Achilles tendonitis is one of the most common causes of ankle pain among active individuals, including walkers, runners, and team-sport players. The cause is complex, but excessive activity within a short timeframe is one of the most critical factors. Recently, it has been discovered that other factors also contribute to the risk of this condition. Studies suggest that the plantaris tendon injury may play a role. What is the plantaris tendon, and how does it contribute to Achilles tendonitis?
What is the Plantaris Tendon?
The plantaris tendon arises from the muscle. This muscle starts at the knee and travels between the large calf muscles. In the middle of the calf, the muscle becomes a small tendon. As the tendon travels down the calf, it courses close to the inside of the Achilles tendon. Finally, it attaches to the inner surface of the large heel bone, the calcaneus.
How does the plantaris tendon lead to Achilles tendonitis?
We are not exactly sure. Dr Masci has teamed up with other researchers to gain further insights. However, overall, we believe that the plantaris courses very closely to the Achilles tendon in some cases. We suspect that this close relationship increases the pressure between the two tendons, leading to swelling in the Achilles tendon. Moreover, Dr Masci showed in a recent study that the tension between these two tendons is most significant at the extremes of ankle joint movement.
Plantaris tendon pain: How do we know?
Dr Masci wrote a paper on this topic a few years ago. Most plantaris tendon injury cases have a few standard features.
Firstly, most patients experience pinpoint pain on the inside (medial) side of the Achilles tendon. They often point to their Achilles pain with one finger. Secondly, the Achilles tendon is most tender at this pain point (see diagram below). Finally, ultrasound reveals a more prominent and enlarged plantaris tendon than usual, along with corresponding tendinosis on the inside of the Achilles tendon. A special ultrasound technique, Ultrasound Tissue Characterisation, helps confirm plantaris interference. Combining ultrasound with UTC will pick up over 90% of cases.
We are unsure how many patients with Achilles pain have an enlarged plantaris tendon, but we estimate it to be a small number.
Plantaris Tendon Pain Treatment
Treatment is similar for patients with Achilles pain and swelling caused by other conditions. However, a recent paper co-authored by Dr Masci suggests that exercise should be modified to reduce the pressure between the two tendons. It is best to avoid heavy loading of the Achilles tendon at the top and bottom of a calf raise. Working closely with an experienced therapist who can guide you through this program is essential.
What Happens if Rehab is Unsuccessful?
We also use other treatments, such as shockwave therapy, GTN patches, and tendon injections, with some success.
In persistent cases, Dr Masci injects hyaluronic acid between the two tendons to reduce the pressure between tendons. We often use hyaluronic acid injections for arthritis. However, hyaluronic acid injection is often used to treat Achilles pain when the plantaris tendon is involved.
Finally, some problematic cases need surgery to remove the plantaris tendon. This surgery is typically performed under local anaesthesia. Evidence from a paper by Dr Masci suggests that outcomes of plantaris tendon surgery are good in the short and long term, with patients resuming full activity in most cases. However, surgery is not without risk, so it should be reserved only for people who have failed other treatments, including a hyaluronic acid injection.
What about Plantaris Tendon Rupture?
In some cases, the plantaris tendon ruptures. Generally, ruptures occur in the lower part of the calf near the Achilles tendon and can be mistaken for an Achilles tendon rupture.
Symptoms of plantaris tendon rupture include sudden pain, swelling, and limping close to the Achilles tendon. In some cases, a plantaris tendon tear occurs in the mid-calf, mimicking a calf muscle tear.
We use ultrasound or MRI to diagnose a complete rupture of the plantaris tendon.
Treatment is similar to that for Achilles tendon pain: a boot or heel raise for a few days, calf-loading exercises, and a progressive return to running.
Final word from Sportdoctorlondon about Plantaris Tendon Injury
Consider the plantaris in cases of Achilles tendonitis that are particularly challenging. Additionally, sudden pain near the Achilles or lower calf may indicate a plantaris tendon injury. You should see an experienced Sports Doctor for a proper diagnosis and management plan.
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