Group-based Trajectory Modeling: A Novel Approach to Classifying Discriminative Functional Status Following Adult Spinal Deformity Surgery: Study of a 3-year Follow-up Group.

Study Design: Retrospective review of prospectively collected database.
Objective: To delineate and visualize trajectories of the functional status in surgically-treated adult spinal deformity (ASD) patients.
Summary of Background Data: Classifying long-term recovery following ASD surgery is not well defined.
Methods: One thousand one hundred seventy-one surgically-treated patients with a minimum of 3-year follow-up were included. The group-based trajectory modeling (GBTM) was used to identify distinct trajectories of functional status over time, measured by Oswestry Disability Index (ODI). Patient profiles were then compared according to the observed functional patterns.
Results: The GBTM identified four distinct functional patterns. The first group (10.0%) started with minimal disability (ODI: 15 ± 10) and ended up almost disability-free (low-low). The fourth group (21.5%) began with high ODI (66 ± 11) and improvement was minimal (high-high). Groups two (40.1%) and three (28.4%) had moderate disability (ODI: 39 ± 11 vs. 49 ± 11, P < 0.001) before surgery. Following surgery, marked improvement was seen in group two (median-low), but deterioration/no change was observed in group three (median-high). The low-low group primarily included adult idiopathic scoliosis, while the high-high group had the oldest and the most severe patients as compared with the rest of the groups. A subgroup analysis was performed between groups two and three with propensity score matching on age, body mass index, baseline physical component score (PCS), and severity of deformity. Notably, the baseline mental status of the median-high group was significantly worse than that of the median-low group, though the differences in demographics, surgery, and deformity no longer existed.
Conclusions: Patients with moderate-to-low disability are more likely to obtain better functional postoperative outcomes. Earlier surgical interventions should be considered to prevent progression of deformity, and to optimize favorable outcomes. Greatest improvement appears to occur in moderately disabled patients with good mental health. GBTM permits classification into distinct groups, which can help in surgical decision making and setting expectations regarding recovery.
Level of Evidence: 3.