Figure 1 (left): An obvious corn with a large focal circular area of hyperkeratinization. Figure 2 (right): A less obvious corn with a small central black spot, blanching, and surface wear of the pad.Images courtesy Michael Guilliard It has been a little over four years since the flexor tendon cutting procedures were first reported for the treatment of corns in sighthounds in Veterinary Practice News.1 Since then, the surgical technique has evolved to become recognized as the most successful method of treating this chronic, painful, and debilitating condition. A corn, also known as a paw pad keratoma, is a focal area of hyperkeratinization found in the digital foot pads of sighthound breeds—notably, the greyhound, whippet, and lurcher. It rarely occurs in other breeds or in the metacarpal/tarsal pads. The area of hyperkeratinization may extend internally to the underlying deep digital flexor tendon (DDFT) having the appearance of a hollow root, causing pathological changes to the surrounding tissues (as extensively documented in the previously published article).1 Visual presentation is varied from a large circular, extruding area of thickened pad (Figure 1) to barely discernible changes (Figure 2). Mediolateral digital examination of the pad may detect a thickened hard area, and digital pressure applied in orthogonal directions across the corn usually produces a pain response. The main presenting sign is lameness, which can be non-weightbearing, with the owner reporting marked improvement on soft ground. In the consulting room, some patients stand holding up the foot. The lameness is poorly responsive to pain-relieving medication, and the human analogy would be akin to having a stone in your shoe. These dogs are lacking vitality and are depressed, proven by a rapid reversal after successful surgery with greatly improved demeanor and willingness to exercise. The incidence of corns in the greyhound population taken from two surveys of multiple veterinary practices is reported to be 5.9 percent and 2.4 percent, making it the most common dermatological condition in this breed.2,3 The incidence of corns, however, will be under-reported from misdiagnoses. Modern diagnostic imaging often detects abnormalities of no or little clinical relevance. Demographics According to two studies, one of 30 dogs with 40 corns4 and the other of 100 dogs with 161 corns,5 demographics are as follows: Age: One to 13 years. Limb distribution: Approximately 90 percent of corns occur in the thoracic limbs and 10 percent in the pelvic limbs. Vertical forces when walking are 1.1 times the body weight in the thoracic limbs compared with 0.8 times in the pelvic limbs.6 Digit distribution: Approximately 90 percent occur in digits 3 and 4 in both thoracic and pelvic limbs. These are the main weight-bearing digits. Multiple corns: Thirty-eight percent of dogs in the larger survey, either at initial presentation or subsequently, developed corns in other pads. There was no pattern to the distribution and could occur in the same foot, the contralateral foot, or in the other set of limbs. Occasionally, there was a symmetrical distribution. Aetiology Figure 3 (left): Hyperflexion of the proximal interphalangeal joint. There was thickening of the superficial digital flexor tendon from a previous injury. Figure 4 (right): The anatomy of the foot. The main theories of the aetiology of canine corns have been viral infection (notably, papilloma virus, as found in the human verruca), foreign body in the pad, or previous penetration and repeated mechanical trauma. Most studies have failed to find evidence of papilloma virus. As such, this theory has now been discounted.7 Likewise, foreign bodies were absent macroscopically and radiographically in the study of 40 corns4 and from histological examinations of more than 1,000 corns (Doughty, unpublished data); however, 4.5 percent of corns in these studies had some extraneous material present in the soft central portion, which was thought to be from secondary penetration. Anecdotally, this author has observed the formation of corns after successful foreign body removal, and his present protocol is to combine the surgery with a superficial digital flexor tendonectomy. The mechanical theory is now dominant. As seen in humans, this is where corns develop from extrinsic factors, such as ill-fitting shoes, or intrinsically from anatomic malformation, such as hammer toe. The study of 40 corns found 40 percent showed some anatomical abnormality in the foot,4 but the significance of most of these is unclear, apart from distal digital amputation, hyperflexion of the proximal interphalangeal joint (PIP) (Figure 3), and fracture of the third phalanx (P3). More compelling evidence is seen in two cases of revision of distal amputations for corn occurrence, with the corns exfoliating naturally after the unloading of the pad.4 Historic treatments Many of the historic treatments of corns in sighthounds have revolved around conservative management and surgical interventions. The former refers to protective, cushioned footwear, accompanied by the use of topical medicants to either soften or break down the corn, while the latter involves hulling or complete excision. Partial excision, known as hulling, is a vague procedure that removes corn tissue from varying depths and gives temporary relief. Surgical excision removing the entire corn has a 50 percent recurrence rate within one year.4 The reason why these treatments ultimately fail is because the cause of abnormal pad loading has not been addressed. This finding provided a working hypothesis for the procedures involving cutting the digital flexor tendons to unload the pad. Anatomy of the foot Figure 5 (left): The position of the digit after a superficial digital flexor tendonectomy. The P1/P2 joint is less flexed and is lower than the joint on adjacent digits to the ground. The digit is extended cranially, but the nail remains in contact with the ground. Figure 6 (right): The position of the digit after a combined tenotomy. The digit is flattened with a raised nail. The canine foot has two digital flexor tendons, the superficial (SDFT) and the deep (DDFT), tracking down the palmar/plantar aspects of the metacarpus/tarsus to insert on the phalanges. The SDFT inserts on the proximal end of the second phalanx (P2), and the DDFT on the flexor process of P3 having been held against P2 by the distal annular ligament. These are counterbalanced by the digital extensor tendon and elastic ligament, which share an insertion on the dorsal aspect of P3 (Figure 4). The action of the SDFT is to flex the PIP joint and its severance results in reduced flexion in the joint but not collapse due to tension provided by the DDFT running through the distal annular ligament (Figure 5). The action of the DDFT is to flex P3, keeping the nail in contact with the ground. Its severance causes the nail and pad to rotate dorsally from the action of the elastic ligament. A flat digit with P3 rotation is seen from severance of both ligaments. Digital flexor tendon tenotomy/tendonectomy The original surgery method involved a tenotomy of both tendons on the palmar/plantar aspect of P1. When performed on a foot with a missing or an adjacent damaged digit, complications arose due to the need for the full support of adjacent digits. This led to the adoption of the SDF tenotomy procedure, which had a further evolution into a tendonectomy following some cases of tendon reconnection and corn recurrence. Superficial digital flexor tendonectomy is now the surgery of choice; the combined tenotomy, however, is used for many revision surgeries. (Details of various surgeries are graphically described in Veterinary Dermatology.7) Superficial digital flexor tendonectomy After standard surgical preparation and draping, the canine patient is placed in lateral recumbency with the affected digit uppermost to the axis of the foot. Using one hand, an assistant holds and rotates the limb to expose the surgical site; the other hand is used to place one finger on the dorsal PIP joint, while pressing on the pad with another. This forces the digit into full extension. By observation and palpation, the relevant flexor tendon is identified on the palmar/plantar aspect of the metacarpus/tarsus. A one- to two-cm linear skin incision is made along the tendon at the level of the distal third of the metacarpus/tarsus, immediately exposing the white superficial tendon. This is carefully dissected free of the surrounding connecting tissue, avoiding the many blood vessels, enabling fine, curved mosquito forceps to be placed under the thin, strap-like tendon. By moving the forceps back and forth, a length of tendon is freed allowing its removal. A minimum length of one cm is recommended. Skin closure is routine. Combined tenotomies at P1 With a similar limb preparation and positioning, a linear skin incision is made over the tendons, beginning two millimeters from the metacarpal/tarsal pad, running towards the digital pad exposing the underlying combined tendon sheath. Careful dissection of the adjacent connective tissues will allow mosquito forceps to be placed under the tendon bundles (Figure 7). These are transected and not excised. The release of the flexor tendons, felt by the assistant, allows full extension of the digit. It is imperative the site is inspected to ensure no tendon bundles remain intact. Skin closure is routine. Aftercare Figure 7: Intraoperative view of a combined tenotomy with mosquito forceps isolating the tendon bundles prior to incision. Non-steroidal anti-inflammatories are given for pain relief. The foot is bandaged for only 24 hours and exercise is restricted to lead walks for 10 days. Complications Hemorrhage can occur during surgery, but this is controllable with digital pressure. The author does not recommend a tourniquet. A major painful complication of a full tenotomy is hyperextension of the PIP joint, with an incidence of about five percent of cases causing weight-bearing on the skin overlying the joint with keratoma formation. Arthrodesis/ankylosis of the joint in flexion can resolve the lameness. The other major complication of all procedures is corn recurrence after successful initial surgery due to the tendon(s) reconnecting and contracting. This can occur up to three years later and requires revision. The author has performed 27 revisions on more than 500 corn surgeries, but, since the switch from SDF tenotomy to tendonectomy, the incidence is lower. Revision can be at either site, but, due to scar tissue, a fresh site may be preferable. Results Short-term results from a study of 100 dogs with 161 corns which underwent either combined tenotomy (113 corns) or SDF tenotomy (48 corns) were obtained by telephone.5 At seven days post-surgery, 77 percent showed a marked improvement, and, at eight weeks, 97 percent showed either no or slight lameness. Longer-term evaluation from six months to one year in 56 dogs showed similar outcomes. In both groups, 95 percent of the corns at eight weeks had exfoliated. Combined tenotomy and SDF tenotomy produces comparable results. Discussion The breed exclusivity of digital pad corns to sighthound is thought to be from decreased cushioning of the pads. These breeds have noticeably thinner skin and pads with less subdermal fibro-adipose tissue in comparison with other breeds of similar weights. Familial cases have occurred and, with some dogs being prone to multiple corns, a genetic role is likely. Hyperkeratinization is a natural response to low-grade repetitive trauma by adding further cushioning and protection to the integument, but it appears to be counter-productive in the pad, as its presence increases the loading and, hence, the response to the trauma. Any increase in focal pad loading, of whatever cause, can result in corn formation. The success of the tendon cutting procedures with the exfoliation of the corn strongly supports the hypothesis that corns are a result of repeated mechanical trauma. These are also the only treatments offering consistent, good results with minimal post-operative discomfort. As such, SDF tendonectomy is the recommended primary treatment. Michael Guilliard, MA, VetMB, CertSAO, FRCVS graduated from the University of Cambridge Veterinary School in 1972. Working in private practice for his entire career, he developed an interest in the racing greyhound. This led to several publications on greyhound injuries in peer-reviewed veterinary journals for which Dr. Guilliard twice received the British Small Animal Veterinary Association (BSAVA) Dunkin Award for the most valuable article published in the Journal of Small Animal Practice by a small animal practitioner. In 2012, he became a fellow of the Royal College of Veterinary Surgeons (RCVS) for his thesis entitled, “The nature, incidence and response to treatment of injuries to the distal limbs in the racing greyhound,” and in 2014 received BSAVA’s Simon Award for outstanding contributions in the field of veterinary surgery. Guilliard now runs his own orthopedic veterinary practice in the U.K., with running dogs contributing to 50 percent of his workload. He can be contacted at guilliard@talk21.com. References Doughty. RW, Guilliard. MJ. Pad corns: A pain for both dog and veterinarian. Veterinary Practice News Canada September 26, 2018: https://www.veterinarypracticenews.com/corns-in-dogs-september-2018. Lord. LK, Yaissle. JE, Marin. L, Couto. CG. Results of a Web-Based Health Survey of Retired Racing Greyhounds. J Vet Intern Med 2007; 21: 1243-1250. https://pubmed.ncbi.nlm.nih.gov/18196733 O’Neill. DG, Rooney. NJ, Brock. C, Church. DB. Brodbelt. DC. Pegram C. Greyhounds under general veterinary care in the UK during 2016: demography and common disorders. Canine Genet Epidem 2019; 6, 4. https://pubmed.ncbi.nlm.nih.gov/31179010 Guilliard. MJ, Segboer. I, Shearer. DH. Corns in dogs; signalment, possible aetiology and response to surgical treatment. J Small Anim Pract 2010; 51, 3, 162-168. https://pubmed.ncbi.nlm.nih.gov/20406358 Guilliard. MJ, Doughty. RW. Digital flexor tenotomy for the treatment of digital pad corns in sighthounds. Aust Vet Pract 2021; 51(3):151-158. https://cpd.vettimes.co.uk/cpd-plus/companion-animal/cpd-dermatology/digital-flexor-tenotomy-for-treatment-of-corns-in-dogs Hutton. WC, Freeman. MAR. Swanson. SAV. The forces exerted on the pads of walking dogs. J Small Anim Pract 1969;10, 71-77. https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1748-5827.1969.tb04022.x Guilliard. MJ, Doughty. RW. Superficial digital flexor tendonectomy for the treatment of corns. Vet Dermatol 2022:1-6. https://onlinelibrary.wiley.com/doi/10.1111/vde.13117#:~:text=A%20novel%20treatment%20for%20corns,tendon%20at%20the%20metacarpus%2Fmetatarsus
