Advantages of Biodegradable Pins Over Metal Fixation

Introduction The field of internal fixation has long been dominated by the use of metal implants, in particular those manufactured from stainless steel, cobalt chrome and, in more recent years, titanium. However, despite widespread use and availability, utilisation of metal implants in fracture repair is not without its disadvantages.

Metal implants e.g. plates, pins, wires, mesh etc. have been associated with many physical problems including:

  • Pain (Alpert and Seligson 1996, Schmidt et al. 1998)
  • Corrosion (Agins et al. 1988)
  • Accumulation of metals in tissues (Jorgenson et al. 1997, Katou et al. 1996, Kim et al. 1997, Rosenberg et al. 1993, Schliephake et al. 1993)
  • Hypersensitivity to titanium (Hunt et al. 1994, Katou et al. 1996, Lalor et al. 1991)
  • Imaging and radiotherapy interference (Castillo et al. 1988, Sullivan et al. 1994, Sirlin et al. 2001)
  • Stress shielding - metal implants can prevent appropriate stimulation of the bone. Without loading, weakness and atrophy of the underlying bone can occur (Brodke et al. 2001, Kennady et al. 19891, Kennady et al. 19892, Uhthoff and Finnegan 1983, Uhthoff et al. 1994)
  • Growth restriction in children (Yaremchuk 1994)

Metal pins, for example in the form of Kirschner wires (K-wires), can be used in the repair of many types of bone defects, e.g. fractures and osteochondral/chondral lesions. These implants in particular have been linked to several other problems. The most evident of these is the need to remove the implant once its purpose has been served (Jani and Parker 2004), specifically to remove protruding wires involved in the repair of hand and foot fractures. This causes added stress and discomfort to the patient and necessitates a further expensive and time-consuming procedure.

Additional disadvantages of using metal pins include infection and pin migration, bending or breaking. There is, therefore, an obvious need for the widespread
adoption of improved materials, and biodegradable polymers were introduced to alleviate the problems seen with metal. Poor initial results with first-generation biodegradable implants meant that surgeons could not justify the use of biodegradable pins (Korner et al. 2001), however, recent major developments mean that their use now has to be re-evaluated.

A new generation of biodegradable implants has been created using the Inion OPTIMATM family of materials. By blending L lactide, D lactide, TMC (Tri-Methylene Carbonate) and occasionally also Glycolide (when particularly fast degradation is required), Inion has been able to establish a ’library’ of materials from which to select those with the most appropriate strength, toughness and degradation profile to meet specific clinical requirements.