Corrosion-induced fracture of a double-modular hip prosthesis: a case report

Are Corrosion and Material Loss a Threat for Titanium-Titanium Tapers in Total Hip Arthroplasty Modular Acetabular Components?

BACKGROUND

Extensive research has reported on fretting corrosion and material loss for a variety of metal taper interfaces in orthopedic devices. For modular acetabular shell-liner constructs, the interfaces studied thus far have consisted of mixed-metal pairings, and the risk of fretting corrosion and material loss for the all-titanium (Ti) shell-liner taper junction in one ceramic-on-ceramic (COC) design remains poorly understood. We asked: do Ti shell-liner taper interfaces in COC total hip arthroplasty devices show in vivo evidence of (1) fretting and/or corrosion, and (2) quantifiable potential material loss?

METHODS

We examined 22 shell-liner pairs and 22 single liners from retrieved COC components. The taper interface surfaces were assessed for fretting corrosion using a semiquantitative scoring method and imaged with scanning electron microscopy. A subcohort of components was measured with a coordinate measuring machine, and volumetric material loss and maximum wear depth were calculated.

RESULTS

Fretting corrosion at the taper interfaces was minimal to mild for 95% of liners and 100% of shells. Imaging revealed fretting marks within a band of corrosion on some implants and evidence of corrosion not in the proximity of mechanical damage. Estimated material loss ranged from 0.2 to 1.3 mm3 for liners, and 0.5 to 1.1 mm3 for shells. Maximum wear depth for all components was 0.03 mm or less.

CONCLUSIONS

Our results indicate that, compared to other taper junctions in total joint arthroplasty, the risk of corrosion and material loss may be minimal for Ti shell-liner interfaces.

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.

Mid-term results of titanium-titanium modular neck femoral stem in primary total hip arthroplasty

BACKGROUND

Modular neck femoral stems are advantageous because they can accurately restore the ideal hip geometry using various options in terms of offset, length, and version. However, there are concerns regarding junctional problems. Despite several reports on such issues, there is a lack of study on mid- to long-term results of these stems. The current study evaluated the mid-term results of patients who underwent primary total hip arthroplasty using a titanium-titanium (Ti-Ti) modular neck femoral stem.

METHODS

In total, data on 47 hips (42 patients) that could be followed-up for ≥ 5 years after primary total hip arthroplasty using the Ti-Ti modular neck femoral stem from 2011 to 2015 were reviewed. There were 22 male and 20 female patients, and their mean age was 56.3 (range: 31-76) years. The mean follow-up period was 8 (range: 5-12) years. Functional and radiological outcomes, complications, and reoperations were investigated. In addition, we conducted a comparative analysis of the outcomes between those who underwent surgery using the Ti-Ti modular neck femoral stem and 41 hips (35 patients, 19 males and 16 females) that underwent primary total hip arthroplasty using nonmodular femoral stems as a control.

RESULTS

In all Ti-Ti cases, the mean Harris Hip Scores were 50.6 (range: 6-59) preoperatively and 92.7 (range: 78-99) at the last follow-up (P < 0.001). Regarding the neck component's modularity, straight neck components were used in all Ti-Ti cases, and an anteverted or a retroverted neck was not used in any case. Stem revision was performed in one hip due to aseptic loosening. One hip underwent open reduction and internal fixation due to periprosthetic fracture without stem loosening. There were no cases of osteolysis and periprosthetic joint infection and clinically detectable junctional problems. The stem survival rate, with any stem revision as the endpoint, at 12 years was 96.6%. No significant difference was observed in the functional and radiological outcomes beween the Ti-Ti and nonmodular groups.

CONCLUSIONS

The Ti-Ti modular neck femoral stem had comparable results with broadly used nonmodular femoral stems; hence, it can be a reliable option in primary total hip arthroplasty. However, in terms of the modularity itself of the modular neck femoral stem, whether the modular neck femoral stem is useful in uncomplicated primary total hip arthroplasty is unclear.

Metallosis in Total Hip Arthroplasty

» Metallosis is a rare but significant complication that can occur after total hip arthroplasty (THA) for a variety of reasons but most commonly in patients with metal-on-metal implants.» It is characterized by the visible staining, necrosis, and fibrosis of the periprosthetic soft tissues, along with the variable presence of aseptic cysts and solid soft tissue masses called pseudotumors secondary to the corrosion and deposition of metal debris.» Metallosis can present with a spectrum of complications ranging from pain and inflammation to more severe symptoms such as osteolysis, soft tissue damage, and pseudotumor formation.» Workup of metallosis includes a clinical evaluation of the patient's symptoms, imaging studies, serum metal-ion levels, and intraoperative visualization of the staining of tissues. Inflammatory markers such as erythrocyte sedimentation rate and C-reactive protein along with intraoperative frozen slice analysis may be useful in certain cases to rule out concurrent periprosthetic joint infection.» Management depends on the severity and extent of the condition; however, revision THA is often required to prevent rapid progression of bone loss and tissue necrosis.

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.

Femoral prosthesis fracture after hip arthroplasty revision: A Case Report and Review of Literature

RATIONALE

A solution revision prosthesis has a multilayer microporous Porocoat coating, and the availability of multiple stem body sizes ensures that the prosthesis is adapted to each patient's anatomical structure so that there a firm attachment with the bone cortex in the middle of the femur. Therefore, the Solution prosthesis is one of the most commonly used and most effective prostheses in total hip arthroplasty worldwide.

PATIENT CONCERNS

We reported a case of a 54-year-old female patient with periprosthetic femoral fractures after hip arthroplasty.

DIAGNOSIS

The case was identified as type B2 prosthesis loosening according to the Vancouver classification.

INTERVENTIONS

We performed revision surgery on her using the Solution prosthesis. Seven months after the surgery, the patient developed a mid-femoral prosthesis fracture for no apparent reason. We performed a second revision surgery of the hip joint and allogeneic bone plate fixation.

OUTCOMES

The patient was satisfied with the treatment.

LESSONS

For patients with type B2 prosthesis loosening and prosthesis fracture, hip arthroplasty revision and an allogeneic bone plate could be used to ensure more stable support.

Discussion of Orientation and Performance of Crosslinked Ultrahigh-Molecular-Weight Polyethylene Used for Artificial Joints

Previously, the orientation structure of ultrahigh-molecular-weight polyethylene (UHMWPE) for artificial joints was considered to be unchanged after irradiation crosslinking. Therefore, much of the research related to the long-term failure of artificial joints has focused on material improvements. In this study, ultrasmall-angle X-ray scattering (USAXS) and the small/wide-angle X-ray scattering (SAXS-WAXS) combined technique reveal that the orientation structures of UHMWPE materials at all scales (nanoscale to microscale) are responsible for the long-term failure of artificial joints. To further illustrate the formation of these hierarchical oriented structures, a simple model is presented. In this model, first, the migration of free radicals plays a vital role, and the different steric hindrances in different directions directly lead to uneven migration behavior of free radicals. Second, the uneven migration of free radicals contributes to an inhomogeneous concentration of free radicals, thus resulting in observable crosslinking nonuniformities. Finally, all the hierarchical structural nonuniformities promote long-term failure of artificial joints after long-term wear.

Pseudotumor and delayed recurrent dislocation after total hip arthroplasty with a modular femoral neck: A case report

RATIONALE

Pseudotumor formation after hip arthroplasty is a rare complication that can occur not only at the head-neck junction but also at the modular neck-stem junction. Dislocation is a challenging and common complication of primary and revision total hip arthroplasty compared with other complications. Similarly, the association between pseudotumors and delayed recurrent dislocation remains unclear.

PATIENT CONCERNS

We report the case of a 73-year-old woman with pseudotumor formation after total hip arthroplasty combined with a modular femoral neck. A delayed recurrent dislocation occurred in this case. Approximately 4weeks after the first revision surgery, redislocation occurred.

DIAGNOSIS

The patient was eventually diagnosed with delayed recurrent artificial hip dislocation combined with a periprosthetic pseudotumor of the right hip.

INTERVENTIONS

During the first revision surgery, a thickened, indurated cyst measuring 8×3×8cm with a red-brown wall containing brown fluid was completely excised. A cemented stem, combined with a BIOLOX Forte ceramic head, was implanted. Approximately 4weeks after surgery, redislocation occurred, and we cemented an elevated rim liner on the acetabular component with a metal head.

OUTCOMES

At the last follow-up, 49 months after revision surgery, the patient was asymptomatic with a Harris hip score of 90. The patient had a satisfactory prognosis after treatment.

LESSONS

The application of the modular-neck stem should be cautiously performed, particularly for modular prostheses containing different alloys. Pseudotumors and insufficient soft-tissue tension both contribute to hip instability, which may eventually lead to delayed repeated dislocation. In addition, femoral offset must be considered. Cement-liner technology may be used for aging patients who are less active. This case report, focusing on pseudotumors and delayed recurrent dislocations, aimed to identify factors that may support this diagnosis, which is easy to miss. Consequently, it can provide further details on the treatment process and alert orthopedic surgeons to this infrequent but important cause of delayed recurrent dislocation.

Risk factors of dislocation after total hip arthroplasty in patients with developmental dysplasia of the hip

PURPOSE

Dislocation following total hip arthroplasty (THA) is a well-known complication. However, there is little data on its rate and predictors in patients with developmental dysplasia of the hip (DDH). The current study is aimed to determine the rate and specific risk factors of dislocation following THA in DDH patients.

METHODS

All the medico-surgical records of primary THAs from January 2014 to January 2019 were retrospectively reviewed. They were categorized into three main groups: primary OA, DDH, and others. Pre-operative and post-operative radiographs, past medical and surgical history, and surgical notes were reviewed in DDH cases.

RESULTS

In a total of 171 patients with DDH, 21 suffered from dislocation after THA (12%) which was significantly more frequent than those with primary OA. In univariate analysis, higher grade of dysplasia, smaller head size, intra-operative fracture, Wagner Cone stem, failure of offset restoration, and implanting the cup outside the Lewinnek's safe zone were identified as predictors of dislocation. In multiple regression analysis, however, only higher Crowe grade, intra-operative fracture, and post-operative acetabular offset less than 16 mm were independent predictors of dislocation.

CONCLUSION

Dysplastic hips can be more prone to post-THA dislocation than those with primary OA. Higher grades of dysplasia, failure of offset restoration, and intra-operative fracture can increase the rate of dislocation in this group of patients.

Future of total hip arthroplasty with the Metha short stem in modern surgeries

The aim of the study was to analyse the results of uncemented total hip replacement, using the Metha (metaphyseal) stem. A total of 158 patients (70 females and 88 males) were qualified to the study and submitted to total hip arthroplasty (183 procedures altogether), using the Metha stem. The mean age of the patients on the day of surgery was 51.7 years (the range from 17 to 69 years). The mean follow up period was 9.2 years (the range from 5 to 13.5 years). Preoperative assessments gave poor scores, according to the Merle d’Aubigne and Postel classification, modified by Charnley. The average improvement after surgery, according to the used scale, was 6.9 points. A very good outcome was recorded in 154 cases (84.2%), a good outcome was achieved in 20 cases (10.9%) and a poor outcome was confirmed in 9 cases, while no satisfactory case was observed. Poor outcomes were associated with implant loosening. Extraskeletal ossification was noted in 10 cases (5.5%). According to the Kaplan–Meier estimator, the 10-year survival was 93.2% and 97.3% for the whole implant and the stem alone, respectively. 1. Our follow-up period of more than 9 years on the average, indicates that Metha stems produce excellent clinical and functional results in operated young patients with advanced degenerative changes of the hip joint. 2. Assuming a proper qualification for the procedure, the absence of complications and a correct surgical technique, which is slightly more difficult, when compared to standard stem implantation, the risk of aseptic loosening is fairly negligible.

Osteolysis in total hip arthroplasty in relation to metal ion release: Comparison between monolithic prostheses and different modularities

BACKGROUND

Among the various complications associated with total hip arthroplasty (THA) periprosthetic osteolysis and wear phenomena due to the release of metal particles, are two of the most common and have been reported to be correlated because of inflammatory responses directed towards released particles that generally activate macrophagic osteolytic effects. Therein, new masses known as pseudotumors can appear in soft tissues around a prosthetic implant. To date, there is paucity of reliable data from studies investigating for any association between the above mentioned adverse events.

AIM

To investigate for the existence of any association between serum and urine concentrations of metal-ions released in THA and periprosthetic osteolysis for modular neck and monolithic implants.

METHODS

Overall, 76 patients were divided into three groups according to the type of hip prosthesis implants: Monoblock, modular with metal head and modular with ceramic head. With an average f-up of 4 years, we conducted a radiological evaluation in order to detect any area of osteolysis around the prosthesis of both the femur and the acetabulum. Moreover, serum and urinary tests were performed to assess the values of Chromium and Cobalt released. Statistical analysis was performed to determine any association between the ion release and osteolysis.

RESULTS

For the 3 study groups, the monolithic, modular ceramic-headed and modular metal-headed implants had different incidences of osteolysis events, which were higher for the modular implants. Furthermore, the most serious of these (grade 3) were detected almost exclusively for the modular implants with metal heads. A mapping of the affected areas was performed revealing that the highest incidences of osteolysis were evidenced in the pertrochanteric region at the femur level, and in the supero-external region at the acetabular level. Regarding the evaluation of the release of metals-ions from wear processes, serum and urinary chromium and cobalt values were found to be higher in cases of modularity, and even more so for those with metal head. Statistical linear correlation test results suggested positive correlations between increasing metal concentrations and incidences areas of osteolysis. However, no cases of pseudo-tumor were detected.

CONCLUSION

Future studies are needed to identify risk factors that increase peri-prosthetic metal ion levels and whether these factors might be implicated in the triggering of local events, including osteolysis and aseptic loosening.

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.

Evaluation of femoral anteversion, hip rotation, and lateral patellar tilt after total hip arthroplasty using a changeable neck system

In patients with secondary osteoarthritis due to acetabular dysplasia, femoral anteversion has many variations. A changeable neck system is one useful option to adjust the femoral anteversion. Retroverted necks can effectively adjust anatomical anteversion (AA), femoral rotational angle (FRA), and functional anteversion (FA); however, effectiveness of anteverted necks for these adjustments has not been investigated. Moreover, although the lateral patellar tilt after total hip arthroplasty (THA) has been reported to externally rotate, the influence on lateral patellar tilt using a changeable neck system remains unknown. To clarify the effectiveness of anteverted necks in THA, 96 consecutive patients (111 hips) who underwent THA using anatomical short stem with a changeable neck system were retrospectively investigated using pre- and post-operative computed tomography. Patients were divided into the straight (ST) group using straight and 4-mm-high-offset neck (N = 34) and the anteverted (AV) group using 15°-anteverted and 15°-anteverted/3-mm-high-offset neck (N = 34) after age, body mass index, and surgical approach were matched using propensity scores. AA did not change in the ST group, while it increased by 14.0° in the AV group. FRA decreased after surgery in both groups. FA decreased after surgery in the ST group, while it did not change in the AV group. Lateral patella tilt did not significantly change in both groups between pre- and post-operative position. In conclusion, with a changeable neck system, straight and anteverted necks can adjust AA to achieve pre-operative planning while not influencing lateral patellar tilt.

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.

Unexpected varus deformity and concomitant metal ion release and MRI findings of modular-neck hip stems: descriptive RSA study in 75 hips with 8 years' follow-up

Background and purpose - Modular-neck hip stems have been identified with corrosion-related problems from the neck-stem junction. We report an ongoing varus deformity of modular-neck hip stems with simultaneous metal ion release observed during a study comparing the migration of modular vs. standard hip stems.Patients and methods - We followed 50 patients with modular and 25 with standard neck stems using radiostereometry (RSA). At 5-year follow-up, we noted a compromised integrity of the modular stem with varus deformity in the neck-stem interface. Changes in head-tip distance as well as whole-blood ion concentration and MRI findings were analyzed. The modular stems were followed further up to 8 years.Results - The head-tip distance decreased continuously by 0.15 mm per year resulting in 1.2 (95% CI 1.0-1.4) mm at 8 years for modular stems, while for the standard stems at 5 years, the decrease was 0.09 (CI 0.0-0.2) mm or 0.02 mm/year. For the modular stems, the reduction in head-tip distance correlated to the increase in whole-blood cobalt concentration at 8 years but not to the MRI grading of tissue reactions. At 5 years, cobalt levels were 4.9 µg/L for modular stems and at 8 years 4.8 µg/L, whereas for standard stems this was 1.0 µg/L. After 8 years, 9 of 72 stems had been revised for different reasons, but only 1 with obvious adverse local tissue reaction (ALTR).Interpretation - We present a surprisingly large progressive deformation at the modular neck-stem junction, but so far without a definite clinical problem. Even the femoral head seems to show slight compression onto the taper over time. A high rate of revisions for the modular type of this stem has raised general concerns, and it has been recalled from the market.

Sensitivity and Specificity of Serum and Synovial Fluid Markers in Diagnosis of Infection in Head-Neck Taper Corrosion of Metal-On-Polyethylene Total Hip Arthroplasty

BACKGROUND

The accurate diagnosis of periprosthetic joint infection (PJI) in the setting of adverse local tissue reactions in patients with metal-on-polyethylene (MoP) total hip arthroplasty (THA) secondary to head-neck taper junction corrosion is challenging as it frequently has the appearance of purulence. The aim of this study is to evaluate the utility of erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and synovial fluid markers in diagnosing PJI in failed MoP THA due to head-neck taper corrosion.

METHODS

A total of 89 consecutive patients with MoP THA with head-neck taper corrosion in 2 groups was evaluated: (1) infection group (n = 11) and (2) noninfection group (n = 78). All patients had highly crossed polyethylene with cobalt chromium femoral heads and had preoperative synovial fluid aspiration. In addition, serum cobalt and chromium levels were analyzed.

RESULTS

The optimal cutoff value for synovial white blood cell was 2144 with 93% sensitivity and 84% specificity. Neutrophil count optimal cutoff value was 82% with 93% sensitivity and 82% specificity. Receiver operating characteristic analysis of ESR and CRP determined optimal cutoff at 57 mm/h and 35 mg/L with 57% sensitivity and 94% specificity and 93% sensitivity and 76% specificity, respectively. There were no significant differences in metal ion levels between the infected and noninfected groups.

CONCLUSION

The results of this study suggest that ESR and CRP are useful in excluding PJI, whereas both synovial white blood cell count and neutrophil percentage in hip aspirate are useful markers for diagnosing infection in MoP THA patients with head-neck taper corrosion associated adverse local tissue reaction.

Fretting corrosion of Si3 N4 vs CoCrMo femoral heads on Ti-6Al-V trunnions

Fretting corrosion at the head-neck taper junction was compared between silicon nitride (Si₃ N₄ ) and commercially available cobalt chrome (CoCrMo) femoral heads on titanium (Ti-6Al-4V) trunnions. An electrochemical setup was used to capture the fretting currents (characterized by oxide abrasion and repassivation) during cyclic loading. Onset load, pull-off force (disassembly load), short term and long term (1 million cycles) fretting currents were used to compare the fretting corrosion performance between the test group (Si₃ N₄ /Ti-6Al-4V) and the control group (CoCrMo/Ti-6Al-4V). Incremental cyclic fretting corrosion tests showed that the Si₃ N₄ /Ti-6Al-4V combination had statistically lower (P < .05) average fretting current of 0.189 µA (SD = 0.114 µA) compared to 0.685 µA (SD = 0.630 µA) for CoCrMo/Ti-6Al-4V for cyclic load of 3200 N. Similarly, for the one million cycle fretting corrosion tests, the Si₃ N₄ /Ti-6Al-4V couples had statistically lower (P < .05) average current (0.048 µA, SD = 0.025 µA) vs CoCrMo/Ti-6Al-4V couples (0.366 µA, SD = 0.143 µA). The Si₃ N₄ heads also had higher onset loads (P < .05) for fretting (vs CoCrMo, 2200 N vs 1740 N) indicating a difference in surface contact mechanics between the two groups. Scanning electron microscopy with energy dispersive spectroscopy confirmed material transfer from the trunnions to the heads for both groups tested, and from head to trunnion for the CoCrMo heads. Minimal Si₃ N₄ transfer was noted. The electrochemical, mechanical, and microscopic inspection data supported the hypothesis that Si₃ N₄ /Ti-6Al-4Vcombination had better fretting corrosion performance compared to CoCrMo/Ti-6Al-4V.

Disassociation of a Cold-Welded Bimodular Titanium Femoral Stem by Intraoperative Ice Cooling

Modularity in total hip arthroplasty allows a surgeon to have intraoperative versatility, allowing for fine adjustments of the femoral offset, leg length, and version. However, modularity can be a source of multiple complications. This case report describes a novel intraoperative solution for the problem of cold welding of a neck-stem junction using sterile ice to cryogenically disengage the modular components.

Revision of a Fractured Titanium Modular Revision Hip Stem Without Removal of the Well-Fixed Part of the Stem: A New Approach Using a Cemented Tube

Component fracture is a rare cause for revision in total hip arthroplasty. For a fractured well-fixed long femoral stem, the options are limited. We sought to develop a technique to address this problem with lower morbidity. A newly developed cemented tube was constructed and cemented onto a fractured Revitan revision hip femoral stem to retain the distal well-fixed component. At the 2-year follow-up, the Harris Hip Score, pain level, and radiographic images were analyzed. At the 2-year follow-up, no radiological signs of loosening or failure could be observed. The patient's preoperative Harris Hip Score improved from 42.8 to 97 points. The pain level improved from 7/10 to 0/10. Our case report depicts excellent clinical and radiographic outcomes at 2-year follow-up by a newly developed cemented tube technique. This technique is a potential new option for revision of fractured well-fixed diaphyseal stems without major bone loss. Our successful results suggest this technique is worthy of consideration and further study.

Multilayering as a solution to medical device failure

There are three main problems associated with medical device implants: biofilm, wear and corrosion, and bio rejection. A potential solution to these problems is multilayering. Polyelectrolyte multilayered films composed of polyallylamine hydrochloride and poly(4-vinylphenol) have been demonstrated to inhibit Staphylococcus epidermidis growth. Another study examined the wear behavior of polyelectrolyte multilayer coated orthopedic surfaces composed of poly(acrylic acid) and poly(allylamine hydrochloride) and found coated systems resulted in 33 % less wear than uncoated systems. Additionally, a heparin/collagen anti-CD34 antibody ((HEP/COL)₅-CD34) multilayer system provided accelerated adhesion of endothelial cells with a significant number of endothelial cells attaching in the first 5 min. This allowed for re-endothelialization to occur possibly reducing cardiac stent bio rejection. This review explores various ways multilayering has been utilized to prolong medical device use and decrease the number of complications associated with them.

Clinical Results of Revision Hip Arthroplasty for Neck-Taper Corrosion and Adverse Local Tissue Reactions Around a Modular Neck Stem

BACKGROUND

Adverse local tissue reactions (ALTRs) around a modular neck stem at our institution lead to a 13.5% rate of revision. The purpose of this study was to report the clinical results of revision total hip arthroplasty (THA) in this patient population.

METHODS

We identified 80 hips in 77 patients who underwent revision THA due to neck-stem corrosion. Intraoperative and postoperative complications, clinical outcomes, re-revision rates, and the postoperative ion levels were recorded.

RESULTS

The mean follow-up period after revision was 45.3 ± 16.3 months (range 24-81 months). There were no intraoperative mechanical complications during the revision surgery. Eight hips (10%) had postoperative complications related to the revision implant, of which 6/8 came to re-revision: postoperative implant dislocation in 4 hips-2 treated nonsurgically, aseptic loosening of femoral component in 2 hips, and periprosthetic femoral fracture in 2 hips. No patients had recurrence of ALTR nor the recurrence of groin pain within the follow-up period. With 2 exceptions, ion levels normalized within one year of the revision surgery. The survival rate was 94% (95% confidence interval 84-98) at 32 months and 82% (95% confidence interval 56-93) at 63 months after revision THA (using re-revision THA due to any reason as the endpoint).

CONCLUSION

Intraoperative complication, postoperative complication, and re-revision rates are equivalent to femoral revision surgeries for other causes (infection, fracture, loosening). We recommend selecting revision-type stems to minimize the risk of femoral loosening or periprosthetic fracture, and larger femoral heads or dual mobility bearings to minimize the risk of dislocation.

Patients With Modular-Neck Total Hip Arthroplasty: A Brief Five-Year Follow-Up Study

BACKGROUND

We have previously reported the early clinical results of a modular-neck stem identifying an early 2-year revision rate of 13% due to neck-stem corrosion. This report updates our findings to a midterm mean follow-up of 5 years.

METHODS

This is a consecutive retrospective review of 186 modular-neck hips in 175 patients with a mean follow-up period was 60.1 ± 22.9 months (range 24-100). We reviewed clinical findings, routine radiographs, detailed imaging (metal artifact reduction software-magnetic resonance imaging, ultrasound), and serum ion levels of cobalt and chromium. We performed a survival analysis with the endpoint defined as revision total hip arthroplasty due to neck-stem corrosion.

RESULTS

We revised 41 hips (22.0%) for neck-stem corrosion. Clinical symptoms (groin pain ± local swelling) were consistently present in those that came for revision. Mean serum cobalt ion levels increased as time passed in all patients. Detailed image findings showed that larger fluid collections and local soft tissue masses were seen predominately in symptomatic patients. However, 14% of patients who underwent revision did not have positive magnetic resonance imaging or ultrasound findings. The survival rate was 87% (95% confidence interval 81-92) at 3 years postoperatively and 72% (95% confidence interval 64-80) at 7 years postoperatively.

CONCLUSION

The revision rate for this modular-neck stem due to neck-stem corrosion at mid-term follow-up almost doubled in comparison to previous short-term results. It seems reasonable to consider clinical follow-up alone as symptoms, rather than blood testing for ion levels, seem to be the defining characteristic of failure.

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.

Lower limb joint repair and replacement: an overview

In the last few years, much has been published concerning total joint arthroplasty, and debates and discussions to new questions and points of view started many years ago. In this commentary, we report the latest evidence of best practice in the field of lower limb arthroplasty; this evidence is based on a literature search conducted by using PubMed and Scopus databases with a time limit of five years. We found novel evidence regarding cemented and not cemented implant, implant design, anticoagulant use, tourniquets, and other aspects of joints replacement surgery that we consider a common part of modern orthopedic practice. We specifically focus on lower limb joint replacement.

Clinical outcomes and survival rate of cementless modular distal fixation femoral stem for revision hip arthroplasty: A minimum 6-year follow-up

PURPOSE

Revision hip arthroplasty is a very challenging procedure. Use of a modular distal fixation stem is one of the available options for revision arthroplasty in patients with proximal femoral bone deficiency. The purpose of this study was to evaluate mid- to long-term outcomes of cementless modular distal fixation femoral stem implantation in revision hip surgery.

METHODS

Clinical and radiological findings, complications, and stem survival rate were analyzed for 46 patients (48 hips) who underwent revision hip arthroplasty using a cementless modular distal fixation femoral stem. The mean patient age was 58.8 years (range 31-82 years) and the mean follow-up period was 95 months (72-122 months). The preoperative diagnoses were aseptic loosening (36 hips), infection (4 hips), ceramic fracture (4 hips), and femoral periprosthetic fracture (4 hips).

RESULTS

The mean Harris hip score improved from 56.6 preoperatively to 88.2 postoperatively at the last follow-up. All hips showed stable osteointegration and firm fixation. Complications involved four hips (8.3%); there was one case each of periprosthetic fracture, delayed union of osteotomy site, femoral perforation, and infection. One stem re-revision was performed for deep infection of the femoral side. The Kaplan-Meier survival rate was 97.6% at the final follow-up.

CONCLUSION

Revision hip arthroplasty using a cementless modular distal fixation femoral stem showed satisfactory initial firm fixation and mid- to long-term survival rate. Complications can be minimized by careful surgical planning and meticulous procedure.

Femoral head disengagement from Accolade femoral stem in MOM Arthroplasty: a case study and literature review

Background: Metal on Metal Hip arthroplasty was commonly used until the last decade. However Hip Arthroplasty registries of many countries showed increased revision rates of MOM Hips – these high rates of revision caused by trunnionosis, adverse tissue reactions (ALTRs) and Pseudotumor formation.

The Case: Our Case is 73 years old gentleman who had left MOM THR in 2008, and was doing fine till the beginning of 2018 when his left leg stuck while getting out of the car. Despite he heard the pop and his leg was shortened and externally rotated, but he was still walking on it for a while. On reviewing him in our orthopedic clinic and after getting the CT-scan showed that he had dislocated femoral head from the stem.

Titanium neck-titanium stem taper corrosion in a modular neck stem

An 81-year-old woman presented with progressive groin pain after metal-on-polyethylene total hip arthroplasty with a modular neck stem and was found to have adverse local tissue reaction. As we report for the first time with this implant, we observed titanium neck-titanium stem taper corrosion intraoperatively. We also found head-neck taper corrosion. The patient underwent revision surgery to a modular fluted tapered stem with ceramic head and was asymptomatic at 3-year follow-up visit. In conclusion, consideration should be given to avoiding the routine use of this modular neck stem in total hip arthroplasty. Patients with this prosthesis should be closely monitored for adverse local tissue reaction.

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.

Breakage of metal hip arthroplasty components: Retrieval and structural analysis

BACKGROUND

Breakage of joint arthroplasty components are rare, yet during an implant retrieval program we found several cases.

OBJECTIVE

In this study we examined the components to determine the causes and mechanisms of breakage of these implants.

METHODS

From our collection of 849 retrievals we selected 682 cases with metal parts (503 hip, 79 knee arthroplasties) and identified fractured components: seven hip resurfacing implants, five total hip replacement stems, one monopolar femoral head, and one modular revision femoral stem from. Implants were examined using optical and scanning electron microscopy; metallographic sections were prepared and samples of periprosthetic tissues underwent microscopic examination.

RESULTS

In the resurfacing components breakage occurred in small stems placed in the femoral neck due to necrosis of femoral heads, with no metal flaws detected. Fatigue breakage of femoral stems was caused by presence of material flaws in the CoCrMo alloy, and corrosion. The monopolar head failed in fatigue fracture mechanism, breakage was initiated in an undercut near the taper connection for femoral component. The modular stem from Ti alloy sustained fatigue fracture induced by corrosion caused by debris from previously revised stem; no material flaws were detected in this sample. In most cases periprosthetic tissues had a morphology typical for aseptic loosening.

CONCLUSIONS

In our series failure was caused by material flaws, presence of stress raisers and localized corrosion. Our findings indicate that sharp edges and other features which can act as stress raisers should be avoided in newly designed implants. Corrosion induced fracture of the modular Ti stem indicates the need for a detailed debridement of periprosthetic tissues during revision arthroplasties.

Late fracture of an old-generation modular neck in a titanium alloy femoral stem of a cementless total hip arthroplasty

Neck-stem modularity gained recent popularity in hip arthroplasty for clinical advantages, and few complications have been reported. We describe an unusual two-stage failure of the bimodular neck of a cementless forged titanium alloy stem implanted 12 years before. The retrieved neck was forwarded to the manufacturer for metallurgic evaluation and failure analysis. Lengthening and bending of the superolateral aspect of the neck and double depression of the medial part prove that the prosthetic neck underwent a medial displacement and a varus rotation. The crack initiated from the superolateral corner of the fracture section, and the neck probably underwent two subsequent unstable configurations. The first horizontal part of the fracture occurred in the external surface as a result of physiological load carried on abnormal conditions of frictions. Due to increased oscillations, the end of the fracture section knocked against the inner aspect of the proximal hole of the stem, preventing further valgus displacement of the neck, which was moved forward. Consequently, the neck achieved a second unstable configuration, and the fracture propagated in the weaker direction creating a bent track. Finally, the neck broke unexpectedly as a result of the traumatic event. An incorrect placement into the femoral component during surgery was the initiation of the failure of the bimodular neck. The transitory but repeated interface motion between the neck and the stem induced a local surface irregularity acting as a starting point for crack propagation of fatigue fracture. Final failure followed a direct trauma.

Role of corrosion in taper failure and head disassociation in total hip arthroplasty of a single design

Modular junctions have been associated with corrosion in total hip arthroplasty. In a small number of cases, disassociation of the femoral head from the stem following gross wear of the taper has been reported. The purpose of this study was to investigate the role of corrosion in the development of mechanical changes leading to disassociation. Twenty-one retrieved stems and heads of one design previously reported with head disassociation were identified in an IRB-approved database. Components were scored for corrosion and measured for material loss. Stem alloy hardness was measured. Parametric and non-parametric statistics were performed (α < 0.05). Seven of twenty-one stems demonstrated gross material loss of the stem taper and head disassociation. The maximum linear depth (MLD) of material loss on stem tapers without dissociation and all head bores was 7.63 ± 6.04 and 63.76 ± 60.83 μm, respectively. Hardness of the stem material was statistically distinct, but similar to other stem materials. Results suggest material loss via corrosion at the head bore loosens the taper lock, allowing relative motion leading to abrasive wear of the stem taper. All cases of disassociation occurred at greater than 65 months with a minimum of 50 μm of loss at on the head bore. It may be warranted to survey patients with systems reporting head disassociation; for this system, including recalled heads, risk appears to begin after 6 years in vivo. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2996-3003, 2018.

Surface integrity of polyethylene liners following trunnionosis of a dual modular neck total hip implant

BACKGROUND

There has been a trend in the evolution of total hip arthroplasty towards increased modularity; with this increase in modularity come some potentially harmful consequences. Modularity at the neck shaft junction has been linked to corrosion, adverse reaction to metal debris and pseudotumour formation.

AIM

The aim of this retrieval study is to assess whether the surface integrity of the polyethylene (PE) liner is affected by metal wear debris in a single implant design series of THA revised for trunnionosis.

METHODS

A retrieval analysis of thirty dual-taper modular neck hip prostheses was performed; the mean time from implantation to revision was 2.7 years (1.02-6.2). PE liners were analysed using a scanning electron microscope with an energy dispersive spectrometer to assess for metal particles embedded on the liner surface. Serum metal ion levels and inflammatory markers were also analysed.

RESULTS

There were small numbers of metal particles present on the PE liners. The mean number of metal particles per liner was four and the particles varied in size from 0.5 µm to 122 µm mean 16 µm. All patients had elevated metal ion levels: cobalt 6.02 µg/l, chromium 1.22 µg/l, titanium 3.11 µg/l. The cobalt:chromium ratio was 7.55:1. Inflammatory markers were also marginally raised (ESR 17; CRP 10).

CONCLUSION

These results suggest that retention of PE liners may be reasonable when performing isolated revision of the femoral component in cases of failure at the modular neck stem junction, especially when the inner diameter of the liner is already optimised for head size and stability.

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.

The Fate of Elevated Metal Ion Levels After Revision Surgery for Head-Neck Taper Corrosion in Patients With Metal-on-Polyethylene Total Hip Arthroplasty

BACKGROUND

Elevated metal ion levels have been associated with the presence of adverse local tissue reactions in patients with metal-on-polyethylene (MoP) total hip arthroplasty (THA) secondary to corrosion at head-neck taper junction. Patients are frequently concerned with their elevated systemic metal ion levels. This study investigated the rate of decline of serum cobalt and chromium ion levels after revision surgery.

METHODS

A total of 39 patients with MoP THA were revised because of the presence of symptomatic adverse local tissue reactions on magnetic resonance imaging with elevated serum metal ion levels. The time between initial implantation of MoP THA (index surgery) and revision surgery was considered the duration of metal exposure. The prerevision measure of ion level was considered the intensity of exposure. Prerevision median serum Co and Cr levels, as well as revision serum Co/Cr ratio, were reported.

RESULTS

The median serum levels of cobalt and cobalt-to-chromium ratio significantly decreased from prerevision levels of 8.2 μg/L (0.2-56.1 μg/L) and 5.6 μg/L (0.1-53.3 μg/L) to 3.1 μg/L (0.2-14 μg/L) and 1.7 μg/L (0.4-3.8 μg/L) at postrevision (P < .01), respectively. The rate of decline of Co was 0.45% per day during the first month. For chromium, the rate of decline was slower with 0.08% per day during the first month.

CONCLUSION

At 3 months after revision surgery, cobalt and chromium ion levels declined by 34% and 8% of prerevision level, respectively. This study provides evidence-based practical information for surgeons to provide MoP THA patients when considering revision surgery for head-neck taper corrosion.

Factors influencing taper failure of modular revision hip stems

Stem modularity of revision hip implant systems offers the advantage of the restoration of individual patient geometry but introduces additional interfaces, which are subjected to repetitive bending loading and have a propensity for fretting corrosion. The male stem taper is the weakest part of the modular junction due to its reduced cross section compared to the outside diameter of the stem. Taper fractures can be the consequence of overloading in combination with corrosion. The purpose of this study was to assess the influence of implant design factors, patient factors, and surgical factors on the risk of taper failure of the modular junction of revision stems. An analytical bending model was used to estimate the strength of the taper connection for pristine, fatigued and corroded conditions. Additionally, a finite element contact model of the taper connection was developed to assess the relative motion and potential for surface damage at the taper interface under physiological loading for varyied assembly and design parameters. Increasing the male taper diameter was shown to be the most effective means for increasing taper strength but would require a concurrent increase in the outer implant diameter to limit a greater risk of total surface damage for a thinner female taper wall. Increasing the assembly force decreases the total surface damage but not local magnitudes, which are probably responsible for crack initiation. It is suggested that in unfavourable loading conditions a monobloc implant system will reduce the risk of failure.

Serum Metal Levels for Diagnosis of Adverse Local Tissue Reactions Secondary to Corrosion in Metal-on-Polyethylene Total Hip Arthroplasty

BACKGROUND

Recently, corrosion at the head-neck junction in metal-on-polyethylene bearing surface total hip arthroplasty (THA) has been recognized as a cause of adverse local tissue reactions (ALTRs). Serum metal levels have been advocated as a tool for the diagnosis of ALTR; however, no prior studies have specifically examined their utility. The purpose of this study was to determine the optimal cutoff values for serum cobalt and chromium levels in diagnosing ALTR after metal-on-polyethylene bearing surface THA.

METHODS

We reviewed 447 consecutive patients with serum metal levels tested at our institution and identified 64 patients with a metal-on-polyethylene bearing who had axial imaging or underwent reoperation to confirm the presence or absence of ALTR. Receiver-operating characteristic curves were produced to identify cutoff thresholds to optimize sensitivity, and diagnostic test performance was characterized.

RESULTS

Forty-four of the 64 patients (69%) were positive for an ALTR. The best test for the diagnosis of ALTR was the serum cobalt level (area under the curve [AUC] = 99%). A threshold cutoff of ≥1.0 ng/mL had a sensitivity of 100%, specificity of 90%, positive predictive value (PPV) of 96%, and negative predictive value (NPV) of 100%. Serum chromium levels were also diagnostic (AUC = 87%). A threshold cutoff of ≥0.15 ng/mL had a sensitivity of 100%, specificity of 50%, PPV of 81%, and NPV of 100%. Finally, serum cobalt-to-chromium ratio was also helpful for diagnosis (AUC = 90%). A threshold cutoff value of 1.4 for the cobalt-to-chromium ratio offered a sensitivity of 93%, specificity of 70%, PPV of 87%, and NPV of 82%.

CONCLUSION

Measurement of serum cobalt level with a threshold value of 1.0 ng/mL in our experience is the best test for identifying the presence of ALTR in patients with a metal-on-polyethylene THA. Measurement of chromium level and the ratio of cobalt-to-chromium levels are also of value.

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.

Assessment of Corrosion, Fretting, and Material Loss of Retrieved Modular Total Knee Arthroplasties

BACKGROUND

Modular junctions in total hip arthroplasties have been associated with fretting, corrosion, and debris release. The purpose of this study is to analyze damage severity in total knee arthroplasties of a single design by qualitative visual assessment and quantitative material loss measurements to evaluate implant performance and patient impact via material loss.

METHODS

Twenty-two modular knee retrievals of the same manufacturer were identified from an institutional review board-approved database. Junction designs included tapers with an axial screw and tapers with a radial screw. Constructs consisted of 2 metal alloys: CoCr and Ti6Al4V. Components were qualitatively scored and quantitatively measured for corrosion and fretting. Negative values represent adhered material. Statistical differences were analyzed using sign tests. Correlations were tested with a Spearman rank order test (P < .05).

RESULTS

The median volumetric material loss and the maximum linear depth for the total population were -0.23 mm³ and 5.84 μm, respectively. CoCr components in mixed metal junctions had higher maximum linear depth (P = .007) than corresponding Ti components. Fretting scores of Ti6Al4V alloy components in mixed metal junctions were statistically higher than the remaining groups. Taper angle did not correlate with material loss.

CONCLUSION

Results suggest that CoCr components in mixed metal junctions are more vulnerable to corrosion than other components, suggesting preferential corrosion when interfacing with Ti6Al4V. Overall, although corrosion was noted in this series, material loss was low, and none were revised for clinical metal-related reaction. This suggests the clinical impact from corrosion in total knee arthroplasty is low.

The taper corrosion pattern observed for one bi-modular stem design is related to geometry-determined taper mechanics

Bi-modular primary hip stems exhibit high revision rates owing to corrosion at the stem-neck taper, and are associated with local adverse tissue reactions. The aim of this study was to relate the wear patterns observed for one bi-modular design to its design-specific stem-neck taper geometry. Wear patterns and initial geometry of the taper junctions were determined for 27 retrieved bi-modular primary hip arthroplasty stems (Rejuvenate, Stryker Orthopaedics) using a tactile coordinate-measuring device. Regions of high-gradient wear patterns were additionally analyzed via optical and electron microscopy. The determined geometry of the taper junction revealed design-related engagement at its opening (angle mismatch), concentrated at the medial and lateral apexes (axes mismatch). A patch of retained topography on the proximal medial neck-piece taper apex was observed, surrounded by regions of high wear. On the patch, a deposit from the opposing female stem taper-containing Ti, Mo, Zr, and O-was observed. High stress concentrations were focused at the taper apexes owing to the specific geometry. A medial canting of the components may have augmented the inhomogeneous stress distributions in vivo. In the regions with high normal loads interfacial slip and consequently fretting was inhibited, which explains the observed pattern of wear.

The use of femoral stems with exchangeable necks in primary total hip arthroplasty increases the rate of revision

Aims

Femoral stems with exchangeable (modular) necks were introduced to offer surgeons an increased choice when determining the version, offset and length of the femoral neck during total hip arthroplasty (THA). It was hoped that this would improve outcomes and reduce complications, particularly dislocation. In 2010, the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) first reported an increased rate of revision after primary THA using femoral stems with an exchangeable neck. The aim of this study was to provide a more comprehensive up-to-date analysis of primary THA using femoral stems with exchangeable and fixed necks.

Materials and Methods

The data included all primary THA procedures performed for osteoarthritis (OA), reported to the AOANJRR between 01 September 1999 and 31 December 2014. There were 9289 femoral stems with an exchangeable neck and 253 165 femoral stems with a fixed neck. The characteristics of the patients and prostheses including the bearing surface and stem/neck metal combinations were examined using Cox proportional hazard ratios (HRs) and Kaplan-Meier estimates of survivorship.

Results

It was found that prostheses with an exchangeable neck had a higher rate of revision and this was evident regardless of the bearing surface or the size of the femoral head. Exchangeable neck prostheses with a titanium stem and a cobalt-chromium neck had a significantly higher rate of revision compared with titanium stem/titanium neck combinations (HR 1.83, 95% confidence interval 1.49 to 2.23, p < 0.001). Revisions were higher for these combinations compared with femoral stems with a fixed neck.

Conclusion

There appears to be little evidence to support the continued use of prostheses with an exchangeable neck in primary THA undertaken for OA. Cite this article: Bone Joint J 2017;99-B:766–73.

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.

Sensitivity and Specificity of Metal Ion Levels in Predicting "Pseudotumors" due to Taper Corrosion in Patients With Dual Taper Modular Total Hip Arthroplasty

BACKGROUND

Currently, no serum metal ion threshold exists to identify adverse tissue reactions in total hip arthroplasty (THA) patients with taper corrosion. Our study aims to investigate the sensitivity and specificity of serum metal ions in detecting taper corrosion related pseudotumors in patients with dual taper modular THA.

METHODS

A total of 148 patients with dual taper modular THA were investigated: (1) 90 patients with pseudotumors detected with metal artifact reduction sequence-magnetic resonance imaging (MARS-MRI) and (2) 58 patients without pseudotumors on MARS-MRI. Receiver operating characteristic curves were constructed to determine the sensitivity and specificity using different metal ion thresholds. The severity of intraoperative tissue damage was correlated with preoperative metal ion levels.

RESULTS

Pseudotumor was associated with higher cobalt (5.0 μg/L vs 3.7 μg/L, P < .01) and Co/Cr ratio (6.0 vs 3.7, P < .01). The sensitivity and specificity for cobalt level of 2.8 μg/L and Co/Cr ratio of 3.8 in detecting taper corrosion-related pseudotumors on MARS-MRI was 88% and 32% and 70% and 50%, respectively. Higher intraoperative tissue damage grades demonstrated significantly higher Co/Cr ratios (8.6 vs 3.4, P = .03).

CONCLUSION

Although metal ion levels alone should not be relied on as the sole parameter to determine revision surgery, cobalt level >2.8 μg/L and the Co/Cr ratio >3.8 are useful clinical diagnostic adjuncts in the systematic clinical evaluation for taper corrosion-related adverse tissue reactions in patients with dual modular taper THA.

Why do some titanium-alloy total hip arthroplasty modular necks fail?

BACKGROUND

Increased modularity in total hip arthroplasty (THA) through extra junction between the neck and the femoral stem is gaining popularity among orthopaedic community. However, the advantage of the additional junction is shadowed by an increased risk of mechanical failure. The aim of this study was to describe the exact mechanism of fracture of the modular femoral neck in an uncemented stem.

METHODS

Clinical, metallurgical, and mechanical analysis including finite-element modelling and elemental-sensitive tissue analysis with the micro-PIXE method was performed on two patients treated with fully modular primary THA made from Titanium alloy of the same oval taper-cone design. In patient A revision was performed 7.8 years after the unilateral primary procedure because of modular femoral neck fracture, while patient B was left-side revised 15 years after the bilateral primary procedure because of aseptic loosening of the femoral stem.

RESULTS

Body weight was 30% higher and the arm of implanted modular femoral neck was 51% longer in patient A compared to patient B. Therefore, the stress ratio on the modular femoral neck of patient A was calculated to be 2.45 times higher than in patient B, preventing cold welding and producing taper damage and degradation at the neck-stem junction. Large clusters of metallic debris containing Titanium and Vanadium from the alloy were present in the periprosthetic soft tissues of patient A.

CONCLUSIONS

Patients with higher body mass index treated with fully modular Ti-alloy THA may be at increased risk to experience catastrophic failure of the device. Orthopaedic surgeons should avoid using long necks whenever possible, as these are especially prone to develop a vicious circle starting with the fretting process and crevice corrosion at the taper-cone connection, leading to crack initiation and crack propagation, accelerated by the increased vulnerability of the Ti-alloy in biologic media, ultimately ending as fracture at the typical site. Serum Ti concentration may represent a rough estimation of taper degradation and patients with elevated levels should be warned and followed accordingly.

Early fracture of the modular neck of a MODULUS femoral stem

We present the case of a 46-year-old woman who underwent revision surgery approximately 4 years after total hip arthroplasty because of a fracture of the modular neck of a MODULUS femoral stem. The fractured surfaces of the retrieved implant were inspected using optical and scanning electron microscopy. Three-dimensional finite element analysis was also performed to identify the stresses that might have caused the failure. We concluded that active, obese patients who are implanted with a high-offset, small-sized modular component could experience stress-induced fractures of the modular neck, with proper fixation and osseointegration of the distal stem, especially if residual bone or tissue is present on the inner surface of the neck that could contribute to micromovement and decreased proximal fixation.