Introduction

While fixation on the acetabular side in resurfacing implants has been uncemented, the femoral component is usually cemented. The most common causes for early revision in hip resurfacing are femoral head and or neck fractures and aseptic loosening of the femoral component. Later failures appear to be more related to adverse soft-tissue reactions due to metal wear. Little is known about the effect of cementing techniques on the clinical outcome in hip resurfacing, since retrieval analysis of failed hip resurfacing show large variations. Two cementing techniques have dominated. The indirect low viscosity (LV) technique as for the Birmingham Hip resurfacing (BHR) system and the direct high viscosity (HV) technique as for the Articular Surface replacement (ASR) system. The ASR was withdrawn from the market in 2010 due to inferior short and midterm clinical outcome. This study presents an in vitro experiment on the cement mantle parameters and penetration into ASR resurfaced femoral heads comparing both techniques.

Background: The standard fixation of femoral stems used for patients with femoral neck fractures is bone cement. Bone cement has side effects related to co-morbidity. The purpose of this study is to evaluate fixation, bone remodelling and clinical results with a new uncemented, fully hydroxyapatite-coated tapered femoral stem (Fracture Stem^®) designed for press-fit insertion in patients with femoral neck fractures.

Methods: Forty patients (25 women, 15 men) at a mean 82 (70–92) years of age with an acute displaced femoral neck fracture were included in the study. The patients were operated with the new stem and received a total hip arthroplasty. Tantalum markers were placed in the proximal femur during surgery. We have so far followed the patients for 1 year postoperatively with radiostereometric measurements, dual-energy x-ray absorptiometry and clinical evaluation including Harris hip score, pain numerical rating scale and health related quality of life.

Results: The stem showed good fixation. Subsidence and stem rotation for all stems but five were close to zero. Maximum total point motion increased above precision error at the 6 weeks follow-up but did not increase significantly after that. All stems with significant migration were stable after 3 months. We have had no per–or postoperative fracture. One stem has had to be revised because of a deep infection. Median bone loss after 6 months was significant (p=0.018 to 0.028) in all zones but Gruen zone 4. Bone loss was greatest in Gruen zone 1, 2, 6 and 7 with 29%, 22%, 18% and 32% loss respectively. Median Harris hip score decreased significantly (p=0.003) from 89 before fracture to 75 and 78 at the 6 weeks and 6 months follow-up. Pain numerical rating scale and Health related quality of life decreased until the 6 week visit but returned to prefracture value at 6 months.

Conclusions: According to these early 1-year results, Fracture Stem^® shows good fixation and fast ingrowth in osteoporotic bone. Periprosthetic bone loss due to stress-shielding was significant in all zones but zone 4. Clinically the stem behaved as expected. According to our results, we propose a randomized cinical trial in a larger patient population as the next step to evaluate this femoral stem.