Page 288 - WSAVA2017
P. 288

An Urban Experience
Surgical treatment of OS.
Amputation is the standard local treatment for appendicular OS. It is performed as a forequarter amputation for the front leg, as an amputation at the diaphysis of the femur or at the coxofemoral joint depending on the location and extent of the tumour for the hind leg. Even large and giant breed dogs function well after amputation and their owners are pleased with the mobility and quality of life of their pets. Amputation alone is considered a palliative treatment.
Another option, that is increasingly applied, is limb- sparing surgery. Limb sparing is a complicated and long process that requires efforts from the owner, surgeon, oncologist, and radiologist. There are certain prerequisites, for the selection of suitable candidates for a limb sparing procedure. These include dogs with OS clinically and radiographically confined to the leg, the primary tumour does not affect more than 50% of the bone, and the patient should be in an otherwise good health. Other criteria for consideration are the absence of pathological fracture and less than 3600 involvement of soft tissues.
These patients can receive a pre-operative treatment: intra-arterial cisplatin, intra-venous cisplatin, radiotherapy of the bone, or combination of the above. Pre- operative treatment with cisplatin has no additional advantage
on survival time over post-operative treatment. So
far, pretreatment with radiation has revealed to be unsatisfactory for the preservation of the limb and even of life but can be used successfully for palliation.
The most suitable cases for limb sparing are those
with a confined tumour in the distal radius or ulna, the distal fibula, and scapula. The carpal joint is suitable
for arthrodesis in these cases. In all other cases, where arthrodesis of the scapulohumeral, coxofemoral, stifle, or tarsal joints is performed, a limb sparing procedure has given so far only fair to poor function of the patient. The latter in combination with the high complication rate of limb sparring procedures leads surgeons away from recommending limb sparing near these joints.
There are several limb spearing procedures described. Their advantages and disadvantages are described in the following Table:
 Limb sparing procedure
  fresh frozen cortical allograft
 Absence of external fixation Little owner involvement
 High infection rate 40-50%
  Metal endoprosthesis
    Commercially available
   No allograft is needed
     Pasteurized tumoural autograft
   Tumour is pasteurized at 650C 40 min
  No need for allograft, anatomic apposition is excellent
  15% local recurrence, 31% infection, 23% implant failure
  Longitudinal bone transport osteogenesis
   Distraction osteogenesis with circular fixator
  No need for allograft Low risk of infection Remodeling bone overtime
  Extensive client involvement Extensive time needed for distraction
  Ulnar transposition
  Ipsilateral distal ulna is autograft
 No morbidity donor site Autologous replacement Vascularized graft Low risk of infection
 Prone to biomechanical complication in post-operative period Permanent implant
 Intraoperative extracorporal radiation
 Single 70-Gy radiation only of the tumour
   Sparing of immediate joint function
   50% implant revision 30% local recurrence 30% infection
 On the overall, 80% of the limb spared OS-patients experience a good to excellent limb function. For a successful limb sparing process, a dedicated owner and veterinary expert team are essential. There is, on the overall, no significant difference in the survival rate for dogs treated with limb sparring and cisplatin compared to dogs treated with amputation and cisplatin.
Canine limb spare patients have a high infection
rate of 31-68%. Once there is an infection it can be controlled with long-term antibiotic therapy based on
an antibiogram. However, the infection rarely, if ever, resolves. These infections can result in draining tracts, exposure of the fixation material or the graft, and can result into loosening of the implanted material. Revision surgery is common practice is such cases. In case there is a catastrophic implant failure amputation of the limb
is required. Unexpectedly, allograft infection is related
to a significantly longer survival time compared to dogs
with no allograft infection. It is unclear how this can be explained, but it is speculated that the immune system is activated by humoral factors and plays a role in the elimination of the cancer cells.
The surgical treatment (amputation or limb- sparing), if used alone, is considered a palliative treatment and does not change the prognosis of the OS patient. The latter is attributed to poor medical control of the (micro-) metastasis. Therefore, surgical treatment is combined with one or more of the following adjuvant therapies:

   286   287   288   289   290