Biomechanical Study of Novel Unilateral Fixation Combining Unilateral Pedicle and Contralateral Translaminar Screws in the Subaxial Cervical Spine

Introduction In several situations, the stability of the subaxial cervical spine is damaged and involves the lateral mass of 1 side; in these cases, a pedicle screw (PS) or lateral mass screw (LMS) may not be suitable for placement on the affected side. Therefore, salvage short-segment fixation with satisfactory stability is needed when bilateral fixation is not feasible. Methods Seven fresh-frozen human cervical spine specimens were used to test the 3-plane range of motion (ROM) of the C4-C5 segment. Quasistatic 2-Nm flexibility testing was performed in the following sequence: 1) intact; 2) destabilization (using 3-column injury models) treated with bilateral mass screws (BMSs); 3) destabilization treated with a unilateral PS combined with a contralateral translaminar screw (UPS+CTLS); and 4) destabilization treated with bilateral PSs (BPSs). Then, a pullout strength test was performed for the PSs, LMSs, and translaminar screws (TLSs) using 7 isolated C4 and C5 vertebrae. Results The UPS+CTLS group showed no significant difference from the BMS group in the 3-plane ROM or from the BPS group in the axial rotation or flexion-extension ROM but showed a significantly greater lateral bending ROM than did the BPS group. The pullout strength test showed that both C4 and C5 TLSs had strength similar to that of LMSs but poorer than that of PSs. Conclusions Fixation with the hybrid UPS+CTLS construct performed as well as BMS fixation in our biomechanical tests and may play a clinical role when BPS or BMS placement is not feasible for short-segment fixation.