Barbara Bartmeyer | PubMed Health

PubMed2006

Simulation of cell differentiation in fracture healing: mechanically loaded composite scaffolds in a novel bioreactor system.

Cell differentiation during bone healing following a fracture is influenced by various biological and mechanical factors. We introduce a method for the examination of cell and tissue differentiation simulating a fracture gap in vitro. A closed bioreactor system allows the imitation of the biological, mechanical, and biochemical conditions in vitro. The initial hematoma formed in a fracture is simulated with a mixed construct composed of lyophilized cancellous bone and a fibrin matrix in a sandwich configuration. The construct may be loaded with osteoprogenitor cells. Exemplarily, constructs were loaded with rabbit periosteal cells and cultivated under mechanical loading with 7 kPa at 0.05 Hz for up to two weeks. During the observation period, cell morphology and correlating protein synthesis changed under mechanical stimulation. Cell differentiation differed between the various regions of the constructs. The periosteal cells were arranged perpendicularly to the mechanical loading and differentiated to osteoblastic forms with rising collagen type I synthesis, constant alkaline phosphatase activity, and initiation of the calcification of the extracellular matrix. The observed pattern of cell and tissue differentiation was similar to the one seen in the early phase of bone healing. In conclusion, the presented method allows simulation of cell and tissue differentiation during the early phase of fracture healing. It could serve as an in vitro model for the examination of mechanical and pharmacological influences during the early phase of bone healing on a cellular level.

Animals↗

PubMed2003

Does partial weight bearing unload a healing bone in external ring fixation?

BACKGROUND: Partial weight bearing is thought to unload and protect the healing bone. Until now, there has been no objective method of assessing the amount of weight placed on the healing zone by the patient. The goal of this study was to determine the effects of partial weight bearing on the loading of the healing bone in tibial osteotomies. MATERIALS AND METHODS: Six patients with complex tibial osteotomies, stabilized with Ilizarov ring fixator constructs, took part in this study. Three-dimensional interfragmentary movements were measured with reflective markers that were attached to the Schanz screws of the fixator. Patients were asked to rest, to co-contract the musculi gastrocnemii, to stand up, to walk slowly and to load partially the affected limb with 20 kg of weight. RESULTS: Compared with co-contraction, ground reaction forces of partial weight bearing, standing up and walking were significantly increased (P<0.05). The interfragmentary movements during partial weight bearing were, however, comparable in partial weight bearing, standing up and walking (P>>0.05). CONCLUSIONS: Partial weight bearing did not unload the defect zone. No direct relationship between interfragmentary movement magnitudes and ground reaction forces was identified. Therefore, the concept of partial weight bearing cannot reliably reduce loading of a healing zone. It may, however, help to prevent patients from undergoing critical situations, such as stumbling, by increasing their general awareness.

Adult↗