Bilateral changes in tendon structure of patients diagnosed with unilateral insertional or midportion achilles tendinopathy or patellar tendinopathy

Key points

1. 01Patients with tendon pain on one side had measurable structural changes on both sides, not just the painful one.
2. 02The symptomatic tendon was the most disorganised, but the pain-free tendon was also abnormal compared with healthy controls.
3. 03Different tendon problems showed different patterns: insertional Achilles, midportion Achilles, and patellar tendinopathy each had distinct echo-type changes.
4. 04The bilateral differences were larger than the test's measurement error, so they are unlikely to be just noise.
5. 05The authors recommend monitoring and assessing both limbs during rehabilitation rather than using the unaffected side as the benchmark.

How it was conducted

Design

Cross-sectional comparison of tendinopathy patients versus healthy controls

Participants

46 unilateral Achilles tendinopathy (16 insertional, 30 midportion) and 38 unilateral patellar tendinopathy patients, plus controls (18 Achilles, 25 patellar tendons)

Groups

Symptomatic tendon vs asymptomatic (contralateral) tendon vs control tendons

Measurement

Ultrasound tissue characterisation (UTC) quantifying echo types I to IV, where echo I is most organised/stable and echo IV least

Primary outcome

Differences in echo-type percentages between symptomatic, asymptomatic, and control tendons

What they found

• Significant differences were found in echo types I, III, and IV between symptomatic, asymptomatic, and control tendons.
• The symptomatic side differed from the asymptomatic side at all tendon locations studied.
• Insertional Achilles tendinopathy: more echo type III on the symptomatic side.
• Midportion Achilles tendinopathy: less echo type I and more echo types III and IV on the symptomatic side.
• Patellar tendinopathy: more echo types III and IV on the symptomatic side.
• Reported between-side differences exceeded the minimal detectable change (measurement error).

Limitations

• Cross-sectional design shows associations at one point in time and cannot establish cause or predict who develops symptoms.
• Relatively small control groups (18 Achilles and 25 patellar tendons) limit precision of the comparisons.
• The provided text reports the direction of differences but not the underlying percentages, confidence intervals, or p-values for most findings.
• Findings come from a single hospital tendinopathy cohort and may not generalise to all populations.

Why it matters

For patients

If you have tendon pain on one side, the other side may not be as healthy as it feels and is worth checking too.

For clinicians

Do not use the contralateral asymptomatic tendon as a normal reference; assess and monitor both limbs during diagnosis and rehabilitation.

For readers

Imaging abnormalities and structural changes can be present in tendons without pain, so symptoms alone do not capture tendon health.