Measurement of Healthy and Injured Triceps Surae Morphology
Summary
Ultrasound imaging is becoming more accessible in clinical and research settings, and a consistent protocol will be beneficial for comparison between studies and for clinical interpretations. This protocol for ultrasound evaluation is a valid and reliable method to evaluate Achilles tendon morphology in healthy, tendinopathic, and ruptured tendons.
Abstract
Achilles tendon injuries occur throughout the lifespan and can negatively affect quality of life and overall health. Achilles tendinopathy is generally classified as an overuse injury associated with fusiform tendon thickening, neovascularization, and interstitial tendon degeneration. Current literature suggests these structural changes are associated with symptoms and lower physical activity levels, as well as symptoms and lower extremity function in the long term. Surgically and non-surgically managed Achilles tendon ruptures result in increased tendon cross-sectional area (CSA) and a lengthened Achilles tendon. Both structural outcomes have clinical implications, as larger CSA positively predicts function, whereas increased tendon lengthening predicts reduced function after Achilles tendon rupture. Given the relationship between structural changes associated with Achilles tendon injuries for both injury severity and injury recovery, it is critical to be able to quantify Achilles tendon structure reliably and accurately. Silbernagel's group has established a valid and reliable method for efficiently evaluating triceps surae muscle and tendon structure. In this protocol, B-mode musculoskeletal ultrasound imaging is used to measure triceps surae structure, including Achilles tendon thickness and CSA, soleus thickness, and the presence of additional findings (calcifications and bursitis). B-mode extended field-of-view is used to measure Achilles tendon length and gastrocnemius anatomical CSA. Finally, power Doppler is used to identify intratendinous neovascularization. Quantification of triceps surae structure allows for comparison between limbs as well as longitudinal changes in response to exercise and treatment for healthy individuals and those with Achilles tendon injuries. This protocol has been used in many research studies to date and proves valuable in understanding the relationship between tendon structure and injury development, severity, and recovery. As ultrasound devices are becoming more affordable and portable, this protocol proves promising as a clinical tool, given its quick and efficient methods.
Introduction
The Achilles tendon originates at the myotendinous junctions of the gastrocnemius and soleus muscles and inserts on the posterior calcaneus. The Achilles tendon consists primarily of densely packed, organized collagen tissue arranged in a hierarchical fashion to maximize tensile strength1. Despite its ability to withstand heavy forces, the Achilles tendon is susceptible to several types of injuries throughout one's lifespan. These injuries, such as Achilles tendinopathy and Achilles tendon ruptures, are often accompanied by changes in the structure of the triceps surae and surrounding tissues. In Achilles tendinopathy, patients often exhibit fusiform tendon thickening, tendinosis, collagen disorganization, and neovascularization, a process of proliferation of vascular and neural tissue into the tendon2. Additionally, pathological changes associated with Achilles tendinopathy include paratendinitis, intratendinous, and/or entheseal calcifications, and bursitis2,3. After Achilles tendon ruptures, structural changes are common occurrences, irrespective of treatment, and include Achilles tendon thickening and increased tendon length4,5. Furthermore, muscular changes, such as triceps surae muscular atrophy, are also commonly associated with Achilles tendon injuries5,6.
The ability to assess triceps surae and surrounding tissue structures provides valuable insight into structural integrity, tissue quality, and size, which are known to relate to symptoms, function, and prognosis4,7,8,9. Ultrasound imaging is a reliable and valid assessment tool of these structures, including, but not limited to, Achilles tendon length10, thickness10,11, cross-sectional area (CSA)12, gastrocnemius anatomical CSA13, and neovascularization14,15. Assessment of these measures provides valuable insight into the understanding of healthy triceps surae tissue, as well as quantification of structural alterations to evaluate injury risk, severity, and recovery, as well as understanding healthy tissue qualities16.
Despite the clinical and research utility of ultrasound imaging in assessing triceps surae structure, there are often differences in imaging techniques and measurement parameters among clinical and research studies17,18. As a result, comparisons between studies are difficult. Therefore, the purpose of this methods paper is to describe a valid and reliable protocol for efficiently evaluating triceps surae muscle and tendon structure using musculoskeletal ultrasound imaging. This protocol aims to demonstrate the feasibility of incorporating this tool into research and clinical settings through its entirety or as specific parts in healthy and injured individuals. In addition, representative values for healthy and injured triceps surae are provided.
Protocol
Representative Results
Discussion
Critical steps in the protocol to ensure the validity and reliability of the methods include the use of skin markings on participants to guide the ultrasound exam and the required training of individuals performing the measurements used in research studies. Skin markings at specific documented locations assist in the ability to assess variables of interest consistently and accurately at the same locations in the same individual over time. Furthermore, applying skin markings to different individuals in the same systematic…
Disclosures
The authors have nothing to disclose.
Acknowledgements
The authors would like to thank past and current members of the Delaware Tendon Research Group who have assisted in data collection using this protocol. Research reported in this publication was supported by the National Institute of Arthritis and Musculoskeletal and Skin Diseases of the National Institutes of Health under Award Numbers R01AR072034, R01AR078898, F31AR081663, R21AR067390, and by Eunice Kennedy Shriver National Institute of Child Health and Human Development of the National Institutes of Health under the award number T32HD007490. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. Research reported in this publication was also supported by grants provided by the Swedish Research Council for Sport Science, the Stockholm County Council (ALF project), and the Swedish Research Council. This work was also supported in part by a Promotion of Doctoral Studies Scholarship from the Foundation for Physical Therapy Research and by the Rheumatology Research Foundation Medical and Graduate Student Preceptorship.
Materials
| Aquaflex Stand Off Pad | Parker Laboratories | E8317C | |
| Aquasonic ultrasound Gel | Parker Laboratories | E8365AF | |
| Linear Array Ultrasound Probe L4-12t-RS | GE Healthcare | 5495987 | |
| LOGIC e Ultrasound | GE Healthcare | E8349PA | |
| Osirix Dicom Viewer | Pixmeo SARL | Software for measurements |
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