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.