The halo fixation device is used widely for treating traumatic injury to the cervical spine. Its major complications, pin loosening and infection, can be minimized by retightening, increasing torque and practicing local pin care. Local pin care includes applying a reagent to the skin at the pin site and to the halo ring hole or pin threads. The coefficient of friction at the halo ring/pin thread interface is a major determining factor in the relationship between the applied torque and the radial compressive stress applied to the skull. This relationship was determined for halo pins coated with reagents in common clinical use. The type of reagent used had a profound effect on the coefficient of friction and the radial compressive stress. At 0.9 N-m (8 in. -lbs.) the mean radial compressive stress using pins coated with betadine, hibiclens and hydrogen peroxide averaged52 MPa (7,550psi), 49.1 MPa (7,130psi) and53.5 MPa (7,770 psi), respectively, compared to uncoated pins and pins coated with antibiotic ointment, which averaged 66.7MPa (9,680psi) and 70.3MPa (10,200psi), respectively. These latter two radial compressive stresses were precipitously close to the ultimate radial compressive strength of cranial bone.
© 1993 American Academy of Orthotists & Prosthetists