Anterior cruciate ligament (ACL) reconstruction using autologous hamstring tendon grafts is a commonly performed procedure. Although the semitendinosus and gracilis tendons demonstrate regeneration at the donor site, the structural and biomechanical properties of the regenerated tissue may differ from native tendon, potentially affecting muscle function.

This study aims to quantitatively assess the elasticity of regenerated hamstring tendons using shear-wave elastography (SWE) and to compare these measurements with the contralateral intact side. Additionally, the relationship between tendon elasticity and isokinetic hamstring muscle strength will be evaluated. Secondary objectives include investigating the association between elastography findings and functional clinical outcomes, as well as the effect of postoperative time and patient-related factors such as age and body mass index.

Anterior cruciate ligament reconstruction with autologous hamstring tendon grafts, typically using the semitendinosus and gracilis tendons, is widely used in orthopedic practice. Following graft harvesting, these tendons may regenerate over time; however, the regenerated tissue often demonstrates altered histological and biomechanical characteristics, including disorganized collagen structure and reduced type I collagen content. These changes may lead to decreased tendon elasticity and impaired force transmission, potentially contributing to deficits in muscle strength and functional performance.

Shear-wave elastography (SWE) is a non-invasive imaging modality that enables quantitative assessment of tissue stiffness by measuring elastic modulus or shear-wave velocity. This technique has increasingly been used to evaluate musculoskeletal tissues and may provide objective insight into tendon regeneration quality. Isokinetic dynamometry, on the other hand, allows precise measurement of muscle strength at different angular velocities and is widely used in functional assessment after ACL reconstruction.

The primary objective of this study is to evaluate the elasticity of regenerated semitendinosus and gracilis tendons using SWE in patients who have undergone ACL reconstruction with hamstring autografts. Elastography measurements will be compared with those obtained from the contralateral intact side. Furthermore, the association between tendon elasticity and isokinetic hamstring muscle strength will be analyzed.

Secondary objectives include examining the relationship between elastography findings and functional clinical scores, including the International Knee Documentation Committee (IKDC), Lysholm, and Tegner scores, as well as functional performance tests. The effect of postoperative duration will also be assessed by comparing early (6-12 months) and late (>12 months) postoperative periods. In addition, the influence of demographic factors such as age and body mass index on tendon elasticity and muscle strength will be evaluated.

This study is designed as a prospective cross-sectional observational study. Patients who have undergone ACL reconstruction with autologous hamstring grafts and have completed at least 6 months of postoperative follow-up will be included. Participants will undergo shear-wave elastography assessment of the hamstring tendons. Previously obtained magnetic resonance imaging (MRI) and isokinetic muscle strength (Cybex) data will be collected from institutional records. MRI will be evaluated for graft signal characteristics, tunnel position, and graft thickness, while isokinetic testing will provide quantitative measurements of hamstring strength at different angular velocities.

All data will be analyzed to determine correlations between tendon elasticity, muscle strength, imaging findings, and clinical outcomes. The findings of this study are expected to improve understanding of tendon regeneration following ACL reconstruction and may contribute to more individualized rehabilitation strategies and postoperative assessment using non-invasive biomarkers such as SWE.

Inclusion Criteria:

• Patients who have undergone anterior cruciate ligament (ACL) reconstruction using autologous hamstring tendon grafts (semitendinosus and gracilis)
• At least 6 months of postoperative follow-up
• Availability of postoperative magnetic resonance imaging (MRI) and isokinetic muscle strength (Cybex) measurements
• Willingness to participate and provide informed consent

Exclusion Criteria:

• History of previous surgery on the same lower extremity (other than the index ACL reconstruction)
• Presence of neuromuscular disorders affecting lower extremity function
• Incomplete clinical, imaging, or functional data
• Inability to undergo elastography assessment

The study population will consist of adult patients who have undergone anterior cruciate ligament (ACL) reconstruction using autologous hamstring tendon grafts (semitendinosus and gracilis) and have completed at least 6 months of postoperative follow-up. Participants will be selected from a single tertiary referral center and will have available postoperative magnetic resonance imaging (MRI) and isokinetic muscle strength (Cybex) data. All eligible patients will undergo shear-wave elastography (SWE) assessment of the regenerated hamstring tendons at the time of study enrollment.

Individual participant data (IPD) will not be shared.