Plantaris-associated Achilles tendinopathy: a potential cause of persistent Achilles pain

  • Thursday 23 October 2014

Achilles tendon pain or tendinopathy is a common problem in active individuals. The cause of this condition is multifactorial but excessive tendon loading is the most important contributing factor.

Recent studies suggest that the plantaris tendon may play a role in Achilles tendinopathy. This small inconspicuous tendon starts at the knee and travels distally between the two large calf muscles to find itself close to the medial aspect of the Achilles tendon close to the heel. Studies in cadavers have found a high variability in the course and position of the plantaris tendon. In 20% of cases, the tendon is compressed against the medial aspect of the tendon

How does compression lead to Achilles tendinopathy? In-vitro compression of tendon leads to matrix changes similar to tendinopathy. Plantaris has been sown to be less compliant than the Achilles tendon and could compress the medial aspect of the Achilles tendon on full stretch. It has been suggested that compression of the medial Achilles by the plantaris leads to localised medial Achilles tendinopathy.

How do you diagnose a plantaris-associated tendinoapthy?

I'm lucky enough to work in a lower limb tendon clinic and see many cases of Achilles tendinopathy. Many of these cases have failed a conservative program. We estimate that up to 40% of our Achilles patients have plantaris-associated Achilles tendinopathy. I have followed a case series of plantaris-associated Achilles tendinopathy and have documented the following observations:

  • Most cases have a history of recurrent Achilles tendon pain
  • Most patients have pain at the medial (or inside) aspect of the tendon and usually at the medial soleal muscle/tendon junction
  • Some patients describe a flicking sensation in the medial aspect of the tendon
  • Majority of cases had palpable tenderness at the medial aspect of the tendon
  • Approximately 80% of cases had a visible plantaris on ultrasound scan (see fig 1)
  • Ultrasound Tissue Characterisation can visualise the plantaris indirectly by detecting focal disorganised changes in the medial aspect of the Achilles (see fig 2: red changes medically)
  • Combining ultrasound and a Ultrasound tissue Characterisation increases the detection of plantaris to over 90%
  • Cases are difficult to manage conservatively but a trial of loading in full planterflexion +/- high volume injection is always indicated
  • Removal or excision of the plantaris is successful in about 80% of cases

Fig 1

Fig 2

I've presented these findings at a recent tendon conference in Oxford (http://www.ibme.ox.ac.uk/ists2014/Home.html) and have been invited to present at BMUS in December 2014 (www.bmus.org)

In summary, there seems to be a direct association between a thickened plantaris and chronic recurrent tendon pain. Plantaris compression should be considered in anyone presenting with longstanding Achilles pain, particularly if pain is located at the medial (inside) aspect of the tendon. Diagnosis is based on clinical presentation, ultrasound and UTC findings. Ultrasound Tissue Characterisation is particularly useful in detecting changes suspicious for plantaris compression. And in an on-going study on a review of patients who have undergone plantaris excision, UTC has shown improvement in structure correlating with improvement in pain/function. Yes, there IS (perhaps) a relatonship between stucture and function and UTC may be the imaging modailty to prove it!


Tags: achilles tendinopathyplantarisAchilles pain

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