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Initial Tendon Retraction is Associated with Muscle Degeneration After Nonoperatively Treated Proximal Hamstring
Sofia Laszlo1, Anne-Mari Rosenlund2,3, Elsa Pihl4
1Department of Surgical Sciences, Unit of Orthopedic Surgery, Uppsala University, Uppsala University Hospital, 75185, Uppsala, Sweden.
Sports Medicine - Open
|May 6, 2026
Summary
Greater initial tendon retraction in proximal hamstring avulsions (PHA) predicts more muscle degeneration. This finding highlights the prognostic value of pre-treatment MRI for nonoperative PHA management.
Area of Science:
- Orthopedics
- Radiology
- Sports Medicine
Background:
- Proximal hamstring avulsions (PHA) are common injuries where tendon retraction is a key pathological feature.
- Magnetic resonance imaging (MRI) is crucial for diagnosing PHA and may offer prognostic insights into muscle degeneration.
- Understanding predictors of muscle degeneration is vital for managing nonoperative PHA cases.
Purpose of the Study:
- To investigate whether pre-treatment MRI findings, specifically tendon retraction, predict subsequent muscle degeneration and clinical outcomes in patients with nonoperatively treated PHA.
- To assess the association between initial MRI characteristics and long-term muscle changes and strength.
Main Methods:
- A post hoc analysis of 95 nonoperatively treated PHA patients from the PHACT trial.
- Diagnostic MRIs were evaluated for tendon retraction, Wood classification, number of avulsed tendons, and hematoma size.
- Muscle degeneration (loss of lean muscle volume [LMV] and increase in muscle fat fraction [MFF]) and maximum hamstring isometric force were assessed at 24 months using DIXON MRI and expressed as limb symmetry index (LSI).
- Linear regression models analyzed the relationship between MRI findings, patient factors, and LSI outcomes.
Main Results:
- At 24 months, median LSIs for LMV, MFF, and maximum strength were 78%, 139%, and 84%, respectively.
- Multivariate regression indicated that tendon retraction, age, sex, hematoma size, and dominant limb injury explained 48% of LMV variance, 48% of MFF variance, and 23% of maximum force variance.
- Tendon retraction emerged as the strongest predictor of muscle degeneration in nonoperatively managed PHA.
Conclusions:
- Increased initial tendon retraction in proximal hamstring avulsions is significantly associated with greater muscle atrophy and fat infiltration.
- Pre-treatment MRI assessment of tendon retraction provides valuable prognostic information for nonoperative PHA management.
