Hydroxyapatite coated stainless-steel external fixation pins

The use of stainless steel pins is the state of the art for bone fracture treatment with external fixation. The tightening force applied by the surgeon during pin insertion is an important parameter which influences the stability of the bone pin interface. This force depends on the material and surface characteristics of the pin, the helix geometry and the biomechanical properties of the surrounding bone. The force needed for pin removal at the end of the treatment depends on the osteointegration of the pin and the strength of the bone pin interface. It is obvious that the optimization of pin insertion torque should lead to a significant reduction in treatment failure. Various coatings have been proposed as effective methods of improving the bone-implant interface in orthopaedic surgery. Hydroxyapatite has shown the ability to bind chemically to bone. The purpose of this paper was: first, to develop and standardize a method of measurement of insertion and extraction torque of external fixation pins implanted in both plastic materials and bone; second, to compare the results obtained from the pins implanted in bone with results from pins implanted in plastic blocks; and finally, to study hydroxyapatite coated pins to improve the bone pin contact and consequently the mechanical stability of the bone pin interface.