Introduction: Bone resorption in the proximal femur is commonly seen after cementless total hip arthroplasty (THA). One of the main determinants of bone remodeling seems to be prosthesis design. With DXA, the amount of bone mass after THA can be precisely determined. We evaluated the BMD behavior of two different ultra-short implants with proximal load transfer, in order to study how a design can affect femoral bone remodeling. The rationale behind these designs is the experimental evidence that loading the medial and the lateral flare effectively preserves in time metaphyseal bone stock. Moreover, biomechanical tests have confirmed that this kind of stress distribution allows to remove the diaphyseal portion of the stem.

Methods: A total of 33 patients operated with a cementless femoral implant were included in this study. Two slightly different designs were tested: Type 1 (Stanmore Orthopaedics), featuring an extremely short distal stem (n=10), and Type 2 (DePuy International Ltd), where distal stem was virtually absent (n=23). All implants were customized based on pre-operative CT data. The main features of these implants were the ultra-short stem and the large lateral flare. The rationale was to preserve bone stock and gain a more physiologic load transfer to the proximal femur thus preventing stress-shielding. DXA examination was performed on all patients 3 years after THA. Due to the peculiar design, a specific protocol of analysis with five regions of interest (ROI) was developed: ROI1 (greater trochanter), ROI2 and ROI4 (respectively lateral and medial of the ultra-short stem), ROI3 (below the tip) and ROI5 (calcar). The same protocol was applied to the non-operated contralateral femur and percentage contralateral BMD was calculated with the following formula: (BMD of operated hip/BMD of contralateral hip)×100. A standard DXA of contralateral hip and lumbar spine was also performed to evaluate the skeletal bone mineralization.

Results: No differences were found in the anthropometric data and sex between the two groups. Age was found lower (p=0.001) in Type 2. BMD of lumbar spine and contralateral femur from standard DXA were not different in the two groups. BMD was higher in Type 2 in ROI4 and ROI5 (p< 0.001). The calculated percentage contralateral BMD was higher in Type 2 in ROI2 (p=0.009), ROI4 (p< 0.001) and ROI5 (p=0.01).

Conclusions: This study confirms that progressive shortening of femoral stem produces a more proximal loading, which effectively preserves in time metaphyseal bone stock and increases periprosthetic BMD in the medial ROIs. The increased BMD in periprosthetic lateral and medial proximal regions in the operated hip respect to the contralateral femur seems to be due not only to the increased weight-bearing, but also to the specific ultra-short stem design.

Introduction Significant cortical bone mass has been demonstrated at the proximo-lateral flare of the femur (Fetto et al). Experiments have shown that if a femoral stem has a medial and lateral flare proximally, the loads are transferred to the proximal femur and stress protection in this area is avoided. Furthermore, the results suggested that a stem below the lesser trochanter was unnecessary (Walker et al).

Methodology This paper reports on two cohorts of ten patients that had either a short stemmed fully coated implant (Group I) or an unstemmed metaphyseal implant on which all but the polished tip was coated (Group II). All implants were customised based on pre-operative CT data. All hips had serial post-operative AP and lateral radiographs and bone densitometry was assessed with DEXA scanning.

Results The most recent post-operative radiographs of all patients in Group I revealed buttressing in zone IV with trabeculae streaming from the cortices onto the tip of the stem. Qualitatively there appeared to be osteope-nia in Gruen zones I and VII. The x-rays of the Group II patients revealed good condensation of bone along the textured surface in zone I and VII with preservation of bone density in these regions. These findings were confirmed by the DEXA results which showed a reduction of the BMD in zones I and VII in Group I, while Group II revealed preservation of the BMD in these zones.

Conclusion A conservative prosthesis without a stem which effectively loads both medial and lateral proximal femoral flares not only removes less bone at the index operation but preserves proximal bone stock in the longer term.

Introduction A wide range of stress-shielding phenomena following THA have been described in the past 20 years. Bone densitometry (DXA) stars as a golden standard in evaluating bone stock and bone density redistribution after total hip replacement.

In this study, DXA scan was employed to evaluate and compare the behaviour of different femoral components including a recently developed stemless implant which features complete stress transfer over the proximal femur.

Methodology A total of 120 patients, operated with six different femoral implants, were included in the present study. Five of these stems are widely commercially available (ABG, CFP, IPS, Mayo, Zweymueller) and present different patterns of stress distribution. The sixth is a custom made implant and features a pronounced lateral flare and complete femoral neck preservation. Rationale of this design is to obtain full load transfer on the proximal femur.

Average interval between the operation and the DXA exam was 3 years, each group included 20 patients. Bone mineral density was measured by DXA in the seven Gruen femoral regions (ROI), using the software metal removal (Hologic QDR 4500 W, MA-USA).

Results Differences in bone density were found in each group as well as between different groups. Significant differences (p< 0.001) were found between the stemless implant and the other five groups in zone I, IV and VII.

CFP, IPS and ABG groups showed decreased bone density in ROI I, while Mayo, IPS, ABG and Zweym-ueller were osteopenic in ROI VII. An increased bone density in ROI IV was found in Zweymueller, Mayo, ABG and IPS groups.

Conclusion Our data suggest that a conservative stemless implant with complete proximal load transfer, produces a homogeneous and more physiologic redistribution of bone density, allowing maintenance of proximal periprosthetic bone stock.