In a society whereby the incidence of obesity is increasing and medico-legal implications of treatment failure are more frequently ending with the consulting doctor, clarity is required as to any restrictions placed on common orthopaedic implants by manufacturing companies. The aim of this study was to identify any restrictions placed on the commonly used femoral stem implants in total hip replacement (THR) surgery, by the manufacturers, based on patient weight. The United Kingdom (UK) National Joint Registry (NJR) was used to identify the five most commonly used cemented and uncemented femoral stem implants during 2012. The manufacturing companies responsible for these implants were asked to provide details of any weight restrictions placed on these implants. The Corail size 6 stem is the only implant to have a weight restriction (60Kg). All other stems, both cemented and uncemented, were free of any restrictions. Fatigue fracture of the femoral stem has been well documented in the literature, particularly involving the high nitrogen stainless steel cemented femoral stems and to a lesser extent the cemented cobalt chrome and uncemented femoral stems. In all cases excessive patient weight leading to increased cantilever bending of the femoral stem was thought to be a major factor contributing to the failure mechanism. From the current literature there is clearly an association between excessive patient weight and fatigue failure of the femoral stem. We suggest avoiding, where possible, the insertion of small stems (particularly cemented stems) and large offset stems (particularly those with a modular neck) in overweight patients.
The treatment of acute full thickness chondral damage within the knee is a surgical challenge. Frequently used surgical techniques include chondroplasty, micro-fracture and chondrocyte implantation. These procedures give unpredictable functional outcomes and if the formation of neocartilage is achieved it is predominantly composed of type 1 collagen. The TruFit osteochondral plug was designed to provide a scaffold for cell proliferation into full thickness chondral defects. It is a composite polymer composed of polylactide co-glycolide, calcium sulphate and poly-glycolide fibres. It is composed of 2 layers, one with a similar trabecular network to cancellous bone and a superficial layer designed to simulate articular lining. The TruFit bone plug was analysed using micro-computed tomography. Its morphology characteristics, granulometry, mechanical performance and image guided failure were tested as well as numerical modelling to assess the permeability of TruFit. Morphological parameters of the TruFit bone plug compared favourably with those of human tissue. Under load the scaffold exhibited shear bands throughout the composite leading to a failure mechanism similar to cancellous bone. Stress relaxation rates of the scaffolds were greatly decreased under wet conditions, likely due to plasticisation of the scaffold by water. The biomechanical properties of the TruFit bone plugs are a cause for concern. The Scaffolds mechanical performance under load rapidly deteriorates in wet conditions at body temperature (the natural knee environment). This early failure will lead to defects in the articular surface where the plug has been inserted. Clinical data is sparse. This study correlates with work performed by Dockery et al & Spalding et al. These clinical studies have shown that the TruFit implant shows no evidence of bone ingrowth or osteoconductivity. It provides no subchondral support to neocartilage or tissue that was stimulated to form around the defects and surgical sites.
