Sonoelastography of canine patellar tendon: feasibility, repeatability and reproducibility.

INTRODUCTION Sonoelastography (EUS) is a recent ultrasound technique for the evaluation of tissue elasticity and the me- chanical properties of tissues by estimating their strain, defined as the fractional change in length of a tissue when an external force is applied. Nowadays in veterinary medicine, there are only few publications about the use of EUS for the assessment of abdominal tissues in cat and dogs and musculoskeletal system in horses. The aims of the present study were to describe the sonoelastographic characteristic of the patellar tendon in clinical healthy dogs, to in- vestigate if EUS is a feasible, repeatable and reproducible technique for the evaluation of the patellar ten- don and to establish the normal pattern at EUS of the patellar tendon in healthy dogs. MATERIALS AND METHODS Fourteen dogs were considered in this prospective study. Each dog enrolled, had a normal physical and or- thopaedic examination, a normal blood workup and a normal B-mode patellar tendon ultrasonographic ex- amination in both legs. EUS was performed without sedation by two different operators: a well-trained ultrasonographer and a sen- ior student. For EUS dogs were positioned in lateral recumbency with the knee in maximal passive flexion. EUS images were obtained by applying light rhythmic pressure with the probe. Only longitudinal sections were acquired, and the operators evaluated each patellar tendon twice. Investigation was made blindly and each operator was not aware about the results of the acquisition of the other operator. Ultrasonographic and sonoelastographic evaluation were carried out using an Esaote My LabTMClass C ul- trasound machine equipped with a 12-18 MHz linear transducer. For the EUS evaluation was used the ESAOTE ElaXto software. Only images without artifacts were evaluated. Subsequently ROIs were drawn in the central area of the ten- don, in order to measure the softness of the tissue (Elx-t%sft, the percentage of softness of the tissue in the ROI). Categorical, qualitative data analysis was performed using a weighted kappa statistic for repeated evalua- tions by the same (repeatability) and by a different observer (reproducibility). A categorical qualitative as- sessment was performed based on a grading scale of 1–5 (1 = soft; 2 = mostly soft; 3 = intermediate; 4 = mostly hard; 5 = hard), where tissue stiffness was depicted by a color scale (blue = hard, red = soft, green=intermediate). Values were assigned as follows; Elx-t%sft > 70% = 1, 50% < Elx-t%sft < 70% = 2, 30% < Elx-t%sft < 50% = 3, 20% < Elx-t%sft < 30% = 4, Elx-t%sft < 20% = 5. Percentages of concordant observations were given for comparison. RESULTS Qualitatively, all the 28 patellar tendons evaluated were predominantly red (soft), with a mean +/- SD Elx- t%sft of 94.9% +/-9.3, while the peritendinous tissue was mostly green (intermediate). The overlying dermal layer appeared mostly blue (hard), while the underlying fat pad was mostly green (intermediate) with red (soft) striations. Overall, 89.3% of the patellar tendons were graded as soft or mostly soft, whilst the re- maining 10.7% were classified as intermediate. Repeatability was 86.2%, with a weighted kappa of 0.64 (good), for the well-trained sonographer and 83.3%, with a weighted kappa of 0.53 (moderate), for the senior student. Reproducibility was 86.2%, with a weighed kappa of 0.65 (good). CONCLUSION The results of this study suggest that EUS is a feasible imaging modality to evaluate tissue strain and soft- ness/stiffness in the patellar tendon in dogs. Similarly to the patellar tendon in humans, the normal canine patellar tendon showed a highly soft and homogeneous elastogram. The semi-quantitative analysis demon- strated that EUS was moderately repeatable and reproducible. In conclusion, EUS could be useful in the evaluation of the canine patellar tendon in dogs. More studies are needed in dogs with patellar tendon anomalies, such as injuries, thickening and tendinosis. REFERENCES Porta F, Damjanov N, Galluccio F et al. (2014): Ultrasound elastography is a reproducible and feasible tool for the eval- uation of the patellar tendon in healthy subjects. International journal of Rheumatic diseases; 17:762-766. White J, Gay J, Farnsworth R et al. (2014): Ultrasound elastography of the liver, spleen, and kidneys in clinically normal cats. Veterinary Radiology & Ultrasound; 55:428-434. Lustgarten M, Redding WR, Labens R et al. (2014): Elastographic charateristics of the metacarpal tendon in horses with- out clinical evidence of tendon injury. Veterinary Radiology & Ultrasound; 55:92-101. Jeon S, Lee G, Lee SK et al. (2015): Ultrasonographic elastography of the liver, spleen, kidneys and prostate in clinical- ly nor-mal beagle dogs [corrected]. Veterinary Radiology & Ultrasound; 56:425-431.