Fixation and loosening of the cemented Muller straight stem: a long-term clinical and radiological review

Biomechanical analysis of different THA cementless femoral stem designs in physiological and osteoporotic bone during static loading conditions

BACKGROUND

The influence of THA stem design on periprosthetic femoral fractures (PFFs) risk is subject of debate. This study aims to compare the effects of different cementless stem designs on stress-strain distributions in both physiological and osteoporotic femur under various loading conditions.

MATERIALS

A biomechanical study using finite-element analysis was conducted. Four models were developed: three with implanted femurs and a native one chosen as control. Each model was analyzed for both healthy and osteoporotic bone. The following stem designs were examined: short anatomical stem with femoral neck preservation, double-wedge stem, and anatomical standard stem. Three loading conditions were assessed: gait, sideways falling, and four-point bending.

RESULTS

During gait in physiological bone, the anatomical stem and the short anatomical stem with femoral neck preservation showed stress distribution similar to the native model. The double-wedge stem reduced stress in the proximal area but concentrated it in the meta-diaphysis. In osteoporotic bone, the double-wedge stem design increased average stress by up to 10%. During sideways falling, the double-wedge stem exhibited higher stresses in osteoporotic bone. No significant differences in average stress were found in any of the studied models during four-point bending.

CONCLUSION

In physiological bone, anatomical stems demonstrated stress distribution comparable to the native model. The double-wedge stem showed uneven stress distribution, which may contribute to long-term stress shielding. In the case of osteoporotic bone, the double-wedge stem design resulted in a significant increase in average stress during both gait and sideways falling, potentially indicating a higher theoretical risk of PFF.

A 24-year single-centre experience with Collum Femoris Preserving stem: clinical and radiological results in young and elderly population

OBJECTIVE

The primary aim was to evaluate the long-term follow-up of Collum Femoris Preserving (CFP) stem, specifically focusing on stem survivorship, complications, as well as on clinical and radiological results. The secondary study objective is an age-based sub-analysis (<65 years vs. ⩾65 years) of long-term results.

MATERIALS AND METHODS

We performed a retrospective analysis of patients who underwent CFP implantation between 1997 and 2009. A total of 311 patients (342 hips) were included with a mean follow-up of 15.8 ± 2.2 (range 11-24) years. 2 age groups were analysed: Group-Y (age <65) and Group-E (age ⩾65). Group-Y included 182 hips (mean follow-up 16.3 ± 4.2 years), whereas Group-E included 160 hips (mean follow-up 15.5 ± 3.7 years). Clinical (HHS, OHS and VAS) and radiological data were obtained at final follow-up. Any complications, reoperations, prosthetic components revisions and stem revisions were analysed.

RESULTS

According to HSS score, 95% of patients reported excellent/good results (95.6% Group-Y vs. 94.4% Group-E) with an overall stem survival rate of 93.3% (94% Group-Y vs. 92.5% Group-E; p = 0.37). Overall, 87% of stem revisions were performed with primary stems. The rate of prosthetic components revision was 9.9 % (9.9% in Group-Y vs. 10% in Group-E; p = 1). The reoperation rate was 10.8% (11.5% in Group-Y vs. 10.0% in Group-E; p = 0.73).

CONCLUSIONS

The CFP stem provides good clinical and radiological long-term results with low rate of complications in both young and elderly patients. No significant difference in stem revision and reoperation rates was observed between the 2 groups. Both in elderly and young patients, CFP stem allows revisions to be performed with primary stems.

Cemented femoral stem fixation through the anterior approach has fewer early complications than cementless fixation

AIMS

To achieve the functional benefits of the direct anterior (DA) approach and the fixation benefits of cemented replacement, this study combined the two techniques posing the following questions: does the limited access of the DA approach adversely affect the cement technique?; and does such a cementing technique reduce the incidence of cementless complications?

METHODS

A consecutive series of 341 patients (360 hips) receiving the DA approach between 2016 and 2018 were reviewed. There were 203 cementless stems and 157 cemented stems. Mean age was 75 years (70 to 86) in the cementless group and 76 years (52 to 94) in the cemented group, with 239 (70%) females in the whole series. Femoral complications were compared between the two groups. Mean follow-up was 1.5 years (0.1 to 4.4) for patients in the cementless group and 1.3 years (0.0 to 3.9) for patients in the cemented group.

RESULTS

The cementless group had a higher rate of femoral complications (8 vs 0; p = 0.011). There were two loose stems and six fractures, all requiring revision. Fractures occurred a mean 14.5 days (2 to 31) postoperatively and loosening at 189 days and 422 days postoperatively. Femoral cementing can be done using the DA approach safely and reduces the number of complications compared with a contemporary cementless series.

CONCLUSION

A higher rate of early fractures and loosening occurred with cementless stems. This was not observed in our cemented stem cohort and cementing was safely accomplished through the DA approach. The modern femoral cementing process with the DA approach does not add to surgical complexity or time, has fewer early complications, and is a safer option for older patients compared to cementless femoral arthroplasties. Cite this article: Bone Joint J 2021;103-B(7 Supple B):33-37.

Current concepts and outcomes in cemented femoral stem design and cementation techniques: the argument for a new classification system

Cemented implant fixation design principles have evolved since the 1950s, and various femoral stem designs are currently in use to provide a stable construct between the implant-cement and cement-bone interfaces.Cemented stems have classically been classified into two broad categories: taper slip or force closed, and composite beams or shaped closed designs. While these simplifications are acceptable general categories, there are other important surgical details that need to be taken into consideration such as different broaching techniques, cementing techniques and mantle thickness.With the evolution of cemented implants, the introduction of newer implants which have hybrid properties, and the use of different broaching techniques, the classification of a very heterogenous group of implants into simple binary categories becomes increasingly difficult. A more comprehensive classification system would aid in comparison of results and better understanding of the implants' biomechanics.We review these differing stem designs, their respective cementing techniques and geometries. We then propose a simple four-part classification system and summarize the long-term outcomes and international registry data for each respective type of cemented prosthesis. Cite this article: EFORT Open Rev 2020;5:241-252. DOI: 10.1302/2058-5241.5.190034.

Debridement, Antibiotics and Implant Retention for Hip Periprosthetic Joint Infection: Analysis of Implant Survival after Cure of Infection

Background: Debridement, antibiotics and implant retention (DAIR) is a valuable option for treating early and acute periprosthetic joint infection (PJI). The inflammation caused by the infection and the surgical intervention during DAIR may influence the long-term stability of the implant. In this study, we analyzed the sequelae of DAIR on implant survival in hip PJI after cure of infection.

Methods: Total hip arthroplasties (THAs) from our database implanted between 1992 and 2016 were included in a retrospective double-cohort study. THAs were exposed (DAIR cohort) or not exposed to DAIR (control cohort). The control cohort comprised patients matched 3:1 to the DAIR cohort. The outcome was implant failure over time. It was evaluated for (i) revision for any reason, (ii) aseptic loosening of any component, and (iii) radiographic evidence of loosening.

Results: 57 THAs (56 patients) were included in the DAIR cohort and 170 THAs (168 patients) in the control cohort. The mean follow-up periods in the DAIR and control cohorts were 6.1 and 7.8 years, respectively. During follow-up, 20 (36%) patients in the DAIR cohort and 54 (32%) in the control cohort died after a mean of 4.1 and 7.2 years, respectively. Revision for any reason was performed in 9 (16%) THAs in the DAIR cohort and in 10 (6%) THAs (p=0.03) in the control cohort, and revision for aseptic loosening of any component in 5 (9%) and 8 (5%) THAs (p=0.32), respectively. Radiological analysis included 56 THAs in the DAIR cohort and 168 THAs in the control cohort. Two (4%) stems and 2 (4%) cups in the DAIR cohort and 7 (4%) and 1 (0.6%) in the control cohort, respectively, demonstrated radiological signs of failure (p=1).

Conclusions: THAs exposed to DAIR were revised for any reason more frequently than were THAs in the control cohort. The difference was mainly caused by septic failures. After cure of PJI, the difference in revisions for aseptic loosening was not significant. There was no significant difference in radiographic evidence of loosening of any component between cohorts. These data suggest that cured hip PJI previously exposed to DAIR do not fail more frequently for aseptic reasons than do THAs not exposed to DAIR.

Is cemented revision total hip arthroplasty a reasonable treatment option in an elderly population?

Revision THA is increasingly performed especially in the elderly population. The surgeon’s challenge is to provide a solution that supports immediate full weight-bearing, despite poor bone quality. Shape-closed revision stems facilitate that by combining cement fixation with additional press-fit anchoring. The design tolerates varying cement mantle thickness and inconsistent cancellous bone lining of the femoral canal. Following that philosophy, we present our mid-term results using a long version of a cemented Charnley- Kerboull type stem. From 2010 to 2017, 38 long Charnley-Kerboull revision stems (Centris^®, Mathys European Orthopaedics, Bettlach, Switzerland) were implanted and followed prospectively. Surgery was performed via a Hardinge approach in supine position with a third generation cementing technique. Patients were mobilized using full-weight bearing as early as possible. Survival was determined for stem revision for aseptic loosening and stem and/or cup revision for any reason. 20 stems had a minimum follow-up (f/u) of 2 years and were included for further radiological analysis. Detailed subsidence analysis as an early predictor for later aseptic loosening was performed using EBRA-FCA software. Further, the presence of osteolysis and cement debonding was evaluated. Mean follow- up was 4 years. No patient was lost to f/u.18 died of causes unrelated to THA. Stem survival was 100%. Survival for any re-operation was 82.2% (two early infections, one soft-tissue debridement, one cup exchange for recurrent dislocations). None of the cases revised for septic loosening showed signs of persistent infection at final f/u. EBRA-FCA revealed two oligosymptomatic cases of subsidence of 5mm and 6mm over a course of 2 and 12 months, respectively, with stable implants thereafter. Neither required revision. There was no development of osteolysis or debonding. The stem provides a reliable early fullweight bearing solution for revision THA with excellent mid-term survival in an elderly population. Even in two cases where subsidence was present, mobility was not impaired and re-revision could be avoided.

7-year results of primary total hip arthroplasty with the uncemented Avenir stem

AIMS

The aim of the present study was to evaluate the 7-year functional outcome and radiographic results of primary total hip arthroplasties (THAs) performed with the uncemented Avenir stem.

PATIENTS AND METHODS

Between January 2006 and October 2008, 100 consecutive primary hips in 92 patients were enrolled at 2 centres. The mean age at operation was 58.5 years (27-87 years). Mini-incision (50%) and standard approaches (50%) were used to implant 22 standard and 78 lateralised stems.

RESULTS

The 7-year Kaplan-Meier survival rate was 98.9% (95% CI, 92.9-99.8) with stem revision for any reason as endpoint. No stem related complications occurred. 1 stem revision was due to deep infection at 51 months post-op. We had 4 acetabular revisions. The mean Harris Hip Score (HHS) at 7 years follow-up was 93.1 points (60-100). Radiographic analysis showed 2 patients had non-progressive radiolucent lines and no patient had any signs of stem subsidence or loosening.

CONCLUSION

The 7-year implant survival and the functional outcomes for THA performed with the study device are excellent and were in line with those documented for comparable contemporary uncemented fully HA-coated stems. Longer term follow-up of this consecutive series needs to be performed.

Five-year prospective subsidence analysis of 100 cemented polished straight stems: A concise clinical and radiological follow-up observation

Early subsidence (>1.5mm) has been shown to be an indicator for later aseptic loosening of cemented hip stems. For the cemented twinSys^® stem we published excellent short-term results at 2 years. Midterm data for this stem are available from national registers (NZL, NL), however in all of these sources, clinical and radiological results are missing. Aim of our study was to analyse mid-term survival and radiological changes around the cemented twinSys^® stem with special emphasis on subsidence using EBRA-FCA. We conducted a prospective clinical and radiological 5- year follow-up study of 100 consecutive hybrid total hip arthroplasties (THA) using a polished, cemented collarless straight stem (twinSys^®, Mathys AG^® Bettlach, Switzerland) with a cementless monobloc pressfit cup (RM pressfit^®, Mathys AG^® Bettlach, Switzerland). Median age at surgery was 79 (69 to 93) years. No patient was lost to follow-up. Survival rates were calculated using the Kaplan-Meier method. Clinical (Harris Hip Score [HHS]) and radiological (cementing quality, alignment, osteolysis, debonding and cortical atrophy) outcomes and an in-depth subsidence analysis using EBRA-FCA were performed. 22 patients died in the course of follow-up unrelated to surgery, 21 stems had an incomplete radiological follow-up. 2 stems were revised, both due to an infection. The survival rate for the stem at 5 years was 98.0% (95% CI 95.3-100%). The survival rate of the stem for revision due to aseptic loosening at 5 years was 100%. The HHS improved from 53 (14-86) points preoperatively to 90 (49-100) points 5 years after surgery. Osteolysis was found in 2 stems without clinical symptoms. In 49 out of 55 patients with a complete radiological follow- up, the EBRA-FCA analysis was possible and showed an average subsidence of 0.66 (95% CI 0.46 to 0.86) mm 5 years after surgery. 10 patients showed a subsidence >1 mm, 5 of which bigger than 1.5 mm. Subsidence was independent from radiological changes and cementing quality. The cemented twinSys^® stem showed excellent clinical and radiological mid-term results at five years' follow-up and seems to be a reliable implant.

Long-term survival of the cemented Müller CDH stem: a minimum follow-up of 10 years

INTRODUCTION

Total hip arthroplasty in patients with altered anatomy of the hip and femur, such as in congenital dysplasia of the hip, is challenging and often requires specially designed stems. Müller straight stems have shown excellent long-term results; however, long-term data on the analogous cemented Müller CDH stem are still missing. The aim of this study was to analyze long-term survival, identify potential risk factors for aseptic loosening, and analyze radiological outcome of the cemented Müller CDH stems.

MATERIALS AND METHODS

Between 01/1985 and 06/2005, 95 Müller CDH stems (Zimmer, Winterthur, Switzerland) made up of 3 different materials were cemented using 2 different bone cements: 38 of stainless steel/high-viscosity cement, 31 of a cobalt-chrome-based alloy (CoCr)/low-viscosity cement, and 26 of a titanium-based alloy (Ti)/low-viscosity cement. All patients had a prospective clinical and radiological follow-up according to the standards of our institution. The cumulative incidence for revision of the stem was calculated using a competing risk model. To identify demographic and implant-related risk factors for aseptic loosening of the stem, a multivariate regression model for competing risks was performed.

RESULTS

The cumulative risk of revision at 15 years was 12.5% (95% CI 6.6-20.5%) for aseptic loosening of the stem as endpoint, with marked differences for the various stem materials used: stainless steel 2.7% (0.2-12.3%), CoCr 12.9% (4.0-27.3%), and Ti 24.5% (9.6-43.1%). Regression modeling revealed that Ti stems in combination with low-viscosity cement (HR 10.2) and implantation with an axis deviation greater than 3° (HR 3.8) are risk factors for aseptic loosening.

CONCLUSIONS

Long-term survival of the cemented Müller CDH stem is comparable to other Müller-type straight stems and uncemented implants. Similar to the original Ti Müller straight stem, the Ti Müller CDH stem also showed an increased risk for aseptic loosening and should, therefore, no longer be used.

Long-term results of revision total hip arthroplasty with a cemented femoral component

INTRODUCTION

In revision total hip arthroplasty (THA), the cancellous bone is normally completely removed out of the femoral canal during stem extraction. This situation is comparable to primary THA following the shape-closed concept, with some authors advocating to remove the metaphyseal cancellous bone to enhance press-fit stability ("French paradox"). The aim of this study was to investigate the long-term outcome, regarding survival and radiological results, of a cemented straight stem when used for revision THA and to compare these results to the results of the same stem in primary THA.

MATERIALS AND METHODS

178 stem revisions performed between 01/1994 and 08/2008 using the Virtec straight stem were included. The cumulative incidence for re-revision was calculated using a competing risk model. Risk factors for re-revision of the stem were analyzed using an absolute risk regression model. Radiographs analyzed for osteolysis, debonding and subsidence had a minimum follow-up of 10 years.

RESULTS

The cumulative incidence for re-revision due to aseptic loosening of the stem was 5.5% (95% CI, 2.9-10.2%) at 10 years. Aseptic loosening was associated with younger age, larger defect size and larger stem size. After a minimum 10-year follow-up, osteolysis was seen in 39 of 80 revision THA. Compared to the results in primary THA, the survival in revision THA with the same implant was inferior.

CONCLUSIONS

Cemented straight stems used for revision THA showed excellent long-term results regarding survivorship and radiological outcome. This stem therefore offers a valuable and cost-effective option in revision THA.

Debridement and implant retention in the management of hip periprosthetic joint infection: outcomes following guided and rapid treatment at a single centre

AIMS

To analyse the effectiveness of debridement and implant retention (DAIR) in patients with hip periprosthetic joint infection (PJI) and the relationship to patient characteristics. The outcome was evaluated in hips with confirmed PJI and a follow-up of not less than two years.

PATIENTS AND METHODS

Patients in whom DAIR was performed were identified from our hip arthroplasty register (between 2004 and 2013). Adherence to criteria for DAIR was assessed according to a previously published algorithm.

RESULTS

DAIR was performed as part of a curative procedure in 46 hips in 42 patients. The mean age was 73.2 years (44.6 to 87.7), including 20 women and 22 men. In 34 hips in 32 patients (73.9%), PJI was confirmed. In 12 hips, the criteria for PJI were not fulfilled and antibiotics stopped. In 41 (89.1%) of all hips and in 32 (94.1%) of the confirmed PJIs, all criteria for DAIR were fulfilled. In patients with exogenous PJI, DAIR was performed not more than three days after referral. In haematogenous infections, the duration of symptoms did not exceed 21 days. In 28 hips, a single debridement and in six hips two surgical debridements were required. In 28 (87.5%) of 32 patients, the total treatment duration was three months. Failure was noted in three hips (9%). Long-term follow-up results (mean 4.0 years, 1.4 to 10) were available in 30 of 34 (88.2%) confirmed PJIs. The overall successful outcome rate was 91% in 34 hips, and 90% in 30 hips with long-term follow-up results.

CONCLUSION

Prompt surgical treatment with DAIR, following strict diagnostic and therapeutic criteria, in patients with suspected periprosthetic joint infection, can lead to high rates of success in eradicating the infection. Cite this article: Bone Joint J 2017;99-B:330-6.

Prospective two-year subsidence analysis of 100 cemented polished straight stems - a short-term clinical and radiological observation

Background

Cemented stems show good long-term results and the survival of new implants can be predicted by their early subsidence. With EBRA-FCA (Femoral Component Analysis using Einzel-Bild-Röntgen-Analyse) early subsidence as an early indicator for later aseptic loosening can be analysed. For the cemented TwinSys stem mid- and long-term data is only avalible from the New Zeeland Arthroplasty register, thus close monitoring of this implant system is still mandatory.

Methods

We conducted a 2 year follow up of 100 consecutive hybrid THA (Total hip arthroplasty) of a series of 285 primary THA operated between Jan 2009 und Oct 2010. These 100 received a polished, cemented collarless straight stem (twinSys®, Mathys AG® Bettlach, Switzerland) with an uncemented monobloc pressfit cup (RM pressfit®, Mathys AG® Bettlach, Switzerland). The other patients were treated with the uncemented version of this stem and the same cup. Clinical (Harris Hip Score) and radiological (ap and axial x-rays, cementing quality according to Barrack, alignment) outcomes besides an EBRA-FCA subsidence analysis were performed.

Results

Median age at operation was 78 (68 to 93) years. 5 patients died in the course of follow-up unrelated to surgery. The KM (Kaplan-Meier) survival at 2 years for the endpoint reoperation for any reason was 94.9 (95 % confidence interval 90.6–100 %). Survival for the endpoint aseptic loosening at 2 years was 100 %.

The HHS (Harris Hip Score) improved from 56 (14–86) preoperatively to 95 (60–100) 2 years after the operation. Cementing results were judged 47 % Grade A, 45 % Grade B and 7 % Grade C.

Osteolysis was found in 2 stems without clinical symptoms or correlation to subsidence or cementing quality. The EBRA-FCA analysis showed an average subsidence of -0.30 mm (95 % CI -0.5 mm to -0.1 mm). 11 patients showed a subsidence of more than 1 mm. In this group one patient showed a subsidence of 1.5 mm and one of 3.1 mm without further radiological changes.

Conclusions

The twinSys stem showed excellent clinical and radiologic short term results at 2 years follow-up and seems to be a reliable implant.

Similar effect of stem geometry on radiological changes with 2 types of cemented straight stem: The Müller stem and the Virtec stem compared in 711 hips

BACKGROUND AND PURPOSE

There are 2 basic principles in cemented stem fixation: shape-closed and force-closed. We investigated 2 shape-closed straight stems, the Müller (MSS) and the Virtec (VSS), which differ only in geometrical cross section, to determine whether the difference in stem shape would affect the radiological results or long-term survival.

PATIENTS AND METHODS

We included 711 hips (in 646 patients) that were operated on between July 1996 and July 2003. Patients randomly received either an MSS (n = 356) or a VSS (n = 355) and were followed prospectively. Radiographs taken at a follow-up of > 10 years were analyzed for osteolysis. Kaplan-Meier (KM) survival analysis was performed using various endpoints. We also performed Cox regression analysis to identify risk factors for aseptic loosening and osteolysis of the stem.

RESULTS

After 10 years, KM survival with "revision of any component for any reason" was 92% (95% CI: 88-95) for the MSS and 95% (CI: 92-97) for the VSS (p = 0.1). With "revision for aseptic loosening of the stem" as the endpoint, KM survival was 96% (CI: 9-98) for the MSS and 98% (CI: 97-100) for the VSS (p = 0.2). Cox regression showed that none of the risk factors analyzed were independent regarding aseptic loosening of the stem or regarding osteolysis.

INTERPRETATION

The MSS and the VSS showed excellent survival for aseptic loosening after 10 years. For the 2 different stem designs, we did not find any independent risk factors for aseptic loosening or development of osteolysis.

Systematic review of literature of cemented femoral components: what is the durability at minimum 20 years followup?

BACKGROUND

Cemented femoral total hip arthroplasty may be one of the most successful surgical interventions of all time. However, although results are very encouraging over the early to mid-term followup, relatively few studies have analyzed the durability of these implants beyond 20 years followup. To evaluate the performance of contemporary implants, it is important to understand how previous implants perform at 20 or more years of followup; one way to do this is to aggregate the available data in the form of a systematic review.

QUESTIONS/PURPOSES

(1) How durable is cemented femoral fixation in the long term (minimum 20-year followup) with respect to aseptic loosening? (2) Is the durability of cemented femoral fixation dependent on age of the patient? (3) Are the long-term results of the cemented femoral fixation dependent on any identifiable characteristics of the prosthesis such as surface finish?

METHODS

A systematic review was performed to identify long-term studies of cemented femoral components. After application of inclusion and exclusion criteria to 1228 articles found with a search in PubMed and EMBASE, 17 studies with a minimum of 20-year followup on cemented femoral components were thoroughly analyzed in an attempt to answer the questions of this review. The quality of the studies reviewed was assessed with the Methodological Index for Nonrandomized Studies (MINORS) instrument. All studies were case series and cohort sizes ranged from 110 to 2000 hips for patients older than 50 years of age and 41 to 93 hips for patients younger than 50 years at the time of surgery.

RESULTS

Among the six case series performed in patients older than 50 years of age, survivorship for aseptic loosening of the femoral component ranged from 86% to 98% at 20 years followup. There were no obvious differences for younger patients when analyzing the five studies in patients younger than age 50 years in which survivorship free from aseptic loosening for these studies ranged from 77% at 20 years in one study and 68% to 94% at 25 years in the other studies. Although data pooling could not be performed because of heterogeneity of the studies included here, it appeared that stems with a rougher surface finish did not perform as well as polished stems; survivorship of stems with rougher surface finishes varied between 86% and 87%, whereas those with smoother finishes ranged between 93.5% and 98% at 20 years.

CONCLUSIONS

Excellent long-term fixation in both older and younger patients can be obtained with cemented, polished femoral stems. These results provide material for comparison with procedures performed with newer cementing techniques and newer designs, both cemented and cementless, at this extended duration of followup.

Dynamics of femoral bone remodelling in well fixed total hip arthroplasty. A 20-year follow-up of 20 hips

The aim of our study was to investigate the dynamics of cortical thinning around well fixed cemented Muller straight stems without osteolysis at different time periods during long term follow-up. We investigated patients operated on for osteoarthritis with a cemented Muller straight stem, all with more than 15 years follow-up and no radiological signs of osteolysis. Cortical thinning in 20 THA hips (19 patients) followed for a mean of 20 (16 to 22) years was measured medially and laterally at six levels from the first postoperative, five, 10 years and the last follow-up x-rays. Sixty percent of observed cortical thinning occurred during the first five postoperative years, which was more evident proximally. We conclude that significantly greater cortical bone loss occurs around cemented Muller straight stems during the first five years, than is seen subsequently. We feel that this is a non-pathological process mainly related to the Muller straight stem.

Bond strength analysis of the bone cement- stem interface of hip arthroplasties

OBJECTIVE

To study and establish the preliminary linear and modified models for the interface shear mechanics performance between implant and bone cement and to explore its damage significance.

METHOD

The loosening research between artificial hip joint prosthesis stem and bone cement interface performance can be evaluated by the push-in test. Based on the debonding performance test, the analytical expressions of the average load and displacement from the debonding failure and splitting failure process were deduced and determined. The correlations of the expressions of the average load-displacement and statistical experimental data were analyzed.

RESULTS

It demonstrated that the interface debonding failure mechanical model could be characterized as interface bond strength mechanical performance. Based on analysis of models and experimental data by the three statistical analysis methods, the results indicated the modified model could be better represented by the interfacial debonding strength properties. The bond stress τ and relative sliding s distribution along the embedment regional were coupling affected by both pressure arch effect and shear lag effect in bone cement. Two stress peaks of implant have been found at the distance from 0.175La loading tip to 0.325La free tip, which also verified the early loosening clinical reports for the proximal and latter region. As the bone cement arch effect, the bond stress peak tend to move to the free tip when the debonding failure would be changed into the splitting failure, which presents a preliminary study on the mechanism of early debonding failure for the stem-cement interface.

CONCLUSIONS

Functional models of the stem-bone cement interfacial debonding failure are developed to analyze the relevant mechanism. The different locational titanium alloy stress, and the interfacial bond stress and the relative slides are evaluated to acquire a guide of the different positions of interfacial damage. The coupling effect which is original from the pressure arch and the interfacial shear hysteresis cumulative effect has influence on the interfacial debonding and damage process.

Cemented Müller straight stem total hip replacement: 18 year survival, clinical and radiological outcomes

AIM: To present the 18 year survival and the clinical and radiological outcomes of the Müller straight stem, cemented, total hip arthroplasty (THA).

METHODS: Between 1989 and 2007, 176 primary total hip arthroplasties in 164 consecutive patients were performed in our institution by the senior author. All patients received a Müller cemented straight stem and a cemented polyethylene liner. The mean age of the patients was 62 years (45-78). The diagnosis was primary osteoarthritis in 151 hips, dysplasia of the hip in 12 and subcapital fracture of the femur in 13. Following discharge, serial follow-up consisted of clinical evaluation based on the Harris Hip Score and radiological assessment. The survival of the prosthesis using revision for any reason as an end-point was calculated by Kaplan-Meier analysis.

RESULTS: Twenty-four (15%) patients died during the follow-up study, 6 (4%) patients were lost, while the remaining 134 patients (141 hips) were followed-up for a mean of 10 years (3-18 years). HSS score at the latest follow-up revealed that 84 hips (59.5%) had excellent results, 30 (22.2%) good, 11 (7.8%) fair and 9 (6.3%) poor. There were 3 acetabular revisions due to aseptic loosening. Six (4.2%) stems were diagnosed as having radiographic definitive loosening; however, only 1 was revised. 30% of the surviving stems showed no radiological changes of radiolucency, while 70% showed some changes. Survival of the prosthesis for any reason was 96% at 10 years and 81% at 18 years.

CONCLUSION: The 18 year survival of the Müller straight stem, cemented THA is comparable to those of other successful cemented systems.

Risk factors for aseptic loosening of Müller-type straight stems: a registry-based analysis of 828 consecutive cases with a minimum follow-up of 16 years

Background and purpose Even small differences in design variables for the femoral stem may influence the outcome of a hip arthroplasty. We performed a risk factor analysis for aseptic loosening of 4 different versions of cemented Müller-type straight stems with special emphasis on design modifications (2 shapes, MSS or SL, and 2 materials, CoNiCrMo (Co) or Ti-6Al-7Nb (Ti)). Methods We investigated 828 total hip replacements, which were followed prospectively in our in-house register. All stems were operated in the same setup, using Sulfix-6 bone cement and a second-generation cementing technique. Demographic and design-specific risk factors were analyzed using an adjusted Cox regression model. Results The 4 versions showed marked differences in 15-year stem survival with aseptic loosening as the endpoint: 94% (95% CI: 89-99) for MSS Co, 83% (CI: 75-91) for SL Co, 81% (CI: 76-87) for MSS Ti and 63% (CI: 56-71) for SL Ti. Cox regression analysis showed a relative risk (RR) for aseptic loosening of 3 (CI: 2-5) for stems made of Ti and of 2 (CI: 1-2) for the SL design. The RR for aseptic stem loosening increased to 8 (CI: 4-15) when comparing the most and the least successful designs (MSS Co and SL Ti). Interpretation Cemented Müller-type straight stems should be MSS-shaped and made of a material with high flexural strength (e.g. cobalt-chrome). The surface finish should be polished (Ra < 0.4 µm). These technical aspects combined with modern cementing techniques would improve the survival of Müller-type straight stems. This may be true for all types of cemented stems.

Long-term femoral bone remodeling after cemented hip arthroplasty with the Müller straight stem in the operated and nonoperated femora

We investigated the cortical bone changes in 35 patients with total hip arthroplasty operated on only for osteoarthritis with more than 10 years of follow-up and with nonrevised femoral components and without radiologic signs of loosening. The mean follow-up was 16 ± 5 years. The thicknesses of femoral cortices were measured medially and laterally at 6 levels from the first postoperative and the last follow-up x-rays. A comparison with 10 patients who had a nonoperated contralateral hip was performed. We found a significant decrease in cortical thicknesses in total hip arthroplasty. The cortical thinning was significant at all periprosthetic levels but less expressed distally. Prosthetic femora were associated with greater cortical thinning as compared with the contralateral nonoperated femora, exceeding that caused by natural aging.

Clinical outcome of the metal-on-metal hybrid Corin Cormet 2000 hip resurfacing system: an up to 11-year follow-up study

This report extends the follow-up for the largest center of the first multicenter US Food and Drug Administration investigational device exemption study on metal-on-metal hip resurfacing arthroplasty up to 11 years. A single surgeon performed 373 hip resurfacing arthroplasties using the hybrid Corin Cormet 2000 system. The Kaplan-Meier survivorship at 11 years was 93% when revision for any reason was used as an end point and 91% if radiographic failures were included. The clinical results demonstrate an acceptable failure rate with use of this system. Loosening of the cemented femoral components was the most common source of failure and occurred at all follow-up intervals. A learning curve that persisted for at least 200 cases was confirmed. All femoral neck fractures occurred before 6 months postoperatively.

The histology around the cemented Müller straight stem: A post-mortem analysis of eight well-fixed stems with a mean follow-up of 12.1 years

The aim of this study was to obtain detailed long-term data on the cement-bone interface in patients with cemented stems, implanted using the constrained fixation technique. A total of eight stems were removed together with adjacent bone during post-mortem examinations of patients with well-functioning prostheses. Specimens were cut at four defined levels, contact radiographs were obtained for each level, and slices were prepared for histological analysis. Clinical data, clinical radiographs, contact radiographs and histological samples were examined for signs of loosening and remodelling. The mean radiological follow-up was 9.6 years and all stems were well-fixed, based on clinical and radiological criteria. Contact radiographs revealed an incomplete cement mantle but a complete filling of the medullary canal for all implants. Various amounts of polyethylene particles were evident at the cement-bone interface of seven stems, with no accompanying inflammatory reaction. Cortical atrophy and the formation of an 'inner cortex' were confirmed in six of eight stems by contact radiographs and histology, but were only visible on two clinical radiographs. Our results confirm that a complete cement mantle is not essential for the survival of Müller straight stems into the mid term, and support our hypothesis that no benefit to long-term survival can be expected from modern cementing techniques.

Male gender, Charnley class C, and severity of bone defects predict the risk for aseptic loosening in the cup of ABG I hip arthroplasty

Background

We studied which factor could predict aseptic loosening in ABG I hip prosthesis with hydroxyapatite coating. Aseptic loosening and periprosthetic osteolysis are believed to be caused, at least in part, by increased polyethylene (PE) wear rate via particle disease. Based on it, increased PE wear rate should be associated with aseptic loosening regardless of the type of implant.

Methods

We analyzed data from 155 revisions of ABG I hip prostheses to examine the influence of patient, implant, surgery, and wear related factors on the rate of aseptic loosening at the site of the cup. This was calculated by stepwise logistic regression analysis. The stability of the implant and severity of bone defects were evaluated intraoperatively.

Results

We found that men (odds ratio, OR = 5.6; p = 0.004), patients with Charnley class C (OR = 6.71; p = 0.013), those having more severe acetabular bone defects (OR = 4 for each degree of severity; p = 0.002), and longer time to revision surgery (OR = 1.51 for each additional year; p = 0.012) had a greater chance of aseptic loosening of the cup. However, aseptic loosening was not directly predicted by polyethylene wear rate in our patients.

Conclusion

Severity of bone defects predicts the risk for aseptic loosening in ABG I cup. Factors potentially associated with the quality of bone bed and biomechanics of the hip might influence on the risk of aseptic loosening in this implant.