Rev Rom Med Vet (2021) 31 | 1: 33-38 33

ISSN: 1220-3173; E-ISSN: 2457-7618

HIND LIMB FIRST (DEWCLAW) IN : MORPHOLOGIC AND X-RAY INVESTIGATIONS IN RELATION WITH GENETIC AND SURGICAL ASPECTS DEGETUL I (PINTENUL) LA MEMBRUL PELVIN LA CÂINE: INVESTIGAȚII MORFOLOGICE ȘI RADIOLOGICE, ÎN CORELAȚIE CU ASPECTE GENETICE ȘI CHIRURGICALE

C.T. COVAȘĂ1),*), C. ȘERBAN1)

The domestic carnivores have five digits in front Carnivorele domestice au cinci degete la mem- limbs and generally, four in the pelvic limbs, the first brele anterioare și de obicei patru la membrele poste- digit being absent. Scarcely ever in and more fre- rioare, lipsind degetul I. Foarte rar la pisică, dar mai quently in , the first digit can be present in pelvic frecvent la câine, degetul I poate fi prezent și la mem- limbs, as a rudiment, more or less developed, being brele posterioare sub formă rudimentară, cu un grad known as “dewclaw”. This term is used also for the first mai mare sau mai redus de dezvoltare, fiind cunoscut digit of the thoracic limb, being more reduced than the sub denumirea de pinten. Acest termen este folosit și rest of the digits, but is more proper for the pelvic limb. pentru degetul I al membrului toracic, fiind mai redus Genetically, the presence of the dewclaw in pelvic decât celelalte, dar este mai propriu membrului pelvin. limb, simple or double, and double in thoracic limb is Din punct de vedere genetic, prezența pintenului la known as hind-limb-specific preaxial polydactyly – membrele posterioare, simplu sau chiar dedublat și a PPD. Taking into account these aspects, we set out to pintenului dedublat la membrele anterioare este des- analyse the morphological and structural variability of crisă sub denumirea de hind-limb-specific preaxial po- the hind limb dewclaw in dogs, in relation with the de- lydactyly – PPD. velopment degree of the first metatarsal bone, using Date fiind aceste aspecte, ne-am propus o analiză clinical and imagistic exam. The most of the animals a variabilității morfologice și structurale a pintenului la were patients of two veterinary clinics having various membrul posterior, în corelație cu dezvoltarea meta- pathologies of the legs. Clinically were identified two tarsului I, prin examene clinice și imagistice. animals having dewclaw in pelvic limb, one being sim- Cele mai multe animale luate în studiu au fost pa- ple and not joined and the other one, double and cienți care au fost aduși la două clinici veterinare pen- joined. The X-ray exam, even the number of the ani- tru diverse afecțiuni ale membrelor posterioare. Clinic mals with dewclaw wasn't high, revealed many mor- a fost înregistrată prezența pintenului la două ani- phologic types of the dewclaw: simple and not joined male, din rasă comună, la unul fiind simplu și nearti- dewclaw, without phalanges (one case); simple and culat, iar la celălalt bifid și articulat. not joined dewclaw, in his structure having one or two Imagistic, deși pintenul nu a fost observat la un phalanges (three cases); simple and joined dewclaw, număr mare de animale, s-au constatat și identificat the osseous structure including two phalanges, simul- mai multe variante morfologice: pinten simplu, nearti- taneously being present the first metatarsal bone re- culat, fără structură osoasă (1 caz); pinten simplu, presented by the proximal and distal extremity (two nearticulat, având în structura sa una, respectiv două cases); simple dewclaw, well developed, with two pha- falange (3 cazuri); pinten simplu, dar articulat, cu un langes and joined with the first metatarsal bone com- schelet format din două falange (2 cazuri), conco- pletely developed (two cases). In most of the cases mitent cu prezența metatarsului rudimentar I, (seven) was noted the lack of the dewclaw, but the reprezentat prin extremitatea proximală și distală; presence of the proximal extremity of the first meta- pinten simplu, bine dezvoltat, cu două falange și arti- tarsal bone and, in other two cases the first metatarsal culat cu metatarsul I complet dezvoltat (2 cazuri). La bone was completely absent. Can be noted firstly an cele mai multe animale (șapte), pintenul a fost absent, obvious polymorphism of the dewclaw in dogs, this as- dar s-a observat prezența numai a extremității proxi- pect being important especially when the surgical re- male a metatarsului I, iar la alte două animale și meta- moval is necessary. tarsul I a fost total absent. Se poate remarca în primul Keywords: dewclaw, dog, structure, x-ray exam rând un polimorfism accentuat al pintenului la câine, aspect important mai ales atunci când se ridică proble- ma îndepărtării chirurgicale a acestuia. 1) University of Agronomic Sciences and Veterinary Medicine Faculty of Veterinary Medicine, Iași, Romania Cuvinte cheie: pinten, câine, *) Corresponding author: [email protected] structură, examen radiografic 34 Rev Rom Med Vet (2021) 31 | 1

The autopodium is that segment of the locomotor ment. In forelimb commonly it presents two phalan- appendix which presents the largest morphological ges, proximal and distal one, and makes joint with the variability from a species to another. This variability is Ist metacarpal bones. There are breeds, as the Norwe- present inside to a vertebrate class but also from a gian Lundehund, which have a double dewclaw. In the class to another, being in a close relationship with the pelic limb the dewclaw is more vestigial, commonly locomotion type (3). has no phalanges or sometimes a rudimentary distal Both thoracic and pelvic autopodium include three phalanx. Generally, it is attached by the metapodium segments namely: basipodium, consisting of carpal only through the skin (9, 26). In some cases, the pel- bones for thoracic limb and tarsal bones for the pelvic vic dewclaw presents a complete skeleton and is one; metapodium, which includes the metacarpal joined with the first metatarsal bone. bones in case of the thoracic limb and metatarsal The presence of the dewclaw in hind limb can con- bones in case of the pelvic one and the acropodium, duct to some pathologies, especially when it is poorly which is represented by the skeleton of the digits that connected with the leg. Hind limb dewclaws tend to be includes the phalangeal and the sesamoid bones (2, removed more frequently because they are loosely 12, 17, 18). attached by skin and pose more of a risk of getting The most important inter-species peculiarities tar- caught on something or ripped (24). get the acropodium, between domestic spe- Our observations were focused to analyse the va- cies existing a large variability of the digits number. riability on the conformation and the structure of the Generally, the number of digits is directly correlated hind limb dewclaw in dogs using the clinical and ima- with the number of metacarpal or metatarsal bones. gistic methods. When exist rudimentary metacarpal or metatarsal bones, there is no corresponding digit, as in the case of MATERIAL AND METHODS the 2nd and 4th metacarpal/metatarsal bones in or the 5th metacarpal bone in ruminants (2, 3). The investigations were made on 19 canine spe- In domestic carnivores the thoracic acropodium is cimens, both males (11) and females (8). The most of complete, including 5 digits (I-V) corresponding to the the animals were half breed. Other breeds were: Pe- metacarpal bones (I-V).The first digit is more reduced, kingese (1 animal), Rottweiler (1 animal), Bichon (4 his skeleton has two phalanges (proximal and distal) animals). The age varied between 9 months and 13 and generally has no function to support (3, 10). At the years. Except two dogs, the animals were patients of pelvic limb dogs in general have four digits (II-V), two veterinary clinics from Iasi (Romania) and were presumably due to an evolutionary adaptation (7, 14), brought to clinics for various pathologies of the legs. corresponding to the metatarsal bones II-V. The first The dogs were clinically examined and then subjected digit (I), usually misses. In dogs occasionally, and to imagistic examination, more exactly x-ray exam in exceptionally in cats, the first digit can exist also for two instances: mediolateral (ML) and dorsoplantar the pelvic limb (19), as a rudiment and it is named (DPL). The x-rays images obtained for the pathologies dewclaw (also for the thoracic limb). When the dew- were used also to study and analyse the morphology exists in cats, the Ist digit has no phalanges, only and the structure of the dewclaw. Totally, there were the horny sheath. analysed x-rays images of 3420 dogs to find the ani- A dewclaw is a vestigial digit in some animals, on mals which had dewclaws. Two canine specimens were the of many , and (inclu- not patients but were included into the study having ding some extinct orders, like certain theropods). It dewclaws, and there was no possibility to complete the commonly grows higher on the leg than the rest of the clinical observations with imagistic exam. foot, such that in or unguligrade species it The obtained images were examined in a compa- does not make contact with the ground when the ani- rative way to analyse as complete is possible the mor- mal is standing. The name refers to the dewclaw's alle- phological details. To describe these aspects, we used ged tendency to brush dew away from the grass (4). On the terms in accordance with the NAV, Sixth Edition, dogs and cats, the dewclaws are on the inside of the 2017 (11). front legs, positioned analogously to a human (22). Although many animals have dewclaws, other RESULTS AND DISSCUTIONS similar species do not, such as horses, giraffes and the (8, 23, 27). From the beginning it was observed the structural Although both fore limb and hind limb first digits are polymorphism of the dewclaw in examined animals, commonly referred to as “dewclaws”, only the vestigial clinically but also radiological. Firstly, in the two dogs digits inside the hind limbs are dewclaws proper (5). which were only clinically analysed, the morphology of The morphology and the structure of the dewclaw the dewclaw was different. In the first case (Fig. 1) it can vary greatly in relation with the degree of develop- was observed a forked or double dewclaw. Rev Rom Med Vet (2021) 31 | 1 35

Through palpation it was concluded that there sent, being rudimentary. There were developed only exists a joint with the metatarsus, being a joined digit the proximal (Basis) and distal extremity (Caput), the because the mobility was reduced. In the second case last one being joined with the proximal phalanx of the it was noticed a simple dewclaw (Fig. 2) which presen- dewclaw (Fig. 7, Fig. 8). ted a high degree of mobility. We supposed that there Also, for the Ist metatarsal bone (Os matatarsale I) was no joint with metatarsus, and the connection was there were remarked different degrees of develop- provided by the soft tissue (skin). Unfortunately, for ment from a dog to another. In the most of the animals these two animals was no possibility of radiologic the x-ray exam revealed the lack of the first exam for structural details. metatarsal bone (2 cases) (Fig. 9) or the presence of the proximal extremity (Basis), being joined with the first tarsal bone (Os tarsale I) (7 cases) (Fig. 10.). In other two animals, as previously was described, both extremities were present (Fig. 7, Fig. 8). Finally, in two animals it was noticed a complete and well developed Ist metatarsal bone, short (Fig. 11) or even long, al- most similar to the other metatarsal bones (Fig. 12). Also, in first case, it could be observed a complete and joined dewclaw, well developed, in the second one the x-ray image did not include the view of the dewclaw.

Fig. 1. Double and joined dewclaw (A)

Fig. 3. Simple and not joined dewclaw without osseous structure (A) Fig. 2. Simple and not joined dewclaw (A)

Through the X-ray exam, it was observed a diffe- rent osseous structure of the dewclaw and a various development of the first metatarsal bone. In a dog was registered a simple and not joined dewclaw, no pha- lanx being present. Only the horny sheath can be ob- served (Fig. 3). In other three cases it was noticed that the dewclaw is also simple, not joined, but the skele- ton included two phalanges in two dogs (Fig. 4 and Fig. 5) and a single phalanx - distal one (Phalanx distalis) in the third one (Fig. 6). These three animals had or not the vestige (proximal extremity) of the Ist meta- tarsal bone (Os metatarsale I). In other two dogs, it was noticed a joined dewclaw, having also a complete skeleton including the proximal (Phalnx proximalis) and the distal phalanx (Phalanx distalis). In a case (Fig. 8), on x-ray image can be observed only the pro- ximal phalanx, but most probably it had also the distal Fig. 4 & 5. Simple and not joined dewclaw one. In these dogs the first metatarsal bone was pre- with two phalanges (A) 36 Rev Rom Med Vet (2021) 31 | 1

Fig. 6. Simple and not joined Fig. 11. Well-developed first metatarsal bone (A); dewclaw with a phalanx (A) simple, joined and well-developed dewclaw Fig. 7. Simple and joined dewclaw with two phalanges (B) with two phalanges and distal part of Fig. 12. Complete developed first the first metatarsal bone (B); proximal metatarsal bone (arrow) part of the first metatarsal bone (A) According to the dates, a joined first digit of the fore limb consists of a proximal phalanx and a distal phalanx. The distal phalanx has a claw attached. The digit articulates with the first metacarpal bone via the metacarpophalangeal joint. Also, for the hind limb, a fully developed digit consists of a proximal phalanx and a distal phalanx. The distal phalanx has a claw attached. The digit articulates with the first metatarsal bone via a metatarsophalangeal joint (15, 26). A non- articulated first digit (dewclaw) is a vestigial structure composed of a terminal phalanx with a claw attached and connected to the limb only by skin tissue. It is variably present on the hind limb of dogs, and on occasion may also be seen on a fore limb (26). In some breeds, there are two dewclaws. When a Fig. 8. Simple and joined dewclaw with two dog has extra dewclaws in addition to the usual one on phalanges and distal part of the first metatarsal each front leg, the dog is said to be double dewclawed bone (B) – only the proximal phalanx is visible; (4, 26). proximal part of the first metatarsal bone (A) Unlike front dewclaws, rear dewclaws tend to have little bone or muscle structure in most breeds. It is normal, although not biologically necessary, that cer- tain breeds will have more than one dewclaw on the same paw. At least one of these dewclaws will be poor- ly connected to the leg, and in this case, it is often sur- gically removed (1). The hind dewclaws do not have associated ten- dons and are considered non-functional (though they may be required for some breed standards) (24). The dewclaw articulates with metatarsal bone I, which is often small and may be fused to tarsal bone I. If two dewclaws are present, there may be, on occa- sion, complete duplication of the phalanges and meta- Fig. 9. The lack of the first metatarsal bone tarsal bone I. Metatarsal bone I may also exist as two Fig. 10. Vestige of the first metatarsal bone segments united by fibrous tissue or present with a – proximal extremity (A) distinct joint between the segments (24). Rev Rom Med Vet (2021) 31 | 1 37

In a few breeds, five or six digits have been inten- Thus, for working dogs it is best for the dewclaws tionally maintained through breeding. Examples of not to be amputated. If the dewclaw does suffer a breeds that must have the dewclaw present in order to traumatic injury, the problem can be dealt with at that be recognized as the breed standard include Great time, including amputation if needed (22). Pyrenees, Bauceron, St. Bernard, Briard, Icelandic There is some debate as to whether dewclaws Sheepdog, Anatolian Shepard (24, 22). should be surgically removed. The argument for remo- In addition, most breeds often display this extra val states that dewclaws are a weak digit, barely atta- digit as a genetic variation, although the number of ched to the leg, and thus they can rip partway off or digits (five) in the forelimb is essentially unchanged. easily catch on something and break, which can be This type of dominant genetic alteration has been co- painful and prone to infection. mmonly called “dewclaw”. A more technical term for Dewclaw removal is most easily performed when these additional digits on the rear legs is hind-limb- the dog is young, around 2–5 days of age. It can also specific preaxial polydactyly. Several genetic mecha- be performed on older dogs if necessary though the nisms can cause rear dewclaws; they involve the surgery may be more difficult then. The surgery is fair- LMBR1 gene and related parts of the genome (16). ly straightforward and may be done with local anaes- Rarely, polydactyl mutations involving both the fore thetics if the digit is not well connected to the leg (4, and hind limbs occur, as reported in breeds like the 13, 21). Norwegian Lundehund (6), although their genetic ba- In some breeds of dogs, front limb dewclaws are ses are poorly understood. Except for its exclusive routinely removed to improve the dog's front-end appearance in the hind limb, hind-limb-specific canine appearance in the show ring. In some cases, a dog's PPD resembles human PPD type I, which increases front dewclaw is removed if it has been severely in- one or more biphalangeal (6, 16). jured or has developed a disease (e.g., cancerous tu- According to the literature, if in the fore limb the mour). In these cases, it is certainly in the dog's best dewclaw can be even useful, in case of the hind limb interest to remove it. In speaking with numerous vete- can cause damages and raises the issue of surgical re- rinarians, it has been found that dewclaws are the moval. The dewclaws are not dead appendages. They least injured digit of the canine carpus. can be used to lightly grip bones and other items that Hindlimb dewclaws tend to be removed more fre- dogs hold with the paws. In some dogs these quently because they are loosely attached by skin and may not appear to be connected to the leg at all except pose more of a risk of getting caught on something or by a flap of skin; in such dogs the claws do not have a ripped (24). use for gripping as the claw can easily fold or turn (10). For certain dog breeds a dewclaw is considered a Four of the toes (equivalent to our fingers), are in necessity, e.g. a Beauceron for sheep herding and for contact with the ground when the dog is standing. navigating snowy terrain (4). As such, there is some When a dog runs, however, the entire foot from the debate about whether a dewclaw helps dogs to gain carpus to the toes contacts the ground. If the dog then traction when they run because in some dogs, the turns, it can dig the dewclaw (the equivalent of our dewclaw makes contact when they are running and thumb) into the ground to stabilize the leg and reduce the on the dewclaw often wears down in the same torque on the rest of the leg. There is a great deal of way that the nails on their other toes do, from contact misconception about front dewclaws. The fact that with the ground. In many dogs the dewclaws never they are not in contact with the ground when the dog is contact the ground. In this case, the dewclaw's nail standing still has led people to mistakenly believe that never wears away, and it is often trimmed to maintain they have no function in movement. As a result, the it at a safe length (23). dewclaws are removed from many purebred puppies soon after birth. Many breeders feel this gives a clea- CONCLUSIONS ner, straighter look to the dog's front legs. Others be- lieve that the dewclaws should be removed so that The investigation revealed an evident polymor- they will not get injured. But stop-action photographs phism of the dewclaw in dogs, in correlation with the clearly demonstrate that they are in contact with the development degree of the first metatarsal bone. ground whenever the dog canters or gallops. In addition to clinical investigations, the x-ray e- Further proof of the front dewclaws' functionality xam can be successfully used to observe the peculia- comes from anatomical studies demonstrating that rities of the dewclaw structure, the data being impor- there are several tendons that connect muscles of the tant especially for surgical removal. lower limb to the dewclaw. Some report The study did not reveal an obvious specificity of a higher incidence of foot and carpus injuries and ar- the presence/structure of the dewclaw and first meta- thritis in dogs that lack dewclaws, likely because of tarsal bone for some animals depending on breed, additional torque on the leg. age, sex, etc. 38 Rev Rom Med Vet (2021) 31 | 1

1. Becker D. M., (2012), Should I Remove My Dog's 16. Park K., Kang J., Subedi K. P., Ha J-H., Park C., Dewclaws? Vetstreet. Available at: http://www. (2008), Canine polydactyl mutations with hetero- vetstreet.com/dr-marty-becker/does-our-puppy- geneous origin in the conserved intronic sequence need-his-dewclaws [Accessed: 05/05/2020] of LMBR1. Genetics, 179(4):2163-2172 2. Coțofan V., Palicica R., Hrițcu V., Enciu V., (1999), 17. Predoi G., Georgescu B., Belu C., Roșu P. M., Anatomy of domestic animals, Vol. I [in Roma- Dumitrescu I., (2019), Anatomie des animaux do- nian], (Ed.) Orizonturi Universitare, Timisoara, Ro- mestiques, Ostéologie, Arthrologie et Myologie, mania (Ed.) Ex Terra Aurum, Bucharest, Romania 3. Covașă C.T., Munteanu A., (2020), Anatomical 18. Predoi G., Georgescu B., Belu C., Dumitrescu I., peculiarities of the broad-snouted caiman's limb Șeicaru A., Roșu P., (2011), Comparative anatomy bones (Caiman latirostris). Lucr Șt USAMV Iași, of domestic animals, Osteology, Arthrology, Myolo- Seria Medicină Veterinară, 63 (22):3 gy, (Ed.) Ceres, Bucharest, Romania 4. Danziger D., McCrum M., (2008), The Thingummy: 19. Rice D., (2008), The complete book of dog bree- A book about those everyday objects you just can't ding, 2nd edition, (Ed.) Barron's Educational Series, name, (Ed.) Doubleday, London, UK Hauppauge, New York, USA 5. Evans H., De Lahunta A., (2016), Guide to the Di- 20. Veterinary Council of New Zealand, (2005), Code ssection of the Dog, (Ed.) Saunders Elsevier, St of professional conduct. Available at: http://www. Louis, New York, USA vetcouncil.org.nz/CPC/index.php. [Accessed: 6. Fogle B., (2000), Domestic Dog Breeds: The New 15/01/2021] Encyclopedia of the Dog, (Ed.) Dorling Kindersley, 21. Vetinfo, (2015), Dog Dew Claw Removal. Available London, UK at: https://www.vetinfo.com/dog-dew-claw- 7. Galis F., Van Alphen J. J. M., MetzJ. A. J., (2001), removal.html [Accessed: 15/01/2021] Why five fingers ? Evolutionary constraints on digit 22. Zink M. C., (2016), Form Follows Function – A New numbers, Trends Ecol Evol, 16:637-646 Perspective on an Old Adage. Penn Vet Working 8. Heather F.S., Brent A., Rahul K., Ryan A., Aryeh Dog Center. Available at: https://web.archive.org/ G., (2020), Adaptations to cursoriality and digit re- web/20160304044624/http:/pennvetwdc.org/wp duction in the forelimb of the African wild dog (Ly- -content/uploads/2011/09/9-Zink.pdf [Accessed: caon pictus), PeerJ, 8:e9866D 15/01/2021] 9. Hosgood G., (1998), Small Animal Paediatric Medi- 23. *** (2021), Dewclaw, In Wikipedia. Available at: cine and Surgery, (Ed.) Butterworth-Heinemann, https://en.wikipedia.org/wiki/Dewclaw [Ac- Oxford, UK cessed: 15/01/2021] 10. Hoskins J.D., (2001), Veterinary paediatrics: dogs 24. *** (2018), Dewclaw Function 101. In: WorksSO and cats from birth to six months, 3rd Edition, (Ed.) well. Available at: https://1tdc.com/dewclaw- Saunders, Philadelphia, USA function-101/ [Accessed: 15/01/2021] 11. I.C.V.G.A.N., (2017), Nomina Anatomica Veteri- 25. *** (2020), Atlas of anatomy on x-ray images of naria, 6th Edition, (Ed.) Committee Hanover, (Ger- the dog. In: vet-Anatomy. Available at: https:// many), Ghent (Belgium), Columbia, MO (USA), Rio www.imaios.com/en/vet-Anatomy/Dog/Dog- de Janeiro (Brazil) Osteology-Radiographs [Accessed: 15/01/2021] 12. König H.E., Liebich H-G., (2007), Veterinary ana- 26. *** (2021), Policy: First digit amputation in dogs. tomy of domestic mammals, Textbook and colour Available at: https://www.nzva.org.nz/page/ atlas, 3rd Edition, (Ed.) Schattauer, Stuttgart, policyfirstdigit [Accessed: 15/01/2021] Germany 27. *** (2020), African wild dogs have vestigial first 13. Lotz K. N., (2015), The Dewclaws Debate – Keep digit and muscular adaptations for life on the run. Them or Lose Them? iheartdogs.com. Available at: In:Science Daily.Available at: https://www.science https://iheartdogs.com/the-dewclaws-debate- daily.com/releases/2020/09/200907080346 keep-them-or-lose-them/[Accessed: 15/01/2021] [Accessed: 15/01/2021]. 14. Macdonald D.W, (1984), The encyclopedia of ma- mmals, (Ed.) Facts on File, New York, USA 15. New Zealand Legislation, (2018), Animal Welfare (Care and Procedures) Regulations, Removing dogs' first digits (dew claws). Available at: http:// www.legislation.govt.nz/regulation/public/2018/0 050/latest/whole.html#LMS22927. [Accessed: 15/01/2021]