• Burt Yaszay, John A Bendo, Jeffrey A Goldstein, Martin Quirno, Jeffrey M Spivak, and Thomas J Errico.
• Department of Orthopedic Surgery, NYU Hospital for Joint Diseases, New York, NY 10003, USA.
• Spine. 2008 Mar 1; 33 (5): 508-12; discussion 513.

Study DesignRetrospective study of patients enrolled in prospective randomized Food and Drug Administration trial.ObjectiveTo evaluate the influence of pre- and postoperative disc height on postoperative motion and clinical outcomes.Summary Of Background DataOur understanding of the factors that influence motion and ultimately patient satisfaction after lumbar disc replacement continues to evolve.MethodsForty-two patients with a single level ProDisc-L at either the L4/5 or L5-S1 were selected. Pre- and postoperative disc height and range of motion (ROM) were measured from standing lateral and flexion-extension radiographs. Oswestry Disability Index and visual analog scale were also collected. Student t test and Spearman rho tests were performed to determine if there was any correlation or "threshold" effect between the disc height and ROM or clinical outcome.ResultsThe mean anterior and posterior disc height significantly increased from 10.8 mm to 17.6 mm and 4.4 mm to 7.9 mm, respectively (P < 0.01). The mean ROM decreased from 7.0 degrees to 5.7 degrees (P = 0.21). Patients with less than 9 mm of preoperative anterior disc height had an increase in their ROM (2.2 degrees) compared with a loss of ROM (-2.2 degrees) in patients with more than 9 mm of preoperative disc height (P = 0.02). Patients with between 16 mm and 18 mm of postoperative anterior disc height have greater ROM (7.5 degrees) than those above or below this range (3.6 degrees and 3.6 degrees respectively, P < 0.05). There was no correlation or threshold effect between clinical outcomes and disc height.ConclusionPatients with greater disc collapse benefit more in ROM from a total disc replacement. The optimal range to maximize ROM for postoperative anterior disc height is 16 mm to 18 mm. This optimal range did not translate into better clinical outcome at 2 years follow-up.

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