by Elizabeth Hofheinz, M.P.H., M.Ed.
How far can you stretch indications before they “break?” A team of researchers has delved into this and more in a new study, “Potential Selection Bias in Observational Studies Comparing Cervical Disc Arthroplasty to Anterior Cervical Discectomy and Fusion.” The work, which appears in the July 15, 2020 edition of Spine.
The authors point to several recently published non-randomized observational studies that seem to be attempting to expand CDA in “…patients with myelopathy, multilevel disease, as part of hybrid constructs combining ACDF and CDA, traumatic disc herniations, and more. Studies that are non-randomized are prone to selection bias and confounding from both measured and unmeasured factors, leading to potentially misleading conclusions.”
Co-author William Ryan Spiker M.D., an orthopedic spine surgeon at the University of Utah in Salt Lake City, told OSN, “We were seeing surgeons stretch the indications for cervical disc arthroplasty and apply data from a very specific cohort that was studied to a much larger group of cervical spine patients. Further, we felt that surgeons were biased by the excellent results that they were seeing in their own disc arthroplasty patients because these were young, healthy individuals that were very likely to do well with either a disc replacement or a fusion.”
Using data from 2004 to 2014 that was part of the Agency for Healthcare Research and Quality’s National Inpatient Sample, the researchers looked at perioperative demographics, comorbidities, complications, and cost. A total of 219,419 procedures were included in the analysis—98.2% ACDF and 1.8% CDA.
“Cost, mortality, and complications were compared between ACDF and CDA cohorts,” say the authors, “using models that adjusted for demographics and comorbidities, as well as ‘naïve’ models that did not.”
The authors wrote, “The naïve logistic regression model showed that hospital costs for CDA were, on average, $549 lower than ACDF. However, in the fully specified model, CDA was $574 more expensive. The naïve model for medical complications suggests a protective advantage for CDA over ACDF. However, this apparent benefit is also attenuated in the fully specified model. Similarly, the risk of in-hospital mortality with CDR relative to ACDF, increased in the fully specified model compared with the naïve model, although it was not statistically significant compared with ACDF in either.”
Dr. Spiker: “I think the most important results are that retrospective studies on disc arthroplasty have to be closely scrutinized to ensure that factors such as age, socioeconomic status, and general health are controlled for.”
“This article supports that while cervical disc arthroplasty is an excellent option for some patients, ACDFs remain an excellent surgical option with very similar costs and outcomes for nearly all patients with cervical radiculopathy.”
Co-author Vadim Goz, M.D. is an orthopedic surgeon at the Reno Orthopedic Clinic in Nevada. “I would add that one aspect that lead to this work is that while the original studies on cervical disc arthroplasty were well done randomized controlled trials on a carefully selected group of patients, subsequent studies on expanded indications were less rigorous in nature. Our study highlights the potential issues with retrospective studies on this topic, which must be considered when investigating any application of cervical disc arthroplasty beyond that which was studied in the original randomized trials.”