Orthopaedic implant technology: biomaterials from past to future

Orthopaedic implant technology is heavily based on the development and use of biomaterials. These are non-living materials (e.g. metals, polymers and ceramics) that are introduced into the human body as constituents of implants that fulfill or replace some important function. Examples would be prosthetic joint replacements and fracture fixation implants. For orthopaedic biomaterials to succeed in their desired functions and outcomes in the body, a number of factors need to be considered. The most obvious mechanical properties of the implants are that they need to suit their intended function, and various classes and types of biomaterials have been developed and characterised for use in different implant components depending on their demands. Less well understood but no less important are the interactions that occur between the constituent biomaterials and the living cells and tissues, both of the human host as well as pathogens such as bacteria. Biomaterials used for orthopaedic applications are generally considered to be biocompatible. However, adverse effects arising from interactions at the implant interface can result in various modes of implant failure, such as aseptic loosening and implant infection. This review paper uses the illustrative example of total hip replacement (which has been called the operation of the century) to highlight key points in the evolution of orthopaedic biomaterials. It will also examine research strategies that seek to address some of the major problems that orthopaedic implant surgery are facing today.

Vascular endothelial growth factor (VEGF) is expressed during articular cartilage growth and re-expressed in osteoarthritis

<p><b>INTRODUCTION</b>Vascular endothelial growth factor (VEGF) is expressed in osteoarthritic articular cartilage. However, the pattern of VEGF expression throughout the whole life cycle of articular cartilage is not well elucidated. The aim of the study was to investigate the spatiotemporal expression of VEGF and its receptors, vascular endothelial growth factor receptor-1 (VEGFR1) and vascular endothelial growth factor receptor-2 (VEGFR2), in articular cartilage during growth, maturation and degeneration, using the guinea pig model of spontaneous osteoarthritis.</p><p><b>MATERIALS AND METHODS</b>Sections of tibial plateaus aged 2, 6 and 12 months were obtained, representing growing, mature and osteoarthritic cartilage respectively. Expression of VEGF and its receptors was determined by immunohistochemistry and in situ hybridisation.</p><p><b>RESULTS</b>At 2 months, VEGF and its receptors were expressed in chondrocytes within the superficial layer of the articular cartilage. At 6 months, no expression of VEGF and its receptors was noted. In the 12-month-old specimens, VEGF and its receptors were expressed in chondrocytes within articular cartilage that exhibited osteoarthritic changes (medial tibial plateaus), but not in the histologically normal lateral plateaus.</p><p><b>CONCLUSION</b>This spatiotemporal distribution of VEGF and its receptors suggests that VEGF is expressed during articular cartilage growth, becomes quiescent at maturity, and is re-expressed in osteoarthritis.</p>