Spine Journal - 2026-04-24 - Journal Article
Adult Spinal Deformity with Low Pelvic Incidence: A Challenging Condition Demanding a Tailored Strategy.
Zhang H, Li J, Qin X, Shi B, Mao S, Zhu Z, Qiu Y, Liu Z
Topics
Key Takeaway
In ASD patients with low pelvic incidence (PI ≤41°), the SSS-LLMC correction strategy reduced mechanical complications to 8.6% versus 47.4% in undercorrected and 56.8% in insufficient sacral slope patients.
Summary Depth
Choose how much analysis to show on this article page.
Summary
This study asked whether a tailored sagittal correction strategy based on normative low-PI spinopelvic parameters reduces mechanical complications in ASD patients with PI ≤41°. Using a linear SS-LL relationship (LL = 1.122×SS + 10.84) derived from 274 asymptomatic low-PI adults, the authors stratified 103 surgical patients by sacral slope adequacy and LL matching accuracy. SSS-LLMC was independently protective against mechanical complications (OR 0.116; 95% CI 0.031–0.435), while preoperative SVA was an independent risk factor (OR 1.224 per cm; 95% CI 1.088–1.377), and apex location modulated the relative importance of LL precision versus SS restoration alone.
Key Limitation
The retrospective design cannot exclude selection bias in surgical planning, as surgeons may have unconsciously achieved better alignment in patients with more favorable anatomy, inflating the apparent protective effect of SSS-LLMC.
Original Abstract
BACKGROUND CONTEXT
Existing surgical alignment goals derived from populations with a high pelvic incidence (PI) are not applicable for patients with adult spinal deformity (ASD) and a low PI, who account for a high proportion of Asian populations. The surgical treatment for patients with a low PI is challenging because of their limited pelvic compensation capacity and because there are no criteria to guide corrective spinal deformity surgery in this population.
PURPOSE
To develop and validate a tailored sagittal correction strategy for patients with ASD and a low PI.
STUDY DESIGN/SETTING
Cross-sectional normative analysis and retrospective cohort study.
PATIENT SAMPLE
Stage I included 852 asymptomatic Chinese adults (age 50-79 years). Stage II included 103 patients with ASD and a PI of ≤41° who underwent posterior long-segment fusion and follow-up evaluation for ≥2 years, stratified by kyphotic apex into a TL group (kyphotic apex at L1 or above; n = 59) and an L group (kyphotic apex at L2 or below; n = 44).
OUTCOME MEASURES
Mechanical complications (MCs) and health-related quality of life (HRQOL), as measured by the Oswestry Disability Index and a visual analog scale for back and leg pain.
METHODS
Normative spinopelvic parameters were used to define a low-PI subgroup (PI ≤ 41°) and to derive the sufficient sacral slope-lumbar lordosis matched correction (SSS-LLMC) strategy. The 25th percentile sacral slope (SS) in asymptomatic adults with a low PI (41°) was adopted as the minimal SS target (SS ≥ 21°). Patients with ASD and a low PI were divided into sufficient sacral slope (SSS, postoperative SS ≥ 21°) or an insufficient sacral slope (ISS, postoperative SS < 21°). According to the linear sacral slope-lumbar lordosis (SS-LL) relationship (LL = 1.122 × SS + 10.84) established in asymptomatic adults with a low PI, the group of patients with an SSS was further stratified into lumbar lordosis matched correction (LLMC), lumbar lordosis undercorrection (LLUC), and lumbar lordosis overcorrection (LLOC). MCs and HRQOL over a minimum 2-year follow-up period were compared across these subgroups within the TL and L groups, and multivariate logistic regression identified independent predictors of MCs in the overall and apex-stratified cohorts. In addition, this strategy was compared with conventional alignment goals, such as the Scoliosis Research Society-Schwab modification of the pelvic incidence to lumbar lordosis (PI-LL) mismatch and the global alignment and proportion (GAP) score, to evaluate the ability of these approaches to reduce MCs.
RESULTS
A low PI (≤ 41°) accounted for 32.2% (274/852) of the asymptomatic cohort. Among 103 patients with ASD and a low PI, 36 (35.0%) developed MCs. MCs occurred in 56.8% (20/34) of patients with an ISS versus 23.2% (16/69) of patients with a SSS (P < 0.001). Within the SSS group, MC rates were 47.4% (9/19) in LLUC, 8.6% (3/35) in LLMC, and 26.7% (4/15) in LLOC (P = 0.004). In the TL group, SSS-LLMC had the lowest MC rate (12.5%), whereas in the L group no MCs occurred in SSS-LLMC (0/10) and the MC rate in SSS-LLOC (14.3%; 2/14) was lower than in SSS-LLUC (57.6%; 19/33). Preoperative SVA was an independent risk factor for MCs (odds ratio [OR] = 1.224; 95% confidence interval [CI], 1.088-1.377; P < 0.001), and SSS-LLMC was independently protective (OR, 0.116; 95% CI, 0.031-0.435; P = 0.001). In the L group, SSS alone was independently protective (OR, 0.187; 95% CI, 0.047-0.753; P = 0.018). At the final follow-up evaluation, the ODI were similar between the ISS and the SSS groups. In the TL group, the SSS group showed a lower mean VAS for the back compared to ISS group (2.7 ± 1.0 vs 3.4 ± 1.0; P = 0.028), while all other between-group comparisons yielded no statistically significant results.
CONCLUSIONS
Patients with ASD and a low PI who require posterior long-segment fusion treatment represent a distinct anatomic subtype requiring individualized correction targets. The SSS-LLMC strategy prioritizes restoring SS as a foundation before precisely matching LL to this established orientation. In addition, the target for LL reconstruction should take into account the different locations of the kyphotic apex.