Rapidly Progressing Cervical Adjacent Segment Disease
A 56-year-old woman presents with a history of worsening neck and left shoulder pain. She has had some relief with C4-C5 epidurals, but her pain has persisted. She has had previous C6-C7 anterior cervical discectomy and fusion (ACDF) with plate in 2002. That was followed by explanation of instrumentation and subsequent C5-C6 ACDF in 2007. All procedures were done in another state.
Patient has increased neck pain with flexion and left lateral bending. Left deltoid is 4+/5. The remainder of her exam is normal.
She has undergone physical therapy (PT) and epidural steroid injections with no long lasting relief.
Well-healed fusions at C5-C6 with plate and C6-C7 without plate. Junctional disease is seen at C4-C5 with spondylosis and bridging osteophyte. There is a significant amount of prevertebral soft tissue at the previous operative sites, even accounting for the esophagus. (Figure 1)
Flexion-extension x-rays that demonstrate mobility at the index level with overriding C4 osteophyte. There is no movement at the previously-treated levels although interbody graft appears to have caused some osteolysis of the superior endplate of C6. (Figure 2)
T2 axial MRI that shows significant neural foraminal narrowing from spondylosis. (Figure 3)
The patient was diagnosed with junctional segment disease with C4-C5 spondylosis and anterior spur.
Her current plate position illustrates the problem of using long constructs in the cervical spine. The altered biomechanics of the plate buttressing an otherwise healthy disc, combined with the long moment arm from the two-level fusion below, may have accelerated the adjacent segment disease.
The current trend seems to be using as short a plate as possible or internal plated devices.
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The patient underwent C4-C5 ACDF with integrated plate and spacer filled with calcium-phosphate ceramic bone graft with bone marrow aspirate.
The implant I elected to use has variable angle screws. The single screw up and down allowed greater flexibility in placing this kind of implant. Similar systems have more screws or locking cams that could not have been deployed in this case.
Post-op anteroposterior (AP) films demonstrate well-placed graft. Note that the inferior screw does not contact the existing instrumentation. (Figure 4)
The superior screw was intentionally inserted at a shallow angle to better capture the cortical endplate. Both screws could have been longer to afford bicortical purchase. (Figure 5)
The patient noted marked improvement in her radiculopathy and mechanical neck pain post-op. Follow-up at 1 year shows solid fusion and no further degeneration. The C3-C4 level remains disease free.
The author utilized a relatively new type of instrumentation that is all intradiscal. These devices have advantages over the standard plating systems under several circumstances. Examples include cases in which a patient has a long plate with an adjacent-level disc herniation. Rather than remove the long plate, one can simply place one of these devices at the adjacent level. Another indication is at the upper cervical levels, where the no-profile nature of these devices have an advantage over a traditional plate.
There are also disadvantages to these types of devices. First, it is difficult to implant these devices at the extreme ends of the cervical spine (eg, C2-C3 or C7-T1). This is because the screws have to be angled away from the disc space. For example at C2-C3, angling the C3 screw caudally or at C7-T1, angling the C7 screw cranially may be quite challenging. Even with extensive soft tissue dissection, the jaw at C2-C3 and the clavicle at C7-T1 can interfere with drilling and screwing at these levels. Although the manufacturers of these devices have angled drills and screw drivers that can help facilitate this, it can nevertheless remain challenging and sometimes impossible.
A second disadvantage is that the cage portion of the device is made of PEEK, which is hydrophobic and will never bond to bone. Therefore, to achieve a solid fusion, one has to select a filler that has a high likelihood of fusing. While the author states that the use of a ceramic filler with bone marrow aspirate achieved a solid fusion at 1 year, there are no studies that I am aware of that has examined the success rate of such a combination for these devices. It would be helpful to see the 1 year post-operative dynamic x-rays to verify the fusion.
Author's Concluding Comments
Dr. Riew describes well the limitations of this technology. It is often touted as a viable alternative to removing hardware. However, in reality removing a typical plate with anteriorly directed screws is typically less challenging than matching the appropriate angles of these devices at either end of the exposure.
Additionally the lumen of these devices is restricted by the indwelling screw. Consequently the fusion mass is quite small as evidenced by the follow-up imaging.