Establishing the minimum clinically important difference in Neck Disability Index and modified Japanese Orthopaedic Association scores for adult cervical deformity

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  • 1 Department of Orthopaedic Surgery, University of Calgary, Alberta, Canada;
  • 2 Department of Neurosurgery, University of Virginia Health System, Charlottesville, Virginia;
  • 3 Department of Neurological Surgery, University of California, San Francisco, California;
  • 4 Department of Orthopaedic Surgery, Washington University, St. Louis, Missouri;
  • 5 Department of Orthopaedic Surgery, New York University, New York, New York;
  • 6 Department of Orthopaedic Surgery, Norton Leatherman Spine Center, Louisville, Kentucky;
  • 7 Department of Orthopaedic Surgery, Hospital for Special Surgery, New York, New York;
  • 8 Department of Orthopaedic Surgery, Scripps, San Diego, California;
  • 9 Department of Orthopaedic Surgery, University of California, Davis, Sacramento, California;
  • 10 Department of Orthopaedic Surgery, University of Kansas, Kansas City, Kansas; and
  • 11 Department of Orthopaedic Surgery, Denver International Spine Center, Denver, Colorado
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OBJECTIVE

It is being increasingly recognized that adult cervical deformity (ACD) is correlated with significant pain, myelopathy, and disability, and that patients who undergo deformity correction gain significant benefit. However, there are no defined thresholds of minimum clinically important difference (MCID) in Neck Disability Index (NDI) and modified Japanese Orthopaedic Association (mJOA) scores.

METHODS

Patients of interest were consecutive patients with ACD who underwent cervical deformity correction. ACD was defined as C2–7 sagittal Cobb angle ≥ 10° (kyphosis), C2–7 coronal Cobb angle ≥ 10° (cervical scoliosis), C2–7 sagittal vertical axis ≥ 4 cm, and/or chin-brow vertical angle ≥ 25°. Data were obtained from a consecutive cohort of patients from a multiinstitutional prospective database maintained across 13 sites. Distribution-based MCID, anchor-based MCID, and minimally detectable measurement difference (MDMD) were calculated.

RESULTS

A total of 73 patients met inclusion criteria and had sufficient 1-year follow-up. In the cohort, 42 patients (57.5%) were female. The mean age at the time of surgery was 62.23 years, and average body mass index was 29.28. The mean preoperative NDI was 46.49 and mJOA was 13.17. There was significant improvement in NDI at 1 year (46.49 vs 37.04; p = 0.0001). There was no significant difference in preoperative and 1-year mJOA (13.17 vs 13.7; p = 0.12). Using multiple techniques to yield MCID thresholds specific to the ACD population, the authors obtained values of 5.42 to 7.48 for the NDI, and 1.00 to 1.39 for the mJOA. The MDMD was 6.4 for the NDI, and 1.8 for the mJOA. Therefore, based on their results, the authors recommend using an MCID threshold of 1.8 for the mJOA, and 7.0 for the NDI in patients with ACD.

CONCLUSIONS

The ACD-specific MCID thresholds for NDI and mJOA are similar to the reported MCID following surgery for degenerative cervical disease. Additional studies are needed to verify these findings. Nonetheless, the findings here will be useful for future studies evaluating the success of surgery for patients with ACD undergoing deformity correction.

ABBREVIATIONS ACD = adult cervical deformity; ASD = adult spinal deformity; EQ-VAS = EQ visual analog scale; MCID = minimum clinically important difference; MDMD = minimally detectable measurement difference; mJOA = modified Japanese Orthopaedic Association; NDI = Neck Disability Index; PRO = patient-reported outcome; ROC = receiver operating characteristic; SEM = standard error of measurement.

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Contributor Notes

Correspondence Darryl Lau: University of California, San Francisco, CA. darryl.lau@ucsf.edu.

INCLUDE WHEN CITING Published online May 29, 2020; DOI: 10.3171/2020.3.SPINE191232.

Disclosures Dr. Ames is an employee of UCSF. He is a consultant for DePuy Synthes, Medtronic, Stryker, Medicrea, K2M, and Biomet Zimmer. He receives royalties from Stryker, Biomet Zimmer Spine, DePuy Synthes, NuVasive, Next Orthosurgical, K2M, and Medicrea. He received educational research grants from Titan Spine, DePuy Synthes, and the International Spine Study Group (ISSG). He serves on the editorial board of Operative Neurosurgery. He has received grant funding from the Scoliosis Research Society (SRS), and he is on the executive committee of the ISSG and Global Spinal Analytics. Dr. Bess is a consultant for K2M Stryker and a patent holder with K2M. He received clinical or research support for the study described (includes equipment or material) from the ISSG Foundation, and he also received support of non–study-related clinical or research efforts that he oversaw from the ISSG Foundation. Dr. Burton received clinical or research support for the study described (includes equipment or material) from DePuy and Pfizer. He is a patent holder with DePuy. He has direct stock ownership in Progenerative Medical, and is a consultant for Bioventus. Dr. Gum is an employee of Norton Healthcare. He is a consultant for Medtronic, DePuy, Stryker, Acuity, K2M, PacMed, and NuVasive. He received clinical or research support for the study described (includes equipment or material) from Intellirod, Integra, Pfizer, and the International Spine Study Group. He has direct stock ownership in Cingulate Therapeutics, and he is a patent holder with Medtronic. He receives royalties from Acuity. Dr. Gupta has direct stock ownership in J&J (Johnson & Johnson) and P&G (Procter & Gamble). He is a consultant for Medtronic and DePuy. He receives royalties from Innomed and from DePuy, and he also has acted in an advisory capacity for DePuy. He has received support for travel from Medicrea, Alphatec, SRS, DePuy, AO Spine, and Mizuho. OMeGA and AO Spine paid grants to his institution for fellowships, and AO Spine also paid him an honorarium. Dr. Kelly received support of a non–study-related clinical or research effort that he oversaw from DePuy Synthes. Dr. Klineberg is a consultant for DePuy Synthes, Stryker, and Medicrea. He received a fellowship grant and honoraria from AO Spine. Dr. Lafage is a consultant for Globus Medical and receives royalties from NuVasive. She received honoraria from The Permanente Medical Group and DePuy Synthes. She is on the executive committee of the International Spine Study Group. Dr. Mundis is a consultant for NuVasive, K2M, Viseon, and Seaspine. He has direct stock ownership in NuVasive and Viseon. He receives royalties from NuVasive and K2M. Dr. Passias is a consultant for SpineWave and Medicrea. He is a paid presenter or speaker for Zimmer and Globus Medical. He received clinical or research support for the study described (includes equipment or material) from the Cervical Scoliosis Research Society. He also received support of non–study-related clinical or research efforts that he oversaw from Allosource. Dr. Protopsaltis is a consultant for Globus, Stryker, K2M, NuVasive, Medicrea, and Innovasis. He receives royalties from Altus. Dr. Smith is a consultant for K2M/Stryker, AlloSource, Cerapedics, Zimmer Biomet, NuVasive, and DePuy Synthes. He received clinical or research support for the study described (includes equipment or material) from DePuy Synthes/ISSG. He also received support of non–study-related clinical or research efforts that he oversaw from DePuy Synthes/ISSG and AO Spine. Other conflicts include the following: royalties from Zimmer Biomet and NuVasive; fellowship funding from NREF and AO Spine; research support from AO Spine; and stock ownership in Alphatec.

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