The stabilizing potential of anterior, posterior and combined techniques for the reconstruction of a 2-level cervical corpectomy model: biomechanical study and first results of ATPS prototyping

Abstract

Clinical studies reported frequent failure with anterior instrumented multilevel cervical corpectomies. Hence, posterior augmentation was recommended but necessitates a second approach. Thus, an author group evaluated the feasibility, pull-out characteristics, and accuracy of anterior transpedicular screw (ATPS) fixation. Although first success with clinical application of ATPS has already been reported, no data exist on biomechanical characteristics of an ATPS-plate system enabling transpedicular end-level fixation in advanced instabilities. Therefore, we evaluated biomechanical qualities of an ATPS prototype C4-C7 for reduction of range of motion (ROM) and primary stability in a non-destructive setup among five constructs: anterior plate, posterior all-lateral mass screw construct, posterior construct with lateral mass screws C5 ? C6 and end-level fixation using pedicle screws unilaterally or bilaterally, and a 360°construct. 12 human spines C3-T1 were divided into two groups. Four constructs were tested in group 1 and three in group 2; the ATPS prototypes were tested in both groups. Specimens were subjected to flexibility test in a spine motion tester at intact state and after 2-level corpectomy C5-C6 with subsequent reconstruction using a distractable cage and one of the osteosynthesis mentioned above. ROM in flexionextension, axial rotation, and lateral bending was reported as normalized values. All instrumentations but the anterior plate showed significant reduction of ROM for all directions compared to the intact state. The 360°construct outperformed all others in terms of reducing ROM. While there were no significant differences between the 360°a nd posterior constructs in flexion-extension and lateral bending, the 360°constructs were significantly more stable in axial rotation. Concerning primary stability of ATPS prototypes, there were no significant differences compared to posterior-only constructs in flexion-extension and axial rotation. The 360°construct showed significant differences to the ATPS prototypes in flexionextension, while no significant differences existed in axial rotation. But in lateral bending, the ATPS prototype and the anterior plate performed significantly worse than the posterior constructs. ATPS was shown to confer increased primary stability compared to the anterior plate in flexion-extension and axial rotation with the latter yielding significance. We showed that primary stability after 2-level corpectomy reconstruction using ATPS prototypes compared favorably to posterior systems and superior to anterior plates. From the biomechanical point, the 360°i nstrumentation was shown the most efficient for reconstruction of 2-level corpectomies. Further studies will elucidate whether fatigue testing will enhance the benefit of transpedicular anchorage with posterior constructs and ATPS.

Zero-profile hybrid fusion construct versus 2-level plate fixation to treat adjacent-level disease in the cervical spine

“…5 It is also possible that a rigid ACP will less effectively resist LB and AR compared with FE, as has been shown in other studies. 7,10,23,35 The trend found that the ZPD may more effectively reduce motion in AR, and LB may be concordant with the kinematics of a rigid anterior device. The fixation point of the ZPD is closer to the operated segment's native instantaneous axis of rotation, which may reduce the lever arm and, therefore, bending moment experienced by the dorsal elements with the 2-level ACP.…”

“…The fixation point of the ZPD is closer to the operated segment's native instantaneous axis of rotation, which may reduce the lever arm and, therefore, bending moment experienced by the dorsal elements with the 2-level ACP. 5 These attributes of ACP fixation are more apparent in 2-and 3-column injuries 23 and multilevel corpectomies 7 ; however, the same principles likely contribute to the nonstatistically significant differences observed herein.…”

Anterior transpedicular screw fixation of cervical spine: Is it safe? Morphological feasibility, technical properties, and accuracy of manual insertion

“…Although, unilateral screw placement may be associated with low biomechanical quality, Koller et al showed that unilateral cervical pedicle screw fixation was sufficient to maintain a primary stability when compared with bilateral pedicle anchorage, even in advanced instabilities. 20 Second, the high pedicle breach rate in this study (23%) remains a concern with respect to the use of fluoroscopic guidance as an adjunctive technique for ATPS placement. Therefore we strongly recommend the use of intraoperative CT navigation systems, which help to determine the screw length and trajectory, especially at the levels of C-3, C-4, and C-5.…”

“…19,20,33 Therefore, tumor-or trauma-related 3-column instability and multilevel corpectomies (2 or more levels) for degenerative and infection diseases, which call for combined anteroposterior stabilization, would be the clinical indications for this technique.…”

“…in posterior approaches. 20,36 Additionally, ATPS fixation may avoid the need for postoperative rigid cervical orthoses such as the halo vest fixation device or sterno-occipito-mandibular immobilization (SOMI) device in patients treated with multilevel corpectomy.…”