• Avinash G Patwardhan, Gerard Carandang, Leonard I Voronov, Robert M Havey, Gary A Paul, Carl Lauryssen, Domagoj Coric, Thomas Dimmig, and David Musante.
• *Edward Hines Jr. VA Hospital, Hines, IL †Loyola University Stritch School of Medicine, Maywood, IL ‡Spinal Kinetics, San Jose, CA §NeuroTexas Brain and Spinal Surgery, Austin, TX ¶Carolina Neurosurgery and Spine Associates, Charlotte, NC ||Triangle Orthopedic Associates, Durham, NC.
• Spine. 2016 Dec 15; 41 (24): 1866-1875.

Study DesignAnalysis of prospectively collected radiographic data.ObjectiveTo investigate the influence of preoperative index-level range of motion (ROM) and disc height on postoperative ROM after cervical total disc arthroplasty (TDA) using compressible disc prostheses.Summary Of Background DataClinical studies demonstrate benefits of motion preservation over fusion; however, questions remain unanswered as to which preoperative factors have the ability to identify patients who are most likely to have good postoperative motion, which is the primary rationale for TDA.MethodsWe analyzed prospectively collected data from a single-arm, multicenter study with 2-year follow up of 30 patients with 48 implanted levels. All received compressible cervical disc prostheses of 6 mm-height (M6C, Spinal Kinetics, Sunnyvale, CA). The influence of index-level preoperative disc height and ROM (each with two levels: below-median and above-median) on postoperative ROM was analyzed using 2 x 2 ANOVA. We further analyzed the radiographic outcomes of a subset of discs with preoperative height less than 3 mm, the so-called "collapsed" discs.ResultsShorter (3.0 ± 0.4 mm) discs were significantly less mobile preoperatively than taller (4.4 ± 0.5 mm) discs (6.7° vs. 10.5°, P = 0.01). The postoperative ROM did not differ between the shorter and taller discs (5.6° vs. 5.0°, P = 0.63). Tall discs that were less mobile preoperatively had significantly smaller postoperative ROM than short discs with above-median preoperative mobility (P < 0.05). The "collapsed discs" (n = 8) were less mobile preoperatively compared with all discs combined (5.1° vs. 8.6°, P < 0.01). These discs were distracted to more than two times the preoperative height, from 2.6 to 5.7 mm, and had significantly greater postoperative ROM than all discs combined (7.6° vs. 5.3°, P < 0.05).ConclusionWe observed a significant interaction between preoperative index-level disc height and ROM in influencing postoperative ROM. Although limited by small sample size, the results suggest discs with preoperative height less than 3 mm may be amenable to disc arthroplasty using compressible disc prostheses.Level Of Evidence2.

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