Clinical implications for spine patients not clear
A complete explanation of adjacent-segment degenerative disk disease and the impact of surgical fusion remains elusive. Although some patients develop symptomatic degenerative disease at levels adjacent to fusions, the effects of the fusion itself and the underlying degenerative disease are difficult to separate as factors.
A study in the July 6 Journal of Bone and Joint Surgery–American may provide some clarity. The retrospective analysis involving 46 patients who had undergone either a Bryan total disk arthroplasty (TDA) or an arthrodesis found that, at 2 years and 4 years after surgery, patients who had undergone plated anterior cervical diskectomy fusion had a significant increase in the prevalence and severity of adjacent-level ossification compared with those who had undergone TDA.
The Level III study, “Adjacent-level Cervical Ossification After Bryan Cervical Disc Arthroplasty Compared with Anterior Cervical Discectomy and Fusion,” authored by Ben J. Garrido, MD, and colleagues, does not shed new light on the causes of adjacent-segment disease nor does it elucidate the clinical implication of the radiographic findings. It is nonetheless “compelling” in demonstrating a disease correlation with fusion, according to Robert A. Hart, MD, MA, associate professor at Oregon Health & Science University, whose commentary on the article appears in the online edition of the journal.
The patients, all treated at one center, had been included in a Level I original study seeking to assess clinical outcomes; in this analysis, the authors compared the radiographic severity of adjacent-level ossification development in the two treatment arms.
The two types of treatment were almost evenly distributed (21 TDA; 25 arthrodesis). All the patients had single-level cervical spine disease at C3 through C7 with radiculopathy or myelopathy; at least 6 weeks of nonsurgical treatment had been unsuccessful. Patients were excluded if they exhibited notable anatomic abnormalities, identified as an angular deformity of greater than 11 degrees, translation of greater than 3 mm, and/or evidence of advanced spondylosis or previous adjacent-level ossification development on cervical radiograph. Two spine fellows and an experienced spine surgeon independently reviewed the lateral images, on which the single surgical level was blacked out so that observers could not tell whether the patient had been managed with arthroplasty or fusion (Fig 1). Preoperatively, ossification development was not different between groups and patients were not subjected to any intervention to avoid it.
By the ossification classification system used, Grade 1 is characterized by ossification occupying less than 50 percent of the adjacent disc space height, Grade 2 is ossification extending beyond 50 percent, and Grade 3 is 100 percent bridging of the space with bone (Fig 2).
Two- and four-year follow-up median scores were determined for both cohorts. In the arthrodesis group, the scores were significantly higher after both 2 years (p = 0.003) and 4 years (p = 0.004). Both cohorts showed significant increases in ossification from the 2-year follow-up to the 4-year follow-up (p = 0.001 for the arthrodesis group, p = 0.008 for the arthroplasty group). In the fusion group, 9 patients (36 percent) had no ossification at 2 years and 4 patients (16 percent) had no ossification at 4 years. Among the arthroplasty patients, 16 (76 percent) had no ossification at 2 years and 10 (48 percent) had none at 4 years. Six of the fusion patients had a plate-to-disk level of less than 5 mm; only three developed adjacent-level ossification.
Whether these findings will continue over the long term is unknown, although a previous study on the timing of adjacent-level ossification development demonstrated that adjacent-level ossification was unlikely to occur beyond 12 to 24 months after surgery.
The limitations of the study include the small number of patients, the subjective rating of adjacent-level ossification development, and the use of only one arthroplasty device. The authors also note that the impact of adjacent-level ossification on clinical symptoms and long-term outcomes is controversial. And the findings of this study do not necessarily isolate the degree to which arthrodesis is a causative factor.
“Cervical spondylosis adjacent to fused segments is likely multifactorial, being both genetically predetermined as part of a degenerative cascade and iatrogenically altered through arthrodesis of normal motion segments,” the authors write.
In his commentary, Dr. Hart concludes that the study “contributes in a meaningful way” to the discussion of this subject. “The authors can fairly conclude that there is an increased rate and severity of adjacent-level ossification development among patients managed with anterior cervical diskectomy and fusion as opposed to total disk replacement.”
“The authors do not overstate the conclusions that their work produces,” continues Dr. Hart. “The results lend further support to the argument that cervical total disk replacement may reduce the prevalence of adjacent-segment disease compared with anterior cervical diskectomy and fusion.” He hopes that the study will lead to increased acceptance of arthroplasty.
Dr. Garrido’s coauthors are Jon Wilhite, MD; Masato Nakano, MD; Charles Crawford, MD; Christine Baldus, RN, MHS; K. Daniel Riew, MD; and Rick C. Sasso, MD.
Disclosure information: Dr. Riew—Biomet, Medtronic, Amedica, Benvenue, Expanding Orthopedics, Nexgen, Osprey, Paradigm Spine, PSD, Spinal Kinetics, Spineology, Vertiflex, Journal of Bone and Joint Surgery–American, Spine; Dr. Sasso—Medtronic, Biomet, Cerapedics, Smith & Nephew, Stryker, Elsevier, Journal of Spinal Disorders and Technique, Spine, Arthroplasty; Dr. Hart—SeaSpine, Dupuy, Medtronic, Synthes, Spine, AAOS, American Orthopaedic Association, Cervical Spine Research Society, Lumbar Spine Research Society, North American Spine Society, Oregon Association of Orthopaedics, Orthopaedic Research and Education Foundation, Scoliosis Research Society. The remaining authors reported no conflicts.
Terry Stanton is senior science writer for AAOS Now. He can be reached at firstname.lastname@example.org
- The phenomenon of adjacent-segment degenerative disease is not fully understood.
- Cervical fusion has previously been associated with adjacent-segment disease but not isolated as a factor.
- This study of 46 patients demonstrated greater prevalence and severity of disease in patients who underwent fusion versus those who underwent arthroplasty.
- The clinical significance of the findings is not known.
- Long-term, multicenter studies are needed to determine whether the observed differences in this study should guide decisions on the use of anterior cervical surgical procedures to treat degenerative disk disease.