Osseointegration of hydroxyapatite and remodeling-resorption of tricalciumphosphate ceramics.

BACKGROUND: Cancellous bone defects surrounded by still intact bone structures never heal. Ceramics offer a solution providing osteoconductive scaffolds. PURPOSE: The purpose of the study is to evaluate whether structured ß-TCP and HA implants can reconstruct cancellous bone defects, which role micro- and macro-porosity, stiffness and surface area play; finally the indication for both materials based on its resorbability. MATERIAL & METHODS: 10 German Shepard dogs were operated on both tibial heads implanting shell-like fully interconnected ceramic cylinders, using a wet grinding hollow drill coated with diamonds. ß-TCP was compared with HA. A polychromatic sequential labelling with 4 different fluorochromes controlled bone formation dynamics. Non-decalcifying histology after perfusion fixation and vessel casting was performed. µ-CT was combined with high resolution microradiography and histology on thin ground crossections. The stages after 6 weeks, 2, 3, 4 months and 15 months were evaluated. RESULTS: In spite of osseointegration of HA and ß-TCP, the osseointegration of both materials was completely different. Both shell-like bone void fillers were osseointegrated in a sandwich-like manner. HA yielded primarily a reinforcement of the recipient's cancellous-bone bed and full osseointegration after 4 months, whereas ß-TCP-implants were fully osseointegrated after 6 weeks. HA did not show signs of resorption. The resorption of the ß-TCP resulted during remodelling. The final stage showed restitution "ad integrum" of the ß-TCP defects with a physiological architecture, whereas HA was integrated in the cancellous bone construction providing 600 µm measuring macropores showing osteoinductive properties.

Value and limits of µ-CT for nondemineralized bone tissue processing.

An experimental approach was performed on 20 giant rabbits to establish the possibilities and limitations of µ-CT for routine processing of nondemineralized bone tissue. Hydroxyapatite (HA) or ß-tricalciumphosphate (ß-TCP) bead implants or a melange of both, microchambered and solid, were implanted into a standardized and precise defect in the patellar groove. The bone-healing phase was chosen for the histology considering 1 or 2 days, and 2, 3, and 6 weeks. Normal X-ray and µ-CT were applied on all specimens; five specimens in the 6-week stage were additionally processed according to the full range of conventional nondemineralized bone processing methods. µ-CT increased the possibilities of nondemineralized histology with respect to bone morphometry and a complete sequence of sections, thus providing a complete analysis of the bone response. µ-CT was limited in differentiating bone quality, cell analyses, and mineralization stages. The investigation based on normal X-rays is limited to defining integration and excluding the fibrous and bony encapsulation of loose implants. µ-CT allows a 3D evaluation of newly formed bone which is clearly marked against the ceramic implant. It does not allow, however, for the differentiation between woven and lamellar bone, the presentation of the canalicular lacunar system, or on the cell level, revealing canaliculi or details of the mineralization process which can be documented by high-resolution microradiography. Titer dynamics of bone formation remains the domain of polychromatic sequential labeling. The complete sequence of µ-CT slices enhances the possibilities for routine histology, tremendously allowing to the focus on detail histology to topographically well-defined cuts, thus providing more precise conclusions which take into consideration the whole implant.

Immunosuppression and lung cancer of donor origin after bilateral lung transplantation.

Analysis of databases from transplant recipients revealed a 3-5 fold higher risk to develop de novo malignancies under continued immunosuppression. The underlying mechanisms are poorly understood. Here we describe a patient who received a bilateral lung transplantation for end-stage 'usual interstitial pneumonia' (UIP) resulting in idiopathic lung fibrosis. The recipient presented with a non-small cell lung carcinoma (NSCLC) in the donor lung 7 months later. Molecular and immunological typing of the tumor revealed a cancer of donor origin with a prominent intratumoral immune cell infiltrate without detectable effector function. This is a unique case of de novo outgrowth of a NSCLC of donor origin under continued immunosuppression, supporting the concept of tumor immunosurveillance in vivo.

Ultrastructural changes in acute lung allograft rejection: novel insights from an animal study.

BACKGROUND: Acute rejection (AR) episodes after lung transplantation (Tx) are orchestrated by cells of the innate and adaptive immune system targeting the engrafted organ. The assessment and classification of pathologic changes of AR relies essentially on conventional histology. Herein we apply the technique of scanning electron microscopy (SEM) to identify and characterize ultrastructural changes of the pulmonary graft after lung Tx. METHODS: Orthotopic single-lung Tx was performed between BALB/c (donor) and C57BL/6 (recipient) mice. At Day 5 after Tx, lung allografts were recovered for SEM and for histologic analysis. RESULTS: Upon Tx, high numbers of leukocytes and thrombocytes were found, showing an activated surface pattern and a change of their cell body shape. These cells adhered and partly transmigrated through the endothelium of vessels. Larger vessels were more affected than smaller vessels and the endothelium was roughened in its surface texture throughout. As a phenomenon, airways were partly covered by activated dendritic cells. Numerous thrombocytes and macrophages accumulated on the endothelium of the cuff anastomosis region exposing this area to a particularly higher risk of thrombosis. CONCLUSIONS: SEM allows for detection of morphologic changes during pulmonary allograft rejection and adds important data to conventional histology when making the diagnosis of acute rejection.

Ischaemia-reperfusion injury in orthotopic mouse lung transplants - a scanning electron microscopy study.

Lung ischaemia-reperfusion (I/R) injury remains a major cause of graft failure in lung transplantation (Tx). With the implementation of orthotopic lung Tx in mice, a physiological model on the base of a perfused and ventilated graft became available for the investigation of I/R injury. Using the scanning electron microscopy (SEM) technique, we here present an analysis of early and late morphological changes of pulmonary I/R injury. Syngeneic lungs were orthotopically transplanted between C57BL/6 mice. Grafts were exposed to 2 h of cold ischaemia. Transplants and right lungs were examined by SEM with corresponding haematoxylin-eosin histology 30 min and 4 h after reperfusion. Thirty minutes after reperfusion, the alveolar surface of transplants showed a discontinued lining of surfactant, while the lining of the non-transplanted lung was normal. Within the graft, leucocytes displayed an irregular surface with development of pseudopodia, and microvilli were detected on the membrane of pneumocytes. At 4 h after reperfusion, leucocytes significantly increased in numbers within the alveolar space. Also, the number of microvilli on pneumocytes increased significantly. Similar to these, the endothelium of vessels increasingly developed microvilli from 30 min towards 4 h after reperfusion. The airways of transplanted grafts showed mild changes with thickening of the bronchial epithelium and a destruction of kinocilia. Taken together, SEM detects pathological events of I/R that are previously not described in normal histology. These findings may influence the interpretation of studies investigating the I/R injury in the mouse model of lung Tx.