Investigation of long lateral mass screw insertion torque

Here, we assessed a new trajectory and insertion torque for the placement of a long lateral mass screw (LLMS) that offers stronger posterior fixation versus a shorter lateral mass screw (LMS) in the posterior cervical spine. We report a short technical note of the insertion torque of LLMS.

The insertion trajectory/torque was evaluated in 30 patients (10 males and 20 females) undergoing posterior cervical LLMS fusions (2021-2023). Patients averaged 65 years of age. Pathology included eight cervical spine injuries, ten cord injuries, four dislocations/fractures, and eight other entities. Variables studied included the length of the LLMS inserted from C3-7, screw deviation rates, insertion torque, and adverse events.

A total of 146 screws were inserted: 11 pedicle screws (PSs) and 135 LLMS. The average insertion torque was 105.9 cNm for PS and 64.9 cNm for LLMS. As the screw lengthened by 1 mm, the insertion torque increased by approximately 4.4 cNm.

Here, we documented that the insertion torque of LLMS was 66.1 cNm, greater than the 51.0 cNm for LMS, which should provide stronger posterior cervical fixation.