Anterior cervical discectomy and fusion (ACDF) is among the most commonly performed and most successful procedures in spine surgery. But like any fusion, it has a known long-term consequence: the segments directly above and below the fused level are exposed to increased mechanical stress, and over years to decades, a portion of patients develop symptomatic degeneration at those adjacent levels — a phenomenon called adjacent segment disease.
When adjacent segment disease develops after a prior ACDF, the conventional approach has been to fuse the new symptomatic level as well, extending the construct by one segment. This is often the right answer. But for selected patients, there is another option: placing a cervical disc replacement at the new symptomatic level adjacent to the prior fusion — the hybrid construct.
What the Hybrid Construct Is
A hybrid cervical construct combines an existing fusion at one level with a disc replacement at an adjacent level. For example, a patient who had a C5–6 ACDF and now has symptomatic C4–5 disc disease might have a cervical disc replacement placed at C4–5, immediately above the prior fusion. The result is a construct that addresses both levels — one fused, one replaced — without extending the fusion.
The appeal of this approach is conceptually straightforward: every additional fused level further concentrates mechanical load on the remaining mobile segments. A disc replacement at the new symptomatic level preserves motion there and avoids adding another fixed point to an already-constrained cervical spine.
What the Evidence Shows
The hybrid construct for adjacent segment disease after ACDF is not experimental — it is a well-described technique with published outcomes data at mid-term follow-up. Studies examining hybrid constructs in this setting have generally found:
- Arm pain relief and neurological recovery comparable to extending the fusion
- Preserved motion at the disc replacement level confirmed on long-term imaging
- No evidence of increased complication rates compared to extension ACDF in matched cohorts
Dr. Sardar co-authored a national database analysis examining the short-term complication profile and readmission rates of hybrid anterior cervical constructs compared to ACDF extension, published in Global Spine Journal in 2021.
Clinical reference: Boddapati V, Lee NJ, Mathew J, et al., Sardar ZM, Lehman RA, Riew KD. Hybrid Anterior Cervical Discectomy and Fusion and Cervical Disc Arthroplasty: An Analysis of Short-Term Complications, Reoperations, and Readmissions. Global Spine J. 2021;11(8):1183–1189. PMID 32705903 — Dr. Sardar co-authored this national analysis of hybrid cervical construct outcomes.
Who Is a Candidate for the Hybrid Approach
Candidacy for a hybrid construct requires that the new symptomatic level independently meets the criteria for cervical disc replacement — most importantly, that the facet joints at that level are healthy enough to tolerate preserved motion. The key assessment points are:
- Facet joint health at the new symptomatic level. This is the primary gate. Arthritis in the facets at the adjacent level is a contraindication to disc replacement there, and the hybrid construct would not be appropriate.
- Cervical alignment. Preserved lordosis at the adjacent level is required for disc replacement candidacy, just as in any other cervical disc replacement situation.
- The prior fusion construct. The existing fusion must be solid and stable. Hardware loosening, pseudarthrosis at the prior level, or adjacent segment instability at the planned disc replacement level need to be assessed and excluded.
- Overall cervical alignment. The geometry of the combined construct — fused segment plus disc replacement — must be evaluated preoperatively to ensure the planned approach produces a biomechanically reasonable result.
When Extension Fusion Is the Right Answer Instead
The hybrid construct is not appropriate for every patient with adjacent segment disease after ACDF. Extension fusion remains the correct answer when:
- Significant facet arthritis is present at the adjacent level
- Cervical kyphosis or instability is present at the adjacent level
- The adjacent segment disease involves multiple new levels
- Myelopathy requiring posterior decompression is the primary indication
The decision between the hybrid construct and extension fusion requires detailed imaging review and clinical judgment. It is exactly the type of decision that benefits from evaluation by a surgeon with specific disc replacement training and experience — because the surgeon who does not offer disc replacement cannot assess hybrid candidacy accurately.
For more on cervical disc replacement candidacy, see the full Cervical Disc Replacement page. For context on adjacent segment disease and revision surgery more broadly, see Complex Revision Spine Surgery.
About Dr. Zeeshan Sardar
Dr. Sardar, MD, MSc, F.R.C.S.C, is Co-Chief of Spinal Deformity Surgery at NewYork-Presbyterian / Columbia University. He completed a dedicated fellowship in artificial disc replacement at the Texas Back Institute and evaluates patients with adjacent segment disease after prior ACDF for both hybrid construct and extension fusion candidacy. To schedule a consultation, call 212-932-5187 or visit the contact page. Telemedicine available in NY, NJ, CT, FL, PA, MO, CA, and TX.
This post is for educational purposes only and does not constitute individualized medical advice. Please consult a qualified spine specialist to discuss your specific situation.