Stability of Clinical Outcome Measures Following Anterior Cervical Spine Surgery Donna D. Ohnmeiss, Dr.Med., Richard D. Guyer, M.D., Jack E. Zigler, M.D., Scott L. Blumenthal, M.D. Disclosures: Ohnmeiss Employed by Texas Back Institute Research Foundation; Guyer: Royalties Alphatech, Stock Spinal Motion, Consulting and/or Scientific Advisory Board DePuy Synthes, K2M, Flexuspine, Spinal Kinetics, Nanovis, Crocker, MiMedx; Zigler: royalties Zimmer, stock Flexuspine, Expanding Ortho, Consulting and speaking DePuy Synthes, Ohnmeiss Nothing to disclose; Blumenthal: stock options Spinal Motion, Vertiflex, Anulex, FzioMed, Centinel Spine, Ranier, Consulting and/or Scientific Advisory Board Aesculap, Fziomed, Vertiflex, speaker Paradigm
Introduction Two-year follow-up is often thought of as the minimum required term for evaluating clinical outcomes, although rationale for such is not obvious Purpose: to investigate the stability of: Outcome measures over time following anterior cervical surgery for groups of patients in various studies Individual patient scores over time
Methods Literature search conducted to identify prospective studies involving anterior cervical spine surgery: In >100 patients Collecting data at multiple predefined time points Minimum 24 month follow-up
Methods Part 1: Literature reviewed to determine if significant changes in group outcome scores during follow-up Part 2: Using internal dataset, determined stability of individual patient s scores over time (pre-op, 6 wk, 3, 6, 12, 24 mo) Calculated percentage of patients with at least one 15 point change in NDI scores (minimal clinically important difference value)
Results 13 articles from 6 countries reviewed Topic: TDR and/or ACF Most frequently used assessments were NDI and VAS pain scales with SF-36 used in fewer studies Regardless of assessment, in no study was there statistically significant changes in mean scores after 3 mo follow-up, nor a trend toward worsening scores after 3 mo Also true of studies with follow-up extending beyond 2 yr
Results: Mean Scores in Literature Author N Topic Outcome measures Change Mummaneni, 2007 USA 276 TDR Prestige, ACF NDI, VAS, SF-36 Stable after 6 wk to 3 mo 265 ACF Heller, 2009 USA 242 TDR 221 ACF Bryan, ACF NDI, VAS, SF-36, composite success Stable after 6 wk to 3 mo except success with stabilized at 6 mo Murrey, 2009 USA 103 TDR 106 ACF ProDisc-C, ACF NDI, VAS, satisfaction Stable after 6 wk to 3 mo Coric, 2011 USA 136 TDR Kineflex-C, ACF NDI, VAS Stable after 6 wk to 3 mo 133 ACF Hisey, 2014 USA 179 TDR; 81 ACF 1 level Mobi-C NDI, VAS, SF-36, composite success Stable after 6 wk to 3 mo except success due to radiographic Davis, 2013 USA 225 TDR; 105 ACF 2 level Mobi-C NDI, VAS, SF-36, composite success scores Stable after 6 wk to 3 mo except success due to radiographic scores Phillips, 2013 USA 189 TDR PCM, ACF NDI, VAS, SF-36, Stable after 6 wk to 3 mo 153 ACF satisfaction Vaccaro, 2013 USA 151 TDR Secure-C NDI, VAS, SF-36 Stable after 6 wk to 3 mo 140 ACF Pitzen, 2009 Germany 132 ACF Anterior plates NDI, VAS Stable after 3 mo Schluessmann, 2010 808 TDR Multiple TDRs EQ-5D, COSS, VAS Stable after 3 mo Switzerland Huppert, 2011 France 231 TDR Mobi-C NDI, VAS, SF-36 Stable after 3 mo Fay, 2014 Taiwan 151 TDR Bryan, Prestige NDI, VAS, JOA, Nurik Stable after 6 mo (did not report earlier FU) Hou, 2014 China 149 TDR 196 ACF Discover, ACF NDI, VAS Stable after 3 mo
Mean NDI Scores (Internal Dataset) 70 60 50 40 49.9 Mean NDI scores remained stable after 3 mo; however, the bars representing standard deviation indicated relatively high variation in scores 30 20 10 23.3 16.6 16.0 15.9 16.9 0-10 Pre-op 6 wk 3 mo 6 mo 12 mo 24 mo
Individual NDI Scores When analyzing individual pts in the group (from whom stable mean scores were generated): 63.9% had at least one 15 point change in NDI scores between follow-up visits (value considered to be clinically relevant change) Among 55 patients completing all follow-up visits at 36, 48, and 60 mo, 69.0% had at least one 15 point change in NDI score
Discussion In the 13 studies reviewed, mean outcome scores for groups of patients improved significantly by 6 wk or 3 mo post-op and were stable during 2-year follow-up This occurred regardless of device, surgical technique, or outcome assessment used
Discussion For individual patient NDI scores, majority had at least one 15 point change during 24-mo follow-up suggesting that stable mean scores are produced by compensatory improving and worsening between individual patients Results suggest that while mean group scores are stable during follow-up, it should not be presumed that each patient s scores remain stable over time