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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

Lookup NU author(s): Oday Al-Dadah


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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.

Publication metadata

Author(s): Picken S, Summers H, Al-Dadah O

Publication type: Article

Publication status: Published

Journal: Skeletal Radiology

Year: 2021

Pages: epub ahead of print

Online publication date: 31/10/2021

Acceptance date: 07/10/2021

ISSN (print): 0364-2348

ISSN (electronic): 1432-2161

Publisher: Springer


DOI: 10.1007/s00256-021-03937-y

PubMed id: 34718849


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