Variability in Assessing Spinopelvic Parameters with Lumbosacral Transitional Vertebrae: Inter- and Intra-observer Reliability among Spine Surgeons.

STUDY DESIGN: Prospectively-collected survey study OBJECTIVE.: To determine the consistency with which spino-pelvic parameters (SPP) are determined in patients with lumbosacral transitional vertebrae (LSTV).

SUMMARY OF BACKGROUND DATA: The incidence of LSTV in the general population is as high as 35.6%. The often fixed nature of LSTV relative to the pelvis, but lumbar-type appearance, may lead to differential use of the S1 endplate when performing SPP assessment. This could have significant impact on SPP derived from these landmarks, resulting in considerable variation in surgical planning and decision making.

METHODS: 20 patients demonstrating LSTV on standing lateral 36-in spinal radiographs were randomly arranged and independently analyzed by 16 experienced spine surgeons using the same computer software. Pelvic incidence (PI), pelvic tilt (PT), lumbar lordosis (LL), and T1 pelvic angle (TPA) were captured. Two weeks after the first assessment, surgeons repeated the measurements after image sequence re-randomization. Intraclass correlation coefficient (ICC) was calculated to evaluate IOR for each SPP. Intra-observer reliability (IAOR) was assessed through an average Pearson's correlation coefficient for each parameter for each surgeon.

RESULTS: 16 surgeons completed initial measurements. IOR was poor for TPA (0.35, 95% CI 0.20, 0.58) and PI (0.42, 95% CI 0.26, 0.65) and fair for LL (0.67, 95% CI 0.51, 0.82) and PT (0.63, 95% CI 0.47, 0.81). 14 surgeons completed phase-2 measurements to assess IAOR. Average parameter PPC showed excellent IAOR (LL 0.86, TPA 0.77, PI 0.78, PT 0.86). Kappa coefficient showed fair agreement for raters choosing the same endplate for measurement (Phase 1 0.38, Phase 2 0.32). By patient, the percentage of raters that chose the S1 endplate for measurement varied from 6.3% to 85.7%.

CONCLUSIONS: Significant variability exists when surgeons measure SPP in patients with LSTV. These parameters are critical in determining the goals of surgical reconstruction and such variability may have considerable implications for radiographic goals and outcomes of surgical reconstruction.

LEVEL OF EVIDENCE: 4.