Sural Sumit
Department of Orthopaedics,
Maulana Azad Medical College, New Delhi, INDIA
Abstract
Various type of implants is used in Orthopaedic surgery which are kept inside the human body for a significant period of time, sometimes permanently, in order to perform specific functions like fixation of fractures, replacement of joints and such devices are classified as Class D or high risk devices. These implants may be made of metals (pure metals like titanium or newer ones like tantalum) or metal alloys, like stainless steels (corrosion resistant low carbon 316L), cobalt chrome (used in non cemented arthroplasty), Ti-Al-Va (titanium-aluminium-vanadium) or non metals like ceramics (low friction hip arthroplasty), Polyether ether ketone (PEEK cages for spine fusion) and various types of bone cements. Implant failure may be defined as failure of the implant to produce satisfactory results due to inadequacy of the function expected of it. Failure of metal implants may be classified as plastic failure (due to plastic deformation before the yield point resulting in failure of clinical outcome); brittle failure (due to defect in manufacturing or fabrication process of the metal) and fatigue failure (due to repetitive biomechanical loading of the device). Various factors individually or in combination may be associated with implant failure. Implant related factors may result in early corrosion, bending or breaking of implant due to fault in manufacturing process. Patient related factors include unstable and comminuted fractures, non compliance regarding weight bearing after surgery or surgical site infections. Surgeon related factors may include improper selection of size or design of the implant and improper handling of metal surfaces leading to scratches and possibility of corrosion. Corrosion is found to occur at junctional area of two metals like plate and screw and breakage of implants are found at sites of holes in the implants like fenestration in femoral arthroplasty stem or holes in interlocking nails. Metal hypersensitivity reaction is found 6 times more common in failed implants. One of the major disasters was metallos is occurring in the metal on metal hips where the metal particles (haptens) released due to corrosion and wear induced a hypersensitivity response with formation of immune complexes, antibodies and inflammatory markers. Localized ALVAL (Aseptic Lymphocyte Vasculitis Associated Lesion) around these implants resulted in marked loosening and implant failure. Materiovigilance is the need of the hour and a registry needs to be maintained across centers, institutions, states and the country, since the incidence is quite low and may not occur immediately. Statutory bodies like the Bureau of Indian Standards play a vital role to ensure quality of implants meet international standards like CE and ISO. Regulatory bodies need to ensure standard quality implants are manufactured and dispensed by local or indigenous manufacturers and public awareness is important for them to select standard quality implants.