4- And 5-Level Anterior Fusions Of The Cervical Spine

Performing arthrodesis on four or five levels in the cervical spine is an infrequent surgical procedure, even in high-volume spine centers. Currently, multilevel discectomies and corpectomies are typically only necessary for the treatment of degenerative conditions, post-traumatic or post-surgical deformities, and instability related to neoplasms.

In such cases, the prevalence of diffuse spinal canal constriction and kyphosis is high, and the viable surgical alternatives are mainly anterior. Re-establishing cervical lordosis may be advantageous in terms of neurological recovery and clinical outcomes.

The biomechanical basis for successful multilevel anterior cervical procedures should be highlighted in light of the results and challenges associated with 4- and 5-level cervical fusions. Literature has raised concerns about the limitations of graft, cage, and plate failures, especially in multilevel corpectomies, despite the use of plates with rigid screw-plate locking mechanisms.

Confirmed complications associated with multilevel strut grafting and end-construct plate fixation without posterior fixation include dislodgement or loosening of the graft, cage, or plate at screw-plate or screw-bone interfaces, postsurgical kyphosis, and pseudoarthrosis.

As the number of decompressed levels increased, there was an increase in the rate of failures. Some of the possible outcomes include injury to the vascular system, esophagus, or nerves. A direct relationship has been observed between the mechanical stability of the fusion construct and the fusion rates in the spine.

The hybrid technique is a solution to this concern in multilevel procedures. A successful alternative to multilevel corpectomies for patients requiring decompression and fusion at three or more levels is to perform discontinuous corpectomies combined with adjacent-level discectomy while retaining the intervening body.

This approach has been effective in avoiding plate loosening or graft migration. The hybrid technique enhances the natural mechanical stability of the construct, aids in correcting kyphotic deformity, preserves the reconstructed alignment, and reduces the risk of deterioration at the screw-bone interface. The use of hybrid or continuous ACDF techniques increases the number of graft/bone interfaces that need to undergo osseous union compared to long interbody grafts and cages.

The stability of the spine that is achieved with an anterior cervical screw-plate system depends on several factors such as the plate design, the quality of bone-screw and plate-screw interfaces, the diameter and depth of the major screw, and the density of the bone. A larger and longer screw placement can enhance the initial stability of cervical osteosynthesis, as observed in our patients.

Screw toggling refers to a phenomenon where forces from non-fixed cantilever beam screws cause damage to both the bone and the screw-bone interface. The screw can move and come into contact with the interface between the bone graft and plate, which can reduce the contact surface and potentially decrease the likelihood of achieving a solid fusion.

Currently, clinical failures of constrained anterior cervical plates (with or without dynamic features) are typically not due to implant breakage or bending, but rather at the interface between the bone and instrumentation.

Loosening of screws in the CS-plate may occur due to the implant’s rigid long fixed-moment arm cantilever beam, which may not provide sufficient resistance to translational forces, resulting in the deterioration of the screw-bone interface and eventual failure.

The longer the implant, the more susceptible it is to these effects. To enhance resistance against axial and translational loads, additional points of fixation can be incorporated, as is the case with the hybrid technique or by using posterior fixation.

In terms of maintaining reconstructed lordosis and construct rigidity, CS plate systems are generally more effective than NC-ones. When 360 stabilization techniques are utilized in testing or measuring, there is a high level of certainty, especially in cases where long corpectomies are performed.

In such cases, it has been demonstrated that posterior stabilization on its own is more effective than anteriorly plated reconstructions. The combination of the hybrid technique and multilevel ACDF can provide ample decompression even in cases of significant cervical stenosis. This approach also reduces the number of corpectomy levels needed, consequently decreasing the requirement for posterior support.

Influence Of Cervical Lordosis

The sagittal plane neutral geometry of the cervical spine is crucial to maintaining an upright posture with minimal muscular effort. However, cervical kyphosis (CK) can cause overload of the anterior parts of the spine and result in painful attenuation of the posterior ligaments and facet capsules, muscle fatigue, and imbalance.

Failed surgical restoration of lordosis is one of the main causes of CK. Although a ‘normal’ or ‘pathological’ cervical curvature has not been defined, it is essential to restore a lordotic curvature to balance the sagittal profile and prevent further kyphosis.

Hybrid and ACDF techniques are useful in the reconstruction of cervical lordosis. The segmental distraction and lordotic restoration obtained using wedged interbody grafts/cages with ACPS are useful in foraminal and central decompression as the cord slightly shifts posteriorly, away from mainly anteriorly situated stenosis. Mean correction in patients with 2- and 3-level corpectomies was 6.8 in the series.

Adjacent Disc Degeneration

The impingement of adjacent-level ACPs during primary and secondary migration can lead to adjacent-level pathology and implant loosening, causing changes in construct geometry.

Although symptomatic secondary plate impingement is observed only once in a series of patients, its incidence should be prevented by enhanced constructed rigidity. Symptomatic adjacent-level pathology after ACDF is reviewed as high as 15%. The progression of ADD also seems to reflect the normal course of adjacent levels not included in the fusion construct at the index procedure.

If there is sufficient TCL and lordosis at the fusion block with an anteriorly located stenosis accompanying ADD, the authors currently recommend implant removal and ACDF at the involved segment. In case of ADD, particularly at the CTJ, 360 stabilization should be considered to prevent construct failure due to the long lever-arm resulting from the preexisting cephalad fusion block.

Clinical Failures In Multilevel Anterior Cervical Constructs

The clinical outcomes of multilevel cervical anterior fusion vary and there is a lack of details on the number of instrumented vertebrae, decompressed levels, and the usage of the Halo. Anecdotal reports of construct failures in multilevel corpectomies with stand-alone strut grafts have been reviewed as high as 10-50%. Studies suggest that anterior devices in multilevel fusions and corpectomy cases should be supported by posterior stabilization, particularly pedicle screw fixation.

However, added posterior stabilization comes with added risks, particularly in elderly and frail patients, such as a higher rate of infection, surgical morbidity, increased hospital stay, myofascial pain, and axial neck pain. Added stabilization with circumferential instrumentation of plated multilevel discectomies and corpectomies can improve outcomes.

Clinical Outcome And Surgical Complications

Surgical complications for 4- and 5-level anterior fusions are comparable and even lower than what is reported in the literature. Temporary dysphagia is observed in 17.6% and transient hoarseness in 11.8% of patients.

The incidence of RLN symptoms is the highest with 9.5% in anterior redo surgeries. No serious complications such as dural, neural, esophageal, or vertebral artery injury are observed. The majority of patients show good or excellent outcomes following an average follow-up of 27.4 months. Loss of cervical motion is not a significant concern, and the evidence of PACS has no adverse effect on clinical outcomes.

The majority of patients show a lordotic cervical posture at follow-up, and reconstruction of cervical lordosis is favorable. However, further investigation is needed to determine the amount of lordosis that needs to be reconstructed and the cut-offs below which clinical outcomes decrease.

If a comprehensive approach including complete decompression, distraction, grafting, reconstruction of a cervical posture with lordosis, and the use of anterior cervical plating system is implemented, it is possible to attain favorable clinical outcomes in multilevel ACDF procedures.

Constrained plates within ACPS provide greater stability to the structure compared to non-constrained plates. It is advisable to plan for early stabilization and fusion with 360-degree coverage, such as after corpectomies involving more than two levels.

Based on the risks associated with using current anterior non-locking and locking plate systems to stabilize multilevel corpectomies in the cervical spine, it is necessary to develop stronger anterior fixation devices that can eliminate the need for posterior supplemental fusion in highly unstable multilevel decompressions.

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