[Defect models for the regeneration of articular cartilage in large animals]. / Defektmodelle für die Gelenkknorpelregeneration im Großtier.

BACKGROUND: Several animal models are available for the analysis of regeneration of articular cartilage in large animals, such as sheep, pigs, goats, dogs and horses. The subchondral bone lamella must be considered when ACT and MACT techniques are examined in order to protect the implant against migration of cells from the bone marrow, although recruitment of cells is often desirable in the regeneration of human cartilage. MATERIAL AND METHODS: The defects are mainly positioned at the condyles and the trochlea often bilaterally and spontaneous healing should be excluded. The follow-up period for assessment of the effectiveness of cartilage regeneration is 6-12 months. Shorter observation times up to 12 weeks can be used for pilot studies. Scores based on histological, immunohistological and biochemical staining are mostly used for assessing the regenerated tissue. Biomechanical tests with destructive features need isolated specimens from the animal but modern slice imaging techniques can reflect the progression of the healing processes over the time span of the study in vivo. CONCLUSION: Approaches to standardize the evaluation of the regeneration of articular cartilage have been sporadically described whereas they are required from the point of view of the approval of new concepts for therapy and the protection of animals.

In vitro mapping of 1H ultrashort T2* and T2 of porcine menisci.

In this study, mapping of ultrashort T2 and T2* of acutely isolated porcine menisci at B0 = 9.4 T was investigated. Maps of T2 were measured from a slice through the pars intermedia with a spin echo-prepared two-dimensional ultrashort-TE T2 mapping technique published previously. T2* mapping was performed by two-dimensional ultrashort-TE MRI with variable acquisition delay. The measured signal decays were fitted by monoexponential, biexponential and Gaussian-exponential fitting functions. The occurrence of Gaussian-like signal decays is outlined theoretically. The quality of the curve fits was visualized by mapping the value δ = abs(1 - χ(2) red). For T2 mapping, the Gaussian-exponential fit showed the best performance, whereas the monoexponential and biexponential fits showed regionally high values of δ (δ > 20). Interpretation of the Gaussian-exponential parameter maps was found to be difficult, because a Gaussian signal component can be related to mesoscopic (collagen texture) or macroscopic (slice profile, shim, sample geometry) magnetic field inhomogeneities and/or residual (1) H dipole-dipole couplings. It seems likely that an interplay of these effects yielded the observed signal decays. Modulation of the T2* signal decay caused by chemical shift was observed and addressed to fat protons by means of histology. In the T2 measurements, no modulation of the signal decay was observed and the biexponential and Gaussian-exponential fits showed the best performance with comparable values of δ. Our results suggest that T2 mapping provides the more robust method for the characterization of meniscal tissue by means of MRI relaxometry. However, mapping of ultrashort T2, as performed in this study, is time consuming and provides less signal-to-noise ratio per time than the mapping of T2*. If T2* mapping is used, pixel-wise monitoring of the fitting quality based on reduced χ(2) should be employed and great care should be taken when interpreting the parameter maps of the fits.

[Tribological assessment of articular cartilage. A system for the analysis of the friction coefficient of cartilage, regenerates and tissue engineering constructs; initial results]. / Tribologische Messungen am Gelenkknorpel. Ein Prüfstand zur Messung der Reibungszahlen von Knorpel gegen Knorpel, Regeneraten und TE-Konstrukten und erste Ergebnisse.

Values for the friction coefficient of articular cartilage are given in ranges of percentage and lower and are calculated as a quotient of the friction force and the perpendicular loading force acting on it. Thus, a sophisticated system has to be provided for analysing the friction coefficient under different conditions in particular when cartilage should be coupled as friction partner. It is possible to deep-freeze articular cartilage before measuring the friction coefficient as the procedure has no influence on the results. The presented tribological system was able to distinguish between altered and native cartilage. Furthermore, tissue engineered constructs for cartilage repair were differentiated from native cartilage probes by their friction coefficient. In conclusion a tribological equipment is presented to analyze the friction coefficient of articular cartilage, in vivo generated cartilage regenerates and in vitro tissue engineered constructs regarding their biomechanical properties for quality assessment.

[Osseointegration of ceramic cement-free acetabular cups]. / Osteointegration zementfreier Hüftpfannen aus Keramik.

INTRODUCTION: A stable osseointegration of an alumina-matrix-composite-ceramic (AMC) could facilitate the use of a thin-walled monoblock acetabular cup for hip arthroplasty with large ball-heads providing advantages like reduced risk of dislocation. The aim of the pilot study was to examine the osseointegration of porous-coated alumina-matrix-composite-ceramic-monoblock cups after implantation in a sheep model. MATERIAL AND METHODS: The porous coated AMC-ceramic cups were taken out after a healing period of 8 and 52 weeks after unilateral implantation in 5 and 6 sheep, respectively. The osseointegration was analysed histomorphologically and histomorphometrically by representative serial sections after dying according to Masson-Goldner. The examination was stratified according the pole and the rim areas as a press-fit cup with an extended rim was used. Two animals had a hip dislocation after 8 weeks and these animals were excluded from the study and replaced. RESULTS: The cups were appraised as stable in the bony bed. Histologically, the rim area of the acetabular cup showed a higher osseointegration rate than the pole area. The rate of osseointegration in total was 3% after 8 weeks and 7% after 52 weeks. The rim area furnished 5.1% after 8 and 8.6% after 52 weeks. At the pole the osseointegration was 1,2% after 8 and 5.5% after 52 weeks. No significant differences were seen between both assessed time periods regarding the osseointegration rates. The bone showed an interlocking aspect with the pores of the coating as bony tissue was determined in the pores. CONCLUSION: The presented pilot study revealed a stable osseointegration of porous-coated AMC-ceramic monoblock cups one year after surgery in a weight-bearing animal model. Interlocking of bone and porous coating may provide a stable osseointegration in the presence of low osseointegration rates, whose enhancement seems to be preferable.

Scintigraphic evaluation of rhBMP-2-biocoated implants reveals no ectopic bone formation.

The main objectives of the study described below were of two-fold nature: (1) to examine if rhBMP-2-biocoated implants in a pig model could lead to ectopic bone formation and (2) if quantitative and/or qualitative differences could be found between adhesively and covalently bonded BMP II using the scintigraphic method. In order to examine these central questions, 26 Göttingen minipigs were allocated to three groups with a control group (n=7) and two study groups (n=9 each) receiving one of three implant types: (a) chromosulfuric acid treated titanium surface as control, (b) non-covalently bonded BMP-2, and (c) covalently bonded and immobilized rhBMP-2. Each animal received four barbell-shaped implants, one in the proximal and distal metaphysis of each femur. The scintigraphic analyses were conducted after four, eight, and 12 weeks postoperatively. The visual (qualitative) analysis failed to show ectopic bone formation in any of the three groups. The statistical analysis of the relative values for bone formation yielded no significant differences between the groups, although the limitation in the applied methods do not enable one to draw conclusions regarding the histomophometric results.

Bone morphogenetic protein 7 (bmp-7) stimulates proteoglycan synthesis in human osteoarthritic chondrocytes in vitro.

BMP-7 is a member of the TGF-beta superfamily which is supposed to be one of the most potent anabolic factors of chondrocytes. In this study we analysed the effect of BMP-7 on three dimensional cultured chondrocytes with and without serum. Cartilage samples from fourteen patients with osteoarthritis of the knee were harvested and chondrocytes were cultivated in alginate-beads with and without serum supplementation (10% FCS). BMP-7 was added in three different concentrations (200, 600 and 1000 ng/ml). After 4 and 21 days PG concentration was determined by a Blyscan-Assay. For gene expression analysis of aggrecan (AGG) quantitative Lightcycler-PCR was used to estimate the mRNA levels. Under serumfree culture conditions there was no stimulation after 4 days but there was a twofold increase of PG concentration after 21 days. Using BMP-7 together with serum supplemented medium we found comparable results, however not as pronounced. AGG expression was increased only after 4 days but not after 21 days. Beside a stimulatory effect under serumfree conditions we also found a stimulatory effect of BMP-7 in the presence of serum. This study pronounces that BMP-7 might be a suitable anabolic activator of osteoarthritic chondrocytes.

Test bed for assessment of the kinematical determination of navigation systems for total knee arthroplasty. Does a limited range of motion of the hip joint influence the accuracy of the determination?

OBJECTIVE: To locate the rotational center of the hip joint, CT-less navigation systems for artificial knee-joint replacement use movements of the femur with a rigid body attached. It cannot be assumed that the hip joint provides free mobility at all times. The purpose of the present study was: 1) To build a mechanical model to assess the system's accuracy in locating the rotational center of the hip by simulating a step-wise reduction of the range of motion (ROM) of the hip joint. 2) To determine the system's resolution by assessing a critical distance between two positions of the same femoral rigid body during the process of locating the rotational center of the hip. 3) To determine the sensitivity of the navigation system to the rotation of a femoral rigid body relative to the femoral bone while locating the rotational center of the hip joint. MATERIAL AND METHODS: To assess the impact that a limited ROM of the hip joint has on the accuracy of determination of the hip joint's rotational center, a test bed was built. This enables validation of the algorithm used by a CT-less navigation system. RESULTS: In the first part of the study, it was shown that a reduction of the ROM of the hip joint to 30% of its initial value had no evident influence on the accuracy of locating the rotational center of the joint. In the second part of the study, it was determined that the limit of resolution between two spatial points of the pivoting process is between 4.4 and 8.7 cm. The third part of the study showed that the examined system rejected the determination of the hip center even when the rigid body was only rotated through 22.5 degrees . CONCLUSIONS: The results show that osteoarthritis of the hip with a limited ROM, for example, cannot be taken as a contraindication for the use of the evaluated CT-less navigation system. However, the surgeon should ensure that the pivoting of the femur is performed without hindrance within the free range of motion of the hip joint. In accordance with the vendor's recommendation, a minimum distance of 10 cm should be maintained between two spatial points. To ensure safe and unconstrained operation, the rigid body must be firmly attached to the bone and must not be dislocated.

Primary stability of threaded cups in THR--an experimental study.

Four threaded cups were tested up to their lever-out moments, torque-in moments and their resistance to failure. A was a parabolic-shaped, B was a spherical, C was a spherical-shaped too, and D was a conical shaped cup. Cup A and D represent cups which have proven themselves in clinical applications, but not cup B. The threads were determined and showed different constructive features. The cups were torqued into precise cavities in PVC foam cubes, after that they were levered out in a testing machine. The lever-out moments of all the cups showed significant differences; the results were: A: 78.4 Nm, B: 88.7 Nm, C: 117.5 Nm, D; 136.6 Nm. In the case of the torque-in moments there were no significant differences between A and B, neither between C and D. The differences in stiffness between B and C were not significant, but they were between the others. The primary stability against lever-out and the torque-in moment of threaded cups for artificial hip replacement can be basically influenced by different constructive features. Hence lever-out moment and torque-in moment should be understood and tested as independent variables.

Design and construction of a simulator for testing finger joint replacements.

A simulator for testing finger joint replacements was developed. Movement intervals of 15 degrees at flexion and extension plain can be set using an adjustable crank drive. The maximum range of motion is 105 degrees, 90 degrees being the maximum flexion and 15 degrees the extension. Thus, the simulator is also suitable for impingement tests. A constant joint load is infinitely variable from 20 N to 500 N. Test frequency is also infinitely variable from 0.2 Hz to 2 Hz. A modular assembly of the components of the prosthesis means that these can be positioned as required, and that any type of prosthesis may be tested. The design and the material allow for an all-round lubrication at a heat up to 37 degrees C. The equipment is designed for permanent operation. Pre-clinical quality assurance for finger joint replacements can be considerably improved by the implementation of the present simulator.

[Simulator for migration processes and wear in the artificial hip acetabulum for radiologic measurement]. / Simulator für Wanderungsvorgänge und Abrieb bei künstlichen Hüftpfannen zur radiologischen Vermessung.

For assessing migration of cups, standard X-rays or stereo radiological images (SRI) are available. In addition, software is also available for measurements. The accuracies of the various systems are established statistically, in part combined with phantoms, and compared. To date, no known phantom is available for the simulation of acetabular cup migration with account being taken of the position of the pelvis in the X-ray beam. Such an appliance covering 8 different parameters has now been developed, the cup can be moved horizontally, vertically and in the loading direction. Angular accuracy is +/- 0.5 degree, and wear of a magnitude of 0.25 mm can be simulated. Two degree elevation of the pelvis, left or right, can be simulated. The position of the pelvis around the horizontal axis permits continuous variation. This appliance can simulate migratory movements of the acetabular cup within a pelvis, and wear within the cup. In addition, the spatial position of the pelvis can be varied. The X-ray images can be used to investigate the accuracy of evaluation strategies.

Ischemic hepatitis in a patient with congestive cardiomyopathy: an innovative approach to therapy using intravenous dobutamine.

Patients who sustain a transient period of hypotension or low cardiac output can develop massive elevations of the serum transaminases without serum markers of acute hepatitis, a recent myocardial infarction or exposure to toxins and chemicals. This condition is often termed "ischemic hepatitis" (IH), with its pathological correlate being centrilobular necrosis. Recognition of IH can help in the appropriate management of these patients, and avoid unnecessary diagnostic testing. The authors describe a patient with congestive cardiomyopathy in whom IH developed as part of a complicated hospital course. The condition appeared to reverse with the administration of dobutamine, suggesting inotropic therapy as an appropriate treatment modality.

A radiographic sign of left sided mediastinal lymph node enlargement.

This report draws attention to an apparent clear space, which is normally present on routine chest posterior-anterior roentgenograms, composed of the descending aorta, pulmonary outflow tract and left upper lobe vessels which form its medial, inferior and lateral boundaries respectively. The medial margin of this space has a concave outer border. Lymph nodes of the ligamentum group lie in close proximity to this space. In the absence of other processes involving structures of the middle mediastinum, encroachment of this space from the medial direction, with formation of a convex outer border is a reliable and frequently the first radiographic sign of left-sided mediastinal lymph node enlargement.

Application of delayed reinforcement procedures to the behavior of an elementary school child.

Delayed reinforcement techniques were applied, in a multiple baseline experimental design, to modify the behavior of a mildly maladjusted sixth-grade child. The following behaviors were chosen for modification: face-touching, posture, and voice-loudness. Videotape recordings were made of the subject's behavior during mathematics and spelling periods each day. The recordings from the mathematics period was shown to her after school, and consequences for behavior exhibited during mathematics were dispensed during the after-school viewing. This delayed reinforcement procedure produced the desired behavior changes during the mathematics period. Tapes from the spelling period, which were taken without the child's knowledge, indicated that the behavior changes generalized to portions of the day other than the mathematics period.