Use of strain and shear wave elastography in the ultrasonographic evaluation of the intermediate patellar ligament in horses: comparison and consistency of data.

Overview

• This study evaluated the use of two elastosonography techniques—strain elastography (SE) and two-dimensional shear wave elastography (2D-SWE)—to assess the intermediate patellar ligament (IPL) in horses, especially aiming to characterize its tissue elasticity and detect differences related to injury or lameness.
• The research found that both SE and 2D-SWE are feasible and reliable methods to examine the equine IPL, with strain elastography showing the ability to distinguish between healthy and lame horses based on ligament stiffness.

Background and Purpose

• The intermediate patellar ligament (IPL) in horses plays a role in stifle (knee) function but the clinical implications of IPL injuries or desmopathy (ligament disease) remain unclear and debate continues over the specificity of ultrasonographic features.
• Traditional ultrasonography provides structural images but does not quantify tissue stiffness or elasticity, which can better reflect tissue health or pathology.
• Elastosonography techniques such as SE and 2D-SWE assess tissue elasticity by measuring how the ligament deforms or transmits shear waves under external mechanical stimuli, offering functional insights into tissue biomechanics.
• The study aimed to describe normal elastosonographic characteristics of the IPL, test the feasibility of SE and 2D-SWE in horses, compare the data obtained by both methods, and evaluate whether these techniques can detect differences between healthy horses and those with IPL lesions and lameness.

Study Design and Methods

• Twenty adult horses of varying breed, sex, and athletic usage were selected and divided into two groups:
  • Sound Group (GS): 15 horses with no lameness and normal orthopedic exams
  • Lame Group (GL): 5 horses with lameness originating from the stifle or evidence of IPL lesions on ultrasound
• Both strain elastography (SE) and two-dimensional shear wave elastography (2D-SWE) were performed on both left and right IPLs using longitudinal and transverse ultrasound scans.
• Measurements involved:
  • Elasticity Index (EI) – an indicator from SE measuring tissue stiffness
  • Strain Ratio (SR) – comparing strain of the IPL to infrapatellar fat pad in SE
  • Shear Wave Velocity (in m/s) and Young’s modulus (in kPa) using the 2D-SWE technique to quantify tissue stiffness
• Regions of Interest (ROIs) for the elastosonographic measurements were standardized for consistency.
• Additional data on IPL diameter/thickness ratio were also gathered for correlation analysis with elastosonographic parameters.
• Statistical analyses assessed:
  • Feasibility via Intraclass Correlation Coefficients (ICCs)
  • Left vs right limb differences and intraoperator repeatability using the Wilcoxon test
  • Correlation between SE/SWE variables and ligament morphometrics (diameter/thickness)
  • Comparison of SE and SWE parameters between sound and lame horses

Key Findings

• Both SE and 2D-SWE techniques were feasible with good reliability, indicated by ICC values between 0.7 and 0.9 statistically significant at p < 0.05.
• No significant differences in elastosonographic measurements were found between left and right limbs or across repeated measurements by the same operator, indicating good repeatability and symmetric ligament properties in sound horses.
• No significant correlation was observed between elasticity parameters (EI, SR, velocity, Young’s modulus) and IPL diameter/thickness ratio, suggesting that tissue stiffness is independent of size/thickness metrics.
• Strain elastography (SE) demonstrated the ability to differentiate between sound and lame horses:
  • The Elasticity Index (EI) was statistically higher (indicating stiffer tissue) in sound horses compared to lame horses during transverse scanning (EI of 1.9 vs 1.7; p=0.001).
  • This indicates that chronic IPL injuries in lame horses are associated with increased ligament stiffness detectable by SE.
• The IPL in horses behaves as a hard, relatively non-deformable structure under elastosonographic assessment.

Clinical and Research Implications

• Elastosonography, specifically strain elastography and 2D shear wave elastography, provides a non-invasive and reliable way to assess mechanical properties of the IPL beyond conventional ultrasound.
• SE may have a clinical role in identifying chronic IPL pathology by detecting increased stiffness, which could improve diagnostic precision when evaluating horses with stifle-related lameness.
• Lack of correlation with ligament size reinforces that stiffness changes are functional and not merely due to anatomical changes like swelling or thickening.
• Data support the use of elastosonography in clinical practice and future research on equine stifle injuries, potentially guiding prognosis or monitoring healing over time.
• Further studies with larger groups and longitudinal designs are needed to explore the full diagnostic accuracy and prognostic value of elastosonography in IPL desmopathy.