Introduction
The human patellar tendon (PT) plays a crucial role in locomotion by transmitting force from the quadriceps muscle group to the tibia, via the patellar. Tendon is a viscoelastic tissue and will deform under loading (
Magnusson et al., 2008- Magnusson SP
- Narici MV
- Maganaris CN
- Kjaer M.
Human tendon behaviour and adaptation, in vivo.
), with the degree of loading corresponding to the structural properties of the tissue (
). These structural properties, such as tendon stiffness and Young's modulus (YM), determine the compliance of the tendon, which in turn can affect the behavior of the muscle–tendon unit during locomotion (
Fukunaga et al., 2002- Fukunaga T
- Kawakami Y
- Kubo K
- Kanehisa H.
Muscle and tendon interaction during human movements.
). To calculate tendon stiffness and YM, the cross-sectional area (CSA) of the PT needs to be accurately measured. Moreover, measuring PT CSA can determine adaptations of the PT in response to mechanical loading (
Kongsgaard et al., 2007- Kongsgaard M
- Reitelseder S
- Pedersen TG
- Holm L
- Aagaard P
- Kjaer M
- Magnusson SP.
Region specific patellar tendon hypertrophy in humans following resistance training.
;
Couppe et al., 2008- Couppe C
- Kongsgaard M
- Aagaard P
- Hansen P
- Bojsen-Moller J
- Kjaer M
- Magnusson SP.
Habitual loading results in tendon hypertrophy and increased stiffness of the human patellar tendon.
) or immobilization (
Maganaris et al., 2006- Maganaris CN
- Reeves ND
- Rittweger J
- Sargeant AJ
- Jones DA
- Gerrits K
- De Haan A.
Adaptive response of human tendon to paralysis.
). Therefore, accurate and reliable measurements of PT CSA must be obtained to quantify the associated properties and adaptations of the PT.
Methods of assessing tendon morphology
in vivo include magnetic resonance imaging (MRI) and 2-D B-mode ultrasound imaging (US). Several studies have validated the accuracy of MRI in measuring tendon properties (
Berthoty et al., 1989- Berthoty D
- Haghighi P
- Sartoris DJ
- Resnick D.
Osseous invasion by soft-tissue sarcoma seen better on MR than on CT.
;
Sonin et al., 1996- Sonin AH
- Peduto AJ
- Fitzgerald SW
- Callahan CM
- Bresler ME.
MR imaging of the rotator cuff mechanism: Comparison of spin-echo and turbo spin-echo sequences.
;
Carrino et al., 1997- Carrino JA
- McCauley TR
- Katz LD
- Smith RC
- Lange RC.
Rotator cuff: Evaluation with fast spin-echo versus conventional spin-echo MR imaging.
), and it is considered the “gold standard” tool in validating other measurement techniques (
Bohm et al., 2016- Bohm S
- Mersmann F
- Schroll A
- Mäkitalo N
- Arampatzis A.
Insufficient accuracy of the ultrasound-based determination of Achilles tendon cross-sectional area.
;
Kruse et al., 2017- Kruse A
- Stafilidis S
- Tilp M.
Ultrasound and magnetic resonance imaging are not interchangeable to assess the Achilles tendon cross-sectional-area.
). However, previous research suggested that US outperformed MRI with respect to the reliability of measuring tendon morphology.
Brushøj et al., 2006- Brushøj C
- Henriksen BM
- Albrecht-Beste E
- Hölmich P
- Larsen K
- Bachmann Nielsen M.
Reproducibility of ultrasound and magnetic resonance imaging measurements of tendon size.
found that US, when compared with MRI, had smaller within- and between-rater limits of agreement for Achilles tendon (AT) thickness. Moreover, the same study reported that US measures of AT thickness, CSA and width resulted in lower within-rater coefficients of variation, when compared with MRI. The use of US is recommended as a first-line imaging modality according to the last clinical indications of the European Society of Musculoskeletal radiology (
Klauser et al., 2012- Klauser AS
- Tagliafico A
- Allen GM
- Boutry N
- Campbell R
- Court-Payen M
- Grainger A
- Guerini H
- McNally E
- O'Connor PJ
- Ostlere S
- Petroons P
- Reijnierse M
- Sconfienza LM
- Silvestri E
- Wilson DJ
- Martinoli C
Clinical indications for musculoskeletal ultrasound: A Delphi-based consensus paper of the European Society of Musculoskeletal Radiology.
). In addition, US is an attractive alternative to assess tendon properties because of its affordability, time efficiency, portability and non-invasive nature. Despite the widespread use of US in musculoskeletal research, the reliability of US tendon measures is debated within the literature (
Gellhorn and Carlson, 2013Inter-rater, intra-rater, and inter-machine reliability of quantitative ultrasound measurements of the patellar tendon.
;
McAuliffe et al., 2017- McAuliffe S
- McCreesh K
- Purtill H
- O'Sullivan K
A systematic review of the reliability of diagnostic ultrasound imaging in measuring tendon size: Is the error clinically acceptable?.
). For example, US measures of PT CSA have been reported to be reliable when measured on multiple days (
), by multiple operators with different experience, using multiple machines (
Gellhorn and Carlson, 2013Inter-rater, intra-rater, and inter-machine reliability of quantitative ultrasound measurements of the patellar tendon.
). In contrast, more recent studies have found US to be unreliable when measuring PT and AT CSA (
Ekizos et al., 2013- Ekizos A
- Papatzika F
- Charcharis G
- Bohm S
- Mersmann F
- Arampatzis A.
Ultrasound does not provide reliable results for the measurement of the patellar tendon cross sectional area.
;
Bohm et al., 2016- Bohm S
- Mersmann F
- Schroll A
- Mäkitalo N
- Arampatzis A.
Insufficient accuracy of the ultrasound-based determination of Achilles tendon cross-sectional area.
), which was attributable, in part, to poor definition of tendon borders. With respect to the relationship between US and MRI, conflicting results have been reported in the literature.
Albano et al., 2017- Albano D
- Messina C
- Usuelli FG
- De Girolamo L
- Grassi M
- Maccario C
- Bignotti B
- Tagliafico A
- Sconfienza LM.
Magnetic resonance and ultrasound in Achilles tendinopathy: Predictive role and response assessment to platelet-rich plasma and adipose-derived stromal vascular fraction injection.
reported excellent agreement between MRI and US measures of AT (ICC = 0.986).
Kruse et al., 2017- Kruse A
- Stafilidis S
- Tilp M.
Ultrasound and magnetic resonance imaging are not interchangeable to assess the Achilles tendon cross-sectional-area.
reported that intra-rater US measures AT were reliable, but not interchangeable with MRI measures, as US underestimated AT CSA by ∼5.5%. Additionally, recent research by
Stenroth et al., 2019- Stenroth L
- Sefa S
- Arokoski J
- Toyras J.
Does magnetic resonance imaging provide superior reliability for Achilles and patellar tendon cross-sectional area measurements compared with ultrasound imaging?.
revealed that systematic differences between US and MRI measures of the PT were noted for inexperienced raters, with US underestimating PT CSA by 13.9% compared with MRI, but not for more experienced raters with more than 5 y of experience in musculoskeletal imaging and segmentation. This suggests a need to investigate the experience of the rater when assessing the reliability of US and MRI estimations of tendon measurements.
A typical approach when assessing tendon CSA is to measure the tendon at multiple sites, typically 25%, 50% and 75% of tendon length, and calculate an average based on those collective measures (
Onambele et al., 2007- Onambele GNL
- Burgess K
- Pearson SJ.
Gender-specific in vivo measurement of the structural and mechanical properties of the human patellar tendon.
;
Hicks et al., 2013- Hicks KM
- Onambele-Pearson GL
- Winwood K
- Morse CI.
Gender differences in fascicular lengthening during eccentric contractions: The role of the patellar tendon stiffness.
). However, studies investigating the reliability of US- and MRI-derived measures of tendons have only reported the results of the combined averages of the tendon and not each specific measurement site, despite taking multiple measurements along the tendon (
Kruse et al., 2017- Kruse A
- Stafilidis S
- Tilp M.
Ultrasound and magnetic resonance imaging are not interchangeable to assess the Achilles tendon cross-sectional-area.
;
Stenroth et al., 2019- Stenroth L
- Sefa S
- Arokoski J
- Toyras J.
Does magnetic resonance imaging provide superior reliability for Achilles and patellar tendon cross-sectional area measurements compared with ultrasound imaging?.
). Therefore, whether reliability differs between measurement sites for both US and MRI remains unknown, warranting further investigation.
An additional consideration when using estimates of tendon CSA to calculate structural properties such as tendon stiffness and YM is joint angle. Typically, PT stiffness and YM are calculated with the participant performing a ramped, isometric maximal voluntary contraction (iMVC) in an isokinetic dynamometer with the knee angle fixed at 90°. As PT CSA is an integral part of the equation used to calculate PT YM (PT stiffness × [PT length {mm}/PT CSA {mm
2}]) (
Onambele et al., 2007- Onambele GNL
- Burgess K
- Pearson SJ.
Gender-specific in vivo measurement of the structural and mechanical properties of the human patellar tendon.
), it would be prudent to calculate PT CSA at the knee angle relevant to the iMVC being performed. This would minimize any miscalculations caused by changes in PT CSA as a result of Poisson's ratio, whereby diameter would decrease at a constant to the strain (
Poisson, 1827Note sur l’extension des fils et des plaques élastiques.
), which would occur with an increase in knee joint angle. However, to date, no other study investigating the validity and reliability of PT CSA via US or MRI has employed a knee angle of 90°; therefore, the effects of knee joint angle on the accuracy of these measures remain unknown.
Collectively, these data suggest that the reliability and validity of US and MRI measures of tendon CSA are inconsistent and require further investigation. Therefore, the aims of this study were threefold: (i) to determine the agreement between US and MRI measures of PT CSA for two independent raters; (ii) to determine the within-day, inter- and intra-rater reliability for US and MRI measures of PT CSA; and (iii) to determine the between-day, inter- and intra-rater reliability of US measures of PT CSA.
Acknowledgments
The work was funded by the collaborative doctoral scheme between Northumbria University, UK, and the Talented Athlete Scholarships Scheme (TASS), UK, and by the Research Development Fund (RDF) Studentship Scheme. The magnetic resonance imaging costs were met by Newcastle Clinic, Newcastle, UK.
Data availability statement
The data that support the findings of this study are available from the corresponding author on reasonable request.
Article info
Publication history
Published online: November 11, 2022
Accepted:
October 14,
2022
Received in revised form:
September 27,
2022
Received:
June 21,
2022
Copyright
© 2022 The Author(s). Published by Elsevier Inc. on behalf of World Federation for Ultrasound in Medicine & Biology.