Cervical Symptoms Recur after Artificial Disc Replacement
This 48-year-old male patient underwent artificial disc replacement (ADR) at C6-C7 for foraminal stenosis 2 years earlier with another surgeon. His pain was reduced by 50% and he did reasonably well until approximately 6 months ago.
He describes a gradual onset of paresthesias and "buzzing" in the left trapezial region (~80% of his symptoms), right upper neck pain (~20% of his symptoms) that radiates into the right paracervical region with diffuse aching of the mid to inferior axial neck region. Furthermore, he indicates decreased energy and fatigue, and has stopped his P90X workouts (the patient thought the workouts helped reduce symptoms), and reports chronic pain has negatively impacted his enjoyment of life.
Current Pain on Visual Analogue Scale (0 to 10)
- Neck pain is a 3 becoming a 7
- Left trapezial pain is a 2 becoming an 8
There is no myelopathy or radicular symptoms. Pain in the left trapezius worsens with sitting and/or cervical flexion lasting longer than five to 10 minutes. He reports cervical extension is "okay."
AP and lateral radiographic views show ADR failure and inferior endplate erosion (Figures 1, 2).
The inferior endplate of the ADR at C6 is congruent and at 90-degrees. However, the superior endplate of the ADR at C7 has recessed by about 6 to 7 mm leaving a 34-degree angulation between the anterior body and anterior flange of the artificial disc; it should be parallel to the endplate and perpendicular to the anterior edge of the body. The disc subsided into the C7 vertebra causing mechanical failure and foraminal stenosis.
Flexion (Figure 3) and extension (Figure 4) demonstrate little ADR motion.
AP and lateral CT scans demonstrate inferior endplate erosion (Figures 5, 6).
ADR subsidence causing mechanical failure and foraminal stenosis at C6-C7
The patient's pain did not improve with 6 months of conservative treatment that included physical therapy and epidural injections.
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The artificial disc was removed and an anterior cervical discectomy and fusion (ACDF) with iliac crest bone graft was performed to reconstruct the C6-C7 level. The anterior plate had to be placed somewhat skewed as the original C7 screw holes were cavitated due to artificial disc subsidence.
Post-op AP x-ray (Figure 7) shows the plate is slightly askew; due to need for good bone purchase (prior ADR bone screw holes were cavitated).
Post-op lateral x-ray shows the ADR revision into an ACDF (Figure 8).
The patient's post-operative recovery was uneventful. At his 6 month follow-up, he continues to do well.
Dr. Corenman describes an interesting case of a complication from implantation of a Prestige® cervical artificial disc that led to recurrent symptoms, subsidence, and loss of motion. The procedure was salvaged successfully with explantation and interbody fusion.
Several points are worth discussing:
1. Only a 50% reduction in pain after the index procedure is not typical for the outcome for this procedure. To my mind, it suggests inadequate decompression of the uncovertebral joints with persisting stenosis.
2. No x-rays are available immediately after the initial surgery, which was performed elsewhere. The technique necessitates minimal endplate preparation. Subsidence should only occur if the bone quality is poor, excessive endplate resection occurs, or oversizing the implant overloads the interspace. Any or all of these factors would lead to subsidence, loss of motion, and foraminal collapse with focal kyphosis. The x-rays suggest the level has ankylosed.
3. Revision was possible because of the nature of the artificial disc device. Unscrewing the superior and inferior segments allowed easier disarticulation. Devices with rails or keels would necessitate partial or complete corpectomies or explantation.
In short, the author demonstates the perils of poor surgical technique with artificial disc implantation that can lead to radiological and clinical failure. Excessive endplate preparation, potentially oversizing the implant in relation to the interspace, or pre-operative bone quality issues can all lead to endplate failure. Well salvaged.
Thank you Dr. Sekhon for your articulate discussion. I agree that removal of some of the other artificial discs require more work. I have also removed some Synthes® Prodisc-C prostheses, and the ingrowth in these devices is limited. A thin osteotome in the interface between the prosthesis and bone will remove this device without much force. I have not found a corpectomy is necessary. I cannot comment yet on removal of a Bryan® disc.