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Inter- and intra-observer reliability of patellar height measurements in patients with and without patellar instability on plain radiographs and magnetic resonance imaging

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Abstract

Introduction

Many patella height indices exist in the literature. There is no single universally accepted radiological assessment for measuring patella height. The aims of this study were to determine which of the commonly used indices can most reliably measure patella height and compare the findings on both plain X-ray and magnetic resonance imaging (MRI) of the knee.

Methods

This case-controlled study compared patients with recurrent patella instability (patella group) to a control group. Two observers measured six validated patella height indices on X-ray and MRI of both groups at two separate time periods. Between-group and within-group statistical analysis was undertaken of the data. The inter- and intra-observer reliability was assessed using the intraclass correlation coefficient (ICC) and the kappa measure of agreement (k).

Results

Forty-four patients comprised the patella group and 50 patients the control group. There was a significant difference of most indices between the two groups (p < 0.05). There was a significant difference of most indices between the two imaging modalities (p < 0.05). The Insall-Salvati ratio had the greatest inter-observer reliability for both X-ray and MRI (ICC = 0.79 to 0.97; p < 0.001) (k = 0.50 to 1.00; p < 0.001).

Conclusion

Patella height indices significantly differ when measured on X-ray as compared to MRI. This may infer that a different set of normative values are required for each radiological modality, which we have proposed in this study. Overall, the Insall-Salvati ratio performed best and shows a high degree of intra- and inter-observer reliability on both X-ray and MRI.

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Authors and Affiliations

  1. Department of Trauma and Orthopaedic Surgery, South Tyneside District Hospital, Harton Lane, South Tyneside, NE34 0PL, UK

    Stephen Picken & Oday Al-Dadah

  2. The Medical School, Newcastle University, Framlington Place, Newcastle-upon-Tyne, NE2 4HH, UK

    Harry Summers

  3. Translational and Clinical Research Institute, Faculty of Medical Sciences, Newcastle University, Framlington Place, Newcastle-upon-Tyne, NE2 4HH, UK

    Oday Al-Dadah

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  1. Stephen Picken
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  2. Harry Summers
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Correspondence to Stephen Picken.

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This was a retrospective case–control radiological study which did not require IRB/ethics committee approval.

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The authors declare no competing interests.

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Picken, S., Summers, H. & Al-Dadah, O. Inter- and intra-observer reliability of patellar height measurements in patients with and without patellar instability on plain radiographs and magnetic resonance imaging. Skeletal Radiol 51, 1201–1214 (2022). https://doi.org/10.1007/s00256-021-03937-y

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  • DOI: https://doi.org/10.1007/s00256-021-03937-y

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