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Background <p>The migration index (MI) is a quantitative measurement of femoral head extrusion used to help risk stratify neuromuscular hip dysplasia. However, MI relies upon the radiographically visible ossified capital femoral epiphysis which is only partially ossified in young children and therefore may potentially underestimate hip extrusion.</p> Objective <p>To compare proof-of-concept accuracy of using a metaphyseal and traditional MI to measure femoral head extrusion in children&#xa0;compared with an MRI-based anatomic reference standard.</p> Materials and methods <p>We reviewed 205 normal hips, each by MRI and x-ray, in patients aged 6&#xa0;months - 6&#xa0;years old. Three femoral head MI measurements were performed: (1) MRI-MI: percentage of the cartilaginous femoral head uncovered by the osseous acetabulum&#xa0;(anatomic reference standard); (2) traditional MI (TMI) x-ray: percentage of osseous capital femoral head uncovered by the osseous acetabulum; (3) metaphyseal MI x-ray (MeMI): percentage of the femoral head uncovered by the osseous acetabulum, using the metaphyseal vertex used as a surrogate for lateral margin of the cartilaginous femoral head. Statistical analysis of the three measurement techniques was performed using paired <i>t</i>-tests. Intraclass correlation coefficient was calculated.</p> Results <p>There was a statistically significant underestimation of femoral head extrusion using TMI and MeMI (<i>P</i>&lt;0.05)&#xa0;when compared with MRI-MI, but MeMI more closely approximated the MRI-MI. Inter-reader reliability showed excellent agreement.</p> Conclusion <p>The MeMI better approximates the MRI anatomic landmarks for measuring the true degree of femoral head extrusion in children 6&#xa0;months - 5&#xa0;years of age. Its usage should be considered in lieu of the TMI in children under 5&#xa0;years of age for radiographically determining MI.</p>

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The radiographic metaphyseal migration index: a new proposed radiographic landmark for correct quantification of femoral head extrusion in preschool children

  • 期刊论文

  • 发表日期：

    2026年1月22日

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  • Austin McCullough,
  • Rida Salman,
  • Kathryn Milks,
  • Collin Troester,
  • Andy Sher,
  • Edward Wright,
  • J Herman Kan

摘要

Background

The migration index (MI) is a quantitative measurement of femoral head extrusion used to help risk stratify neuromuscular hip dysplasia. However, MI relies upon the radiographically visible ossified capital femoral epiphysis which is only partially ossified in young children and therefore may potentially underestimate hip extrusion.

Objective

To compare proof-of-concept accuracy of using a metaphyseal and traditional MI to measure femoral head extrusion in children compared with an MRI-based anatomic reference standard.

Materials and methods

We reviewed 205 normal hips, each by MRI and x-ray, in patients aged 6 months - 6 years old. Three femoral head MI measurements were performed: (1) MRI-MI: percentage of the cartilaginous femoral head uncovered by the osseous acetabulum (anatomic reference standard); (2) traditional MI (TMI) x-ray: percentage of osseous capital femoral head uncovered by the osseous acetabulum; (3) metaphyseal MI x-ray (MeMI): percentage of the femoral head uncovered by the osseous acetabulum, using the metaphyseal vertex used as a surrogate for lateral margin of the cartilaginous femoral head. Statistical analysis of the three measurement techniques was performed using paired t-tests. Intraclass correlation coefficient was calculated.

Results

There was a statistically significant underestimation of femoral head extrusion using TMI and MeMI (P<0.05) when compared with MRI-MI, but MeMI more closely approximated the MRI-MI. Inter-reader reliability showed excellent agreement.

Conclusion

The MeMI better approximates the MRI anatomic landmarks for measuring the true degree of femoral head extrusion in children 6 months - 5 years of age. Its usage should be considered in lieu of the TMI in children under 5 years of age for radiographically determining MI.