Complete resolution of a hamstring intramuscular tendon injury on MRI is not necessary for a clinically successful return to play

Key points

1. 01At return to play, 56% of clinically recovered athletes still had a partial or complete tendon discontinuity visible on MRI
2. 02Reinjury rates were similar whether the tendon appeared continuous or still disrupted on MRI at return to play (HR 0.65, 95% CI 0.16-2.73, p=0.56)
3. 03Considerable healing did occur during rehabilitation: waviness dropped from 61% to 12% and most partial discontinuities improved
4. 04Tendon thickening was present in 88% of tendons at return to play, likely reflecting active remodelling
5. 05MRI of intramuscular tendon injuries appears to be of limited benefit as a standalone return-to-play decision tool

How it was conducted

Design

Pooled cohort study drawn from two double-blind placebo-controlled RCTs (Dutch and Qatari)

Participants

41 male athletes (40 male, 1 female) with MRI-confirmed hamstring intramuscular tendon injury, median age 27 years (IQR 22-31)

Sport

Mostly football players; also field hockey, futsal, athletics, and running at professional, competitive, and recreational levels

MRI timing

Baseline MRI within 5 days of injury; return-to-play MRI within 7 days of return to play

Primary outcome

MRI characteristics of the intramuscular tendon at return to play (is the tendon normal?)

Follow-up

Reinjury surveillance by phone for up to 12 months after return to play

What they found

• At return to play, 56% (23/41) of athletes still had a partial or complete thickness intramuscular tendon discontinuity on MRI
• 54% (22/41) had a partial-thickness discontinuity at return to play, down from 83% (34/41) at baseline
• 2% (1/41) had a complete thickness discontinuity at return to play, down from 17% (7/41) at baseline
• 18 of 34 (53%) partial-thickness discontinuities at baseline became continuous by return to play; disruption length change was statistically significant (p<0.001)
• 6 of 7 complete thickness discontinuities at baseline became partial-thickness at return to play
• Waviness decreased from 61% (25/41) at baseline to 12% (5/41) at return to play
• Tendon thickening was present in 88% (36/41) of tendons at return to play versus 0% at baseline
• Overall reinjury rate was 20% (8/41) within 1 year; 15% within the first 2 months
• No difference in reinjury rates between athletes with or without intramuscular tendon involvement at return to play (HR 0.65, 95% CI 0.16 to 2.73, p=0.56)
• Median disruption length in partial discontinuities at return to play: 28 mm (IQR 22-50 mm) in those who reinjured vs 22.5 mm (IQR 14.1-52 mm) in those who did not
• Median return-to-play time was 31 days (IQR 22-42 days)

Limitations

• Small sample with only 8 reinjuries, leaving the study underpowered to detect differences in reinjury risk between MRI subgroups
• Population was predominantly male football players; findings may not generalise to women or other sports with different biomechanical demands
• Blinding of radiologists may have been compromised because tendon thickening at return to play was very common and could signal scan timing
• MRI at the time of reinjury was not standardised, so exact location and extent of reinjuries were largely unknown

Why it matters

For patients

Athletes with a hamstring intramuscular tendon injury can be cleared to return to play based on clinical and functional criteria even if their MRI still shows tendon abnormalities, without an apparent increase in reinjury risk.

For clinicians

A return-to-play MRI showing residual tendon discontinuity should not, on its own, prevent clearance; clinical criteria-based rehabilitation protocols appear sufficient for safe return-to-play decisions in this injury subtype.

For readers

This study challenges the assumption that MRI normalisation is a prerequisite for safe sport return after hamstring intramuscular tendon injuries, shifting focus toward functional readiness over imaging appearance.