Are Terminally Threaded Guide Pins From Cannulated Screw Systems Dangerous?

Abstract

Threaded and smooth pins are often used in orthopedic surgery. Although uncommon, injury to the soft tissues can and do occur, including nerve or vessel injury from aberrant pin placement. The purpose of this study was to compare the risk of nerve injury from threaded pins versus smooth guide pins due to: (1) past-point-drilling of the pin, or (2) entanglement of the pin with soft tissue. Past-point drilling was tested by a blindfolded participant drilling a 1.6-mm guide pin (terminally threaded or smooth) through a porcine femur until they felt they had drilled through the second cortex. The distance over-drilled was measured in millimeters. Twenty trials were randomly completed, 10 with each pin type. Entanglement of soft tissue was tested by placing the terminal portion of the guide pin on the nerve. Two drilling positions were tested: (1) drilling at 90° and (2) parallel to the nerve. The drill was run for 1 second and assessed for entanglement and magnitude of entanglement (measured in millimeters of nerve wrapped by the pin). Sixty trials were completed, 15 with each pin type, and in each of the 2 positions. The average past-point drilling depths were 4.6 and 16.9 mm for the smooth and threaded pins, respectively (P<.05). The mean nerve overwrapping was 0.45 and 4.7 mm, for the smooth and threaded pins, respectively (P<.05), drilled at 90° and 0.15 and 0.92 mm, respectively (P<.05) in the parallel position. In 13 of 60 trials with the smooth pin and 50 of 60 trials with the threaded pin, wrapping was observed (P<.05). This study demonstrates that it is difficult to determine by feel when the threaded pin has drilled through the second cortex of the bone, in contrast to the smooth pin. Furthermore, soft tissue entanglement is more likely and to a greater magnitude with threaded pins than with smooth.