Fig. 7.1
Fusion technology is extremely useful, especially in following up lesions, since the overlay of the initial US and MRI scans enables superimposition of further scans and demonstration of any changes
7.4 Elastography
Elastography is currently available in all ultrasound scanners. It is based on the principle that a distinctive vibration is associated with the degree of elasticity of the tissue being examined. The vibration, obtained by moderate tissue compression with the probe, is translated by the software into a colour map (Fig. 7.2a–b).
Fig. 7.2
(a–b) Elastography is a useful technique to assess musculoskeletal conditions, thanks to the vibrating probe and the generation of a colour map reporting the degree of tissue elasticity (from soft to hard). Note the altered elasticity due to contracture of the left anterior rectus abdominis muscle
Elastography allows excellent follow-up assessment of muscle and tendon lesions by demonstrating the recovery of elasticity in areas that have suffered injury.
The technique can be applied to all anatomical structures, including cartilage, ligaments, vessels, and bone.
Notably, second-generation machines are endowed with electronic control, which eliminates artefacts due to differences in tissue compression by the operator.
7.5 Muscles
7.5.1 Trauma-Related Conditions
Muscle traumas are divided into minor and major.
7.5.1.1 Minor Traumas
Minor muscle traumas include elongations, contusions, and contractures as well as crush injury involving subcutaneous adipose tissue, such as lipodystrophy, lymphoedema, and fat necrosis.
In the latter three conditions, US plays a key role: dynamic US provides a highly accurate and detailed assessment of the involvement of subcutaneous fat tissue and of blood extravasation, to exclude subfascial involvement, while vascular injuries are assessed with colour and power Doppler.
Elastography is a key technique, since it allows monitoring the possible loss of elasticity of subcutaneous adipose tissue due to injury (Fig. 7.3).
Fig. 7.3
Typical loss of subcutaneous adipose tissue elasticity due to contusion and compression
B-mode US does not play a large role in assessing elongations and contractures, because the absence of fibre lesions entails that there forms no haematoma but only a moderate and diffuse intramuscular oedema.
Oedema is not clearly depicted by US, but power Doppler accurately shows obvious vascular injuries, at least compared with the contralateral muscles (Fig. 7.4a).
Fig. 7.4
(a) A power Doppler scan always shows hypervascularity in the area affected by minor traumas like elongations and contractures. (b) Elastography documents a high degree of tissue elasticity at the site of the injury, due to reactive oedema
Elastography is the method of choice to assess contractures and elongations, since it clearly demonstrates the actual loss of elasticity of muscle component during compression.
As regards contusions, US is not very informative, whereas elastography demonstrates increased tissue elasticity related to the diffuse oedema (Fig. 7.4b).
Elastography is conclusive in patients with delayed-onset muscle soreness (DOMS) (Fig. 7.5).
Fig. 7.5
Elastography is the method of choice to assess DOMS, because it depicts the area characterized by a higher degree of elasticity due to haematoma formation and fluid infiltration through the fascia
7.5.1.2 Major Traumas
Major muscle traumas are divided into partial and complete ruptures.
The US report should always provide a detailed and accurate description of the lesion, its extent, and any involvement of adjacent structures.
Partial ruptures are divided into grade 1 and 2.
In grade 1 lesions, the US scan is sometimes poorly informative, because a small lesion may be barely identifiable in patients with extensive injury. In such cases, the partial lesion is more clearly demonstrated by MRI and elastography.
Grade 2 ruptures should be assessed by dynamic US, because in patients with limited injury extension static, US may fail to depict a small lesion, due to the bundling up of muscle fascicles.
If a lesion is indeed present, dynamic US affords optimal evaluation, because during the contraction phase, the muscle fibres separate, and the haematoma is clearly visualized (Fig. 7.6a–b).
Fig. 7.6
(a–b) In patients with minor partial lesions, dynamic US provides key diagnostic information by demonstrating stump retraction during muscle contraction, whereas the bundling up of muscle fascicles in static US scans may lead to misdiagnosis
In such cases, elastography shows an area of higher elasticity related to haematoma colliquation.
7.5.2 Complete Ruptures
Complete muscle ruptures are full-thickness, grade 3 lesions that may extend predominantly in longitudinal or vertical direction.
Timely US diagnosis is of crucial importance, because full-thickness lesions with a predominantly vertical pattern can be repaired if surgery is promptly performed (Fig. 7.7).
Fig. 7.7
Nearly complete rupture of the triceps brachii muscle assessed ca. 12 h after the trauma (acute phase). The lesion is predominantly vertical and is thus amenable to repair, if surgery is promptly performed
Lesions that extend longitudinally over several centimetres are rarely amenable to surgery.
On US examination, complete lesions always have the classic “bell clapper” appearance, due to retraction of the muscle stumps in opposite directions (Fig. 7.8).
Fig. 7.8
Distinctive “bell clapper” sign due to muscle retraction as a result of complete rupture associated with haematoma and marked vascular inflammation, demonstrated by power Doppler
The US and MRI scan of the haematoma share several similarities, depicting the haemoglobin phases from the early stage of formation to its organization (Fig. 7.9).
Fig. 7.9
Acute musculotendinous disinsertion at the level of the proximal insertion of the adductor longus tendon. Note the haematoma between the stumps
US examination of partial and complete ruptures should be performed within 48–72 h of the trauma, because after this time the acute oedema makes it more difficult to evaluate the extent of the lesion.
7.5.3 Myotendinous Disinsertion
Muscle lesions do not always occur within the muscle belly.
In those at the level of the myotendinous junction, US plays a key role, since prompt and accurate examinations are crucial for successful surgical repair.
The US scans show the typical downstream retraction of the tendon stump; the retracted, tapering muscle; and a large interposed haematoma.
Elastography is extremely useful, since it depicts the complete loss of tendon tension and the increased, marked elasticity of the muscle due to retraction and the haematoma.
7.5.4 Myofascial Disinsertion
Myofascial disinsertions are often difficult to detect by US, because if they are extensive and, especially, they are assessed in the acute phase, it may underestimate their extent.
In such cases, elastography provides key information by depicting the altered elasticity of the myofascial components at the lesion site. MRI is conclusive, because it demonstrates lesion extension and the detached muscle fibres at the site of the injury.
7.5.5 Myotendinous Avulsion
US does not play a primary role in the assessment of these lesions, due to the frequent presence of periosteal fragments.
In these patients, US examination is hampered by the common presence of tendon changes that date back to adolescence, where ossification centres on both sides hamper the differential diagnosis.
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