[Dislocation tendency, stabilizing effect and sintering tendency of different lumbar vertebrae cages in an in vitro experiment]. / Dislokationstendenz, stabilisierende Wirkung und Einbruchtendenz unterschiedlicher LWS-Cages im In-vitro-Experiment.

For biomechanical purposes, interbody fusion cages should not dislocate, should provide high stability, and should have a low subsidence risk. Zientek (Marquardt Medzintechnik), Stryker (Stryker Implants), and Ray lumbar interbody fusion cages (Surgical Dynamics) were tested in this study. They were implanted by pairs from a posterior approach without further stabilization. In a first step, each cage design was implanted into four human L3-4 segments and extracted posteriorly under an axial preload of 200 N. In a second step, standard flexibility tests were carried out with 24 human L2-3 and L4-5 specimens in an intact condition, directly after cage implantation, and after cyclic axial compression loading (200-1000 N, 40,000 cycles, 5 Hz). In a third step, a destructive axial compression test was carried out. Maximum pullout force was highest with Ray cages (median 945 N), followed by Zientek (605 N) and Stryker cages (130 N). With all three cage designs, primary stability was higher in lateral bending and flexion than in extension and axial rotation. Implantation of Ray cages caused a decreased range of motion in all three loading directions ranging between 49% and 99%. Zientek cages only stabilized in lateral bending, flexion, and extension (45-78%) and Stryker cages in none of the three loading directions. Cyclic loading caused an increased range of motion in all cases up to 190%. Axial compression force at failure was 8413 N with Ray cages, 8359 N with Stryker cages, and 5486 N with Zientek cages. The cage design seems to influence the dislocation tendency. In this regard, threaded cages or cages with anchorage systems seem to provide more security. The stabilizing effect seems to be mainly influenced by factors such as the degree of distraction or destruction of the facet joints rather than by the cage design.

Resistance of the lumbar spine against axial compression forces after implantation of three different posterior lumbar interbody cages.

BACKGROUND: The aim of using interbody fusion cages is to distract the degeneratively decreased disc height to decompress the neural structures in the intervertebral foramina and allow bony fusion. Prerequisite for a successful fusion therapy is a high resistance against subsidence and breakage. METHOD: Three types of implants, a cylindrical threaded titanium cage (Ray) (1c), a bullet shaped PEEK cage (Stryker) (1a) and a rectangular titanium cage with an endplate anchorage device (Marquardt) (1b) were implanted in eight monosegmental lumbar spine specimens (L 2/3 and L 4/5). Each specimen underwent a cyclic loading test with 40000 cycles at a rate of 5 Hz. A cyclic axial compression force ranging from 200 Newton [N] to 1000 N was applied and the axial translation recorded simultaneously to determine the subsidence tendency. After this procedure the specimens were tested with a progressive axial force until breakage. FINDINGS: There were only small differences in the subsidence tendency for the three cage designs. The height reduction due to cyclic loading ranged between 0.9 mm (Marquardt), 1.2 mm (Stryker) and 1.4 mm (Ray). The median break force ranged from 5486 N (Marquardt), 8359 N (Stryker) to 8413 N (Ray). No correlation between bone mineral density and failure load could be detected. INTERPRETATION: Endplate preparation and cage design of the tested implants do not seem to influence the resistance of the segment against cyclic axial compression. The compression with a continuously increasing load revealed that an implant-bone failure is not to be expected in physiological limits for all three cage types.

Stabilizing effect of posterior lumbar interbody fusion cages before and after cyclic loading.

OBJECT: The function of interbody fusion cages is to stabilize spinal segments primarily by distracting them as well as by allowing bone ingrowth and fusion. An important condition for efficient formation of bone tissue is achieving adequate spinal stability. However, the initial stability may be reduced due to repeated movements of the spine during everyday activity. Therefore, in addition to immediate stability, stability after cyclic loading is of remarkable relevance; however, this has not yet been investigated. The object of this study was to investigate the immediate stabilizing effect of three different posterior lumbar interbody fusion cages and to clarify the effect of cyclic loading on the stabilization. METHODS: Before and directly after implantation of a Zientek, Stryker, or Ray posterior lumbar interbody fusion cage, 24 lumbar spine segment specimens were each evaluated in a spine tester. Pure lateral bending, flexion-extension, and axial rotation moments (+/- 7.5 Nm) were applied continuously. The motion in each specimen was measured simultaneously. The specimens were then loaded cyclically (40,000 cycles, 5 Hz) with an axial compression force ranging from 200 to 1000 N. Finally, they were tested once again in the spine tester. CONCLUSIONS: In general, a decrease of movement in all loading directions was noted after insertion of the Zientek and Ray cages and an increase of movement after implantation of a Stryker cage. In all three cage groups greater stability was demonstrated in lateral bending and flexion than in extension and axial rotation. Reduced stability during cyclic loading was observed in all three cage groups; however, loss of stability was most pronounced when the Ray cage was used.

Fasting and postprandial disposition of R(-)- and S(+)-ibuprofen following oral administration of racemic drug in healthy individuals.

The effects of preceding food intake on the plasma concentrations of R(-)-ibuprofen and the pharmacologically active enantiomer S(+)-ibuprofen were investigated in healthy subjects. A single oral dose of 400 mg racemic ibuprofen was administered either fasting or following a standardized meal. As compared to fasting administration postprandial drug intake resulted in a clear reduction of R(-) and S(+)- ibuprofen plasma concentrations mainly during the initial three hours. The ratio of S(+)/R(-)-ibuprofen postprandially was increased for Cmax and AUC o-tmax as well as for AUC o-infinity. These data are compatible with a meal-induced enhancement of chiral inversion of R(-) to S(+)-ibuprofen. The significant reduction of plasma concentrations of ibuprofen mainly during the initial three hours suggests that the analgesic efficacy is diminished when the drug is taken after a meal. This may to a slight extent be compensated for by a small increase of the metabolic inversion of the R(-)-enantiomer into the active S(+)-form of the drug.

[Congenital coronary artery aneurysm: a rare cause of acute myocardial infarct]. / Kongenitales Koronararterienaneurysma: Eine seltene Ursache des akuten Myokardinfarktes.

An 18-year-old female presented with acute posterior wall infarction after exercise stress. Coronary angiography showed an aneurysm of the proximal right coronary artery partially occluded with thrombi, followed by a complete occlusion of the vessel. The left coronary artery was normal. Despite immediate intracoronary thrombolysis she developed a large posterior wall necrosis. Angiographic follow-up revealed worsening left ventricular function but not progression of the aneurysmatic ectasia. The diagnosis congenital coronary artery aneurysm was made since there was no evidence for an atherosclerotic, infectious or inflammatory vascular disease. The patient was treated conservatively and within 2 years of follow-up the clinical course was uneventful.

[Intramedullary spinal metastasis of bronchial carcinoma coincident with intramedullary spinal angioma]. / Intramedulläre spinale Bronchialkarzinommetastase in Koinzidenz mit intramedullärem spinalem Angiom.

We report on a case of a man of 51 years, who presented with pain and symptoms of progressive spinal cord compression caused by an intramedullary spinal tumor at T8. Before surgery a bronchial carcinoma was diagnosed. A MRI-study detected an edema of the spinal cord at T8. Myelography and spinal Angiography revealed a spinal vascular malformation at the same level. Both lesion were removed and the histological examination confirmed the coexistence of an intramedullary spinal metastasis from a carcinoma of the bronchus with a spinal vascular malformation.

[Topographic-surgical anatomy of the pediatric pars plana]. / Topographisch-chirurgische Anatomie der kindlichen Pars plana.

The width of the pars plana and the distances between the corneo-limbal junction and the posterior aspect of the pars plicata as well as of the ora serrata were determined by measurement in 17 autopsy eyes and additional 12 dissected autopsy eyes of premature and mature babies and infants. The data were correlated to age and length of the globe. The site of sclerotomy in transscleral lensectomy of congenital cataracts is discussed.