The following is a summary of “Biomechanical Analysis of Multilevel Posterior Cervical Spinal Fusion Constructs,” published in the June 2023 issue of Clinical Spine Surgery by Murphy et al.
The study design used was a Laboratory Controlled Study. The objective is to compare multilevel posterior cervical fusion (PCF) constructs stopping at C7, T1, and T2 to ascertain the range of motion (ROM) between the lowest instrumented level and lowest instrumented-adjacent level (LIV-1). According to a summary of relevant background data, PCF is a mainstay treatment for various cervical spine disorders. At the cervicothoracic junction, the transition between the malleable cervical spine and rigid thoracic spine can result in structural failure. There is insufficient evidence to determine the optimal level to terminate a multilevel PCF. Fifteen cadaveric human cervicothoracic spines were assigned randomly to one of three treatment groups: PCF halting at C7, T1, or T2.
The specimens were evaluated in their native state after a PCF simulation and cyclic loading. The samples underwent flexion extension, lateral bending, and axial rotation loading. To evaluate ROM, three-dimensional kinematics were recorded. Following instrumentation (10.1±70.83 degrees vs. 2.77±1.66 degrees and 1.06±0.55 degrees, P<0.001) and cyclic loading (10.42±2.30 degrees vs. 2.47±0.64 degrees and 1.99±1.25 degrees, P<0.001), the C7 group demonstrated more excellent flexion-extension motion than the T1 and T2 groups. No difference between the T1 and T2 groups was statistically significant.
After instrumentation and cyclic loading, the C7 group had more excellent lateral bending ROM than both thoracic groups (8.81±3.44 degrees vs. 3.51±2.51 degrees and 1.99±1.99 degrees, P=0.013 and 0.003, respectively). Following cyclic loading, the C7 group exhibited more excellent axial rotation motion than the thoracic groups (4.462.27 degrees vs. 1.260.69 degrees, P=0.010; and 0.73±0.73 degrees, P=0.003). Motion at the cervicothoracic junction is substantially more significant when a multilevel PCF terminates at C7 instead of T1 or T2. This is most likely due to the change from a flexible cervical spine to a rigid thoracic spine. Even though this does not account for in vivo fusion, surgeons should contemplate extending multilevel PCF constructs to T1 whenever possible.
