The plantaris tendon and a potential role in mid-portion Achilles tendinopathy: an observational anatomical study

The source of pain and the background to the pain mechanisms associated with mid-portion Achilles tendinopathy have not yet been clarified. Intratendinous degenerative changes are most often addressed when present. However, it is questionable if degeneration of the tendon itself is the main cause of pain. Pain is often most prominent on the medial side, 2-7cm from the insertion onto the calcaneus. The medial location of the pain has been explained to be caused by enhanced stress on the calcaneal tendon due to hyperpronation. However, on this medial side the plantaris tendon is also located. It has been postulated that the plantaris tendon might play a role in these medially located symptoms. To our knowledge, the exact anatomy and relationship between the plantaris- and calcaneal tendon at the level of complaints have not been anatomically assessed. This was the purpose of our study. One-hundred and seven lower extremities were dissected. After opening the superficial fascia and paratendon, the plantaris tendon was bluntly released from the calcaneal tendon moving distally. The incidence of the plantaris tendon, its course, site of insertion and possible connections were documented. When with manual force the plantaris tendon could not be released, it was defined as a 'connection' with the calcaneal tendon. In all specimens a plantaris tendon was identified. Nine different sites of insertion were found, mostly medial and fan-shaped onto the calcaneus. In 11 specimens (10%) firm connections were found at the level of the calcaneal tendon mid-portion. Clinical and histological studies are needed to confirm the role of the plantaris tendon in mid-portion Achilles tendinopathy.