Measurement-level clustering of ligamentum flavum thickness identifies distinct phenotypes associated with lumbar lordosis in adult spinal deformity: a proof-of-concept study.
- 1School of Medicine, University of Missouri-Kansas City, Kansas City, MO, United States.
- 2Department of Neurosurgery, Saint Luke's Marion Bloch Neuroscience Institute, Kansas City, MO, United States.
- 3Department of Neurosurgery, University of Texas Southwestern Medical Center, Dallas, TX, United States.
Abstract
Retrospective cohort study. To identify distinct ligamentum flavum (LF) thickness phenotypes in adult spinal deformity (ASD) using measurement-level clustering and to characterize their association with traditional spinopelvic parameters in a proof-of-concept analysis. LF thickness was measured on preoperative MRI in 44 consecutive ASD patients (2018-2023), yielding 1,250 measurements; complete clinical and radiographic data were available in 40. K-means clustering (k = 3) was performed at the measurement level, treating thickness regimes as exploratory and unsupervised. Patients were assigned to a dominant phenotype, and all inferential comparisons were performed at the patient level. Between-phenotype differences in spinopelvic parameters were assessed with independent-samples t-tests and Mann-Whitney U-tests, with Hedges g effect sizes. Preliminary clinical and radiological outcomes were reported descriptively. Three measurement-level thickness regimes were identified: Low LF (2.21 ± 0.51 mm, n = 619 measurements), Medium LF (3.92 ± 0.56 mm, n = 499), and High LF (6.11 ± 0.90 mm, n = 132). High-cluster measurements were distributed across 32 patients, but only one patient had High LF as a dominant phenotype and was excluded from comparisons (43 patients analyzed; 25 Low, 18 Medium). Lumbar lordosis differed significantly between Low and Medium phenotypes (Low: -44.6 ± 12.0° vs. Medium: -32.5 ± 8.9°; p = 0.003; Hedges g = -1.10, 95% CI -1.81 to -0.39), a large effect that was robust to nonparametric testing. Cluster purity was higher in Low LF (61.9% vs. 53.3%, p = 0.027; g = 0.70). Principal component analysis of standard parameters showed that mean LF thickness was moderately correlated with the dominant pelvic-morphology component (r = -0.44, p = 0.008), indicating that LF thickness is partially related to, rather than independent of, traditional parameters. Intra-rater reliability, assessed by blinded re-measurement of 15 patients, was moderate [ICC(2,1) = 0.632, 95% CI 0.242-0.855; Cohen kappa for phenotype = 0.524], and sensitivity analysis showed that the phenotype-lordosis association does not survive substitution of the re-read values (p = 0.005 to p = 0.245). In contrast, the continuous rank correlation does (rho = + 0.496, p = 0.0015). Measurement-level clustering identifies distinct LF thickness phenotypes in ASD that are associated with lumbar lordosis. These exploratory findings establish a methodological foundation and motivate larger, outcome-based studies with formal measurement-reliability assessment to determine clinical utility.
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BibTeX
@article{glaser2026measurementlevel,
title = {{Measurement-level clustering of ligamentum flavum thickness identifies distinct phenotypes associated with lumbar lordosis in adult spinal deformity: a proof-of-concept study.}},
author = {Dylan Glaser and Ahmad K AlMekkawi and Ashlesha Bhojane and Ali Ebada and Christopher Carron and Salah G Aoun and Andrew Abumoussa and Carlos A Bagley},
journal = {Frontiers in surgery},
year = {2026},
month = oct,
doi = {10.3389/fsurg.2026.1888647},
url = {https://europepmc.org/article/MED/42952922},
note = {CC BY},
}
RIS
TY - JOUR
TI - Measurement-level clustering of ligamentum flavum thickness identifies distinct phenotypes associated with lumbar lordosis in adult spinal deformity: a proof-of-concept study.
AU - Dylan Glaser
AU - Ahmad K AlMekkawi
AU - Ashlesha Bhojane
AU - Ali Ebada
AU - Christopher Carron
AU - Salah G Aoun
AU - Andrew Abumoussa
AU - Carlos A Bagley
PY - 2026
DA - 2026/10/14
JO - Frontiers in surgery
DO - 10.3389/fsurg.2026.1888647
UR - https://europepmc.org/article/MED/42952922
AB - Retrospective cohort study. To identify distinct ligamentum flavum (LF) thickness phenotypes in adult spinal deformity (ASD) using measurement-level clustering and to characterize their association with traditional spinopelvic parameters in a proof-of-concept analysis. LF thickness was measured on preoperative MRI in 44 consecutive ASD patients (2018-2023), yielding 1,250 measurements; complete clinical and radiographic data were available in 40. K-means clustering (k = 3) was performed at the measurement level, treating thickness regimes as exploratory and unsupervised. Patients were assigned to a dominant phenotype, and all inferential comparisons were performed at the patient level. Between-phenotype differences in spinopelvic parameters were assessed with independent-samples t-tests and Mann-Whitney U-tests, with Hedges g effect sizes. Preliminary clinical and radiological outcomes were reported descriptively. Three measurement-level thickness regimes were identified: Low LF (2.21 ± 0.51 mm, n = 619 measurements), Medium LF (3.92 ± 0.56 mm, n = 499), and High LF (6.11 ± 0.90 mm, n = 132). High-cluster measurements were distributed across 32 patients, but only one patient had High LF as a dominant phenotype and was excluded from comparisons (43 patients analyzed; 25 Low, 18 Medium). Lumbar lordosis differed significantly between Low and Medium phenotypes (Low: -44.6 ± 12.0° vs. Medium: -32.5 ± 8.9°; p = 0.003; Hedges g = -1.10, 95% CI -1.81 to -0.39), a large effect that was robust to nonparametric testing. Cluster purity was higher in Low LF (61.9% vs. 53.3%, p = 0.027; g = 0.70). Principal component analysis of standard parameters showed that mean LF thickness was moderately correlated with the dominant pelvic-morphology component (r = -0.44, p = 0.008), indicating that LF thickness is partially related to, rather than independent of, traditional parameters. Intra-rater reliability, assessed by blinded re-measurement of 15 patients, was moderate [ICC(2,1) = 0.632, 95% CI 0.242-0.855; Cohen kappa for phenotype = 0.524], and sensitivity analysis showed that the phenotype-lordosis association does not survive substitution of the re-read values (p = 0.005 to p = 0.245). In contrast, the continuous rank correlation does (rho = + 0.496, p = 0.0015). Measurement-level clustering identifies distinct LF thickness phenotypes in ASD that are associated with lumbar lordosis. These exploratory findings establish a methodological foundation and motivate larger, outcome-based studies with formal measurement-reliability assessment to determine clinical utility.
SN - 2296-875X
ER -