Preoperative bone quality as a factor in dual-energy X-ray absorptiometry analysis comparing bone remodelling between two implant types

Clinical results at 10 years of minimum follow-up with the ABG 2 hip arthroplasty, matched with ceramic-on-ceramic bearings

Introduction: The current study aimed as a primary goal is to assess the results of a ceramic-on-ceramic (CoC) bearing hip system matched with ABG (Anatomic Benoist Girard) 2 components in terms of survivorship. Secondary objectives addressed specifically ceramic-related complications as well as specific patterns at the bone-implant interface. Material and methods: This is a retrospective bicentric continuous series involving 147 patients (95 males vs. 52 females) who underwent ABG 2 arthroplasties with CoC bearings. One hundred and twenty-five hips were closely followed-up at a mean period of 11.3 years. Results and discussion: With a mean follow-up of 11.3 years, nine cases (5.7%) underwent revision surgery, four caused by acetabular aseptic loosening, three by deep infections, one ceramic head fracture, and one femoro-acetabular impingement. The global survivorship was 92.2% at 12.7 years. The Harris Hip Score (HHS) mean scores increased post-operatively from 50.1 up to 96.1 points (p < 0.001). All stems featured patterns of radiological osseous integration onto the hydroxyapatite (HA)-coated zones. No radiological wear or osteolysis of ceramic bearings was demonstrated however, five patients reported hip squeaking using this bearing. This study demonstrated excellent results at mid-term follow-up in patients younger than 70 years of age using cementless ABG 2 components coupled with CoC bearings with no increase in complication rate.

Periprosthetic fracture as a late mode of failure of the Anatomique Benoist Girard II femoral prosthesis

Aim

The Anatomique Benoist Girard (ABG) II femoral implant was a commonly used stem for primary total hip replacement (THR) at our institution (Launceston, Tasmania Australia). We identified peri‐prosthetic fracture as the main cause of late failure.

Methods

The late periprosthetic fracture rate for ABG II implants was reviewed with national statistics, using Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) data. National revision rates for periprosthetic fracture were used to compare ABG II with all other cementless femoral stems.

Result

ABG II stems accounted for 1% (2719 implants) of all femoral stem implants in Australia during the 12‐year review period, compared to 23% (587 implants) in Launceston Hospitals. Although the Launceston cumulative percent revision rate for the ABG II stem was lower than the National rate at all time points, the reasons for revision were similar. The most common reason for revision of ABG II was fracture (56.8%), followed by loosening (15.3%). This differs from the reasons for revision in other cementless prostheses (loosening 23.9%, fracture 20.8%, dislocation 18.7%). Cumulative percent revision rates from late periprosthetic fracture, were higher for the ABG II stem than other cementless femoral prostheses.

Conclusion

This review of the AOANJRR has confirmed a local and national higher revision rate of the ABG II stem due to late periprosthetic fracture compared with other cementless stems. Stem design must be considered to reduce the risk of late periprosthetic fracture.

Short-term success of proximal bone stock preservation in short hip stems: a systematic review of the literature

Total hip arthroplasty is performed more frequently in younger patients nowadays, making long-term bone stock preservation an important topic. A mechanism for late implant failure is periprosthetic bone loss, caused by stress shielding around the hip stem due to different load distribution. Short stems are designed to keep the physical loading in the proximal part of the femur to reduce stress shielding. The aim of this review is to give more insight into how short and anatomic stems behave and whether they succeed in preservation of proximal bone stock.

A systematic literature search was performed to find all published studies on bone mineral density in short and anatomic hip stems. Results on periprosthetic femoral bone mineral density, measured with dual-energy X-ray absorptiometry (DEXA), were compiled and analysed per Gruen zone in percentual change.

A total of 29 studies were included. In short stems, Gruen 1 showed bone loss of 5% after one year (n = 855) and 5% after two years (n = 266). Gruen 7 showed bone loss of 10% after one year and –11% after two years. In anatomic stems, Gruen 1 showed bone loss of 8% after one year (n = 731) and 11% after two years (n = 227). Gruen 7 showed bone loss of 14% after one year and 15% after two years.

Short stems are capable of preserving proximal bone stock and have slightly less proximal bone loss in the first years, compared to anatomic stems.

Cite this article: EFORT Open Rev 2021;6:1040-1051. DOI: 10.1302/2058-5241.6.210030

No difference for changes in BMD between two different cementless hip stem designs 2 years after THA

This study evaluates how 2 different total hip arthroplasty (THA) stems compares regarding adaptive bone remodelling. The stems are both proximally porous coated, aiming for proximal fixation, but with different dispersal of the coating. They are also differently designed regarding the distal tip of the stem. We aimed to investigate if there is a difference in periprosthetic adaptive bone remodelling between two different designs. From February 2016 to September 2017, we randomised 62 patients, 1:1 (mean age = 64 years, Female/Male = 28/34), scheduled for an uncemented THA to receive either an EBM or a BM THA stem. We performed dual-energy x-ray absorptiometry (DEXA) scans within a week after surgery and at 3, 6, 12 and 24 months with measurements of bone mineral density (BMD) in the 7 Gruen zones (region of interest (ROI) 1–7). Additionally, Oxford Hip Score and Harris Hip Score were collected at 6, 12 and 24 months. We found a decrease in BMD between the postoperative and the 24-months values in all ROIs for both stems. The greatest decrease over time was seen for both groups in the ROI1 (BM = − 8.4%, p = 0.044, and EBM = − 6.5%, p = 0.001) and ROI7 (BM = − 7%, p = 0.005, and EBM = − 8.6%, p < 0.0005). We found a tendency in ROI2–4 of a higher degree of bone loss in the EBM group. However, this difference only continued beyond 6 months in ROI4 (24 months: BM = − 1.2% and EBM = − 2.8%, p = 0.001). The stems show similar adaptive bone remodelling and are clinically performing well.

Perioperative patient-specific factors-based nomograms predict short-term periprosthetic bone loss after total hip arthroplasty

BACKGROUND

Although medical intervention of periprosthetic bone loss in the immediate postoperative period was recommended, not all the patients experienced periprosthetic bone loss after total hip arthroplasty (THA). Prediction tools that enrolled all potential risk factors to calculate an individualized prediction of postoperative periprosthetic bone loss were strongly needed for clinical decision-making.

METHODS

Data of the patients who underwent primary unilateral cementless THA between April 2015 and October 2017 in our center were retrospectively collected. Candidate variables included demographic data and bone mineral density (BMD) in spine, hip, and periprosthetic regions that measured 1 week after THA. Outcomes of interest included the risk of postoperative periprosthetic bone loss in Gruen zone 1, 7, and total zones in the 1st postoperative year. Nomograms were presented based on multiple logistic regressions via R language. One thousand Bootstraps were used for internal validation.

RESULTS

Five hundred sixty-three patients met the inclusion criteria were enrolled, and the final analysis was performed in 427 patients (195 male and 232 female) after the exclusion. The mean BMD of Gruen zone 1, 7, and total were decreased by 4.1%, 6.4%, and 1.7% at the 1st year after THA, respectively. 61.1% of the patients (261/427) experienced bone loss in Gruen zone 1 at the 1st postoperative year, while there were 58.1% (248/427) in Gruen zone 7 and 63.0% (269/427) in Gruen zone total. Bias-corrected C-index for risk of postoperative bone loss in Gruen zone 1, 7, and total zones in the 1st postoperative year were 0.700, 0.785, and 0.696, respectively. The most highly influential factors for the postoperative periprosthetic bone loss were primary diagnosis and BMD in the corresponding Gruen zones at the baseline.

CONCLUSIONS

To the best of our knowledge, our study represented the first time to use the nomograms in estimating the risk of postoperative periprosthetic bone loss with adequate predictive discrimination and calibration. Those predictive models would help surgeons to identify high-risk patients who may benefit from anti-bone-resorptive treatment in the early postoperative period effectively. It is also beneficial for patients, as they can choose the treatment options based on a reasonable expectation following surgery.

Efficiency of Zoledronic Acid in Inhibiting Accelerated Periprosthetic Bone Loss After Cementless Total Hip Arthroplasty in Osteoporotic Patients: A Prospective, Cohort Study

Objective

To investigate the influence of preoperative osteopenia/osteoporosis on periprosthetic bone loss after total hip arthroplasty (THA) and the efficiency of zoledronate (ZOL) treatment in periprosthetic bone preservation.

Methods

This multicenter, prospective cohort study was conducted in four centers between April 2015 and October 2017. Patients were assigned to Normal BMD, Osteopenia, and Osteoporosis+ZOL groups. Patients with osteopenia received daily oral calcium (600 mg/d) and vitamin D (0.5 μg/d), while patients in the Osteoporosis+ZOL group received additional ZOL annually (5 mg/year). Periprosthetic bone mineral density (BMD) in seven Gruen zones, radiographic parameters, Harris hip score, EuroQol 5‐Dimensions (EQ‐5D) score, and BMD in hip and spine were measured within 7 days, 3 months, 12 months postoperation and annually thereafter.

Results

A total of 266 patients were enrolled, while 81 patients that completed the first year follow‐up were involved in the statistical analysis. The mean follow‐up time was 1.3 years. There were significant decreases of mean BMD in total Gruen zones (−4.55%, P < 0.05) and Gruen zone 1 (−10.22%, P < 0.01) in patients with osteopenia during the first postoperative year. Patients in the Osteoporosis+ZOL group experienced a marked increase in BMD in Gruen zone 1 (+16%) at the first postoperative year, which had a significant difference when compared with the Normal BMD group (P < 0.05) and the Osteopenia Group (P < 0.001). Low preoperative BMD in hip and spine was predictive of bone loss in Gruen zone 1 at 12 months after THA in patients with normal BMD (R² = 0.40, P < 0.05).

Conclusions

Patients with osteopenia are prone to higher bone loss in the proximal femur after cementless total hip arthroplasty (THA). ZOL, not solely calcium and vitamin D, could prevent the accelerated periprosthetic bone loss after THA in patients with osteopenia and osteoporosis.

High periprosthetic bone mineral density measured in immediate postoperative period may not guarantee less periprosthetic bone loss in the proximal femur after cementless total hip arthroplasty - A retrospective study

Background

Total hip arthroplasty is the most common orthopaedic procedure for the end-stage hip diseases. Periprosthetic bone loss is closely related to the increased risk of implant loosening and periprosthetic fractures, but the predictive value of periprosthetic bone mineral density (BMD) measured immediately after surgery has not yet been investigated.

Methods

From April 2015 to October 2017, 64 patients with femoral neck fracture, hip osteoarthritis, femoral head necrosis, or developmental dysplasia of the hip underwent unilateral total hip arthroplasty. Demographic data, bone mineral density of the hip and spine, periprosthetic BMD of 7 Gruen zones, and radiographic parameters measured preoperatively, 1 week, 3 months, and 12 months after surgery were collected. A p value < 0.05 was considered to be statistically significant.

Results

Significant decreases of the periprosthetic BMD were found in Gruen zone 1 (− 8.0%; p < 0.05), Gruen zone 2 (− 6.3%; p < 0.05), Gruen zone 7 (− 8.6%; p < 0.05), and total Gruen zone (− 4.7%; p < 0.05) in the first postoperative year, compared with the values measured 1 week after surgery. The relationship between the preoperative BMD of the hip/spine and the BMD of Gruen zone 1 and Gruen zone 7 measured 1 week after surgery did not reach statistical significance. The multiple linear regression analysis illustrated that the bone loss in Gruen zone 7 at the end of the follow-up period was negatively affected (β = − 0.703) by the BMD of Gruen zone 7 measured 1 week after surgery, with a R² of 0.486 (p < 0.05). Similar results were also found in Gruen zone 1 (β = − 0.448, R² = 0.186; p < 0.05).

Conclusion

There were marked decreases in periprosthetic BMD of the proximal femur in the first postoperative year. The predictive values of preoperative BMD of hip and spine on periprosthetic bone loss after THA were limited. Higher periprosthetic BMD measured in immediate postoperative period may not guarantee less periprosthetic bone loss in the proximal femur after cementless THA.

Good stability of a cementless, anatomically designed femoral stem in aging women: a 9-year RSA study of 32 patients

Background and purpose - We previously reported a transient, bone mineral density (BMD)-dependent early migration of anatomically designed hydroxyapatite-coated femoral stems with ceramic-ceramic bearing surfaces (ABG-II) in aging osteoarthritic women undergoing cementless total hip arthroplasty. To evaluate the clinical significance of the finding, we performed a follow-up study for repeated radiostereometric analysis (RSA) 9 years after surgery. Patients and methods - Of the 53 female patients examined at 2 years post-surgery in the original study, 32 were able to undergo repeated RSA of femoral stem migration at a median of 9 years (7.8-9.3) after surgery. Standard hip radiographs were obtained, and the subjects completed the Harris Hip Score and Western Ontario and McMaster Universities Osteoarthritis Index outcome questionnaires. Results - Paired comparisons revealed no statistically significant migration of the femoral stems between 2 and 9 years post-surgery. 1 patient exhibited minor but progressive RSA stem migration. All radiographs exhibited uniform stem osseointegration. No stem was revised for mechanical loosening. The clinical outcome scores were similar between 2 and 9 years post-surgery. Interpretation - Despite the BMD-related early migration observed during the first 3 postoperative months, the anatomically designed femoral stems in aging women are osseointegrated, as evaluated by RSA and radiographs, and exhibit good clinical function at 9 years.

Daily activity and initial bone mineral density are associated with periprosthetic bone mineral density after total hip arthroplasty

OBJECTIVES

To evaluate periprosthetic bone mineral density (BMD) changes around a cementless short tapered-wedge stem and determine correlations between BMD changes and various clinical factors, including daily activity, after total hip arthroplasty (THA) with a tapered-wedge stem.

METHODS

65 patients underwent THA with a TriLock BPS stem. At baseline and at 6, 12, and 24 months postoperatively the BMD of the 7 Gruen zones were evaluated using dual-energy x-ray absorptiometry. Correlations were determined between BMD changes and clinical factors, including the Harris Hip Score, body mass index, University of California at Los Angeles (UCLA) activity rating score, age at surgery, and initial spine BMD. Radiographic parameters, including the proximal femoral geometry (Dorr Classification), canal filling ratio, canal flare index, and calcar-to-canal ratio were also assessed.

RESULTS

Minimal BMD changes were noted in the distal femur. However, significant BMD loss was noted in zone 7 at each time point. BMD loss was also noted in zone 1 at 6 and 12 months postoperatively, but BMD recovered after 18 months. Significant positive correlations were noted between BMD changes and the UCLA activity score in zones 1, 6, and 7. Additionally, negative correlations were noted between BMD changes and the preoperative lumbar BMD in zones 2 and 3. No correlations were noted between BMD changes and the radiographic parameters. Periprosthetic BMD was was virtually unchanged in the proximal femur, especially Gruen zone 1.

CONCLUSIONS

Daily activity may reflect improvements in periprosthetic bone quality after THA; however, the use of this tapered-wedge stem is not recommended in patients with poor bone quality.

A plasma-sprayed titanium proximal coating reduces the risk of periprosthetic femoral fracture in cementless hip arthroplasty

BACKGROUND

The design of femoral component used in total hip arthroplasty is known to influence the incidence of periprosthetic femoral fractures (PFFs) in cementless hip arthroplasty.

OBJECTIVE

This study was undertaken to determine if 2 potential changes to an existing ABG II-standard cementless implant - addition of a roughened titanium plasma-sprayed proximal coating (ABG II-plasma) and lack of medial scales (ABG II-NMS) could decrease the risk of PFF in the intraoperative and early postoperative periods.

METHODS

Six pairs of human cadaveric femurs were harvested and divided into 2 groups, each receiving either of the altered implants and ABG II-standard (control). Each implant was tested in a biomechanical setup in a single-legged stance orientation. Surface strains were measured in intact femurs, during implant insertion, cyclic loading of the bone with the implant, and loading to failure. Strains with the ABG II-standard and the altered implants were compared.

FINDINGS

ABG II-plasma showed better load-bearing capacity, with an average 42% greater failure load than that of ABG II-standard. The cortical hoop, axial and mean strains ABG II-plasma were less than those of ABG II-standard, demonstrating decreased tensile behaviour and better load transfer to the proximal femur. The final residual hoop strains in ABG II-plasma were closer to those of intact bone as compared to the standard stem. No differences in strains were observed between the standard stem and ABG II-NMS.

CONCLUSION

The increased load-bearing capacity and decreased proximal surface strains on femurs implanted with ABG II-plasma stem should reduce the risks of intraoperative and early postoperative PFF.

Stem anteversion affects periprosthetic bone mineral density after total hip arthroplasty

AIMS

The present study aimed to evaluate periprosthetic bone mineral density (BMD) changes around a cementless short tapered-wedge stem used for total hip arthroplasty (THA) and to determine the correlation between BMD changes and stem alignment after THA.

METHODS

The study included 21 patients (21 joints) who underwent THA with a TriLock stem. At baseline and 6, 12, 18, and 24 months postoperatively, the BMDs in the 7 Gruen zones were evaluated using dual-energy X-ray absorptiometry. BMD changes and stem alignment, that is, anteversion, varus, and anterior tilt, were correlated.

RESULTS

Minimal BMD changes were found in the distal femur (Gruen zones 3, 4, and 5), but significant BMD loss was noted in zone 7. BMD loss was also noted in zone 1 at 6 and 12 months postoperatively, but it recovered after 18 months. No correlation was found between BMD changes and anterior tilt. However, significant negative correlations were found between BMD changes and anteversion. Furthermore, significant negative correlations were found between BMD changes and varus in Gruen zone 1, while positive correlations were found between BMD changes and varus in Gruen zone 7.

CONCLUSIONS

We demonstrated that periprosthetic BMD was well maintained in the proximal femur after THA with a short tapered-wedge stem and that stem anteversion affects periprosthetic BMD after THA.

Densitometric evaluation of bone remodelling around Trabecular Metal Primary stem: a 24-month follow-up

BACKGROUND

Today, an increasing number of total hip arthroplasty (THA) procedures are being performed. Osseointegration is a physiological phenomenon that leads to the direct anchorage of an implant by the formation of bony tissue around the implant without the growth of fibrous tissue at the bone-implant interface. Several factors may affect this phenomenon: some of these depend on the patient and others may depend on implant design and materials. Variations in periprosthetic bone mineral density (BMD) can be studied through several scans by dual energy X-ray absorptiometry (DEXA) around the femoral stem.

AIMS

The purpose of this study is to investigate correlations between periprosthetic BMD and the factors affecting osseointegration.

METHODS

We retrospectively analysed patients who underwent primary THA. In all the patients, Trabecular Metal Primary (TMP), a standard uncemented tapered stem with a proximal porous tantalum coating, was implanted. Preoperatively, postoperatively, 3 and 6 months, 1 year and 2 years after implantation, DEXA scans were performed around the femoral stem. The patients were matched for diagnosis, sex, BMD of the lumbar spine and contralateral femur, Body Mass Index and age.

RESULTS

One hundred and eight patients (51 males and 57 females) with a mean age of 73 years were studied. Different BMD changing patterns were observed and a greater bone resorption was noted in all the conditions associated with poor bone quality.

DISCUSSION

The proximal coating of Trabecular Metal Primary (TMP) seemed to be effective in promoting new bone formation in the proximal femur also in the conditions associated with poor bone quality.

CONCLUSIONS

At the present time, DEXA is considered the most reliable tool for evaluating bone remodelling after THA.

Postoperative development of bone mineral density and muscle strength in the lower limb after cemented and uncemented total hip replacement

BACKGROUND

Numerous studies have shown reduction of periprosthetic bone mineral density (BMD) after hip replacement. The effect on the whole limb, however, is still unexplored. This study's objective was to analyse the postoperative development of BMD and muscle strength of the limb after total hip replacement (THR) and to determine links between these parameters.

METHODS

55 patients, who underwent THR, were included. Depending on therapeutic indication, either an uncemented stem (Group A, n=30) or a cemented stem (Group B, n=25) has been implanted. In the limbs, the measurement of BMD using DEXA and the maximum isometric muscle strength, detected by a leg press, were undertaken preoperatively and after 3, 6 and 12 months.

RESULTS

A total of 12 patients (Group A: n = 6, Group B: n = 6) were excluded due to reasons which were not relevant to the study. So, the results refer to the data of 43 patients. In Group A (uncemented, n = 24), a significant decrease of BMD on the operated extremity was seen after 3, 6 and 12 months compared with preoperative values. Isometric muscle strength on the affected extremity increased significantly after 6 and 12 months. In Group B (cemented, n = 19), with a lower baseline compared to group A, an increase in BMD of the affected limb was seen postoperatively. This rise was significant after 12 months. With regard to the isometric muscle strength, a significant increase could be observed in this group after 6 and 12 months.

CONCLUSION

Analogous to postoperative reduction of periprosthetic bone density, a decrease of the entire limb BMD on the operated leg occurred after implantation of uncemented hip stems. In contrast, an increase in BMD was recorded for cemented stems. Regardless of the type of anchoring, a substantial increase in muscular strength could be observed postoperatively in both groups.

Painful prosthesis: approaching the patient with persistent pain following total hip and knee arthroplasty

BACKGROUND

Symptomatic severe osteoarthritis and hip osteoporotic fractures are the main conditions requiring total hip arthroplasty (THA), whereas total knee arthroplasty (TKA) is mainly performed for pain, disability or deformity due to osteoarthritis. After surgery, some patients suffer from "painful prosthesis", which currently represents a clinical problem.

METHODS

A systematic review of scientific literature has been performed. A panel of experts has examined the issue of persistent pain following total hip or knee arthroplasty, in order to characterize etiopathological mechanisms and define how to cope with this condition.

RESULTS

Four major categories (non infective, septic, other and idiopathic causes) have been identified as possible origin of persistent pain after total joint arthroplasty (TJA). Time to surgery, pain level and function impairment before surgical intervention, mechanical stress following prosthesis implant, osseointegration deficiency, and post-traumatic or allergic inflammatory response are all factors playing an important role in causing persistent pain after joint arthroplasty. Diagnosis of persistent pain should be made in case of post-operative pain (self-reported as VAS ≥3) persisting for at least 4 months after surgery, or new onset of pain (VAS ≥3) after the first 4 months, lasting ≥2 months. Acute pain reported as VAS score ≥7 in patients who underwent TJA should be always immediately investigated.

CONCLUSIONS

The cause of pain needs always to be indentified and removed whenever possible. Implant revision is indicated only when septic or aseptic loosening is diagnosed. Current evidence has shown that peri-and/or post-operative administration of bisphosphonates may have a role in pain management and periprosthetic bone loss prevention.

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.

Measurement of early bone loss around an uncemented femoral stem

BACKGROUND AND PURPOSE

Dual-energy X-ray absorptiometry (DXA) is a precise method to study changes in bone mineral density (BMD), including the pattern of bone remodeling around an implant. Results from implant studies are usually presented as changes in BMD as a function of time. The baseline and reference value for such calculations is the first measurement after the operation. The baseline measurement has been performed at different time points in different studies. If there is rapid bone loss immediately after an operation, this will influence the reference value and hence the results. To evaluate DXA as a method, we studied the very early changes by doing 3 DXA measurements within the first 2 weeks after surgery.

PATIENTS AND METHODS

We included 23 hips in 23 patients who were operated with an uncemented total hip prosthesis (THP). Each Gruen region was measured with DXA at 1, 5, and 14 days, and 3 and 12 months after the operation. 16 of the patients completed all 5 follow-ups.

RESULTS

There was no detectable change in BMD in the first 14 days after the operation. In all zones, the lowest BMD was measured after 3 months.

INTERPRETATION

We conclude that DXA measurements done within 14 days after the operation can be used as reference measurements for later follow-up studies.

Quality of intertrochanteric cancellous bone as predictor of femoral stem RSA migration in cementless total hip arthroplasty

In cementless total hip arthroplasty, osteoporosis may jeopardize the achievement of immediate stability and lead to migration of anatomically shaped femoral stems. Poor quality of proximal cancellous bone per se may also affect the rate of osseointegration. In a selected group of female total hip arthroplasty patients (mean age 64 years) with unremarkable medical history, intertrochanteric cancellous bone biopsy was taken from the site of stem implantation. Local bone quality, determined by structural μCT imaging and destructive compression testing of the biopsy tissue, was used as the predictor of three-dimensional stem migration determined by radiostereometric analysis (RSA) up to 24 months. The patients exhibited major differences in mechanical properties of the intertrochanteric cancellous bone, which were closely related to the structural parameters calculated from μCT data. Unexpectedly, the major differences observed in the quality of trochanteric cancellous bone had only minor reflections in the RSA migration of the femoral stems. In statistical analysis, the μCT-based bone mineral density quartile (low, middle, high) was the only significant predictor for stem translation at 24 months (p=0.022) but only a small portion (R(2)=0.16) of the difference in translation could be explained by changes in bone mineral density quartile. None of the other parameters investigated predicted stem migration in translation or rotation. In conclusion, poor quality of intertrochanteric cancellous bone seems to contribute to the risk of implant migration less than expected. Probably also the importance of surgical preservation of intertrochanteric cancellous bone has been over-emphasized for osseointegration of cementless stem.

Study of bone remodeling of two models of femoral cementless stems by means of DEXA and finite elements

BACKGROUND

A hip replacement with a cemented or cementless femoral stem produces an effect on the bone called adaptive remodelling, attributable to mechanical and biological factors. All of the cementless prostheses designs try to achieve an optimal load transfer in order to avoid stress-shielding, which produces an osteopenia.Long-term densitometric studies taken after implanting ABG-I and ABG-II stems confirm that the changes made to the design and alloy of the ABG-II stem help produce less proximal atrophy of the femur. The simulation with FE allowed us to study the biomechanical behaviour of two stems. The aim of this study was, if possible, to correlate the biological and mechanical findings.

METHODS

Both models with prostheses ABG-I and II have been simulated in five different moments of time which coincide with the DEXA measurements: postoperative, 6 months, 1, 3 and 5 years, in addition to the healthy femur as the initial reference. For the complete comparative analysis of both stems, all of the possible combinations of bone mass (group I and group II of pacients in two controlled studies for ABG-I and II stems, respectively), prosthetic geometry (ABG-I and ABG-II) and stem material (Wrought Titanium or TMZF) were simulated.

RESULTS AND DISCUSSION

In both groups of bone mass an increase of stress in the area of the cancellous bone is produced, which coincides with the end of the HA coating, as a consequence of the bottleneck effect which is produced in the transmission of loads, and corresponds to Gruen zones 2 and 6, where no osteopenia can be seen in contrast to zones 1 and 7.

CONCLUSIONS

In this study it is shown that the ABG-II stem is more effective than the ABG-I given that it generates higher tensional values on the bone, due to which proximal bone atrophy diminishes. This biomechanical behaviour with an improved transmission of loads confirmed by means of FE simulation corresponds to the biological findings obtained with Dual-Energy X-Ray Absorptiometry (DEXA).

Retrospective and consecutive analysis of the long-term outcomes of the SBG stem: a 15-year follow-up study

BACKGROUND

In 1991, 230 cementless total hip arthroplasties (THAs) with anatomical Stolzalpe-Buchner-Graf (SBG) stems were implanted in 230 patients at our hospital. Patients were examined retrospectively and consecutively 15 years after the operations.

METHODS

In total, 118 patients were available for follow-up (average 12.8 +/- 3.8 years postoperatively), with 44 examined clinically/radiologically at our hospital and 74 interviewed by telephone. Five THAs needed revision (stem explantation), three for aseptic loosening. Average patient age at the time of surgery was 61 years (27-91 years). For all THAs, we implanted ceramic-to-metal heads in combination with ultra-high molecular weight polyethylene inlay (ceramic/polyethylene and metal/polyethylene articulating components).

RESULTS

The survival rate of the SBG stem was 98.13% (CI 94.32-99.39%) with aseptic loosening as the endpoint and 96.98% (CI 92.85-98.74%) with revision and stem explantation for any other reason as the endpoint. The average Harris Hip Score was 36.0 +/- 6.9 (range 22-45) preoperatively, increasing to 88.2 +/- 15.3 (30-100) for clinically evaluated patients and 80.3 +/- 11.3 (27-91) for telephone-interviewed patients at 15 years postoperatively. Osteolysis and radiolucent lines around the prosthetic stem were rarely observed (mainly at the proximal diaphysis).

CONCLUSION

These follow-up results emphasize the excellent long-term outcomes associated with the SBG stem.

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.

Female patients with low systemic BMD are prone to bone loss in Gruen zone 7 after cementless total hip arthroplasty

BACKGROUND AND PURPOSE

Factors that lead to periprosthetic bone loss following total hip arthroplasty (THA) may not only depend on biomechanical implant-related factors, but also on various patient-related factors. We investigated the association between early changes in periprosthetic bone mineral density (BMD) and patient-related factors.

PATIENTS AND METHODS

39 female patients underwent cementless THA (ABG II) with ceramic-ceramic bearing surfaces. Periprosthetic BMD in the proximal femur was determined with DXA after surgery and at 3, 6, 12, and 24 months. 27 patient-related factors were analyzed for their value in prediction of periprosthetic bone loss.

RESULTS

Total periprosthetic BMD was temporarily reduced by 3.7% at 3 months (p < 0.001), by 3.8% at 6 months (p < 0.01), and by 2.6% at 12 months (p < 0.01), but recovered thereafter up to 24 months. Preoperative systemic osteopenia and osteoporosis, but not the local BMD of the operated hip, was predictive of bone loss in Gruen zone 7 (p = 0.04), which was the only region with a statistically significant decrease in BMD (23%, p < 0.001) at 24 months. Preoperative serum markers of bone turnover predicted the early temporary changes of periprosthetic BMD. The other patient-related factors failed to show any association with the periprosthetic BMD changes.

INTERPRETATION

Female patients with low systemic BMD show greater bone loss in Gruen zone 7 after cementless THA than patients with normal BMD. Systemic DXA screening for osteoporosis in postmenopausal patients before THA could be used to identify patients in need of prophylactic anti-resorptive therapy.

Comparison between DEXA and finite element studies in the long-term bone remodeling of an anatomical femoral stem

The implantation of a cemented or cementless femoral stem changes the physiological load transfer on the femur producing an effect on the bone called adaptative remodeling. The patterns of this remodeling are attributed to mechanical and biological factors, and those changes in bone mineral density have been determined in long-term densitometry studies. This technique has proved to be a useful tool able to quantify small changes in bone density in different femoral areas, and it is considered to be ideal for long-term studies. On the other hand, the finite element (FE) simulation allows the study of the biomechanical changes produced in the femur after the implantation of a femoral stem. The aim of this study was to contrast the findings obtained from a 5 year follow-up densitometry study that used a newly designed femoral stem (73 patients were included in this study), with the results obtained using a finite element simulation that reproduces the pattern of load transfer that this stem causes on the femur. In this study we have obtained a good comparison between the results of stress of FE simulation and the bone mass values of the densitometry study establishing a ratio between the increases in stress (%) versus the increases in bone density (%). Hence, the changes in bone density in the long term, compared with the healthy femur, are due to different load transfers after stem implantation. It has been checked that in the Gruen zone 7 at 5 years, the most important reduction in stress (7.85%) is produced, which coincides with the highest loss of bone mass (23.89%). Furthermore, the simulation model can be used with different stems with several load conditions and at different time periods to carry out the study of biomechanical behavior in the interaction between the stem and the femur, explaining the evolution of bone density in accordance to Wolff's law, which validates the simulation model.