Clinical and Radiographic Parameters Associated with Best versus Worst Clinical Outcomes in Minimally Invasive Deformity Surgery

Abstract

BACKGROUND CONTEXT: To date, the factors that predict patient success or failure after minimally invasive spinal (MIS) fusion for adult deformity are unclear. Knowledge of such factors can help with patient selection and surgical decision-making. PURPOSE: We hypothesized that patients who have the best clinical outcomes after MIS deformity surgery have postoperative sagittal vertical axis (SVA) < 5 cm and pelvic incidence-lumbar lordosis (PI-LL) matched within 10degree, whereas those who do the worst have continued PI-LL mismatch and sagittal imbalance regardless of decompression of their stenosis. STUDY DESIGN/SETTING: Retrospective review. PATIENT SAMPLE: Multicenter cohort of MIS deformity cases. OUTCOME MEASURES: Oswestry Disability Index (ODI), visual analog scale (VAS) back pain, VAS leg pain. METHODS: A study of a consecutively enrolled, retrospective, multicenter database of adult spinal deformity (Cobb >20degree, SVA >5cm, PT >20, PILL >10, or Thoracic Kyphosis >60degree) patients treated with circumferential MIS (cMIS) surgery. Radiographic and clinical outcomes were compared between the top 20% in terms of ODI improvement at 2 years (best) were compared with the worst 20% (worst). RESULTS: A total of 426 patients were identified, and 104 patients with a minimum of 2-year follow-up were included for analysis. There was no statistically significant difference in age, BMI, pre- and postop Cobb angle, PT, PI, levels fused, OR time and blood loss between the best and worst groups. However, the preop ODI was significantly worse at baseline in the group that had the greatest change in ODI. There was no difference in preop PI-LL mismatch (12.8degree best vs 19.5degree worst, p=0.298). Compared to patients who did worst, patients who did best after MIS fusion had lower postop SVA (3.4 cm best vs 6.9 cm worst, p=0.043) and had matched PILL (10degree best vs 19degree worst, p=0.027). The best group also had better postop VAS back and leg pain scores (p<0.05). CONCLUSIONS: MIS deformity surgeons should focus on correcting a patient's PI-LL mismatch to within 10degree and restoring SVA to less than 5 cm. Restoration of these parameters seems to positively correlate with greatest improvement in ODI. Conversely, patients with insufficient correction appear to do worse, possibly related to having a ''fixed'' deformity after their fusion, and were significantly worse clinically at postop. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs.