Magnitude, Location, and Factors Related to Regional and Global Correction Loss in Long Adult Deformity Constructs: Report of 183 Patients with 2-Year Follow-Up

Abstract

Introduction Adult deformity patients (pts) have previously been shown to lose spino-pelvic correction over time especially in the sagittal plane. The goal of this study was to analyze the source of this correction loss and specifically to quantitate the change that occurs in fused verses unfused segments. Variables examined include presence of interbody fusion, rod diameter, rod material, age, and pre-op sagittal alignment. Materials and Methods A retrospective review of a multicenter, prospective ASD database was conducted. Inclusion criteria were age ≥ 18 years, ASD, no revisions between > 6 weeks and < 2 years postop. Spinal pelvic parameters, thoracic kyphosis (TK:T2–T12) and lumbar lordosis (LL:L1–S1) were both measured overall as well as within and outside the instrumented segments. Overall, SVA, PT, Pi-LL change, and TK and LL change between 6 weeks and 2 years post-op was calculated. Of these pts, the amount of TH loss and TL loss within and outside of the instrumented segments was also determined as well as a percentage of the total loss for each region. Results A total of 183 pts met criteria. Between 6 weeks and 2 years post-op 61.7% of pts lost SVA (4.4 ± 4.3 cm), 65.0% lost PT (4.7 ± 4.0 deg), and 40.4% lost PI–LL (16.2 ± 9.3 deg). Overall, 63.9% had TH loss (8.0 ± 8.9 deg) and 56.8% had LL loss (5.8 ± 4.5 deg). Overall, 41.5% lost > 2 cm SVA. Of the pts with > 2 cm SVA loss, 60.5% had LL loss, and of those, 82.6% was within instrumented segments. Of the pts with LL loss, 13.8% had > 10 deg loss. Pts with an interbody fusion have a 2.3 times ( p = 0.0076) likelihood of having any LL loss, but the interbody fusion was protective against > 10 deg change (7.1%). Pts ≥ 65 years' old are 9.4 times ( p < 0.0001) more likely to have LL loss than pts ≤ 45 years' old (4.4%). Pts with pre-op C7 SVA > 5 cm are 2.4 times ( p = 0.0035) more likely to have LL loss. Conclusion Loss of initial regional and global sagittal correction is common in ASD surgery and also occurs inside the instrumented segments between 6 weeks and 2 years postop. Older age and pre-op sagittal deformity are risk factors for overall loss of correction and for loss of correction within the instrumented segments. In our study, interbody fusion was only protective for LL loss > 10 deg.