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Patellar height measurements: Insall-Salvati ratio is most reliable method.

Abstract

PURPOSE

Patella alta is a risk factor for patellofemoral pain and instability. Several measurement methods and imaging modalities are in use to measure patellar height. The first aim of this study was to determine the intra- and interrater reliability of different patellar height measurement methods on conventional radiography (CR), CT and MRI. The second aim was to examine the applicability of patellar height measurement methods originally designed for CR on CT and MRI.

METHODS

Forty-eight patients who were treated for patellar instability were included. All patients had undergone a pre-operative conventional radiograph, CT scan and MRI. Five methods for measuring patellar height were performed on radiographs, CT and MRI by four observers. For each measurement, the intra- and interrater reliability was determined by calculating the intra-class correlation coefficient (ICC). A Bland-Altman analysis was performed for measurements with an ICC ≥ 0.70.

RESULTS

The Insall-Salvati (IS) ratio was the only measurement that showed good intra- and inter-observer reliability on CR, CT and MRI. The intra- and inter-observer reliability of the patellotrochlear index (PTI) for MRI was good to excellent for all observers. The IS ratio showed a moderate to good reliability for comparison of all three imaging modalities with the best agreement between radiography and MRI. The other patellar height measurements showed only poor to moderate inter-method agreement.

CONCLUSION

In this study, the Insall-Salvati ratio shows better intra- and inter-observer reliability than the Blackburne-Peel ratio, the Caton-Deschamps ratio and the modified Insall-Salvati ratio on all imaging modalities. Radiography and CT seem to have better reliability than MRI. The patellotrochlear index, however, shows good inter- and intra-observer reliability on MRI. Only for the IS method was there acceptable agreement between CR and MRI. This means that the established Insall-Salvati normal values could be used for MRI as well. This study shows that the most reliable method to measure patella height is the Insall-Salvati ratio measured on conventional radiographs or the patellotrochlear index on MRI.

LEVEL OF EVIDENCE

Level II diagnostic.

Authors+Show Affiliations

Department of Orthopaedic Surgery, Canisius Wilhelmina Hospital, Postbus 9015, Nijmegen, 6500 GS, The Netherlands. fleur@verhulst.info.Department of Orthopaedic Surgery, Canisius Wilhelmina Hospital, Postbus 9015, Nijmegen, 6500 GS, The Netherlands.Radboud University, Nijmegen, The Netherlands.Department of Radiology, Canisius Wilhelmina Hospital, Nijmegen, The Netherlands.Department of Orthopaedic Surgery, Canisius Wilhelmina Hospital, Postbus 9015, Nijmegen, 6500 GS, The Netherlands.

Pub Type(s)

Journal Article

Language

eng

PubMed ID

31089790

Citation

Verhulst, Fleur V., et al. "Patellar Height Measurements: Insall-Salvati Ratio Is Most Reliable Method." Knee Surgery, Sports Traumatology, Arthroscopy : Official Journal of the ESSKA, 2019.
Verhulst FV, van Sambeeck JDP, Olthuis GS, et al. Patellar height measurements: Insall-Salvati ratio is most reliable method. Knee Surg Sports Traumatol Arthrosc. 2019.
Verhulst, F. V., van Sambeeck, J. D. P., Olthuis, G. S., van der Ree, J., & Koëter, S. (2019). Patellar height measurements: Insall-Salvati ratio is most reliable method. Knee Surgery, Sports Traumatology, Arthroscopy : Official Journal of the ESSKA, doi:10.1007/s00167-019-05531-1.
Verhulst FV, et al. Patellar Height Measurements: Insall-Salvati Ratio Is Most Reliable Method. Knee Surg Sports Traumatol Arthrosc. 2019 May 14; PubMed PMID: 31089790.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Patellar height measurements: Insall-Salvati ratio is most reliable method. AU - Verhulst,Fleur V, AU - van Sambeeck,Jordy D P, AU - Olthuis,Geerte S, AU - van der Ree,Jasper, AU - Koëter,Sander, Y1 - 2019/05/14/ PY - 2018/09/05/received PY - 2019/05/02/accepted PY - 2019/5/16/entrez PY - 2019/5/16/pubmed PY - 2019/5/16/medline KW - CT KW - Inter-observer reliability KW - MRI KW - Patellar height KW - Radiography JF - Knee surgery, sports traumatology, arthroscopy : official journal of the ESSKA JO - Knee Surg Sports Traumatol Arthrosc N2 - PURPOSE: Patella alta is a risk factor for patellofemoral pain and instability. Several measurement methods and imaging modalities are in use to measure patellar height. The first aim of this study was to determine the intra- and interrater reliability of different patellar height measurement methods on conventional radiography (CR), CT and MRI. The second aim was to examine the applicability of patellar height measurement methods originally designed for CR on CT and MRI. METHODS: Forty-eight patients who were treated for patellar instability were included. All patients had undergone a pre-operative conventional radiograph, CT scan and MRI. Five methods for measuring patellar height were performed on radiographs, CT and MRI by four observers. For each measurement, the intra- and interrater reliability was determined by calculating the intra-class correlation coefficient (ICC). A Bland-Altman analysis was performed for measurements with an ICC ≥ 0.70. RESULTS: The Insall-Salvati (IS) ratio was the only measurement that showed good intra- and inter-observer reliability on CR, CT and MRI. The intra- and inter-observer reliability of the patellotrochlear index (PTI) for MRI was good to excellent for all observers. The IS ratio showed a moderate to good reliability for comparison of all three imaging modalities with the best agreement between radiography and MRI. The other patellar height measurements showed only poor to moderate inter-method agreement. CONCLUSION: In this study, the Insall-Salvati ratio shows better intra- and inter-observer reliability than the Blackburne-Peel ratio, the Caton-Deschamps ratio and the modified Insall-Salvati ratio on all imaging modalities. Radiography and CT seem to have better reliability than MRI. The patellotrochlear index, however, shows good inter- and intra-observer reliability on MRI. Only for the IS method was there acceptable agreement between CR and MRI. This means that the established Insall-Salvati normal values could be used for MRI as well. This study shows that the most reliable method to measure patella height is the Insall-Salvati ratio measured on conventional radiographs or the patellotrochlear index on MRI. LEVEL OF EVIDENCE: Level II diagnostic. SN - 1433-7347 UR - https://www.unboundmedicine.com/medline/citation/31089790/Patellar_height_measurements:_Insall-Salvati_ratio_is_most_reliable_method L2 - https://dx.doi.org/10.1007/s00167-019-05531-1 DB - PRIME DP - Unbound Medicine ER -