Corrosion at the stem-sleeve interface of a modular titanium alloy femoral component as a reason for impaired disengagement

Additively manufactured Ti-29Nb-21Zr shows improved oxide polarization resistance versus Ti-6Al-4V in inflammatory simulating solution

Retrieval studies in the past two decades show severe corrosion of titanium and its alloys in orthopedic implants. This damage is promoted by mechanically assisted crevice corrosion (MACC), particularly within modular titanium-titanium junctions. During MACC, titanium interfaces may be subject to negative potentials and reactive oxygen species (ROS), generated from cathodic activation and/or inflammation. Additive manufacturing (AM) may be able to produce new, corrosion-resistant titanium alloys and admixtures that are less susceptible to these adverse electrochemical events. In this study, we characterize the impedance and corrosion properties of three new AM titanium materials, including Ti-6Al-4V with added 1% nano-yttria stabilized ZrO2 , admixed Ti-29Nb-21Zr, and pre-alloyed Ti-29Nb-21Zr. We aim to elucidate how these materials perform when subjected to high ROS solutions. We include conventionally and additively manufactured Ti-6Al-4V in our study as comparison groups. A 0.1 M H2 O2 phosphate-buffered saline (PBS) solution, simulating inflammatory conditions, significantly increased biomaterial OCP (-0.14 V vs. Ag/AgCl) compared to PBS only (-0.38 V, p = .000). During anodic polarization, Ti-6Al-4V passive current density more than doubled from 1.28 × 10-7 to 3.81 × 10-7  A/cm2 when exposed to 0.1 M H2 O2 . In contrast, Ti-29Nb-21Zr passive current density remained relatively unchanged, slightly increasing from 7.49 × 10-8 in PBS to 9.31 × 10-8 in 0.1 M H2 O2 . Ti-29Nb-21Zr oxide polarization resistance (Rp ) was not affected by 0.1 M H2 O2 , maintaining a high value (1.09 × 106 vs. 1.89 × 106  Ω cm2 ), while Ti-6Al-4V in 0.1 M H2 O2 solution had significantly diminished Rp (4.38 × 106 in PBS vs. 7.24 × 104  Ω cm2 in H2 O2 ). These results indicate that Ti-29Nb-21Zr has improved corrosion resistance in ROS containing solutions when compared with Ti-6Al-4V based biomaterials.

Predicting Corrosion Damage in the Human Body Using Artificial Intelligence: In Vitro Progress and Future Applications

Artificial intelligence (AI) is used in the clinic to improve patient care. While the successes illustrate AI's impact, few studies have led to improved clinical outcomes. In this review, we focus on how AI models implemented in nonorthopedic fields of corrosion science may apply to the study of orthopedic alloys. We first define and introduce fundamental AI concepts and models, as well as physiologically relevant corrosion damage modes. We then systematically review the corrosion/AI literature. Finally, we identify several AI models that may be implemented to study fretting, crevice, and pitting corrosion of titanium and cobalt chrome alloys.

Cathodic activation and inflammatory species are critical to simulating in vivo Ti-6Al-4V selective dissolution

In vivo retrievals of metallic orthopedic implants have shown selective dissolution of Ti-6Al-4V, where the vanadium-rich β phase preferentially corrodes from the surface. This damage, typically observed in crevices, is not directly caused by wear mechanics and the underlying electrochemical mechanism remains poorly understood. Previous studies show that fretting corrosion can cause negative potential drops, resulting in a decrease in surface oxide passivation resistance and the electrochemical generation of reactive oxygen species (ROS) at metallic surfaces. In this study, we combine cathodic activation and hydrogen peroxide to induce selective dissolution in vitro. After a 600 s -1 V hold and 4 h recovery in 20 °C 1 M H₂O₂ solution, the Ti-6Al-4V β phase was preferentially dissolved. An initial activation threshold of -0.5 V induced a significant increase in β dissolution (p = 0.000). Above this threshold, little selective dissolution occurred. In an Arrhenius-like fashion, decreasing solution concentration to 0.1 M required 72 h to generate β dissolution instead of 4 h at 1 M. Heating 0.1 M solution to body temperature (37 °C) resulted in a decrease in the time needed to replicate a similar level of β dissolution (>90%). Electrochemical impedance shows that both cathodic activation and inflammatory species are necessary to induce selective dissolution, where the combinatorial effect causes a significant drop in oxide passivation resistance from 10⁶ to 10² (p = 0.000). STATEMENT OF SIGNIFICANCE: Though hip arthroplasties are considered a successful procedure, revision rates of 2-4% result in tens of thousands of additional surgeries within the United States, subjecting patients to increased risk of complications. Corrosion is associated with implant failure and retrieval studies show that titanium and its alloys can severely corrode in vivo in ways not yet duplicated in vitro. Here, we reproduce selective dissolution of Ti-6Al-4V β phase simulating key characteristics of in vivo degradation observed in orthopedic retrievals. We establish both cathodically activated corrosion, a relatively unexplored concept, and the presence of inflammatory species as prerequisites, furthering our understanding of this clinically relevant damage mode. We introduce an Arrhenius-based approach to assess the concentration-temperature-time interactions present.

Effect of femoral head material on head-to-trunnion impaction motion and taper

The purpose of this study was to evaluate the effect of femoral head material on the impaction force, relative motion, and stability of the trunnion. There were three groups with different head materials (n = 5 per group)-CoCr Group: 36 mm CoCr heads, Ceramic Group: 36 mm ceramic heads, Ceramic + Sleeve Group: 36 mm ceramic heads with a titanium sleeve-that were all impacted twice and disengaged onto titanium alloy (Ti6al4V) trunnions in in vitro conditions. A high-speed camera system was utilized to characterize relative displacement behavior of the head-trunnion junction motion. The first impact force of Ceramic + Sleeve Group (14,241    SD, 935) was significantly lower than the first impact force in Ceramic Group (14,961 N, SD = 184). Ceramic + Sleeve Group had a lower magnitude bounce-back displacement following the first impact (17.7 μm, SD = 11), p < 0.05) compared to CoCr Group (298.8 μm, SD = 84) and Group 2 (196.5 μm, SD = 31). Ceramic + Sleeve Group sat further on the trunnion (cumulative final displacement, 366.8 μm, SD = 71, p < 0.001) compared to CoCr Group (142.5 μm, SD = 41.8) and Ceramic Group (183.8 μm, SD = 30). Ceramic + Sleeve Group demonstrated two distinct disengagement patterns-(a) the sleeve disengaged from the trunnion (pull-off force 6810 N), and (b) the femoral head disengaged from the sleeve (pull-off force 18,620 N), with large fluctuations in pull-off force. The presence of a titanium sleeve with a ceramic head resulted in significant differences in impaction force on the trunnion, motion and displacement, and unique mechanisms for disengagement. Further investigation is required to determine potential clinical impact.

Clinical outcomes and dislocation rates after hip reconstruction using the Bioball system

INTRODUCTION

Instability accounts for 1/3 of revision total hip arthroplasty (rTHA) performed in the UK. Removal of well-fixed femoral stems in rTHA is challenging with a risk of blood loss and iatrogenic damage to the femur. The Bioball universal adaptor (BUA), a modular head neck extension adaptor, provides a mechanism for optimisation of femoral offset, leg length and femoral anteversion. This can avoid the need for femoral stem revision in selected cases.The aim of this study is to present the clinical results and rate of instability following revision with this BUA at a minimum of 2 years follow-up.

PATIENTS AND METHODS

A review of our prospectively collected database was performed. All patients treated with the Bioball device were included. Clinical and radiologic review were performed pre- and post-surgery. Specific enquiry for instability was made. The Oxford Hip Score (OHS), EuroQol (EQ-5D) score and WOMAC scores were calculated pre-and post-operatively. Complications were recorded.

RESULTS

32 rTHA procedures were performed using the Bioball device between 2013 and 2016. 4 patients did not wish to complete post-operative questionnaires. 2 patients (2/28, 7%) complained of recurrent dislocations following their rTHA procedure. 1 patient complained of instability but no dislocation. The median pre-operative EQ-5D was 0.195 (range -0.07-0.85), OHS was 20 (range 5-43) and WOMAC was 29.8 (range 15.5-52.3). The median EQ-5D was 0.85 (range 0.59-1), OHS was 39 (range 21-48) and WOMAC was 91.1 (range 44.5-99.2) at final follow-up. There were significant improvements in the EQ-5D (p = 0.0009), OHS (p = 0.0004) and WOMAC (p = 0.0001).

CONCLUSION

The BUA is associated with significant functional improvement and relatively low dislocation rates in revision THA. It is a viable option for use in the revision setting.

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.

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.

Fracture of an S-ROM stem at the sleeve-stem junction

Fracture of a well-ingrown femoral component is a rare and often challenging complication. Modular junctions and sleeve interfaces have been identified as one potential point of weakness with corrosion and fretting being contributing factors to ultimate femoral component fracture. Stem fractures at the sleeve interface were reported occasionally for the proximal ingrowth modular Emperion System (Smith and Nephew, Memphis, TN). However, this failure mechanism has been reported infrequently, often associated with corrosion at the modular junction, for the similarly designed S-ROM system (DePuy Orthopedics Inc., Warsaw, IN). We present the case of a 52-year-old patient, with a body weight of 84 kg (185 lbs) and a body mass index of 30.6 kg/m², who suffered a fatigue fracture of a 14 × 09 × 130 mm S-ROM stem 42 months after implantation. The present study presents the results of the surface analysis, discusses possible failure mechanisms, provides treatment guidelines, and a review of the literature revealing 15 cases of failure at the level of the stem-sleeve junction. In particular, modifiable risk factors for potential stem failure, including stem diameter, stem offset, and the resulting cantilever bending forces on the proximal sleeve-stem junction, are discussed in detail.

Effects of hip implant modular neck material and assembly method on fatigue life and distraction force

Hip implant neck fractures and adverse tissue reactions associated with fretting-corrosion damage at modular interfaces are a major source of concern. Therefore, there is an urgent clinical need to develop accurate in vitro test procedures to better understand, predict and prevent in vivo implant failures. This study aimed to simulate in vivo fatigue fracture and distraction of modular necks in an in vitro setting, and to assess the effects of neck material (Ti6Al4V vs. CoCrMo) and assembly method (hand vs. impact) on the fatigue life and distraction of the necks. Fatigue tests were performed on the cementless PROFEMUR® Total Hip Modular Neck System under two different loads and number of cycles: 2.3 kN for 5 million cycles, and 7.0 kN for 1.3 million cycles. The developed in vitro simulation setup successfully reproduced in vivo modular neck fracture mode and location. Neck failure occurred at the neck-stem taper and the fracture ran from the distal lateral neck surface to the proximal medial entry point of the neck into the stem. None of the necks failed under the 2.3 kN load. However, all hand-assembled Ti6Al4V necks failed under the 7.0 kN load. In contrast, none of the hand-assembled CoCrMo necks and impact-assembled necks (Ti6Al4V or CoCrMo) failed under this higher load. In conclusion, Ti6Al4V necks were more susceptible to fatigue failure than CoCrMo necks. In addition, impact assembly substantially improved the fatigue life of Ti6Al4V necks and also led to overall higher distraction forces for both neck materials. Overall, this study shows that the material and assembly method can affect the fatigue strength of modular necks. Finally, improper implant assembly during surgery may result in diminished modular neck survivability and increased failure rates. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2023-2030, 2017.

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.

Clinical Cold Welding of the Modular Total Hip Arthroplasty Prosthesis

BACKGROUND

A head that is "clinically cold welded" to a stem is one of the commonest reasons for unplanned removal of the stem. It is not clear which hip designs are at greatest risk of clinical cold welding.

METHODS

This was a case-control study of consecutively received hip implant retrievals; we chose the design of hip that had the greatest number of truly cold-welded heads (n = 11). For our controls, we chose retrieved hips of the same design but without cold welding of the head (n = 35). We compared the clinical variables between these 2 groups using nonparametric Mann-Whitney tests to investigate the significance of differences between the cold-welded and non-cold-welded groups.

RESULTS

The design that most commonly caused cold welding was a combination of a Ti stem and Ti taper: 11 out of 48 (23%) were truly cold welded. Comparison of the clinical data showed that no individual factor could be used to predict this preoperatively with none of the 4 predictors tested showing any significance: (1) time to revision (P = .687), (2) head size (P = .067), (3) patient age at primary (P = .380), and (4) gender (P = .054).

CONCLUSION

We have shown that clinical cold welding is most prevalent in Ti-Ti combinations of the stem and taper; approximately 25% of cases received at our center were cold welded. Analysis of clinical variables showed that it is not possible to predict which will be cold welded preoperatively. Surgeons should be aware of this potential complication when revising a Ti-Ti stem/head junction.

Total Hip Arthroplasty Using the S-ROM-A Prosthesis for Anatomically Difficult Asian Patients

Background. The S-ROM-A prosthesis has been designed for the Asian proximal femur with a small deformed shape and narrow canal. In this study, the clinical and radiological results using the S-ROM-A prosthesis for Japanese patients with severe deformity due to dysplasia and excessive posterior pelvic tilt were examined. Methods. 94 hips were followed up for a mean of 55 months, with a mean age at surgery of 61 years. The primary diagnoses were 94 coxarthritis cases, including 51 dysplasia and 37 primary OA, 1 avascular necrosis, 2 traumatic arthritis, and 3 Perthes disease. Thirty-one hips had been treated with osteotomy of the hip joints. Preoperative intramedullary canal shapes were stovepipe in 23 hips, normal in 51 hips, and champagne-flute in 5 hips. The maximum pelvic inclination angle was 56°. Results. The mean JOA score improved from 46 points preoperatively to 80 points at final follow-up. On radiological evaluation of the fixation of the implants according to the Engh classification, 92 (97%) hips were classified as “bone ingrown fixation.” Conclusion. In primary THA, using the S-ROM-A prosthesis for Asian patients with proximal femoral deformity, even after osteotomy and with posterior pelvic tilt, provided good short- to midterm results.

Outcome of a modular head-neck adapter system in revision hip arthroplasty

PURPOSE

Revision hip arthroplasty using a modular head-neck adapter gives the possibility of keeping a well-fixed femoral component while revising the acetabular prosthesis or femoral head and adapt leg length and femoral offset to the individual anatomy intraoperatively. The success of this kind of surgery is still unclear due to the lack of medium- to long-term follow-up. Therefore, we analyzed the clinical and radiological outcome of the modular Merete BioBall© adapter system in revision hip surgery.

METHODS

In this retrospective study, we included 95 consecutive patients with a Merete BioBall© adapter system implanted during revision hip arthroplasty. The average follow-up was 52.5 months. For clinical evaluation, we used the Harris Hip Score. The health-related quality of life was determined with the visual analog pain scale.

RESULTS

The surgeries were performed 97 months after prior hip arthroplasty on average. The main indications for the Merete BioBall© adapter system were dislocation, acetabular loosening, and wear. In the clinical outcome, patients achieved 80.9 points in the Harris Hip Score. The mean level of persisting pain was 1.4 (VAS). The overall survival of the Merete BioBall© system in revision hip arthroplasty revealed 92.8 % survival at 8.17 years follow-up with a repeat revision rate of 5.2 %.

CONCLUSIONS

Performing revision hip arthroplasty using the Merete BioBall

Variations in the trunnion surface topography between different commercially available hip replacement stems

Modular hip implants allows for the adjustment of leg length, offset, and the ability to remove the head for acetabular exposure during primary and revision surgery. The design of the Morse taper facilitates the intimate contact of the conical trunnion of the femoral stem (male component), with the conical bore of the femoral head (female component). Orthopaedic trunnion tapers are not standardized and vary in length, taper angle, and base dimension. Variations in the design and surface characteristics of the trunnion, will directly reflect on the interface at the taper junction and can influence the likelihood of subsequent wear, corrosion and longevity of the implant. The effect of surface topography of trunnions on commercially available hip stems has not yet been considered as a possible contributing factor in the corrosion observed at taper junctions. In this study we analyzed the surface topography and surface roughness of randomly selected commercially available femoral hip stem trunnions to obtain a greater insight into their surface characteristics.

Significantly reduced leg length discrepancy and increased femoral offset by application of a head-neck adapter in revision total hip arthroplasty

Head-neck adapters in total hip arthroplasty (THA) promise the reconstruction of optimal femoral offset and leg length in revision THA while retaining stable implants. Radiological parameters after adapter implantation in THA revision were determined in 37 cases. Significant reduction of leg length discrepancy and improvement of femoral offset (P < 0.001) were found. Clinical endpoints were determined in 20 cases (mean follow-up 4.0 years). Clinical scores were rather poor (median Harris hip score 54, WOMAC score 41) due to age and comorbidities, postoperative dislocation occurred in 3 cases. Only one stable femoral stem had to be revised due to recurrent postoperative dislocation. In conclusion, a head-neck adapter can be a valuable tool in certain cases of revision THA with acceptable dislocation rates while allowing the retention of stable implants.

The local effects of metal corrosion in total hip arthroplasty

Corrosion has long been recognized to occur in total hip arthroplasty, but the local effects of this process have only recently become better understood. This article provides an overview of corrosion at modular junctions, and discusses the various etiologic factors for corrosion and the biologic response to metal debris released from this junction. Algorithms are provided for diagnosis and treatment, in accordance with the best available data.

A modified S-ROM stem in primary total hip arthroplasty for developmental dysplasia of the hip

This study examined the clinical outcome of 220 hips in 196 Asian patients who underwent primary total hip arthroplasty (THA) for treatment of developmental dysplasia of the hip (DDH) using a modified S-ROM modular (S-ROM-A) stem designed for Asians, after 2-5 years (mean, 3.3 years) of follow-up. The stem was placed so that the anteversion angle of the neck was decreased against the sleeve in 56% of the hips and increased in 18% of the hips. Bone ingrown fixation was achieved in 99.5% of the hips on X-ray at final follow-up. There were 2 (0.9%) dislocations postoperatively. In primary THA for treatment of DDH accompanied by femoral rotational deformity, the freely-rotatable modular stem provided favorable short-term outcomes by affording both morphological and functional advantages.

Taper corrosion in modular hip prostheses: analysis of serum metal ions in 19 patients

Recently, concerns have been raised about the use of metal-on-metal (MoM) implants. This has led to the recall of several resurfacing and large-diameter total hip arthroplasties (THA). Any MoM interface can be the cause of metal debris and adverse tissue reactions. We analyzed serum metal ions and HOOS scores in 19 of 306 patients treated with a THA with modular neck section. The only MoM interface in this particular implant is the taper between the neck and the stem. The articulating surface consists of a ceramic-on-polyethylene or ceramic-on-ceramic interface. As such, this study looks at the metal ion production from the modular neck section. One of 306 implants needed revision at 52-month follow-up because of an adverse reaction to metal debris (ARMD).

Failure of a modular hip implant at the stem-sleeve interface

In the current era of total hip arthroplasty (THA), orthopedic surgeons have several fixation options at their disposal. The modern monoblock prosthesis, introduced by Dr. Sir John Charnley, has seen many modifications since its inception in the 1970s and continues to be the most commonly used prosthesis style for primary and revision THA. Proximal modular sleeve technology was introduced in 1967 by Konstantin Sivash, modifying his original 1956 Sivash Stem design. The design is now known as the S-ROM, and although design modifications continue to date, the fundamental structure of the S-ROM remains essentially unchanged. Several other proximal modular prostheses are now currently available for use in THA. Although this similarity in design enables considerable surgical flexibility, it also links their potential for catastrophic failure. This aim of this article was to present a brief history of proximal modularity in THA and to add to the small body of literature regarding catastrophic failure in modular hip implants, including its proposed etiologies including micromotion, fretting and corrosion.

Femoral stem fracture and in vivo corrosion of retrieved modular femoral hips

A series of 78 retrieved modular hip devices were assessed for fretting and corrosion. Damage was common at both the head-neck junction (54% showing corrosion; 88% showing fretting) and at the stem-sleeve junction (88% corrosion; 65% fretting). Corrosion correlated to in vivo duration, patient activity, and metal (vs ceramic) femoral heads but did not correlate to head carbon content. Femoral stem fatigue fracture was observed in seven retrievals; all had severe corrosion, were under increased stress, and were in vivo longer than the non-fractured cohort. This study emphasizes the potential for stem fracture when small diameter femoral stems with large offsets are used in heavy and active patients. Designs which reduce fretting and corrosion in modular implants is warranted as patients demand longer lasting implants.

Severe corrosion after malpositioning of a metallic head over the Morse taper of a cementless hip arthroplasty. A case report

Morse tapers are frequently used in total hip replacement to achieve precise adjustment of lengths and femoral offset. Mechanically, they do not raise any specific problems so long as strict positioning requirements are observed and elements from different manufacturers are not mixed together. We report a case in which the implant induced unexplained pain at 2 years, in relation to a defective fit between the metallic head and the Morse taper. Asymmetric partial fit of the head onto the taper was detected on control X-ray and was implicated as causing metallosis due to excessive release of metal debris from the Morse taper. Revision required femoral stem exchange because of the damage to the Morse taper as well as replacing the cup with new metal-metal bearings. Evolution was favorable at 3 years' follow-up. Most hip replacements include a Morse taper; the present clinical case is a reminder that strict positioning rules are to be respected, without which corrosion and wear may lead to mechanical failure.