Are Ultrasound Measurements of Achilles Tendon Size Reliable? A Systematic Review of Rater Reliability

Measuring Ultrasonographic Thickness of the Achilles Tendon Insertion Is Less Reliable Than the Midportion in Healthy Tendons and Patients With Tendinopathy

INTRODUCTION

Ultrasound is the preferred imaging method in the diagnostic process of Achilles tendinopathy (AT). Ultrasound tissue characterization (UTC) is a frequently used, standardized and valid method to assess tendon geometry in AT patients. It is unknown whether UTC is reliable for measuring Achilles tendon thickness. The aim of the study was to assess intra- and inter-rater reliability of Achilles tendon thickness measurements using UTC in both asymptomatic individuals and patients with AT, and to evaluate if the reliability of thickness measurements differs between the midportion and insertional area.

METHODS

Exactly 50 patients with AT and 50 asymptomatic individuals were included. Using the conventional US and standardized UTC procedure maximum thickness was measured in the midportion and insertion region. To determine inter- and intra-rater reliabilities, the intraclass correlation coefficient (ICC) was used.

RESULTS

The ICC values for inter- and intra-rater reliability were classified as "excellent," for the AT group (0.93 [95% CI: 0.88-0.96] and 0.95 [0.92-0.97]) and asymptomatic participants (0.91 [0.87-0.94] and 0.94 [0.92-0.96]). The reliability of measuring tendon thickness in the midportion region was "excellent," with both inter-rater (0.97 [0.95-0.98]) and intra-rater (0.98 [0.96-0.99]) ICC values indicating high levels of agreement. In the insertional region, ICC values for inter-rater (0.79 [0.69-0.87]) and intra-rater (0.89 [0.84-0.93]) reliability were "moderate to good."

CONCLUSION

We showed excellent reliability for measuring the US thickness of the midportion and good reliability of measuring the insertional region in patients with AT. Significantly lower ICCs were observed for the reliability of thickness measurements in the insertional region when compared with the midportion.

Early Tendon Morphology as a Biomarker of Long-term Patient Outcomes After Surgical Repair of Achilles Tendon Rupture: A Prospective Cohort Study

Background

Patient outcome after acute Achilles tendon rupture (ATR) varies and is difficult to predict. Whether early variations in healing, visualized with ultrasonography, can predict long-term patient outcome is unclear.

Purpose

To (1) examine the associations of Achilles tendon cross-sectional area (CSA) and elongation (TE) during healing of ATR repair with patient outcomes at 12 months postoperatively and (2) investigate the predictive or diagnostic capacity of the morphological biomarkers.

Study Design

Cohort study; Level of evidence, 2.

Methods

This study was based on previously collected data from 86 patients who underwent acute standardized ATR repair between 2013 and 2018 and who were included in a prior randomized trial investigating early functional mobilization (EFM). In the EFM group, loading was allowed immediately after surgery, while in the comparison group, loading was allowed first at 2 weeks postoperatively. Achilles tendon CSA and length were measured with ultrasound at 6 weeks, 6 months, and 12 months postoperatively. CSA ratio and absolute difference in the length of the healthy and injured tendons were calculated. Patient-reported outcome was registered with the validated Achilles tendon Total Rupture Score and functional outcome with the heel-rise endurance test at 12 months postoperatively. The limb symmetry index (LSI) was calculated for maximum heel-rise height (HRHmax) and total concentric work. Multiple linear regression adjusted for age was used, and the area under the receiver operating characteristic curve (AUC) was calculated to evaluate predictive capacity.

Results

A larger CSA ratio at 6 weeks was associated with higher LSI HRHmax at 12 months (R2, 0.35; P < .001) and exhibited good predictive capacity (AUC, 0.82). More TE at 12 months was associated with lower LSI total concentric work at 12 months (R2, 0.21; P = .001) and exhibited acceptable predictive capacity (AUC, 0.71).

Conclusion

Greater Achilles tendon CSA seen on ultrasound 6 weeks after surgical repair had good clinical prediction for long-term functional outcome. TE at 12 months was predictive of inferior functional outcome.

Registration

NCT02318472 (ClinicalTrials.gov identifier).

B-Mode Ultrasonography Is a Reliable and Valid Alternative to Magnetic Resonance Imaging for Measuring Patellar Tendon Cross-Sectional Area

This study investigated the validity and reliability of measuring patellar tendon (PT) cross-sectional area (CSA) using magnetic resonance imaging (MRI) and ultrasound (US) imaging. Nineteen healthy participants (10 women, 9 men) participated in three imaging sessions of the PT, once via MRI and twice via US, with image acquisition conducted by two raters, one experienced (rater 2) and one inexperienced (rater 1). All PT segmentations were analyzed by both raters. The validity of US-derived estimates of PT CSA against MRI estimates was analyzed using linear regression. Within-day reliability of US and MRI measurements and between-day reliability of US measurements were quantified using typical error (TE) and intra-class correlation coefficients (ICC_3,1). There was good agreement between US- and MRI-derived estimations of PT CSA (standard errors of the estimate of 3.3 mm² for rater 1 and 2.6 mm² for rater 2; Pearson's r = 0.97 and 0.98 for raters 1 and 2, respectively). Within-session reliability for estimations of total PT CSA from US and MRI were excellent (ICC_3,1 >0.95, coefficient of variation [CV] <4.1%, TE = 1.3-3.6 mm². Between-day reliability for US was excellent (ICC_3,1 >0.97, CV <2.7%, TE = 1.6-2.3 mm²), with little difference between raters. These findings suggest that MRI and US both provide reliable estimates of PT CSA and that US can provide a valid measure of PT CSA.

A Narrative Review of the Classification and Use of Diagnostic Ultrasound for Conditions of the Achilles Tendon

Enthesitis is a cardinal feature of spondyloarthropathies. The Achilles insertion on the calcaneus is a commonly evaluated enthesis located at the hindfoot, generally resulting in hindfoot pain and possible tendon enlargement. For decades, diagnosis of enthesitis was based upon patient history of hindfoot or posterior ankle pain and clinical examination revealing tenderness and/or enlargement at the site of the tendon insertion. However, not all hindfoot or posterior ankle symptoms are related to enthesitis. Advanced imaging, including magnetic resonance imaging (MRI) and ultrasound (US), has allowed for more precise evaluation of hindfoot and posterior ankle conditions. Use of US in diagnosis has helped confirm some of these cases but also identified other conditions that may have otherwise been misclassified without use of advanced imaging diagnostics. Conditions that may result in hindfoot and posterior ankle symptoms related to the Achilles tendon include enthesitis (which can include retrocalcaneal bursitis and insertional tendonopathy), midportion tendonopathy, paratenonopathy, superficial calcaneal bursitis, calcaneal ossification (Haglund deformity), and calcific tendonopathy. With regard to classification of these conditions, much of the existing literature uses confusing nomenclature to describe conditions in this region of the body. Some terminology may imply inflammation when in fact there may be none. A more uniform approach to classifying these conditions based off anatomic location, symptoms, clinical findings, and histopathology is needed. There has been much debate regarding appropriate use of tendonitis when there is no true inflammation, calling instead for use of the terms tendinosis or tendonopathy. To date, there has not been clear examination of a similar overuse of the term enthesitis in conditions where there is no underlying inflammation, thus raising the need for more comprehensive taxonomy.

Techniques for In Vivo Measurement of Ligament and Tendon Strain: A Review

The critical clinical and scientific insights achieved through knowledge of in vivo musculoskeletal soft tissue strains has motivated the development of relevant measurement techniques. This review provides a comprehensive summary of the key findings, limitations, and clinical impacts of these techniques to quantify musculoskeletal soft tissue strains during dynamic movements. Current technologies generally leverage three techniques to quantify in vivo strain patterns, including implantable strain sensors, virtual fibre elongation, and ultrasound. (1) Implantable strain sensors enable direct measurements of tissue strains with high accuracy and minimal artefact, but are highly invasive and current designs are not clinically viable. (2) The virtual fibre elongation method tracks the relative displacement of tissue attachments to measure strains in both deep and superficial tissues. However, the associated imaging techniques often require exposure to radiation, limit the activities that can be performed, and only quantify bone-to-bone tissue strains. (3) Ultrasound methods enable safe and non-invasive imaging of soft tissue deformation. However, ultrasound can only image superficial tissues, and measurements are confounded by out-of-plane tissue motion. Finally, all in vivo strain measurement methods are limited in their ability to establish the slack length of musculoskeletal soft tissue structures. Despite the many challenges and limitations of these measurement techniques, knowledge of in vivo soft tissue strain has led to improved clinical treatments for many musculoskeletal pathologies including anterior cruciate ligament reconstruction, Achilles tendon repair, and total knee replacement. This review provides a comprehensive understanding of these measurement techniques and identifies the key features of in vivo strain measurement that can facilitate innovative personalized sports medicine treatment.

Proposing a Minimal Data Set of Musculoskeletal Ultrasound Imaging Biomarkers to Inform Clinical Practice: An Analysis Founded on the Achilles Tendon

Tendon integrity can be described using a wide range of biomarkers via specialized analysis software for images recorded by musculoskeletal ultrasonography. This study proposes a minimal biomarker data set to characterize Achilles tendon ultrasound images and to differentiate between symptomatic and asymptomatic Achilles tendon images. Forty-one individuals with unilateral Achilles tendinopathy and 35 healthy controls had their Achilles tendon images recorded bilaterally by ultrasonography in the longitudinal and transverse planes. A set of 22 biomarkers, organized around three dimensions (geometric, composition and texture), were computed in each plane. A symmetry index, reflecting relative side differences, was compared between groups and analyzed through principal component analysis to isolate biomarkers that best explained data variance. A specific minimal data set was identified by linear regression in the longitudinal (mean thickness, echogenicity, variance and homogeneity at 90°) and transverse (mean thickness, echogenicity and mean homogeneity) planes to characterize and differentiate Achilles tendon integrity.

Does Magnetic Resonance Imaging Provide Superior Reliability for Achilles and Patellar Tendon Cross-Sectional Area Measurements Compared with Ultrasound Imaging?

This study investigated the reliability of Achilles and patellar tendon cross-sectional area (CSA) measurement using ultrasound imaging (USI) and magnetic resonance imaging (MRI). Fifteen healthy adults were imaged twice on two occasions, interrupted by a tendon loading protocol. Tendon CSA segmentations were conducted by an experienced and an inexperienced rater blinded to information regarding subject, session and loading status. USI provided good test-retest reliability (intra-class correlation coefficient [ICC] 2,1 > 0.85, standard error of measurement [SEM] 5%-6%), while with MRI it was excellent (ICC 2,1 > 0.92, SEM 4%) for the experienced rater. This study suggests that MRI provides superior reliability for tendon CSA measurements compared with USI. However, the difference in reliability between the methods was small, and the results were inconclusive regarding objectivity and sensitivity to change when assessed based on the effect of loading. We concluded that both methods can be used for reliable CSA measurements of the Achilles and patellar tendons when using a highly standardized measurement protocol and when conducted by an experienced rater.