Abstract
Background:
Shear wave elastography (SWE) is used to assess the stiffness-related properties of musculoskeletal soft tissues. However, its application to small and superficial structures in cats remains limited.

Aim:
This study aimed to evaluate the feasibility and repeatability of SWE measurements of the patellar ligament and selected stifle-associated muscles in conscious, healthy cats and to determine whether probe orientation influences muscle shear wave speed.

Methods:
Fifteen clinically healthy cats were included. SWE was performed without sedation or anesthesia using a linear transducer. The patellar ligament was evaluated in the long-axis orientation at the proximal, middle, and distal regions. The sartorius and rectus femoris muscles were evaluated in both long- and short-axis orientations, whereas the vastus lateralis, vastus medialis, and vastus intermedius muscles were evaluated in the short-axis orientation. Shear wave speed, measurement depth, coefficient of variation, number of quality-accepted regions of interest (ROIs), ROI pass rate, and intraclass correlation coefficients were assessed.

Results:
SWE measurements were obtained from all target structures. In the patellar ligament, the middle region showed the highest shear wave speed, whereas repeatability was highest in the proximal region. ROI pass rates were approximately 90% in all patellar ligament regions. Long-axis measurements of the sartorius and rectus femoris muscles showed significantly higher shear wave speeds than the corresponding short-axis measurements, whereas ROI pass rates did not differ significantly between orientations. Among the muscles evaluated in the short-axis orientation, the vastus lateralis showed the lowest ROI pass rate and repeatability. Measurement depth and ROI pass rate were not significantly correlated with shear wave speed.

Conclusion:
SWE measurements of the feline patellar ligament and selected stifle-associated muscles were feasible without sedation or anesthesia. However, repeatability and acquisition quality were structure-dependent. Muscle shear wave speed was influenced by probe orientation, indicating that long- and short-axis measurements should be interpreted separately in future feline stifle SWE studies.

Key words: Feline; Patellar ligament; Probe orientation; Shear wave elastography; Stifle joint.