only some mechanoreceptors in the medioventral parts of the knee joint capsule close to the tendon of the great muscle could be identified. Thus, when the Payr access is used there is no interruption of the sensibility transmitted by proprioceptors.

Adult↗