Biomechanics of Circumferential Cervical Fixation Using Posterior Facet Cages: A Cadaveric Study

Abstract

Objective: Anterior cervical discectomy and fusion (ACDF) is a common procedure for the treatment of cervical disease. Circumferential procedures are options for multilevel pathology. Potential complications of multilevel anterior procedures are dysphagia and pseudarthrosis, whereas potential complications of posterior surgery include development of cervical kyphosis and postoperative chronic neck pain. The addition of posterior cervical cages (PCCs) to multilevel ACDF is a minimally invasive option to perform circumferential fusion. This study evaluated the biomechanical performance of 3-level circumferential fusion with PCCs as supplemental fixation to anteriorly placed allografts, with and without anterior plate fixation.

Methods: Nondestructive flexibility tests (1.5 Nm) performed on 6 cervical C2-7 cadaveric specimens intact and after discectomy (C3-6) in 3 instrumented conditions: allograft with anterior plate (G+P), PCC with allograft and plate (PCC+G+P), and PCC with allograft alone (PCC+G). Range of motion (ROM) data were analyzed using 1-way repeated-measures analysis of variance.

Results: All instrumented conditions resulted in significantly reduced ROM at the 3 instrumented levels (C3-6) compared to intact spinal segments in flexion, extension, lateral bending, and axial rotation (p < 0.001). No significant difference in ROM was found between G+P and PCC+G+P conditions or between G+P and PCC+G conditions, indicating similar stability between these conditions in all directions of motion.

Conclusion: All instrumented conditions resulted in considerable reduction in ROM. The added reduction in ROM through the addition of PCCs did not reach statistical significance. Circumferential fusion with anterior allograft, without plate and with PCCs, has comparable stability to ACDF with allograft and plate.

Keywords: Allografts; Cadaver; Diskectomy; Range of motion; Rotation; Spine.

Fig. 1.

Radiographic images of the 4 spinal conditions studied: (A) intact spine; (B) spine after C3–6 anterior cervical discectomy with allograft spacers and 3-level anterior cervical plate (G+P); (C) lateral view of the spine after C3–6 anterior cervical discectomy with posterior cervical cages, allograft spacers, and plate (PCC+G+P); and (D) spine with posterior cervical cages and allograft spacers after anterior plate removal (PCC+G).

Fig. 2.

Test setup. Photograph of a cervical test specimen mounted in a gantry-style 6-degree-of-freedom robotically controlled test system with real-time load control. Specimens were tested multidirectionally under continuously applied pure moment loads at a global rotation rate of 1.7° per second. Optical LED markers were attached to Kirschner wires secured into each vertebral body to record vertebral body movement.

Fig. 3.

Mean cervical range of motion at each cervical level for each of the 4 spinal conditions tested: (A) flexion, (B) extension, (C) pooled left-right lateral bending, and (D) pooled left-right axial rotation. Error bars indicate one standard deviation. *Significant difference compared to the intact condition (p < 0.001). **Significant difference at C4–5 in extension between posterior cervical cages with allograft (PCC+G) and posterior cervical cages, allograft spacers, and plate (PCC+G+P) (p = 0.02). ROM, range of motion; PCC, posterior cervical cage.