MRI is considered the gold standard examination in the detection of muscle traumas,
but the advantages of US over MRI in the acute and hyperacute phase consist in decreased cost,
wide availability and superior portability.
US also has an increased spatial resolution over MRI because it allows additional scans in all planes depending on the anatomical site of the lesions and a dynamic evaluation of the injury.
[2,
3]
US examination is limited by operator dependency and limited field of view (FOV) acquisition.
Linear high-frequencies arrays have low tissue penetration capability and US can miss deep lesions.
In these cases,
MRI should be regarded as the imaging modality of choice because a panoramic and extended FOV allows a more accurate assessment of subtle and deep muscle injuries.
[1]
Another important limit of US examination is that US demonstrated low sensitivity in detection of minor traumas (75% vs 97% in case of major traumas),
because US findings are vague and indistinct with poor oedema and without significant fiber disruption.
This was due to the ultrasonographic lack of contrast between the relatively low echotexture of normal muscle and the low echogenicity of muscle edema in mild injuries.
Megliola et al [4] confirmed this discrepancy between minor and major traumas (US sensibility 76.9% vs 92.7%) and demonstrated that the ability of US to evaluate muscle traumas is related to the presence of severe muscle oedema.
Studying 26 patients with minor traumas,
Megliola et al observed that US sensibility was low in detecting DOMS (57%),
lengthening (80%) and mild contusions (87.5%) because of the presence of small oedema and no significant muscle damage.
Therefore,
in the same study,
Megliola et al also observed that in 29 patients with major traumas (severe contusions),
US was in total agreement with MRI in detecting the presence and the extent of large hematomas.
Connell et al [5] studied 60 professional football players with suspected acute hamstring strain and confirmed that MRI and US are equally useful to identify muscle injuries at baseline.
The extent of the injuries was consistently larger on MRI than on ultrasonography and this discrepancy was due to the increased sensitivity of MRI in showing subtle edema.
Studying 17 patients suffering of acute injury of the rectus femoris,
Bianchi et al [6] confirmed that US demonstrated high sensibility in detection of superficial muscular lesions and hematomas and that ultrasonographic data were straightly correlated with MR findings.
Bianchi et al concluded that US should be considered the first-line technique in the evaluation of injuries of superficial muscles.
Muscle injuries are extremely common either in professional or in amateur athletes and are a major cause of loss of competitive playing time.
Imaging now plays an increasing role in lesion detection,
grading and prognosis of muscle injury.
US is the first-line technique for examination of muscle injuries,
because it is readily accessible,
cheap and dynamic.
US also have the benefits of real-time evaluation and Doppler imaging and the ability to perform interventional procedures.
Direct and indirect muscle injuries and their complications are readily assessed using either US or MRI (the gold standard imaging technique),
but US is preferred in follow up.
The main limit of US examination is evident in muscular injuries with only slight muscle alterations and without significant fiber disruption and may produce false negative results such as in mild contusions,
lengthenings and DOMS.