Modes of periacetabular load transfer to cortical and cancellous bone after cemented versus uncemented total hip arthroplasty: a prospective study using computed tomography-assisted osteodensitometry

Change in CT-measured acetabular bone density following total hip arthroplasty: a systematic review and meta-analysis

BACKGROUND AND PURPOSE

Assessing peri-acetabular bone quality is valuable for optimizing the outcomes of primary total hip arthroplasty (THA) as preservation of good quality bone stock likely affects implant stability. The aim of this study was to perform a meta-analysis of peri-acetabular bone mineral density (BMD) changes over time measured using quantitative computer tomography (CT) and, second, to investigate the influence of age, sex, and fixation on the change in BMD over time.

METHODS

A systematic search of Embase, Scopus, Web of Science, and PubMed databases identified 19 studies that measured BMD using CT following THA. The regions of interest (ROI), reporting of BMD results, and scan protocols were extracted. A meta-analysis of BMD was performed on 12 studies that reported measurements immediately postoperatively and at follow-up.

RESULTS

The meta-analysis determined that periacetabular BMD around both cemented and uncemented components decreases over time. The amount of BMD loss increased relative to proximity of the acetabular component. There was a greater decrease in cortical BMD over time in females and cancellous BMD for young patients of any sex.

CONCLUSION

Peri-acetabular BMD decreases at different rates relative to its proximity to the acetabular component. Cancellous BMD decreases more in young patients and cortical bone decreases more in females. Standardized reporting parameters and suggested ROI to measure peri-acetabular BMD are proposed, to enable comparison between implant and patient variables in the future.

Does Total Hip Arthroplasty Influence the Development and Localization of Sacral Insufficiency Fractures?

BACKGROUND

Sacral insufficiency fractures (SIFs) are fractures related to reduced bone strength. In a previous study, we noticed that many patients with SIF had undergone total hip arthroplasty (THA). Therefore, the purpose of the present study was to research the localization of clinically apparent SIFs in relation to unilateral THA as well as the influence of unilateral THA on bone mineral density changes in the sacrum.

METHODS

In this retrospective study, 171 patients with SIFs were screened for unilateral THA. In the group of patients with SIF and THA, the rate of SIF ipsilateral and contralateral to the side of the THA was determined. In a second cohort of 39 THA patients with healthy bone, changes in bone mineral density at the sacral alae ipsilateral and contralateral to the THA were analyzed by use of computed tomography immediately postoperatively and at the 1-year follow-up.

RESULTS

Of the 171 patients with SIF, 50 (40 female; mean age, 79 years; range, 54 to 101 years) were previously treated with THA. Of the 50, 31 patients were treated with unilateral THA. The proportion of patients with an SIF contralateral to the THA was 42% (13 of 31) and ipsilateral to the THA was 19% (6 of 31). Twelve patients had bilateral SIFs. The mean age of the THA group without SIF was 62 years (range, 49 to 79 years); 17 were female. The median bone mineral density decreased significantly (p = 0.023), from 35.0 to 13.0 HU, at the sacral ala contralateral to the THA, whereas the decrease of ipsilateral bone mineral density, from 24.0 to 17.0 HU, was not significant (p = 0.361).

CONCLUSIONS

The proportion of patients with an SIF contralateral to a THA was twice as high as that of patients with an SIF ipsilateral to a THA. These findings are supported by the second cohort's decrease in bone mineral density at the sacral ala contralateral to the THA at 1 year after surgery. We conclude that THA can lead to spatially different remodeling of the sacrum, possibly affecting the development of SIFs.

LEVEL OF EVIDENCE

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

An Isoelastic Monoblock Cup Retains More Acetabular and Femoral Bone Than a Modular Press-Fit Cup: A Prospective Randomized Controlled Trial

BACKGROUND

For cup revision after total hip arthroplasty, sufficiently good periacetabular bone stock is a prerequisite for fixation of the revision implant. Cementless cups can lead to a relevant reduction of peri-implant bone mineral density (BMD) through stress-shielding.

METHODS

Fifty patients were included in this prospective randomized controlled trial. Group 1 (RM group) received an isoelastic monoblock cup (RM Pressfit vitamys; Mathys). Group 2 (IT group) received a modular titanium cup (Allofit-S IT Alloclassic with a polyethylene liner; Zimmer). Periacetabular BMD was determined and subdivided into 4 regions of interest by dual x-ray absorptiometry at 1 week (baseline) and at 4 years postoperatively. Our primary outcome was reduction in periacetabular BMD.

RESULTS

Periacetabular BMD was reduced by an average of 15.1% in the RM group and 16.5% in the IT group at 4 years postoperatively. No significant difference was found between the 2 groups over the periacetabular structure as a whole. However, the decrease of BMD in the polar region was significantly different in the RM group (4.9% ± 10.0%) compared with the IT group (15.9% ± 14.9%, p = 0.005). Use of the isoelastic RM cup showed significantly less bone loss than the modular IT cup.

CONCLUSIONS

Relevant loss of BMD at 4 years after surgery was identified in the periacetabular region in both groups. No differences between the 2 cup systems were found when looking at the overall periacetabular region. As a secondary outcome, less postoperative periacetabular bone loss occurred in the polar region when an isoelastic cup was used. Longer follow-up is required to allow for conclusions to be drawn about the long-term course of the 2 cup systems.

LEVEL OF EVIDENCE

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

Uncemented versus cemented arthroplasty after metal-on-metal total hip replacement in patients with femoral neck fractures: a retrospective study

OBJECTIVE

To compare the clinical outcomes of primary metal-on-metal total hip replacement (MoM-TR) converted to uncemented total hip replacement (UTR) or cemented total hip replacement (CTR) in patients with femoral neck fractures (AO/OTA: 31B/C).

METHODS

Patient data of 234 UTR or CTR revisions after primary MoM-TR failure from March 2007 to January 2018 were retrospectively identified. Clinical outcomes, including the Harris hip score (HHS) and key orthopaedic complications, were collected at 3, 6, and 12 months following conversion and every 12 months thereafter.

RESULTS

The mean follow-up was 84.12 (67-100) months for UTR and 84.23 (66-101) months for CTR. At the last follow-up, the HHS was better in the CTR- than UTR-treated patients. Noteworthy dissimilarities were correspondingly detected in the key orthopaedic complication rates (16.1% for CTR vs. 47.4% for UTR). Statistically significant differences in specific orthopaedic complications were also detected in the re-revision rate (10.3% for UTR vs. 2.5% for CTR), prosthesis loosening rate (16.3% for UTR vs. 5.9% for CTR), and periprosthetic fracture rate (12.0% for UTR vs. 4.2% for CTR).

CONCLUSION

In the setting of revision of failed primary MoM-TR, CTR may demonstrate advantages over UTR in improving functional outcomes and reducing key orthopaedic complications.

Texture analysis of trabecular bone around RM-Pressfit cementless acetabulum in a series of 46 patients during a 5 year period

BACKGROUND

Cementless total hip arthroplasty (THA) is a common procedure producing excellent clinical results. Their long-term survival is nevertheless burdened by loosening of the acetabular part caused by changes in the distribution of strains around the cup. In this context the RM-Pressfit® cup has been developed, resulting in a more harmonious distribution of the strains.

HYPOTHESIS

Texture analysis of X-ray films can evaluate the evolution of trabecular bone micro-architecture during the five years following THA with a RM-Pressfit® cup.

MATERIAL AND METHOD

A monocentric series of 46 hips was reviewed regularly within five years post- surgery. Radiographic evaluation of the operated hip was done on frontal digitized radiographs of the pelvis to follow evolution of bone micro-architecture in the #2 zone of De Lee and Charnley. Texture analysis using fractal algorithms was done at D0, 6 months, 1, 2 and 5 years post-THA. The fractal methods used included the skyscrapers and the dynamic blanket methods with 3 different structuring elements (a cross, a horizontal and a vertical vector).

RESULTS

The RM-Pressfit® caused significant changes in the distribution of strains around the acetabulum that preserved the bone volume over a 5-year period post-surgery. This corresponds to an improvement of the trabecular micro-architecture around the acetabular cups.

CONCLUSION

A statistically significant increase in the four fractal dimensions considered corresponded to an improved trabecular bone micro-architecture revealed by texture analysis, a non-invasive method that can be used on digitized X-ray images.

LEVEL OF EVIDENCE

IIIb, Case control study, retrospective design.

To cement or not to cement acetabular cups in total hip arthroplasty: a systematic review and re-evaluation

INTRODUCTION

Total Hip Arthroplasty (THA) in the treatment of primary osteoarthritis of the hip has evolved to a very safe and cost-effective intervention with revision rates below 5% after 10 years. To this day, however, controversy remains on whether or not to cement the acetabular cup.

METHODS

A comprehensive PubMed search of the English literature for studies published between 2007 and 2018 was performed. Studies comparing the clinical (revision rate, functionality), radiological (wear) or economic (cost) differences between cemented (cemented stem with cemented cup) and hybrid (cemented stem with uncemented cup) prostheses for primary osteoarthritis of the hip were identified as eligible.

RESULTS

A total of 1032 studies were identified whereof twelve were included for qualitative synthesis. All studies concerning the risk of revision were based on registry data, covering a total of 365,693 cups. Cemented prostheses had a similar or lower risk of revision compared to hybrid prostheses in every study, but performed slightly worse on functionality and quality of life. While cemented prostheses were the cheapest option, hybrids were the most cost-effective.

DISCUSSION

The widespread preference for cementless fixation of the acetabulum cannot be explained by a superior survival of cementless or hybrid models. Irrespective of age, cemented fixation of the acetabulum remains the gold standard to which other techniques should be compared.

Bone density measurements adjacent to acetabular cups in total hip arthroplasty using dual-energy CT: an in vivo reliability and agreement study

Background

Measuring bone mineral density (BMD) around acetabular prosthetic components with computed tomography (CT) is challenged by the complex anatomy and metal artifacts. Three-dimensional (3D) segmentation is required for the analysis, but it is usually not practically applicable on current CT workstations

Purpose

To test the between-scan agreement and reliability of custom segmentation software for BMD measurements adjacent to cemented and uncemented acetabular cups in dual-energy CT (DECT).

Material and Methods

Twenty-four male patients with total hip arthroplasty were scanned and rescanned using 130-keV virtual monochromatic DECT images. Hemispherical regions of interest were defined slice-by-slice and BMD was calculated around the acetabular cup using custom segmentation software.

Results

In the uncemented cup, the mean BMD was 153 mg/cm³ with a between-scan difference of 10 mg/cm³ (P < 0.0001). In the cemented cup, the mean BMD was 186 mg/cm³ with a between-scan difference of 6 mg/cm³ (P = 0.15). In both uncemented and cemented cups the intraclass correlation coefficient between repeated measurements was >0.95 and narrow Bland–Altman Limits of Agreement.

Conclusion

BMD can be measured with high absolute between-scan agreement and good reliability adjacent to acetabular cemented and uncemented cups using DECT and segmentation software.

The effect of cement mantle thickness on strain energy density distribution and prediction of bone density changes around cemented acetabular component

Cement mantle thickness is known to be one of the important parameters to reduce the failure of the cemented acetabular component. The thickness of the cement mantle is also often influenced by the positioning of the acetabular cup. The aim of this study is to determine the effect of uniform and non-uniform cement mantle thickness on strain energy density distribution and prediction of the possibility of bone remodelling around the acetabular region. Furthermore, tensile stress distribution in the cement mantle due to non-uniform cement mantle thickness was also investigated. Three-dimensional finite element models of intact and 17 implanted pelvic bone were developed based on computed tomography data sets. Results indicate that implantation with non-uniform cement thickness variation in the anterior-posterior direction has a significant influence on strain energy density distribution around the acetabulum as compared to thickness variation in the superior-inferior direction. Increase in density is predicted at the anterior part of the acetabulum, whereas density decrease is predicted at the posterior, inferior and superior part of the acetabulum. The non-uniform cement mantle thickness affected the tensile stress distribution in the cement mantle, in particularly superiorly placed acetabular cup. This study concludes that uniform cement thickness is desired for the longer success of the cemented acetabular component.

Intra- and inter-observer agreement and reliability of bone mineral density measurements around acetabular cup: a porcine ex-vivo study using single- and dual-energy computed tomography

Background

Periprosthetic bone loss is considered to be a potentially contributing factor in aseptic loosening of acetabular hip components, but no studies have shown this association. The lack of association might be caused by insufficient image quality because of metal artifacts and challenges in measuring bone density (BMD) in complex anatomic structures which might be overcome using dual-energy computed tomography (DECT).

Purpose

To test inter- and intra-observer agreement and reliability of in-house segmentation software measuring BMD adjacent to acetabular cup and to compare measurements performed with single-energy CT (SECT) and DECT in cemented and cementless cups.

Material and Methods

Twenty-four acetabular cups inserted in porcine hip specimens were scanned with SECT and DECT. Bone density was measured in a three-dimensional volume adjacent to the cup. Double measurements were performed.

Results

BMD derived from SECT was approximately four times higher than that of DECT. In both scan modes, intraclass correlation coefficient (ICC) was >0.90 with no differences between repeated measurements, except for uncemented cups where a statistically significant difference of 11 mg/cm³ was found with DECT. DECT showed narrower limits of agreement than SECT. Inter-observer analysis showed small differences.

Conclusion

BMD can be estimated with high intra- and inter-observer reliability with SECT and DECT around acetabular cups using custom software. The intra- and inter-observer agreement of DECT is superior to that of SECT and better in the cementless concept. Good intra- and inter-observer reliability can be obtained in both cemented and cementless cups using the segmentation software. SECT and DECT cannot be used interchangeably.

Agreement and precision of periprosthetic bone density measurements in micro-CT, single and dual energy CT

The objective of this study was to test the precision and agreement between bone mineral density measurements performed in micro CT, single and dual energy computed tomography, to determine how the keV level influences density measurements and to assess the usefulness of quantitative dual energy computed tomography as a research tool for longitudinal studies aiming to measure bone loss adjacent to total hip replacements. Samples from 10 fresh-frozen porcine femoral heads were placed in a Perspex phantom and computed tomography was performed with two acquisition modes. Bone mineral density was calculated and compared with measurements derived from micro CT. Repeated scans and dual measurements were performed in order to measure between- and within-scan precision. Mean density difference between micro CT and single energy computed tomography was 72 mg HA/cm³ . For dual energy CT, the mean difference at 100 keV was 128 mg HA/cm³ while the mean difference at 110-140 keV ranged from -84 to -67 mg HA/cm³ compared with micro CT. Rescanning the samples resulted in a non-significant overall between-scan difference of 13 mg HA/cm³ . Bland-Altman limits of agreement were wide and intraclass correlation coefficients ranged from 0.29 to 0.72, while 95% confidence intervals covered almost the full possible range. Repeating the density measurements for within-scan precision resulted in ICCs >0.99 and narrow limits of agreement. Single and dual energy quantitative CT showed excellent within-scan precision, but poor between-scan precision. No significant density differences were found in dual energy quantitative CT at keV-levels above 110 keV. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1470-1477, 2017.

Cancellous and cortical bone mineral density around an elastic press-fit socket in total hip arthroplasty

Background and purpose - The acetabular component has remained the weakest link in hip arthroplasty for achievement of long-term survival. One of the possible explanatory factors for acetabular failure has been acetabular stress shielding. For this, we investigated the effects of a cementless elastic socket on acetabular bone mineral density (BMD). Patients and methods - During 2008-2009, we performed a single-center prospective cohort trial on 25 patients (mean age 64 (SD 4), 18 females) in whom we implanted a cementless elastic press-fit socket. Using quantitative BMD measurements on CT, we determined the change in BMD surrounding the acetabular component over a 2-year follow-up period. Results - We found a statistically significant decrease in cancellous BMD (-14% to -35%) and a stable level of cortical BMD (5% to -5%) surrounding the elastic press-fit cup during the follow-up period. The main decrease was seen during the first 6 months after implantation. During the second year, cancellous BMD showed a further decrease in the medial and lower acetabular regions. Interpretation - We found no evidence that an elastic press-fit socket would prevent acetabular stress shielding during a 2-year follow-up.

Finite element modelling for assessing effect of acetabular component orientation on the basic stress path above acetabular dome

OBJECTIVE

To investigate the effect of acetabular component orientation on the basic stress path above the acetabular dome in the recommended safe zone.

METHODS

A subject-specific normal hip finite element model was generated and a convergence study carried out to determine the number of material properties for trabecular bone using a normal hip model. Four abduction angles (35°, 40°, 45° and 50°) and four anteversion angles (10°, 15°, 20° and 25°) from the recommended safe zone of acetabular cup orientation were chosen to simulate acetabular reconstruction. The distribution and level of periacetabular stress was assessed using a normal hip model as a control and 16 reconstructed acetabula in simulated single-legged stances.

RESULTS

The error of the average stress between plans four and five (50 and 100 materials for trabecular bone respectively) was 4.8%, which is less than the previously defined 5% error. The effect of acetabular component orientation on stress distribution in trabecular bone was not pronounced. When the acetabular component was at 15° anteversion and the abduction angle was 40° or 45°, the stress level on posterolateral cortical bone above the acetabular dome was as stable as that in the normal hip model.

CONCLUSIONS

Acetabular component orientation affects the basic stress path above the acetabular dome. Thus, orientation should be considered when attempting to restore normal biomechanics in the main load-bearing area.

Bone loss around a stable, partly threaded hydroxyapatite-coated cup: a prospective cohort study using RSA and DXA

STUDY PURPOSE

Aseptic loosening of the acetabular component is the most common reason for revision after primary THA, and periprosthetic demineralisation has been described as a potential cause for this process. The trabeculae-oriented pattern (TOP)-cup is a flat, hydroxyapatite (HA)-coated titanium shell with a threaded rim that was developed in order to minimise periprosthetic bone loss. We hypothesised that this cup provides good primary stability and improves preservation of periprosthetic bone mineral density (BMD).

BASIC PROCEDURES

A prospective cohort study on 30 patients receiving the TOP cup was carried out. Preoperative total hip BMD and postoperative periprosthetic BMD in five periprosthetic regions of interest were investigated by dual energy radiographic absorptiometry (DXA), cup migration was analysed by radiostereometry (RSA), and the Harris hips score (HHS) was determined.

MAIN FINDINGS

Mean HHS increased from 49 (24-79) preoperatively to 99 (92-100) after two years. DXA after one year demonstrated substantial BMD loss in the proximal periprosthetic zones 1 (-18%), zone 2 (-16 %) and zone 3 (-9%, all p<0.001 when compared with baseline BMD determined immediately postoperatively). The bone loss in these regions did not recover after two years. RSA (performed on 16 patients) showed that only very limited micromotion of the implant occurred: Mean cranial migration was 0.01 mm (95% confidence interval (CI): -0.09-0.12) and mean inclination decreased by 0.02º (CI: -0.43-0.39) after two years.

CONCLUSION

We conclude that the TOP cup provides good primary stability in the short-term. However, substantial BMD loss in proximal periprosthetic areas indicates that the design of this cup cannot prevent periprosthetic bone loss that has also been observed around other uncemented cups.

Cementless RM Pressfit Cup: a clinical and radiological study of 91 cases with at least four years follow-up

Cementless metal-back acetabular cups have good long-term results, but some problems have appeared due to the shell's stiffness, modularity and required bearing surfaces. The RM Pressfit Cup is a single-piece polyethylene cementless acetabular cup that is covered by a thin layer of titanium. This allows for bone integration without limitations related to the stiffness of a metal-back shell. There is very little published information about this new, innovative implant design. The purpose of this study was to evaluate the clinical and radiological results from a continuous series of 91 cups (85 patients) with a follow-up of at least 4 years. No patients were lost to follow-up. The Harris Hip Score (HHS) was used to assess the clinical outcome. To assess the radiological outcomes, digital X-rays were used to evaluate the cup position and integration; wear was measured using Livermore's technique. The clinical results were excellent: the mean HHS was 94 and 82% of cases had good or excellent scores. Three of the cups had to be revised because of dislocation brought on by incorrect positioning. X-rays revealed that three implants had shifted during the first 6 weeks, but had stabilized afterwards. Bone integration on X-rays was satisfactory in all cases with no signs of osteolysis. The configuration of the bone trabeculae showed that loads between the implant and peri-acetabular cancellous bone were evenly distributed. The wear of the polyethylene cup-ceramic head bearing was 0.07 mm/year. The results of this series are consistent with recent published studies with the RM Pressfit Cup.

LEVEL OF EVIDENCE

IV.

Three-year prospective clinical and radiological results of a new flexible horseshoe acetabular cup

We report the three-year results of a new flexible, horseshoe-shaped acetabular cup, with a carbon fibre reinforced polyetheretherketone (CFR-PEEK) bearing surface. The 3 mm thick composite cup is designed to conserve acetabular bone stock and reproduce a near-physiological stress distribution to the adjacent bone. The cup is intended to articulate against a large diameter ceramic femoral head to produce a low-wear bearing couple that generates minimal wear debris. A prospective, two-centre clinical study of the MITCH PCR cup was started in January 2007, to verify its safety and performance. Twenty-five MITCH PCR cups were implanted by three surgeons. There were 12 men and 13 women, with a mean age of 67.9 years (range 57.4 to 74.9). The mean Oxford hip score improved from 19.6 (SD 7.5) preoperatively to 43.5 (SD 7) at 3 years. The mean Harris hip score improved from 52.9 (SD 7) to 91.4 (SD 13.8) and the Euroqol-5D score increased from 62.6 (SD 18.4) to 82.8 (SD 19). One revision of the acetabular cup was undertaken at 21 months for squeaking. This has been investigated and modification of the articular geometry has resolved the problem, on in-vitro testing. Radiological analysis showed good early osseointegration of the MITCH PCR cup. However at three years, five cases of acetabular component migration and calcar resorption were observed. Three patients have subsequently undergone revision of the acetabular cup, at 41, 42 and 50 months respectively. The cause of the osteolysis is the subject of on-going investigation.

Periacetabular cortical and cancellous bone mineral density loss after press-fit cup fixation: a prospective 7-year follow-up

The impact of total hip arthroplasty on strain adaptive bone remodeling has been extensively analyzed by dual-energy x-ray absorptiometry. In this study, we present a prospective computed tomography-assisted study of periacetabular cortical and cancellous bone mineral density (in milligrams of calcium hydroxyapatite [CaHA] per milliliter, or mgCaHA/mL) changes 10 days and 1, 3, and 7 years after press-fit cup implantation for 38 hips in vivo. Cancellous bone mineral density decreased by Ø -63% ventral and Ø -85% dorsal to the cup; cortical bone mineral density, by Ø -22% ventral and Ø -18% dorsal to the cup. The presented periacetabular strain adaptive bone mineral density data are the most extensive of the current literature. Even the measured extensive cancellous bone mineral density loss was thus far of no clinical relevance because all cups showed radiographic signs of stable ingrowth.

Supra acetabular bone mineral density measurements after hip resurfacing arthroplasty at short term follow up

Implantation of a cementless press-fit acetabular cup during hip arthroplasty alters stress transfer to the periacetabular bone, resulting in stress shielding of cancellous bone and enhanced load transfer to cortical bone. Theoretically, the thicker, stiffer and larger acetabular cup of a hip resurfacing may increase periacetabular bone stress shielding. We attempted to assess the matter (at a minimum of 2 years after surgery) by measuring any difference in supra acetabular bone mineral density (BMD) between the side implanted with a thick monoblock cobalt-chromium (Co-Cr) acetabular component during hip resurfacing (HR) and the opposite non-operated side. We retrospectively recruited 44 patients who had undergone metal-on-metal hybrid hip resurfacing for unilateral osteoarthritis of the hip joint . BMD of the supra acetabular bone of both hips was measured using a dual energy X-ray absorptiometry (DEXA) scan. The BMD measured in Zone 2 was not different on the operated side (1.69 g/cm2 ± 0.48) compared with the non-operated side (1.70 g/cm2 ±0.49) (p=0.904). Contrary to our expectations, implantation of a monoblock Co-Cr acetabular component during HR did not cause significant stress-shielding of supra acetabular cancellous bone.

A randomised study of peri-prosthetic bone density after cemented versus trabecular fixation of a polyethylene acetabular component

The ideal acetabular component is characterised by reliable, long-term fixation with physiological loading of bone and a low rate of wear. Trabecular metal is a porous construct of tantalum which promotes bony ingrowth, has a modulus of elasticity similar to that of cancellous bone, and should be an excellent material for fixation. Between 2004 and 2006, 55 patients were randomised to receive either a cemented polyethylene or a monobloc trabecular metal acetabular component with a polyethylene articular surface. We measured the peri-prosthetic bone density around the acetabular components for up to two years using dual-energy x-ray absorptiometry. We found evidence that the cemented acetabular component loaded the acetabular bone centromedially whereas the trabecular metal monobloc loaded the lateral rim and behaved like a hemispherical rigid metal component with regard to loading of the acetabular bone. We suspect that this was due to the peripheral titanium rim used for the mechanism of insertion.

Direct comparison of polyethylene wear in cemented and uncemented acetabular cups

Background

It has been indicated that, in the long term, the rate of wear and the degree of osteolysis observed with uncemented acetabular components are greater than those associated with cemented cups, but most studies which compare the wear characteristics of cementless with cemented cups have used historical controls. We report a direct comparison of wear of a cemented and an uncemented cup with similar design, polyethylene, and sterilization method.

Materials and methods

The study cohort includes 92 patients who were operated in 1997 with primary total hip replacement and have been followed for a period of 9–10 years. All patients were operated by posterolateral approach. In patients 70 years or older we used a cemented cup, in those 60 years or younger we used an uncemented cup, and in patients between 60 and 70 years we used either a cemented or uncemented cup as decided by the surgeon. At follow-up, radiographic imaging was obtained as standard anterioposterior view of the pelvis, and mean wear was determined as described by Livermore et al.

Results

The overall wear of the cemented acetabular components was 1.07 ± 0.78 mm, and that of the uncemented cups was 1.18 ± 0.61 mm (P = 0.529). Wear was significantly associated with male sex (P = 0.003), younger age (P = 0.003), and degree of inclination (P < 0.001), but wear was not significantly associated with cemented versus uncemented cup (P = 0.437).

Conclusion

Our findings in this 9–10-year follow-up study suggest that cementless cups wear no more than cemented cups of similar design.

[Comparison of different cup revision systems]

Aseptic loosening of hip cups results in cranial and medial migration, which induces bone resorption and defects. Despite these defects, it is the aim in cup revision arthroplasty to get a stable fixation and a restoration of the hip center. Depending on the size of the defect, which can be classified by different scoring systems, various strategies requiring an experienced surgeon can be used to reach this aim. If defects are localized, bigger primary cemented or cement-free cups can be used. Larger defects may need bone transplantation or special designs such as oval cups or reinforcement rings. They can be used with or without plates in combination with cement for inlay fixation. In the case of bigger defects or pelvic discontinuity, modular systems or a socket cup may be necessary.