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A 5-year-old, male neutered, mixed breed dog was presented for left forelimb lameness and swelling over the left distal radius. A primary bone tumor of the distal radius was diagnosed and limb-sparing surgery of the left forelimb was performed using a tantalum metal-DCP endoprosthesis. Post-operative histopathology confirmed osteosarcoma.
Chirurgie pour sauver un membre à l’aide d’une endoprothèse de métal de tantale chez un chien atteint d’ostéosarcome du radius distal. Un chien mâle de race croisée stérilisé et âgé de 5 ans a été présenté pour une boiterie de la patte avant gauche et de l’enflure sur le radius distal gauche. Une tumeur osseuse primaire du radius distal a été diagnostiquée et une chirurgie pour sauver la patte avant gauche a été réalisée à l’aide d’une endoprothèse DCP en métal de tantale. Un examen histopathologique postopératoire a confirmé l’ostéosarcome.
(Traduit par Isabelle Vallières)
A 5-year-old, neutered, male Leonberger mixed breed dog was presented for evaluation of a left forelimb lameness and swelling over the left distal radius noted after running. Radiographs of the left forelimb performed prior to referral revealed a lytic lesion involving the distal 8 cm of the radius. Cortical bone thinning and lucency throughout the medullary cavity were noted in this region. There was minimal radiographic abnormality within the adjacent soft tissue. The ulna and associated carpal bones were radiographically unremarkable. Palpation of the limb over the distal radius elicited a repeatable painful response. Based on radiographic changes, a primary bone tumor was suspected. Thoracic radiographs, abdominal ultrasound, and cardiac ultrasound were performed on presentation and were all found to be unremarkable. A general diagnostic blood panel revealed no abnormal findings. Based on the high index of suspicion for a primary bone tumor in this patient, the owners elected to forego a preoperative bone biopsy. Palliative and curative-intent treatment options for the suspected primary bone tumor were discussed and the owners elected to proceed with limb salvage surgery. A custom tantalum endoprosthesis was prepared for implantation. The purpose of this paper is to document the first reported use of a tantalum metal endoprosthesis in limb salvage surgery in a dog.
Based on preoperative radiographs and size of the patient, an implant size was estimated. Using the limited sizes available, an appropriate implant size was ordered from Biomedtrix (Boonton, New Jersey, USA) approximately 2 wk prior to surgery. Custom implants can be manufactured upon request, but would likely require more time for delivery.
The patient was anesthetized using thiopental sodium (Hospira Health Care Corportion, Vaughan, Ontario), 15 mg/kg body weight (BW), IV and diazepam (Hoffmann-La Roche, Mississauga, Ontario), 0.2 mg/kg BW, IV for induction, followed by maintenance with isoflurane inhalant (Abbott Laboratory, Saint-Laurent, Quebec). A computed tomography (CT) scan (Picker PQS spiral CT; Universal Systems, Solon, Ohio, USA) of the thorax and left forelimb was performed with a slice interval of 2 mm, followed by radiographs of the left forelimb. There was no evidence of macroscopic pulmonary metastatic disease. In the region of the distal left radius, a markedly destructive lesion was noted. Expansion and widening of the bone and cortical irregularity with areas of complete cortical bone loss were identified (Figure 1). The adjacent soft tissues and the ulna were unremarkable.
The left forelimb, left proximal humerus, and right proximal tibia were surgically prepared. Cefazolin sodium (Novopharm), 22 mg/kg BW, IV was administered pre-operatively and every 90 min intra-operatively. Hydromorphone hydrochloride (Sandoz Canada, Boucherville, Quebec), 0.05 mg/kg BW, IV was administered every 90 min intraoperatively. Cancellous bone graft was harvested from the left proximal humerus and right proximal tibia. A craniolateral approach to the left radius, carpus and metacarpal region was performed. A distal radial osteotomy was performed proximal to the tumor margin, as determined by forelimb radiographs and CT scan (1,2). The osteotomy was made approximately 9 cm proximal to the radiocarpal joint using an oscillating bone saw. The bone appeared grossly normal at the level of the osteotomy. There were no gross abnormalities noted in the adjacent soft tissues in the region of the distal radius. The extensor tendons running over the distal radius were en bloc resected with the underlying diseased radial bone. The radiocarpal joint was disarticulated and the resected portion of the radius was removed with care not to disturb the tumor pseudocapsule. The resected segment was radiographed to confirm the margins of the radiographic lesions (Figure 2). The carpal, intercarpal, and carpometacarpal joints were debrided of their articular cartilage using a high speed bur. Cancellous bone graft was packed into these regions. A 10 cm × 2 cm tantalum radial limb salvage component with a 2.5 cm distal flare (Biomedtrix) was then positioned into the defect (Figure 3). A pancarpal arthrodesis was performed using an 11.5 × 18 hole stainless steel limb salvage plate (Veterinary Orthopedic Implants, South Burlington, Vermont, USA) extending distally from the proximal radius, over the carpus and onto the 3rd metacarpal bone. All screw holes were filled with 3.5 mm stainless steel cortical bone screws (Biomedtrix). Screws were also placed through the plate into the tantalum implant. Overall stability of this construct intraoperatively was judged to be very good. The area was copiously lavaged with sterile 0.9% NaCl. The remaining cancellous bone graft was packed into areas of implant-bone interface, as well as around the external surface of the implant itself. The soft tissues were apposed using 0 polydioxanone suture (Ethicon, Somerville, New Jersey, USA) in a simple continuous pattern in the fascia and muscle planes and 2-0 polydioxanone suture (Ethicon) in a simple continuous pattern in the subcutaneous layer. Skin was apposed using 3-0 nylon suture (Ethicon) in a Ford interlocking pattern. Post-operative radiographs revealed good implant placement and limb alignment (Figure 4a). A soft padded bandage and caudal fiberglass splint were placed on the limb.
Post-operative analgesia consisted of hydromorphone (0.05 mg/kg BW, IV) as needed, and oral Percocet (Oxycodone 5 mg and Acetaminophen 325 mg; Purdue Pharma, Stamford, Connecticut, USA), 1.5 tablets q8h. Oral cephalexin (cephalexin monohydrate; Teva Pharmaceuticals, Sellersville, Pennsylvania, USA), 22 mg/kg BW, q8h and oral orbifloxacin (Schering Canada, Pointe-Claire, Quebec), 2.5 mg/kg BW, q24h, were administered for 30 d. Exercise was restricted to short, leashed walks for 8 wk. The fiberglass splint was maintained for 5 wk. A soft padded bandage was maintained for 7 wk post-surgery. Lameness progressively improved from 1 d post-surgery to full weight bearing when walking at 5 wk post-surgery. A mild mechanical gait abnormality consistent with loss of carpal mobility secondary to carpal arthrodesis persisted at 332 d after surgery.
Histopathology performed post-operatively on the resected left radius segment confirmed osteosarcoma. Surgical resection was considered complete with no evidence of tumor in the proximal segment of the resected radius. Grading was not performed on this specimen.
Beginning at 3 d post-surgery, the patient was treated with an alternating protocol of carboplatin (Novopharm), 300 mg/m2 IV, and doxorubicin (doxorubicin hydrochloride, Novopharm), 30 mg/m2 IV, every 3 wk for 5 treatments.
A low grade surgical site infection was noted 80 d post-surgery. Draining tracts over the distal aspect of the pancarpal arthrodesis plate and mild lameness were observed upon discontinuation of antibiotic therapy. These clinical signs resolved quickly with antibiotic therapy, but recurred after completion of each course of therapy. Resolution was achieved with continuous treatment with oral orbifloxacin 2.5 mg/kg q24h and clindamycin 10 mg/kg q12h (clindamycin hydrochloride, Novopharm).
Radiographs of the left forelimb taken at 332 d post-surgery showed good alignment of the tantalum-DCP implant within the radius and no evidence of implant instability or radiolucency around the endoprosthetic construct. Follow-up thoracic radiographs taken at 248 d post-surgery revealed a pulmonary lesion consistent with early metastatic disease. The patient continued to weight bear well on the affected limb and quality of life was described as very good by the owner at 332 d post-surgery.
Canine osteosarcoma represents the majority (85%) of canine primary bone tumors, with approximately 75% of cases occurring in the appendicular skeleton (3,4). Surgical excision of the primary tumor and adjuvant chemotherapy significantly improve survival of patients with appendicular osteosarcoma (3,5,6), with median survival times ranging from 262 d to 540 d (3,5). With the progression of increased survival times, limb-sparing surgery has become more sought after in the treatment of canine appendicular osteosarcoma (3). Limb salvage does not affect overall survival when compared with amputation and similar adjuvant chemotherapy (3,4), and provides some distinct advantages over traditional amputation of the affected limb. The most profound advantage is the excellent return to limb function observed in approximately 80% of dogs (3) and the preservation of quadruped status in a large breed patient. The distal radius is an ideal site for limb salvage surgery in the dog as arthrodesis of the carpus is generally well tolerated (4).
A variety of methods for limb-sparing surgery have been described (3). The most commonly performed techniques include allograft limb sparing, metal endoprosthesis limb sparing, pasteurized tumoral autograft, intraoperative extracorpo-real radiation (IER), longitudinal bone transport osteogenesis (BTO), and ulna transposition limb sparing (3,7–10). While each method presents advantages and disadvantages, techniques involving allograft implantation require the availability of a donor bone bank and have been associated with high postoperative infection rates, allograft non-union, and fracture (3). Autograft techniques may require prolonged surgical time (pasteurization), extensive post-operative recovery time (BTO), or specialized equipment that is not available at some centres (IER) (3,7–9,11). Complications including local tumor recurrence and biomechanical complications (fracture, implant resorption) have been reported with autograft techniques (3,7,9).
Metal endoprosthesis limb salvage procedures eliminate the need for large cortical allografts and specialized equipment, making limb salvage a widely available procedure. Current techniques utilize a commercial solid metal endoprosthesis with a modified bone plate (3). Complications associated with traditional metal (such as surgical steel) endoprostheses include post-operative infection and construct failure secondary to cyclic loading (6,10).
Tantalum is a trabecular metal that can be machined to form custom endoprostheses. It has a strong, low stiffness that is similar to that of bone (12). The structural integrity of tantalum allows it to be formed into customized bulk shapes and sizes of implants without compromising the strength of the implant (13,14). Trabecular metal is uniform and highly fatigue resistant, thus it maintains its strength for the duration of clinical usage (12). The trabecular structure, with its regular shape, provides high volumetric porosity (up to 80% porous) which is similar to that of cancellous bone (12,13). Tantalum also has a unique surface micro texture that results in a high coefficient of friction (12). Microtextured surfaces have also been shown to be highly osteophilic (13,14). These characteristics facilitate biological attachment at the cellular level, allowing for new bone ingrowth and soft tissue attachment (13–16). Reactive osseointegration at the implant-bone interface has been shown in tantalum femoral and tibial implants in humans (14,17). This biologic fixation supplements the stability of the implant and can increase the ultimate strength, longevity, and durability of the endoprosthetic construct (14).
Tantalum metal has been used successfully in human orthopedic surgery in a variety of manners including various joint reconstruction applications, soft tissue attachment devices, and bulk (void-filling) structural applications (12–14,17). In veterinary surgery, tantalum coating has been used successfully in components used in cementless total hip revision (16,18).
In comparison with other metal endoprostheses, the porosity of tantalum is higher than that of traditional solid materials as well as more recent sintered-bead and fiber metal coatings (16,18). This provides a higher fraction of material available for bone ingrowth, resulting in earlier development of interfacial shear strength in porous tantalum transcortical implants compared to other metal endoprostheses (16,18). This increased rate of stability enables decreased load bearing on the surgical plate used to stabilize the implant. In this case, it was demonstrated that drilling and screw placement into the tantalum implant was achievable with standard surgical tools. This characteristic provides good opportunity for intraoperative soft tissue reattachment when necessary. In addition to the structural advantages, tantalum also has an inherent bacteriophobic effect (19) and is associated with lower or similar adhesion of Staphylococcus aureus and S. epidermidis when compared with commonly used orthopedic metallic implants (19).
Compared to structural bone allograft and autograft techniques, tantalum implants provide similar or greater potential for osseous ingrowth (17). Conversely, tantalum implants offer a more simplified surgical technique, resulting in likely shorter operative time and potential decreased infection risk. The risk of disease transmission associated with structural allograft is minimized. As well, the risk of implant failure due to implant resorption or implant collapse is eliminated (17).
The primary disadvantages to the use of tantalum endoprostheses in veterinary orthopedic surgery include the difficulty in removing these implants if required, as well as the current increased cost of the tantalum bulk implant compared with other metallic or allograft implants.
This is the first reported application of a customized bulk tantalum endoprosthesis in limb-sparing surgery in a dog. Results to date have been favorable and indicate that this application provides acceptable post-operative return to function of the affected limb. The only post-operative complication observed in this patient was a recurrent low-grade infection that has been well managed with long-term antibiotic therapy. Although postoperative infection and subsequent management is a significant concern for the patient and owner, median survival times are significantly longer for dogs undergoing limb salvage procedures that have been diagnosed with post-operative wound infection, when compared with those that do not develop surgical site infections (6,10). Post-operative infection is a common complication of limb sparing surgery involving endoprostheses (6). Although tantalum does reportedly exhibit some bacteriophobic properties (19), post-operative infection was not prevented in this case. Thus these bacteriophobic properties would not be expected to affect the survival time of limb spare patients in a negative manner.
In summary, the simplified surgical technique and potential increased durability of the tantalum–DCP construct indicate that tantalum endoprostheses may provide a reasonable alternative to traditional implant constructs used in limb-sparing surgery. However, further studies with longer follow-up and direct comparison of this approach with traditional reconstructive techniques will be required to evaluate the clinical effectiveness of this treatment approach. CVJ
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