gms | German Medical Science

Objective: The purpose of this work was to present a case report of a patient with bilateral accessory soleus muscle treated conservatively and to review the literature on this subject.

Material/Methods: The authors reviewed the pertinent findings of the previously reported cases of accessory soleus muscle cited in the literature and the characteristic features, diagnostic methods, and treatment indications and modalities on this subject.

Results: The authors report a symptomatic bilateral accessory soleus muscle in a 19-year-old female that was diagnosed on MRI. The patient experienced pain posteromedial to both ankles, gradually increasing with activity (walking and/or running). The symptoms were relieved by rest. On physical examination, there was a noticeable decrease in the ankles range of motion as well as bilateral equinus. Initial MRI showed a mass with signal characteristics of normal muscle, but in an abnormal location. Following a carefully guided physical therapy program the outcome was very good, the patient's painful symptoms were relieved and she had nearly complete joint movement with symmetrical muscle force. Normal activities were resumed.

Conclusion: The accessory soleus muscle is a rare anatomical variant which, although congenital in origin, may manifest in the second and third decades of life. The delay of onset of symptoms until adolescence is probably due to the increase in muscle mass and muscle activity. This anomaly, although more commonly presenting as an asymptomatic soft tissue mass bulging medially between the distal part of the tibia and the Achilles tendon, may give rise to symptoms such as pain with exertion and swelling. In rare cases it can be associated with clubfoot or equinus deformity. MRI is the diagnostic modality of choice enabling confirmation of the muscle nature of the mass and ruling out the possible diagnosis of tumor. It also demonstrates the muscle’s origin and insertion. The differential diagnosis of a soft tissue mass in the posteromedial aspect of the ankle includes ganglion, lipoma, haemangioma, encapsulated haemangioma, synovioma, sarcoma and haematoma. The key to the differentiation from other lesions is the finding of MRI signal characteristics that are identical to those of muscle, the well-encapsulated nature of the mass and the typical anatomic location. Treatment usually depends on the presence or severity of the symptoms. If a diagnosis of accessory soleus is made, and the patient has no symptoms, observation is recommended. For symptomatic patients, conservative treatment such as orthoses, physical therapy and activity modification may be tried. Surgical approaches include fasciotomy or excision of the muscle. Both have been found to be equally effective. Patients generally do well after surgery and generally become asymptomatic.