Biomechanics of stabilization after cervicothoracic compression-flexion injury.

STUDY DESIGN

Biomechanical laboratory research.

OBJECTIVE

To determine whether anterior, posterior, or combined instrumentation provides the best stability for treating a cervicothoracic compression-flexion injury.

SUMMARY OF BACKGROUND DATA

As the junction between the mobile cervical spine and rigid thoracic spine, the cervicothoracic junction poses unique challenges to the success of any fixation system spanning this region. Although posterior instrumentation is the preferred method of fixation in the unstable cervical spine, it is unknown whether this is the case across the unstable cervicothoracic junction.

METHODS

Flexion, extension, lateral bending, and axial rotation of cadaveric specimens were studied during application of nondestructive pure moments in a sequence of conditions: (1) intact, (2) after destabilization, (3) with posterior instrumentation from C6-T1 or T2, and (4) with corpectomy/graft and anterior alone or combined anterior/posterior instrumentation.

RESULTS

Compared to anterior instrumentation, posterior instrumentation allowed an 89% smaller range of motion (ROM) during lateral bending (P = 0.01) and 64% smaller ROM during axial rotation (P = 0.04). In most loading modes, combined instrumentation outperformed either anterior or posterior instrumentation alone. Most biomechanical measurements of stability improved when posterior instrumentation was extended from T1 to T2. Small and usually insignificant reductions in ROM averaging 15% were observed with C7 included in the posterior construct versus C7 excluded.

CONCLUSIONS

Combined instrumentation provides a significant improvement in stability over either anterior or posterior instrumentation alone. Extension of the posterior instrumentation to include T2 improves stability at T1-T2 as well as rostral levels. Inclusion of C7 in the construct is largely inconsequential biomechanically.