Biomechanical Comparison of Instrumented and Uninstrumented Multilevel Cervical Discectomy Versus Corpectomy

STUDY DESIGN: In vitro flexibility test comparing biomechanics of cervical corpectomy versus discectomy with and without instrumentation. OBJECTIVES: To evaluate whether the additional effort required to perform multilevel discectomies instead of corpectomies is worthwhile biomechanically. SUMMARY OF BACKGROUND DATA: Both cervical corpectomy and discectomy have been shown to be effective clinically. No previous biomechanical comparison exists. METHODS: Fourteen human cadaveric cervical spines were studied: 1) intact, 2) after discectomy and wedge grafting at C4-C5, C5-C6, and C6-C7 (Group 1) or corpectomy and strut grafting of C5 and C6 (Group 2), 3) after attaching a locking metal plate from C4-C7, and 4) after adding posterior locking lateral mass screw/rod instrumentation across C4-C7. Non-constraining, nondestructive torques induced flexion, extension, lateral bending, and axial rotation (maximum, 1.5 Nm) while angular motion was measured stereophotogrammetrically. RESULTS: Discectomy and grafting did not alter the range of motion (ROM) significantly from normal during any loading mode (P > 0.11). Corpectomy and grafting allowed a significantly greater range of motion than normal during flexion, lateral bending, and axial rotation (P < 0.05). Addition of an anterior plate reduced ROM to significantly less than normal during all loading modes in both groups (P < 0.005). Addition of posterior instrumentation further reduced ROM significantly in both groups (P < 0.01). There was no significant difference in ROM between corpectomy and discectomy groups in any loading mode whether uninstrumented (P > 0.18), anteriorly plated (P > 0.33), or anteriorly and posteriorly instrumented (P > 0.30). CONCLUSIONS: Less difference in stability was observed than was predicted between specimens receiving multilevel discectomy versus multilevel corpectomy, regardless of whether specimens were left unplated, plated anteriorly, or fixated with combined anterior/posterior instrumentation.