Neurosurgery notes/Procedures/TL spine procedures/Deformity techniques/Osteotomy/FBI (Full Balance Integrated) osteotomy planning

FBI (Full Balance Integrated) osteotomy planning

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Osteotomy

General

  • The FBI technique stands for Full Balance Integrated and is a new method proposed for osteotomy planning to treat spine imbalance. It is designed to provide a good evaluation of the amount of correction needed to restore harmonious kyphosis and correct sagittal alignment of the vertebral column.

Preoperative Planning:

  • Uses pelvic and spine parameters with Roussouly's classification.
  • Preoperative planning requires a
    • full-body X-ray including the spine from C1 to the femoral head and the first 10 cm of the femur shaft.
    • Standing X-ray scoliogram or EOS system.
  • Planning aim
    • to recover the initial shape of the spine before imbalance occurred, which is crucial to avoid mistakes during osteotomy planning.
    • It also considers general patient parameters like age, osteoporosis, and systemic disease to find an acceptable compromise for rebalancing the spine.

FBI Formula

  • The FBI technique uses three angle measurements to calculate the total angle of correction needed. The formula for the FBI angle of correction is:
      • FBI angle of correction = C7TA + FOA + PTCA.
  1. C7 Translation Angle (C7TA):
      • This angle is calculated using basic goniometry, with (a,c,b)
        • L4 vertebra as a reference point (point c) because the apex of lumbar lordosis is typically around L4.
        • The midpoint of the C7 inferior plateau (point a) is transposed horizontally onto the projected future C7 plumb line (point b), which ideally passes through the S1 plateau on a sagittal standing X-ray.
      • Restoring lumbar lordosis is a common method to re-establish balance, and the goal is for the C7 plumb line to pass through the S1 plateau.
  1. Femur Obliquity Angle (FOA):
      • This angle measures the inclination of the femoral axis to the vertical.
      • Normally, the femurs are vertical. An angulation demonstrates a certain amount of knee flexion, which is a compensation phenomenon for the patient to maintain balance, albeit inefficiently.
      • The FOA, which is the complementary angle to knee flexion, is measured on full spine standing X-rays and should be added to the total correction needed. Patients often adjust their coping mechanism by straightening their legs after osteotomy surgery.
  1. Pelvic Tilt Compensation Angle (PTCA):
      • If the measured PT on standing X-rays is between 15° and 25° = 5° of tilt angle compensation is added.
      • If it is higher than 25° = 10° is added.
      • This angle accounts for pelvic retroversion, which is a compensation phenomenon when the measured pelvic tilt (PT) is higher than its theoretical value.
      • Theoretical PT values are provided by Roussouly’s classification and vary based on pelvic incidence (PI). For instance, average PT is around 15° for over 80% of the population, but can reach 20–25° or more in type 4 spines.
      • This compensatory tilt is based on clinical analysis of operated patients. This is particularly important for patients with high pelvic incidence, who have a greater possibility of pelvic retroversion and require more demanding correction.
notion image

Application and Outcomes:

  • The calculated FBI angle of correction helps surgeons determine the appropriate technique (e.g., Pedicle Subtraction Osteotomy (PSO), Interpedicular Osteotomy (IPO), or Smith Petersen osteotomy) and amount of correction to achieve a good balance.
  • The technique was applied in a retrospective study of 18 patients and a prospective study of 8 cases. The retrospective analysis showed why improper correction was sometimes performed in the past.
  • In the prospective group (Group B), the FBI formula was used pre-operatively, leading to good clinical outcomes and correct spinal alignment. The average correction needed was 38.9°.
  • The analysis confirmed that the FBI technique provided a correct approximation of the needed correction to achieve a C7 plumb line passing through the S1 plateau. When the theoretical FBI correction was achieved, the C7 plumb line was well-positioned, and clinical outcomes were better. This validated the technique, though more cases are needed for further confirmation.
  • The goal is to ensure the C7 plumb line is behind the femoral heads, with femurs in a vertical position, to achieve an ideal and economical balance.

Limitation

  • Lamartina 2012
    • Gross estimation of the amount of pelvic tilt excess
    • Lack of consideration of thoracic hypolordosis which has been shown to jeopardize the accuracy of final correction in patients with flexible thoracic spine
    • It underestimates the amount of needed correction in those patients with normal SVA, no knee flexion and extreme pelvic tilt, a scenario that can present clinically