A 20-year-old male tennis player with acute medial calf pain. Longitudinal ultrasound image reveals a large hematoma (arrows) between the soleus and the medial gastrocnemius aponeurosis with distal myoaponeurotic injury of medial gastrocnemius
Large muscle lesions, inter-aponeurotic collections or muscle retraction suggest a poor prognosis.
With an acute large inter-aponeurotic collection, percutaneous needle aspiration will help aponeurotic scar adhesion. If the collection recurs, the treatment can be repeated during the first 3 weeks of convalescence. If the hematoma has coagulated ultrasound guidance is recommended, between the seventh and 21st day after injury, to verify the potential secondary liquefaction.
Its availability, low cost, ease of use and sensitivity make ultrasound superior to MRI for initial diagnosis and follow-up of lesions. MRI is usually recommended only for high-level athletes (Fig. 21.2).
A 28-year-old athlete with acute medial calf pain. (a) Longitudinal ultrasound image shows a focal aponeurotic thickening of the medial gastrocnemius (arrow). Coronal (b) and axial (c) fat-suppressed T2-weighted MRI confirm grade 1 medial gastrocnemius aponeurotic injury (arrow)
Fat saturated T2 sequences reveal intramuscular and aponeurotic high signal intensities that indicate injury. The inter-aponeurosis collection can be measured precisely, and other associated muscular lesions can be detected. Koulouris found that in a third of these patients, dual site injuries involve the medial gastrocnemius and the soleus muscle (Fig. 21.3) .
A 26-year-old man with acute right calf pain. Transverse ultrasound image (a) and axial fat-suppressed T2-weighted MRI (b) show musculo-aponeurotic injury of the medial gastrocnemius-soleus muscles complex (black arrow) with edema at the musculofascial junction of the soleus and hematoma (white arrows)
22.214.171.124 Other Medial Gastrocnemius Muscle Injuries
Injury to the proximal myotendinous junction of the gastrocnemius posterior to the knee can occur but it is an unusual clinical entity and its imaging appearance is rarely reported. It seems to be related to knee instability injury with posterior angle injury. The clinical significance of proximal injuries is also unclear aside from localization of pain to the knee instead of the midcalf, which can alter the differential diagnosis .
Bony avulsion of the proximal insertion is an unusual diagnosis found in young athletes .
126.96.36.199 Lateral Gastrocnemius Lesion
Lateral gastrocnemius muscle lesions are an uncommon occurrence described as symmetric lateral tennis leg. The injury is most frequently located on the myo-aponeurotic junction of the distal fibers. This diagnosis presents no specific imaging findings.
21.2.3 Soleus Muscle
The soleus is broad and bulky, located superficially to muscles of the deep posterior compartment (flexor hallucis longus muscles, tibialis posterior, and flexor digitorum longus,) and deeply to the gastrocnemius and plantaris.
The soleus has two distinct proximal tendinous fibular and tibial origins. The fibular arises on the posterior aspect of the head. The tibial origin is at the inferior border of a tibial bony ridge called the tibial soleal line [2, 17].
Both proximal tendinous fibers merge to form the tendinous arch of the soleus, and extend proximally into the soleus belly to form a tendinous lamina called the intramuscular aponeurosis of the soleus. The soleus muscular fiber originates proximally on the latter and extends inferiorly, forming a bipennate pattern. The angle of pennation seems to be sex specific, with higher angle pennation in the male soleus muscle .
The majority of soleus fibers originate on the posterior aspect of the intramuscular aponeurosis and converge downward to finish on the anterior aspect and on the borders of a new tendinous lamina, the insertion lamina.
The anterior muscle fibers originate on the anterior aspect of the intramuscular aponeurosis and form distally a central intramuscular tendon.
In the distal segment of the soleus muscle two medial and a posterior sagittal intramuscular aponeurotic band converge with the insertion lamina [8, 19, 20]
This insertion lamina, central muscular tendon and sagittal and medial aponeurosis converge and fuse with the tendinous lamina issuing from the gastrocnemius muscle to form the Achilles tendon.
The role of the soleus muscle is to maintain posture and to assist low energy activities like walking. Moreover the soleus is the main plantar-flexor muscle of the foot and the most powerful muscle of those crossing the ankle.
The lesser susceptibility of soleus to musculotendinous lesions is due to its monoarticular pattern and its composition (96 % of soleus muscle fibers are type I) .
Soleus injuries occur when the ankle is passively dorsiflexed while the knee is flexed.
Balius in a recent work revealed the propensity of proximal strains to occur along the medial side, probably due to the increased length of the intramuscular tendon and a larger musculotendinous junction. It can also be explained by the fact that during a plantar-flexor movement the medial head provides 71 % of its force, while the lateral head contributes only a small part [21, 22].
188.8.131.52 Clinical Signs
Soleus injuries usually appear as a moderate diffuse pain with subacute presentation, resembling delayed onset muscle soreness, probably because the soleus is composed predominantly of type I fibers. The difficulty of distinguishing among gastrocnemius, soleus, plantaris, and proximal Achilles tendon injuries and soleus lesions is usually underestimated.
Furthermore, under-appreciation of soleus strains has likely played a role in the apparently decreased incidence of soleus injuries, which can be attributed in part to the traditional role that ultrasound has played as the imaging modality of choice. Owing to the gradual onset of the injury and the fact that it is usually well tolerated, it is felt that the frequency of soleus lesions is underestimated. Soleus injuries are easily detected on MRI [15, 21].
184.108.40.206 Imaging Diagnosis
Soleus injury semiology and staging is overall the same as for gastrocnemius strains. On the other hand soleus injuries seem to be frequently underdiagnosed on ultrasound. Subtle grade 2 strains, where minimal macroscopic fiber disruption may be the only evident imaging feature (and where hemorrhage is absent), may be missed on ultrasound. Given the deeper location of the soleus muscle, resulting in relatively poorer image quality, and the anatomic complexity, it is likely that low grade and therefore subtle strains are missed, with only higher grade injuries visualized [18, 23].
As Balius noted in a recent study, the variability of injury localization makes ultrasound difficult. Nevertheless strains of the proximal medial musculotendinous junction are the most common type of soleus muscle injuries (56.4 % of all cases) [21, 22].
During ultrasound examination special attention should be given to detection of architectural anomalies of the central muscular and peripheral myo-aponeurosis junction. An isolated collection located in the inter-aponeurosis soleus-gastrocnemius space suggests careful examination of the soleus .
Thus, MRI is the best method to investigate injuries of the soleus (Fig. 21.4). Koulouris showed that the high prevalence of soleus injuries on MRI and the frequent association between different calf muscle injuries suggests that many cases are probably missed on ultrasound (Figs. 21.5 and 21.6) [15, 24].
A 26-year-old man with moderate right calf pain. Transverse ultrasound image (a) shows a 5 mm hypoechoic area in the soleus muscle (arrow). (b) Axial fat-suppressed T2-weighted MRI confirms grade 2 soleus muscle injury (arrow)
A 23-year-old man with acute left calf pain that started during a soccer match. Axial fat-suppressed T2-weighted MRI shows grade 2 injury soleus muscle and grade 1 injury of the lateral gastrocnemius muscle (arrow)
A 24-year-old athlete with acute calf pain. Axial (a) and coronal (b) fat-suppressed T2-weighted MRI show a bifocal musculo-aponeurotic strain of the soleus (grade 2, white arrows) and lateral gastrocnemius muscles (black arrow)
Owing to the gradual onset of the injury and the fact that it is usually well tolerated, the frequency of soleus lesions is probably underestimated. Although soleus injuries are easily detected on MRI, owing to their good prognosis and the expense of MRI it is usually recommended only for high-level athletes
21.3 Plantaris Muscle
The plantaris muscle is the smallest muscle of the calf. It is missing in as much as 7–20 % of the normal population .
The plantaris arises from the supracondylar lateral area of the femur, with a short muscle body located between the aponeurosis of the soleus and lateral gastrocnemius, continues by a thin tendon distally located at the anteromedial border of the Achilles tendon and inserts into the flexor retinaculum or calcaneus. Its distal insertion is separated from the Achilles tendon.
In relation to its small size the mechanical role of the plantaris muscle (flexor of the knee, plantar flexor of ankle) is weak. Nevertheless itis an agonist of the anterior cruciate ligament and participates at the posterolateral complex of the knee.
220.127.116.11 Normal Imaging
Ultrasound examination shows a fibrillar structure, with a hypoechoic belly muscle. The tendon appears in the center of the muscle belly as a hyperechoic structure with a myotendinous junction situated at the proximal one third of the calf [14, 26, 27].
On axial images the proximal part of the plantaris muscle tendon appears as a round structure between the soleus and lateral gastrocnemius belly. The distal part of the tendon is less well defined due to the hyperechoic fat environment .
This fat environment provides good contrast on MRI axial T1 and T2 images without fat saturation. The tendon appears as a rounded structure with well-defined borders in contact with the anteromedial Achilles tendon border.
Lesions are most common in the myotendinous junction of the plantaris, arising during eccentric contractions. Ruptures of the distal tendon or proximal belly lesions have also been reported [29, 30].
18.104.22.168 Clinical Signs
Patients usually describe a strong acute pain of the upper calf or popliteal area that mimics an Achilles tendon injury with preserved plantar flexion and negative Thompson test.
The main diagnoses are Achilles tendon rupture, tennis leg, thrombophlebitis, and acute Baker cyst rupture. Acute lesions of the plantaris muscle itself and medial gastrocnemius are rare.
22.214.171.124 Imaging Diagnosis
Usually tears of the plantaris tendon are located on average 5 cm above its distal insertion and appear as a short discontinuity of the tendon (about 1 cm) (Fig. 21.7) .
A 15-year-old athlete with acute Achilles tendon pain and an isolated tear of the plantaris muscle tendon. (a–c) Axial fat-suppressed T2-weighted MRI show peritendinous Achilles edema with discontinuity of the distal segment of plantaris muscle tendon (arrow)
The diagnosis on ultrasound is based on the disappearance of the fibrillar structure of plantaris tendon and its replacement by a hypoechoic swollen heterogeneous area. The end of the proximal tendon appears thickened. A thin hypoechoic liquid area can be seen between the aponeurosis of the medial gastrocnemius and soleus
MRI axial sequences confirm the discontinuity of the tendon with a focal hypersignal T2 area best seen on T2 images with fat saturation. On ultrasound, the proximal end of the tendon can appear thickened. Edema of the muscular body can be associated with a myotendinous lesion (Fig. 21.8) [26, 27, 34–38].
A 42-year-old male athlete with subacute left calf pain. Sagittal (a) and axial (b) fat-suppressed T2- and axial T1-weighted (c) MRI reveal left acute plantaris muscle injury (grade 2, black arrows) with aponeurotic hematoma (white arrows)
21.4 Popliteus Muscle
The popliteus muscle originates at the posteromedial aspect of the proximal tibial metaphysis and can have several attachments, but inserts primarily on the lateral aspect of the femoral condyle. The popliteus muscle is an internal rotator of the tibia on the femur and assists in flexion of the knee. It is an important stabilizer of the posterolateral corner of the knee and prevents forward translation of the femur on the tibia .