Introduction/Anatomy

Dogs have five digits on the foreleg and four to five digits on the rear leg. The first digit, the “dewclaw,” is not weight‐bearing and is the digit typically absent on the rear leg. Digits 3 and 4 are referred to as “weight‐bearing” digits, while 2 and 5 play a lesser role.¹ Thus, amputation of either digits 2 or 5 should result in minimal clinical impairment.

Each digit consists of three small bones: proximal, middle, and distal phalanges. These bones are also referred to as P1, P2, and P3, respectively. The proximal phalanx of each digit articulates with the metacarpal or metatarsal bones. Each digit has a sesamoid bone over the P1–P2 and the P2–P3 joints on the dorsal surface and paired sesamoid bones on the ventral aspect at the P1–P2 joint. Fractures of the sesamoid bones can occur and are typically treated by removal of the sesamoid fragments. Most surgeons will remove the sesamoids when performing a partial digital amputation.

The vascular supply to the digit is primarily from the dorsal and palmar/plantar digital arteries and their branches that supply each digit along with the corresponding veins. Tendinous insertions of the common digital extensor (digits 1–5) and the lateral digital extensor (digits 3–5) attach to the dorsal aspect of the digits while the superficial and deep digital flexors attach on the palmar/plantar aspect of the paw.² The skin over the proximal portion of the proximal phalanges is fused and then separates to cover each individual digit near the end of the proximal phalanges.

As noted previously, the first digit (i.e., dewclaw) is seldom an issue regarding locomotion or lameness. It is still common to see dewclaws being removed for cosmetic or functional reasons, especially when they are very loosely attached and there is concern about trauma. Digits 2 and 5 are the outside digits and are considered to not be weight‐bearing. Therefore, amputation of one of these digits is seldom associated with significant gait changes or lameness.

When amputating digit 3 or 4, there can be changes to the animal’s gait due to the weight‐bearing nature of these digits. The clinical significance of amputation of the central digits has not been sufficiently documented and may only be significant in working or racing animals. It is generally accepted that more distally located amputations, or partial amputation, will have a more limited clinical impact on the patient.

Indications

Indications for a digital amputation include traumatic injury, osseous or soft tissue infection, and neoplastic conditions are the most common reasons for digital amputation.^2,4 In some situations, owners may request a digital amputation(s) for cosmetic or behavior reasons. Iatrogenic injuries, such as the application of an excessively tight bandage, can also prompt the need for a digital amputation. Traumatic injury can result in dislocation of the digits, phalangeal fractures, or loss of the nail, resulting in a painful toe. Some dogs will further exacerbate the situation by inflicting self‐trauma to the damaged digit. In some situations, digit amputation is used to create tissue for wound or surgical site closure, such as managing significant foot pad injuries by generating digital pad tissues used in reconstructive procedures. Infectious conditions, such as suspected or documented osteomyelitis, soft tissue infections from bacterial or fungal sources, or the chronic presence of foreign material adjacent to a digit, may prompt amputation. In these cases, it is important to get deep tissue samples for bacterial or fungal culture and to have histopathological evaluation of the digit performed.

Several neoplastic conditions can originate on the digits. While osteosarcoma of a digit is reported, neoplasms associated with the soft tissues are more frequently encountered. In the dog, the most common digital tumors include squamous cell carcinoma (SCC), melanoma, soft tissue sarcomas, and mast cell tumors; however, numerous other tumor types have been reported to affect the digit.^3–8 A recent report of 2912 digital amputations from dogs found that 52% of submissions were for suspected neoplasm and 80% of these were malignant tumors.⁶ The most common diagnosis in dogs was SCC, accounting for 63% of diagnosed malignancies, with melanoma, soft tissue sarcomas, and mast cell tumors accounting for another 27%. Tumors originating from the subungual epithelium (nail bed) are thought to have a more aggressive metastatic pattern, and dogs with darker coats, as well as Schnauzers and Poodles, have been suggested to be at higher risk of digital SCC.^7,8 In cats, SCC and fibrosarcoma are the most commonly reported neoplastic conditions. There is a unique condition, “feline lung‐digit syndrome,” in which cats may present with a lameness caused by a metastatic lesion from a bronchogenic carcinoma,^9,10 although metastasis to other sites has also been documented.¹¹ Since most of the cases reported did not have a prior diagnosis of lung cancer, thoracic radiographs should be obtained in cats with digital lesions.

Techniques

In the descriptions below, the terminology used is for amputation of a digit on the foreleg; however, the techniques are applicable to both the front and rear legs.

Surgical preparation of the paw is important and can be time‐consuming. Hair is carefully clipped from the carpus distally toward the digits, including the interdigital spaces and between the digital pads. Once clipped, the paw can be prepared using a standard surgical preparation with chlorhexidine or povidone‐iodine. Some prefer to soak the paw in an aseptic solution; however, gentle mechanical cleansing to remove dirt and debris is still required. For the final surgical prep, it is common to hang the leg, allowing prep solution to run away from the surgical site. This solution should be blotted up prior to release of the limb. The hanging leg positioning also facilitates application of a sterile wrap over the end of the limb (Figure 19.1).

Establishing a “bloodless” surgical field is useful when doing a digital amputation. Typically, this is accomplished by placing a tourniquet on the limb, and this can be accomplished using a standard tourniquet, a pneumatic cuff, or a sterile Penrose drain placed proximal to the surgical site. Application after the leg has been in the hanging leg position for a few minutes will allow gravity to help drain blood from the distal limb. Another useful option is to use a modification of the Esmarch bandage. This type of bandage is both a tourniquet and a method to exsanguinate the distal limb. While a true Esmarch bandage is based on a latex wrap, an elastic bandage material, such as sterile Vetrap^™ (3M^™ Animal Care Products, St. Paul, Minnesota), can be used. When applying the Esmarch, start at the toes, firmly wrap the bandage material around the leg from distal to proximal, forcing blood out of the distal limb. When the wrap is completed, it should extend 2–4 in. beyond the top of the planned incision. The surgeon can now incise through the bandage material, removing the distal portion for access while the proximal portion maintains tourniquet‐like pressure, minimizing blood in the surgical field. As when using a tourniquet, the surgeon needs to be mindful of how long the Esmarch bandage has been in place, and they must ensure the entire bandage is removed after the procedure and not incorporated into the postoperative bandage.

Tourniquet use should be monitored closely and kept in place for the least amount of time possible, which may be facilitated by the circulating nurse or anesthesia personnel charting the time of application and removal. Most sources suggest that application times of less than 60 minutes will result in minimal issue; however, earlier release might be better. Many animals have increased postoperative swelling after tourniquet use, so it is recommended to support the paw with a supportive, compression bandage (modified Robert Jones) and avoid casts and rigid splints for 24–48 hours after surgery.¹

Regional anesthesia is appropriate for a digital amputation. A ring block with an injectable local anesthetic, such as lidocaine or bupivacaine, is a simple technique for adjunctive anesthesia and can be placed at the level of metacarpal/metatarsal bones or immediately above the target digit. Regional limb infusion can also be used for more extensive anesthesia. Details of these techniques are available elsewhere.^3,12

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