A 42-yr-old man had a right lateral calf injury while playing soccer 10 yrs ago. The patient also has a history of previous surgery at the right anterolateral calf complicated by postoperative infection with subsequent incision and drainage. His current complaints are right calf swelling and pain for the past 2 months after playing soccer. Physical examination revealed slight swelling at the lateral calf with no tenderness on palpation. An magnetic resonance imaging (MRI) of the right lower leg was performed and was suggestive of a small peroneus longus muscle hernia (Fig. 1A). A subsequent ultrasound was performed using a linear probe (10–15 MHz) and showed focal herniation of the peroneus longus muscle increasing during ankle dorsiflexion and eversion (Fig. 1B and the Video). The patient declined surgical management including fascial repair with a graft. The patient elected to rest for 6 wks with significant improvement of symptoms. He did not follow any formal physical therapy regimen.
The peroneus longus muscle is located within the lateral compartment of the lower leg, arising from the head and upper two thirds of the lateral fibula, lateral tibial condyle, and the tibiofibular intermuscular septum. The muscle traverses the lateral compartment, lying superficial to the peroneus brevis muscle and tapers to form a long distal tendon. Peroneus longus muscle herniation is rare with most muscle hernias in the lower leg affecting the tibialis anterior muscle. Muscle herniation results from weakness or tearing of the overlying fascia, which may be due to bone fractures, blunt or penetrating trauma, repetitive athletic contusions (eg, playing soccer), or congenital weakening of the fascia. The involved muscle protrudes through the fascial defect into the subcutaneous fat and presents as a soft tissue mass, which can be concerning for a tumor.1
Ultrasound is the diagnostic test of choice because it has the ability to examine the patient dynamically using muscle contraction, which typically increases the conspicuity of the muscle hernia. In this case, dorsiflexion and eversion produced maximal peroneus longus contraction and increased muscle herniation through the fascial defect. Other characteristic sonographic features of a muscle hernia include hypoechogenicity of the herniated and surrounding nonherniated muscle, possibly due to repetitive microtrauma or differential anisotropy.2 Muscle herniation can be subtle, and it is important that plenty of coupling gel and light transducer pressure are used to prevent inadvertent hernia reduction on scanning.
Magnetic resonance imaging can also diagnose muscle hernias and is useful to exclude alternative diagnoses including muscle tears and soft tissue tumors. However, MRI is more expensive than ultrasound and it is possible for subtle muscle hernias to be missed on MRI because of the reduced ability for dynamic imaging.
Most muscle hernias are asymptomatic, although some patients may develop pain because of superficial nerve entrapment or intermittent muscle strangulation. In the case of peroneal muscle herniation, the superficial peroneal nerve is especially vulnerable because it goes from subfascial to subcutaneous. Treatment is typically conservative with reassurance, activity modification, and the use of compression stockings. Few patients with persistent pain may require surgery, which can involve fasciotomy or fascial patch grafting.2,3
This case highlights the important role of dynamic ultrasound and complimentary MRI of the lower leg, in the diagnosis of peroneus longus muscle herniation.
1. Toms AF, Rushton LA, Kennedy NR: Muscle herniation of the peroneus longus muscle triggering superficial fibular nerve paresthesia. Sonography
2. Beggs I: Sonography of muscle hernias. AJR Am J Roentgenol
3. Meyer NB, Jacobson JA, Kalia V, et al.: Musculoskeletal ultrasound: athletic injuries of the lower extremity. Ultrasonography