Search PubMed⌕ Search

Biomedical subjects

R Burgkart

Publications and source records attributed to R Burgkart.

36 records · Page 2Linked to original sources
PubMed2001

Magnetic resonance imaging-based assessment of cartilage loss in severe osteoarthritis: accuracy, precision, and diagnostic value.

OBJECTIVE: To examine the in vivo accuracy and precision of magnetic resonance imaging (MRI)-based assessment of cartilage loss in patients with severe osteoarthritis (OA) of the knee. METHODS: High-resolution MRI images of the tibial cartilage were obtained in 8 patients prior to total knee arthroplasty, using a water-excitation gradient-echo MRI sequence (acquisition time 6 minutes 19 seconds; spatial resolution 1.2 x 0.31 x 0.31 mm3). The MRI measurements were repeated after joint repositioning. The precision of the cartilage volume and thickness computations was determined after 3-dimensional reconstruction. During surgery, the tibial plateaus were resected, and the MRI data were compared with water displacement of surgically retrieved cartilage. RESULTS: The standard deviation (coefficient of variation) of repeated tibial cartilage volume measurements was 56 mm3 (5.5%) medially and 59 mm3 (3.8%) laterally. The deviation from surgically removed tissue was -13%, on average, with a high linear correlation between both methods (r = 0.98). In patients with varus OA, the tissue loss was estimated to be 1,290 mm3 in the medial tibia and 1,150 mm3 in the lateral tibia, compared with the data in healthy volunteers. CONCLUSION: Noninvasive quantitative MRI-based analysis of cartilage morphometry in severe OA is accurate, precise, and displays high potential diagnostic value.

Aged↗
PubMed2001

A survey study for the development of virtual reality technologies in orthopedics.

Virtual reality (VR) technologies have the potential to support medical education and training. In order to orient the development of medical VR applications towards the actual deficiencies and demands in orthopedics, we performed a survey among 56 orthopedic physicians. They were asked to provide information about the kind of physical joint evaluation tests which they perform most often, the importance of physical joint evaluation in comparison to alternative diagnostic methods, and their opinion about current medical education system as well as the prospects of VR applications in orthopedics. The main conclusion of this survey is that VR applications have the potential to improve the lacking medical education and orthopedic training, e.g. by improving the quality of joint evaluation methods, reducing the high number of unhealthy, risky and expensive alternative diagnostic procedures.

Curriculum↗
PubMed2001

Development of a multi-modal virtual human knee joint for education and training in orthopaedics.

Due to limited simultaneous access to a greater pool of patients an effective training of medical students or young orthopedic physicians is difficult. A knee joint simulator that comprises the properties of a healthy or pathological knee can support medical education and training. In this paper a mechatronic system is presented that provides visual, acoustic, and haptic (force) feedback so that it allows a user to touch and move a virtual shank, bones or muscles within the leg, and simultaneously observe the generated movement, feel the contact force, and hear sounds. These and further features enable the user to study and assess the properties of the knee, e.g. by testing the joint laxity and end-point stiffness in six degrees-of-motion (DOF) and by grasping and pulling at muscles, rupturing ligaments or changing muscle/ligament paths. Such a tool can support training of physical knee evaluation required for diagnosis and therapeutic planning, since any kind of pathology of any subject type can be tested at any time. Furthermore, it can provide a better understanding of functional anatomy, e.g. for the education of medical students.

Computer Simulation↗
PubMed2000

Viscoelastic properties of the cell nucleus.

Mechanical factors play an important role in the regulation of cell physiology. One pathway by which mechanical stress may influence gene expression is through a direct physical connection from the extracellular matrix across the plasma membrane and to the nucleus. However, little is known of the mechanical properties or deformation behavior of the nucleus. The goal of this study was to quantify the viscoelastic properties of mechanically and chemically isolated nuclei of articular chondrocytes using micropipet aspiration in conjunction theoretical viscoelastic model. Isolated nuclei behaved as viscoelastic solid materials similar to the cytoplasm, but were 3-4 times stiffer and nearly twice as viscous as the cytoplasm. Quantitative information of the biophysical properties and deformation behavior of the nucleus may provide further insight on the relationships between the stress-strain state of the nucleus and that of the extracellular matrix, as well as potential mechanisms of mechanical signal transduction.

Animals↗
PubMed2000

Precision of tibial cartilage morphometry with a coronal water-excitation MR sequence.

The aim of this study was to analyze the precision of tibial cartilage morphometry, by using a fast, coronal water-excitation sequence with high spatial resolution, to compare the reproducibility of 3D thickness vs volume estimates, and to test the technique in patients with severe osteoarthritis. The tibiae of 8 healthy volunteers and 3 patients selected for total knee arthroplasty were imaged repeatedly with a water-excitation sequence (image time 6 h 19 min, resolution 1.2 x 0.31 x 0.31 mm(3)), with the knee being repositioned between each replicate acquisition. After 3D reconstruction, the cartilage volume, the mean, and the maximal tibial cartilage thickness were determined by 3D Euclidean distance transformation. In the volunteers, the precision of the volume measurements was 2.3 % (CV%) in the medial and 2.6 % in the lateral tibia. The reproducibility of the mean cartilage thickness was similar (2.6 and 2.5 %, respectively), and that of the maximal thickness lower (6.5 and 4.4 %). The patients showed a considerable reduction in volume and thickness, the precision being comparable with that in the volunteers. We find that, using a new imaging protocol and computational algorithm, it is possible to determine tibial cartilage morphometry with high precision in healthy individuals as well as in patients with osteoarthritis.

Adult↗
PubMed1999

Anterior cruciate ligament and intercondylar notch in the coronal oblique plane: anatomy complemented by magnetic resonance imaging in cruciate ligament-intact knees.

We assessed the anatomy of the anterior cruciate ligament (ACL) and femoral intercondylar notch on cryosections from one cadaveric knee specimen in the coronal oblique plane oriented parallel to the intercondylar roof. We determined the course of the ACL, the widths of the cruciate ligaments at intersection, and the intercondylar notch configuration on coronal oblique plane magnetic resonance images in 51 adult cruciate ligament-intact knees (25 women, 26 men; age range, 16 to 47 years). The intercondylar notch widths were measured at the notch entrance, at the intersection of the ACL and posterior cruciate ligament (PCL), and at the notch outlet. In the coronal oblique plane, the ACL exhibited a diagonal course from the central and medial part of the anterior intercondylar area of the tibia distally, across the lateral third of the intercondylar notch, to the intercondylar surface of the lateral femoral condyle proximally. At the cruciate ligament intersection, the absolute widths of the ACLs measured on average 6.1+/-1.1 mm in men and 5.2+/-1.0 mm in women representing 31.9% and 31.1% of the ACL/central intercondylar notch width ratios. The absolute widths of the PCLs measured on average 9.6+/-1.3 mm in men and 8.5+/-1.3 mm in women representing 50.4% and 51.4% of PCL/central intercondylar notch width ratios. On average for both groups, men and women, the absolute widths of the PCLs were significantly larger than the absolute widths of the ACLs. However, the relative widths of the cruciate ligaments with respect to corresponding intercondylar notch widths were not significantly different. In the coronal oblique plane, the intercondylar notch widths showed on average a significant decrease from posterior to intersection and from intersection to anterior. At notch outlet, the mean notch width measured 21.4 mm in men and 18.5 mm in women. At intersection, the mean notch width measured 19.1 mm in men and 16.6 mm in women. At notch entrance, the notch width measured 14.6+/-1.8 mm in men and 12.7+/-2.1 mm in women. We recommend magnetic resonance tomography of the knee in the coronal oblique plane oriented parallel to the intercondylar roof as the imaging modality of choice to visualize accurately the anatomic diagonal course of the ACL and its relation to the intercondylar notch and posterior cruciate ligament complex.

Adolescent↗
PubMed1997

[Conservative treatment of cruciate ligament rupture. Magnetic resonance tomography provides prognostic information for conservative healing].

Ruptures of the cruciate ligaments continue to pose both diagnostic and therapeutic problems. On the basis of structural analysis of MR images obtained after the accident and the results of conservative treatment, it can be shown that function healing of the rupture can result, when, for example, the synovial membrane (capsule) is preserved (70%). It proved possible to show and objectify this using MRI and measurements.

Anterior Cruciate Ligament↗
PubMed1997

Optimization of high-frequency electrosurgery of the meniscus.

In an in vitro study of the sheep's meniscus, the possibilities to reduce the thermal tissue necrosis caused by high-frequency electrosurgery of the meniscus were studied. Under standardized conditions, machine-made sections through the meniscus were cut using electrodes of various thicknesses and different settings of the electric generator. The thermal tissue necrosis near the cut through the meniscus was determined using light microscopy and image analysis on the specimen stained according to Masson-Goldner. With a constant voltage of 250 V tissue necrosis was significantly less for electrodes of a diameter of 0.5 mm than for 1.5-mm electrodes (187.3 microns as compared with 368.0 microns). For electrosections carried out using a commercially available electrode with a low voltage of 250 V as well as with a power-controlled generator, tissue necrosis was also significantly less than with a constant high voltage of 395 V (181.4 microns and 210.2 microns as compared with 325.0 microns). Thus, an effective reduction of thermal tissue necrosis in arthroscopic partial meniscectomy is possible when thin electrodes and power-controlled generators are used.

Animals↗
PubMed1997

Preoperative acute hypervolemic hemodilution with hydroxyethylstarch: an alternative to acute normovolemic hemodilution?

Acute normovolemic hemodilution (ANH) may help to reduce demand for homologous blood but requires extra time and apparatus. A more simple procedure is acute hypervolemic hemodilution (HHD), where hydroxyethylstarch is administered preoperatively without removal of blood. In a prospectively randomized study we compared ANH (preoperatively 15 mL/kg autologous blood removal and replacement with 15 mL/kg of hydroxyethylstarch with HHD (15 mL/kg of hydroxyethylstarch administered preoperatively) in 49 patients undergoing hip arthroplasty. To avoid excessive intravascular volume, we used the vasodilating effect of isoflurane. No significant differences were found between groups (ANH, n = 23; HHD, n = 26) for intraoperative blood loss (ANH versus HHD, median [minimum-maximum]); 545 [295-785] mL versus 520 [315-825] mL) and postoperative blood loss (730 [525-945] mL versus 780 [495-895] mL), postoperative hemoglobin, hemotocrit, platelet count or coagulation variables, and transfusion requirements (ANH 43% versus HHD 35% of patients received homologous blood) (P > 0.05). Heart rate did not change significantly in either group. In the ANH group mean arterial blood pressure (MAP) decreased after hemodilution (P < 0.05) while in the HHD group MAP did not change over time. Mean time required to perform ANH was 58 (46-62) min versus HHD 16 (12-19) min (P < 0.05). Costs for ANH were $63.60 USD and for HHD $32.75 USD (labor costs not included). In orthopedic patients undergoing hip replacement with a predicted blood loss of about 1000 mL, HHD seems to be a simple as well as time- and cost-saving alternative for ANH.

Adult↗
PubMed1995

[Vertebral replacement in palliative tumor therapy. Possible surgical procedures--significant improvement in quality of life].

Complications associated with spinal metastases encompass not only pain, but often neurological deficits and possibly even paralysis due to transverse lesions. The differential indication for dorsal, ventral and combined surgical procedures depends on the nature and extent of the tumor, and the life expectancy and general state of health of the patient. Surgery must be carried out in good time, before additional damage to the spinal cord occurs. In recent years, 20 patients have been treated by GHG-vertebral body replacement. In 19 of these patients, pain was considerably improved. All patients were able to walk following surgery. Preoperative neurological deficits disappeared, in 9 of 13 patients resulting in a major improvement in the patients' quality of life.

Humans↗
PubMed1994

[Hypervolemic hemodilution as a means of preventing homologous blood transfusion. A simple alternative to acute normovolemic hemodilution].

PROBLEM: Acute normovolenic hemodilution (ANH) is timeconsuming and complicated, and has only a small effect in reducing the need for homologous blood. A simpler procedure is hypervolemic hemodilution (HHD). In the present prospective, randomized study, HHD is compared with ANH for its blood-saving effect. STUDY DESIGN: Forty-nine patients undergoing total hip replacement were admitted. Group I (ANH): Withdrawal of 15 ml/kg bodyweight autologous blood and isovolemic replacement by hydroxyethyl starch (200/0.5). Group II (HHD): Infusion of 15 ml/kg bodyweight hydroxyethyl starch (200/0.5). RESULTS: No significant differences were found between the groups in terms of Hb, hematocrit and coagulation. The blood loss (intra-operative+drainage losses) was comparable in the two groups at 1274 +/- 310 ml (HHD) and 130 +/- 335 ml (ANH). During the period under investigation, 66% of the patients in the HHD group and 57% in the ANH group required no homologous blood. CONCLUSION: HHD is just as effective as ANH for reducing homologous blood requirements, and is much simpler to apply.

Blood Loss, Surgical↗
PubMed1994

[Strategies for minimizing homologous blood transfusion in elective interventions].

The risks associated with homologous blood transfusion necessitates the development of strategies for reducing the need for it. The most effective method is certainly preoperative donation of autologous blood, which leads to an increase in the absolute numbers of erythr789789 by the time surgery is performed. Depending on the type of preparation and storage, erythrocytes may be viable for between 49 days (liquid storage) and many years (deep frozen). By employing preoperative plasmapheresis, high-quality autologous fresh frozen plasma can be made available for use during surgery. Donation of autologous blood and plasmapheresis are preoperative measures that need to be organized. Another possibility is the use of a cell separator to recycle blood lost during surgery, and may be applied intra-operatively (aspiration from the surgical wound) or postoperative (drainage). Hemodilution has but little effect in reducing homologous blood requirements. Instead of the technically complex and time-consuming acute normovolemic hemodilution (ANH), the simpler hypervolemic alternative version (HHD) should be employed. Applying all the measures described above, an appreciable reduction in the need for homologous blood can be achieved. A prerequisite, however, is close cooperation between the surgeon an anaesthesiologist.

Blood Transfusion, Autologous↗
PubMed1994

[Management of unstable fractures of the coxal femur. Selection of the appropriate osteosynthesis procedure in elderly patients].

Advantages and disadvantages of various fixation procedures for use in fractures of the femoral neck--blade-plate with temporary fixation by means of Kirschner wire insertion or dynamic hip screws--and hemi- or total allo-arthroplasty are described. The large number of fixation procedures for pertrochanteric fractures reflects the difficulty in achieving mobility and loading stability. On account of the possible intra- and postoperative complications, the highly propagated gamma nailing has proved problematic. Overall, the individual situation of the patient must be taken into account when choosing the appropriate fixation procedure.

Aged↗
PubMed1994

Custom made total knee-replacement in patients with primary and secondary bone tumors.

The authors present an account of a group of 51 patients to whom an individual endoprosthesis of the knee joint was implanted on account of a tumour. A primary bone tumour was involved in 42 cases and a metastatic process in 9 cases. Twenty-four endoprostheses were cemented, 26 were implanted without cement. The mean follow-up period was 43 months. Functional results excellent and good in 61%, poor results only in 5%.

Adolescent↗
PubMed1993

[Current status of cementless hip endoprostheses ].

In young patients, the results of cemented hip joint replacement are less than satisfactory on account of the high rate of aseptic loosening involving in particular the acetabular component. With the aid of suitable uncemented prostheses and a meticulous surgical technique, the results obtained in this group can be improved. On an interim basis, an uncemented acetabular component may be combined with a cemented femoral component. The problem of wear and foreign body-induced bone resorption remains unsolved. New materials will possibly rectify this problem. Customized prostheses have opened up new possibilities, in particular for the severely deformed hip joint, but whether they will improve the results of standard replacements has yet to be shown. Before introducing a new prosthesis, thorough use should be made of the testing possibilities available. In the elderly patient with a reduced life expectancy, the cemented prostheses continue to be the method of first choice, since it permits immediate pain-free weight-bearing.

Adult↗
PubMedDate not supplied

Effects of joint unloading and reloading on human cartilage morphology and function, muscle cross-sectional areas, and bone density - a quantitative case report.

Recent studies have shown that thinning of human cartilage occurs with unloading, but no data are available on the effect of remobilization (after immobilization) on knee joint cartilage status in humans. We examined a 36-year-old patient after 6 weeks of unilateral immobilization. Knee joint cartilage morphology (patella and tibia), patellar cartilage deformation, and thigh muscle cross-sectional areas were assessed with quantitative MR imaging and bone density with peripheral quantitative computed tomography (pQCT) during 24 months of remobilization. The immobilized limb displayed lower muscle cross-sectional areas (MCSA) of the knee extensors (-36%), lower bone density of the femur and tibia (-12/-6%), lower patellar cartilage thickness (-14%), but no side differences of tibial cartilage thickness. During remobilization, side differences decreased to -4% for knee extensor MCSAs, to -6%/-3% for femoral and tibial BMD, and to -8% for patellar cartilage thickness. No change was observed in tibial cartilage. Patellar deformation decreased from 9% to 4% after 15 months. In conclusion, we observed substantial changes of thigh MCSAs, but little (patella) to no (tibia) change in cartilage thickness during remobilization. These preliminary results indicate that human cartilage macro-morphology may be less adaptive to variations of the mechanical loading than muscle and bone.

Adult↗