Dr. Vladislav Zlatinov
Central Vet Clinic – Sofia
Synovial cell sarcoma is the most common joint tumor in dogs. It is a malignant neoplasm arising from mesenchymal cells outside the synovial membrane of joints and bursas1 . In dogs, synovial cell sarcomas usually occur in large breeds, with a predisposition for flat-coated and golden retrievers1,2 . Middle-aged dogs are most commonly affected, and there is no sex predilection. Synovial cell sarcomas usually involve the larger joints, but any joint can be affected.
Other joint tumors reported in dogs include fibrosarcoma, myxoma, malignant giant cell tumor of soft tissue and others. Recently, histiocytic sarcomas have been reported in the periarticular tissue of large appendicular joints3 .
Synovial cell sarcomas are locally aggressive with a moderate-to-high metastatic potential, depending on histologic grade. The average survival time with SCS is around 30 months, which is significantly better prognosis compared to the most common canine neoplasia- osteosarcoma.
Limb amputation is recommended for treatment of the SCS tumor because local recurrence is significantly lower compared to marginal resection.
In the recent years, an amputation alternative- limb sparing procedure, was developed. The first animal case (2008) with integrated prosthesis included bilateral tibial stem implantation4. The more recent procedure ITAP (Integrated Tanscutaneous Amputee Prosthesis)-Stanmore Implants Worldwide Ltd, UK, is demanding technique that consists of low limb amputation and metal stem medullary canal insertion, aiming long term bone-implant integration. Suggested period for this integration has been suggested to be 6 weeks5. This is the most vulnerable period that demands high degree of implant stability, allowing bone tissue ingrowth into the implant micropores. Once stable implant- stem fixation occurs, an external limb prosthesis attachment gives the opportunity for weight baring and some degree of limb functional recovery.
This case report presents the short term functional result after application of ITAP technique in a five years old golden retriever. The dog’s tarsal joint was affected by synovial sarcoma. Custom manufactured implant with rigid locking plate fixation was developed. The goal of the implant design was solid fixation allowance of immediate weight baring, even before the stem integration. The follow up period of the case is 3 months post operatively. The patient revealed very good pain free limb function, starting almost immediately after the amputation.
A 5 years old male Golden retriever dog, weighting 39 kg was presented at Central Vet Clinic – Sofia. The owner reported low grade lameness with the left hind leg, lasting for more than one month and badly responding to NSAIDs.
We did a thorough clinical exam, revealing normal over-all condition, moderate obese body score, choleric temperament. We found mild (II/IV) left hind leg weight baring lameness. Thickening of the left hock joint was noticed. Mildy decreased ROM with mild pain were appreciated in the affected joint.
Orthogonal radiographs of the left hock revealed diffuse intrinsic joint swelling. We found aggressive bone lysis areas (mostly severe at distal fibula) and moderate aggressive periosteal reaction (mostly affecting the tarsal bones). No abnormalities were detected on preoperative 3-view thoracic radiographs, abdominal ultrasound, echocardiography, and blood tests.
Fine- needle aspirates were taken. Cytology revealed numerous clusters of plump, oval to spindloid cells often with moderate cellular atypia. Considering this , the signalment and the imaging findings, a diagnosis of joint sarcoma was suggested.
A decision for limb sparing surgery by low trans-tibial amputation and integrated limb prosthesis (ITAP) was made.
Implant planing and manufacturing
A custom-made ITAP implant was manufactured using CNC machinery with additional welding process. Medical titanium (grade 4) was used for the production. The implant desired shape and size of the was predetermined using only radiographs. The straight shape and straight medullary canal made the design simple enough, so no necessity for computer tomography imaging and planning was found. The ITAP implant components included a 7 mm (rough surface) intramedulary stem, 3, 5 mm locking plate part, drilled titanium collar (flange) and most distally smooth 8 mm titanium rod (outside part). Locking 4 mm screws were produced corresponding to the plate locking mechanism.
A custom made exoprostheis was manufactured using combination of plastic polymer, rubber and metal elements. The length was conformed (with mild underestimation) to the natural foot size. Angulation of 135 degree of was planned to mimic the natural hock joint position. Shock absorbing (spring) design was developed.
The titanium flange role is the reduction of epithelial downgrowth and good soft-tissue integration.
Premedication with Medetomidine and Butorphanol was used, followed by Propofol induction. The maintenance was sustained by Isoflurane and Ketamin drop in the fluid sack. Epidural block with Ropivacaine was provided just before the surgery.
Cimicoxib (Cimalgex) was prescribed for 7 days post op. No opioids were used in the recovery period.
For the surgical intervention, the dog was positioned in dorsal recumbency. After macroscopic evaluation, transverse sharp dissection of soft tissues, covering the distal tibial dyapihis was done. Four centimetres distance proximally from the edge of the tarsal lump was aimed. Muscles tendons (including common calcaneal tendon) were severed. A strict haemostasis by electrocautery and ligation of the main blood vessels was achieved. Minimally invasive approach (bone tunnelling) was used for the insertion of the plate element under the soft tissue on the medial side. Mild contouring of the proximal plate part was needed to fit the tibia shape. No canal drilling was needed- the stem part was impacted quite easily into the soft bone marrow tissue. Gentle axial hammering ensured good bone to flange contact.
Muscle tendons and crural fascia free ends were sutured to the special designed flange holes. After gentle subcutaneous fat debridement the skin edges were sutured over the flange surface. Special attention was emphasised so the circular skin defect was closed with an “appropriate” tension- no skin abundance, but also with no excessive tension on the stitches.
Immediate post op care
Preventive antibiotic therapy (Amoxcillin calvulonic acid) and NSAIDs (Cimalgex) was prescribed for 7 days
A Modified Robert Jones bandage was applied over the amputee stump. The bandage was removed after three days and the exoprosthesis was attached, with similar soft bandage applied around the stump.
Strict cage rest with very short leash walks was emphasised in the immediate post op period.
A recheck radiograph at six weeks post op demonstrated solidly homogenous bone-implant contact area, suggesting osteointegration in process.
“Moderate differentiated synovial cell sarcoma.”
Atypical spindle shaped cells with indistinct borders and variable amounts of eosinophilic fibrillar cytoplasm and stroma. The long term prognosis is good but still variable.
The dog revealed very good comfort after the procedure, with immediate weight baring. Light protective bandage was used to cover the distal stump area and prosthesis for two months post op. The followed period (within 3 months) revealed very fast and pain free limb usage with milld lameness (II/V)
Leash walk 6 day post op.
Going for a walk 14 day post op.
2 months post op
3 months post op
Locking plate ITAP design can provide adequate stability needed for implant osteointegration, while early limb usage is allowed. The role of shock absorbing exoprosthesis for success is unclear. This fast functional recovery can make the ITAP procedure more attractive and better accepted by the owners of pets that need similar limb sparing surgeries. Further investigations may demonstrate ITAP complications variabilities (ratio) and long term results.