A Geometrical Explanation for Change in Pelvic Tilt (or Lack of Change) Following Long Spinal Fusions

Gautham Prabhakar; Michael P Kelly; Ezekial Koslosky; Andrew Eck; Chimobi Emukah; Christopher Chaput; Jeffrey Hills

doi:10.1097/BRS.0000000000004970

A Geometrical Explanation for Change in Pelvic Tilt (or Lack of Change) Following Long Spinal Fusions

Spine (Phila Pa 1976). 2024 Feb 19. doi: 10.1097/BRS.0000000000004970. Online ahead of print.

Authors

Gautham Prabhakar¹, Michael P Kelly², Ezekial Koslosky¹, Andrew Eck¹, Chimobi Emukah¹, Christopher Chaput¹, Jeffrey Hills¹

Affiliations

¹ Department of Orthopaedics, University of Texas Health Science Center at San Antonio, San Antonio, TX.
² Division of Orthopedics & Scoliosis at Rady Children's Hospital-San Diego, San Diego, California.

PMID: 38369718
DOI: 10.1097/BRS.0000000000004970

Abstract

Study design: Retrospective Cohort.

Objective: Examine the relationship between compensatory pelvic retroversion, positive sagittal imbalance (measured by C2 tilt), and the C2 pelvic angle (C2PA) in patients prior to long spinal fusions; and to determine the association between changes in C2PA and pelvic tilt (PT) following long spinal fusions.

Background: Adult spinal deformity surgical goals often include a PT target, yet patients frequently demonstrate persistent compensatory pelvic retroversion following surgery.

Materials and methods: Adults>18y undergoing long spinal fusions (>4 levels) with standing preoperative and postoperative radiographs were included. To examine drivers of preoperative sagittal balance, regression models were fit to estimate the association between preoperative C2PA and pelvic incidence, with preoperative PT and C2 tilt. To predict postoperative change in PT, multivariable regression was used to estimate change in PT, adjusting for change in C2PA and preoperative C2 tilt.

Results: Among 80 patients identified, median age was 61 (IQR, 45 to 72) and 46 (58%) were female. Median number of levels fused was 10 (IQR, 8 to 13) and 55 (69%) were instrumented to the sacrum/pelvis. Preoperative C2PA had a significant nonlinear association with preoperative PT (r2=0.81, P<0.001), and preoperative C2 tilt (r2=0.41, P=0.002). Postoperative change in PT was strongly associated with change in C2PA (β=0.81; P<0.001) and preoperative C2 tilt (β=0.55; P<0.001).

Conclusions: Following long spinal fusions, change in PT (or lack thereof) can be reliably predicted based on change in C2PA and preoperative C2 tilt. In patients with normal preoperative C2 tilt, the change in C2PA is nearly equivalent to the change in PT, but in patients with more positive C2 tilt (sagittal imbalance), a greater change in C2PA will be required to achieve equivalent change in PT.

Level of evidence: III.