Relationship between pin type and depth of skull penetration during frame placement for Gamma Knife radiosurgery

Our retrospective study addresses the largely unknown effect of fixation pin type on depth of skull penetration during Gamma Knife frame placement.

Absolute and relative depths were compared for 404 pins of aluminum and titanium in 101 patients who underwent Gamma Knife frame placement at 0.4 Nm (3.5 lb-in) torque.

Effect of pin type was significant: penetration was less in aluminum than titanium pins, for absolute (0.27 mm vs. 0.83 mm) and relative (5.16% vs. 15.53%) depths (p < 0.001 each). Fifty percent of aluminum pins did not measurably penetrate the outer table of the skull whereas 95% of titanium pins penetrated into cancellous bone.

Although these pin penetration differences did not have a clear clinical correlate, we now recommend titanium pins for their consistent, deeper penetration, which may result in greater frame stability favorable for most clinical applications. Future studies may define optimal torque for aluminum pins.