Periprosthetic DXA after total hip arthroplasty with short vs. ultra-short custom-made femoral stems: 37 patients followed for 3 years

Bone integration of new stemless hip implants (proxima vs. nanos). A DXA study: preliminary results

The development of short femoral prostheses has the advantage to preserve bone and soft tissues, restore hip geometry, permit mini-invasive techniques and allow quickly return to an active life, but very few studies described bone reaction to these new designed prostheses. The aim of the present study was to evaluate the osseointegration of two different partial neck retained stemless hip prosthesis at one year after surgery, measured by the changes of periprosthetic bone mineral density (BMD) in 5 regions of interest (ROIs) using a dual-energy X ray absorptiometry (DXA) device. The signs of stress-shielding were evaluated by standard radiographs. Thirty-two uncemented primary total hip arthroplasty (THA) patients allocated into 2 groups were evaluated. In the first group (n=19) a Proxima (De-Puy-J&J) hip stem was implanted. In the second group (n=12) a Nanos (Smith & Nephew) hip stem was used. We found that both the implants preserve metaphyseal bone stock and increase periprosthetic BMD. In Nanos prostheses a significant higher BMD values were observed in region of interest (ROI) 3 and 4 (p<0.05). No differences were found in ROIs 1, 2, and 5. Proxima stem seem to produce a physiological strain distribution in the femur. No signs of stress-shielding were present in both the implants. In conclusion, this preliminary DXA analysis showed a physiological integration of both the stems that reproduces the biomechanical stress of proximal femur. New designed short stem implants showed optimal osseointegration after one year, and therefore appears an excellent alternative to traditional long stem hip prostheses.

Bone remodelling around the Metha short stem in total hip arthroplasty: a prospective dual-energy X-ray absorptiometry study

PURPOSE

On the basis of positive clinical results with mid- and long-term follow-up using the Mayo short stem, the Metha neck-preserving stem (BBraun, Aesculap, Tuttlingen, Germany) was introduced. The purpose of this study was to validate the implant design by direct acquisition of bone remodelling data from total hip arthroplasty (THA) recipients using dual-energy X-ray absorptiometry (DEXA).

METHODS

After power analysis, 25 patients were included in this prospective study. Patients were examined clinically and underwent DEXA examinations preoperatively and postoperatively at one week, six months and one and two years after THA. Gruen zones were adapted to the short stem design (R1-R7).

RESULTS

The Harris Hip Score (HHS) increased significantly by 31 points. No stem had to be revised. Bone mineral density (BMD) in the greater trochanter decreased significantly from 0.78 g/cm(2) postoperatively to 0.72 g/cm(2) two years after surgery. Marginal changes were seen in the lateral distal regions (R4-R5). In the minor trochanter region, BMD increased significantly after two years by 12.9%. In the calcar region, BMD exceeded the baseline value by 6.1% two years after implantation.

CONCLUSIONS

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.

Periprosthetic bone loss after insertion of an uncemented, customized femoral stem and an uncemented anatomical stem. A randomized DXA study with 5-year follow-up

BACKGROUND AND PURPOSE

Customized femoral stems are designed to have a perfect fit and fill in the femur in order to achieve physiological load transfer and minimize stress shielding. Dual-energy X-ray absorptiometry (DXA) is regarded as an accurate method for detection of small alterations in bone mineral density (BMD) around hip prostheses. We present medium-term DXA results from a randomized study comparing a customized and an anatomical femoral stem.

METHODS

100 hips were randomized to receive either the anatomical ABG-I stem or the Unique customized femoral stem, both uncemented. DXA measurements were conducted postoperatively and after 3, 6, 12, 24, 36, and 60 months, and BMD was computed for each of the 7 Gruen zones in the proximal femur.

RESULTS

Results from 87 patients were available for analysis. 78 completed the 5-year follow-up: 35 patients in the ABG group and 43 patients in the Unique group. In both groups, we found the greatest degree of bone loss in the proximal Gruen zones. In zone 1, there was 15% reduction in BMD in the ABG-I group and 14% reduction in the Unique group. In zone 7, the reduction was 28% in the ABG-I group and 27% in the Unique group. The only statistically significant difference between the groups was found in Gruen zone 4, which is distal to the tip of the stem, with 1.6% reduction in BMD in the ABG-I group and 9.7% reduction in the Unique group (p = 0.003).

INTERPRETATION

5-year DXA results showed that because of stress-shielding, proximal bone loss could not be avoided-either for the anatomical ABG-I stem or for the customized Unique stem.

Quantitative computed tomography-assisted osteodensitometry of the pelvis after press-fit cup fixation: a prospective ten-year follow-up

BACKGROUND

As a follow-up of a previously reported three-year study, we analyzed the periprosthetic acetabular cortical and cancellous bone density changes at ten years after implantation of a press-fit cup.

METHODS

Prospective clinical, radiographic, and quantitative computed tomography examinations were performed within ten days and at mean periods of one, three, and ten years after total hip arthroplasty with a press-fit cup, a femoral stem with a tapered design, and alumina-alumina pairing. Periacetabular cortical and cancellous bone density (mg CaHA/mL) in the cranial, ventral, and dorsal regions about the cup were measured for twenty-four hips in vivo.

RESULTS

All acetabular cups showed radiographic signs of stable ingrowth, and no acetabular component had to be revised. The loss of periacetabular cancellous bone density about the cup was as much as -37% cranially, -60% ventrally, and -71% dorsally; the decrease was progressive between the one-year and three-year examinations only. In contrast, cortical bone density above the dome of the acetabular cup remained constant throughout the ten-year follow-up. A moderate change in cortical bone density of -5% to -18% was seen at the level of the cup ten years postoperatively.

CONCLUSIONS

Both periacetabular cortical and cancellous bone density changes were nonprogressive between the three-year and ten-year examinations after press-fit cup fixation.

Tissue differentiation around a short stemmed metaphyseal loading implant employing a modified mechanoregulatory algorithm: a finite element study

Short stemmed cementless implants are being used increasingly to avoid problems associated with their long stemmed counterparts such as size, stiffness, and bulky nature, which can contribute to stress shielding, fractures, and hence loosening. They are also thought to enhance physiological loading of the femur. We performed a computational investigation of the possible tissue differentiation and bone ingrowth processes for a specific type of stemless implant using a mechanoregulatory hypothesis, with modifications to simulate tissue differentiation, and simplified loading conditions. The peak forces during stair climbing and normal walking were investigated to evaluate their influence on the process. The results were compared to clinical studies for relevance and corroboration. The majority of the tissue type formed was fibrous, occupying the proximal regions of the implant. The lateral flare design feature of the implant was predicted to enhance bone and cartilage formation in regions beneath it compared to the same design without a flare. The percentage of bone formed increased through the iterations and accounted for nearly 35% of the tissue at the end of the iterations in Gruen zones 2 and 6, replacing cartilage tissue as differentiation progressed. This agreed well with clinical data showing similar regions of bone formation and suggests that the distal regions of the implant under the lateral flare, resting in the metaphyseal region of the bone, promoted implant stability.

Changes in bone mineral density in the proximal femur after hip resurfacing and uncemented total hip replacement

We undertook a randomised prospective follow-up study of changes in peri-prosthetic bone mineral density (BMD) after hip resurfacing and compared them with the results after total hip replacement. A total of 59 patients were allocated to receive a hip resurfacing (n = 29) or an uncemented distally fixed total hip replacement (n = 30). The BMD was prospectively determined in four separate regions of interest of the femoral neck and in the calcar region corresponding to Gruen zone 7 for the hip resurfacing group and compared only to the calcar region in the total hip replacement group. Standardised measurements were performed pre-operatively and after three, six and 12 months. The groups were well matched in terms of gender distribution and mean age.

The mean BMD in the calcar region increased after one year to 105.2% of baseline levels in the resurfaced group compared with a significant decrease to 82.1% in the total hip replacement group (p < 0.001) by 12 months. For the resurfaced group, there was a decrease in bone density in all four regions of the femoral neck at three months which did not reach statistical significance and was followed by recovery to baseline levels after 12 months.

Hip resurfacing did indeed preserve BMD in the inferior femoral neck. In contrast, a decrease in the mean BMD in Gruen zone 7 followed uncemented distally fixed total hip replacement. Long term follow-up studies are necessary to see whether this benefit in preservation of BMD will be clinically relevant at future revision surgery.

Quantification of bone density of the proximal femur after hip resurfacing arthroplasty--comparison of different DXA acquisition modes

Total hip arthroplasty (THA) is a traditional operative procedure in the treatment of osteoarthritis. The hip resurfacing arthroplasty (HRA) provides an alternative to the THA for young active patients. HRA is a bone-preserving procedure eliminating the problem of proximal femoral stress shielding and osteolysis associated to THA. Unfortunately, there is no standardized methodology to monitor the quality of bone after HRA. In this study, areal bone mineral density (BMD) in the operated hip (10 regions of interests [ROIs] of 34 volunteered HRA patients) was measured using Lunar Prodigy dual-energy X-ray absorptiometry, and the agreement of a standard (dual femur) and an orthopedic (orthopedic hip) acquisition modes was compared. Furthermore, reproducibility of the patient-specific analysis procedures was tested. The analysis procedures were reproducible with both acquisition modes (1.18%-1.37%). The mean (± standard deviation) difference between the acquisition modes was 1.46 ± 0.93%. At ROIs, a strong linear relationship was found between the results from 2 acquisition modes (R(2)=0.801-0.966, p<0.01). In conclusion, both acquisition modes were reproducible, and it is suggested that the error induced by the different acquisition modes does not affect interpretation of BMD changes after HRA surgery.

Mid-term results of a custom-made short proximal loading femoral component

Bone preservation and physiological distribution of forces on the proximal femur are key elements in introducing a successful uncemented total hip replacement. In order to achieve this, in the mid 1990s, we developed an ultra short proximal loading custom-made component with a lateral flare, a high femoral neck osteotomy and without a diaphyseal stem.

We report the outcome of 129 custom-made hydroxyapatite-coated uncemented short femoral components inserted into 109 patients between June 1995 and May 2004. The mean age of the patients was 51 years (21 to 71) and the mean follow-up was eight years (4.9 to 14.1). Bone behaviour around the implant was studied on the post-operative radiographs. The mean Harris hip score improved from 44 (8 to 66) pre-operatively to 95 (76 to 100) at final follow-up. The Western Ontario MacMaster University Osteoarthritis index was 93 of 100 at final review. None of the patients reported thigh pain. A total of five hips were revised, three for polyethylene liner exchange and two for complete revision of the acetabular component. No femoral components were revised. The radiological changes in the proximal femur were generally good, as evidenced by spot welds both on the medial and lateral aspects of the femur. No component migrated. The presence of a lateral flare and use of a high osteotomy of the femoral neck provided good clinical and radiological results. The absence of a diaphyseal portion of the stem did not impair stability.

Periprosthetic bone mineral density and fixation of the uncemented CLS stem related to different weight bearing regimes: A randomized study using DXA and RSA in 38 patients followed for 5 years

BACKGROUND AND PURPOSE

There is no consensus on the best rehabilitation regime after uncemented total hip arthroplasty. Theoretically, bone ingrowth into the implant should benefit from initial partial weight bearing. We investigated whether the degree of postoperative weight bearing influences the periprosthetic bone mineral density (BMD) and/or the stability of the CLS stem.

PATIENTS AND METHODS

38 patients received an uncemented CLS stem and were randomized to either unrestricted postoperative weight bearing or to partial weight bearing for 3 months. Periprosthetic BMD was measured in the 7 Gruen zones with DXA and the stability of the femoral stem was assessed by radiostereometric analysis (RSA) after surgery and at 3, 12, 24, and 60 months.

RESULTS

Periprosthetic BMD was not influenced by the type of postoperative weight bearing. BMD was reduced by 8-15% in all Gruen zones at 3 months. Restoration toward initial BMD was observed in all zones except in zone 7 (calcar region), where BMD was reduced by 22% at 5 years. Immediate weight bearing after surgery had no influence on the stability of the CLS stem, as assessed by RSA.

INTERPRETATION

Immediate full weight bearing after uncemented total hip arthroplasty is safe. There is no difference in the periprosthetic BMD or in stability of the stem as measured by RSA compared to partial weight bearing for 3 months. BMD is reduced by more than 20% in the calcar region around a CLS stem after 5 years.

The Freeman femoral component with hydroxyapatite coating and retention of the neck: an update with a minimum follow-up of 17 years

The outcome at ten years of 100 Freeman hip stems (Finsbury Orthopaedics, Leatherhead, United Kingdom) retaining the neck with a proximal hydroxyapatite coating in a series of 52 men (six bilateral) and 40 women (two bilateral), has been described previously. None required revision for aseptic loosening. We have extended the follow-up to 20 years with a minimum of 17 years. The mean age of the patients at total hip replacement was 58.9 years (19 to 84). Six patients were lost to follow-up, but were included up to their last clinical review. A total of 22 patients (22 hips) had died, all from causes unrelated to their surgery. There have been 43 re-operations for failure of the acetabular component. However, in 38 of these the stem was not revised since it remained stable and there was no associated osteolysis. Two of the revisions were for damage to the trunnion after fracture of a modular ceramic head, and in another two, removal of the femoral component was because of the preference of the surgeon. In all cases the femoral component was well fixed, but could be extracted at the time of acetabular revision. In one case both components were revised for deep infection. There has been one case of aseptic loosening of the stem which occurred at 14 years. This stem had migrated distally by 7.6 mm in ten years and 8.4 mm at the time of revision at which stage it was found to be rotationally loose. With hindsight this component had been undersized at implantation. The survivorship for the stem at 17 years with aseptic loosening as the endpoint was 98.6% (95% confidence interval 95.9 to 100) when 62 hips were at risk. All remaining stems had a satisfactory clinical and radiological outcome. The Freeman proximally hydroxyapatite-coated femoral component is therefore a dependable implant and its continued use can be recommended.

Periprosthetic bone density as outcome of therapeutic response

The bone surrounding a prosthetic implant normally experiences a progressive quantitative reduction as a result of stress shielding and wear debris production, that can lead to the aseptic loosening of the implant. Dual-energy X-ray absorptiometry (DXA), using software algorithms, can ensure a surrogate measure of load redistribution after the implant of the prosthetic components and can be a valid tool to evaluate the efficacy of pharmacological therapy to reduce the periprosthetic bone loss. In several animal and human studies DXA has been able to quantify antiresorptive action of bisphosphonates in the periprosthetic area.