Femoral bone density changes after total hip arthroplasty with uncemented taper-design stem: a five year follow-up study

Stress shielding effect after total hip arthroplasty varies between combinations of stem design and stiffness-a comparing biomechanical finite element analysis

PURPOSE

Total hip arthroplasty (THA) has become a highly frequent orthopaedic procedure. Multiple approaches have been made to design the femoral component for THA with a mechanical behaviour as close as possible to a natural femur. The aim of this study was to compare different combinations of design and biomechanical properties of THA prostheses and their impact on stress shielding of the periprosthetic bone.

METHODS

Virtual implantation of different stem designs (straight standard stem, straight short stem, anatomical short stem) by finite element analysis based on in vivo data from computer tomography was performed. For each stem, three grades of stiffness were generated, followed by a strain analysis.

RESULTS

Reduction of stem stiffness led to less stress shielding. Implantation of an anatomical short-stem prosthesis with low stiffness provided the most physiological strain-loading effect (p < 0.001).

CONCLUSION

A combination of a short and an anatomically designed stem with a low stiffness might provide a more physiological strain transfer during THA. Biomechanical properties of the femoral component for THA should be considered as a multifactorial function of dimensions, design, and stiffness.

Longitudinal Radiographic Bone Density Measurement in Revision Hip Arthroplasty and Its Correlation with Clinical Outcome

The subjective analysis of conventional radiography represents the principal method for bone diagnostics in endoprosthetics. Alternative objective quantitative methods are described but not commonly used. Therefore, semi-quantitative methods are tested using digital computation and artificial intelligence to standardize, simplify, and ultimately improve the assessment. This study aimed to evaluate the correlation between relative density progressions and clinical outcomes. Radiographs and clinical examinations before and 24 and 48 weeks after surgery were obtained from sixty-eight patients with a modular hip stem. For the calculation of the relative bone density, the modal gray values of the Gruen zones were measured using ImageJ and were normalized by gray values of the highest and lowest ROI. The clinical outcomes were measured according to the Harris hip score before evaluating them for correlations. Analyses were performed separately for subgroups and bone regions. The Harris hip score increased from 44.15 ± 15.00 pre-operatively to 66.20 ± 13.87 at the latest follow-up. The relative bone density adjustment of Gruen zone 7 showed a significant correlation to its clinical outcome. Other bone adaptations could be realistically reproduced and differences by regional zones and patients' histories visualized. Next to the simplicity and that no additional examination is required, the method provides good semi-quantitative results and visualizes adaptations, which make it suitable for use.

The anatomical shape of the proximal femur correlates with the distal femur anatomy

PURPOSE

In the case of stemmed implants for lower limb joint arthroplasty procedures, implant stability and survivorship generally rely on the strength of fixation in the medullary canal regardless of whether the procedure is primary or revision surgery. This study aimed to investigate the relationship between the proximal (Dorr classification) and distal (Citak classification) femoral canal geometry classification systems.

METHODS

A total of 200 patients who received standing long leg radiographs (hip to ankle) at our institution were identified using our institutional electronic radiology database. Patients were recruited into 4 groups. There were 100 male and 100 female patients with each of those being split into 50 right-sided and 50 left-sided long-leg standing anteroposterior (AP) radiographs. Two independent, blinded observers reviewed each radiograph on two separate occasions, with a minimum of a one-week interval between sittings to review each respective radiograph.

RESULTS

No statistically significant correlation was found between demographic data and clinical measurements. A statistically significant correlation was found between the patient's age and BMI results and Citak and Dorr measurements. There was excellent inter-observer and intra-observer agreement for the Citak and Dorr Classifications. The mean Cronbach's α coefficient was 0.96 (range 0.93-0.98) for the Citak Classification and 0.95 (range 0.83-0.97) for the Dorr Classification. There was also an excellent intra-observer agreement with 95% average pairwise per cent agreement for the Citak Classification and 95% average pairwise per cent agreement for the Dorr classification. A statistically significant positive correlation was found between Dorr Calcar Isthmus and Citak Ratio (p < 0.05).

CONCLUSION

In this study, the Dorr and Citak classifications are put into relation to each other for the first time. The morphology of the femur was investigated in its entirety and it was shown that there was a positive correlation between the anatomical shape of the proximal and distal medullary canals.

Bionic reconstruction of tension trabeculae in short-stem hip arthroplasty: a finite element analysis

BACKGROUND

Short-stem hip arthroplasty (SHA) is characterized by metaphyseal load transfer that effectively preserves the bone stock, but still suffers from stress shielding in the proximal femur. We designed a tension screw to mimic tension trabeculae in the new bionic collum femoris preserving (BCFP) short stem for bionic reconstruction, aiming to restore the biomechanics of hip joint.

METHODS

Native femur finite element model was constructed to investigate the biomechanics of hip joint based on computed tomography (CT) data. The maximum absolute principal stress/strain cloud chart allowed the direction of stress/strain to be assessed. Six BCFP models with different screw angles (5°, 10°, 15°, 20°, 25°, and 30°) and the Corail model were created. The stress/strain distribution and overall stiffness were compared between each of the BCFP and Corail implanted models.

RESULTS

The native model visualized the transfer pathways of tensile and compressive stress. The BCFP stems showed significantly higher stress and strain distribution in the greater trochanteric region compared to conventional total hip arthroplasty (THA). In particular, the BCFP-5° stem demonstrated the highest average strain in both medial and lateral regions and the overall stiffness was closest to the intact femur.

CONCLUSIONS

Stress transfer pathways of trabecular architecture provide biomechanical insight that serves as the basis for bionic reconstruction. The tension screw improves load transfer pattern in the proximal femur and prevents stress reduction in the greater trochanteric region. The BCFP-5° stem minimizes the stress shielding effect and presents a more bionic mechanical performance.

Design of Titanium Alloy Femoral Stem Cellular Structure for Stress Shielding and Stem Stability: Computational Analysis

The main objective of this study is to design titanium alloy femoral stems with cubic porous structures that will be able to reduce stress shielding and promote stem stability. These porous structure designs were introduced into titanium alloy femoral stems as homogeneous and functionally graded porous structures. First, the cubic cellular structures were simulated under compressive loading to measure the yield and modulus of elasticity for various porosity ranges. Based on the selected porosity range, fifteen different arrangements of radial geometrical functionally graded (FG) designs were developed with average porosities of 30, 50, and 70% respectively. Finite element models were developed with physiological loads presenting three different walking speeds (1, 3, and 5 km/h), where the average human body weight was assumed. Stresses at the bone Gruen zones were measured to check the percentage of stress transfer to the bone for each porous stem design and were compared with the bulk stem. Several FG stem designs were shortlisted for further investigation as candidates for hip implants.

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.

Comparison of Bone Remodeling Between Collum Femoris-Preserving Stems and Ribbed Stems in 1-Stage Bilateral Total Hip Arthroplasty

BACKGROUND This study examined a cohort of patients who underwent bilateral THAs. CFP prostheses and ribbed prostheses were each used on both sides. We assessed the midterm clinical, radiological, and bone remodeling outcomes around prosthesis of these patients. MATERIAL AND METHODS From January 2009 to January 2013, 53 patients were enrolled in our study. We clinically evaluated all patients by recording Harris hip and Oxford hip scores. Some radiological indicators of the femoral prosthesis position were measured. Periprosthetic bone remodeling was assessed via bone mineral density (BMD) measurements. RESULTS The mean preoperative HHS of the CFP group and ribbed group were no significantly different (P=0.570). The neck-shaft angle in the ribbed group was significantly greater than in the CFP group (P<0.001). The CFP group had a greater offset (P<0.001). There was no significant difference in leg-length discrepancy (P=0.727) or Engh score between the 2 groups at the last follow-up (P=0.858). The preoperative BMD was increased at the last follow-up in Gruen zones 3 and 5 (P<0.05) and decreased in Gruen zones 1 and 7 (P<0.05) on the CFP side. BMD was increased in Gruen zone 4 (P=0.007) on the ribbed side. Pearson correlations and rate of complications were not significantly different. CONCLUSIONS Both the CFP and ribbed stem significantly improved the preoperative HHSs and OHSs. The bone remodeling of the CFP stem was more concentrated in the middle and distal regions of the prosthesis, while that of the ribbed stem was more concentrated in the proximal portion of the prosthesis.

An Ultra-Short Femoral Neck-Preserving Hip Prosthesis: A 2-Year Follow-up Study with Radiostereometric Analysis and Dual X-Ray Absorptiometry in a Stepwise Introduction

BACKGROUND

Total hip arthroplasty (THA) with a diaphyseal stem may risk bone loss. In order to save proximal bone stock in young patients with a high activity level and a long life expectancy, the interest in short stems has evolved. The purpose of this prospective observational cohort study was to evaluate the fixation of, and bone remodeling around, the Primoris femoral neck-preserving hip implant.

METHODS

Fifty younger patients with end-stage osteoarthritis were managed with the Primoris hip implant. We evaluated bone mineral density (BMD) using dual x-ray absorptiometry (DXA) and implant migration using radiostereometric analysis (RSA). A region-of-interest (ROI) protocol for 4 ROIs was applied to assess BMD. The association between BMD and migration was evaluated to determine the fixation of the Primoris implant and bone remodeling in the proximal part of the femur. Follow-up evaluation was performed at regular intervals from day 1 (baseline) until 24 months after surgery.

RESULTS

The major stem migrations were subsidence (Y axis; mean, 0.38 mm) at 6 weeks and varus tilt (rotation) (Z axis; mean, 0.93°) at 6 to 12 months. In ROI4 (the calcar area), a significant gain in bone was found with a mean difference of 4.1% (95% confidence interval [CI], 0.8% to 7.4%; p < 0.02) at 24 months postoperatively. Significant bone loss was found in ROI1 and ROI2, with a mean difference of -4.9% (95% CI, -7.4% to -2.4%; p = 0.0003) and -8.9% (95% CI, -11.5% to -6.2%; p = 0.0001), respectively. Linear regression and multivariate regression analysis showed a significant negative association between maximal total point motion and BMD (p = 0.02, R = 15%; and p < 0.05, R = 26%, respectively).

CONCLUSIONS

The Primoris component showed satisfactory primary stability with promising results at the 24-month follow-up. DXA scans showed limited stress-shielding with the proximal loading pattern of the Primoris. Better bone quality was associated with less implant migration.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Computer-aided osteoporosis detection from DXA imaging

BACKGROUND AND OBJECTIVE

Osteoporosis is a skeletal disease caused by a high rate of bone tissue loss, and it is a major cause of bone fracture. In contemporary society, osteoporosis is more common than cancer and stroke and results in a higher rate of morbidity and mortality in the human population. Osteoporosis can conclusively be diagnosed with dual energy X-ray absorptiometry (DXA). In this study, we propose a computer-aided osteoporosis detection (CAOD) technique that automatically measures bone mineral density (BMD) and generates an osteoporosis report from a DXA scan.

METHODS

The CAOD model denoise and segments DXA images using a non-local mean filter, Machine learning pixel label random forest respectively, and locates regions of interest with higher accuracy. Pixel label random forest classifies a pixel either bone or soft tissue; then contours are extracted from binary image to locate regions of interest and calculate BMD from bone and soft tissues pixels. Mean standard deviation and correlation coefficients statistical analysis were used to evaluate the consistency and accuracy of BMD measurements.

RESULTS

During a consistency test of BMD measurements using three consecutive scans from Computerized Imaging Reference Systems' Bona Fide Phantom (CIRS-BFP) for the spine, the CAOD model showed an averaged standard deviation of 0.0029 while the standard deviation from manual measurements on the same data set by three different individuals was recorded as 0.1199. During another correlation study of BMD measurements evaluating real human scan images by the CAOD model versus manual measurement, the model scored a correlation coefficient of R² = 0.9901 while the CIRS-BFP study scored a correlation coefficient of R² = 0.9709.

CONCLUSIONS

The CAOD model increases the preciseness and accuracy of BMD measurements. This CAOD method will help clinicians, untrained DXA operators, and researchers (medical scientists, doctors, and bone researchers) use the DXA system with reliable accuracy and overcome workload challenges. It will also improve osteoporosis diagnosis from DXA systems and increase system performance and value.

Outcome of short versus conventional stem for total hip arthroplasty in the femur with a high cortical index: a five year follow-up prospective multicentre comparative study

BACKGROUND

The uncemented total hip arthroplasty (THA) has become the choice for many hip surgeons. Although conventional uncemented femoral components have a proven track record, there remain concerns about the rate of thigh pain, proximal stress shielding, and consequent loss of bone stock at revision surgery.

METHODS

Inclusion criteria were the following: patients between 50 and 85 years old undergoing primary THA with implant of short (group 1) or conventional (group 2) femoral stem and with femoral shape type A, according to Dorr classification. Clinical follow-up was registered using OHS, HHS, and Womac scores. The radiographic scans were evaluated in order to compare component positioning and bone remodeling at five year follow-up.

RESULTS

We included in the analysis 60 subjects in group 1 and 67 in group 2. No differences were registered between the groups comparing demographic and operative data. One case in group 1 (1.7%) and three cases in group 2 (4.5%) reported an intra-operative fracture. There was a significant improvement in the functional scores in both groups with no significant difference at final follow-up. The incidence of reported thigh pain at follow-up was 14.9% in group 2 and 3.3% in group 1 (p = 0.033). Radiographic analysis documented a difference in terms of stress shielding and thinning of medial and lateral cortex in favour of group 1. Moreover, patients of group 1 showed a higher varus angle at six month follow-up.

CONCLUSION

In patients with high cortical index, a short stem shows better clinical and radiological outcomes at five year follow-up.

Stem length in primary cementless total hip arthroplasty: Does it make a difference in bone remodeling?

PURPOSE

Stem design is usually accused for proximal femoral remodeling following total hip arthroplasty (THA). The aim of this prospective study was to compare the in vivo changes in bone mineral density (BMD) of the proximal femur after implantation of cementless THA with two length alternative stems.

METHODS

Between May 2011 and March 2014, 50 patients, who met our selection criteria and received cementless THA, randomized into two groups. Group A received cementless standard femoral stems, while group B received short stems. Harris Hip Score (HHS) and visual analog scale (VAS) were used for clinical assessment. Stem and cup positions and stability were radiologically evaluated. Dual-energy X-ray absorptiometry was used to follow and compare changes in BMD in different zones of proximal femur between both groups.

RESULTS

After a mean follow-up of 21.4 ± 3.53 months, there was a significant (p < 0.05) improvement in mean HHS and VAS with no significant differences (p > 0.05) between groups. There was no significant difference (p > 0.05) between groups regarding radiological results and rates of complications. The mean overall BMD was decreased by 11.26% for group A and 8.68% for group B at the final follow-up (p > 0.05). The greatest loss was found in greater trochanter region for group A and so for group B, but to a lesser extent (p < 0.05).

CONCLUSIONS

Cementless short stem was not able to hold back proximal femoral bone loss, but only can modify or decrease its incidence within limits.

'Pre-launch' finite element analysis of a short-stem total hip arthroplasty system consisting of two implant types

BACKGROUND

We applied a previously established and validated numerical model to a novel short-stemmed implant for a 'pre-launch' investigation.

METHODS

The implant system consists of two different implant geometries for valgus/varus-positioned proximal femurs with differences in volume distribution, head/neck angle, and calcar alignment. The aim of the design was to achieve a better adaption to the anatomic conditions, resulting in a favourable load transfer. The implant type G showed the best fit to our model, but both stem geometries were implanted; the implant type B was used to compute an 'imperfection scenario'.

FINDINGS

Apparent bone density decreased by 4.3% in the entire femur with the implant type G, and by 12.3% with the implant type B. Bone mass loss was pronounced in the proximal calcar region. Apparent bone density increased at the lateral cortical ring and in the minor trochanter. The apparent bone density in the imperfection scenario was very similar to that of a straight stem, indicating a distal load transfer.

INTERPRETATION

No adverse effects of the A2 short-stemmed implant system on bone remodeling could be detected. The overall bone density reduction was acceptable, and wedge fixation was not observed, indicating that there was no distal load transfer. The simulation of an incongruous implant indicates the sensitivity of our model in response to modifications of implant positioning. Correct implant selection and positioning is crucial when using the A2 system.

Relative radiographic bone density measurement in revision hip arthroplasty and its correlation with qualitative subjective assessment by experienced surgeons

BACKGROUND

Conventional radiography (CR) is the imaging method of choice in monitoring bone remodelling and other stability parameters after total hip arthroplasty (THA). Quantitative roentgen- or computed-tomography-based methods to determine bone density are prone to metal artifacts and often very costly, which is why they are not used as standard in a clinical setting. Since subjective assessment of bone remodelling in CR also has a certain susceptibility to errors, semi-quantitative methods have been developed to help approximate periprosthetic bone density development via CR to open up an additional tool for documentation of radiographic THA follow-up.

OBJECTIVE

Proof-of-principle of a newly designed imaging-software-aided method to measure relative bone density around the femoral stem in a series of conventional radiographs following THA.

METHODS

Eighty-six patients with hip modular tapered, fluted titanium stems were selected from the clinical database and series of baseline and postoperative follow-up radiographs were obtained after 24 and 48 weeks. Relative bone densities were measured per Gruen zones G1-7 with the use of an open-source image analysis package (ImageJ) by means of greyscale histograms. In addition, subjective evaluation of selected cases was performed by three independent, blinded orthopedic surgeons. Besides descriptive and nonparametric analyses, intra-class correlation (ICC) was performed and objective and subjective results were compared by linear regression analysis.

RESULTS

Two individual cases are presented as a proof-of-principle. Increase or decrease of bone density could be measured correctly over time in each case. In a collective analysis there were no significant differences in mean relative bone densities between groups after 24 and 48 weeks, although a positive tendency was visible towards increased bone formation over time. Individual analyses by Gruen zones revealed that some zones, namely the proximal ones (e.g. G6), exhibit a broader scattering than others over time. This could be explained by the design of the evaluated tapered revision stem that achieves distal fixation and allows for proximal micromotion. Correlation analysis with subjective ratings (inter-rater reliability ICC = 0.71) showed a positive correlation with objective results, suggesting a feasibility of the method for clinical use.

CONCLUSIONS

In conclusion the presented method is an easy and accessible tool to quantify relative bone density changes during THA follow-up. It shows a positive correlation to established subjective assessment of bone remodelling and may therefore serve as a quantitative supplement in clinical documentation.

Restoration of proximal periprosthetic bone loss by denosumab in cementless total hip arthroplasty

Denosumab contributed to the restoration of proximal periprosthetic bone loss around the femoral stem that were measured using a DEXA, especially in zone 7, at 1 year after cementless THA in elderly osteoporotic patients.

INTRODUCTION

Although bone quality is an important issue in elderly osteoporotic patients who underwent total hip arthroplasty (THA) with a cementless stem, periprosthetic bone mineral density (BMD) in the proximal femur has been reported to be decreased by 15-40% postoperatively. Some authors have examined the use of several types of bisphosphonates to prevent decreases in BMD in the proximal femur after cementless THA; however, few reports have demonstrated success in restoring BMD in the proximal medial femoral bone, such as zone 7.

METHODS

We conducted prospective study comparing patients who underwent cementless THA administered with denosumab (10 patients) and without denosumab (10 patients). BMD around the femoral stem were measured using a DEXA immediately after surgery, and at 6 months and at 1 year after surgery. No difference was found between the two groups referred to the patient's demographic data.

RESULTS

We found that denosumab displayed definitive effects in increasing the % change in periprosthetic BMD at zone 7 by an average of 7.3% in patients with cementless THA, compared to control group who were given only vitamin D.

CONCLUSION

Denosumab is one of a number of anti-osteoporotic agents to have a definitive effect on the restoration of proximal periprosthetic bone loss, especially in zone 7, after cementless THA. Denosumab contributed to the restoration of decreased periprosthetic BMD to normal levels. As the decrease in BMD in the proximal femur after THA is considered to be apparent at 6-12 months after surgery, it is believed that prevention of the deterioration of bone quality is important in the proximal femur immediately after cementless THA for elderly female patients with osteoporosis.

Long-term bone remodelling around 'legendary' cementless femoral stems

Bone remodelling around a stem is an unavoidable long-term physiological process highly related to implant design. For some predisposed patients, it can lead to periprosthetic bone loss secondary to severe stress-shielding, which is thought to be detrimental by contributing to late loosening, late periprosthetic fracture, and thus rendering revision surgery more complicated.However, these concerns remain theoretical, since late loosening has yet to be documented among bone ingrowth cementless stems demonstrating periprosthetic bone loss associated with stress-shielding.Because none of the stems replicate the physiological load pattern on the proximal femur, each stem design is associated with a specific load pattern leading to specific adaptive periprosthetic bone remodelling. In their daily practice, orthopaedic surgeons need to differentiate physiological long-term bone remodelling patterns from pathological conditions such as loosening, sepsis or osteolysis.To aid in that process, we decided to clarify the behaviour of the five most used femoral stems. In order to provide translational knowledge, we decided to gather the designers' and experts' knowledge and experience related to the design rationale and the long-term bone remodelling of the following femoral stems we deemed 'legendary' and still commonly used: Corail (Depuy); Taperloc (Biomet); AML (Depuy); Alloclassic (Zimmer); and CLS-Spotorno (Zimmer). Cite this article: EFORT Open Rev 2018;3:45-57. DOI: 10.1302/2058-5241.3.170024.

Bone remodelling around the Metha® short stem implant - Clinical and dual-energy x-ray absorptiometry (DXA) results

OBJECTIVE

Bony ingrowth of short stems is under investigation.

METHOD

Over one year bony reactions around the Metha^® stem were investigated using the DXA method in a standardized zonal system (19 ROIs). Clinical results were documented using the HHS.

RESULTS

HHS significantly improved from 46 points to 97 points. After one year bone marrow density (BMD) increased in the lateral distal and lateral proximal areas as well as in the mid medial area. BMD decreased in the proximal medial and mid lateral areas.

CONCLUSION

The concept of metaphyseal ingrowth was confirmed, but distal bony reactions need further investigation.

Finite Element Analysis of porously punched prosthetic short stem virtually designed for simulative uncemented Hip Arthroplasty

Background

There is no universal hip implant suitably fills all femoral types, whether prostheses of porous short-stem suitable for Hip Arthroplasty is to be measured scientifically.

Methods

Ten specimens of femurs scanned by CT were input onto Mimics to rebuild 3D models; their *stl format dataset were imported into Geomagic-Studio for simulative osteotomy; the generated *.igs dataset were interacted by UG to fit solid models; the prosthesis were obtained by the same way from patients, and bored by punching bears designed by Pro-E virtually; cements between femora and prosthesis were extracted by deleting prosthesis; in HyperMesh, all compartments were assembled onto four artificial joint style as: (a) cemented long-stem prosthesis; (b) porous long-stem prosthesis; (c) cemented short-stem prosthesis; (d) porous short-stem prosthesis. Then, these numerical models of Finite Element Analysis were exported to AnSys for numerical solution.

Results

Observed whatever from femur or prosthesis or combinational femora-prostheses, “Kruskal-Wallis” value p > 0.05 demonstrates that displacement of (d) ≈ (a) ≈ (b) ≈ (c) shows nothing different significantly by comparison with 600 N load. If stresses are tested upon prosthesis, (d) ≈ (a) ≈ (b) ≈ (c) is also displayed; if upon femora, (d) ≈ (a) ≈ (b) < (c) is suggested; if upon integral joint, (d) ≈ (a) < (b) < (c) is presented.

Conclusions

Mechanically, these four sorts of artificial joint replacement are stabilized in quantity. Cemented short-stem prostheses present the biggest stress, while porous short-stem & cemented long-stem designs are equivalently better than porous long-stem prostheses and alternatives for femoral-head replacement. The preferred design of those two depends on clinical conditions. The cemented long-stem is favorable for inactive elders with osteoporosis, and porously punched cementless short-stem design is suitable for patients with osteoporosis, while the porously punched cementless short-stem is favorable for those with a cement allergy. Clinically, the strength of this study is to enable preoperative strategy to provide acute correction and decrease procedure time.

Analyzing bone remodeling patterns after total hip arthroplasty using quantitative computed tomography and patient-specific 3D computational models

BACKGROUND

Computational models in the form of finite element analysis technique that incorporates bone remodeling theories along with DEXA scans has been extensively used in predicting bone remodeling patterns around the implant. However, majority of such studies used generic models. Therefore, the aim of this study is to develop patient-specific finite element models of total hip replacement patients using their quantitative computed tomography (QCT) scans and accurately analyse bone remodelling patterns after total hip arthroplasty (THA).

METHODS

Patient-specific finite element models have been generated using the patients' QCT scans from a previous clinical follow-up study. The femur was divided into five regions in proximal-distal direction and then further divided into four quadrants for detailed analysis of bone remodeling patterns. Two types of analysis were performed-inter-patient and intra patient to compare them and then the resulting bone remodeling patterns were quantitatively analyzed.

RESULTS

Our results show that cortical bone density decrease is higher in diaphyseal region over time and the cancellous bone density decreases significantly in metaphyseal region over time. In metaphyseal region, posterior-medial (P-M) quadrant showed high bone loss while diaphyseal regions show high bone loss in anterior-lateral (A-L) quadrant.

CONCLUSIONS

Our study demonstrated that combining QCT with 3D patient-specific models has the ability of monitoring bone density change patterns after THA in much finer details. Future studies include using these findings for the development of a bone remodelling algorithm capable of predicting surgical outcomes for THA patients.

[Influence of preoperative bone mass density in periprosthetic bone remodeling after implantation of ABG-II prosthesis: A 10-year follow-up]

INTRODUCTION

Preoperative bone mass index has shown to be an important factor in peri-prosthetic bone remodelling in short follow-up studies.

MATERIAL AND METHODS

Bone density scans (DXA) were used to perform a 10-year follow-up study of 39 patients with a unilateral, uncemented hip replacement. Bone mass index measurements were made at 6 months, one year, 3 years, 5 years, and 10 years after surgery. Pearson coefficient was used to quantify correlations between preoperative bone mass density (BMD) and peri-prosthetic BMD in the 7 Gruen zones at 6 months, one year, 3 years, 5 years, and 10 years.

RESULTS

Pre-operative BMD was a good predictor of peri-prosthetic BMD one year after surgery in zones 1, 2, 4, 5 and 6 (Pearson index from 0.61 to 0.75). Three years after surgery it has good predictive power in zones 1, 4 and 5 (0.71-0.61), although in zones 3 and 7 low correlation was observed one year after surgery (0.51 and 0.57, respectively). At the end of the follow-up low correlation was observed in the 7 Gruen zones. Sex and BMI were found to not have a statistically significant influence on peri-prosthetic bone remodelling.

CONCLUSION

Although preoperative BMD seems to be an important factor in peri-prosthetic remodelling one year after hip replacement, it loses its predictive power progressively, until not being a major factor in peri-prosthetic remodelling ten years after surgery.

Bone mineral density after implantation of a femoral neck hip prosthesis--a prospective 5 year follow-up

Background

Bone resorption in the proximal femur due to stress shielding has been observed in a number of conventional cementless implants used in total hip arthroplasty. Short femoral-neck implants are claiming less interference with the biomechanics of the proximal femur. The goal of this study was to prospectively investigate the in vivo changes of bone-mineral density as a parameter of bone remodeling around a short, femoral neck prosthesis over the first 5 years following implantation. The secondary goal was to report on its clinical outcome.

Methods

We are reporting on the changes of bone mineral density of the proximal femur and the clinical outcome up to five years after implantation of a short femoral neck prosthesis. Bone mineral density was determined using dual energy x-ray absorptiometry, performed 10 days, three, 12 and 60 months after surgery. 20 patients with a mean age of 47 years (range 17 to 65) were clinically assessed using the Harris Hip Score. The WOMAC was used as a patient-relevant outcome-measure.

Results

In contrast to conventional implants DEXA-scans overall revealed a slight increase of bone mineral density in the proximal femur in the 12 months following the implantation. The Harris Hip Score improved from an average preoperative score of 46 to a postoperative score at 12 months of 91 points and 95 points at 60 months, the global WOMAC index from 5.3 preoperatively to 0.8 at 12 months and 0.6 at 60 months postoperatively.

Conclusion

At 60 months after implantation of a short femoral neck prosthesis, all regions except one (region of interest #5) showed no significant changes in BMD compared to baseline measurements at 10 days which is less to the changes in bone mineral density seen in conventional implants.

Periprosthetic bone remodeling around short stem

Total hip arthroplasty (THA) has become standard treatment for advanced degenerative changes of the hip. A few studies have reported promising clinical outcomes with the Metha stem fixated by metaphyseal anchoring. This study evaluated early bone remodeling around the Metha stem during 12 months of follow-up. The study population included 36 patients (18 women and 18 men) with a mean age of 50.4 years who underwent THA between 2009 and 2011 for advanced degenerative changes of the hip with the Metha stem. Patients were evaluated on the day of surgery, 10 days postoperatively, and then at 3, 6, and 12 months postoperatively. Evaluation included Harris Hip Score and dual-energy x-ray absorptiometry (DEXA) scanning in 7 Gruen zones. At 12 months postoperatively, Harris Hip Score increased significantly by 38 points. A significant change in bone mineral density (BMD) was found immediately after surgery; this change was most pronounced in Gruen zone 3 (+36%), followed by Gruen zones 2 and 5. The smallest postoperative BMD increase was observed in Gruen zone 7 (+3.66%). In contrast, at 3 months postoperatively, a trend toward decreased BMD was observed in all Gruen zones. At 6 months postoperatively, mean BMD decreased in all Gruen zones except for Gruen zone 6. At 12 months postoperatively, mean BMD increased in Gruen zones 2 through 6, with the highest value (30%) observed in Gruen zone 3; in Gruen zones 1 and 2, mean BMD decreased. Short-term assessment of periprosthetic bone remodeling after uncemented Metha stem implantation revealed different host-bone responses. Apparently, the Metha stem can reduce BMD loss in the proximal femur. DEXA is a precise method for assessing BMD changes around implanted Metha stem.

Medium-term comparison of results in obese patients and non-obese hip prostheses with Metha® short stem

INTRODUCTION

Total hip arthroplasty is one of the most successful orthopedic surgeries in terms of results. However, the prevalence of obesity has nearly doubled between 1980 and 2008. There is limited and controversial data on hip replacement results in obese patients. The Metha® prosthesis, introduced in 2004, is a short stem midway between devices maintaining the femoral neck and metaphyseal implants. The purpose of this study was to evaluate the influence of obesity on clinical and radiological results at medium term.

MATERIALS AND METHODS

Eighty-two patients were retrospectively divided into two cohorts based on their BMI. Mean BMI were, respectively, 35.22 kg/m2 in the obese group [30.02-57.79] and 26.15 [23.25-28.72] in the other cohort. Follow-up were 47.16 [26.10-74.33] and 54.06 [28.17-77.73]. The mean ages at surgery were 55 years [39.8-67.8] and 54 [31.3-70.4]. We used self-assessment questionnaires WOMAC and Oxford; two clinical scores Harris Hip Score and Postel-Merle d'Aubigné. ARA score was used for osseointegration evaluation.

RESULTS

Operative times were comparable. The self-assessment questionnaires and clinical scores showed significant poorer results in the obese cohort. HHS were 87.54 [56-100] and 92.49 [25-100]. However, the clinical improvement obtained between pre- and postoperative was identical in both groups: 52 [19-73] and 52 [-6 to 90]. Radiological ARA scores were good or excellent for 97.56 and 92.68%. Survival analysis was comparable with more than 0.96 at 50 months follow-up.

CONCLUSION

The Metha® prosthesis can be implanted at the forefront of primary total hip arthroplasty in normal subjects as well as in obese subjects. However, we cannot yet claim we will reach the same durability we experience with standard prostheses.

Quantitative CT with finite element analysis: towards a predictive tool for bone remodelling around an uncemented tapered stem

PURPOSE

We used quantitative CT in conjunction with finite element analysis to provide a new tool for assessment of bone quality after total hip arthroplasty in vivo. The hypothesis of this prospective five-year study is that the combination of the two modalities allows 3D patient-specific imaging of cortical and cancellous bone changes and stress shielding.

METHOD

We tested quantitative CT in conjunction with finite elements on a cohort of 29 patients (31 hips) who have been scanned postoperatively and at one year, two years and five years follow-up. The method uses cubic Hermite finite element interpolation for efficient mesh generation directly from qCT datasets. The element Gauss points that are used for the geometric interpolation functions are also used for interpolation of osteodensitometry data.

RESULTS

The study showed changes of bone density suggestive of proximal femur diaphysis load transfer with osteointegration and moderate metaphyseal stress shielding. Our model revealed that cortical bone initially became porous in the greater trochanter, but this phenomenon progressed to the cortex of the lesser trochanter and the posterior aspect of the metaphysis. The diaphyseal area did not experience major change in bone density for either cortical or cancellous bone.

CONCLUSION

The combination of quantitative CT with finite element analysis allows visualization of changes to bone density and architecture. It also provides correlation of bone density/architectural changes with stress patterns enabling the study of the effects of stress shielding on bone remodelling in vivo. This technology can be useful in predicting bone remodeling and the quality of implant fixation using prostheses with different design and/or biomaterials.

Total hip arthroplasty in developmental hip dysplasia using cementless tapered stem. Results after a minimum 10-year follow-up

Acetabular and femoral abnormalities make total hip arthroplasty in developmental hip dysplasia a challenging procedure. We present details of long-term follow-up of a series of patients affected by developmental hip dysplasia treated with total hip arthroplasty using a cementless tapered stem. Thirty-five hips in 20 patients (18 women and 2 men) aged between 44 and 60 years (mean 51 years) were observed. Clinical evaluation was conducted using the Harris Hip Score (HHS). Radiographic evaluation consisted in standard anteroposterior and axial view radiographs of the hip. According to Crowe's classification, 25 hips had grade 2 and 10 hips grade 3 dysplasia. All patients were treated with total hip arthroplasty using a cementless tapered stem (Wagner Cone Prosthesis™). After surgery the patients were clinically and radiographically evaluated at 1, 2, 3, 6 and 12 months and annually thereafter. The average follow-up was 12 years (range 10-14 years). The average HHS was 57±7 (range 45-66) preoperatively, 90±7 (range 81-100) 12 months after surgery and 90±6 (range 83-100) at last follow-up. Radiographic evaluation demonstrated excellent osseointegration of the implants in most cases. Signs of bone resorption were present in 5 hips, but no evidence of loosening was observed and none of the implants have been revised. The tapered stem achieved adequate stability and orientation, and may be a suitable option for total hip arthroplasty for arthritis following developmental hip dysplasia.

Periprosthetic bone mineral density with a cementless triple tapered stem is dependent on daily activity

PURPOSE

Periprosthetic bone loss around the femoral stem is frequently found after total hip arthroplasty. We have shown that periprosthetic bone mineral density (BMD) loss using the triple tapered stem is consistently much less in comparison with the straight type component. In this study, we compared periprosthetic BMD change with clinical factors.

METHODS

Postoperative dual-energy X-ray absorptiometry was evaluated at follow-up. BMD was determined based on seven Gruen zones. We further compared BMD with clinical examination: body mass index (BMI), age, Harris hip score (HHS) or University of California at Los Angeles (UCLA) activity rating score.

RESULTS

Periprosthetic BMD loss of the triple tapered stem was maintained. Especially, BMD in Gruen zone 1 which was maintained at 96% in comparison with the straight tapered stem. We compared the BMD change with clinical factors. There is no correlation between BMD and BMI, age or HHS. However, we found significant correlation between BMD and UCLA activity rating score in Gruen zones 1 and 2 of the triple tapered stem. Further, the correlation coefficient was increased at 48 months in comparison with 24 months.

CONCLUSION

The cementless triple tapered stem maintains periprosthetic bone mineral density. Activity may reflect improving periprosthetic bone quality after THA using a triple tapered stem.

Congenital hip dysplasia treated by total hip arthroplasty using cementless tapered stem in patients younger than 50 years old: results after 12-years follow-up

BACKGROUND

Congenital hip dysplasia may lead to severe acetabular and femoral abnormalities that can make total hip arthroplasty a challenging procedure. We assessed a series of patients affected by developmental hip dysplasia treated with total hip arthroplasty using cementless tapered stem and here we report the outcomes at long-term follow-up.

MATERIALS AND METHODS

Twenty-eight patients (24 women and 4 men) aged between 44 and 50 years (mean 47 years) were observed. Clinical evaluation was rated with the Harris Hip Score. Radiographic evaluation consisted in standard anteroposterior and axial view radiographs of the hip. According to Crowe's classification, 16 hips presented dysplasia grade 1, 14 grade 2, and 4 grade 3. All patients were treated with total hip arthroplasty using a cementless tapered stem (Wagner Cone Prosthesis). Six patients were operated bilaterally, with a totally of 34 hips operated. After surgery, the patients were clinically and radiographically checked at 3, 6, and 12 months and yearly thereafter until an average follow-up of 12 years (range 10-14 years).

RESULTS

Average Harris Hip Score was 56 ± 9 (range 45-69) preoperatively, 90 ± 9 (range 81-100) 12 months after surgery, and 91 ± 8 (range 83-100) at last follow-up. Radiographic evaluation demonstrated excellent osteointegration of the implants. Signs of bone resorption were present in 6 hips, nevertheless no evidence of loosening was observed and none of the implants has been revised.

CONCLUSIONS

Even in dysplasic femur, the tapered stem allowed adequate stability and orientation of the implant. We consider tapered stem a suitable option for total hip arthroplasty in developmental hip dysplasia, also in case of young patients, thanks to the favourable long-term results.

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.

Effects of hydroxyapatite coating on survival of an uncemented femoral stem. A Swedish Hip Arthroplasty Register study on 4,772 hips

BACKGROUND AND PURPOSE

Hydroxyapatite (HA) is widely used as a coating for uncemented total hip arthroplasty components. This has been suggested to improve implant ingrowth and long-term stability. However, the evidence behind the use of HA coating on femoral stems is ambiguous. We investigated survival of an uncemented, tapered titanium femoral stem that was available either with or without HA coating (Bi-Metric).

PATIENTS AND METHODS

The stem had been used in 4,772 total hip arthroplasties (THAs) in 4,169 patients registered in the Swedish Hip Arthroplasty Register between 1992 and 2009. 59% of the stems investigated were coated with HA and 41% were uncoated. Kaplan-Meier survival analysis and a Cox regression model with adjustment for age, sex, primary diagnosis, and the type of cup fixation were used to calculate survival rates and adjusted risk ratios (RRs) of the risk of revision for various reasons.

RESULTS

The 10-year survival rates of the HA-coated version and the uncoated version were about equal when we used revision for any reason as the endpoint: 98% (95% CI: 98-99) and 98% (CI: 97-99), respectively. A Cox regression model adjusting for the covariates mentioned above showed that the presence of HA coating did not have any influence on the risk of stem revision for any reason (RR = 1.0, 95% CI: 0.6-1.6) or due to aseptic loosening (RR = 0.5, CI: 0.2-1.5). There was no effect of HA coating on the risk of stem revision due to infection, dislocation, or fracture.

INTERPRETATION

The uncemented Bi-Metric stem showed excellent 10-year survival. Our findings do not support the use of HA coating on this stem to enhance implant survival.