Tenascin expression in normal and pathological conditions of the musculoskeletal system

Tenascin is an extracellular matrix protein with highly regulated expression and uncertain functions. It is prominently expressed during musculoskeletal embryogenesis. The pattern of distribution of tenascin in healthy adult musculoskeletal tissues is spatially and temporally restricted. It can be only detected in a small amount in the muscle-tendon junctions, tendons, perichondrium, periosteum, endosteum, the superficial layer of articular cartilage and the subintimal connective tissue of synovium. Elevated tenascin expression is found in inflammatory, degenerative and neoplastic lesions of the musculoskeletal system. The peculiar pattern of tenascin expression suggests it may play a role in the regulation of cell behavior at the interfaces between different elements of the musculoskeletal system and in various pathological processes, in particular those involving attachment and or detachment of cells from the extracellular matrix and their proliferation and collagenase secretion.Biomedical Reviews 1996; 6: 83-94

The effect of geometry and abduction angle on the stresses in cemented UHMWPE acetabular cups : finite element simulations and experimental tests

Abstract Background Contact pressure of UHMWPE acetabular cup has been shown to correlate with wear in total hip replacement (THR). The aim of the present study was to test the hypotheses that the cup geometry, abduction angle, thickness and clearance can modify the stresses in cemented polyethylene cups. Methods Acetabular cups with different geometries (Link®: IP and Lubinus eccentric) were tested cyclically in a simulator at 45° and 60° abduction angles. Finite element (FE) meshes were generated and two additional designs were reconstructed to test the effects of the cup clearance and thickness. Contact pressures at cup-head and cup-cement interfaces were calculated as a function of loading force at 45°, 60° and 80° abduction angles. Results At the cup-head interface, IP experienced lower contact pressures than the Lubinus eccentric at low loading forces. However, at higher loading forces, much higher contact pressures were produced on the surface of IP cup. An increase in the abduction angle increased contact pressure in the IP model, but this did not occur to any major extent with the Lubinus eccentric model. At the cup-cement interface, IP experienced lower contact pressures. Increased clearance between cup and head increased contact pressure both at cup-head and cup-cement interfaces, whereas a decreased thickness of polyethylene layer increased contact pressure only at the cup-cement interface. FE results were consistent with experimental tests and acetabular cup deformations. Conclusion FE analyses showed that geometrical design, thickness and abduction angle of the acetabular cup, as well as the clearance between the cup and head do change significantly the mechanical stresses experienced by a cemented UHMWPE acetabular cup. These factors should be taken into account in future development of THR prostheses. FE technique is a useful tool with which to address these issues