The Spiron cementless femoral neck prosthesis is based on the idea of proximal force transmission. The concept of osseous anchorages has been proven successful various times. The prosthesis is a conical, self-cutting screw that is inserted without cement into the prepared subcapital implant bearing. It is produced from a corundum blasted titanium-vanadium alloy and is covered with a second-generation calcium phosphate coating. The coating and the form of the thread increase the implant's surface and help to optimize osseointegration. From February 2003 to April 2003, 38 Spiron prostheses were implanted at the DRK hospital in Neuwied (Germany) in 34 patients. Four patients received it for the replacement of both hip joints. The average age of the patients was 60.1 years at the time of the implantation (43-73 years); 20 male and 14 female patients received the prosthesis. We implanted 19 left-sided and 19 right-sided arthroplasties. The preoperative Harris hip score (HHS) was 51 (24-76), n=38. After 1 year, HHS(1) was 94 (86-100), n=20 (of 23 implants). Until now, we have not discovered any prosthesis-specific complications; the rehabilitation time shows a tendency to be shorter than after stem arthroplasty. Revision was necessary in one case because of an early infection. After 3 months, the radiological follow-up examinations showed the development of increasing trabecular reinforcement of the femoral neck and pertrochanteric regions. Until now, there is no evidence of any varus tendency of the Spiron prosthesis.

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.

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