Initial Tendon Retraction is Associated with Muscle Degeneration After Nonoperatively Treated Proximal Hamstring Avulsions

Sofia Laszlo; Anne-Mari Rosenlund; Elsa Pihl; Målfrid Holen Kristoffersen; Olof Sköldenberg; Jörg Schilcher; Martin Eklund; Frede Frihagen; Mikael Skorpil; Kenneth B Jonsson

doi:10.1186/s40798-026-01024-x

Initial Tendon Retraction is Associated with Muscle Degeneration After Nonoperatively Treated Proximal Hamstring Avulsions

Sports Med Open. 2026 May 6;12(1):52. doi: 10.1186/s40798-026-01024-x.

Authors

Sofia Laszlo¹, Anne-Mari Rosenlund^{2

3}, Elsa Pihl⁴, Målfrid Holen Kristoffersen⁵, Olof Sköldenberg⁴, Jörg Schilcher^{6

7}, Martin Eklund⁸, Frede Frihagen^{3

9}, Mikael Skorpil¹⁰, Kenneth B Jonsson¹¹

Affiliations

¹ Department of Surgical Sciences, Unit of Orthopedic Surgery, Uppsala University, Uppsala University Hospital, 75185, Uppsala, Sweden.
² Division of Orthopaedic Surgery, Oslo University Hospital, Oslo, Norway.
³ Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, Oslo, Norway.
⁴ Department of Clinical Sciences at Danderyds Hospital, Karolinska Institutet, Stockholm, Sweden.
⁵ Department of Orthopedic Surgery, Haukeland University Hospital, Bergen, Norway.
⁶ Department of Orthopedic Surgery, Faculty of Health Sciences, Linköping University, Linköping, Sweden.
⁷ Department of Biomedical and Clinical Sciences, Faculty of Health Sciences, Linköping University, Linköping, Sweden.
⁸ Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden.
⁹ Department of Orthopaedic Surgery, Østfold Hospital Trust, Grålum, Norway.
¹⁰ Department of Molecular Medicine and Surgery, Karolinska Institutet, Stockholm, Sweden.
¹¹ Department of Surgical Sciences, Unit of Orthopedic Surgery, Uppsala University, Uppsala University Hospital, 75185, Uppsala, Sweden. Kenneth.Jonsson@uu.se.

Abstract

Background and purpose: Magnetic resonance imaging (MRI) is essential in assessing proximal hamstring avulsions (PHA), where tendon retraction is a key pathological consequence. Beyond its diagnostic role, MRI may also provide prognostic information on subsequent muscle degeneration. This study aimed to determine whether pre-treatment MRI findings, particularly tendon retraction, predict later muscle degeneration and clinical outcomes in nonoperatively treated PHA patients.

Methods: This study is a post hoc analysis of nonoperatively treated patients (n = 95) with complete proximal hamstring avulsions from the Proximal Hamstring Avulsion Clinical Trial (PHACT). Diagnostic MRIs were reassessed for tendon retraction, Wood classification, number of tendons avulsed, and hematoma size. The primary outcome was muscle degeneration, defined by the loss of lean muscle volume (LMV) and an increase in muscle fat fraction (MFF) quantified by DIXON MRI at 24 months. The secondary outcome was maximum hamstring muscle isometric force at 24 months. Outcome data was expressed as the limb symmetry index (LSI), which was the measurement of the injured hamstring expressed as a percentage of measurement of the uninjured hamstring. Linear regression was used to analyze the association between diagnostic MRI measurements, patient factors, and LSIs for LMV, MFF, and maximum isometric force.

Results: The median (IQR) LSIs of the LMV, MFF and maximum strength were 78% (67.2, 87.1), 139% (124.5, 166.8), and 84% (75.4, 94.0), respectively, at 24-month follow-up. A multivariate linear regression model including tendon retraction, age, sex, hematoma size and whether the dominant limb was injured explained 48%, 48% and 23% of the variance in the LSIs of LMV, MFF and maximum force, respectively. Tendon retraction was the strongest explanatory factor for the variance of muscle degeneration observed in patients with nonoperatively treated PHA.

Interpretation: Greater initial tendon retraction is associated with increased muscle atrophy and fat infiltration in the hamstring muscles in patients with nonoperatively treated PHA.

Trial registration: NCT03311997.

Associated data

ClinicalTrials.gov/NCT03311997