Five-year results of the uncemented RM pressfit cup clinical evaluation and migration measurements by EBRA

Mid-term clinical outcomes of the uncemented Robert Mathys pressfit cup

BACKGROUND

The use of uncemented cups during total hip arthroplasty (THA) has gained popularity in recent years. The Robert Mathys (RM) pressfit cup, an uncemented monoblock implant is expected to preserve bone density due to its composition and external surface, while reducing backside wear with its monoblock construction. These factors should lead to a high survival rate of the implant.

AIM

To evaluate the mid-term survival and functional outcome of the RM Pressfit cup in a large study population.

METHODS

Between 2011 and 2020, we included 1324 patients receiving a primary THA using the RM pressfit cup. Final clinical follow-up was performed at 2 years postoperatively with the Dutch arthroplasty register used to assess implant status thereafter. Revision for acetabular failure and reason for revision were reported to evaluate implant survival, while the hip disability and osteoarthritis outcome score (HOOS) scores were used to assess functional outcome.

RESULTS

The mean age at surgery was 64.9 years. The mean follow-up was 4.6 years. Of the 1324 THAs performed, 13 needed cup revisions within 5 years after index THA: 5 due to aseptic loosening, 6 due to infection, 2 due to dislocation and 2 due to other causes. This resulted in a 5-year cup survival of 98.8% (95%CI: 98.1-99.5). Nine of the cup revisions occurred within the first year after index THA. HOOS scores increased significantly in all domains during the first year and levelled out during the second year.

CONCLUSION

In the present study, the RM pressfit cup demonstrated excellent clinical outcomes at mid-term follow-up; however, future studies are needed to assess the long-term outcomes of this acetabular implant.

The 45-year evolution of the Mathys RM monoblock cups: have the paradigm shifts been worthwhile?

INTRODUCTION

The Robert Mathys (RM) monoblock uncemented cup is a design less commonly used in primary total hip replacement. It's purported advantages over modular cemented cups are: (1) its modulus of elasticity approximating bone, thus mimicking load transmission and the biomechanical behaviour of the cup to better match stresses on the acetabulum, leading to bone-preservation; and (2) as a 1-piece cup there is absence of a mobile interface between a liner and shell, preventing backside wear. Since its inception in 1983 there have been 3 major design changes: the RM Classic, the RM Pressfit, and the RM Vitamys with the most modern polyethylene (vitamin E).

METHODS

In a retrospective cohort study of the New Zealand Joint Registry, all designs of RM acetabular cup were reviewed. Data were included from1998 to 2018. All-cause revision rates, reasons for revision and the Oxford Hip Score (OHS) were assessed.

RESULTS

In total 13,272 acetabular cups were included. The all-cause revision rates did not differ between the designs. Revision rates for aseptic loosening in the RM Vitamys were lower, but the follow-up was shorter and more larger heads were used. There was no difference in the OHS.

CONCLUSION

All implant designs were safe. The use of larger heads led to a decrease in revisions due to dislocation. It has to be waited out whether the RM Vitamys performs superior in the long-term due to the highly cross-linked polyethylene.

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.

Anatomical pelvic loading of a monoblock polyethylene acetabular component

AIMS

Uncemented metal acetabular components show good osseointegration, but material stiffness causes stress shielding and retroacetabular bone loss. Cemented monoblock polyethylene components load more physiologically; however, the cement bone interface can suffer fibrous encapsulation and loosening. It was hypothesized that an uncemented titanium-sintered monoblock polyethylene component may offer the optimum combination of osseointegration and anatomical loading.

METHODS

A total of 38 patients were prospectively enrolled and received an uncemented monoblock polyethylene acetabular (pressfit) component. This single cohort was then retrospectively compared with previously reported randomized cohorts of cemented monoblock (cemented) and trabecular metal (trabecular) acetabular implants. The primary outcome measure was periprosthetic bone density using dual-energy x-ray absorptiometry over two years. Secondary outcomes included radiological and clinical analysis.

RESULTS

Although there were differences in the number of males and females in each group, no significant sex bias was noted (p = 0.080). Furthermore, there was no significant difference in age (p = 0.910) or baseline lumbar bone mineral density (BMD) (p = 0.998) found between any of the groups (pressfit, cemented, or trabecular). The pressfit implant initially behaved like the trabecular component with an immediate fall in BMD in the inferior and medial regions, with preserved BMD laterally, suggesting lateral rim loading. However, the pressfit component subsequently showed a reversal in BMD medially with recovery back towards baseline, and a continued rise in lateral BMD. This would suggest that the pressfit component begins to reload the medial bone over time, more akin to the cemented component. Analysis of postoperative radiographs revealed no pressfit component subsidence or movement up to two years postoperatively (100% interobserver reliability). Medial defects seen immediately postoperatively in five cases had completely resolved by two years in four patients.

CONCLUSION

Initially, the uncemented monoblock component behaved similarly to the rigid trabecular metal component with lateral rim loading; however, over two years this changed to more closely resemble the loading pattern of a cemented polyethylene component with increasing medial pelvic loading. This indicates that the uncemented monoblock acetabular component may result in optimized fixation and preservation of retroacetabular bone stock. Cite this article: Bone Joint J 2021;103-B(5):872-880.

Wear and migration are not influenced by head size in a vitamin E-infused highly cross-linked polyethylene acetabular cup

BACKGROUND

Aseptic loosening and periprosthetic osteolysis are frequent complications in total hip arthroplasty requiring revision surgery. Highly cross-linked polyethylene (HXLPE) implants have improved wear resistance, permitting larger femoral heads. However, such implants may experience surface cracking, mechanical failure, and oxidative damage. Vitamin E-infused HXLPE (VEPE) implants were therefore developed to reduce oxidation without compromising mechanical strength. We addressed the following questions: (1) Does femoral head size affect the midterm annual polyethylene wear rates of VEPE acetabular cups? (2) Does femoral head size affect the midterm migration rates of VEPE acetabular cups? (3) Are clinical outcomes affected by femoral head size?

HYPOTHESIS

Annual wear rate, migration rate, and clinical outcomes of VEPE acetabular cups are independent of femoral head size.

PATIENTS AND METHODS

This was a prospective, multicentre, observational study of patients that underwent total hip arthroplasty. Hips were grouped according to the size of femoral head implanted (28 mm, 32 mm, and 36 mm). We determined annual wear rate and migration rate of VEPE acetabular cups using the Einzel-Bild-Röntgen-Analyse software. Clinically, we assessed the Harris Hip Score and visual analog score for pain and satisfaction.

RESULTS

We followed 253 patients (267 hips) for a mean of 55.0±20.6 months in the 28 mm, 46.2±21.4 months in the 32 mm, and 43.8±22.6 months in the 36 mm group. The annual wear rate was 0.025 mm per year from 1 year to the last follow-up and remained similar between the groups (p>0.05). Also, mean two-dimensional migration rates did not exceed 0.05 mm from 2 years to the last follow-up and remained similar between the groups (p=0.355). Finally, clinical outcomes also did not differ between the groups (p>0.05). Two patients required revision surgery.

DISCUSSION

Femoral head size did not influence midterm annual wear rate, migration rate, and clinical outcomes of VEPE acetabular cups. Furthermore, wear and cup migration rates were below the reported values leading to osteolysis and aseptic loosening. Nevertheless, studies with extended follow-up periods will be necessary to confirm these results in the long term.

LEVEL OF EVIDENCE

IV.

The concept of a cementless isoelastic monoblock cup made of highly cross-linked polyethylene infused with vitamin E: radiological analyses of migration and wear using EBRA and clinical outcomes at mid-term follow-up

Background

The newest generation of cementless titanium-coated, isoelastic monoblock cup with vitamin E-blended highly cross-linked polyethylene (HXLPE) was introduced to the market in 2009. The aim of the present study was to obtain mid-term follow-up data including migration and wear analyses.

Methods

This prospective study investigated 101 primary total hip arthroplasty (THA) cases in 96 patients treated at a single institution. Patients were allowed full weight-bearing on the first day postoperatively. Harris hip score (HHS) and pain and satisfication on a visual analogue scale (VAS) were assessed at a mean follow-up of 79.0 months. Migration and wear were assessed using Einzel-Bild-Roentgen-Analyse (EBRA) software. Radiological acetabular bone alterations and complications were documented.

Results

At mid-term follow-up (mean 79.0 months, range: 51.8–101.7), 81 cases with complete clinical and radiological data were analyzed. Utilisable EBRA measurements were obtained for 42 hips. The mean HHS was 91.1 (range 38.0–100.0), VAS satisfaction was 9.6 (range 6.0–10.0), VAS rest pain was 0.2 (range 0.0–4.0), and VAS load pain was 0.6 (range 0.0–9.0). Mean migration was 0.86 mm (range: 0.0–2.56) at 24 months and 1.34 mm (range: 0.09–3.14) at 5 years, and the mean annual migration rate was 0.22 (range: − 0.24–1.34). The mean total wear was 0.4 mm (range: 0.03–1.0), corresponding to a mean annual wear rate of 0.06 mm per year (range: 0.0–0.17). Radiographic analysis did not reveal any cases of osteolysis, and no revision surgeries had to be performed.

Conclusions

After using vitamin-E blended HXLPE in cementless isoelastic monoblock cups, there were no obvious signs of osteolysis or aseptic loosening occurred. No patients required revision surgery after mid-term follow-up. Cup migration and wear values were well below the benchmarks considered predictive for potential future failure.

Trial registration

The trial registration number on ClinicalTrials.gov: NCT04322916 (retrospectively registered at 26.03.2020).

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-021-03981-8.

Good mid-term results with the trident peripheral self-locking cup: a clinical evaluation and migration measurement with EBRA

INTRODUCTION

The most common cause of failure in total hip arthroplasty (THA) is aseptic loosening. Uncemented cup migration analysis by means of Einzel-Bild-Roentgen-Analyse (EBRA) has shown to be a good predictive indicator for early implant failure if the cup migrates more than 2 mm within 4 years after surgery. In this study, we performed a migration analysis of an uncemented peripheral self-locking (PSL) press-fit cup after 4 years follow-up.

MATERIALS AND METHODS

We retrospectively reviewed all patients who received a trident PSL press-fit cup at our department between 2004 and 2017. A total of 636 patients were identified. As inclusion criteria for radiological analysis, a minimum follow-up of 2 years was defined. We reviewed medical histories and performed radiological analysis using EBRA software. EBRA measurements and statistical investigations were performed by two independent investigators.

RESULTS

A total of 149 cups in 146 patients (female 82; male 64) met our inclusion criteria. Mean age at surgery was 65 years (33-89). We found a significant improvement in the WOMAC score pre- to postoperative (p < 0.0001). EBRA migration analysis showed a mean total migration of 0.6 mm (0.0-8.2) over our follow-up period of 4 years. Of the investigated cups, 69.8% showed a migration rate smaller than 2 mm in the investigated follow-up.

CONCLUSION

The acetabular cup used in our study provides low migration at final follow-up. Therefore, a good long-term outcome can be expected for the PSL cup.

TRIAL REGISTRATION

Trial registration number is 20181024-1875 and date of registration is 2018-10-24.

Two-year radiologic assessment of the Pinnacle cup-a migration analysis with EBRA

INTRODUCTION

The most common cause of failure in total hip arthroplasty (THA) is aseptic loosening. Uncemented cup migration analysis by EBRA (Einzel-Bild-Roentgen-Analyse) has shown to be a good predictive indicator for early implant failure if the cup migrates more than 1 milimeter (mm) within the first 2 years after surgery. In this study, we investigated the migration behaviour of an uncemented press-fit cup after 2 years follow-up.

MATERIALS AND METHODS

Applying a retrospective study design, we reviewed all consecutive patients who received an uncemented press-fit cup at our Department between 2013 and 2018. A total of 484 patients were identified. We reviewed medical histories and performed radiological measurements using EBRA-Cup software. EBRA measurements and statistical investigations were performed by two independent investigators.

RESULTS

A total of 165 cups in 159 patients (female: 90; male: 69) met our inclusion criteria. Mean age at surgery was 66.7 (range 18.4-90.5) years. EBRA migration analysis showed a mean total migration of 0.7 mm (range 0.0-6.3) over our follow-up period of 2 years. Of the investigated cups, 53.2% showed less than 1 mm migration in the investigated follow-up period.

CONCLUSION

In conclusion, the Pinnacle cup used in our study provides low mean migration at final follow-up. Based on the assumption of secondary stabilization, good long-term outcome of the Pinnacle cup can be expected.

TRIAL REGISTRATION NUMBER AND DATE OF REGISTRATION

Number: 20181024-1875; Date: 2018-09-20.

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.

Creep and Wear in Vitamin E-Infused Highly Cross-Linked Polyethylene Cups for Total Hip Arthroplasty: A Prospective Randomized Controlled Trial

BACKGROUND

Aseptic loosening, the most common indication for revision surgery in total hip arthroplasty, can result from osteolysis caused by polyethylene (PE) wear particles. PE wear is increased by age-related oxidation of PE and free radicals emerging during irradiation cross-linking. Diffusion of vitamin E into PE stabilizes free radicals to maintain the biomechanical properties of PE. The purpose of this study was to determine whether vitamin E-infused highly cross-linked PE cups could reduce wear rates.

METHODS

We performed a prospective randomized controlled trial, in which 62 patients were allocated to 2 groups: a study group that received a vitamin E-infused highly cross-linked PE (HXLPE/VitE) cup and a control group that received an ultra-high molecular weight PE (UHMWPE) cup. Using radiostereometric analysis, we measured the penetration of the femoral head into the cup 7 days after surgery (baseline) and then again at 6 months and at 1, 2, and 3 years later.

RESULTS

Baseline variables did not differ significantly between the groups. At 1, 2, and 3 years after surgery, the HXLPE/VitE cup showed significantly less cumulative penetration (creep and wear) than the UHMWPE cup (p = 0.004, p < 0.0001, and p < 0.0001, respectively). The cumulative penetration after 3 years was 0.200 mm for the HXLPE/VitE cup versus 0.317 mm for the UHMWPE cup (p < 0.0001). From 1 to 3 years after surgery, after creep had stabilized and further penetration was mainly due to wear, the mean penetration increased only 0.04 mm in the HXLPE/VitE cup and 0.116 mm in the UHMWPE cup.

CONCLUSIONS

Our results confirm that wear rates over the first 3 years following surgery were lower in HXLPE/VitE cups than in UHMWPE cups. This suggests that HXLPE/VitE cups may prevent osteolysis, implant loosening, and eventually revision surgery. Long-term follow-up data continue to be collected to confirm these findings.

LEVEL OF EVIDENCE

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

Stability of small pegs for cementless implant fixation

Most glenoid implants rely on large centrally located fixation features to avoid perforation of the glenoid vault in its peripheral regions. Upon revision of such components there may not be enough bone left for the reinsertion of an anatomical prosthesis. Multiple press-fit small pegs would allow for less bone resection and strong anchoring in the stiffer and denser peripheral subchondral bone. This study assessed the fixation characteristics, measured as the push-in (P_in ) and pull-out (P_out ) forces, and spring-back, measured as the elastic displacement immediately after insertion, for five different small press-fitted peg configurations manufactured out of UHMWPE cylinders (5 mm diameter and length). A total of 16 specimens for each configuration were tested in two types of solid bone substitute: Hard (40 PCF, 0.64 g/cm³ , worst-case scenario of P_in ) and soft (15 PCF, 0.24 g/cm³ , worst-case scenario of spring-back and P_out ). Two different diametric interference-fits were studied. Geometries with lower stiffness fins (large length to width aspect ratio) were the best performing designs in terms of primary fixation stability. They required the lowest force to fully seat, meaning they are less damaging to the bone during implantation, while providing the highest P_out /P_in ratio, indicating that when implanted they provide the strongest anchoring for the glenoid component. It is highlighted that drilling of chamfered holes could minimize spring-back displacements. These findings are relevant for the design of implants press-fitted pegs because primary fixation has been shown to be an important factor in achieving osseointegration and longevity of secondary fixation. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2765-2772, 2017.

Does using a polyethylene RM press-fit cup modify the preparation of the acetabulum and acetabular offset in primary hip arthroplasty?

INTRODUCTION

When performing total hip arthroplasty (THA), it is important to maintain the femoral and acetabular offsets to ensure good joint stability and to restore the function of the hip abductor muscles. In our practice, we mainly use a lateralized stem and hollow out the acetabulum to the quadrilateral plate to accommodate a press-fit polyethylene cup. However, the repercussions of this preparation method, which is driven by the cup's design, are not known. We carried out a retrospective study to assess: (1) the changes in the femoral and acetabular offset; (2) the height of the center of rotation; and (3) the repercussions on wear.

HYPOTHESIS

We hypothesized there would be no significant differences between the preoperative and postoperative femoral and acetabular offsets.

PATIENTS AND METHODS

We reviewed 88 primary THA cases performed with the RM Pressfit™ cup that had a minimum of 5 years' follow-up. A lateralized self-locking Muller-type cemented femoral stem was used in 92.0% of cases and a standard stem in 8.0%. Measurements were done on plain radiographs with MHP™ and Mesurim Pro™ software. The average follow-up was 6.5 years (5-8).

RESULTS

On average, the acetabular offset was reduced by 2.75mm±5.9 mm (range: -17.5 to +10.6 mm) (P<0.001) and the femoral offset was increased by 0.01mm±5.5 mm (range: -17.8 to +11.0 mm) (P=0.99). In terms of total offset, medialization of 2.74mm±7 mm (range: -17.7 to +18.2mm) was found (P=0.001). The acetabular center of rotation was on average 4.77mm±5.1 mm higher (P<0.001). The mean annual wear at the more recent follow-up (min.: 5 years) was 0.068mm (range: 0.01 to 0.25mm) per year. The wear was not impacted by having more than 5mm change in offset.

DISCUSSION

Measurements of acetabular offset revealed statistically significant medialization due to the type of implant used and the surgical technique. The anatomical technique consists of positioning the cup in subchondral bone without contacting the quadrilateral plate. This preserves bone stock, which may be useful later on if the cup is revised, particularly in younger patients. Conversely, the femoral offset did not change significantly, despite the use of lateralized stems in 92.0% of cases. We measured an annual wear rate of 0.068mm per year, which is lower than in other published studies, possibly because our patient population was older.

LEVEL OF EVIDENCE

IV, retrospective study.

The Morscher Press-Fit Acetabular Component: An Independent Long-Term Review at 18-22 Years

BACKGROUND

There are relatively few 20-year results of uncemented acetabular components, and most of these are modular designs. This study reports the 20-year results of a monoblock press-fit acetabular component.

METHODS

A total of 122 total hip arthroplasties (111 patients) using the Morscher cup were reviewed at a mean of 19.7 years. The average age at implantation was 57.3 years (range, 36-74 years), and 81 (66%) were men.

RESULTS

Twenty-two patients (25 hips) had died. Seven hips were revised, including 5 acetabular revisions. Six patients (6 hips) declined to participate but were known not to have been revised. The mean Oxford hip score was 41.1 (range, 22-48), and the mean reduced Western Ontario and McMaster Universities Osteoarthritis Index score was 5.7/48 (range, 0-24). Eccentric wear was seen in 13 (15.7%) and major osteolysis in 14 (17%) of 82 surviving hips with radiographs. The all-cause revision rate was 0.32 per 100 observed component years (95% confidence interval [CI], 0.13-0.66). The 20-year Kaplan-Meier survival was 93.4% (CI, 86.6-96.8) for all-cause revisions, 95.5% (CI, 89.4-98.1) for any acetabular revision, and 97.1% (CI, 91.2-99.1) for acetabular aseptic loosening, wear, or osteolysis.

CONCLUSION

The Morscher acetabular component has continued to perform well at 20 years despite using conventional polyethylene with results that match or surpass other cementless acetabulae.

The RM Pressfit vitamys: 5-year Swiss experience of the first 100 cups

BACKGROUND

The RM Pressfit vitamys is a titanium particle-coated monoblock cup with vitamin E stabilised highly cross-linked polyethylene. Initial fixation is achieved via press-fit with subsequent stability by bone on-growth. This is the first study to report the 5-year results of this design.

METHODS

We performed a prospective cohort study according to STROBE guidelines of 100 consecutive total hip replacements (THRs) in 92 patients all with ceramic heads. Demographic data, pre/postoperative visual analogue scale (VAS) for pain and satisfaction, Harris Hip Scores (HHS) and complications were recorded. Radiographic analysis of osteolysis and loosening was complemented by EBRA (Einzel-Bild-Röntgen-Analyse) evaluation of cup movement.

RESULTS

Our cohort comprised 48 women (mean age 67; SD 10.4) and 44 men (mean age 69; SD 7.8). The mean body mass index was 27 kg/m2 (SD 4.6). Surgical indications were osteoarthritis 96%, avascular necrosis 3% and fracture 1%. 82% had a direct anterior approach, 15% anterolateral and 3% trans-gluteal. 4 surgeons were involved. 1 cup was repositioned and fixed with screws within a week of index surgery. There were 2 intraoperative femoral fractures, 3 haematomata with 1 requiring drainage and 1 deep infection settling with an open washout and modular exchange. Mean VAS satisfaction increased from 3.8 (SD 2.0) to 8.8 at 6 weeks (SD 1.4) and 9.5 (SD 1.3) at 5 years. The HHS functional scores were 58.9 (SD 13.2) preoperatively and 94.6 (SD 6.6) at 5 years. Radiographic analysis showed neither progressive radiolucency nor osteolysis. Mean migration was 1.5 mm after 5 years.

CONCLUSIONS

Mid-term results of the RM Pressfit vitamys cup are encouraging.

RM Pressfit® cup: good preliminary results at 5 to 8 years follow-up for 189 patients

AIM

The RM Classic® cup shows very good results. The RM Pressfit® cup has an equatorial pressfit; it is a monoblock implant without metalback. The aim of this study was to evaluate retrospectively the survival of this implant, monitoring patients for at least 5 years in all consecutive cases operated in our centre.

METHODS

Between February 2006 and December 2008, our department performed 189 consecutive nonselected primary total hip arthroplasties using the RM® Pressfit cup, and all of these were included in the study. The operative technique involved an anterolateral approach. The latest follow-up evaluation was performed at a minimum of 5 years after the index arthroplasty.

RESULTS

The mean follow-up was 6.5 years (5-8 years). We had preoperative information for 186 of the 189 patients. 102 patients were seen in consultation (54.0%), 46 (24.3%) patients were contacted by phone, 37 (19.6%) patients died, and 4 patients (2.1%) were lost for unknown reasons. Of the 189 arthroplasties, 6 (3.2%) required revision; 4 (2.1%) for infection, 1 (0.5%) for significant haematoma with persistent deglobulisation and 1 (0.5%) for periprosthetic calcification during the 5 to 8 years following the operation. No hip was revised because of aseptic loosening. The mean annual wear rate based on the last follow-up at 5 years minimum was 0.065 mm per year. We observed no migration, 1 femoral loosening and no acetabular loosening.

CONCLUSIONS

Our study finds a good survival rate which is compatible with the 94% at 20 years with RM Classic®. These results are suggestive but must be confirmed with long-term studies.

Does a titanium-coated polyethylene press-fit cup give reliable midterm results?

BACKGROUND

Uncemented acetabular components have demonstrated low revision rates and high patient satisfaction but with concerns regarding increased costs compared with monoblock cups. Some newer lower-cost uncemented monoblock options have become available in the last decade, but limited data are available on their performance.

QUESTIONS/PURPOSES

(1) Does an uncemented, titanium-backed all-polyethylene acetabular cup provide reliable fixation? (2) What is the frequency and what are the causes for revision with this cup?

METHODS

Between 2004 and 2008, we elected to use an uncemented, titanium-backed all-polyethylene acetabular cup in older patients with limited physical demands. We performed 615 hip replacements in 550 patients with greater than 5 years of clinical and radiographic followup. When patients who were dead (80 hips in 75 patients), lost to followup (98 hips in 93 patients), or revised (three hips in three patients) were excluded, there were 434 hips in 379 patients for comparison of the postoperative and 5-year radiographs. Two observers not involved in the index surgical procedures (NH, HS) assessed radiographs for signs of migration or loosening. Some degree of early movement sometimes is seen before cup stabilization; however, to be conservative, we defined cups with greater than 3° of change of position (even if they subsequently stabilized) as potentially at risk and report them separately. Revision surgery, time from the index procedure, and the reason for revision were recorded from the New Zealand Joint Registry.

RESULTS

By 5 years there was a median change in inclination of 2° (range, 0°-13°; 95% confidence interval [CI], 2.0-2.4; p < 0.001) and 2° of anteversion (range, 0°-11°; 95% CI, 2.0-2.4; p < 0.001). Although at last followup all cups appeared to have stabilized with no radiolucent lines or medial migration, 22% of the cups (94 of 434) had moved more than 3° and so were deemed to be potentially at risk. There were 11 revision procedures (of 429 hips; 2.5%) of which six were for recurrent dislocation, four for femoral fracture, and one for femoral loosening to give an overall all-cause revision rate for all components of 0.25 per 100 component years (95% CI, 0.13-0.43). No revisions were performed for acetabular loosening.

CONCLUSIONS

The short- to medium-term results of this all-polyethylene monoblock cup demonstrated a low frequency of revision. However, 94 cups were identified as potentially at risk based on movement of > 3° before apparent stabilization. Although those patients seem to be doing well enough now, the current duration of followup may not be sufficient to know that these cups will be durable, because other ongrowth designs have demonstrated a high frequency of late failure after apparent early success.

LEVEL OF EVIDENCE

Level IV, therapeutic study.

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.