Porous threaded titanium implant screws have higher insertional torque compared to standard screws.

Abstract

Purpose: Posterior pelvic ring screw back out and loss of fixation may result from poor screw purchase, prevalent in geriatric pelvic ring injuries where the cancellous bone is often osteoporotic. To reduce screw back out, there has been increasing use of porous threaded titanium implant (PTTI) screws for posterior pelvic fixation rather than standard cannulated, buttress threaded screws. This study aims to assess the insertional torque of PTTI screws compared to standard cannulated screws as there is limited evidence regarding the biomechanical fixation profiles among screws.

Methods: Fifteen orthopedic trauma surgeons inserted screws into a validated surrogate for osteoporotic cancellous bone. Insertional torque was measured during screw placement in three separate scenarios for each surgeon: (1) placement of a standard 7.3 mm (mm) screw into a new bone model, (2) placement of a PTTI screw into a new bone model, and (3) placement of a PTTI screw through a previously placed 7.3 mm screw hole from which it was removed (rescue screw). The insertional torque was calculated across all surgeons and analyses were conducted comparing scenarios (1) and (2), and (1) and (3).

Results: The average insertional torque of 7.3 mm screws was 0.358 ± 0.223 Nm, and the maximum insertional torque was 0.627 ± 0.365 Nm. The average insertional torque for the PTTI screws was 0.929 ± 0.551 Nm, 2.59 times more than that of the 7.3 mm screw (p < 0.001) while the maximum insertional torque was 1.877 ± 0.671 Nm, 2.99 times that of the standard screw (p < 0.001). When placed into the prior 7.3 mm screw hole (rescue), the PTTI screws generated an average insertional torque of 0.711 ± 0.405, still 1.99 times greater than that of the 7.3 mm screw (p < 0.001), and maximum torque of 1.607 ± 0.427 Nm, 2.56 times greater than the standard screw (p < 0.001).

Conclusion: Significantly greater maximum and average insertional torque were generated with the PTTI screws compared to the standard screws, even when used as a rescue screw in cancellous bone models. Further studies assessing clinical outcomes and failure rates with PTTI screws will better define their clinical utility.