Initial stability of a new uncemented short-stem prosthesis, Spiron®, in dog bone.

BACKGROUND Use of the proximal part of the femur in total hip arthroplasty enables preservation of the distal femur for later revisions. To use this advantage, different types of short-stem prosthesis have been developed in recent years. Although cementless hip arthroplasty is not common in the treatment of canine osteoarthritis, the use of cementless short-stems might be an alternative therapy. The new cementless short-stem prosthesis called Spiron® is self-tapping, and is constructed with a conical shape with threads. We measured the relative motion in the bone/prosthesis interface with specified loads in the femora of dogs to investigate two aspects: the primary stability of two systems of uncemented prosthesis with different principles of anchoring, and the theoretical use of the Spiron® in dog bone. We measured the cyclic behaviour (i.e., reversible, elastic), subsidence (i.e., irreversible, plastic, migration) and maximal applied load. METHODS Twenty-four pairs of fresh femur bones from adult German shepherd dogs were used. After measuring the total bone mineral density (TBMD), 16 bones were used in each of the short-stem prosthesis group (group A), the Zweymuller prosthesis group (group B), and the no-prosthesis control group (group C). Micromotion between bone and prostheses was measured for 16,200 N axial load steps, beginning with 200 N and increasing to 3000 N (1600 cycles/femur). Simple analysis of variance and non-parametric tests were used to compare the groups. RESULTS The Spiron prosthesis had significantly less motion in the bone/prosthesis interface compared with the Zweymuller prosthesis. CONCLUSIONS The new principle of anchoring of the Spiron short-stem prosthesis may provide higher primary stability compared with conventional techniques. The findings of this study support the assumption that the use of the Spiron prosthesis to treat osteoarthritis in the dog is feasible.