Limb-shortening limb salvage (LSLS) in a cat with metatarsal osteosarcoma

Abstract

The objective of this report was to document a successful partial limb amputation surgery in a cat with metatarsal osteosarcoma (OSA) including the use of pad grafts from the amputated foot. Limb shortening of the hindlimb through a partial amputation resulted in excellent limb function and usage. The patient retained functional use of the limb after surgery, with no lameness. There was no evidence of metastasis or local recurrence seen 323 days post-surgery. Limb shortening partial amputation is a reasonable option and can result in excellent limb use after surgery despite a significant loss in limb length.

Primary bone tumors in the cat are uncommon with a reported incidence of 3.1 to 4.9 per 100 000 cases, with osteosarcoma (OSA) accounting for 70% to 80% of all cases (1–4). Osteosarcoma typically affects middle-aged to older cats with a mean age of onset of 10.2 y (1,3), and has predisposition for the hindlimbs (1,2). Unlike canine OSA, feline appendicular OSA is less likely to metastasize (3,4), with a reported median survival time of 26 to 49.2 mo with limb amputation alone (2,4). Therefore, the primary management recommendation for feline appendicular osteosarcoma (OSA) is amputation of the affected limb (5).

Despite the current recommendation for full limb amputation and the fact that most cats do very well after amputation (6), some clients wish to pursue limb salvage options in cats. The goal of limb salvage is complete tumor resection with preservation of limb function. To date, limb salvage has been primarily investigated in dogs. Most commonly limb salvage in dogs is associated with distal radial OSA (5,7–9). Generally, limb salvage in dogs involves resection of the involved distal radius and ulna and replacement of the defect with allograft, autograft, or a prosthesis (5,7–9). A recent case report described limb-shortening as a strategy for limb salvage in a dog with distal radial osteosarcoma, in which the defect was acutely shortened after resection of the distal radius and an arthrodesis plate was applied to stabilize the carpus (7). Limb shortening has also been reported experimentally, with dogs tolerating up to 20% shortening of the femur without functional lameness (10). To date there are no published studies or case reports documenting successful limb shortening in feline patients with OSA.

For tumors or trauma of the distal extremity, partial limb amputation has been reported as a potential treatment option, combined with exoprosthesis or endoprosthesis (11). However, partial amputation of the limb either due to trauma or tumor resection poses 2 problems, limb shortening and the lack of an abrasion-resistant surface on the distal stump. The paw pad is a specialized skin structure which provides shock absorption and an abrasion resistant surface (12). Transposition or grafting of the foot pads to the distal stump has been described previously for the treatment of traumatic wounds to the lower extremities resulting in partial foot or digit amputation (13–15).

This case report describes the management of a feline metatarsal OSA with partial amputation and skin grafts of the foot pads from the amputated pes to the distal stump. Despite the resultant limb-shortening, this procedure resulted in limb preservation with complete resection of the tumor and excellent limb function.

Case description

A 13-year-old, neutered male, 6.86-kg, domestic shorthair cat was referred for evaluation and treatment of a presumptive primary bone tumor of the left 4th and 5th metatarsals. The mass was noted 3 wk earlier by the owner, had not changed in size, nor had an impact on the patient’s mobility or comfort. Radiographs performed by the referring veterinarian showed an osteoproductive lesion of the 3rd and 4th metatarsals that was consistent with an aggressive bone lesion (Figures 1, 2). A fine-needle aspirate was taken and the cytological interpretation was that of a sarcoma with the cell origin being unclear. Given the radiographic and cytologic findings, a primary bone tumor was considered likely, and the patient was referred for additional diagnostic tests and treatment.

Figure 1.

AP projection of left distal pes demonstrating the osteoproductive lesion of the 3rd and 4th metatarsals with associated swelling.

Figure 2.

Lateral projection of left distal pes demonstrating the osteoproductive lesion of the 3rd and 4th metatarsals with associated swelling.

On presentation, 3-view thoracic radiographs were taken and showed no evidence of metastatic disease. A mild cardiomegaly was noted, and a cardiac ultrasound was performed and evaluated by a cardiologist. No abnormalities were noted. An abdominal ultrasound, complete blood (cell) count (CBC), and biochemistry were also performed, and no significant abnormalities were noted.

Full limb amputation was recommended to the owner; however, this was declined as the owner preferred to discuss limb salvage options. The option of limb sparing with custom endoprosthesis placement to maintain limb length was discussed and was declined. The owners elected to pursue a novel limb sparing procedure, involving partial limb amputation. The owner was counselled that the patient may ultimately require full limb amputation should it fail.

Preoperative care

The patient was premedicated with hydromorphone (Hydromorphone HCl; Westward Pharmaceuticals, Eatontown, New Jersey, USA), 0.1 mg/kg body weight (BW), IM and maropitant (Cerenia; Zoetis, Kalamazoo, Michigan, USA), 0.1 mg/kg BW, IV. Anesthesia was co-induced with propofol (PropoFlo; Abbott Animal Health, Chicago, Illinois, USA), 2.85 mg/kg BW, IV, and midazolam (Midazolam injection USP; Westward Pharmaceuticals), 2 mg/kg BW, IV, intubated and maintained with inhalant isoflorane. The patient was placed in right lateral recumbency for the procedure. Cefazolin (Cefazolin injectable; Geneva Pharmaceuticals, Dayton, New Jersey, USA), 22 mg/kg BW, IV, was administered before surgery and then every 90 min for the duration of the procedure.

Surgical technique

The left hind quarter including the digits was aseptically prepared for surgery. A radial skin incision was made distal to the level of the left tarsometatarsal joint. The incision was made to allow for more skin on the medial aspect of the limb, approximately 3 cm from the tibiotarasal joint laterally and 4 cm from the tibiotarsal joint medially. The dorsal pedal artery and caudal branch of the saphenous artery were identified and hemostasis was achieved with electrocautery at the level of the tarsometatarsal joint. The superficial digital flexor tendon and deep digital flexor tendon were also incised at this level with sharp dissection, including the insertion of the fibularis longus at the level of the proximal metatarsals. The tarsometarsal joint was then disarticulated through incision of the corresponding medial and lateral collateral ligaments at their insertion point on the proximal metatarsals. Following disarticulation, the incision was closed through apposition of the subcutanous tissue with simple interrupted sutures of 4-0 polydioxanone (PDS; Ethicon, Somerville, New Jersey, USA). The skin was closed using 4-0 polypropylene (Prolene; Ethicon) in a cruciate pattern, taking care to ensure that the incision was not directly over the distal stump. The skin overlying the distal aspect of the amputation stump was then prepared for receipt of the tarsal paw pad grafts, (Figure 3) through the creation of 5 incisional graft sites of 0.5 cm at the base of the stump. Five punch biopsy grafts were taken from the digits of the amputated foot pads using a 6-mm punch biopsy. The punch grafts had their deep fat layer removed through sharp dissection. The grafts were then secured to the graft sites with 4-0 PDS in a simple interupted pattern with 4 sutures per graft site (Figure 4). After surgery a soft padded bandage was applied to protect the graft sites and incision during weight-bearing.

Figure 3.

Intraoperative image of the distal pes of the salvaged limb following preparation of the stump for receiving the graft.

Figure 4.

Intraoperative image of the distal pes of the salvaged limb following paw pad grafts.

Post-operative care

The patient recovered uneventfully from anesthesia and was hospitalized overnight for supportive care and analgesia. The patient was maintained on a fentanyl (Recuvyra; Elanco, Animal Health, Indianapolis, Indiana, USA), continuous rate infusion (CRI), 3 to 5 μg/kg BW per hour, IV, meloxicam (Metacam; Boehringer Ingelheim, Burlington, Ontario), 0.1 mg/kg BW, IV q24h, cefazolin (Geneva Pharmaceuticals), 22 mg/kg BW, IV, q8h and IV Lactated Ringers Solution (LRS, Baxter Animal Healthcare, Deerfield, Illinois, USA). The patient was transitioned to oral medications, Tramadol (Tramadol HCl; Amneal Pharmaceuticals, Brookhaven, New York, USA), 25 mg PO q8h for 5 d and amoxicillin/clavulanic acid (Clavamox; Haupt Pharma, Latina, Italy), 13 mg/kg BW, PO, q12h for 5 d and discharged to his owner’s care 24 h following the surgery. At that time, the cat was ambulatory on all 4 limbs. Bandage changes were scheduled for every 2 to 3 d to monitor the incision and graft integrity. During this time the skin incision was noted to have healed appropriately while the grafts were intact and healthy in appearance (Figure 6); however, a small area of ulceration with moist maceration was noted at the center of the stump. Bandage changes were performed regularly until such time that this resolved (1 mo) and the pet was ambulatory on all 4 limbs with no signs of lameness or discomfort. This patient compensated for the loss of limb length through hyperextension of the stifle.

Figure 6.

Fourteen-day post-operative image of the distal pes of the salvaged limb indicating appropriate healing of the graft site.

Histopathology and adjunctive chemotherapy

Osteosarcoma (OSA) of the 3rd and 4th left metatarsals with clean margins (1.5 cm) was diagnosed on histological examination. The mass was described as a well-demarcated, highly cellular mass composed of cells forming whorls and streams with frequent foci of mineralization and eosinophilic cytoplasm; and a mitotic index of 16/10 high power fields. Due to the high mitotic index noted on histopathology it was recommended that this patient start a course of adjunctive chemotherapy with Carboplatin (Carboplatin; Hospira, Lake Forest, Illinois, USA), 1 mg/kg BW, IV every 3 to 4 wk, for a total of 6 treatments. Dose reductions were instituted as the patient developed evidence of mild renal insufficiency over the course of therapy (IRIS stage I–II based on creatinine levels, non-proteinuric, borderline hypertensive), with a 10% dose reduction as a precautionary measure.

Outcome

The patient has had no signs of pain or discomfort in the salvaged limb and continues to ambulate on all 4 limbs, 323 d after surgery. The patient was re-staged at 142 d and 323 d post-surgery, with 3-view thoracic radiographs, a CBC, biochemistry, urinalysis, and urine protein:creatinine ratio. There was no evidence of metastatic disease. During the course of adjunctive chemotherapy the patient was noted to develop a mild systemic hypertension, consistent with progression of chronic renal disease, and was started on a course of amlodipine (Norvasc; Zoetis), 0.625 mg PO, q24h, 323 d post-surgery.

Discussion

This case report describes a novel strategy for limb salvage in cats with a metatarsal osteosarcoma, through limb shortening with paw pad grafts from the amputated portion of the limb. The technique described here results in the loss of the distal portion of the limb and creation of a stump with functional foot pads distally for weight-bearing. This technique was inspired by previous limb shortening limb salvage (LSLS) procedures in dogs (7) and an experimental study in dogs which found that dogs could tolerate up to 20% of their femur being resected without development of a significant functional lameness (16). It has also been previously reported that patients can overcome loss of hindlimb length through hyperextension of the stifle and tarsocrural joints (10,16). The patient in our case report adapted in a similar fashion to allow full limb use, without the requirement of a prosthesis.

An alternative limb salvage technique would have involved partial amputation with the application of an endoprosthesis in the distal end of the bone with an exoprosthesis to facilitate weight-bearing. This has been described in the veterinary literature in dogs (11), in which an implant is placed within the medullary canal of recipient bone and the prosthesis integrates with the bone to create a contiguous weight-bearing column. Once healed an exoprosthesis is then attached to provide a functional weight-bearing surface. This technique has also been described bilaterally in a feline patient in the media and proceedings; however, there is no published information available at this time (17). Techniques involving endoprosthetic implantation require a high level of training and access to a custom prosthesis and are associated with a high risk of implant failure and infection (16). By comparison, the technique described here is relatively simple from a technical standpoint, inexpensive, and resulted in minimal complications. The incisional complications described in this case report are similar to those seen following full limb amputations (18). Another option would be to do a partial limb amputation and apply an exoprosthesis. However, this may have resulted in ulceration of the distal end of the stump and does not appear to be necessary with this degree of limb shortening. There is limited information on how well-tolerated exoprostheses are in feline patients.

The technique described herein did not maintain limb length and required the patient to compensate through hyperextension of the surrounding joints to achieve weight-bearing. Interestingly, humans do not tolerate limb length discrepancies and there appears to be a correlation between the degree of limb length discrepancies in humans and the development of osteoarthritis (19). Further studies would be required to evaluate the impact these compensatory mechanisms have in veterinary patients.

A weight-bearing surface was created in this patient through the application of paw pad grafts harvested from the amputated limb. These pad grafts provided the patient with an abrasive-resistant surface for traction during ambulation as well as a cushioning system to prevent abrasion of the distal portion of the limb during ambulation, and, in our opinion, prevented ulceration of the distal stump.

The technique herein was effective for the management of neoplasia of the distal extremity in a cat, but could also be adapted for consideration in patients with distal hindlimb extremity injuries due to trauma or bandage injuries. To the authors’ knowledge this is the first reported case of a partial limb amputation in a cat treated with free paw pad grafts.

Figure 5.

Post-operative image depicting the degree of limb length loss.