No abstract

In this study, a characterization of human bone-forming cells responsible for heterotopic ossification was carried out in vitro. The biological and biochemical cell characteristics of the heterotopic osteoblast-like (HOB) cells were compared with those of orthotopic osteoblast-like (OB) cells from normal bone and stromal bone marrow cells believed to contain a subpopulation of osteogenic precursor cells. We found that HOB's from the spongiosa of heterotopic ossification required less time until the beginning of migration and the achievement of confluence in vitro compared with OBs from femoral shaft spongiosa. The fraction of mitotically active cells assessed by a clonogenic assay was higher as well in HOB cells. The in vitro studies of mitogenesis and the efficiency of colony formation of osteogenic cells indicate that with increasing differentiation and relative age they become more dependent on growth factors in the medium, otherwise the morphology of osteoblast-like cells changes and they pass irreversibly into the postmitotic stage of the cell cycle. The activity of the alkaline phosphatase is distinctly higher in the HOB than in the OB cells, HOB cells exhibit a lower level of osteocalcin expression compared with OB cells. No significant difference was found between OB and HOB cells in the amount of procollagen of type I sequestered by the cells. After 30 days, HOB and OB cells formed a mineralized matrix on exposure to 2 mM beta-glycerophosphate. Since HOBs were isolated from heterotopic bone that had developed within 3-6 months after hip surgery, the differences in cellular behavior compared with OBs may be attributed to the relatively young age of HOB cells.

The bad risk for an early onset of osteoarthritis in the knee increases with the size of a cartilage defect. A collateral meniscus- or ligament-tear will enforce this hazard in addition. In order to avoid such a development, relevant full-thickness cartilage defects should be reconstructed biologically and attendant meniscus- or ligament-tears as well as varus- or valgus deformities should be treated. A number of studies, including some prospective-randomized trials, have shown that autologous chondrocyte transplantation (ACT) is the most reliable procedure for a surgical treatment of full-thickness cartilage defects larger than 4 cm (2) in adults. One disadvantage of ACT is the extensive approach to the joint and often a hypertrophy of the repair tissue. To solve these problems, some different biomaterials for a matrix-assisted ACT have been developed. The scaffold we use has a covering membrane upside and a collagen-sponge carrying the chondrocytes. By means of special surgical instruments a minimally invasive implantation is possible, reducing the side-effects of an extensive approach. Animal studies showed the regeneration of a hyaline cartilage using our described system. However, results of current clinical studies with the different scaffolds must be awaited before an universal application of matrix-assisted ACT can be recommended.

At present, autologous chondrocyte transplantation (ACT) is the most reliable method for biological repair of circumscribed lesions of articular cartilage larger than 4 cm 2 in the knee of adults, as shown by long-term results and some prospective randomised studies. However, the conventional ACT using cells in suspension and a periosteal graft for covering the defect exhibits some disadvantages: the application and fixation of the periosteal flap requires a relatively large arthrotomy and, according to current knowledge, carries the risk of transplant hypertrophy. A further disadvantage is its limited use in uncontained defects. To overcome these problems, our group has developed a collagen-based, biphasic carrier for the matrix-assisted variant of ACT. The new biomaterial helps to stabilize the phenotype of seeded chondrocytes and can be implanted into the defect minimally invasive using specialized tools. In the course of developing the matrix, a series of different biomaterials of synthetic and natural origins have been evaluated using human chondrocytes in vitro and in vivo (SCID-mouse model). In this paper some of our most important findings are presented. Finally, new methods for the arthroscopic defect size assessment using the OrthoPilot ™ , as well as for the development of smart biomaterials are introduced. ZusammenfassungLangzeitresultate und prospektiv randomisierte Studien zeigen, dass die autologe Chondrozytentransplantation (ACT) für die biologische Rekonstruktion von umschriebenen Knorpelschäden des Kniegelenks über 4 cm 2 Defektgröße beim Erwachsenen die derzeit zuverlässigste Methode ist. Die konventionelle Form der ACT weist jedoch auch einige Nachteile auf. Hierzu gehören vor allem die häufig erforderliche, langstreckige Arthrotomie für die Periostaufnaht, das Risiko einer Transplantathypertrophie, die nach dem derzeitigen Kenntnisstand vom Periostlappen ausgeht, und die eingeschränkte Anwendbarkeit bei Defekten ohne erhaltenes Containment. Zur Lösung dieser Probleme wurde von unserer Arbeitsgruppe eine kollagenbasierte biphasische Matrix für die trägergekoppelte Form der ACT entwickelt. Das neue Biomaterial stabilisiert den Phänotyp der eingesäten Chondrozyten und lässt sich mithilfe spezieller Instrumente minimalinvasiv in den Defekt implantieren. Im Zuge der Trägerentwicklung wurde eine Reihe von verschiedenen Biomaterialien synthetischer und natürlicher Herkunft mit humanen Chondrozyten in vitro und in der SCID-Maus untersucht. In der vorliegenden Arbeit werden einige der wichtigsten Ergebnisse unserer Untersuchungen mit den verschiedenen Biomaterialien beschrieben. Abschließend wird eine neue Methode zur arthroskopischen Vermessung von Knorpelschäden mit dem OrthoPilot ® sowie ein neues Verfahren zur Entwicklung intelligenter Biomaterialien vorgestellt. Schwerpunktthema 267

With increased shoulder stress, the altered strength ratios reflect specific requirements of the performance attained. However, the importance of muscular dysbalances for the onset of shoulder complaints must be considered more important than their influence on athletic performance capacity.