Quality Of Semitendinosus Tendon Regeneration As A Function Of Time Post-ACL Reconstruction

Abstract

Evidence exists of the semitendinosus tendon (ST) physically regenerating following harvest for ACL reconstruction. However, the quality of regenerated tissue, indicated by elastic modulus, is not well understood. The time-dependency of this regeneration is also important post-ACL reconstruction as the hamstring muscle group is inherently protective of the ACL. PURPOSE: Assess the quality of ST regeneration, as measured with shear modulus, as a function of time post-ACL reconstruction with comparisons to healthy controls. METHODS: Ultrasound Shear Wave Elastography determined shear modulus of the ST tendon on 10 ACL reconstructed individuals (age: 21.6±1.6 years, height: 171.6±8.5cm, mass: 71.4±7.1kg, Tegner scale: 5.9±1.0) and 10 healthy individuals (age: 20.6±2.0 years old, height: 173.4±9.3cm, mass: 71.6±13.0kg, Tegner scale: 5.6±1.1). Time since ST harvest averaged 4.3 years (range: 0.75-12.6 years) and all individuals were since cleared to return to play by their physician. While prone with the knee at full extension and relaxed, three ultrasound images (AIXPLORER, Supersonic Imagine S.A., France) were acquired of the distal ST tendon. Linear regression analysis determined the relationship between ST tendon shear modulus vs. time since tendon harvest. 99% confidence interval (CI) determined the range of tendon compliance in healthy subjects and served as comparison to ACL reconstructed subjects. RESULTS: The relationship between the shear modulus vs. time since ST harvest was R2=0.57 (p=0.012). 3 subjects under 2 years post-reconstruction had low shear modulus of ~100kPa or less. The 99% CI of the healthy tendons was 374-590kPa, and only 1 of the 10 reconstructed subjects reached this range. CONCLUSIONS: Despite these preliminary data supporting long-term time-dependent regeneration, ST quality is highly variable indicating other factors influence this regeneration post-ACL reconstruction. Low shear modulus has an effect on muscle function, which may alter the knee load leading to the early development of knee OA. Future research is needed to assess the clinical importance of regeneration quality post-harvest in order to establish interventions facilitating early material property recovery.