The muscles are affected in about 30% of sports injuries. Blunt trauma is the most prevalent cause of direct muscle injuries in sports (soccer, football, rugby), more common in the lower limbs.
Tennis leg or gastrocnemius muscle injury represents the tear/rupture of the medial head of gastrocnemius at its insertion. After the trauma, an intramuscular fluid collection is typically present within the muscle. In the early stages, the fluid accumulation may appear hyperechogenic, in more advanced stages echos may appear (inhomogeneous) and in chronic stage, the collection becomes anechoic. Perilesional areas of hyperemia are observed with power/color Doppler mode, and are present in the reparative phase. Partial tears have three grades: from grade 1 (small hematomas) to grade 3 (more than 1/3 of the muscle is affected, the hematomas are bigger than 3 cm). In complete tears the muscular continuity is lost, with a gap at the site of lesion.
Other muscular rupture produced by sports activities is plantaris muscle injury, which can be very clinically similar to deep vein thrombosis. The muscular fibers are disorganized, with the presence of hematoma, but in chronic phase fibrosis or granulation tissue is observed.
On fat-suppressed fluid-sensitive sequence, in the acute phase, there is hyperintensity, with interstitial edema, hemorrhage, and muscle swelling.
In the subacute phase, hemorrhagic components may be visible, with a high signal on T1WI. MRI is very useful in depicting intramuscular edema, and if the mechanism of injury is direct, the edema is laid along the direction of force vector (this is not seen in the indirect mechanism). In the early stages, there is muscle laceration, and over time a defined intramuscular fluid accumulation appears, with muscular high signal (STIR sequences) in the periphery of the hematoma. The appearance of the hematoma changes over the time: hyperacute (intermediate on T1WI, hyperintense on T2WI), acute (intermediate on T1WI, hypointense on T2WI), early subacute (hyperintense on T1WI, hypointense on T2WI), late subacute (hyperintense on T1WI, hyperintense on T2WI) and chronic (hypointense on T1WI, hypointense on T2WI).
Fibrosis (hypointense on all MRI sequences) and/or calcification (leading to myositis ossificans) may appear after the hematoma is healing.
Femoral distal fracture occurs in contact sports (football, soccer or basketball) and falling. Frequently affected structures are distal femoral metaphysis or femoral condyles, with or without intra-articular extension. Stress fractures are common in high-level athletes. MRI highlights associated soft tissue injury: cruciate ligament/meniscus tears, neurovascular injury (popliteal artery). According to the Seinsheimer classification, the fractures can be: supracondylar, intercondylar, at the condyle of Hoffa’s fracture. Tibial plateau fractures appear in high-impact sports such as basketball, rugby, mostly involving the lateral plateau. According to the Schatsker classification, the fractures can be with a depressed component (displacement below the level of the surrounding articular surface) or split component (extension from the articular surface to the edge of the metaphyseal cortex). MRI findings are low (T1W1/T2WI) signal intensity fracture line and surrounding edema (high signal T2WI/STIR), and lipo-sero-hemarthrosis can appear. A Segond fracture represents an avulsion fracture of the lateral tibial plateau at the insertion of the midportion of the lateral collateral ligament, with a specific “lateral capsular sign” (elliptical bone fragment parallel to the lateral tibial plateau) and with associated ACL tear.
Ultrasound can demonstrate a discontinuation of the cortical line (normally hyperechogenic), with surrounding fluid.
Osteochondritis dissecans occurs during sports that involve high-impact and can be presented with fluid that fills variable-sized osteochondral defect, well seen on MRI (the composition of the fragment (bone, cartilage, reparative fibrous tissue) affects its appearance). The articular cartilage has in composition a high amount of water, so at ultrasound it will be hypoechogenic, with its sharp margins. The presence of cartilage defects is identified with ultrasonography (areas of hyperechogenicity). Ultrasound can differentiate between degrees of cartilage damage (4 grades: 1. The margin is blurred, without thickness anomaly; 2. Blurring margin of the cartilage with local thinning (<50%); 3. Blurring margin of the cartilage with local thinning (>50%); 4. Complete loss of cartilage, irregular cartilage-bone interface).
Meniscal tears can be horizontal (with or without displaced meniscal flap), longitudinal (‘’bucket-handle’’ lesion, flipped meniscus), radial or complex. About 50% of active soccer players suffer a meniscus injury. The ultrasound technique shows a discrete hypoechoic/anechoic cleft or a defect in the normal hyperechoic meniscus. Meniscal tears are incompletely visualized with ultrasound evaluation, but MRI is the gold standard in the characterization of the meniscal tears. A good clue for the diagnosis of meniscal lesions is the presence of a parameniscal cyst in the periphery of the meniscus (which can be anechoic/hypoechoic/complex). Ultrasound can evaluate the extrusion of the meniscus.
Horizontal tears divide the meniscus into a top and bottom part, and may be associated with displacement of a disc fragment (in the intercondylar notch/medial recesses). Longitudinal tears are seen in young athletes, with a vertically oriented, linear increase intra-meniscal signal (best seen on PDWI) contacting superior and/or inferior articular surface. A bucket-handle tear represents a longitudinal tear with the inner fragment displaced centrally toward or into the intercondylar notch, while the displaced fragment retains anterior/posterior attachments to the remaining peripheral portion. Some specific signs are: truncation of the meniscal body (coronal), irregular posterior horn (sagittal), double PCL sign (displaced meniscal fragment found in the intercondylar fossa-on sagittal). A flipped meniscus is a variation of the "bucket-handle" lesion characterized by a capsular detachment, commonly involving the posterior horn, which flips over the anterior horn. Radial meniscal lesions are perpendicular to the long axis of the meniscus, with a specific ghost meniscus sign that represents no meniscal tissue, best seen on coronal MRI sequence and v-shaped/linear defect at the free edge with varying degrees of peripheral involvement on axial images. Complex lesions present with abnormal meniscus signal intensity extending to at least one articular surface of meniscus, with tear propagating in > 1 plane (stellate pattern), with displaced meniscal flaps. The most popular association is radial and horizontal tear.
Anterior and posterior cruciate ligaments are not fully visualized on ultrasound, but MRI is the best imaging technique for these lesions. Posterior and anterior cruciate ligament tears appear anechoic or hypoechoic and the ligament may be enlarged. An associated lesion is the presence of ganglion cysts. Tibial contusions are signs of ACL lesion. ACL tears the tear usually occurs in the middle portion, with discontinuity and modified MR signal and non-visualization of the ligament. These tears occur during landing with a lightly flexed knee after a jump, as in volleyball, handball. Depending on the age of the lesion the appearance is different, in the acute phase the hematoma can keep together the extremities of the torn ligament, in the subacute phase the hematoma resolves and in the chronic phase a fibrotic lesion is present. Lateral and medial collateral ligaments are located superficially and sonographic evaluation is possible. In grade 1 sprain anechoic/hypoechoic fluid is present but the ligament is intact, in grade 2 (partial tear) is present fibrillar hypoechogenity with adjacent hypoechoic/anechoic fluid and in grade 3 there is complete tear with hemorrhage and fluid. The presence of calcification on the medial collateral ligament can be specific for Pellegrini-Stieda disease. In chronic injury there is fibrosis with no edema.
Jumper's knee, Osgood-Schlatter disease and Sinding-Larsen-Johansson disease are some types of tendon injuries. On ultrasound, the tendons can be hypoechoic and thickened. Color and power Doppler imaging may show hyperemia. The dynamic technique is very helpful for the detection of complete tendon lesions and retraction. Jumper's knee occurs in basketball and tennis players (chronic overuse), with partial or complete tear (osseous avulsion fragment–inferior pole of the patella well seen on MRI) or patellar tendinopathy (tendon thickening and signal heterogeneity). In Osgood-Schlatter disease, increased T2WI signal with thickened distal patellar tendon (hypoechoic on ultrasound), enlarged tibial tubercle with hyperintense bone signal on T2WI are often seen. In Sinding-Larsen-Johansson disease the patellar tendon is hyperintense on T2WI and thickened, the inferior pole of the patellar is irregular (with high T2 signal) and a bone fragment may be visible within the tendon.