For decades, overtightening was blamed for causing surgical screws and plates used in bone repair to irreversibly fuse together, making subsequent removal difficult for the surgeon and traumatic for the patient.
But a new study from the University of Dayton Research Institute, Dayton, OH, explains that proteins present in the human body, rather than too much torque, are responsible for the sticking. The researchers believe this discovery will lead to improvements in manufacturing, as well as fewer complications for surgeons and less trauma for patients if the hardware needs to be removed.
While hardware is often left in place indefinitely, sometimes it must be removed if it is causing pain or other issues for the patient. Titanium alloy is a popular choice among surgeons because of its biocompatibility, corrosion resistance, and high strength-to-weight ratio. While the screws are designed to be removed from the metal plates, the parts sometimes become locked together, thought to be the result of galling, which is when one titanium alloy contacts the same type of alloy under pressure, causing the pieces to fuse.
The team set up tests using titanium alloy plates and screws tightened to the manufacturer’s recommendation and suspended in fluid. Some were placed in fluid containing proteins, others in fluid without. At nine months, the samples with proteins present began sticking. There was no evidence of galling or corrosion, but the screws still stuck, they reported.
The results of the two-year study were presented at the 2012 annual meeting of the American Osteopathic Academy of Orthopedics on October 25.
