Over the last 25 years, total hip replacements in the dog have become a well established method for treating a disabled hip condition. In the past few years, the surgical techniques as well as the models and materials used for the implants have greatly improved.
The underlying concept of the KYON Zurich Cementless canine hip prosthesis involves anchoring the femoral stem into the medial cortex of the femur using locking monocortical screws, whereas the acetabulum is a press-fit component. The monocortical design of the stem attempts to resolve the problem of micromotion at the stem-bone interface. The latter occurs as a result of differing mechanical stresses present on the medial versus lateral bone surfaces, which in turn are linked to long-term loosening. The femoral stem is initially positioned by using a bicortical screw. Subsequently, monocortical screws (3 or 4 depending on the relative size of the stem) are inserted into the area closest to the proximal and medial face of the femur. The femoral stem is compressed against this area, allowing for a greater degree of stability and firmness. During the procedure, the bulk of the weight of the femur of the canine lies in this region, thus, from a biomechanical standpoint, it is more practical for the aligning of the stem to occur on the medial face, rather than placing it centrally as would be the case for cemented prosthesis. By using a highly compliant titanium shell, the current acetabular cup design also attempts to address the problem of interface micromotion with the cancellous bone. Furthermore, the polyethylene cup insert is suspended within this shell, leaving a hydraulically open space between the shell and the insert. As a result, the convective mechanisms of fluid mass transport allow bone ingrowth to reach the holes of the laser-drilled metal shell. The latter also provides a central orifice in which to insert a screw if the surgeon so desires.
The femoral component as well as the acetabular one are designed to facilitate the osteo-integration. In our experience, this process is estimated to last a maximum of 4 to 6 weeks and patients usually recover within 2 months practically without any lameness.
Our past procedures and advanced knowledge of cemented hip prosthesis confirm that the KYON Zürich cementless prosthesis is without doubt one of the greatest advances within the realm of traumatology.
1. Kyon Course on Zürich Cementless Canine THR, Orlando, November 2003.
2. Zürich Hip Dinner Meeting, Washington, DC (ACVS Meeting): October 9 2003.
3. Zürich Hip Dinner Meeting, San Diego, CA (ACVS Meeting): October 17 2002.