Stress shielding seems to occur at the greater trochanter due to the vast cross-section of the implant. However, the aim of proximal load transfer of the Metha stem seems to be partially achieved. DEXA analysis revealed a concentrated load distribution on the medial portion of the femur, which is an important region to guarantee long-term implant survival.

In total hip arthroplasty (THA), short stemmed cementless implants are used because they are thought to stimulate physiological bone remodeling and reduce stress shielding. We performed a numerical investigation on bone remodeling after implantation of a specific short stemmed implant using finite element analysis (FEA). Overall bone mass loss was 2.8% in the entire femur. Bone mass decrease was mostly found in the proximal part of the calcar and in the greater trochanter due to the vast cross section of the implant, probably leading to stress shielding. In the diaphysis, no change in the apparent bone density was proven. The assumptions made agreed well with bone remodeling data from THA recipients who underwent dual-energy X-ray absorptiometry. However, the clinical investigation revealed a bone mass increase in the minor trochanter region that was less pronounced in the FEA. Further comparisons to other stem designs must be done to verify if the relative advantages of the investigated implant can be accepted. Keywords: total hip arthroplasty; finite element analysis; short stemmed implant; dual-energy X-ray absorptiometry; bone remodelingThe ''bone preserving strategy'' in total hip arthroplasty (THA) follows the idea of physiological bone remodeling and bony ingrowth of the femoral component. 1 This lead to the development of ''neck preserving'' short stems that are designed to avoid stress shielding and increase periprosthetic bone formation. 2 The Metha 1 neck preserving stem (AESCULAP AG, Tuttlingen, Germany) was introduced in 2004, along with two other short stemmed implants. This implant follows the design of the successful Mayo short stem (Zimmer, Warsaw, IN), 1,3 but is an advancement over the Mayo prosthesis in terms of femoral neck preservation and the inclusion of an osteoinductive coating.Finite element (FE) simulations are widely accepted for estimating bone remodeling after THA. However, only direct bone remodeling data after implantation of the specific stem can validate predictions made from the simulations. Dual-energy X-ray absorptiometry (DEXA) is considered the most reliable tool to address this issue, 4,5 and is useful for evaluating proximal femoral remodeling following cementless THA. 6 The current experiment is part of our collaborative research efforts at the ''German Research Foundation.'' The scope is to develop FE models for different types of implants, so that bone remodeling can be assessed. We introduced the Metha 1 short stem in our clinic in 2005 and have conducted >1,500 procedures with this stem, representing 35% of our cementless THAs in 2010. Here we present the first numerical calculations on bone remodeling after THA with this specific implant.We asked the following research questions: (i) what is the effect of THA with the Metha 1 short stem on femoral bone remodeling?; (ii) can numerical computations be confirmed by DEXA measurement of bone remodeling?; and (iii) what are the differences and can we explain them? MATERIALS AND METHODSThe study was conducted on...

The aim of this study was to evaluate the clinical and radiological outcome of the treatment of osteonecrosis of the femoral head by implantation of an osteonecrosis intervention rod. In this retrospective study the follow-up of 19 patients with 23 osteonecrotic femoral heads treated with implantation of an osteonecrosis intervention implant was assessed. From 19 patients with 23 necrotic femoral heads, there were 13 cases in which a total hip replacement was necessary. This implies a survival rate of 44% after implantation of an osteonecrosis intervention rod after a mean follow-up of 1.45 years. The outcome after core decompression combined with the insertion of a tantalum osteonecrosis intervention implant did not show superior results compared to core decompression alone. This is in contrast to existing studies. In addition, this study showed that in cases of total hip replacement, no problems appeared during explantation of the tantalum rod.

A number of short stems for total hip arthroplasty have been introduced during the last decade. We describe our experience with the NANOS prosthesis (Smith and Nephew, Marl, Germany). The potential increase of bone mass around a femoral short stem using bone densitometry may be an indicator for secondary ingrowth. We report the outcome of 72 NANOS short stems in 65 patients between March 2003 and October 2007. The mean follow-up was 5.2±0.7 years and the mean age of the patients was 63±8.3 years. Along with demographic data and co-morbidities, the Harris Hip Score, the Merle d'Aubigné mobility score, and a patient-centred questionnaire were evaluated pre-operatively and during follow-up. The Mean Harris Hip Score increased from 47.3±12.2 pre-operatively to 97.6±0.6 at the final follow-up. The Merle d'Aubigné mobility score increased from 7.6±1.4 pre-operatively to 11.8±0.3 at the final follow-up. None of the 72 stems were revised, providing a survival rate of 100%. Radiolucent lines were visible rasiographically in two patients during follow-up. The NANOS short stem demonstrated a satisfactory outcome at mid term follow-up. The clinical and radiological results support to the principle of metaphyseal anchorage of a short stem prosthesis. Long term evaluation will be of interest to determine if these encouraging trends are reflected by prolonged survivorship.

In recent years, various uncemented proximal metaphyseal hip stems were introduced for younger patients as a bone preserving strategy. Initial osteodensitometric analyses of the surrounding bone of short stems indicate an increase of bone mass with secondary bone ingrowth fixation as a predictor of long-term survival of these types of implants. We report the outcome of 151 modular Metha short hip stem implants in 148 patients between March 2005 and October 2007. The mean follow-up was 5.8±0.7 years and the mean age of the patients was 55.7±9.8 years. Along with demographic data and co-morbidities, the Harris Hip Score (HHS), the Hip dysfunction and Osteoarthritis Outcome Score (HOOS), and also the results of a patient-administered questionnaire were recorded pre-operatively and at follow-up. The mean HHS increased from 46±17 pre-operatively to 90±5 the HOOS improved from 55±16 pre-operatively to 89±10 at the final follow-up. A total of three patients have been revised, two for subsidence with femoral revision and one for infection without femoral revision (Kaplan Meier survival estimate 98%). The radiological findings showed no radiolucent lines in any of the patients. The modular Metha short hip stem was implanted in younger patients, who reported an overall high level of satisfaction. The clinical and radiographic results give support to the principle of using short stems with metaphyseal anchorage. However, long-term results are necessary to confirm the success of this concept in the years to come.