Biomechanical Comparison of C1 Lateral Mass - C2 Short Pedicle Screw - C3 Lateral Mass Screw-Rod Construct Versus Goel-Harms Fixation For Atlantoaxial Instability.

STUDY DESIGN: A biomechanical in vitro study using human cadaveric spines.

OBJECTIVE: To compare atlantoaxial stability and stiffness of a C1 lateral mass - C2 short pedicle - C3 lateral mass screw-rod construct versus C1 lateral mass - C2 pedicle screw-rod construct.

SUMMARY OF BACKGROUND DATA: The C1 lateral mass - C2 pedicle screw-rod construct provides excellent atlantoaxial fixation but C2 pedicle screw placement is associated with risk of vertebral artery injury. The use of shorter C2 pedicle screws may mitigate the risk of vascular injury but may result in reduced C1-C2 stabilization. Extending C1 lateral mass - C2 short pedicle screw-rod construct with C3 lateral mass screws may mitigate the risk of vascular injury without compromising C1-C2 fixation.

METHODS: Seven cervical spines were tested with internal control experimental design in the following sequence: intact state, and following creation of type II odontoid fracture, the specimen was instrumented with C1 lateral mass - C2 pedicle screw fixation (C2PED), C1 lateral mass - C2 short pedicle screw fixation (C2SPED) and C1 lateral mass - C2 short pedicle - C3 lateral mass screw fixation (C2SPED-C3LM). For each condition, the angular stiffness and range of motion with 1.5 Nm load in flexion/extension (FE), lateral bending (LB) and right/left axial rotation (RAR/LAR) were quantified.

RESULTS: Instrumented conditions demonstrated significantly lower C1-C2 angular range of motion (ROM) and greater stiffness than the intact state. Compared to C2PED, C2SPED-C3LM demonstrated significantly lower C1-C2 ROM during FE and LB, significantly greater C1-C2 stiffness in flexion and right/left LB, similar C1-C2 ROM and stiffness in RAR/LAR and similar stiffness in extension. C2SPED-C3LM demonstrated significantly greater atlantoaxial stabilization in the sagittal and coronal planes compared to C2PED construct.

CONCLUSIONS: Compared to C2PED, C2SPED-C3LM may be a suitable alternative surgical strategy for atlantoaxial instability that provides superior atlantoaxial fixation.

LEVEL OF EVIDENCE: N/A.