Abstract
Introduction:
Corrosion at modular junctions in total knee arthroplasty (TKA) implants is recognized, but its clinical relevance remains unclear. This study evaluated corrosion at modular stem-bore junctions and examined whether severity correlated with radiographic evidence of adverse local tissue reactions or osteolysis.
Methods:
We evaluated 196 retrieved modular stem and bore components from 98 revision TKA patients, including taper (n = 73) and threaded (n = 25) designs. The median time in situ was 24 months for taper and 15 months for threaded junctions (P = 0.052). The median age at explant was 66 years (interquartile range (IQR), 60.7 to 74.4), and 47% of patients were women. Periprosthetic joint infection (n = 49) and aseptic loosening (n = 29) were the most common indications for component explantation. Fretting corrosion at the modular junction was graded using the modified Goldberg Score (mGS) and quantified using an optical coordinate measuring machine. Radiographs were evaluated for changes around the modular junction. Statistical analyses included Mann-Whitney U-, Chi-Square, and Spearman’s correlation tests.
Results:
Taper junctions demonstrated significantly greater corrosion than threaded designs (P < 0.001). The median mGS for modular tapers was 4 for femoral components, 3 for femoral stems, and two for both tibial components and stems. Threaded junctions showed minimal damage across all interfaces with a median score of 1. Damage patterns included fretting wear, corrosion features, and dark deposits. Among cobalt-chromium (CoCr) femoral bore tapers with mGS of 4, median material loss was 0.56 mm3, while CoCr tibial bores with mGS 4 could not be quantitatively assessed due to technical constraints. The corresponding titanium alloy femoral and tibial stem tapers showed a median loss of 0.071 mm3, and 0.067 mm3, respectively. Corrosion severity did not correlate with localized radiographic findings or the indication for revision.
Conclusion:
In this study of retrieved modular TKA components, taper junctions exhibited significantly more corrosion than threaded junctions. However, corrosion severity was not associated with radiographic findings or etiology of failure. Corrosion products differed from those typically observed in THA, suggesting a distinct mechanism. Further research is required to clarify potential clinical implications.
Keywords: Total knee arthroplasty, fretting corrosion, modular junction, taper damage, revision knee arthroplasty
INTRODUCTION
Complex primary and revision total knee arthroplasty (TKA) is an increasingly common and resource-intensive procedure in the United States, with 108,571 revisions captured in the American Joint Replacement Registry from 2012 to 2024, and national demand projected to continue rising through 2060 [1–3]. Compared with primary TKA, revisions involve greater technical complexity, longer operative times, higher complication rates, and substantially increased cost [3–5].
Modular implant systems are frequently required to address bone loss, achieve zonal fixation, and optimize fixation. The components of these implant systems consist of femoral and tibial components, which have housings to accommodate stem extensions for added stability within the femoral and tibial metadiaphysis. Of the common methods to attach the extension stems to the housing of the femoral and tibial components, two are 1) a Morse-type taper or 2) a threaded extension stem screwed into the housing. Generally, the extension stems are manufactured from titanium alloy (Ti-alloy), while femoral components are manufactured from cobalt-chromium alloy (CoCr). Tibial components can be either Ti-alloy or CoCr. The additional metal-metal interfaces at the implant-stem junction introduce potential sites for mechanical and chemical degradation.
Fretting corrosion occurs when micromotion disrupts the protective oxide layer within a fluid-filled crevice, initiating an electrochemical attack [6–8]. Both CoCr-CoCr and titanium alloy-titanium alloy (Ti-Ti) junctions are susceptible, though mechanisms may differ. Resultant metal ion and particulate release from cobalt-chromium alloys have been implicated in osteolysis and lymphocyte-dominated adverse local tissue reactions (ALTR). The Ti-Ti pairs, though free of galvanic mismatch, remain susceptible to mechanically dominated fretting corrosion [6–9].
In total hip arthroplasty (THA), fretting corrosion at head-neck junctions is a well-established cause of ALTR, osteolysis, and implant failure [10,11]. First described in the 1990s and later confirmed in large retrieval series, these processes are driven by cyclic micromotion, changes in crevice fluid chemistry, and galvanic effects in mixed CoCr-Ti couples [10,12–18]. Fretting corrosion releases Co, Cr, and Ti species locally and systemically, elevating metal ion levels and triggering inflammatory pathways [19–22].
In contrast, the clinical significance of corrosion in modular revision TKA components remains less defined. Prior retrieval studies have consistently demonstrated fretting corrosion at femoral and tibial stem junctions, with large series reporting visible damage in over 90% of modular constructs and higher corrosion scores in taper designs compared with threaded interfaces [6, 8, 23, 24]. Despite this, important knowledge gaps remain regarding the influence of specific junction designs and alloy pairing on corrosion severity, quantitative material loss at TKA junctions – particularly within CoCr components – and whether severe fretting corrosion contributes to clinical failure or ALTR.
Given the continued expansion of modular revision TKA use and parallels to the early THA corrosion experience, further characterization is warranted. The purpose of this study was to evaluate corrosion at modular stem-bore junctions in revision TKA components and assess a potential relationship between corrosion and radiographic evidence of ALTR and osteolysis.
MATERIALS AND METHODS
Retrieved implants from patients who underwent revision procedures at our institution between January 1, 2018 and December 31, 2024 were retrospectively reviewed under an Institutional Review Board approved study. Cases were included if the component-to-stem junction, either in the femoral component or the tibial baseplate, was available for analysis. Implants were eligible if the junction type could be clearly identified as either a press-fit taper or a threaded stem connection and if both mating surfaces, the component bore (female) junction and the stem (male) junction, were present for evaluation (Figure 1).
Figure 1.
STROBE diagram of cohort selection. (Abbreviations: STROBE: STrengthening the Reporting of Observational studies in Epidemiology; TKR: Total Knee Replacement; CoCr: Cobalt-chromium alloy; Ti: Titanium alloy).
A subset of components from 95 patients met the inclusion criteria, but could not be scored due to severe extraction-related damage, incomplete implant disassembly, or other technical limitations (82 patients in the tapered group and 13 in the threaded group). These components were retrieved but could not be evaluated.
After excluding components that could not be scored, the final cohort included 288 evaluable bore and stem surfaces from 98 patients. Among these, 73 patients had components with taper junctions, and 25 patients had components with threaded junctions (Table 1). This resulted in 202 individual taper and bore surfaces for evaluation in the tapered group and 86 surfaces in the threaded group.
Table 1.
Baseline Characteristics of Retrieved Implants
| Characteristics | Overall Knees (N=98) | Knees with Taper Components (N=73) | Knees with Threaded Components (N=25) | P-Value |
|---|---|---|---|---|
| Age at retrieval, years (median, IQR) | 66 (60.7 to 74.4) | 66 (60.6 to 73.2) | 69 (61.3 to 78.3) | 0.30 |
| Sex, n (%) | ||||
| Men | 52 (53) | 40 (55) | 12 (48) | 0.56 |
| Women | 46 (47) | 33 (45) | 13 (52) | |
| Laterality, n (%) | ||||
| Right | 60 (61) | 44 (60) | 16 (64) | 0.74 |
| Left | 38 (39) | 29 (40) | 9 (36) | |
| BMI (mean ± SD, range) | 33 ± 8 (17–58) | 33 ± 8 (17–52) | 35 ± 8 (22–58) | 0.27 |
| Duration in situ, months (median, IQR) | 22.9 (8.2 to 68.1) | 24.0 (11.5 to 71.5) | 14.8 (3.6 to 41.6) | 0.052 |
| Reason for implantation, n (%) | ||||
| PJI | 37 (38) | 21 (29) | 16 (64) | 0.02 |
| Aseptic Loosening | 23 (24) | 20 (27) | 3 (12) | |
| Osteoarthritis | 13 (13) | 12 (16) | 1 (4) | |
| Implant Failure (Unspecified) | 5 (5) | 5 (7) | 0 (0) | |
| Instability | 4 (4) | 2 (3) | 2 (8) | |
| Arthrofibrosis | 2 (2) | 1 (1) | 1 (4) | |
| Failed Extensor Mechanism | 2 (2) | 2 (3) | 0 (0) | |
| Periprosthetic Fracture | 2 (2) | 2 (3) | 0 (0) | |
| Pain | 1 (1) | 0 (0) | 1 (4) | |
| Patella Maltracking | 1 (1) | 1 (1) | 0 (0) | |
| Reason for removal, n (%) | ||||
| PJI | 49 (50) | 33 (45) | 16 (64) | 0.12 |
| Aseptic Loosening | 29 (30) | 24 (33) | 5 (20) | |
| Arthrofibrosis | 4 (4) | 2 (3) | 2 (8) | |
| Implant Failure (Unspecified) | 4 (4) | 4 (6) | 0 (0) | |
| Instability | 3 (3) | 3 (4) | 0 (0) | |
| Failed Extensor Mechanism | 2 (2) | 1 (1) | 1 (4) | |
| Pain | 2 (2) | 2 (3) | 0 (0) | |
| Patellar Tendon Rupture | 2 (2) | 2 (3) | 0 (0) | |
| Periprosthetic Fracture | 2 (2) | 2 (3) | 0 (0) | |
| Metal Hypersensitivity | 1 (1) | 0 (0) | 1 (4) | |
| Hinge joint, n (%) | 9 (9) | 7 (10) | 2 (8) | 0.59 |
| Cemented Components, n (%) | Femur 7 (7), Tibia 4 (4), Both 74 (76), Neither 13 (13) | Femur 6 (8), Tibia 3 (4), Both 56 (77), Neither 8 (11) | Femur 1(4), Tibia 1 (4), Both 18 (72), Neither 5 (20) | 0.64 |
Abbreviations: IQR = interquartile range; BMI = body mass index; PJI = periprosthetic joint infection
This cohort of 98 patients consisted of 52 men and 46 women. The most common indications for explant were periprosthetic joint infection (PJI) (n = 49) and aseptic loosening (n = 29) (Table 1). The median time in situ was 24.0 months (interquartile range (IQR), 11.5 to 71.5) for taper junctions and 14.8 months (IQR, 3.6 to 41.6) for threaded junctions. The taper group had a higher incidence of implantation for osteoarthritis and aseptic loosening (P = 0.02). The median patient age at explant for taper and threaded junctions was 66 (IQR, 60.6 to 73.2) and 69 (IQR, 61.3 to 78.3) years, respectively. Out of the 98 patients, nine had a hinge joint with maximum constraint (Table 1). There were 74 TKAs that had a fully cemented femoral and tibial stems, seven had a cemented femoral stem with hybrid fixation for the tibial component, four had a cemented tibial component and hybrid fixation on the femoral component, and 13 used hybrid fixation for both components (Table 1).
Junction design, classified as taper or threaded, and material pairing, classified as CoCr to Ti-alloy (CoCr-Ti) or Ti-alloy to Ti-alloy (Ti-Ti), or CoCr to CoCr (CoCr-CoCr), were determined from manufacturer specifications and confirmed during retrieval examination. All implants were cleaned of adherent soft tissue and debris using non-abrasive methods to preserve surface features for analysis.
Macroscopic and Stereoscopic Evaluation:
Each modular junction underwent visual inspection and low-power stereomicroscopy to identify qualitative features of fretting corrosion, including discoloration, corrosion product deposition, and pitting. Fretting corrosion severity was graded using the 4-point modified Goldberg scale (mGS), which has been widely applied in taper retrieval studies [6,8,19]. A score of 1 indicated no visible fretting or corrosion; 2 indicated mild damage with isolated fretting scars or discoloration involving less than 30% of the surface; 3 indicated moderate damage affecting 30 to 50% of the surface; and 4 indicated severe damage involving more than 50% of the surface, with deep pits or abundant corrosion debris. Each junction received independent scores for the bore and stem surfaces. There were two experienced observers, blinded to implant design and patient data, who graded all interfaces. Discrepancies were resolved by consensus review.
Scanning Electron Microscopy and Energy-Dispersive Spectroscopy (EDS):
Particle analysis using scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS) was performed on a subset of components (n = 10). These components were selected to represent the range of deposits observed either within bore tapers, on the outer surfaces of stem tapers, or around the outside of the tapers. The location and description of the deposits were first recorded. Using a tungsten needle, a portion of each deposit was removed from the taper and placed on separate aluminum SEM mounts covered with 12 mm diameter high-purity conductive carbon double-coated tabs. The particles were imaged on the SEM (JSM-IT500HR/LV, JEOL, Peabody, Massachusetts) at 20 kV. Particle composition was characterized using EDS (Ultim Max detector, AzTec Software, Oxford Instruments, Oxford, UK) and the data displayed as spectra with element quantification and maps.
Volumetric Material Loss:
Volumetric material loss was measured for the bore tapers of CoCr femoral components with severe corrosion (score = 4) and corresponding Ti-alloy stem tapers using an optical coordinate measuring machine (CMM) system (RedLux, Southampton, UK), a validated technique for taper wear assessment [25,26]. The Ti-alloy stem tapes were measured directly, while high-precision molds (Microset Blue, Microset, Leicestershire, UK) were made for the bore tapers. Tapers were measured with two data points/degree and 70 rotations per millimeter. Volumetric material loss from the taper surfaces was quantified from CMM data using RedLux Studio Version 4.0 software (RedLux, Southampton, UK), by fitting a perfect cone geometry to undamaged areas of the taper. Volume loss was determined in areas deviating from the ideal cone shape. Heat maps of material loss and light intensity maps were generated to visualize areas of material loss and damage features, respectively. The three-dimensional (3D) data files were unwrapped to a two-dimensional (2D), flat representation of the taper surfaces for better illustration.
Radiographic Evaluation:
Standard antero-posterior and lateral radiographs obtained within six weeks of implantation and within six weeks prior to component removal were reviewed by two observers. Radiographic evidence of loosening (partial or complete radiolucent lines) and osteolysis was documented according to the Modern Knee Society Radiographic Evaluation System [27].
Data Analyses:
Data normality was tested using Kolmogorov-Smirnov tests and found to be nonparametric. Corrosion severity scores between taper and threaded junction groups and between femoral CoCr-Ti and tibial Ti-Ti junctions were compared using Mann-Whitney U-tests. Differences in categorical variables between groups were assessed with Chi-Square tests. Associations between continuous variables, including implantation time and corrosion severity, were assessed using Spearman’s rank correlation coefficients using IBM Statistical Package for Social Sciences (SPSS) Statistics for Windows Version 31.0 (IBM Corp., Armonk, NY). Statistical significance was defined as P < 0.05 (two-tailed). P-values are reported only when significant or are listed in Table 1.
This study was approved by the Institutional Review Board at Rush University Medical Center and conducted in accordance with institutional and international research ethical standards.
RESULTS
Modular taper junctions demonstrated significantly greater fretting corrosion scores than threaded designs (P < 0.0001, Tables 2 and 3). Threaded junctions were generally well preserved, with corrosion scores clustered at the lowest grade and a median score of one (IQR, 1 to 1) across all surfaces (Figure 2). All threaded femoral bores and stems showed minimal damage, with 100% (20 of 20) free of severe corrosion. The tibial threaded component bores and stems were similarly preserved, with 96% (22 of 23) of tibial bores and 100% (23 of 23) of tibial stems showing no more than minimal changes.
Table 2:
Corrosion Score Distribution Across Femoral Modular Junctions.
| Surface (Alloy, total scored) |
Junction Type | Median mGS (Range) | Score 1 n (%) |
Score 2 n (%) |
Score 3 n (%) |
Score 4 n (%) |
|---|---|---|---|---|---|---|
| Femoral Component (CoCr, n=54) | Taper | 4 (1–4) | 6 (11) | 8 (15) | 11 (20) | 29 (54) |
| Femoral Stem (Titanium Alloy, n=52) | Taper | 3 (1–4) | 3 (6) | 16 (31) | 13 (25) | 20 (39) |
| Femoral Stem (CoCr, n=2) | Taper | 2 | 0 | 2 (100) | 0 | 0 |
| Femoral Component (CoCr, n=20) | Threaded | 1 | 20 (100) | 0 | 0 | 0 |
| Femoral Stem (Titanium Alloy, n=15) | Threaded | 1 | 15 (100) | 0 | 0 | 0 |
| Femoral Stem (CoCr, n=5) | Threaded | 1 | 5 (100) | 0 | 0 | 0 |
Abbreviations: mGS=modified Goldberg Score; CoCr=Cobalt-chromium alloy
Table 3:
Corrosion Score Distribution Across Tibial Modular Junctions.
| Surface (Alloy, total scored) |
Junction Type | Median mGS (Range) | Score 1 n (%) |
Score 2 n (%) |
Score 3 n (%) |
Score 4 n (%) |
|---|---|---|---|---|---|---|
| Tibial Component (CoCr, n=5) | Taper | 3 (2–4) | 0 | 2 (40) | 1 (20) | 2 (40) |
| Tibial Component (Titanium Alloy, n=42) | Taper | 2 (1–4) | 9 (21) | 15 (36) | 4 (10) | 14 (33) |
| Tibial Stem (Titanium Alloy, n=47) | Taper | 2 (1–4) | 3 (6) | 22 (47) | 7 (15) | 15 (32) |
| Tibial Component (CoCr, n=22) | Threaded | 1 (1–2) | 21 (95) | 1 (5) | 0 | 0 |
| Tibial Component (Titanium Alloy, n=1) | Threaded | 1 | 1 (100) | 0 | 0 | 0 |
| Tibial Stem (CoCr, n=5) | Threaded | 1 | 5 (100) | 0 | 0 | 0 |
| Tibial Stem (Titanium Alloy, n=18) | Threaded | 1 | 18 (100) | 0 | 0 | 0 |
Abbreviations: mGS=modified Goldberg Score; CoCr=Cobalt-chromium alloy
Figure 2.
Comparison of corrosion severity scores between alloy couples (CoCr-Ti, CoCr-CoCr, or Ti-Ti) across femoral and tibial components. Box-and-whisker plots display distribution of mGS within A) femoral component bores, B) femoral stems, C) tibial component bores, and D) tibial stems. E) Pooled analysis of all tapered and threaded junction types (Total Junctions). Corrosion severity was significantly higher in tapered compared with threaded junctions (P < 0.0001). (Abbreviations: CoCr: Cobalt-chromium alloy; Ti: Titanium alloy; mGS: modified Goldberg Score).
In contrast, taper junctions showed substantially higher damage, with median scores of four (IQR, 3 to 4) at the CoCr femoral bore taper, three (IQR, 2 to 4) at the Ti-alloy femoral stem taper, and two (IQR, 2 to 4) at both Ti-alloy tibial bore and stem tapers (Figure 2). Of the five components with CoCr tibial baseplates, the median score was three (IQR, 2 to 4). The damage score distribution on the femoral bore taper and stem taper by junction type and couple material is presented in Table 2. The damage score distribution on the tibial bore taper and stem taper is presented in Table 3. The damage score distribution on the CoCr femoral bore taper and Ti-alloy stem taper (n = 52) was None: 11 and 6%; Mild: 15 and 31%; Moderate: 20 and 25%; and Severe: 54 and 39%; respectively. There were two femoral stems that were CoCr, and both exhibited mild damage (mGS 2). The damage score distribution for Ti-alloy tibial bore and Ti-alloy stem taper (n = 42) was None: 21 and 6%; Mild: 36 and 47%; Moderate: 10 and 15%; and Severe: 33 and 32%; respectively. For the CoCr tibial baseplates (n = 5) the distribution of damage scores was mild: 40%, moderate: 20%, and severe: 40%. There was no difference in damage score distribution between CoCr and Ti-alloy tibial bores, nor between CoCr tibial bores and CoCr femoral bores. For taper and threaded modular junctions, there was no difference in mGS distribution or median mGS between TKAs with a hinge joint and those with less constraint. There was also no difference in median mGS and mGS distribution between cemented and uncemented components on either the femoral or tibial site.
Macroscopic inspection of taper junctions frequently revealed dark discoloration within the bore of modular junctions, corresponding to surface deposits and advanced fretting corrosion (Figure 3). Microscopic examination confirmed the damage features consistent with fretting corrosion. SEM/EDS analysis of fretting corrosion products confirmed the presence of chromium phosphate, cobalt phosphate, and mixed chromium chloride–sulfur compounds around CoCr modular bore tapers regardless of mating material (Figure 4). In contrast, the corresponding Ti-alloy taper exhibited macroscopically visible black deposits, which were confirmed to be titanium-oxide accumulations.
Figure 3.
Examples of taper surfaces with severe fretting corrosion damage (mGS 4) and dark deposits: A) bore taper of a femoral condyle component made from CoCr, B) taper of a femoral extension stem, C) bore taper of a tibial baseplate, and D) taper of a tibial extension stem. B to D components are made from titanium alloy. (Abbreviations: mGS: modified Goldberg Score; CoCr: Cobalt-chromium alloy).
Figure 4.
The energy-dispersive spectroscopy particle analysis of deposits at rim of two femoral extension bore tapers. A) dark particle identified as chromium phosphate corrosion product. B) pink particle identified as cobalt phosphate.
Quantitative volumetric analysis could only be conducted on 23 bore tapers and 19 stem tapers out of 29 femoral components with severe fretting corrosion (mGS 4) at the bore. The remaining tapers with severe corrosion damage were unable to be analyzed for material loss due to severe removal damage or design features (e.g., holes and crevices) that prevented taper molding. The median material loss of the CoCr bore taper was 0.56 (IQR, 0.04 to 1.14) mm3, while the opposing femoral Ti-alloy stem tapers exhibited markedly lower losses, with a median of 0.071 (IQR, 0.014 to 0.282) mm3 (Figure 5). Heat and light intensity maps of the taper surfaces reveal damage progression throughout the taper (Figure 6). On the tibial side, only stem tapers could be quantitatively analyzed. Due to their narrow, elongated geometry and slightly off-center position, tibial bores did not yield molds that could be accurately assessed using the available methodology. Stem tapers had a material loss of 0.067 (IQR, 0.021 to 0.387) mm3 for Ti-alloy tibial stems.
Figure 5.
A) Comparison of the extent of material loss caused by fretting corrosion in severely damaged CoCr alloy bore tapers (mGS 4) and their corresponding titanium alloy stem tapers. B) Comparison of extent material loss in severely damaged (mGS 4) titanium alloy tibial stem tapers coupled with either Ti-alloy or CoCr-Ti tibial baseplates. (Abbreviations: CoCr: Cobalt-chromium alloy; mGS: modified Goldberg Score; Ti: Titanium alloy).
Figure 6.
Heat (top) and light intensity maps (bottom) for a two femoral TKA components with mGS of 4. A) CoCr bore with volume loss of 27.71 mm3. A severe corrosion mark can be seen on the bore taper. B) CoCr bore with volume loss of 1.07 mm3. (Abbreviations: TKA: Total Knee Arthroplasty; mGS: modified Goldberg Score; CoCr: Cobalt-chromium alloy).
Corrosion severity did not demonstrate a significant association with the indication for revision and BMI, and no correlation with implantation duration in situ was identified. There were no implants that were revised specifically for ALTR, and there was no radiographic evidence of ALTR localized to the modular junction. There were no periarticular soft-tissue masses, fluid collections, periosteal reactions, aggressive bone changes, or synovial proliferation that were identified adjacent to the junction. Progressive radiolucent lines or osteolysis was not isolated around the taper junction in any of the cases.
DISCUSSION
This study examined the prevalence and severity of fretting corrosion in modular TKA components and the potential relationship between corrosion and radiographic evidence of ALTR and bone degeneration. Across both femoral and tibial modular interfaces, taper junctions exhibited significantly higher fretting corrosion scores and a greater proportion of severe damage (deep pits or abundant corrosion debris involving more than 50% of the surface) compared with threaded designs. Although severe fretting corrosion was common, particularly in CoCr femoral bores, there was no indication that corrosion products contributed to ALTRs or bone resorption in this cohort.
Severe fretting corrosion occurred in 54% of CoCr femoral bore tapers and 33 to 39% of Ti-alloy tapers across metal pairings, whereas threaded interfaces showed only minimal damage for both CoCr and Ti-alloys (95 to 100%, respectively). Taper junctions rely on an interference fit that may permit subtle micromotion, while threaded couplings gain stability from axial compression, reducing movement under load [6,24]. In contemporary modular TKA systems, femoral junctions typically pair a CoCr femoral component with a Ti-alloy stem, while tibial junctions are typically Ti-Ti. Mixed CoCr-Ti couples may accelerate corrosion of the less noble metal via galvanic effects under fretting, whereas Ti-Ti interfaces, although lacking galvanic mismatch, remain susceptible to mechanically driven fretting wear [6–9]. The prevalence of severe CoCr taper corrosion in TKA is high (54%) compared with THA, where only 8% of CoCr-Ti couples exhibit severe damage [10]. While this high prevalence of fretting corrosion is consistent with prior reports [6,8,25], it is surprising considering that modular TKA constructs are assembled prior to implantation and therefore should have a low likelihood of malseating or taper junction contamination, which is a known cause for downstream fretting corrosion in THA. A larger moment arm, machining tolerances, and overall compliance may play a role in the more frequent occurrence of fretting corrosion in revision TKA. Stem fixation methods and overall ligamentous balance may also play a role. While our study found corrosion not to be prevalent for threaded components, a previous study of 13 threaded cases found severe corrosion in four tibial components and one femoral component, as well as histopathological evidence of ALTR [24].
SEM/EDS analysis identified corrosion products on CoCr femoral bore tapers —specifically chromium phosphate —identical to those reported in THA associated with ALTR, alongside compounds more frequently detected in TKA stems, including chromium chloride and sulfide mixtures and cobalt phosphate [31]. These findings suggest differences in crevice chemistry and electrochemical processes between knee and hip modular junctions. While the prevalence of severe fretting corrosion (mGS 4) in TKA modular junctions is higher than that seen in THA, the median volumetric material loss from CoCr femoral bores was approximately half that reported for CoCr femoral head tapers [13], yet still within the range observed for established THA corrosion mechanisms.
Despite the high prevalence of severe corrosion, radiographic review did not identify periprosthetic soft-tissue masses, progressive osteolysis, or periosteal reaction attributable to ALTR from corrosion, and none were revised primarily for this diagnosis. Corrosion severity did not correlate with radiographic findings or indications for re-revision. Interpretation is limited by substantial pre-existing mechanical or biologic compromise in this revision population and by inconsistent baseline imaging, which may obscure subtle progression. These observations align with prior modular knee reports, contrasting with the well-documented role of taper corrosion in ALTR and pseudotumor formation in THA [6,9,20,24,28,32]. The discrepancy likely reflects knee-specific factors, such as a smaller capsular volume; limited synovial access to the junction, unlike THA; and shielding by cement or bone, all of which may limit the dissemination of corrosion products while sustaining a chemically aggressive crevice environment [30]. Nevertheless, clinically relevant reactions have been reported in TKA, particularly in constructs incorporating additional modular interfaces such as metaphyseal sleeves or cones, where metallosis and osteolysis have been documented [23,33].
From a practical standpoint, these findings support a hierarchy of the corrosion likelihood: the highest corrosion severity occurred in CoCr-Ti femoral taper junctions, where conical geometry, mixed-metal pairing, and location effects converge. CoCr-Ti and Ti-Ti tibial taper junctions showed comparably less, but still noticeable, corrosion damage. Threaded tibial junctions, independent of material couple, generally had the lowest damage, though mild fretting was still observed, reinforcing that no modular interface is completely immune to fretting corrosion. Meticulous intraoperative assembly, therefore, remains critical.
From a design perspective, optimizing junction stability and corrosion resistance remain a priority. In addition, extraction technique must be considered. Tapered junctions can be decoupled in situ, making implant removal more feasible. Evidence from THA retrieval and fretting corrosion studies supports strategies such as applying sufficient assembly loads, optimizing taper geometry and contact length, improving manufacturing tolerances, and controlling surface topography to limit micromotion [28,36]. In TKA, oxidized zirconium femoral components have demonstrated low wear and oxidation rates in retrieval studies, suggesting that material and surface engineering may offer further benefit [37]. These innovations should be paired with ongoing retrieval surveillance and registry evaluations to confirm long-term clinical performance [31].
This study has potential limitations. Retrieval analysis captures only implants that fail or are revised, potentially overrepresenting problematic cases and thus underrepresenting cases of mild corrosion that did not reach clinical symptoms. This cohort lacked information on patient activity level, a confounding factor that may affect the onset of fretting corrosion. Variability in postoperative radiographs limited correlations between radiographic and retrieval findings. Volumetric measurements were only feasible for a subset of CoCr femoral taper bores without extraction damage or obstructive design features and were not possible for tibial bores. While there were no statistical differences in the reason for implant removal between the threaded and tapered groups, a much larger proportion of the tapered components were removed for aseptic loosening, which may affect the load and wear seen at these junctions. Our study sample size was too small to allow for consideration of potential implant design factors due to the large heterogeneity in implant design, material, and component size in this cohort. Nevertheless, this study provides the first high-accuracy volumetric assessment of material loss in TKA taper junctions.
These findings identify high-corrosion risk junction configurations in contemporary modular TKA and underscore the mechanical vulnerability of certain modular designs. Preventive strategies should integrate optimized junction design and precise intraoperative assembly, informed by continuous retrieval investigations, to mitigate the likelihood of corrosion and to establish thresholds for intervention.
CONCLUSION
This retrieval analysis demonstrates that fretting corrosion is prevalent at modular junctions in revision TKA with quantifiable material loss due to the release of corrosion products. Taper junctions exhibited higher corrosion severity than threaded junctions across femoral and tibial locations, with the most pronounced damage observed at the mixed-metal femoral CoCr-Ti interface. Tibial junctions generally showed lower scores, although mechanically dominated fretting damage was still present in taper designs. Despite the frequency of severe corrosion, no association was identified between corrosion severity and radiographic evidence of loosening or ALTR. These results identify high-risk configurations in contemporary revision TKA and underscore the importance of corrosion-resistant implant design, meticulous intraoperative assembly, and continued integration of retrieval analysis with prospective clinical monitoring to better define the long-term mechanical and biological consequences of modular junction corrosion.
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