Ultrasonographic study of the digital flexor tendons of the forelimb in a pure donkey breed

Authors

Parés-Casanova, Pere M.

Abstract

Although there are some studies made by ultrasound techniques in donkeys, few surveys of the measurements and proportions of flexor tendons are available in the literature. This study was designed to evaluate the donkey normal anatomy of the digital flexors in the metacarpal region of Catalan donkeys using diagnostic ultrasound. For this goal we obtained ecographic palmo-dorsal views of 12 adult animals belonging to this breed. Palmar tendons were divided into three levels from proximal to distal metacarpus and thickness of superficial and deep tendons and distal accessory ligament (“check ligament”). Values for those tendons are reported here. There appeared no differences between right and left forelimb nor between levels. Our findings should be considered for clinical evaluation of this and other donkey breeds.

Introduction

There are no muscles in the equine digit, instead we find tendons of insertion of the two extensor muscles and the two flexor muscles of the digit, a superficial and a deep. The deep tendon is enforced by an accessory ligament. The tendon structures located on the palmar area of the equids are (International Committee on Veterinary Gross Anatomical Nomenclature 2017):

- tendons of the digital flexor muscles: superficial (flexor digitorum [digitalis] superficialis), deep (flexor digitorum [digitalis] profundus) tendons

- distal accessory ligament (lig. accessorium, clinically known as “check ligament” or more concisely “inferior check ligament”)

- interosseous tendon (mm. interossei, clinically known as “suspensory ligament”).

Ultrasound is a safe, easy, non-invasive and effective technique for analysis of soft tissue injuries and currently accessible to any veterinarian clinician (Martínez Martínez 2005) (Padaliya et al. 2015) and several studies have proved the correctness of the ultrasonographic inspections of the tendons and ligaments by comparing them with necropsy findings (Vosugh, Nazem, and Lahuti 2017). Therefore, comprehensive values of the digital flexors ultrasonographic images can describe accurately their anatomy. The ultrasound assessment of tendon anatomy focused on the study of echogenicity and size has been done in many horse breeds, such as Andalusian (Martínez Martínez 2005), Arabian (Çelimli, Seyrek-Intas, and Kaya 2010) (Vosugh, Nazem, and Lahuti 2017), Indian breeds (Padaliya et al. 2015), Pyrenean Catalan Horse (Parés-Casanova et al. 2020), Mangalarga (Aristizábal et al. 2005) and Thoroughbreds (Çelimli, Seyrek-Intas, and Kaya 2010), but many few on asinines (Mostafa and Abd-Glil 2008) (Nazem et al. 2015).

The Catalan donkey (“Ruc Català”) is a breed  from Catalonia, in north-eastern Spain and south-western France (Jordana and Folch 1996). It is a large animal weighing between 350–450 kilograms. Jacks average 142 centimetres in height and jennies, 136 centimetres (Porter 2016) (Jordana and Folch 1996). At the end of 2013, the total population in Spain was recorded as 851. The “Ministerio de Agricultura, Alimentación y Medio Ambiente”, the Spanish ministry of agriculture, lists the breed as "in danger of extinction". The objective of this study is to determine the sectional measurement (“thick”) of the flexor tendons in the metacarpal area in a donkey pure breed, and determine if the age, sex, limb and cutting area has any effect on it.

Material and methods

We studied adult 12 animals (2 males and 12 females, age range 4,5 to 19-years-old) belonging to Catalan donkey breed. Subjective assessment of clinical signs, visual and palpable abnormalities of flexor tendons was done, and no animal presented injuries related to the skeletal muscle system. Subjects were restrained with the help of owner in standing position in the original stables or grass, in stand-up position and subjected to physical restriction, not being necessary the use of sedation. All animals included in this work were officially registered as pure breed in the studbook.

Echographic device was equipped with a sectorial-type probe which had a pad adapted. Transverse images were obtained at 5 MHz and thicknesses were measured. Palmo-dorsal measurements (“thick”) were determined in three equal zones, starting from the proximal border of the metacarpal bone (level 1), medium border (level 2) and proximal border of the proximal sesamoid bones (level 3). Therefore, structures of donkeys with different metacarpal lengths were measured at an equal ratio. Both forelimbs were ecographied and digitally recorded. Images were stored and ulteriorly measured with Digimizer freeware (available at http://digimizer.findmysoft.com/).

As data was not-normally distributed, only non-parametric tests were used. On the data sheet, first, a Kruskal-Wallis H test was done to assess differences between limbs (right and left) and levels (1 to 3). Then, a two-way NPMANOVA (“Non Parametric ANalysis Of VAriance”) with correlation measurement was done using “sex” and “age” as factors. Finally, a second Kruskal-Wallis test was done to compare thicknesses.

Statistical analysis
The obtained data were statistically analysed with statistical software program PAST v. 2.17c (Hammer, Harper, and Ryan 2001). Significance levels at p < 0.05 were considered significant.

Results and discussion

The tendons and ligaments of the metacarpal region of the Catalan donkey breed were evaluated ultrasonographically and all parts of the palmar structures were seen on the obtained pictures: skin, subcutaneous tissues, superficial and deep digital flexor tendons, distal accessory ligament and interosseous tendon. The surface of the third metacarpal bone was clearly detected as a hyperechoic line. Wide synovial sheaths between tendons with high echogenicity were seen. Tendons presented a homogenous echogenicity.

No ultrasonographic abnormalities were found. Kruskal-Wallis test reflected no differences between limbs and levels (H=1.025; p=0.960), so for ulterior analysis data were clustered only according to each tendon. Two-way NPMANOVA reflected no statistical differences between sexes (p=0.298) nor ages (p=0.448). Second Kruskal-Wallis test reflected differences between tendons (H=68.32; p<<0.001). Table 1 reflects main descriptive statistics for each tendon. Values are clearly below those described for horses, such as Arabians and Thoroughbreds (Çelimli, Seyrek-Intas, and Kaya 2010).
 

Further details

DISCUSSION

Ultrasound is a widely used technique to evaluate tendon lesions on equids. The most commonly used ultrasound criteria for examining tendon and ligament injuries are the size (area) and echogenicity of tendons. However, to apply them in the equine clinic, they must first know their normal values. In this regard, several studies have been conducted on different breeds of horses, but although some studies of morphometric measurements by ultrasound in asses have been reported, no survey of the measurements and proportions of all flexor tendons and ligaments in the metacarpal region of Catalan donkeys was available in the literature. Our study offers thickness data of flexor tendons for this breed, which are clearly below those found in horses. These differences should be considered for clinical evaluation.

Acknowledgments
The author is thankful to owners of animals for their support and cooperation in carrying out the study.

Competing Interests
The author declares that he has no competing interests.

Ethical approval

All clinical cases in this research were examined and diagnosed as per standard examination and diagnostic procedure without harming or discomforts to animals.

References

Aristizábal, F. A.M., M. V. Souza, J. R.M. Aranzales, and J. I. Ribeiro. 2005. “Valores Biométricos Obtidos Por Ultra-Sonografia Dos Tendões Flexores e Ligamentos Acessório Inferior e Suspensório Da Região Metacárpica Palmar de Cavalos Mangalarga Marchador.” Arquivo Brasileiro de Medicina Veterinaria e Zootecnia 57(2): 156–62.

Çelimli, N., D. Seyrek-Intas, and M. Kaya. 2010. “Morphometric Measurements of Flexor Tendons and Ligaments in Arabian Horses by Ultrasonographic Examination and Comparison with Other Breeds.” Equine Veterinary Education 16(2): 81–85.

Hammer, Ø., D.A.T. Harper, and P.D. Ryan. 2001. “PAST v. 2.17c.” Palaeontologia Electronica 4(1): 1–229.

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Jordana, J., and P. Folch. 1996. “The Endangered Catalonian Donkey Breed: The Main Ancestor of the American Ass or Mammoth.” Journal of Equine Veterinary Science 16(10): 436–41.

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Nazem, M.N., S.M. Sajjadian, D. Vosough, and A. Mirzaesmaeili. 2015. “Topographic Description of Metacarpal Tendons and Ligaments of Anatoly Donkey by Ultrasonography and Introducing a New Ligament.” Anatomical Sciences 12(4): 153–60.

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Parés-Casanova, P.M. et al. 2020. “Estudio Ultrasonográfico de La Región Metapodial En Potros de La Raza "Cavall Pirinenc Català”.” Actas Iberoamericanas de Conservación Animal 14(2019): 4–7.

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Vosugh, D., M.N. Nazem, and S. Lahuti. 2017. “Anatomy and Ultrasonographic Morphometric Measurements of Palmar Metacarpal Tendons and Liga-Ments in Pure Persian Arabian Horses.” Anatomical Sciences 14(4): 153–62.

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  Pere M. Parés-Casanova Thursday, 09 June 2022 - 09:18 UTC

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