Clinical presentation of the accessory soleus muscle: a quantitative systematic review

The accessory soleus muscle (ASM) is a rare anatomical variant and the most common accessory muscle in the leg/ankle region. Though asymptomatic in most cases, ASM could exhibit clinical manifestations leading to medical consultation. Since no evidence-based synthesis has been conducted yet, this review aims to collate pooled quantitative data on the clinical presentation and management of ASM.

The electronic databases of Medline and Embase were searched from inception, met the inclusion criteria. Only clinical cases of symptomatic ASM were included. Clinical and cadaveric incidental findings of ASM were excluded.

Forty-one articles met the inclusion criteria, comprising 134 ASM in 122 patients. The clinical presentation of the ASM was as follows: exertional pain (60%), posteromedial ankle swelling (59%), foot numbness/dysesthesia (5.2%), soft non-tender mass (30%), a tender mass in 9%, a soft mass that becomes hard on plantarflexion (44%), and positive Tinnel's sign (11.2%). The diagnostic modalities used were: x-rays (62.7%), MRI (52.2%), CT scan (24.6%), ultrasound (12.7%) and EMG studies (13.4%). Out of 128 treated cases, conservative management was used in 36.7%, and surgery in 50% of cases including fasciotomy in 22.6%, excision in 20.3%, posterior tibial nerve decompression in 7.8%, and a combined procedure in 1.7%. Regardless of the treatment modality, all surgical patients were satisfied.

The findings of this review would help clinicians to better recognize, diagnose and treat the rare condition of a symptomatic accessory soleus muscle.