Do accessory muscles in the posterior ankle region cause symptoms often?
No, in the majority of cases these accessory muscles are asymptomatic incidental findings. They are however important to report since they can be a cause of symptoms. In addition, this is useful information for a surgeon when they want to perform an ankle arthroscopy or surgery.
What type of symptoms can an accessory posterior ankle muscle (e.g. peroneocalcaneus internus), located deep to the flexor retinaculum, potentially cause?
These accessory muscles can directly or indirectly compress the posterior tibial neurovascular bundle, which has the potential to cause neuropathic symptoms.
Both ankles have an identical accessory muscle deep to the flexor retinaculum and lateral to the flexor hallucis longus.