Tendinopathic plantaris but normal Achilles tendon found in about one-fifth of patients

Key points

1. 01Pain in the mid-Achilles region is not always coming from the Achilles tendon itself.
2. 02In 18% of tendons (19 of 105), the Achilles looked normal and the small nearby plantaris tendon was the painful structure.
3. 03These patients had distinct tenderness on the inner (medial) side of the Achilles but no Achilles thickening.
4. 04Plantaris-only pain was most common in elite athletes (10 of the 14 affected patients).
5. 05Ultrasound plus colour Doppler scanning helped identify the real source and was confirmed at surgery.

How it was conducted

Design

Prospective consecutive surgical case series, single specialised tendon clinic in Malmo, Sweden, August 2020 to November 2023

Participants

81 patients (62 males, 19 females) with persistent midportion Achilles pain longer than 6 months who had failed non-surgical loading programmes

Tendons

105 Achilles midportions operated on under wide awake local anaesthetic no tourniquet (WALANT) surgery

Assessment

Clinical palpation, high-resolution ultrasound and colour Doppler (8 to 13 MHz probe), with diagnosis confirmed at surgery

Outcome

Frequency of plantaris tendinopathy alone with a normal Achilles tendon

What they found

• Plantaris tendinopathy alone with a normal Achilles was found in 19 of 105 tendons (18%), from 14 of the 81 patients.
• These 14 patients had distinct medial-side tenderness but no thickening of the Achilles tendon on examination.
• Ultrasound showed a plantaris tendon close to the medial side of a normal Achilles (regular fibre structure, thickness under 6 mm), and surgery confirmed a varying-size plantaris in close relation to a macroscopically normal Achilles.
• Among the 14 plantaris-only patients, 10 were elite athletes, 3 were recreational athletes, and 1 was non-active.
• Median age was 47 years for males (range 22 to 70) and 46 years for females (range 23 to 64); the overall cohort included 21 elite athletes, 42 recreational, and 18 non-active individuals.
• At surgery, 5 to 8 cm of the plantaris tendon was resected with the interposed fat tissue scraped away.

Limitations

• This is a descriptive case series with only absolute numbers and percentages, no control group and no formal outcome or success measures reported.
• All patients came from a single specialised tendon clinic and were referred for surgery after failing conservative care, so the one-fifth figure may not apply to general Achilles pain patients.
• Diagnosis depended on skilled palpation and ultrasound and on visual surgical inspection rather than a standardised reference test.
• The report does not present treatment results or follow-up outcomes for the plantaris-only patients.

Why it matters

For patients

If your mid-Achilles pain has not improved with exercise and your Achilles looks normal on scans, the pain may be coming from the nearby plantaris tendon rather than meaning the problem is in your head.

For clinicians

Use careful medial-side palpation plus ultrasound and colour Doppler before treating stubborn midportion Achilles pain, because in roughly one-fifth of refractory cases the plantaris tendon alone is the pain source.

For readers

Mid-Achilles pain is not a single diagnosis; a small adjacent tendon can be the culprit, which matters for accurate diagnosis and targeted treatment.