Surgery STAT: Limb sparing procedure is another option for dogs

Amputation remains the standard of care to address most primary tumors of the appendicular skeleton, particularly sarcomas. As a general rule, dogs adapt well to amputation, regardless of size. However, dogs suffering from concurrent orthopedic or neurologic diseases, or those with owners opposed to amputation, may be poor candidates for this procedure. In those cases, limb sparing may be an option. As the name implies, limb sparing is a surgical procedure in which a portion of diseased bone is removed or treated while limb function is preserved.

Proper staging must be performed to ensure the procedure is in the best interest of the patient. Surgical planning to ensure appropriate margins for both soft and bony tissues is essential. Advanced imaging such as CT and MRI may facilitate this, as well as help determine whether the patient is even a candidate for limb sparing.

The techniques for limb sparing, prognosis for functional outcome and complications seen are dependent on the anatomic location of the tumor. The site most amenable to limb spare is the distal ulna. It can be removed and does not need to be replaced. Ideally, the interosseous ligament is preserved. If the styloid process must be excised with the tumor, reconstruction of the lateral collateral ligament or pancarpal arthrodesis will maintain stability of the antebrachiocarpal joint. The prognosis for limb function is usually excellent.

The anatomic site receiving the most attention for limb sparing is the distal radius. It is one of the most common sites for osteosarcoma in dogs. Most commonly, the diseased distal radius is replaced with a cortical allograft (Photo 1). Unfortunately, the complication rate is high, with infection seen in up to 70 percent of limbs and local recurrence and implant problems in as many as 60 percent of the limbs.

Photo 1: Dog undergoing limb sparing surgery using the allograft technique. The allograft is being held by the surgeon. The plate has been applied to the allograft, and it will be placed into the bony defect present from having removed the distal aspect of the radius harboring the tumor. The plate will then be applied to the proximal aspect of the remaining radius and the carpus and metacarpal bone.

This technique does require maintenance of a bone bank or purchase of a commercially available cortical allograft. A metallic endoprosthesis with specialized bone plate now is available as an alternative to cortical allograft. A study comparing the endoprosthesis and cortical allograft found no difference in complication rates.

The distal radius can be replaced with viable autograft using distraction osteogenesis or transfer of an ulnar segment. Distraction osteogenesis utilizes the principles and techniques developed by Ilizarov.

Circular fixators are placed proximal and distal to the ostectomy site. A segment of bone is created at the distal aspect of the remaining proximal radius and is fixed to a ring that can move distally along threaded bars. When the segment is moved approximately 1mm/day, the body will deposit new bone "behind" it without fusing. Once the segment has reached the carpus, a new column of viable bone has been created.

Alternative techniques transport a segment of ulna along a transverse axis across the radial defect, or "rolled over" an ulnar segment along its longitudinal axis, into the heterotopic position and stabilized with the radius via bone plate (Photo 2).

Photo 2: Lateral radiograph of a limb following ulnar rollover transposition.

Pasteurization and extracorporeal radiation allow use of the distal radius as an autologous graft. After removal of the diseased distal radius, it is pasteurized, killing the tumor and bone cells, while preserving the proteins in the bone. These proteins theoretically promote healing of the treated bone to the "healthy" bone when it is reduced and stabilized via pancarpal arthrodesis.

Alternatively, the diseased radius is isolated and exposed, preserving the joint capsule of the carpus and maintaining its attachments to the paw distally. The exposed bone is treated with horizontal beam radiation of 70 gray, killing all cells in the path of the beam. The treated distal segment of the radius is then returned to its normal anatomic position and stabilized with bone plate repair. This technique does not require carpal arthrodesis.

Next month, I will continue this topic and briefly discuss limb sparing techniques for other anatomic locations.

Dr. Bernard Séguin is an ACVS board-certified surgeon who is an assistant professor at the College of Veterinary Medicine, Oregon State University. His research interests include osteosarcoma and limb sparing.