112. Changes in flexion/extension range of motion due to oversizing of cervical total disc arthroplasty

Abstract

BACKGROUND CONTEXT Total disc arthroplasty (TDA) is a popular treatment for cervical degenerative disc because it preserves motion, decreasing the potential for adjacent level disease. However, oversizing the disc may occur due to limited options in artificial disc height and may diminish this motion preservation. In this study, 1- and 2-level disc arthroplasties with mobile core devices (MCD) at C5-C6 and C4-C5 were compared to oversized devices and 2-level fusions. METHODS Eight cadaveric cervical (C2-T1) spine specimens (average age: 43 ± 12 years) were prepared with cranial and caudal ends embedded in bone cement. Each vertebra was instrumented with optoelectronic markers for motion capture. Each specimen was tested using a six degree-of-freedom kinematic spinal simulator up to 2 Nm in three cycles of flexion/extension. All specimens were tested at four intervention points: intact, ALL resection, 1-level TDA @ C5-C6 with an MCD (Mobi-C, Zimmer Biomet), and 2-level TDA @ C4-C6 with MCDs. After these interventions, the specimens were separated into two equal groups (A and B) with two additional interventions: 2-level TDA with overstuffing or increasing the height of the MCD by 1 mm at C5-C6 (Group A) or C4-C5 (Group B), and 2-level fusion @ C4-C6. All moment and motion capture data were imported into Matlab, and the 3rd test cycle was analyzed. Maximum ranges of motion, normalized as percent of intact, were analyzed for the index (C4-C5 and C5-C6) and adjacent (C3-C4 and C6-C7) levels. Two-way ANOVA with one way repeated-measures was performed with post-hoc Tukey's tests to measure changes in maximum ranges of motion. RESULTS Flexion/Extension, Interventions 1-4: No significant differences were observed between all four interventions at C3-C4 and C4-C5. At C5-C6, significantly greater flexion/extension was measured with ALL resection compared to intact and 1-level TDA interventions. Finally, at C6-C7, ALL resection produced significantly higher range of motion vs 2-level TDA. Flexion/Extension, Group A, Interventions 1,3-6: At C3-C4 and C6-C7, no significant differences were measured between any of the interventions. At C4-C5, intactROM was significantly larger than 2-level TDA, overstuffed TDA @ C5-C6, and 2-level fusion @ C4-C6. In addition, 1-level TDAROM was significantly larger than 2-level TDA and 2-level fusion. Finally, ROM for 2-level TDA and overstuffed TDA @ C5-C6 were both significantly larger than 2-level fusion. At C5-C6, intact, 1-level, and 2-level TDA ROM were significantly larger than the overstuffed TDA @ C5-C6 and the 2-level fusion interventions. Also, the overstuffed TDA @ C5-C6 ROM was significantly larger than the 2-level fusion. Flexion/Extension, Group B, Interventions 1,3-6: At C3-C4 and C6-C7, no significant differences were measured between any of the interventions. At C4-C5, Intact ROM was significantly larger than 2-level TDA, overstuffed TDA @ C4-C5, and 2-level fusion. 1- and 2-level TDA ROM were both significantly larger than overstuffed TDA @ C4-C5 and 2-level fusion. Finally, overstuffed TDA @ C4-C5 ROM was significantly larger than 2-level fusion. At C5-C6, ROM of all interventions was significantly larger than 2-level fusion. CONCLUSIONS Mobile-core disc arthroplasty device maintained range of motion at the index levels, and did not increase motion in adjacent levels in both 1- and 2-level disc arthroplasty implantations. In addition, implanting with oversized devices caused significant decreases in range of motion. FDA DEVICE/DRUG STATUS Unavailable from authors at time of publication.