Asymptomatic Pseudotumors in Patients with Taper Corrosion of a Dual-Taper Modular Femoral Stem: MARS-MRI and Metal Ion Study

Kwon, Young-Min MD, PhD; Khormaee, Sariah MD, PhD; Liow, Ming Han Lincoln MD; Tsai, Tsung-Yuan PhD; Freiberg, Andrew A. MD; Rubash, Harry E. MD

Journal of Bone & Joint Surgery - American Volume:
doi: 10.2106/JBJS.15.01325
Scientific Articles
Abstract

Background: Modularity in total hip arthroplasty facilitates intraoperative restoration of patient anatomy. Although dual-taper modular total hip arthroplasty offers potential advantages for optimizing the hip center of rotation, it has been associated with modular taper corrosion. This corrosion has led to adverse local tissue reactions (pseudotumors) at the neck-stem junction and elevated metal-ion levels. However, the occurrence of taper-corrosion-related pseudotumors in patients who remain asymptomatic following total hip arthroplasty with a dual-taper modular femoral stem remains largely unknown. The aims of this study were (1) to determine the prevalence of asymptomatic pseudotumors by utilizing metal artifact reduction sequence magnetic resonance imaging (MARS-MRI) and (2) compare serum metal-ion levels between symptomatic and asymptomatic patients with a dual-taper modular stem total hip replacement.

Methods: We performed a retrospective cross-sectional study of 97 consecutive patients who had been treated with a dual-taper modular femoral stem total hip arthroplasty. Eighty-three patients were stratified into symptomatic and asymptomatic groups and evaluated with MARS-MRI, measurement of serum metal-ion levels, and the University of California at Los Angeles (UCLA) functional hip score.

Results: The prevalence of pseudotumors as determined with MARS-MRI was 15% in our asymptomatic patients and 36% in the overall cohort. The median serum cobalt level and cobalt/chromium ratio were significantly higher in patients with a pseudotumor than in those without a pseudotumor (8.0 versus 2.0 μg/L [p = 0.004] and 10.3 versus 2.4 μg/L [p = 0.012], respectively). However, there was no significant difference in the serum cobalt level or cobalt/chromium ratio between symptomatic patients with a pseudotumor and asymptomatic patients with a pseudotumor (7.6 versus 6.2 μg/L [p = 0.37] and 8.3 versus 10.6 μg/L [p = 0.46], respectively). The UCLA scores of asymptomatic patients with a pseudotumor were similar to those of patients without a pseudotumor (6.7 versus 6.6).

Conclusions: The prevalence of asymptomatic taper-corrosion-related pseudotumors on MARS-MRI in this study demonstrated that the absence of symptoms does not exclude the presence of adverse local tissue reactions. Elevated cobalt levels and cobalt/chromium ratios were associated with the presence of pseudotumors in asymptomatic and symptomatic patients. Cross-sectional imaging such as MARS-MRI is indicated for patients with elevated metal-ion levels. A longitudinal study is required to determine whether asymptomatic patients with taper-corrosion-related pseudotumors will develop symptoms with time.

Level of Evidence: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Author Information

1Department of Orthopaedic Surgery, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts

E-mail address for Y.-M. Kwon: ymkwon@mgh.harvard.edu

Article Outline

Modular implants in total hip arthroplasty facilitate intraoperative optimization and restoration of patient anatomy1. Traditionally, the modularity has been at the head-neck junction of femoral implants. Newer total hip arthroplasty implants have an additional point of modularity at the neck-stem junction2-4. These dual-taper femoral implants possess the potential to allow precise reconstruction of the hip center of rotation through adjustable length, offset, and version. However, this additional modular junction has been associated with device failure5-7. Previous studies have demonstrated failures at the neck-stem junction due to modular neck fracture, junction dissociation, fretting, and corrosion6-11. More recently, taper corrosion from the modular junction has been associated with adverse local tissue reactions, or “pseudotumors,” resembling those seen adjacent to implants with metal-on-metal (MoM) articulations, including MoM total hip arthroplasty and hip resurfacing implants12-16. These adverse local tissue reactions, characterized as large fluid-filled or solid tissue masses adjacent to the implant, are hypothesized to result in part from a host reaction to released metal-ion particles from MoM surface wear17-19, contributing to clinically relevant pain/discomfort, periprosthetic soft-tissue damage, and limitations in function20. The characteristics of adverse local tissue reactions detected on metal artifact reduction sequence magnetic resonance imaging (MARS-MRI) in patients with dual-taper modular implants have been reported to be similar to those observed in patients with MoM hip prostheses21. As a result of concerns about premature implant failure and an increasing number of reports of adverse local tissue reactions associated with dual-taper modular stem taper corrosion12,17,22,23, several implants have been voluntarily withdrawn by the manufacturer24.

The reported prevalences of pseudotumors in asymptomatic patients with MoM total hip arthroplasty and those with MoM hip resurfacing arthroplasty have ranged widely, from 31% to 65%25-29 and from 27.3% to 68%30,31, respectively. However, reported data on the prevalence of taper-corrosion-related pseudotumors in asymptomatic patients with a dual-taper modular stem are limited. Therefore, the aims of the study were (1) to determine the prevalence of asymptomatic pseudotumors with the use of MARS-MRI and (2) to compare serum metal-ion levels between symptomatic and asymptomatic patients with a dual-taper modular total hip arthroplasty stem in a consecutive cohort.

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Materials and Methods

Patients

Ninety-seven consecutive patients who received a Rejuvenate dual-taper modular stem total hip arthroplasty implant (Stryker Orthopaedics) from June 2010 to April 2012 were evaluated in this institutional review board-approved study. All patients were notified of the manufacturer’s voluntary recall of this implant and returned for a follow-up visit at a mean of 22 months (range, 16 to 38 months) postoperatively. Our retrospective cross-sectional evaluation of the patient’s clinical data, metal ion levels, and MARS-MRI images was conducted independently and not associated with the manufacturer’s recall.

Patients were stratified as either asymptomatic or symptomatic on the basis of clinical assessment. They were classified as asymptomatic if they were pleased with the function of the implant and had no documented pain, weakness, or other mechanical symptoms on the side with the implant. Patients who reported pain or any other problems pertaining to their implant were classified as symptomatic. Fourteen patients were excluded from the analysis as they did not undergo MARS-MRI, resulting in 83 patients for analysis. All operations were performed by a single surgeon via a posterior approach, and a beta-titanium alloy (Ti-Mo-Zr-Fe [TMZF]) dual-taper modular stem coupled with a wrought cobalt-chromium-alloy modular neck was used in all patients. The bearing surface was ceramic-on-highly cross-linked polyethylene in all patients.

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MARS-MRI and Metal Ion Levels

All patients underwent MARS-MRI with a 1.5-T-magnet MRI unit (Siemens) performed according to a previously published MARS protocol32. T1-weighted spin-echo and short tau inversion recovery (STIR) coronal and axial sequences were utilized in the MARS-MRI protocol. A high bandwidth was employed to reduce metal artifacts. All MRI scans were interpreted by an experienced musculoskeletal radiologist who was blinded to the clinical details. A pseudotumor was defined as a mass with solid and/or cystic components that was in continuity with the hip joint. The definition and classification of the MRI findings were based on a previously published study32. All pseudotumors detected on MARS-MRI were classified as Type I (cystic with a cyst-wall thickness of <3 mm), Type II (cystic with a cyst-wall thickness of ≥3 mm), or Type III (predominantly solid lesion). Isolated simple fluid collections and thickening or distention of a non-communicating trochanteric bursa were not classified as pseudotumors. Serum cobalt and chromium levels were analyzed in a blinded fashion using an inductively-coupled plasma mass spectrometer (PerkinElmer). The detection limit of cobalt and chromium in serum was 0.3 μg/L.

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Statistical Analysis

Kruskal-Wallis nonparametric analysis of variance was used to compare serum metal-ion levels among asymptomatic patients with a pseudotumor, asymptomatic patients without a pseudotumor, and symptomatic patients with a pseudotumor. The Mann-Whitney U test was used in 2 comparisons: (1) patients with a pseudotumor versus those without a pseudotumor and (2) symptomatic patients with a pseudotumor versus asymptomatic patients with a pseudotumor. The 2-sided Student t test was used to compare functional outcome scores between symptomatic and asymptomatic patients with a pseudotumor.

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Results

Overall Prevalence of Pseudotumors

Overall, a pseudotumor was detected with MARS-MRI in 30 (36%) of the 83 consecutive patients with a dual-taper modular stem. The majority of the pseudotumors were type-II “complex cysts” with irregular, thickened capsular cystic cavities filled with fluid. There were 2 type-I “simple cysts” and 3 type-III solid pseudotumors associated with abductor tears and fascial defects. The dimensions of the pseudotumors ranged from 4.5 × 4.0 × 1.0 cm to 13.0 × 7.9 × 6.0 cm.

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Symptomatic Pseudotumors

Twenty-one (70%) of the 30 patients who had a pseudotumor detected on MARS-MRI were symptomatic. Pain was the most common symptom, with 17 patients (81%) reporting hip, groin or thigh pain. Two patients (10%) reported hip discomfort without frank pain. The most common single location for pain was the groin, followed by the anterior aspect of the thigh, lateral aspect of the thigh, posterior aspect of the thigh, and buttocks. Other reported symptoms included instability (14%), weakness (19%), and a palpable mass or fluid collection (24%). Three patients developed a localized rash, and 2 of them had concomitant hip pain. The majority (17) of the 21 symptomatic patients also had abnormal physical examination findings, including an antalgic gait, pain at the extremes of the range of motion, tenderness to palpation, skin changes, swelling, and masses at the hip.

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Asymptomatic Pseudotumors

Approximately one-third (9) of all 30 pseudotumors detected were asymptomatic. As there were 60 asymptomatic patients in this study, and 9 of them had a pseudotumor, the prevalence of asymptomatic pseudotumors was 15% (Fig. 1). There was no significant difference in sex, preoperative body mass index (BMI), or implant size between patients without a pseudotumor and patients with a pseudotumor (symptomatic or asymptomatic) (Table I). Moreover, there was no significant difference in the type or size of the pseudotumors between the asymptomatic and symptomatic patients. The asymptomatic patients with a pseudotumor were older than the symptomatic patients with a pseudotumor (mean age, 63 versus 57 years). In addition, the mean University of California at Los Angeles (UCLA) hip score was significantly higher for the asymptomatic patients with a pseudotumor than for the symptomatic patients with a pseudotumor (mean [and standard deviation], 6.7 ± 0.7 versus 5.5 ± 2.7, p = 0.002). The mean UCLA scores for the asymptomatic patients with a pseudotumor were similar to those for the patients without a pseudotumor (6.7 versus 6.6) (Table II).

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Metal Ion Levels

The median serum cobalt-ion level was significantly higher in patients with a pseudotumor (8.0 μg/L; range, 3.3 to 18.4 μg/L) than in patients without a pseudotumor (2.0 μg/L; range, 1.0 to 3.7 μg/L) (p = 0.004). In addition, the median cobalt/chromium ratio was significantly higher in patients with a pseudotumor (10.3; range, 4.5 to 68) than in those without a pseudotumor (2.4; range, 0.3 to 3.8) (p = 0.012). The median chromium-ion level did not differ significantly between patients with and those without a pseudotumor (Table III). There was also no significant difference in the median serum cobalt-ion level or cobalt/chromium ratio between symptomatic and asymptomatic patients with a pseudotumor (7.6 versus 6.2 μg/L [p = 0.37] and 8.3 versus 10.6 μg/L [p = 0.46], respectively) (Table IV). Asymptomatic patients with a pseudotumor had a significant lower median chromium-ion level (0.5 μg/L; range, 0.21 to 1.0 μg/L) than symptomatic patients with a pseudotumor (0.9 μg/L; range, 0.20 to 1.1 μg/L) (p = 0.006).

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Discussion

Additional proximal femoral modularity at the neck-stem junction in total hip arthroplasty facilitates anatomic reconstruction of the hip center, allowing adjustments of femoral anteversion, leg length, and offset. However, these implants have been associated with complications arising from fretting and corrosion at their modular neck-stem junction, such as adverse local tissue reactions (pseudotumors)12,22,23. Authors of previous studies have reported the relationship between serum metal-ion levels and imaging findings associated with modular stem-neck junction corrosion11,21,33-38. Although multiple studies have examined the prevalence of pseudotumors in asymptomatic patients with MoM total hip arthroplasty or hip resurfacing arthroplasty25-31, reported data on asymptomatic pseudotumors related to taper corrosion in dual-taper modular total hip replacements are limited. In a study that included 83 hips treated with Rejuvenate modular total hip arthroplasty, Meftah et al.34 reported a prevalence of symptomatic pseudotumors of 43% (10 pseudotumors in 23 hips revised because of pain) at a mean of 2.7 years (range, 12 to 40 months). However, as MARS-MRI was performed only for patients with elevated serum metal-ion levels or symptoms related to the hip, they did not report the prevalence of pseudotumors in the remaining 58 asymptomatic patients in their study. Walsh et al.39 suggested that psoas tendinopathy with partial or complete rupture seen on MRI should be considered a sign of adverse local tissue reaction in symptomatic patients with modular hip implants. However, despite a relatively large number of patients treated with dual-taper modular total hip arthroplasty in their study, they did not describe the patients’ symptomology.

We evaluated one of the largest consecutive series of patients with a dual-taper modular stem screened with MARS-MRI for the presence of an adverse local tissue reaction (pseudotumor). At a mean of 22 months postoperatively, the overall pseudotumor prevalence was 36%. The pseudotumors observed were often large and resembled previously reported adverse local tissue reactions described in association with MoM implants. In addition, our study identified a 15% prevalence of pseudotumors in asymptomatic patients, which accounted for approximately one-third of all pseudotumors detected. Interestingly, asymptomatic patients with a pseudotumor had functional outcomes that were similar to those of patients who did not demonstrate a pseudotumor on MARS-MRI. This finding suggests that the absence of pain or other symptoms should not reduce the physician’s index of suspicion for possible taper-corrosion-related pseudotumor formation in patients with a dual-taper modular stem.

The patients with a pseudotumor had a significantly higher serum cobalt level and cobalt/chromium ratio regardless of symptoms. Elevation in serum metal-ion levels is likely secondary to a combination of fretting and crevice corrosion at the modular neck-body interface22. Our findings are supported by previous studies that demonstrated similar findings in patients with taper corrosion in a dual-taper modular implant, with serum cobalt levels exceeding serum chromium levels17,21,22,38,40. It has been hypothesized that, in contrast to MoM bearing-surface wear, the predominant ion release at modular taper junctions is due to a chemical corrosion process that involves chromium precipitating as chromium orthophosphate and more soluble cobalt dissipating as free ions, resulting in a preferential elevation of serum cobalt and an increased cobalt/chromium ratio17,22,41. Although the precise mechanism remains unknown, the occurrence of pseudotumors after dual-taper total hip arthroplasty with a cobalt-chromium modular neck implant is likely to be associated with excessive taper corrosion at the neck-stem modular junction, which results in preferential elevation of cobalt ion concentrations in vivo. This is supported by retrieval analysis studies5,21,23,34 that demonstrated taper geometry, taper contact area, and taper surface roughness as important contributing factors to taper junction fretting and corrosion. Moreover, in vitro results have demonstrated dose-dependent cytotoxicity with predominantly cobalt, rather than chromium, nanoparticles42.

As it remains unclear whether asymptomatic patients with a pseudotumor will develop symptoms with time, further study is necessary to evaluate the natural history of asymptomatic pseudotumors associated with dual-taper modular stems. Our study suggests that asymptomatic patients should be clinically evaluated. There should be a low threshold for measuring chromium and cobalt ion levels. As both asymptomatic and symptomatic patients with elevated ion levels are more likely to have a pseudotumor, MARS-MRI is indicated for patients with elevated metal-ion levels.

The results of the current study need to be interpreted in light of its potential limitations. First, there was a small number of patients with an asymptomatic pseudotumor. However, our study is one of the largest single-surgeon, single-implant, consecutive cohort studies that has allowed estimation of the prevalence of pseudotumors in patients with a dual-taper modular stem. Second, there may have been a reporting bias that led to patients reporting worsening symptoms after the recall. In addition to the 21 patients with a symptomatic pseudotumor, there were 2 patients who reported symptoms but did not have a pseudotumor. Assuming that these 2 symptomatic patients without a pseudotumor were affected by reporting bias, this would have resulted in a 14.5% prevalence of asymptomatic pseudotumor (9 of 62) instead of the 15% prevalence reported in our study. Third, as periprosthetic tissues can be obscured by metal artifacts when MARS-MRI is used, pseudotumors may have been missed. However, a previously published MARS-MRI protocol32 was used, and all scans were interpreted by an experienced musculoskeletal radiologist. Fourth, measurements of serum metal levels can be confounded by renal impairment and cobalt ions from other sources. However, none of the patients had renal impairment and, as the bearing surface was ceramic-on-highly crossed-linked polyethylene in all patients, none had an additional head-neck taper junction as a potential source of cobalt and chromium corrosion. Fifth, we did not attempt to correlate the findings of our histological analysis and those of a retrieval analyses. Finally, this study included only a single type of implant; thus, generalizability of our results to other types of dual-taper modular stems may be limited.

In conclusion, the prevalence of asymptomatic taper-corrosion-related pseudotumors seen on MARS-MRI in this study demonstrated that the absence of symptoms does not exclude the presence of adverse local tissue reactions. Elevated cobalt levels and cobalt/chromium ratios were associated with the presence of pseudotumors in asymptomatic and symptomatic patients. Cross-sectional imaging such as MARS-MRI is indicated for patients with elevated metal-ion levels. A longitudinal study is required to determine whether asymptomatic patients with a taper-corrosion-related pseudotumor will become symptomatic with time.

Investigation performed at the Center for Metal-on-Metal Hip Replacement Evaluation and Treatment, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts

A commentary by Stephen J. Incavo, MD, is linked to the online version of this article at jbjs.org.

Disclosure: No external funding was received for this study. On the Disclosure of Potential Conflicts of Interest forms, which are provided with the online version of the article, one or more of the authors checked “yes” to indicate that the author had a relevant financial relationship in the biomedical arena outside the submitted work.

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