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A comparison of sagittal MRI and lateral radiography in determining the Insall–Salvati ratio and diagnosing patella alta in the pediatric knee

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Abstract

Background

The Insall–Salvati ratio is a technique for determining patellar height that relies on bony landmarks. Magnetic resonance imaging (MRI) and plain radiography are used interchangeably to assess the Insall–Salvati ratio in the pediatric population despite the lack of validity in the literature.

Objective

The purpose of this study was to investigate if the Insall–Salvati ratio and patella alta as determined on MRI are comparable to those determined on radiography in pediatric patients.

Materials and methods

We conducted a retrospective review of 49 pediatric patients (age range: 7.5–17.0 years) with unfused growth plates who underwent both knee MRI and lateral knee radiography. Measurements for calculating the Insall–Salvati ratio (the ratio of patella tendon length to patella length) were obtained by three observers. Data were analyzed using paired t-tests and Pearson’s correlation. A reliability assessment and inter-method agreements were performed. Patella alta was defined as an Insall–Salvati ratio > 1.2. Additional cutoffs of Insall–Salvati ratios > 1.3 and > 1.4 were also analyzed.

Results

There was no statistically significant difference between Insall–Salvati ratio as determined on MRI (mean: 1.20) and radiographs (mean: 1.25; P > 0.05). There was a strong correlation between Insall–Salvati ratio as determined on MRI and radiographs (Pearson’s r = 0.6) with moderate consistency (Cronbach’s alpha = 0.78). There was a good level of agreement between the diagnosis of patella alta on MRI and radiographs when defined as an Insall–Salvati ratio greater than 1.2 and 1.3 (Cohen’s kappa = 0.61).

Conclusion

The results demonstrate a strong association between Insall–Salvati ratio and patella alta derived from MRI and radiographs in children ages 7.5 years and older.

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Authors and Affiliations

  1. Department of Diagnostic Imaging, McMaster Children’s Hospital, Hamilton Health Sciences, 1200 Main St. W., 2S Radiology, Hamilton, ON, L8N 3Z5, Canada

    Darya Kurowecki, Ravi Shergill, Heba S. R. Takrouri & Kelly E. Ainsworth

  2. Department of Radiology, St. Joseph’s Health Care London, London, ON, Canada

    Kelly M. Cunningham

  3. Department of Orthopedic Surgery, McMaster Children’s Hospital, Hamilton Health Sciences, Hamilton, ON, Canada

    Devin C. Peterson

  4. Bluewater Imaging, Toronto, ON, Canada

    Neuman O. Habib

Authors
  1. Darya Kurowecki
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  2. Ravi Shergill
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  3. Kelly M. Cunningham
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  4. Devin C. Peterson
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  5. Heba S. R. Takrouri
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  6. Neuman O. Habib
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  7. Kelly E. Ainsworth
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Correspondence to Darya Kurowecki.

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Kurowecki, D., Shergill, R., Cunningham, K.M. et al. A comparison of sagittal MRI and lateral radiography in determining the Insall–Salvati ratio and diagnosing patella alta in the pediatric knee. Pediatr Radiol 52, 527–532 (2022). https://doi.org/10.1007/s00247-021-05207-4

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  • DOI: https://doi.org/10.1007/s00247-021-05207-4

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