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Adverse reaction to metal debris

72 citationsUpdated Sep 2026

Overview

Adverse reaction to metal debris (ARMD) is a biological response to metallic wear particles, where excessive wear combined with a hypersensitivity response may initiate early tissue reactions in patients with metal-on-metal implants [1]. While histological features of both innate and adaptive immune responses are present in periprosthetic tissues regardless of metal ion levels [12], metal hypersensitivity does not appear to be the dominant biological mechanism driving ARMD [6]. Metallic debris contributes to the formation of a fibrous membrane around implants, which can act as a conduit for polyethylene debris and promote osteolysis and loosening [14]. Notably, wear debris from titanium-based alloys alone, in the absence of infection or specific immune response, can produce clinically important pain [25].

The incidence of ARMD is higher than previously estimated. In patients with 36 mm metal-on-metal total hip replacements, nine-year survival declined from 96% to 86% under modern follow-up protocols [8]. At an average of 2.1 years postoperatively, 15.4% of evaluated metal-on-metal total hip arthroplasties demonstrated aseptic failure, with all revised hips showing adverse local tissue reactions [17]. The estimated median incidence of ARMD requiring revision surgery is 0.3% [10]. Differences in debris arising from the taper and articulating surfaces may explain the increased incidence of soft-tissue reactions in metal-on-metal total hip arthroplasties compared with hip resurfacings [15]. Furthermore, modular hip hemiarthroplasty patients may be susceptible to metallosis and ARMD despite being less active than total hip arthroplasty recipients [23].

Clinical management relies on a combination of imaging and blood tests, as routine annual blood metal ion testing in asymptomatic large-head metal-on-metal total hip arthroplasty is unnecessary and cannot serve as a sole screening method [20]. Cobalt and chromium levels above 5 and 2.5 ppb, respectively, indicate an increased risk of ARMD and should prompt discussion regarding potential future revision [48]. Although ion levels alone should not determine revision surgery, a cobalt level >2.8 mg/L and a Co/Cr ratio >3.8 are useful diagnostic adjuncts for taper corrosion-related adverse tissue reactions in dual modular taper total hip arthroplasty [27]. Revision surgery results in a marked reduction of blood cobalt and chromium ion concentrations [7] and does not seem to compromise implant ingrowth [7]. Patients undergoing revision for adverse local tissue reactions after metal-on-polyethylene total hip arthroplasty demonstrate major pain relief [2]. Caution is required when choosing bearing surfaces for ARMD revisions [3], as the ceramic-on-metal coupling demonstrates raised metal ions beyond 3 years and increasing revisions, making further use not warranted [11].

Anatomy & Pathophysiology

Bony Anatomy

The hip is a multiaxial joint formed by the articulation between the pelvis and femur, connecting the axial skeleton and the lower extremity [61]. The pelvic girdle consists of two innominate (coxal) bones that articulate with the sacrum and proximal femora [67]. The hemipelvis comprises the ilium, ischium, and pubis, which unite at the triradiate cartilage within the concave acetabulum [61]. The acetabulum features an articular crescent-moon–shaped lunate surface and a nonarticular central fossa that serves as the attachment point for the ligamentum teres [61]. It is incomplete inferiorly, forming a notch through which vital blood vessels and nerves pass to supply the joint [61]. This inferior surface contains the acetabular (cotyloid) notch, which is bound by the transverse acetabular ligament [67]. The posterosuperior articular surface of the acetabulum is thickened to accommodate weight bearing [67].

The femoral head forms two-thirds of a sphere, with a small depression at its center from which the ligamentum teres extends to connect to the acetabular notch [61]. The neck-shaft angle of the femur averages 125° [61], or 127 degrees, beginning at 141 degrees in the fetus [67]. Normal version, defined as the head-neck angle in the frontal plane, averages 15 to 20° [61]. The acetabulum is normally anteverted 15 degrees and obliquely oriented in the coronal plane 45 degrees caudally [67]. The femoral neck is normally anteverted approximately 14 degrees in relation to femoral condyles, with a range of 1–40 degrees [67].

Key bony landmarks include the ilium's anterior-superior iliac spine (ASIS), which is palpable at the lateral edge of the inguinal ligament and serves as the origin of the sartorius muscle and transverse and internal abdominal muscles [67]. The ilium's anterior-inferior iliac spine (AIIS) is the origin of the direct head of the rectus femoris and the iliofemoral ligament [67]. The ischial tuberosity serves as the origin of the hamstrings [67]. The iliopsoas muscle/tendon traverses a groove between the iliopectineal eminence and the AIIS [67].

Soft Tissue Anatomy

The acetabular labrum is a fibrocartilaginous ring attached to the rim of the acetabulum that extends the articulating surface area and increases femoral head coverage [61]. It is triangular in cross section, contributing to its ability to create a pressurized seal of the central compartment of the hip during loading [61]. Only the external one-third of the labrum contains blood vessels, leaving the majority of the structure avascular and limiting its healing ability following injury [61]. The labrum is highly innervated, with the presence of both mechanoreceptors and nociceptors [61]. It is absent in the area of the inferior acetabular notch, where the transverse acetabular ligament serves as the continuation of the labrum [61].

The hip is surrounded by a dense fibrous capsule extending from the periphery of the acetabulum to the intertrochanteric line of the femoral neck [61]. The hip capsule attaches anteriorly and posteriorly along the periphery of the acetabulum outside the labrum [62]. It attaches to the femur anteriorly along the intertrochanteric crest, while on the posterior side it attaches only partially, leaving the basicervical region of the femoral neck and intertrochanteric region extracapsular [62]. The iliofemoral ligament is Y-shaped and is the thickest and strongest of the three main ligaments supporting the hip [61]. It functions to limit external rotation, while its lateral arm limits extension of the joint [61]. The iliofemoral ligament becomes taut in full extension, preventing anterior dislocation and hyperextension of the hip [62]. The twisted orientation of the hip ligaments provides a screw mechanism for the hip in full extension [62].

The ischiofemoral ligament extends from the ischial margin of the acetabulum to the greater trochanter of the femur and restricts internal rotation motion [61]. The pubofemoral ligament extends from the obturator crest of the pubic bone to the femoral neck and acts to limit abduction of the joint [61]. Deep fibers from the iliofemoral, ischiofemoral, and pubofemoral ligaments merge to form the zona orbicularis, which circumvents the femoral neck [61]. The ligamentum teres originates in the cotyloid fossa and attaches on the fovea of the femoral head [62].

The sacrospinous and sacrotuberous ligaments create the boundaries of the greater and lesser sciatic foramina [62]. The piriformis muscle and the sciatic nerve exit from the greater sciatic foramen [62]. The short external rotator muscles exit from the lesser sciatic foramen [62]. Primary hip flexor muscles include the iliopsoas, rectus femoris, and sartorius muscles [69]. The gluteus maximus and hamstring muscles are the most important hip joint extensors [69]. The abductors of the hip are predominantly the gluteus medius and minimus muscles [69]. External rotators include the obturator internus and externus, superior and inferior gemelli, quadratus femoris, and piriformis muscles [69]. The most consistent internal rotators of the hip joint are the gluteus medius and tensor fascia latae muscles [69].

Vascular Anatomy

In adulthood, the major blood supply to the femoral head is from the medial femoral circumflex and lateral epiphyseal arteries [74]. From birth to approximately 4 years of age, the major blood supply comes from the medial and lateral femoral circumflex arteries, with major contributions from the artery of the ligamentum teres [74]. From the age of 4 years to adulthood, the posterosuperior and posteroinferior retinacular arteries from the medial circumflex artery are the major blood supply to the femoral head [74]. The common femoral artery arises from the external iliac artery as it passes underneath the inguinal ligament [74]. It passes anterior and medial to the hip capsule [74]. The common femoral vessels are the most commonly reported extrapelvic vascular structures injured during total hip arthroplasty [74]. The most common mechanism of injury is errant retractor placement anterior to the acetabulum [74].

The profundus or deep femoral artery arises from the lateral aspect of the common femoral artery approximately 3.5 cm below the inguinal ligament [74]. The lateral circumflex artery arises from the lateral side of the proximal profundus femoris artery [74]. The medial circumflex artery most commonly comes from the posteromedial profundus femoris artery and traverses between the pectineus and psoas muscles [74]. The superior gluteal vessels are branches of the posterior division of the internal iliac artery and are closest to the hip as they exit from the sciatic notch [74]. The inferior gluteal vessels and internal vessels are branches of the anterior division of the internal iliac artery and exit the pelvis between the piriformis and coccygeus muscles [74].

The medial femoral circumflex artery is the main blood supply to the femoral head and terminates in the posterior aspect of the extracapsular arterial ring [71]. The lateral femoral circumflex artery gives rise to the anterior aspect of the extracapsular arterial ring [71]. The superior and inferior gluteal arteries contribute branches to the extracapsular arterial ring [71]. The ascending cervical arteries originate from the extracapsular arterial ring and are divided into lateral, medial, posterior, and anterior groups based on their anatomic relationship to the femoral neck [71]. The lateral group of ascending branches is the main blood supply to the femoral head [71]. The ascending branches give off multiple perforator vessels to the femoral neck and terminate in the subsynovial arterial ring located at the margin of the articular surface of the femoral head [71]. The lateral epiphyseal artery penetrates the femoral head and is believed to be the dominant blood supply to the femoral head from this system [71]. Fractures that disrupt the ascending blood flow to the lateral epiphyseal vessel have an increased risk of osteonecrosis [71]. The artery of the ligamentum teres arises from either the obturator or medial femoral circumflex artery and does not provide sufficient blood supply to maintain the viability of the femoral head [71].

The superior gluteal nerve and artery exit the pelvis above the piriformis muscle [69]. The pudendal nerve, internal pudendal artery, nerve to the obturator internus, posterior femoral cutaneous nerve, sciatic nerve, inferior gluteal nerve, inferior gluteal artery, and nerve to the quadratus femoris exit the pelvis below the piriformis [69]. In 10% of cases, the common peroneal component of the sciatic nerve can pass through the division in the piriformis [69].

Pathophysiology of Metal Debris

Excessive wear along with a hypersensitivity response may be at the origin of early adverse tissue reactions reported in some patients with metal-on-metal implants [1]. Debris generated from total hip arthroplasty is known to trigger adverse soft-tissue reactions [22]. Patients with an adverse reaction to metal debris have a variable presentation of pain, soft-tissue pseudotumour, instability, or asymptomatic lesions [22]. The presentation may be confused with periprosthetic joint infection [22]. Debris generated from modular junctions has been reported to cause adverse soft-tissue reactions in both mixed-metal interfaces and similar metal interfaces [22]. The mechanism of debris generation from modular junctions may be fretting, crevice corrosion, or a mixture of both [22].

Arthroplasty disrupts surrounding joint tissues and can greatly perturb the joint's immune homeostasis [34]. Particles released from implants into the surrounding joint tissues activate the body's defense mechanism, eliciting a cascade of events that leads to biotribocorrosion and electrochemical attacks on the implant [34]. Biotribocorrosion and electrochemical attacks on the implant may lead to the release of even more particles [34]. Implant makeup and designs, frictions between bearing surfaces, corrosion of non-moving parts with modular junctions, surgical mistakes, patient factors, comorbidities, and loosened components can alter the expected function of implants [34]. High accumulations of ions and particulates result in metallosis, with accompanying adverse complications [34].

Cobalt does not occur in the elemental state in vivo but exists as either a bi-valent (2+) or tri-valent (3+) cation that can complex with other extra- or intra-cellular molecules to form cobalt oxides, organophosphates, and chlorides [103]. Total hip arthroplasty ion release ultimately occurs from oxidation-reduction reactions with the surrounding environment that liberate cobalt ions from metal surfaces [103]. Metal wear particles are smaller than the debris generated by other total hip arthroplasty materials such as polyethylene, measured in nanometres rather than micrometres [103]. Nanoparticles may enter the intra-cellular environment more efficiently when compared with larger debris particles and can directly affect gene transcription or be involved in direct DNA damage [103]. Nanoparticles are likely to have a different cytotoxicity profile than larger-sized particles [103].

Mechanical wear and the generation of metal particles can occur through contact between intended bearing surfaces, surfaces contaminated with abrasive debris (third-body wear), two non-bearing surfaces, or one intended and one unintended bearing surface [103]. Corrosion is an electro-chemical process of oxidation-reduction reactions resulting in the release of cobalt and other ions from surfaces of cobalt-alloy implants [103]. Corrosion and wear occur simultaneously and may be synergistic [103]. There was no significant correlation between ALVAL scores and prerevision surgery metal ion levels or intraoperative tissue damage, suggesting that the biological mechanism of histologic morphology cannot be solely attributed to elevated metal ion levels and is likely multifactorial [51].

Titanium orthopaedic implants that are large and/or have a sliding mechanism have higher blood titanium levels compared to well-functioning, conventionally sized titanium hips [29]. Increased femoral head diameter in total hip arthroplasty may produce greater fretting damage owing to an increased head-neck moment arm [102]. Differences in taper design characteristics may lead to greater micromotion at the taper-head interface, leading to increased fretting and corrosion [116]. Other factors, such as head-taper engagement and geometry, rather than head size, may affect rates of corrosion and fretting damage at the taper interface [120]. Increased bending moments produced more corrosion at the taper interface [142]. Ceramic heads did not prevent corrosion at the taper interface but significantly reduced it in all loading configurations [142]. The interfaces between tantalum augments and other acetabular components must be stable to preclude macro- or micromotion which might lead to abrasion, corrosion, and consequently metallosis [127].

Metal-on-metal configuration in hip arthroplasty significantly influences the increase in the concentration of chromium and cobalt ions [139]. Thirty-six millimeter metal femoral heads result in larger levels of cobalt compared with 32-mm metal heads [123]. Metal femoral heads do scratch with in vivo use, and cobalt-chromium heads are more scratch resistant than titanium alloy heads [134]. The rotational orientation of femoral head damage has a marked influence on the volumetric wear rate of the opposing polyethylene liner, with wear rate differentials between maximum and minimum orientations often as high as 7-fold [111].

Classification

MRI-based classification: Magnetic resonance imaging distinguishes normal tissue from adverse local tissue reactions (ALTR), metallosis, infection, and polymeric debris based on specific signal characteristics [115]. ALTR presents as a thickened, hyperintense capsule with poor demarcation and necrosis [115]. Metallosis is identified by low signal intensity deposits [115]. Infection manifests as a lamellated synovial lining with pericapsular edema [115].

Pseudotumor definition and grading: Pseudotumors are defined as solid or fluid masses that develop in peri-prosthetic soft tissue [125]. Severity is graded using Metal Artefact Reduction Sequence Magnetic Resonance Imaging, metal ion levels, and symptoms [125]. In a cohort of 248 metal-on-metal hip resurfacings, pseudotumor prevalence was 36.3%, comprising 61 mild, 25 moderate, and 4 severe cases [125].

Hauptfleisch classification: In patients with small-head metal-on-metal total hip arthroplasties, the Hauptfleisch classification categorizes changes into type 1, type 2a, type 2b, and type 3 [118]. Among these patients, 10% of hips had type 1 pseudotumors, 21% had type 2a, 34% had type 2b, and 7% had type 3 changes [118]. In a cohort of 29 hips with small-head metal-on-metal total hip arthroplasties followed for a minimum of 20 years, pseudotumors were found in 72% of hips [118].

Other Considerations: Adverse reactions to metal debris present with a variable clinical picture including pain, soft-tissue pseudotumour, instability, or asymptomatic lesions [22]. This presentation may be confused with periprosthetic joint infection [22]. Medial calcar erosion is considered a late finding in patients with severe adverse local tissue reactions after total hip arthroplasty with dual modular neck stems [35]. In patients with metal-on-metal total hip arthroplasty, medial calcar erosion was present in 50% of hips and was associated with ALTR synovial thickness but not with Anderson grade, diameter, or volume [35]. The presence of medial calcar erosion had a positive predictive value of 0.83 for having an ALTR [35]. The relative risk of having a synovial thickness greater than 3 mm increased by a factor of 3.0 if calcar erosion was observed [35].

Intraoperative tissue necrosis was associated with a high rate of early complications (20%) and revisions (8%) in patients undergoing revision for taper corrosion [16]. Histological features of both innate and adaptive immune response to metal wear are seen in periprosthetic tissues in cases with both elevated and nonelevated metal ion levels [12]. There was no significant correlation between ALVAL scores and prerevision surgery metal ion levels or intraoperative tissue damage in patients with taper corrosion [51]. The biological mechanism of histologic morphology in adverse local tissue reactions is likely multifactorial and cannot be solely attributed to elevated metal ion levels [51]. Metal hypersensitivity does not appear to be the dominant biological reaction involved in the occurrence of adverse reaction to metal debris [6]. The development of soft tissue masses after metal-on-metal arthroplasty can be accompanied by activation of T cells, indicating that this complication may be partly immunologically mediated [21]. A rare long-term complication of metal-on-metal total hip arthroplasty, such as a cystic lesion of the groin, is caused by an immunologically determined inflammation (hypersensitivity) to metal debris without component loosening [5]. Metallic debris may be instrumental in the formation of a fibrous membrane around implants, potentially acting as a conduit for polyethylene debris and contributing to osteolysis and loosening [14]. Many but not all patients with adverse local tissue reactions, including those with pseudotumors, demonstrate high wear [26]. More data and more systematic descriptions of the histopathology are needed to define the amount of wear that induces adverse reactions [26].

Clinical Presentation

Patients with adverse reaction to metal debris present with a variable spectrum of pain, soft-tissue pseudotumour, instability, or asymptomatic lesions [22]. Clinicians should heighten their suspicion for metallosis secondary to hardware failure when encountering patients with skin discoloration in the setting of a painful and poorly functioning hip arthroplasty [90]. Severe adverse events can arise from the release of cobalt from metal-on-metal arthroplasties, and orthopaedic surgeons should be aware of presenting problems and have the knowledge to treat appropriately [30]. A systematic evaluation involving clinical history, physical examination, laboratory tests, and imaging is required to identify potential differential diagnoses in patients with painful non-metal-on-metal total hip arthroplasty [13].

Pseudotumors and Asymptomatic Findings

Pseudotumor formation is present in 53% of patients with a metal-on-metal total hip arthroplasty, of which 40% were asymptomatic [36]. The prevalence of asymptomatic taper-corrosion-related pseudotumors on MARS-MRI demonstrated that the absence of symptoms does not exclude the presence of adverse local tissue reactions [45]. Asymptomatic pseudotumours after metal-on-metal hip resurfacing show little change within one year [42]. Pseudotumors that could be detected on magnetic resonance imaging were seen in 69% (107) of 156 patients with ASR XL total hip replacements [44].

Imaging and Radiographic Findings

Subtle erosions of the medial calcar after metal-on-metal total hip arthroplasty may be an early indicator of an adverse reaction to wear particles warranting cross-sectional imaging [35]. Medial calcar erosion was present in 54 hips (50%) and was associated with ALTR synovial thickness but not with Anderson grade, diameter, or volume [35]. The relative risk of having a synovial thickness > 3 mm increased by a factor of 3.0 (95% confidence interval 1.3-6.5) if calcar erosion was observed [35]. Radiographic osteolysis was evident in 7% (eleven patients) of the 156 patients with ASR XL total hip replacements [44]. An abnormal cobalt level was significantly associated with the presence of periprosthetic lucency on radiographs and pseudotumor on magnetic resonance imaging [44]. Intraoperative tissue necrosis was associated with a high rate of early complications (20%) and revisions (8%), suggesting the importance of a systematic evaluation including metal ion levels and metal artifact reduction sequence magnetic resonance imaging in optimizing revision outcome [16].

Laboratory Findings

At a threshold of 5 ppb, no association was detected between abnormal metal ion levels and patient symptoms, prosthetic femoral head size, or acetabular cup inclination [44]. An ion level greater than 4.5 ppb (Cr or Co) may serve as a threshold for when abnormal wear is occurring, and is suggested as a trigger for a MARS MRI scan [87]. Cobalt level >2.8 mg/L and the Co/Cr ratio >3.8 are useful clinical diagnostic adjuncts in the systematic clinical evaluation for taper corrosion-related adverse tissue reactions in patients with dual modular taper THA [27]. The cobalt-to-chromium ratio 'may be' a key marker for adverse local tissue reactions in metal-on-metal hip patients, and well-designed studies involving large patient cohorts are needed before the ratio can be recommended or dismissed as a marker [98]. Alpha-defensin testing is prone to false-positive results in the setting of adverse local tissue reaction [43]. Similar to synovial fluid white blood cell count, alpha-defensin testing is prone to false-positive results in the setting of ALTR [43]. Many but not all patients with ALTR, including those with pseudotumors, demonstrate high wear, but more data and more systematic descriptions of the histopathology are needed to define the amount of wear that induces adverse reactions [26].

Systemic and Neurological Manifestations

The development of soft tissue masses after metal-on-metal arthroplasty could be accompanied by activation of T cells, indicating that this complication may be partly immunologically mediated [21]. On a large scale, neurologic side effects previously described do not occur as a common attributable complication of metal-on-metal total hip arthroplasty [33]. Cases of systemic neurotoxicity may be due to individual patient hypersensitivity to metal ions [33].

Investigations

Clinical Evaluation and Differential Diagnosis

Patients with adverse reaction to metal debris present with a variable clinical picture, ranging from pain, soft-tissue pseudotumour, and instability to asymptomatic lesions [22]. Clinical decision-making for revision surgery requires a comprehensive approach; overreliance on any single investigative tool should be avoided [131].

Laboratory Testing (Metal Ions)

Laboratory: Serum metal ion levels provide limited diagnostic specificity in certain cohorts. In patients with ASR XL total hip replacements, no association was detected between abnormal metal ion levels and patient symptoms, prosthetic femoral head size, or acetabular cup inclination at a threshold of 5 ppb [44]. The median cobalt level in this cohort was 1.8 ppb, and the median chromium level was 1.0 ppb, which is at or below the measurement threshold [44]. However, an abnormal cobalt level was significantly associated with the presence of periprosthetic lucency on radiographs and pseudotumor on magnetic resonance imaging in these patients [44]. Synovial fluid metal levels serve as a useful adjunct in specific clinical situations [144].

Imaging

Plain radiography: Radiographic osteolysis was evident in 7% (eleven patients) of a cohort of 156 patients with ASR XL total hip replacements [44]. Calcar erosion was present in 54 hips (50%) and was associated with ALTR synovial thickness, but not with Anderson grade, diameter, or volume, in patients with MoM THA [35]. Most hips with calcar erosion (n = 45) had an ALTR, yielding a positive predictive value of 0.83 (95% confidence interval 0.70-0.92) [35]. Subtle erosions of the medial calcar after MoM THA may be an early indicator of an adverse reaction to wear particles, warranting cross-sectional imaging [35].

MRI: Careful follow-up and cross-sectional imaging are needed to detect adverse local tissue reaction for early revision [99]. Synovial thickness may be more relevant than absolute size in the classification of adverse local tissue reactions [35]. Major MRI findings that help predict histologic ALVAL scores include synovial thickening, synovitis, synovial volume, abductor disruption, and soft-tissue edema [81]. MRI evidence of abductor insufficiency and adverse reaction to metal debris may predict a significant risk of rerevision and dislocation following revision hip arthroplasty [114]. A systematic evaluation including metal ion levels and metal artifact reduction sequence magnetic resonance imaging is important in optimizing revision outcome for patients with intraoperative tissue necrosis [16].

Treatment

Non-Operative

The provided evidence does not support specific conservative management protocols such as weight loss, physical therapy, NSAIDs, or injections for adverse reactions to metal debris.

Operative

Indications: The presence of metallosis is an indication for urgent revision arthroplasty to prevent severe loss of bone stock by the accompanying osteolysis [92]. While metal ion levels alone should not be relied on as the sole parameter to determine revision surgery, a cobalt level >2.8 mg/L and a Co/Cr ratio >3.8 are useful clinical diagnostic adjuncts in the systematic clinical evaluation for taper corrosion-related adverse tissue reactions in patients with dual modular taper THA [27]. An aggressive approach to ruling out periprosthetic joint infection, including routine aspiration of all hips with adverse local tissue reaction before revision, is recommended [43].

Surgical Approach / Technique: Intraoperative tissue necrosis was associated with a high rate of early complications (20%) and revisions (8%) in patients undergoing revision surgery for taper corrosion of dual taper total hip arthroplasty [16].

Implant Selection: Ceramic femoral heads can significantly decrease metal ion generation and potentially reduce complications associated with adverse local tissue reactions [28]. The CoM coupling demonstrates raised metal ions beyond 3 years and increasing revisions for adverse reaction to metal debris, making further exploration or use not warranted [11]. Conversely, concerns with corrosion for metal heads do not appear to result in significantly elevated revision risk for MOP at up to 10 years [56].

Revision: In the vast majority of patients with elevated ion levels, metal ion levels declined to very low levels following revision surgery for adverse tissue reactions in MoP THA patients due to head-neck taper corrosion [4]. Revision of Metal-on-metal Hip Prostheses results in a marked reduction of blood cobalt and chromium ion concentrations [7].

Other Considerations: The estimated median incidence of adverse reaction to metal debris (ARMD) requiring revision surgery is 0.3% in modular dual-mobility constructs [10]. Fifty-nine percent of patients with documented mechanically assisted crevice corrosion have undergone revision [38]. Adverse reactions to metal debris are more common in patients with 36 mm MoM THRs than previously thought, with nine-year survival declining from 96% to 86% under a modern follow-up protocol [8]. The differences in debris arising from the taper and the articulating surfaces may provide some understanding of the increased incidence of soft-tissue reactions reported in patients implanted with MoM total hip arthroplasties compared with patients with hip resurfacings [15]. Excessive wear along with a hypersensitivity response may be at the origin of the early adverse tissue reactions reported in some patients with metal-on-metal implants [1]. Severe adverse events can arise from the release of cobalt from metal-on-metal arthroplasties [30].

Complications

Pathophysiology and Mechanisms

Excessive wear combined with a hypersensitivity response may be the origin of early adverse tissue reactions in patients with metal-on-metal implants [1]. The development of soft tissue masses after metal-on-metal arthroplasty may be accompanied by activation of T cells, indicating that the complication may be partly immunologically mediated [21]. A rare long-term complication of metal-on-metal total hip arthroplasty, such as a cystic lesion of the groin, is caused by an immunologically determined inflammation to metal debris without component loosening [5]. Differences in debris arising from the taper and articulating surfaces may explain the increased incidence of soft-tissue reactions in patients with metal-on-metal total hip arthroplasties compared with those with hip resurfacings [15]. Debris generated from modular junctions can cause adverse soft-tissue reactions through mechanisms including fretting, crevice corrosion, or a mixture of both [22].

Clinical Presentation and Prevalence

Patients with adverse reaction to metal debris present with variable symptoms including pain, soft-tissue pseudotumour, instability, or asymptomatic lesions [22]. In a cohort of 306 patients with modular hip prostheses, one patient required revision due to adverse reaction to metal debris [9]. The estimated median incidence of adverse reaction to metal debris requiring revision surgery is 0.3% [10]. In a series of 4813 metal-on-polyethylene total hip arthroplasties, the re-operation rate for pseudotumours was 0.25% [22]. Symptoms and adverse local tissue reactions are each present about one-half of the time in patients with documented mechanically assisted crevice corrosion [38].

Diagnostic Limitations and Surveillance

MRI features associated with progressive pseudotumours include increased cystic wall thickness and "atypical" mixed fluid signal [106]. MRI pseudotumour progression was not associated with metal ion levels [106].

Natural History of Asymptomatic Lesions

Most adverse local tissue reactions in asymptomatic patients with modular metal-on-metal total hip arthroplasties that underwent repeat MARS MRI decreased in size, with 15 of 19 (79%) showing a decrease [104]. The natural history of type I cystic pseudotumours continues to be nonprogressive in most "asymptomatic" metal-on-metal hip arthroplasty patients at minimum 4 years [106]. At a minimum of 4-year follow-up, 4 Type II pseudotumours (11%) demonstrated MRI evidence of progression [106]. At a minimum of 4-year follow-up, 5 Type I pseudotumours (14%) were found to have "regressed" [106]. No measurable MRI progression was detected in the remaining 75% of patients in a longitudinal study of asymptomatic pseudotumours [106].

Systemic Effects

There was no statistically significant difference in new diagnoses of neurologic side effects, including peripheral neuropathy, sensorineural hearing loss, visual impairment, paresthesias, tinnitus, and vertigo, between metal-on-metal and metal-on-polyethylene total hip arthroplasty patients over 5 years [33]. Neurologic side effects previously described in isolated cases do not occur as a common attributable complication on a large scale [33]. There was no adverse effect on renal function during a 2-year study period following metal-on-metal hip resurfacing [37].

Revision Outcomes and Complications

Intraoperative tissue necrosis was associated with a high rate of early complications (20%) and revisions (8%) in patients undergoing revision surgery for taper corrosion [16].

Recovery

Other Considerations: The biological response to metal debris involves complex pathophysiological mechanisms. The development of soft tissue masses after metal-on-metal arthroplasty may be accompanied by activation of T cells, indicating the complication may be partly immunologically mediated [21]. A rare long-term complication of metallosis, such as a cystic lesion of the groin, is caused by an immunologically determined inflammation (hypersensitivity) to metal debris without component loosening [5].

Surveillance and diagnostic strategies require careful interpretation. Routine annual blood metal ion testing in asymptomatic large-head metal-on-metal total hip arthroplasty is unnecessary, time-consuming, resource-consuming, and cannot be considered a sole method for screening for adverse reaction to metal debris [20]. Intraoperative tissue necrosis is associated with a high rate of early complications (20%) and revisions (8%), suggesting the importance of systematic evaluation including metal ion levels and metal artifact reduction sequence magnetic resonance imaging in optimizing revision outcome [16].

Clinical outcomes in patients with mechanically assisted crevice corrosion show significant morbidity. Symptoms and adverse local tissue reactions are each present about one-half of the time in patients with mechanically assisted crevice corrosion, and 59% of those with documented mechanically assisted crevice corrosion have undergone revision [38].

Key Evidence

  • [L5] Excessive wear along with a hypersensitivity response may be at the origin of the early adverse tissue reactions reported in some patients with metal-on-metal implants. [1] (10.2106/jbjs.j.01877)
  • [L3] Patients with adverse local tissue reactions after metal-on-polyethylene total hip arthroplasty undergoing revision surgery demonstrated major pain relief. [2] (10.1016/j.arth.2022.06.012)
  • [L3] Caution should be exercised when choosing bearing surfaces for adverse reaction to metal debris revisions. [3] (10.1302/0301-620x.96b12.33473)
  • [L4] In the vast majority of patients with elevated ion levels, metal ion levels declined to very low levels following revision surgery for adverse tissue reactions in MoP THA patients due to head-neck taper corrosion. [4] (10.1016/j.arth.2018.03.061)
  • [L5] This rare long-term complication is caused by an immunologically determined inflammation (hypersensitivity) to metal debris without component loosening. [5] (10.1016/j.arth.2006.10.002)
  • [L4] Metal hypersensitivity does not appear to be the dominant biological reaction involved in the occurrence of adverse reaction to metal debris (ARMD). [6] (10.1186/s12891-016-1069-9)
  • [L4] Adverse reactions to metal debris do not seem to compromise implant ingrowth after revision surgery. [7] (10.1007/s11999-015-4156-6)
  • [L3] Adverse reactions to metal debris are more common in patients with 36 mm MoM THRs than previously thought, with nine-year survival declining from 96% to 86% under a modern follow-up protocol. [8] (10.1302/0301-620x.96b12.33742)
  • [L4] One patient in the total cohort of 306 required revision due to adverse reaction to metal debris. [9] (10.1016/j.arth.2013.01.018)
  • [L1] The estimated median incidence of adverse reaction to metal debris (ARMD) requiring revision surgery is 0.3%. [10] (10.1302/2058-5241.6.200146)
  • [L1] However, the CoM coupling demonstrates raised metal ions beyond 3 years and increasing revisions for adverse reaction to metal debris, making further exploration or use not warranted. [11] (10.1016/j.arth.2019.08.002)
  • [L4] Histological features of both innate and adaptive immune response to metal wear are seen in periprosthetic tissues in cases with both elevated and nonelevated metal ion levels. [12] (10.1007/s00402-017-2723-x)
  • [L5] A systematic evaluation involving clinical history, physical examination, laboratory tests, and imaging is required to identify potential differential diagnoses in patients with painful non-metal-on-metal total hip arthroplasty. [13] (10.1016/j.arth.2022.01.063)
  • [L5] Metallic debris may be instrumental in the formation of a fibrous membrane around implants, potentially acting as a conduit for polyethylene debris and contributing to osteolysis and loosening. [14] (10.2106/00004623-199306000-00005)
  • [L4] The differences in debris arising from the taper and the articulating surfaces may provide some understanding of the increased incidence of soft-tissue reactions reported in patients implanted with MoM total hip arthroplasties compared with patients with hip resurfacings. [15] (10.1302/0301-620x.98b7.37029)
  • [L4] This pilot study demonstrates that intraoperative tissue necrosis was associated with a high rate of early complications (20%) and revisions (8%), suggesting the importance of a systematic evaluation of these patients including metal ion levels and metal artifact reduction sequence magnetic resonance imaging in optimizing revision outcome. [16] (10.1016/j.arth.2016.01.015)
  • [L3] At an average of 2.1 years postoperatively, 15.4% of the evaluated metal-on-metal THAs demonstrated aseptic failure, with all revised hips showing adverse local tissue reactions. [17] (10.1016/j.arth.2012.10.005)
  • [L3] One-component revision is an effective procedure for hip resurfacing procedures that have failed as the result of an adverse reaction to metal wear debris. [18] (10.1016/j.arth.2013.04.011)
  • [L4] Revision surgery is indicated for symptomatic adverse local tissue reaction secondary to corrosion at the head-neck junction, typically by removing the metal head in favor of a ceramic one. [19] (10.1016/j.arth.2016.02.082)
  • [L2] Routine annual blood metal ion testing in asymptomatic large-head metal-on-metal total hip arthroplasty is unnecessary, time-consuming, and resource-consuming, and cannot be considered a sole method for screening for adverse reaction to metal debris. [20] (10.1016/j.arth.2017.07.015)
  • [L3] Thus, the development of soft tissue masses after metal-on-metal arthroplasty could be accompanied by activation of T cells, indicating that this complication may be partly immunologically mediated. [21] (10.1007/s11999-013-3307-x)
  • [L4] [22] (10.1302/0301-620x.97b8.34682)
  • [L3] Modular hip hemiarthroplasty patients may be susceptible to metallosis and adverse reaction to metal debris despite being less active individuals than those who receive a total hip arthroplasty. [23] (10.1302/0301-620x.107b4.bjj-2024-0576.r1)
  • [Case_report] Wear debris from titanium-based alloy alone, in the absence of infection or specific immune response, can produce clinically important pain. [25] (10.2106/00004623-199072010-00021)
  • [L4] Many but not all patients with ALTR, including those with pseudotumors, demonstrate high wear, but more data and more systematic descriptions of the histopathology are needed to define the amount of wear that induces adverse reactions. [26] (10.1007/s11999-014-3893-2)
  • [L3] Although metal ion levels alone should not be relied on as the sole parameter to determine revision surgery, cobalt level >2.8 mg/L and the Co/Cr ratio >3.8 are useful clinical diagnostic adjuncts in the systematic clinical evaluation for taper corrosion-related adverse tissue reactions in patients with dual modular taper THA. [27] (10.1016/j.arth.2016.08.040)
  • [L5] Ceramic femoral heads can significantly decrease metal ion generation and potentially reduce complications associated with adverse local tissue reactions. [28] (10.1016/j.arth.2019.11.031)
  • [L4] This study showed that titanium orthopaedic implants that are large and/or have a sliding mechanism have higher blood titanium levels compared to well-functioning, conventionally sized titanium hips. [29] (10.1186/s12891-022-05717-8)
  • [L4] Severe adverse events can arise from the release of cobalt from metal-on-metal arthroplasties, and orthopaedic surgeons should be aware of presenting problems and have the knowledge to treat appropriately. [30] (10.1302/0301-620x.98b1.36712)
  • [L3] [33] (10.1016/j.arth.2016.03.035)
  • [L5] [34] (10.1007/s40883-021-00222-1)
  • [L3] [35] (10.1016/j.arth.2016.04.005)
  • [L3] Pseudotumor formation is present in 53% of patients with a metal-on-metal total hip arthroplasty, of which 40% were asymptomatic. [36] (10.1016/j.arth.2018.03.039)
  • [L3] There was no adverse effect on renal function during the 2-year study period, and all implants were functioning well with no radiographic evidence of loosening. [37] (10.1097/01.blo.0000166901.84323.5d)
  • [L3] Symptoms and adverse local tissue reactions are each present about one-half of the time, and 59% of those with documented MACC have undergone revision. [38] (10.1016/j.arth.2021.11.026)
  • [L3] [42] (10.1302/0301-620x.95b12.32248)
  • [L3] [43] (10.1016/j.arth.2018.01.007)
  • [L4] [44] (10.2106/jbjs.l.01481)
  • [L4] The prevalence of asymptomatic taper-corrosion-related pseudotumors on MARS-MRI demonstrated that the absence of symptoms does not exclude the presence of adverse local tissue reactions. [45] (10.2106/jbjs.15.01325)
  • [L3] Cobalt and chromium levels above 5 and 2.5 ppb, respectively, demonstrated an increased risk of adverse reaction to metal debris (ARMD) and should be considered as a lower cutoff for discussion with patients about the potential for future revision. [48] (10.1016/j.arth.2017.02.031)
  • [L3] [51] (10.1016/j.arth.2016.01.041)
  • [L3] Concerns with corrosion for metal heads do not appear to result in significantly elevated revision risk for MOP at up to 10 years. [56] (10.1016/j.arth.2020.05.007)
  • [L5] [87] (10.1016/j.arth.2014.02.005)
  • [L4] Clinicians should heighten their suspicion for metallosis secondary to hardware failure when encountering patients with skin discoloration in the setting of a painful and poorly functioning hip arthroplasty. [90] (10.1016/j.arth.2012.01.008)
  • [L5] The presence of metallosis is an indication for urgent revision arthroplasty to prevent severe loss of bone stock by the accompanying osteolysis. [92] (10.1007/s00256-007-0362-y)
  • [L5] The cobalt-to-chromium ratio 'may be' a key marker for adverse local tissue reactions in metal-on-metal hip patients, and well-designed studies involving large patient cohorts are needed before the ratio can be recommended or dismissed as a marker. [98] (10.1016/j.arth.2015.09.047)
  • [L3] Careful follow-up and cross-sectional imaging are needed to detect adverse local tissue reaction for early revision. [99] (10.1186/s13018-023-03510-4)
  • [L4] Increased femoral head diameter in THA may produce greater fretting damage owing to an increased head-neck moment arm. [102] (10.1016/j.arth.2016.03.009)
  • [L5] [103] (10.1302/0301-620x.98b1.36374)
  • [L3] [104] (10.1016/j.arth.2016.01.020)
  • [L3] [106] (10.1016/j.arth.2016.02.070)
  • [L5] The rotational orientation of femoral head damage has a marked influence on the volumetric wear rate of the opposing polyethylene liner, with wear rate differentials between maximum and minimum orientations often as high as 7-fold. [111] (10.1016/j.arth.2015.01.030)
  • [L3] However, there is a significant risk of rerevision and dislocation, which may be predicted with MRI evidence of abductor insufficiency and adverse reaction to metal debris. [114] (10.1016/j.arth.2025.04.082)
  • [L3] [115] (10.1097/corr.0000000000001882)
  • [L4] Differences in taper design characteristics may lead to greater micromotion at the taper-head interface, leading to increased fretting and corrosion. [116] (10.1016/j.arth.2019.02.058)
  • [L3] [118] (10.1016/j.arth.2021.03.022)
  • [L4] Other factors, such as head-taper engagement and geometry, rather than head size, may affect rates of corrosion and fretting damage at the taper interface. [120] (10.1016/j.arth.2017.10.010)
  • [L3] Thirty-six millimeter metal femoral heads result in larger levels of cobalt compared with 32-mm metal heads. [123] (10.1016/j.arth.2016.03.024)
  • [L3] [125] (10.1016/j.arth.2013.06.021)
  • [L5] The interfaces between tantalum augments and other acetabular components must be stable to preclude macro- or micromotion which might lead to abrasion, corrosion, and consequently metallosis. [127] (10.3109/17453674.2014.950816)
  • [L5] Although specialized tests such as metal ion analysis and MARS MRI are useful, overreliance on any single investigative tool in the clinical decision-making process for revision surgery should be avoided. [131] (10.1016/j.arth.2016.01.074)
  • [L4] Metal femoral heads do scratch with in vivo use, and cobalt-chromium heads are more scratch resistant than titanium alloy heads. [134] (10.1097/01.blo.0000193813.08458.e2)
  • [L3] Metal-on-metal configuration in hip arthroplasty significantly influences the increase in the concentration of chromium and cobalt ions in a double assessment. [139] (10.1186/s13018-023-03618-7)
  • [L5] Increased bending moments produced more corrosion, and while ceramic heads did not prevent corrosion, they significantly reduced it in all loading configurations. [142] (10.1302/0301-620x.97b4.34800)
  • [L3] Synovial fluid metal levels are a useful adjunct in certain situations. [144] (10.1016/j.arth.2020.01.010)

See Also

References

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[2] Risk Stratification and Pain Outcomes Following Revision Total Hip Arthroplasty for Adverse Local Tissue Reactions. The Journal of Arthroplasty. 2022. DOI: 10.1016/j.arth.2022.06.012

[3] Predictors of time to revision and clinical outcomes following revision of metal-on-metal hip replacements for adverse reaction to metal debris. The Bone & Joint Journal. 2014. DOI: 10.1302/0301-620x.96b12.33473

[4] The Fate of Elevated Metal Ion Levels After Revision Surgery for Head-Neck Taper Corrosion in Patients With Metal-on-Polyethylene Total Hip Arthroplasty. The Journal of Arthroplasty. 2018. DOI: 10.1016/j.arth.2018.03.061

[5] Cystic Lesion of the Groin due to Metallosis: A Rare Long-Term Complication of Metal-on-Metal Total Hip Arthroplasty. The Journal of Arthroplasty. 2007. DOI: 10.1016/j.arth.2006.10.002

[6] Immune response in adverse reactions to metal debris following metal-on-metal total hip arthroplasty. BMC Musculoskeletal Disorders. 2016. DOI: 10.1186/s12891-016-1069-9

[7] Revision of Metal-on-metal Hip Prostheses Results in Marked Reduction of Blood Cobalt and Chromium Ion Concentrations. Clinical Orthopaedics & Related Research. 2015. DOI: 10.1007/s11999-015-4156-6

[8] Adverse reaction to metal debris is more common in patients following MoM total hip replacement with a 36 mm femoral head than previously thought. The Bone & Joint Journal. 2014. DOI: 10.1302/0301-620x.96b12.33742

[9] Taper Corrosion in Modular Hip Prostheses. The Journal of Arthroplasty. 2013. DOI: 10.1016/j.arth.2013.01.018

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[11] Early Results of Our International, Multicenter, Multisurgeon, Double-Blinded, Prospective, Randomized, Controlled Trial Comparing Metal-on-Metal With Ceramic-on-Metal in Total Hip Arthroplasty. The Journal of Arthroplasty. 2020. DOI: 10.1016/j.arth.2019.08.002

[12] Correlation of serum metal ion levels with pathological changes of ARMD in failed metal-on-metal-hip-resurfacing arthroplasties. Archives of Orthopaedic and Trauma Surgery. 2017. DOI: 10.1007/s00402-017-2723-x

[13] Metal Articulations as a Source of Total Hip Arthroplasty Pain. The Journal of Arthroplasty. 2022. DOI: 10.1016/j.arth.2022.01.063

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[16] Early Outcomes of Revision Surgery for Taper Corrosion of Dual Taper Total Hip Arthroplasty in 187 Patients. The Journal of Arthroplasty. 2016. DOI: 10.1016/j.arth.2016.01.015

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[18] One-Component Revision of Failed Hip Resurfacing from Adverse Reaction to Metal Wear Debris. The Journal of Arthroplasty. 2014. DOI: 10.1016/j.arth.2013.04.011

[19] Diagnosis and Treatment of Adverse Local Tissue Reactions at the Head-Neck Junction. The Journal of Arthroplasty. 2016. DOI: 10.1016/j.arth.2016.02.082

[20] Blood Metal Ion Levels Have Limited Utility in the Surveillance of Asymptomatic Large-Head Metal-on-Metal Total Hip Arthroplasties. The Journal of Arthroplasty. 2017. DOI: 10.1016/j.arth.2017.07.015

[21] High Metal Ion Levels After Use of the ASR™ Device Correlate With Development of Pseudotumors and T Cell Activation. Clinical Orthopaedics & Related Research. 2014. DOI: 10.1007/s11999-013-3307-x

[22] Adverse local tissue reactions in metal-on-polyethylene total hip arthroplasty due to trunnion corrosion. The Bone & Joint Journal. 2015. DOI: 10.1302/0301-620x.97b8.34682

[23] A case series of modular hip hemiarthroplasties employing a metal-on-metal taper-trunnion junction. The Bone & Joint Journal. 2025. DOI: 10.1302/0301-620x.107b4.bjj-2024-0576.r1

[25] Metallosis associated with a stable titanium-alloy femoral component in total hip replacement. A case report.. The Journal of Bone & Joint Surgery. 1990. DOI: 10.2106/00004623-199072010-00021

[26] Do Retrieval Analysis and Blood Metal Measurements Contribute to Our Understanding of Adverse Local Tissue Reactions?. Clinical Orthopaedics and Related Research®. 2014. DOI: 10.1007/s11999-014-3893-2

[27] Sensitivity and Specificity of Metal Ion Levels in Predicting “Pseudotumors” due to Taper Corrosion in Patients With Dual Taper Modular Total Hip Arthroplasty. The Journal of Arthroplasty. 2017. DOI: 10.1016/j.arth.2016.08.040

[28] Cobalt and Chromium Ion Release in Metal-on-Polyethylene and Ceramic-on-Polyethylene THA: A Simulator Study With Cellular and Microbiological Correlations. The Journal of Arthroplasty. 2020. DOI: 10.1016/j.arth.2019.11.031

[29] Blood titanium levels in patients with large and sliding titanium implants. BMC Musculoskeletal Disorders. 2022. DOI: 10.1186/s12891-022-05717-8

[30] Systemic cobalt toxicity from total hip arthroplasties. The Bone & Joint Journal. 2016. DOI: 10.1302/0301-620x.98b1.36712

[33] Is Metal-On-Metal Total Hip Arthroplasty Associated With Neurotoxicity?. The Journal of Arthroplasty. 2016. DOI: 10.1016/j.arth.2016.03.035

[34] The Mechanism of Metallosis After Total Hip Arthroplasty. Regenerative Engineering and Translational Medicine. 2021. DOI: 10.1007/s40883-021-00222-1

[35] Medial Calcar Erosion Is Associated With Synovial Thickness in Patients With ASR XL Total Hip Arthroplasty. The Journal of Arthroplasty. 2016. DOI: 10.1016/j.arth.2016.04.005

[36] Association Between Pseudotumor Formation and Patient Factors in Metal-on-Metal Total Hip Arthroplasty Population. The Journal of Arthroplasty. 2018. DOI: 10.1016/j.arth.2018.03.039

[37] How Do Serum Cobalt and Chromium Levels Change after Metal-on-Metal Hip Resurfacing?. Clinical Orthopaedics and Related Research. 2005. DOI: 10.1097/01.blo.0000166901.84323.5d

[38] High Incidence of Mechanically Assisted Crevice Corrosion at 10 Years in Non-Cemented, Non-Recalled, Contemporary Total Hip Arthroplasties. The Journal of Arthroplasty. 2022. DOI: 10.1016/j.arth.2021.11.026

[42] Asymptomatic pseudotumours after metal-on-metal hip resurfacing show little change within one year. The Bone & Joint Journal. 2013. DOI: 10.1302/0301-620x.95b12.32248

[43] The Alpha-Defensin Test for Diagnosing Periprosthetic Joint Infection in the Setting of an Adverse Local Tissue Reaction Secondary to a Failed Metal-on-Metal Bearing or Corrosion at the Head-Neck Junction. The Journal of Arthroplasty. 2018. DOI: 10.1016/j.arth.2018.01.007

[44] Relationship of Plasma Metal Ions and Clinical and Imaging Findings in Patients with ASR XL Metal-on-Metal Total Hip Replacements. Journal of Bone and Joint Surgery. 2013. DOI: 10.2106/jbjs.l.01481

[45] Asymptomatic Pseudotumors in Patients with Taper Corrosion of a Dual-Taper Modular Femoral Stem. Journal of Bone and Joint Surgery. 2016. DOI: 10.2106/jbjs.15.01325

[48] The Utility of Metal Ion Trends in Predicting Revision in Metal-on-Metal Total Hip Arthroplasty. The Journal of Arthroplasty. 2017. DOI: 10.1016/j.arth.2017.02.031

[51] Metal Ion Levels Are Not Correlated With Histopathology of Adverse Local Tissue Reactions in Taper Corrosion of Total Hip Arthroplasty. The Journal of Arthroplasty. 2016. DOI: 10.1016/j.arth.2016.01.041

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Section 2 -- Scope.

a. License grant.

1. Subject to the terms and conditions of this Public License, the Licensor hereby grants You a worldwide, royalty-free, non-sublicensable, non-exclusive, irrevocable license to exercise the Licensed Rights in the Licensed Material to:

a. reproduce and Share the Licensed Material, in whole or in part, for NonCommercial purposes only; and

b. produce, reproduce, and Share Adapted Material for NonCommercial purposes only.

2. Exceptions and Limitations. For the avoidance of doubt, where Exceptions and Limitations apply to Your use, this Public License does not apply, and You do not need to comply with its terms and conditions.

3. Term. The term of this Public License is specified in Section 6(a).

4. Media and formats; technical modifications allowed. The Licensor authorizes You to exercise the Licensed Rights in all media and formats whether now known or hereafter created, and to make technical modifications necessary to do so. The Licensor waives and/or agrees not to assert any right or authority to forbid You from making technical modifications necessary to exercise the Licensed Rights, including technical modifications necessary to circumvent Effective Technological Measures. For purposes of this Public License, simply making modifications authorized by this Section 2(a) (4) never produces Adapted Material.

5. Downstream recipients.

a. Offer from the Licensor -- Licensed Material. Every recipient of the Licensed Material automatically receives an offer from the Licensor to exercise the Licensed Rights under the terms and conditions of this Public License.

b. No downstream restrictions. You may not offer or impose any additional or different terms or conditions on, or apply any Effective Technological Measures to, the Licensed Material if doing so restricts exercise of the Licensed Rights by any recipient of the Licensed Material.

6. No endorsement. Nothing in this Public License constitutes or may be construed as permission to assert or imply that You are, or that Your use of the Licensed Material is, connected with, or sponsored, endorsed, or granted official status by, the Licensor or others designated to receive attribution as provided in Section 3(a)(1)(A)(i).

b. Other rights.

1. Moral rights, such as the right of integrity, are not licensed under this Public License, nor are publicity, privacy, and/or other similar personality rights; however, to the extent possible, the Licensor waives and/or agrees not to assert any such rights held by the Licensor to the limited extent necessary to allow You to exercise the Licensed Rights, but not otherwise.

2. Patent and trademark rights are not licensed under this Public License.

3. To the extent possible, the Licensor waives any right to collect royalties from You for the exercise of the Licensed Rights, whether directly or through a collecting society under any voluntary or waivable statutory or compulsory licensing scheme. In all other cases the Licensor expressly reserves any right to collect such royalties, including when the Licensed Material is used other than for NonCommercial purposes.

Section 3 -- License Conditions.

Your exercise of the Licensed Rights is expressly made subject to the following conditions.

a. Attribution.

1. If You Share the Licensed Material (including in modified form), You must:

a. retain the following if it is supplied by the Licensor with the Licensed Material:

i. identification of the creator(s) of the Licensed Material and any others designated to receive attribution, in any reasonable manner requested by the Licensor (including by pseudonym if designated);

ii. a copyright notice;

iii. a notice that refers to this Public License;

iv. a notice that refers to the disclaimer of warranties;

v. a URI or hyperlink to the Licensed Material to the extent reasonably practicable;

b. indicate if You modified the Licensed Material and retain an indication of any previous modifications; and

c. indicate the Licensed Material is licensed under this Public License, and include the text of, or the URI or hyperlink to, this Public License.

2. You may satisfy the conditions in Section 3(a)(1) in any reasonable manner based on the medium, means, and context in which You Share the Licensed Material. For example, it may be reasonable to satisfy the conditions by providing a URI or hyperlink to a resource that includes the required information.

3. If requested by the Licensor, You must remove any of the information required by Section 3(a)(1)(A) to the extent reasonably practicable.

4. If You Share Adapted Material You produce, the Adapter's License You apply must not prevent recipients of the Adapted Material from complying with this Public License.

Section 4 -- Sui Generis Database Rights.

Where the Licensed Rights include Sui Generis Database Rights that apply to Your use of the Licensed Material:

a. for the avoidance of doubt, Section 2(a)(1) grants You the right to extract, reuse, reproduce, and Share all or a substantial portion of the contents of the database for NonCommercial purposes only;

b. if You include all or a substantial portion of the database contents in a database in which You have Sui Generis Database Rights, then the database in which You have Sui Generis Database Rights (but not its individual contents) is Adapted Material; and

c. You must comply with the conditions in Section 3(a) if You Share all or a substantial portion of the contents of the database.

For the avoidance of doubt, this Section 4 supplements and does not replace Your obligations under this Public License where the Licensed Rights include other Copyright and Similar Rights.

Section 5 -- Disclaimer of Warranties and Limitation of Liability.

a. UNLESS OTHERWISE SEPARATELY UNDERTAKEN BY THE LICENSOR, TO THE EXTENT POSSIBLE, THE LICENSOR OFFERS THE LICENSED MATERIAL AS-IS AND AS-AVAILABLE, AND MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND CONCERNING THE LICENSED MATERIAL, WHETHER EXPRESS, IMPLIED, STATUTORY, OR OTHER. THIS INCLUDES, WITHOUT LIMITATION, WARRANTIES OF TITLE, MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, NON-INFRINGEMENT, ABSENCE OF LATENT OR OTHER DEFECTS, ACCURACY, OR THE PRESENCE OR ABSENCE OF ERRORS, WHETHER OR NOT KNOWN OR DISCOVERABLE. WHERE DISCLAIMERS OF WARRANTIES ARE NOT ALLOWED IN FULL OR IN PART, THIS DISCLAIMER MAY NOT APPLY TO YOU.

b. TO THE EXTENT POSSIBLE, IN NO EVENT WILL THE LICENSOR BE LIABLE TO YOU ON ANY LEGAL THEORY (INCLUDING, WITHOUT LIMITATION, NEGLIGENCE) OR OTHERWISE FOR ANY DIRECT, SPECIAL, INDIRECT, INCIDENTAL, CONSEQUENTIAL, PUNITIVE, EXEMPLARY, OR OTHER LOSSES, COSTS, EXPENSES, OR DAMAGES ARISING OUT OF THIS PUBLIC LICENSE OR USE OF THE LICENSED MATERIAL, EVEN IF THE LICENSOR HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH LOSSES, COSTS, EXPENSES, OR DAMAGES. WHERE A LIMITATION OF LIABILITY IS NOT ALLOWED IN FULL OR IN PART, THIS LIMITATION MAY NOT APPLY TO YOU.

c. The disclaimer of warranties and limitation of liability provided above shall be interpreted in a manner that, to the extent possible, most closely approximates an absolute disclaimer and waiver of all liability.

Section 6 -- Term and Termination.

a. This Public License applies for the term of the Copyright and Similar Rights licensed here. However, if You fail to comply with this Public License, then Your rights under this Public License terminate automatically.

b. Where Your right to use the Licensed Material has terminated under Section 6(a), it reinstates:

1. automatically as of the date the violation is cured, provided it is cured within 30 days of Your discovery of the violation; or

2. upon express reinstatement by the Licensor.

For the avoidance of doubt, this Section 6(b) does not affect any right the Licensor may have to seek remedies for Your violations of this Public License.

c. For the avoidance of doubt, the Licensor may also offer the Licensed Material under separate terms or conditions or stop distributing the Licensed Material at any time; however, doing so will not terminate this Public License.

d. Sections 1, 5, 6, 7, and 8 survive termination of this Public License.

Section 7 -- Other Terms and Conditions.

a. The Licensor shall not be bound by any additional or different terms or conditions communicated by You unless expressly agreed.

b. Any arrangements, understandings, or agreements regarding the Licensed Material not stated herein are separate from and independent of the terms and conditions of this Public License.

Section 8 -- Interpretation.

a. For the avoidance of doubt, this Public License does not, and shall not be interpreted to, reduce, limit, restrict, or impose conditions on any use of the Licensed Material that could lawfully be made without permission under this Public License.

b. To the extent possible, if any provision of this Public License is deemed unenforceable, it shall be automatically reformed to the minimum extent necessary to make it enforceable. If the provision cannot be reformed, it shall be severed from this Public License without affecting the enforceability of the remaining terms and conditions.

c. No term or condition of this Public License will be waived and no failure to comply consented to unless expressly agreed to by the Licensor.

d. Nothing in this Public License constitutes or may be interpreted as a limitation upon, or waiver of, any privileges and immunities that apply to the Licensor or You, including from the legal processes of any jurisdiction or authority.

Creative Commons is not a party to its public licenses. Notwithstanding, Creative Commons may elect to apply one of its public licenses to material it publishes and in those instances will be considered the “Licensor.” The text of the Creative Commons public licenses is dedicated to the public domain under the CC0 Public Domain Dedication. Except for the limited purpose of indicating that material is shared under a Creative Commons public license or as otherwise permitted by the Creative Commons policies published at creativecommons.org/policies, Creative Commons does not authorize the use of the trademark "Creative Commons" or any other trademark or logo of Creative Commons without its prior written consent including, without limitation, in connection with any unauthorized modifications to any of its public licenses or any other arrangements, understandings, or agreements concerning use of licensed material. For the avoidance of doubt, this paragraph does not form part of the public licenses.

Creative Commons may be contacted at creativecommons.org.