Analysis of Segmental Cervical Spine Vertebral Motion After Prodisc-C Cervical Disc Replacement

Study Design. Retrospective study of patients enrolled in a prospective randomized Food and Drug Administration trial with single level cervical disc replacement (CDR) with the ProDisc-C (Synthes, Paoli, PA). Objective. Evaluate the segmental range of motion ( ROM) in the cervical spine pre- and postoperative after CDR. Summary of Background Information. Each cervical level is believed to have its own biomechanical characteristics, ultimately leading to different sagittal and lateral ROM. Our understanding of the factors that influence motion after CDR continues to change and expand. Methods. One hundred sixty-four patients with single level ProDisc-C arthroplasty were evaluated radiographically using Medical Metrics (QMATM, Medical Metrics, Inc., Houston, TX). Pre- and postoperative disc height and ROM were measured from standing lateral and flexion-extension radiographs. Of these 164 patients, 44 had a CDR at C6/C7, 96 at C5/C6, 18 at C4/C5, and 6 at C3/C4. The mean follow-up was of 24 months. Statistical analysis evaluated the difference in mean ROM between the groups. Results. Before surgery, C4/C5 had more sagittal ROM compared with C3/C4, C5/C6, and C6/C7 (P < 0.001.) Before surgery, C4/C5 also had more lateral ROM compared with C3/C4, C5/C6, and C6/C7 (P = 0.015). After surgery, there were no significant differences in sagittal and lateral ROM between C3/C4, C4/C5, C5/C6, and C6/C7. The delta ( difference between pre- and postoperative) proved that the C4/C5 CDR actually lost sagittal ROM (-2.5 degrees) compared with the other levels, which gained sagittal ROM, C3/C4 (0.9), C5/C6 (1.8), and C6/C7 (1.6); P = 0.037. There was no significant difference in the delta lateral ROM between the segments: C3/C4, C4/C5, C5/C6, and C6/C7. Conclusion. CDR approximates the different segmental sagittal and lateral ROM. Although C4/C5 had negative delta ROM in the sagittal and lateral planes, it provided a satisfactory final ROM. Long-term clinical outcome studies are needed to properly evaluate if these differences could ultimately affect the patients everyday life.