Neck-stem Interface Research Articles

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.

Retrieval Findings of Recalled Dual-Taper Hips.

Background:The recent high-profile recalls of several dual-taper hip designs pose questions regarding why those designs perform poorly. We aimed to characterize taper damage in 1 recalled design to understand failure mechanisms to inform surgeons on which patients should be considered at risk of revision and when to revise.Methods:High-precision measurement equipment was used to characterize the metal loss from the neck-stem interface of 116 retrieved Rejuvenate femoral stems (Stryker Howmedica Osteonics) revised because of an adverse reaction to metal debris. Head-neck taper surfaces were also investigated, and clinical and laboratory data were examined.Results:The neck-stem junction of each implant was moderately to severely corroded and showed a characteristic wear pattern on both male and female taper surfaces. The severity of taper damage was positively correlated with time to revision (coefficient, 0.040 [95% confidence interval (CI), 0.028 to 0.051]; p < 0.0001) and with serum cobalt concentration (coefficient, 0.02 [95% CI, 0.01 to 0.02]; p < 0.0001) and serum chromium concentration (coefficient, 0.04 [95% CI, 0.009 to 0.070]; p = 0.0142).Conclusions:A forensic examination of the retrieved components that failed secondary to an adverse reaction to metal debris showed, in all cases, visible corrosion. Of the implant and patient factors investigated, we did not identify any predictors of corrosion. The severity of damage was found to increase with time; cobalt was significantly elevated over chromium.Clinical Relevance:Surgeons should scrupulously follow and consider revision for patients with this implant design to avoid extensive tissue excision. Blood metal ion tests may aid in identifying the mechanisms of taper corrosion.

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

BackgroundAdded 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. MethodsA 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. ResultsIncreased 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. ConclusionAt 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.

Surface and subsurface changes as a result of tribocorrosion at the stem-neck interface of bi-modular prosthesis

This study presents a detailed multi-scale analysis of the degradation processes occurring on both the CoCrMo and TMZF alloy surfaces at different regions across the taper interface. Co-ordinate measurement machine, scanning electron microscopy, transmission electron microscopy and X-ray diffraction methods have been utilised to identify the roles of degradation from the mm to nm scale. Depending on the region of interest, varying topographies and subsurface morphologies were observed across both surfaces. In regions where high pressures are expected, retention of the surface topography was seen on the CoCrMo trunnion. This was complimented by gross shear and plastic deformation of the subsurface material. In regions where maximum penetration was seen, evidence of fretting-corrosion was seen and a loss of the nano-crystalline layer. For the TMZF surface, refinement of the alloy was seen in the top 5μm, with fatigue cracks within the bulk present. Precipitation and formation of oxide species were observed at depths of 2μm. The degradation of a bi-modular prosthesis is a complex multifactorial process. It is hypothesised that this formation of oxide species at the interface and within the bulk alloy plays an important role in the degradation through a combined work-hardening and corrosion process.

Assembly force and taper angle difference influence the relative motion at the stem–neck interface of bi-modular hip prostheses

Bi-modular hip arthroplasty prostheses allow adaptation to the individual patient anatomy and the combination of different materials but introduce an additional interface, which was related lately to current clinical issues. Relative motion at the additional taper interface might increase the overall risk of fretting, corrosion, metallic debris and early failure. The aim of this study was to investigate whether the assembly force influences the relative motion and seating behaviour at the stem-neck interface of a bi-modular hip prosthesis (Metha(®); Aesculap AG, Tuttlingen, Germany) and whether this relation is influenced by the taper angle difference between male and female taper angles. Neck adapters made of titanium (Ti6Al4V) and CoCr (CoCr29Mo) were assembled with a titanium stem using varying assembly forces and mechanically loaded. A contactless eddy current measurement system was used to record the relative motion between prosthesis stem and neck adapter. Higher relative motion was observed for Ti neck adapters compared to the CoCr ones (p < 0.001). Higher assembly forces caused increased seating distances (p < 0.001) and led to significantly reduced relative motion (p = 0.019). Independent of neck material type, prostheses with larger taper angle difference between male and female taper angles exhibited decreased relative motion (p < 0.001). Surgeons should carefully use assembly forces above 4 kN to decrease the amount of relative motion within the taper interface. Maximum assembly forces, however, should be limited to prevent periprosthetic fractures. Manufacturers should optimize taper angle differences to increase the resistance against relative motion.

Stem Migration and Fretting Corrosion of the Antirotation Pin in the K2/Apex Hip System

BackgroundMany exchangeable neck hip systems have been withdrawn because of fretting corrosion at the neck/stem coupling. MethodOur prospective randomized study evaluating stem stability (Roentgen stereophotogrammetric analysis, dual-energy x-ray absorptiometry) and clinical outcomes between the K2/Apex hip systems was ceased early because of a withdrawal of the stems which had an unfavorably high early revision rate reported in the Australian Orthopaedic Association National Joint Registry (9.3% at 3 years). ResultsAt 2 years, there are no clinical differences between the stems. Roentgen stereophotogrammetric analysis has identified a high proportion of potentially concerning subsidence and retroversion in both groups, more marked in the K2 stem, although mostly in asymptomatic patients. Dual-energy x-ray absorptiometry has shown similar bone density around the stems. Retrieval analysis of 3 study patients showed fretting corrosion of the antirotation pin and aseptic lymphocyte-dominated vasculitis-associated lesion, with no relationship to bearing type or size. Analysis of 7 further nonstudy K2/Apex stems confirmed similar corrosion. ConclusionThis study shows potentially concerning subsidence of both stems and is the first to describe corrosion at the neck-stem interface and a relationship to metal-related pathology.

Corrosion and Fretting of a Modular Hip System: A Retrieval Analysis of 60 Rejuvenate Stems

Femoral stems with dual-taper modularity were introduced to allow independent control of length, offset, and version. Corrosion and fretting related to micromotion at the neck-stem junction are thought to stimulate an adverse local tissue reaction (ALTR). Analysis of 60 consecutively retrieved modular-neck stem implants (Rejuvenate, Stryker) revised primarily for ALTR was done to determine the variables influencing corrosion and fretting patterns at the neck-stem interface. Taper damage evaluation was performed with stereomicrocopic analysis with two observers. Evidence of fretting and corrosion was seen at the neck-stem taper in all implants, including three implants revised for periprosthetic fractures within four weeks of the index surgery indicating that this process starts early. Femoral stems paired with the long overall neck lengths had significantly higher corrosion scores. Correlation of the corrosion severity at particular locations with the length of implantation suggests that the neck-stem junction experiences cyclic cantilever bending in vivo. The positive correlation between the length of implantation and fretting/corrosion scores bodes poorly for patients who still have this implant. Scanning electron microscopy on a subset of specimens was also performed to evaluate the black corrosion material. We strongly urge frequent follow-up exams for every patient with this particular modular hip stem.

Réaction tissulaire à la corrosion de la jonction col-tige d’une prothèse modulaire de hanche de première intention

Complications related to the neck-stem junction of modular stems used for total hip arthroplasty (THA) are generating increasing concern. A 74-year-old male had increasing pain and a cutaneous reaction around the scar 1 year after THA with a modular-neck stem. Imaging revealed osteolysis of the calcar and a pseudo-tumour adjacent to the neck-stem junction. Serum cobalt levels were elevated. Revision surgery to exchange the stem and liner and to resect the pseudo-tumour was performed. Analysis of the stem by scanning electron microscopy and by energy dispersive X-ray and white light interferometry showed fretting corrosion at the neck-stem junction contrasting with minimal changes at the head-neck junction. Thus, despite dry assembly of the neck and stem on the back table at primary THA, full neck-stem contact was not achieved, and the resulting micromotion at the interface led to fretting corrosion. This case highlights the mechanism of fretting corrosion at the neck-stem interface responsible for adverse local tissue reactions. Clinical and radiological follow-up is mandatory in patients with dual-modular stems.

Adverse tissue reaction to corrosion at the neck-stem junction after modular primary total hip arthroplasty

Complications related to the neck-stem junction of modular stems used for total hip arthroplasty (THA) are generating increasing concern. A 74-year-old male had increasing pain and a cutaneous reaction around the scar 1 year after THA with a modular neck-stem. Imaging revealed osteolysis of the calcar and a pseudo-tumour adjacent to the neck-stem junction. Serum cobalt levels were elevated. Revision surgery to exchange the stem and liner and to resect the pseudo-tumour was performed. Analysis of the stem by scanning electron microscopy and by energy dispersive X-ray and white light interferometry showed fretting corrosion at the neck-stem junction contrasting with minimal changes at the head-neck junction. Thus, despite dry assembly of the neck and stem on the back table at primary THA, full neck-stem contact was not achieved, and the resulting micromotion at the interface led to fretting corrosion. This case highlights the mechanism of fretting corrosion at the neck-stem interface responsible for adverse local tissue reactions. Clinical and radiological follow-up is mandatory in patients with dual-modular stems.

Total Hip Arthroplasty With a Non-Modular Conical Stem and Transverse Subtrochanteric Osteotomy in Treatment of High Dislocated Hips

Conventional stems may be unsuitable for hypoplastic femurs associated with severe dysplasia, meanwhile, custom-made or modular stems in total hip arthroplasty are often complex and expensive. This series included 21 Crowe type IV dysplastic hips in which a non-modular cementless conical stem was implanted with transverse subtrochanteric femoral osteotomy. Follow up averaged 40months. Twenty hips survived with mean Harris hip score improved from 52 to 90. One hip failed for stem loosening. The average leg lengthening was 3.8cm with transient sciatic nerve palsy occurring in three hips. Femoral offset averaged 3.3cm postoperatively. The non-modular conical stem not only obviated the complexities, high medical cost and potential risk at the neck-stem interface associated with stem modularity, but also simplified surgical technique.

A Rare Dissociation at the Neck–Stem Interface

The authors report a case of dissociation at the neck–stem interface without hip dislocation that occurred during walking, and discuss strategies to avoid and treat this complication of THA. Introduction Modular femoral components have the advantages of:•Reducing the need to stock numerous stem and head sizes •Allowing the final choice of neck length and head size to be made after stem implantation With moduar femoral components, neck orientation can also be changed after implantation, which is a well-known cause of early dislocation. The incidence of postoperative dislocation of modular total hip arthroplasty (THA) varies from 0.5% to 4% [1].Dissociation at the neck–stem interface is rare. To the best of our knowledge, only three case reports have been published [2-4], but they pertained to dissociation at the neck–head interface.We report a case of dissociation at the neck–stem interface without hip dislocation that occurred during walking, and we discuss the causes of dissociation as well as strategies to avoid and treat this complication.

Design parameters and the material coupling are decisive for the micromotion magnitude at the stem–neck interface of bi-modular hip implants

Several bi-modular hip prostheses exhibit an elevated number of fretting-related postoperative complications most probably caused by excessive micromotions at taper connections. This study investigated micromotions at the stem–neck interface of two different designs: one design (Metha, Aesculap AG) has demonstrated a substantial number of in vivo neck fractures for Ti–Ti couplings, but there are no documented fractures for Ti–CoCr couplings. Conversely, for a comparable design (H-Max M, Limacorporate) with a Ti–Ti coupling only one clinical failure has been reported. Prostheses were mechanically tested and the micromotions were recorded using a contactless measurement system.For Ti–Ti couplings, the Metha prosthesis showed a trend towards higher micromotions compared to the H-Max M (6.5±1.6μm vs. 3.6±1.5μm, p=0.08). Independent of the design, prostheses with Ti neck adapter caused significantly higher interface micromotions than those with CoCr ones (5.1±2.1μm vs. 0.8±1.6μm, p=0.001). No differences in micromotions between the Metha prosthesis with CoCr neck and the H-Max M with Ti neck were observed (2.6±2.0μm, p=0.25).The material coupling and the design are both crucial for the micromotions magnitude. The extent of micromotions seems to correspond to the number of clinically observed fractures and confirm the relationship between those and the occurrence of fretting corrosion.

New type of hip arthroplasty failure related to modular femoral components: Breakage at the neck-stem junction

Total hip replacements (THR) with modular femoral components (stem-neck interface) make it possible to adapt to extramedullary femoral parameters (anteversion, offset, and length) theoretically improving muscle function and stability. Nevertheless, adding a new interface has its disadvantages: reduced mechanical resistance, fretting corrosion and material fatigue fracture. We report the case of a femoral stem fracture of the female part of the component where the modular morse taper of the neck is inserted. An extended trochanteric osteotomy was necessary during revision surgery because the femoral stump could not be grasped for extraction, so that a long stem had to be used. In this case, the patient had the usual risk factors for modular neck failure: he was an active overweight male patient with a long varus neck. This report shows that the female part of the stem of a small femoral component may also be at increased failure risk and should be added to the list of risk factors. To our knowledge, this is the first reported case of this type of failure.

Symptomatic Aseptic Hydrogen Pneumarthrosis as a Sign of Crevice Corrosion Following Total Hip Arthroplasty with a Modular Neck: A Case Report.

Weber, Alexander E. MD1; Skendzel, Jack G. MD1; Waxman, David L. MD2; Blaha, John D. MD1 Author Information

Femoral neck modularity: A bridge too far

Modular femoral neck use in total hip arthroplasty (THA) affords the operating surgeon increased intra-operative flexibility with regard to offset, version, and leg length. Proponents also advocate a reduced dislocation rate, reduced impingement issues, and ease of revision of acetabular component, head, or neck. However, the increased intra-operative flexibility and potential postoperative advantages come at a significant price. Adverse events and complications associated with modular femoral neck usage are being reported with increasing frequency. Modular femoral neck fractures as a result of patient- and implant-related factors are prevalent. Corrosion at the neck–stem interface is associated with a number of sequelae, including osteolysis, synovitis, adverse local tissue reactions (ALTRs), and aseptic lymphocyte-laminated vascular-associated lesions (ALVAL). Systemic complications of metallosis are also pertinent following corrosion at the neck–stem junction. Failure to disassemble the neck from the stem due to corrosion and cold welding is a documented complication and obviates a potential benefit of modularity at the time of revision. Modular femoral necks have a twofold increase in overall revision rate in the Australian registry data as compared to fixed-neck stems. Lastly, modular femoral necks add significant cost to each THA. The purpose of this review article is to discuss the current state of femoral neck modularity and provide the readership with pause prior to the continued use of modular femoral neck THA. Given the current and emerging literature, the modular femoral neck is a bridge too far.

Micromotions at the taper interface between stem and neck adapter of a bimodular hip prosthesis during activities of daily living

The stem-neck taper interface of bimodular hip endoprostheses bears the risk of micromotions that can result in ongoing corrosion due to removal of the passive layer and ultimately cause implant fracture. We investigated the extent of micromotions at the stem-neck interface and the seating behavior of necks of one design made from different alloys during daily activities. Modular hip prostheses (n = 36, Metha®, Aesculap AG, Germany) with neck adapters (CoCr29Mo6 or Ti6Al4V) were embedded in PMMA (ISO 7206-4) and exposed to cyclic loading with peak loads ranging from walking (Fmax = 2.3 kN) to stumbling (Fmax = 5.3 kN). Translational and rotational micromotions at the taper interface and seating characteristics during assembly and loading were determined using four eddy-current sensors. Seating during loading after implant assembly was dependent on load magnitude but not on material coupling. Micromotions in the stem-neck interface correlated positively with load levels (CoCr: 2.6-6.3 µm, Ti: 4.6-13.8 µm; p < 0.001) with Ti neck adapters exhibiting significantly larger micromotions than CoCr (p < 0.001). These findings explain why high body weights and activities related to higher loads could increase the risk of fretting-induced implant failures in clinical application, especially for Ti-Ti combinations. Still, the role of taper seating is not clearly understood.

Adverse Tissue Reactions in Modular Exchangeable Neck Implants: A Report of Two Cases

Dual-modular femoral stems with exchangeable necks theoretically allow optimization of hip joint biomechanics via selective restoration of femoral anteversion, offset, and limb length. A potential disadvantage is the possible generation of metal ions and debris by fretting and crevice corrosion at the additional stem-neck interface. We present 2 cases of early-onset adverse inflammatory tissue reactions as a result of accelerated corrosion at the stem-neck interface of a dual-modular implant, requiring subsequent revision of well-fixed components.

LOW CCD – ANGLES CAUSE HIGHER MICROMOTIONS AT THE NECK TAPER JUNCTION OF BI-MODULAR HIP STEMS

Bi-modular hip prostheses enable an individual reconstruction of the joint centre after implantation of the stem by choosing suitable neck adapters. They require an additional taper between stem and neck adapter. Tapers always bear the risk of micromotions, fretting corrosion and ion or wear debris release. Propagation of cracks in the taper interface can ultimately lead to implant failure [Atwood, 2010]. The purpose of this study was the investigation of the influence of the Caput-Collum-Diaphysis (CCD) angle and material coupling on the magnitude of micromotions in the stem-neck interface of a bi-modular hip prosthesis with the hypothesis that a varus situation does increase micromotions.

Dissociation of modular total hip arthroplasty at the neck–stem interface without dislocation

Modular femoral and acetabular components are now widely used, but only a few complications related to the modularity itself have been reported. We describe a case of dissociation of the modular total hip arthroplasty (THA) at the femoral neck–stem interface during walking. The possible causes of this dissociation are discussed. Successful treatment was provided with surgical revision and replacement of the modular neck components. Surgeons who use modular components in hip arthroplasties should be aware of possible early complications in which the modularity of the prostheses is the major factor of failure.

Influence of material coupling and assembly condition on the magnitude of micromotion at the stem–neck interface of a modular hip endoprosthesis

Hip prostheses with a modular neck exhibit, compared to monobloc prostheses, an additional interface which bears the risk of fretting as well as corrosion. Failures at the neck adapter of modular prostheses have been observed for a number of different designs. It has been speculated that micromotions at the stem–neck interface were responsible for these implant failures. The purpose of this study was to investigate the influence of material combinations and assembly conditions on the magnitude of micromotions at the stem–neck interface during cyclic loading.Modular (n=24) and monobloc (n=3) hip prostheses of a similar design (Metha, Aesculap AG, Tuttlingen, Germany) were subjected to mechanical testing according to ISO 7206-4 (Fmin=230N, Fmax=2300N, f=1Hz, n=10,000 cycles). The neck adapters (Ti–6Al–4V or Co–Cr29–Mo alloy) were assembled with a clean or contaminated interface. The micromotion between stem and neck adapter was calculated at five reference points based on the measurements of the three eddy current sensors.The largest micromotions were observed at the lateral edge of the stem–neck taper connection, which is in accordance with the crack location of clinically failed prostheses. Titanium neck adapters showed significantly larger micromotions than cobalt–chromium neck adapters (p=0.005). Contaminated interfaces also exhibited significantly larger micromotions (p<0.001). Since excessive micromotions at the stem–neck interface might be involved in the process of implant failure, special care should be taken to clean the interface prior to assembly and titanium neck adapters with titanium stems should generally be used with caution.