WHEN TO USE US, MR OR BOTH

– Written by Marcelo Bordalo, Maryam Al-Naimi, Eduardo Yamashiro, Qatar

INTRODUCTION

Traumatic muscle injuries represent a significant issue for athletes, contributing to as much as 30% of professional sports-related injuries¹. These injuries result in substantial time lost in competitions, up to 40% for professional athletes, highlighting their considerable economic and social impact². Consequently, there has been a strong focus on developing diagnostic and therapeutic strategies to expedite recovery and minimize the likelihood of recurrence. In professional sports, the primary objective is to ensure an athlete’s swift and safe return to training and competition, while minimizing the risk of reinjury or exacerbation. A comprehensive initial clinical evaluation is essential for determining prognosis and appropriate treatment, aimed at reducing recovery time. Imaging techniques, such as ultrasound (US) and magnetic resonance (MR) imaging, are instrumental in guiding the prognosis, treatment, and assessment of return-to-play timelines³. We explore the clinical relevance of US and MR imaging in the evaluation of muscle injuries, providing a comparison of these modalities.

TECHNICAL AND CLINICAL ASPECTS OF ULTRASOUND

Contemporary ultrasound (US) technology offers exceptional spatial resolution, enabling the visualization of muscle fascicles and perimysium at less than 200 micrometers, surpassing the resolution of MR imaging⁴. High-frequency linear probes (greater than 10 MHz) are typically utilized to detect muscle tears. In patients with substantial adipose tissue or thick musculature, low-frequency convex probes may also be employed⁵. The superior spatial resolution of high-frequency probes facilitates the differentiation of tissue structures. However, these probes are less effective in visualizing deeper tissues due to greater absorption of ultrasound waves at higher frequencies. Advances in technology, such as tissue harmonic imaging and postprocessing algorithms, alongside probes with frequencies up to 20 MHz, enhance tissue contrast and allow for better visualization of muscle architecture. Extended field-of-view imaging is particularly advantageous for evaluating large lesions.

US imaging typically shows muscle fascicles as hypoechoic linear structures, with the perimysium appearing as hyperechoic lines (Figure 1). During contraction, muscle fascicles thicken and shorten, creating a hypoechoic appearance⁶.

A systematic imaging protocol begins with identifying the suspected lesion site on longitudinal and transverse planes, followed by scanning the entire muscle belly, including the proximal and distal entheses, myotendinous junction, and fascia⁷. Comparing findings with the contralateral asymptomatic side can aid in accurate assessment. Dynamic evaluation during muscle contraction or passive mobilization helps in grading the severity and extent of tears (Figure 2).

Ideally, US examinations should be conducted 48 hours post-injury to minimize false negatives or underestimations⁸. Ultrasound characteristics of muscle injuries include a disrupted fascicular pattern, the presence of hypoechoic and/or hyperechoic focal areas within the muscle, and either partial or complete discontinuity of muscle fibers (Figure 3). These disruptions are commonly observed near the myofascial or myotendinous junctions but can occur anywhere within the muscle. Following direct or indirect tears, interstitial hemorrhage is typically seen as a hyperechoic region with poorly defined boundaries. In cases of severe tears, intramuscular hematomas may form, exhibiting variable echogenicity depending on the stage of the lesion. During the acute phase (within the first 48 hours), hematomas appear hyperechoic, transitioning to iso- or hypoechoic as liquefaction and resorption progress (Figure 4), often accompanied by internal debris (Figure 5). Chronic stages may result in the formation of a focal hyperechoic scar (Figure 6).

Power or color Doppler imaging can reveal hyperemia surrounding the site of the tear, attributable to the formation of granulation tissue. This feature is particularly valuable for follow-up evaluations, helping to distinguish chronic tears from recent re-injuries (Figure 7). Hyperemia, caused by angiogenesis around the tear, typically becomes evident 3 to 8 days post-injury and subsides after approximately 12 weeks⁹. Persistent Doppler signals suggest ongoing activity within the tear, although there is no established correlation between Doppler positivity and the timeline for healing or return to physical activity. Therefore, clinical assessment remains an essential component of patient evaluation.

IMAGING METHOD: MR IMAGING

While MR imaging does not offer the same spatial resolution as US, it is highly sensitive to low-grade injuries, especially in deeply situated muscles. It provides excellent tissue contrast, reproducibility, and is particularly effective for identifying injuries in inaccessible locations. Typical MR imaging features of muscle injuries include diffuse, ill-defined high-signal intensity on fluid-sensitive sequences, indicative of edema, often presenting with a “feathery” appearance around the musculotendinous junction (Figure 8)¹⁰. Fiber discontinuity is observed as focal, well-defined high-signal regions, and unique injuries such as intramuscular degloving tears can also be identified (Figure 9)¹¹. Muscle injuries occurring far from connective tissue attachments are less common and usually associated with direct trauma or contusions (Figure 10).

ULTRASOUND OR MR IMAGING: WHICH MODALITY TO USE?

Both US and MR imaging possess unique advantages for evaluating muscle injuries (Table 1). US is cost-effective, accessible, quick, and offers real-time dynamic assessments. It is particularly useful for visualizing superficial tears and differentiating connective tissue structures masked by edema in MR imaging. However, US is less sensitive to low-grade injuries and heavily operator-dependent. MR imaging remains the gold standard due to its superior contrast resolution and ability to evaluate deep and proximal injuries, as well as bone and soft tissue structures. It is often preferred for assessing high-performance athletes, guiding surgical decisions, and resolving diagnostic uncertainties in chronic or complex cases. However, US in experienced hands is comparable to MR imaging in the detection of muscle injuries¹².

US and MR imaging complement each other in many clinical scenarios, with the choice of modality often dictated by the clinical setting, severity, and location of the injury, as well as the specific diagnostic or therapeutic goals.

Marcelo Bordalo M.D., Ph.D.

Radiologist

Chief of Radiology

Maryam Al-Naimi M.D.

Radiology Consultant

Eduardo Yamashiro M.D.

Radiology Consultant

Aspetar Orthopaedic and Sports Medicine Hospital

Doha, Qatar

Contact: marcelo.bordalo@aspetar.com

References

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