Influence of positioning of L4–5 disc prostheses on functional outcomes and sagittal balance: 2-year follow-up of a cohort of 38 patients

Abstract

OBJECTIVEThe main objective of this study was to evaluate the influence of L4–5 total disc replacement (TDR) positioning on functional outcome at the 2-year follow-up. The secondary objective was to assess its influence on sagittal balance.METHODSProspective data were compiled for 38 single-level L4–5 ProDisc-O TDRs. Anteroposterior placement (APP) was the distance between the center of the implant and the center of the L5 endplate divided by the total length of the L5 endplate. This ratio was expressed as a percentage (APP 0%–49%, anterior off-centering; 50%, perfect centering; and 51%–100%, posterior off-centering). The patients were divided into 3 groups depending on the APP and using quartile values: group 1, anterior placement (APP 0%–46%); group 2, central placement (APP 46.1%–52%, the 2 central quartiles); and group 3, posterior placement (APP 52.1%–100%). The sagittal balance parameters assessed were overall lordosis, segmental lordosis, and pelvic incidence. Adequate lordosis was defined for each patient according to their pelvic incidence. The Oswestry Disability Index and visual analog scale (VAS) scores for back and leg pain were assessed.RESULTSThe average APP was 48% (range 40%–64%). There were 10 patients in group 1, 18 in group 2, and 10 in group 3. There was a significant difference in functional outcomes among the 3 groups. APP influenced the VAS back (p = 0.04) and VAS leg (p = 0.05) scores. Group 1 consistently showed the highest performance scores. No significant association between APP and the sagittal balance parameters was found. Patients who had preoperative sagittal imbalance or those who significantly modified their balance after the surgery had the poorest outcomes.CONCLUSIONSDisc prostheses at L4–5 seem to provide better functional outcome when they are positioned anteriorly to the center of the vertebral body.