High Risk of Failure With Bimodular Femoral Components in THA

Fracture of femoral neck in modular total hip arthroplasty: a systematic review of the literature

BACKGROUND

Modular femoral stems have the advantage of anatomic hip reconstruction by restoring the femoral offset thus minimising the bearing surface wear, implant loosening and dislocation.

AIM

This study aims to investigate the existing literature on modular neck fractures, to identify predisposing factors and guide the decision-making process in the management of these difficult cases.

METHODS

A systematic literature review was conducted until July 2022. PRISMA guidelines were followed, eligibility criteria were set, and methodology assessment of included studies was conducted based on MINORS criteria, size and primary outcome. Data were extracted and analysed thoroughly.

RESULTS

5657 studies were initially screened; the full texts of 124 records were assessed and finally, 32 reports were included. There were 7 clinical studies and 25 case reports. A total of 4825 patients (5204 hips) with a mean age 62.38 years and a mean BMI 29.06 kg/m2 were analysed in the 7 clinical studies. The reported overall weighted revision rate was 0.86%, while the weighted mean modular neck fracture rate was 0.26%. The usual history was sudden experience of hip pain and instability. The average time interval to neck fracture was 4.57 (range 3-4.7) years and a long modular neck was identified in 91.17% of them. Data from case reports showed a mean age and average BMI of 55.85 and 31.63 kg/m2. 82.35% of the patients were male. Necks were fractured after an average time interval of 64.5 ± 8.8 months.

CONCLUSIONS

The incidence of modular neck fracture is significant. The profile of a male, obese patient with a long modular neck increased risk of neck fracture. Microstructural investigation of the retrieved implants demonstrated a higher incidence of fracture line in the base of the neck junction and at its anterolateral distal part. Surgeons should be aware of this complication while using or revising such protheses.

15-year survivorship of a unique dual-modular femoral stem in primary hip arthroplasty

BACKGROUND

Hip offset, version, and length are interdependent femoral variables which determine stability and leg length. Balancing these competing variables remains a core challenge in hip arthroplasty. The potential benefits of modular femoral stems have been overshadowed by higher rates of failure. The objective of this study was to assess the survivorship of a unique dual-modular femoral stem at an average 15-year follow-up period.

METHODS

The records of all patients with osteoarthritis who underwent primary total hip arthroplasty with this device between 2004-2009 were reviewed. There were no exclusions for BMI or other factors. We examined the data with Kaplan-Meier survival analysis. The primary endpoint for survival was mechanical failure of the modular neck-body junction.

RESULTS

The survivorship of this device in 172 subjects was 100% with none experiencing mechanical failure of the modular junction at an average of 15 years. 60 patients died of causes unrelated to their THA and 9 patients were lost to follow-up. There were three early (≤ 12 months) dislocations (1.7%), and seven total dislocations (4.1%). 16 patients underwent reoperations during the follow-up period, none for any complication of the modular junction. Radiographic results showed well-fixed femoral stems in all cases. There were no leg length discrepancies of greater than 10 mm, and 85% were within 5 mm.

CONCLUSION

There were no mechanical failures of the modular junction in any of the subjects over the average 15-year period, demonstrating that this dual-modular design is not associated with increased failure rates. We achieved a 1.7% early dislocation rate and a 4.1% total dislocation rate without any clinically significant leg length discrepancies.

Bimodular femoral stems in primary total hip arthroplasty

INTRODUCTION

This review critically examines the efficacy of dual-modular stems in primary total hip arthroplasty. Given the variability and non-comparability of certain femoral stem designs and stem-neck couplings, with some even being withdrawn from the market, this review offers an in-depth analysis of predominant implant performances.

AREAS COVERED

The paper explores a brief historical summary related to dual-modular stems, including the complications associated with their use, diagnostic tools for evaluation, analysis of both recalled and currently available models, as well as alternative therapeutic options. This information is pertinent for both clinical and research domains.

EXPERT OPINION

While dual-modular systems were initially touted to offer several advantages, the evidence substantiating these benefits has been ambiguous. Further, these systems introduce the risk of alternative complications. In specific cases involving patients with developmental hip dysplasia and certain proximal femoral deformities requiring complex reconstructions, dual-modular systems might be relevant. Nonetheless, the use of long interchangeable necks in patients with a body mass index above 30 kg/m2 is discouraged, and pairing a long varus-oriented neck with an extra-long femoral head should be avoided in all patients.

Dual-Modular Versus Single-Modular Stems for Primary Total Hip Arthroplasty: A Long-Term Survival Analysis

Background and Objectives: Increased revision rate of dual-modular (DM) femoral stems in primary total hip arthroplasty (THA) because of modular-neck breakage and adverse local tissue reactions (ALTRs) to additional junction damage products is well established and some designs have been recalled from the market. However, some long-term studies of specific DM stems did not confirm the inferiority of these stems compared to standard single-modular (SM) stems, and a head-to-head comparison THA is missing. The objectives of this multicentre study were to determine the survivorship and complication rates of a common DM stem design compared to a similar SM stem. Materials and Methods: In a time frame from January 2012 to November 2015, a cohort of 807 patients (882 hips) consecutively underwent primary cementless THAs at two orthopaedic centres. 377 hips were treated with a Zweimüller-type DM stem THA system and 505 hips with a similar SM stem THA system, both including a modern press-fit acetabulum. Kaplan-Meier survivorship and complication rates were compared between both groups in a median follow-up of 9.0 years (maximum, 9.9 years). Results: The 9-year survivorship of the DM stem THA system (92.6%, 95% CI 89.9-95.3) was significantly lower than that of the SM stem THA system (97.0%, 95% CI 95.2-98.8). There were no differences in revision rates for septic loosening, dislocation, and periprosthetic fractures between the two groups. One ceramic inlay and one Ti-alloy modular neck breakage occurred in the DM stem THA system group, but the main reason for revision in this group was aseptic loosening of components. Conclusions: The survivorship of the DM stem THA system was lower than the similar SM stem THA system in a comparable clinical environment with long-term follow-up. Our results confirmed that no rationale for stem modularity exists in primary THAs.

Long-term survivorship of an exchangeable-neck hip prosthesis with a Ti-alloy/Ti-alloy neck-stem junction

INTRODUCTION

Breakage of exchangeable-neck (EN) and adverse local tissue reactions (ALTRs) to neck-stem junction (NSJ) damage products are responsible for increasing the revision rate of EN hip prostheses. We investigated the survivorship of an EN hip prosthesis including a NSJ with both components made of titanium alloy (Ti-alloy/Ti-alloy) to assess whether, and to what extent, EN breakage and NSJ damage affected implant survivorship.

MATERIALS AND METHODS

Using data from a hip replacement registry, we determined survivorship of 2857 EN prostheses. Long-offset configurations of head and EN were implanted in heavy (> 90 kg) patients only in 23 hips. We investigated under which conditions EN breakages or ALTRs occurred. We also measured titanium (Ti) and vanadium (V) blood concentrations in 24 patients with a unilateral well-working prosthesis.

RESULTS

The 17-year survival rates for any reason and aseptic loosening of any component were 88.9% (95%CI 87.5-90.1; 857 hips at risk) and 96.9% (95%CI 96.0-97.6), respectively. There were two cases of EN breakage and one case of ALTR (metallosis), due to rim-neck impingement, out of 276 revisions. After an average period of 9.8 years (range 7.8-12.8 years), the maximum Ti and V blood concentrations in patients with a well-working prosthesis were 5.0 µg/l and 0.16 µg/l, respectively.

CONCLUSION

The present incidence of EN breakage or ALTR is lower than those reported in other studies evaluating EN hip prosthesis survivorship. This study suggests that (i) the risk of EN breakage is reduced by limiting the use of long-offset configurations in heavy patients and (ii) Ti-alloy/Ti-alloy NSJ damage products do not promote ALTR nor significantly alter the rate of implant loosening. Since design decisions and implant configuration determine the NSJ strength, the NSJ strength in working conditions must be thoroughly investigated to proper define the clinical indications for any EN design.

Modular neck stems in total hip arthroplasty: current concepts

Modular neck (MN) implants can restore the anatomy, especially in deformed hips such as sequelae of development dysplasia.

Early designs for MN implants had problems with neck fractures and adverse local tissue, so their use was restricted to limited indications.

Results of the latest generation of MN prostheses seem to demonstrate that these problems have been at least mitigated.

Given the results of the studies presented in this review, surgeons might consider MN total hip arthroplasty (THA) for a narrower patient selection when a complex reconstruction is required.

Long MN THA should be avoided in case of body mass index > 30, and should be used with extreme caution in association with high offset femoral necks with long or extra-long heads. Cr-Co necks should be abandoned, in favour of a titanium alloy connection.

Restoring the correct anatomic femoral offset remains a challenge in THA surgeries.

MN implants have been introduced to try to solve this problem. The MN design allows surgeons to choose the appropriate degree and length of the neck for desired stability and range of motion.

Cite this article: EFORT Open Rev 2021;6:751-758. DOI: 10.1302/2058-5241.6.200064

Dual Modular Titanium Alloy Femoral Stem Failure Mechanisms and Suggested Clinical Approaches

Titanium (Ti) alloys have been proven to be one of the most suitable materials for orthopaedic implants. Dual modular stems have been introduced to primary total hip arthroplasty (THA) to enable better control of the femoral offset, leg length, and hip stability. This systematic review highlights information acquired for dual modular Ti stem complications published in the last 12 years and offers a conclusive discussion of the gathered knowledge. Articles referring to dual modular stem usage, survivorship, and complications in English were searched from 2009 to the present day. A qualitative synthesis of literature was carried out, excluding articles referring solely to other types of junctions or problems with cobalt-chromium alloys in detail. In total, 515 records were identified through database searching and 78 journal articles or conference proceedings were found. The reasons for a modular neck fracture of a Ti alloy are multifactorial. Even though dual modular stems have not shown any clinical benefits for patients and have been associated with worse results regarding durability than monolithic stems, some designs are still marketed worldwide. Orthopaedic surgeons should use Ti6Al4V dual modular stem designs for primary THA in special cases only.

Systematic review of primary total hip arthroplasty using titanium-titanium modular-neck prostheses: the true risk of revision

AIMS

Modular-neck femoral implants are used to enable more variability in femoral neck version, offset and length. It has been reported that these implants carry a higher rate of revision. The aim of this review was to assess the overall and cause-specific revision rate of titanium-titanium alloy modular-neck implants in primary total hip arthroplasty (THA).

METHODS

A systematic review was conducted following PRISMA guidelines and utilising multiple databases. All results were screened for eligibility. Studies published from 2000 onwards, using a current-generation, titanium-titanium, modular-neck implant were included. Overall and cause-specific revision rates were analysed, comparing to fixed-neck prostheses where applicable.

RESULTS

920 studies were screened. After applying exclusion criteria, 23 were assessed in full and 14 included. These consisted of 12 case series and 2 joint registry analyses. 21,841 patients underwent a modular-neck implant with a weighted mean follow-up of 5.7 years, mean age of 62.4 years, and average body mass index (BMI) of 28.4kg/m². The overall revision rate was 3.95% and 2.98% for modular and fixed-neck prostheses, respectively. For studies with >5 years follow-up the mean revision rate was 3.08%. There was no difference in cause-specific revision rates by implant design. Mean improvement in Harris Hip Score was 41.9.

CONCLUSIONS

At medium-term, revision rates for titanium-titanium primary modular-neck THA are acceptable. These prostheses are a sensible management option in patients with considerable anatomical hip deformity not amenable to correction with standard fixed-neck implants. Patients of male gender, high BMI and requiring prostheses with a larger neck, offset or head are at higher risk of implant failure.

Bilateral neck fracture in bimodular femoral stem after primary total hip arthroplasty: a case report

Background

Bi-modular stems were introduced in primary total hip arthroplasty (THA) to enable better control of the femoral offset, leg length, and hip stability. Despite numerous reports on modular femoral neck fractures, some designs are still marketed worldwide. While the risk factors for the sudden failure are multifactorial and mostly known, the timing of this new THA complication is not predictable by any means.

Case presentation

In this report, the literature regarding one of the most popular bi-modular stems with specific neck-stem coupling (oval Morse taper) is reviewed and illustrated with a case of bilateral modular neck fracture in a patient with idiopathic aseptic necrosis of femoral heads treated with primary bi-modular THA. Because of bilateral modular femoral neck fracture, which occurred 3 years on the left side and 20 years after implantation on the right side, the patient required a total of 6 revisions and 208 days of hospitalized care.

Conclusion

To our knowledge, this is the first report of bilateral modular neck fracture in a single patient. Even though the same surgeon performed both operations and used the same neck length and orientation, fractures occurred with a 17-year time difference after implantation. This shows that we cannot predict with certainty when a fracture might occur. Orthopaedic surgeons should use bi-modular stem designs for primary THA very cautiously.

Femoral Stem Fracture in Hip Revision Arthroplasty: A Systematic Literature Review of the Real-World Evidence

Background Total hip arthroplasty (THA) presents as an excellent treatment for the osteoarthritic hip, demonstrating good survival rates. However, aseptic loosening and infection are the main causes of operative revision. The methods used in revision surgery are non-modular or modular THA implants. In addition to the abovementioned revision reasons for THA, this treatment could be associated with the possibility of femoral stem fracture, especially in the modular system. The topic of material failure has been focused on in the public media. The question arises as to how such media reports correlate with the published literature. The observed mentioned number of cases concerning a femoral stem fracture vary between one single case and up to 18.5% within a clinical study, thus presenting an inhomogeneous data situation with a large span. The specific aim of this systematic review is to establish facts and clarify the number of unforeseen events of a femoral stem fracture based on peer review articles and registry data. This clarification is important to us, as these media reports have led to uncertainty among patients.

Methods A systematic review was performed in accordance with the PRISMA statement. Peer review articles in English and German, presenting original articles, meta-analyses, or case reports, were searched from the turn of the millennium up to December 2019. Only articles that reported a femoral stem component fracture, with content of clinical data as well as register data, were included. Relevant papers published after the defined research time frame were taken into account within the discussion.

Results In total, 218 fractures of a femoral stem (141 primary and 77 revision THA) component could be identified within the selected literature. Most cases of a femoral stem fracture occurred in the modular THA implants compared to the non-modular stems. Regarding revision THA, in summary, 77 implants, presenting 23 non-modular and 54 modular implants, failed by means of femoral stem fracture. A review of 11 National Joint Registries shows a revision rate between 0.04 and 0.05% in only 2 registers according to the specific subject of a femoral stem fracture. For the remaining 9 registers, however, detailed information is lacking and only nonspecific information such as a generic “implant failure” or “other reason” (which can cover a multitude of causes) is supplied.

Conclusion A femoral stem fracture presents a devastating complication for the patient, the surgeon as well as for the manufacturer of the implant. Modular THA implants play an increasingly valuable role concerning restoration of individual anatomy in modern THA revision surgery, especially within complex cases. Regarding revision procedures, data suggests a lower risk of femoral stem fracture for modular implants compared to primary procedures, while the risk of fracture for non-modular implants seems to increase during revision. Ultimately, it cannot be proven whether this is actually applicable, since the absolute number of implanted prosthesis systems is not known. Various implant-, patient-, and surgeon-related factors may lead to these reported femoral stem fractures. However, this systematic review suggests that this is, in general, a rare complication.

Incidence of Pseudotumors in a Dual Modular Stem Construct With and Without Metal-on-Metal Bearing Surface

BACKGROUND

The purpose of this study was to compare the incidence of pseudotumors in metal-on-metal (MoM) titanium modular neck hip arthroplasties to non-MoM modular neck hip arthroplasties. A secondary goal was to determine whether a correlation exists between elevated metal concentrations and pseudotumor incidence.

METHODS

The data were collected and evaluated from 49 MoM joints and 26 non-MoM joints between the years 2012 and 2017. Hip ultrasonography was done after a minimum of 5 years postimplantation. Whole serum metal (titanium, cobalt, and chromium) concentrations were measured at the hip ultrasonography study.

RESULTS

The average time elapsed between surgery and ultrasonography visit was 7.6 years. In the 49 patients with MoM joints, 22.4% (n = 11) had a pseudotumor. In the 26 patients with non-MoM joints, 9.1% of metal-on-polyethylene hips (n = 1) and 0% of ceramic-on-ceramic/polyethylene hips developed a pseudotumor. No significant statistical correlation was observed between serum metal concentrations and pseudotumor formation (P > 0.05). A significant correlation was observed of serum titanium concentration to pseudotumor size (P = 0.024).

CONCLUSION

The incidence of pseudotumor formation in MoM total hip arthroplasties was more than five times the incidence associated with non-MoM bearings. The correlation between serum titanium concentration and pseudotumor size suggests that titanium levels may be a useful indicator for pseudotumor formation in patients with this particular titanium modular neck femoral implant. No notable correlation was observed between serum cobalt and chromium concentration and pseudotumor formation or size.

Mid-term results of total hip arthroplasty using a novel uncemented short femoral stem with metaphyso-diaphyseal fixation

PURPOSE

Short stems were developed with the promise of providing easier implantation, facilitating revision, reducing thigh pain and proximal stress shielding. The aim of this study is to present the mid-term clinical results of a titanium short stem with modular neck.

METHODS

This is a prospective case series of 144 THAs performed on a series of 131 patients using the PROFEMUR Preserve Femoral Stem (MicroPort Orthopedics, Arlington, TN, USA). 2 surgeons, operated on the patients using a mini-posterior approach. The primary outcomes evaluated were stem revision for aseptic loosening and all-cause stem revision. Clinical and radiographic outcomes were also assessed.

RESULTS

Of the 144 THAs, there were 43 males and 101 females, with an average age of 61 (range 22-92) years at surgery. After a mean of 78 (range 53-87) months follow-up, there were 2 (1.5%) femoral implant revisions; 1 for early femoral periprosthetic fracture and 1 for fatigue failure of the modular femoral neck. There were no cases of stem aseptic loosening and radiographic analysis demonstrated no cases of stem migration. The mean UCLA activity, WOMAC and Fogotten Joint scores were respectively 6.1, 10.7 and 86.6. 70% of prosthetic hips were observed as having no restriction and 99.2% of patients were satisfied with their THA.

CONCLUSIONS

This short modular stem produced satisfactory clinical and radiological results at mid-term, with 98.5% implant survival for any cause of stem revision and no revisions for aseptic loosening. Long-term results are required to further evaluate the stem's promising early results.

Risk factors for femoral stem breakage: an analysis of the AOANJRR results

INTRODUCTION

Breakage of the femoral stem component of a total hip replacement is now uncommon but continues to be seen with certain stem designs and in certain patient groups. Data previously published on this topic has been limited, either gathered from a single surgeon or centre, or included only a single stem design.

METHODS

We reviewed the data from the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR), identified and analysed 143 stem breakages over a period of 16 years, covering 44 different stem designs.

RESULTS

Our data confirms previously published findings that risk factors for stem breakage include patient age at implantation of under 70, male gender, as well as the use of exchangeable necks. We found no association with initial diagnosis, or type of acetabular component implanted. We did however also find, excluding exchangeable neck designs, that after 4.5 years a cemented stem had a significantly higher risk of breakage then a cementless stem.

DISCUSSION

To our knowledge this is the 1st paper to suggest cemented fixation as a specific risk factor for stem breakage. The analysis of rare complications such as stem breakage is only possible through large data collection systems such as the AOANJRR. Whilst there have been recent advances in materials and manufacturing techniques, we recommend that surgeons are aware of all the specific risks when considering implant choices for individual patients.

How to proceed with asymptomatic modular dual taper hip stems in the case of acetabular revision

How to proceed with a clinically asymptomatic modular Metha® Ti alloy stem with dual taper CoCr neck adapter in case of acetabular revision? To systematically answer this question the status of research and appropriate diagnostic methods in context to clinically symptomatic and asymptomatic dual taper stem-neck couplings has been evaluated based on a systematic literature review. A retrieval analysis of thirteen Metha® modular dual taper CoCr/Ti alloy hip stems has been performed and a rational decision making model as basis for a clinical recommendation was developed. From our observations we propose that in cases of acetabular revision, that for patients with a serum cobalt level of > 4 µg/L and a Co/Cr ratio > 3.6, the revision of the modular dual taper stem may be considered. Prior to acetabular revision surgery a systematic diagnostic evaluation should be executed, using specific tests such as serum metal (Co, Cr) ion analysis, plain antero-posterior and lateral radiographs and cross-sectional imaging modalities (Metal Artefact Reduction Sequence Magnetic Resonance Imaging). For an asymptomatic Metha® dual taper Ti alloy/CoCr stem-neck coupling at the stage of acetabular revision careful clinical decision making according to the proposed model should be followed and overreliance on any single examination should be avoided, considering the complete individual differential diagnosis and patient situation.

What Factors Are Associated With Neck Fracture in One Commonly Used Bimodular THA Design? A Multicenter, Nationwide Study in Slovenia

BACKGROUND

Femoral stems with bimodular (head-neck as well as neck-body) junctions were designed to help surgeons address patients' hip anatomy individually. However, arthroplasty registers have reported higher revision rates in stems with bimodular junctions than in stems with modularity limited to the head-neck trunnion. However, to our knowledge, no epidemiologic study has identified patient-specific risk factors for modular femoral neck fractures, and some stems using these designs still are produced and marketed.

QUESTIONS/PURPOSES

The purposes of this study were (1) to establish the survival rate free from aseptic loosening of one widely used bimodular THA design; (2) to define the proportion of patients who experienced a fracture of the stem's modular femoral neck; and (3) to determine factors associated with neck fracture.

METHODS

In this retrospective, nationwide, multicenter study, we reviewed 2767 bimodular Profemur® Z stems from four hospitals in Slovenia with a mean followup of 8 years (range, 3 days to 15 years). Between 2002 and 2015, the four participating hospitals performed 26,132 primary THAs; this implant was used in 2767 of them (11%). The general indications for using this implant were primary osteoarthritis (OA) in 2198 (79%) hips and other indications in 569 (21%) hips. We followed patients from the date of the index operation to the date of death, date of revision, or the end of followup on March 1, 2018. We believe that all revisions would be captured in our sample, except for patients who may have emigrated outside the country, but the proportion of people immigrating to Slovenia is higher than the proportion of those emigrating from it; however, no formal accounting for loss to followup is possible in a study of this design. There were 1438 (52%) stems implanted in female and 1329 (48%) in male patients, respectively. A titanium alloy neck was used in 2489 hips (90%) and a cobalt-chromium neck in 278 (10%) hips. The mean body mass index (BMI) at the time of operation was 29 kg/m (SD ± 5 kg/m). We used Kaplan-Meier analysis to establish survival rates, and we performed a chart review to determine the proportion of patients who experienced femoral neck fractures. A binary logistic regression model that controlled for the potential confounding variables of age, sex, BMI, time since implantation, type of bearing, diagnosis, hospital, neck length, and neck material was used to analyze neck fractures.

RESULTS

There were 55 (2%) aseptic stem revisions. Survival rate free from aseptic loosening at 12 years was 97% (95% confidence interval [CI] ± 1%). Fracture of the modular neck occurred in 23 patients (0.83%) with a mean BMI of 29 kg/m (SD ± 4 kg/m.) Twenty patients with neck fractures were males and 19 of 23 fractured necks were long. Time since implantation (odds ratio [OR], 0.55; 95% CI 0.46-0.66; p < 0.001), a long neck (OR, 6.77; 95% CI, 2.1-22.2; p = 0.002), a cobalt-chromium alloy neck (OR, 5.7; 95% CI, 1.6-21.1; p = 0.008), younger age (OR, 0.91; 95% CI, 0.86-0.96; p < 0.001), and male sex (OR, 3.98; 95% CI, 1.04-14.55; p = 0.043) were factors associated with neck fracture.

CONCLUSIONS

The loosening and neck fracture rates of the Profemur® Z stem were lower than in some of previously published series. However, the use of modular femoral necks in primary THA increases the risk for neck fracture, particularly in young male patients with cobalt-chromium long femoral necks. The bimodular stem we analyzed fractured unacceptably often, especially in younger male patients. For most patients, the risks of using this device outweigh the benefits, and several dozen patients had revisions and complications they would not have had if a different stem had been used.

LEVEL OF EVIDENCE

Level III, therapeutic study.

Modular femoral neck failure after revision of a total hip arthroplasty: a finite element analysis

The authors report on a case of modular femoral neck fracture which appeared 21 months after revision of acetabular component. The revision surgery was performed 8 years after the primary total hip arthroplasty due to aseptic loosening of the acetabular component. During acetabular revision, the primary implanted short (S, - 3.5 mm) femoral head was also exchanged with extra-long (XL, + 7.0 mm) femoral head fitting the modular femoral neck with a longer lever arm. Numerical analysis has shown that this has resulted in a 19.9% increase in tensile stress at the neck-stem coupling during normal walking cycle. This could result in microcrack initiation and propagation and finally lead to modular neck failure of the otherwise well-fixed stem. Surgeons should avoid excessive loading of the exchangeable neck (dual-modular) femoral stem designs as the stem-neck couplings are subject to corrosion and are not as reliable as monoblock stems.

Effect of Femoral Stem Modular Neck's Material on Metal Ion Release

Background:

In recent decades, the popularity of modular necks in total hip arthroplasty (THA) has increased since modular necks offer the potential to restore the patient’s native anatomy, and thus improve stability. Unfortunately, modular necks are associated with higher complication rates, including implant fracture and modular junction corrosion with adverse local tissue reaction to metal debris.

Objective:

The objective of this study was to determine the impact of modular neck material on titanium (Ti), chrome (Cr), and cobalt (Co) metal ion levels in patients who underwent a THA with Ti femoral stem, Ti or CrCo modular neck, and ceramic-on-ceramic (CoC) bearing.

Methods:

Whole blood Ti, Cr, and Co levels were compared at a minimum 1-year follow-up in 36 patients who underwent unilateral, primary CoC large-diameter head THA with Profemur^® Preserve modular femoral stems (MicroPort, Arlington, TX, USA).

Results:

Higher Co concentrations were observed in the CrCo modular neck group (0.46 versus 0.26 µg/l in the Ti neck group, P=0.004) and higher Ti concentrations were observed in the Ti modular neck group (1.98 vs 1.59 µg/l in the CrCo neck group, P=0.007). However, these differences were not clinically meaningful since the absolute values remained within what is considered the safe range of Ti, Cr, and Co ions in whole blood. No patients were re-operated or revised.

Conclusion:

Modular neck materials had an impact on whole blood metal ion levels but the concentrations measured remained within the safe range at 1-year follow-up. There were no indirect signs of modular junction corrosion with either CrCo or Ti femoral necks.

Cementless modular neck stems: are they a safe option in primary total hip arthroplasty?

PURPOSE

The objective was to assess aseptic complications and functional outcome using a primary total hip arthroplasty with modular neck.

METHODS

Prospective cohort of 317 consecutive patients. The mean age was 61.1 (range, 41-84) years. The H-Max-M model (Lima, Italy) system was used in all patients. The functional assessment was made by the Harris Hip Score, Short Form-36 (SF-36), Western Ontario and McMaster Universities Osteoarthritis Index and visual analogue scale for pain. Radiological outcomes were also assessed, and adverse events and complications were noted.

RESULTS

The mean follow-up was 6.1 (range, 2-8) years. Functional outcome significantly improved in most patients. There were 3 deep infections (0.9%) and 17 aseptic complications (5.3%) including 1 intraoperative acetabular fracture, 3 later periprosthetic femoral fractures, 1 broken ceramic insert, 1 acetabular loosening, 3 femoral loosening and 1 broken titanium modular neck in a obese patient. No pseudotumors or elevated serum levels of metal ions were found among the patients with radiolucent lines or aseptic loosening.

CONCLUSIONS

The findings in the present study showed that the H-MAX-M stem provided satisfactory functional outcome in most patients with a low rate of complications attributable to the modular neck design. We consider that using this novel modular neck-stem coupling design can be an alternative to the conventional monoblock stems in patients without overweight.

A Single-Center Experience With a Titanium Modular Neck Total Hip Arthroplasty

BACKGROUND

Added modular junction has been associated with implant-related failures. We report our experience with a titanium-titanium modular neck-stem interface to assess complications, possible clinical factors influencing use of neck modularity, and whether modularity reduced the incidence of dislocation.

METHODS

A total of 809 total hip arthroplasties completed between 2005 and 2012 from a prospectively collected database were reviewed. The mean follow-up interval was 5.7 years (3.3-10.3 years). Forty-five percent were male (360 of 809), and 55% were female (449 of 809). All stems were uncemented PROFEMUR TL (titanium, flat-tapered, wedge) or PROFEMUR Z (titanium, rectangular, dual-tapered) with a titanium neck.

RESULTS

Increased modularity (anteverted/retroverted and anteverted/retroverted varus/valgus (anteverted/retroverted + anteverted/retroverted varus/valgus) was used in 39.4% (135 of 343) of cases using the posterior approach compared with 6.8% (20 of 293) of anterior and 23.7% (41 of 173) of lateral approaches. Four males sustained neck fractures at a mean of 95.5 months (69.3-115.6 months) after primary surgery. Overall dislocation rate was 1.1% (9 of 809). The posterior approach had both the highest utilization of increased modularity and the highest dislocation rate (2.3%), of which the most were recurrent. The anterior (0.3%) and lateral (0%) approaches had lower dislocation rates with no recurrences.

CONCLUSION

At a mean 5.7 years, our experience demonstrates a low neck fracture (0.5%) and a low dislocation rate (1.1%). Use of increased modularity may not improve dislocation risk for the posterior approach. Continued surveillance of this group will be necessary to determine long term survivorship of this modular titanium implant.

Corrosion and adverse local tissue reaction after total hip arthroplasty with a modular titanium alloy femoral neck

This report describes a case of mechanically assisted crevice corrosion and secondary adverse local tissue reaction in a patient following a total hip arthroplasty, utilizing a modular neck (bi-modular) femoral component. Radiographic evaluation demonstrated a well-positioned, stable, cementless arthroplasty. Upon further evaluation, the patient had elevated serum cobalt and chromium levels, and magnetic resonance imaging demonstrated a periprosthetic pseudotumor. Corrosion of both the neck-stem and head-neck junctions was suspected. At the time of surgery, the neck-body junction was pristine; however, the head-neck junction of the implant demonstrated severe corrosive wear, a problem that has been reported only once previously with this particular bi-modular implant. This serves as a reminder that any modular junction may be susceptible to corrosion and not all bi-modular designs behave similarly.