Biomechanik der Hüfte und des proximalen Femurs

Die Hüfte spielte in der Evolution des Menschen und die Entwicklung seiner grundlegendsten motorischen Fähigkeiten wie Stehen oder Gehen eine wichtige Rolle. Gerade durch diese Fähigkeiten wird das Hüftgelenk jedoch stark beansprucht und Verletzungen oder Erkrankungen sind besonders störend. Deutlich wird dies bei Arthrose oder hüftnahen Frakturen. Betroffene leiden unter einer teilweise starken Einschränkung der Mobilität und einer verminderten Lebensqualität. Da der Hüfte primär eine biomechanische Funktion zukommt, ist das Verständnis der Biomechanik des Hüftgelenks essenziell. Für die Biomechanik der Hüfte spielen vor allem die um das Gelenk wirkenden Muskeln eine große Rolle. Die Muskelkräfte verursachen Dehnungen im Femur, die für dessen Morphologie entscheidend sind. Um den wirkenden Kräften standzuhalten, optimiert er seine eigene Topologie durch ein an mechanische Reize adaptiertes Knochenwachstum. Wie die Dehnungsverteilung und die entsprechende Topologie im Femur genau aussieht ist Teil vieler Studien. Dieses Wissen ist vor allem dann wichtig, wenn hüftgelenksnahe Frakturen mit Implantaten versorgt werden müssen oder Endoprothesen zum Einsatz kommen.

X-ray resonant photoexcitation: linewidths and energies of Kα transitions in highly charged Fe ions

Photoabsorption by and fluorescence of the Kα transitions in highly charged iron ions are essential mechanisms for x-ray radiation transfer in astrophysical environments. We study photoabsorption due to the main Kα transitions in highly charged iron ions from heliumlike to fluorinelike (Fe24+ to Fe17+) using monochromatic x rays around 6.6 keV at the PETRA III synchrotron photon source. Natural linewidths were determined with hitherto unattained accuracy. The observed transitions are of particular interest for the understanding of photoexcited plasmas found in x-ray binary stars and active galactic nuclei.

Distal radius fracture fixation with volar locking plates and additional bone augmentation in osteoporotic bone: a biomechanical study in a cadaveric model

BACKGROUND

Fractures of the distal radius represent the most common fractures in adults. Volar locked plating has become a popular method for treating these fractures, but has been subject to several shortcomings in osteoporotic bone, such as loss of reduction and screw purchase. In order to overcome these shortcomings, cement augmentation has been proposed.

METHODS

AO-type 23-A3.3 fractures were made in 8 pairs of fresh frozen osteoporotic cadaveric radial bones. All specimens were treated with volar plating, and divided into cement augmentation or non-augmentation groups (n = 8/group). Constructs were tested dynamically and load to failure, construct-stiffness, fracture gap movement and screw cutting distance were measured.

RESULTS

Cement augmentation resulted in a significant increase in cycles and load to failure, as well as construct stiffness at loads higher than 325 N. When compared to the non-augmented group, fracture gap movement decreased significantly at this load and higher, as did screw cutting distance at the holes of the ulnar column. The cycles to failure depend on the BMD in the distal region of the radius.

CONCLUSION

Cement augmentation improves biomechanical properties in volar plating of the distal radius.

Comparison of 128-section single-shot technique with conventional spiral multisection CT for imaging of the temporal bone

BACKGROUND AND PURPOSE

Computed tomography is an essential modality for imaging of the temporal bone. Newest generation scanners allow the coverage of large examination volumes with a single gantry rotation. The objective of this study was to compare a 128-section SST (1 single rotation of the x-ray tube) with conventional spiral MSCT (ultra-high-resolution mode) for imaging of the temporal bone.

MATERIALS AND METHODS

Fifty-four temporal bones in 27 patients were scanned with both a conventional MSCT and 128-section SST. After blinding and randomization of both examinations, 2 observers assessed the visualization of 38 anatomic structures (eg, various segments of the facial nerve canal, mallear ligaments) by using multiplanar reconstructions in the axial and coronal planes. The differences in evaluation scores obtained for the 2 techniques were analyzed by using a Wilcoxon signed rank test, with a P value of < .05 considered significant. For both methods, imaging time and radiation exposure were noted.

RESULTS

Overall visualization of anatomic structures did not differ significantly between the 2 techniques (P > .05). When we compared the anatomic structures separately, there was better visualization of the lateral mallear ligament with MSCT, whereas the cochlear septa were ranked higher with SST (P < .05). Imaging time and average DLP for MSCT were 12.3 seconds and 306 mGy cm, respectively; for SST, values they were 1 second and 64 mGy cm, respectively (ie, a dose reduction of 79%).

CONCLUSIONS

For imaging of the temporal bone with adequate diagnostic quality, 128-section SST can be used. The main advantages over MSCT are the dramatic reductions of imaging time and radiation exposure, which are particularly important when scanning uncooperative patients or children.

A Biomechanical Evaluation of Orthopaedic Implants for Hip Fractures by Finite Element Analysis and In-Vitro Tests

The aim of this study was to test the hypothesis that a reinforced gamma nail for the fixation of subtrochanteric fractures would experience less stress during loading compared with a common gamma nail. The issue of whether the use of the stronger implant would result in more stress shielding in the surrounding bone was also addressed.

A finite element analysis (FEA) of a synthetic bone was employed to calculate the stress distribution in implant and bone for two fracture types (AO 31-A3.1 and AO 31-A3.3). The FEA was validated by mechanical tests on six synthetic femurs. To test the hypothesis in vitro, mechanical tests on six pairs of fresh-frozen human femurs were conducted. The femurs were supplied with a common or a reinforced gamma nail in a cross-over study design. Strains were measured on the nail shaft to quantify the loading of the nail.

The FEA resulted in 3—51 per cent lower stresses for the reinforced gamma nail. No increase in stress shielding could be observed. In the in-vitro tests, the reinforced gamma nail experienced less strain during loading ( p < 0.016). The study demonstrated the benefit of a reinforced gamma nail in subtrochanteric fractures. It experienced less stress but did not result in more stress shielding.

The stability of a hip fracture determines the fatigue of an intramedullary nail

The purpose of this study was to address the question of how the stability of a proximal hip fracture determines the fatigue and failure mechanism of an intramedullary implant. To answer this question, mechanical experiments and finite element simulations with two different loading scenarios were conducted. The two load scenarios differed in the mechanical support of the fracture by an artificial bone sleeve, representing the femoral head and neck. The experiments confirmed that an intramedullary nail fails at a lower load in an unstable fracture situation in the proximal femur than in a stable fracture. The nails with an unstable support failed at a load 28 per cent lower than the nails with a stable support by the femoral neck. Hence, the mechanical support of a fracture is crucial to the fatigue failure of an implant. The simulation showed why the fatigue fracture of the nail starts at the aperture of the lag screw. It is the location of the highest von Mises stress, which is the failure criterion for ductile materials.

[CEA determination to differentiate between pheochromocytoma with ectopic calcitonin formation and type-II multiple endocrine neoplasms]

Plasma levels of calcitonin and carcinoembryonic antigen (CEA) were determined pre-operatively and two months postoperatively in ten patients with C-cell carcinoma as part of multiple endocrine neoplasia type II. In addition, CEA was measured in extracts from 20 different phaeochromocytomas (five from patients with multiple endocrine neoplasia type II, 15 from patients with sporadic phaeochromocytoma). In comparison, CEA concentration was determined in extracts from five C-cell carcinomas of patients with multiple endocrine neoplasia type II. When correlating pre- and postoperative calcitonin and CEA levels, there was a significant linear relationship (P less than 0.001). CEA concentration in extracts from phaeochromocytomas was at the lower level of sensitivity (4.7 +/- 12.2 pg/mg tumour wet-weight). In extracts from C-cell carcinomas they were much higher (6402 +/- 4570 pg/mg tumour wet-weight). The results suggest that it is possible, in patients with phaeochromocytoma and high calcitonin levels, to differentiate by additional CEA determination between C-cell carcinoma in the course of multiple endocrine neoplasia type II and sporadic phaeochromocytoma with ectopic calcitonin liberation.

[Ectopic hormone formation in multiple endocrine type IIa neoplasia (author's transl)]

A patient with high-grade osteoporosis had elevated levels of ACTH, cortisol and carcinoembryonic antigen (CEA). Computed tomography demonstrated enlarged adrenal glands. Despite intensive search no ACTH-producing tumour was found. A central Cushing's syndrome was thus possible, and a radiologically normal sella turcica made a microadenoma of the hypophysis a possibility. However, a one-time hypertensive crisis with elevated catecholamines raised the suspicion of an additional phaeochromocytoma and thus provided the first pointer to a multiple endocrine neoplasia. Bilateral phaeochromocytomas, discovered at adrenalectomy, as well as raised serum-calcitonin levels, strongly suggested coexistence of a C-cell carcinoma, which previously had not been demonstrated either by thyroid scanning or fine-needle biopsy. A total thyroidectomy revealed a multifocal and metastasizing C-cell carcinoma. On extraction it contained a high concentration of calcitonin, typical for a C-cell carcinoma. An unusual finding was of ACTH in extracts of both the C-cell carcinoma and the phaeochromocytoma. It was immunologically identical with the synthetic ACTH used as a standard.