Metal-on-Metal Pseudotumours
Pseudotumours associated with metal-on-metal hip resurfacings
Pandit H · J Bone Joint Surg Br · 2008
This seminal retrospective case series described the clinical, radiological, and histological presentation of soft-tissue pseudotumours in patients following metal-on-metal hip resurfacing arthroplasty. It established pseudotumours as a primary failure mode of metal-on-metal bearings, highlighting that they occur predominantly in women and are mediated by excessive wear debris and cell-mediated hypersensitivity.
Citation & links
Pandit H, Glyn-Jones S, McLardy-Smith P, Gundle R, Whitwell D, Gibbons CL, Ostlere S, Athanasou N, Gill HS, Murray DW. Pseudotumours associated with metal-on-metal hip resurfacings. J Bone Joint Surg Br. 2008 Jul;90(7):847-51.
Key findings
- 1.A total of 20 patients (21 hips) developed symptomatic, non-infective, non-neoplastic soft-tissue masses (pseudotumours), representing an overall incidence of approximately 1% at a mean follow-up of 61 months (cumulative rate ~1.6% at 5 years).
- 2.Females were disproportionately affected, accounting for over 70% of pseudotumour cases, with the incidence in women being roughly eight times higher than in men.
- 3.Presenting symptoms varied widely; groin discomfort was the most frequent symptom, followed by palpable masses, spontaneous hip dislocation, neurovascular compression (femoral or sciatic nerve palsy), and severe pain.
- 4.Imaging (US, CT, and MRI) revealed masses that were either cystic, solid, or mixed, with extensive abductor muscle necrosis, extensive joint effusions, and adjacent bony erosion.
- 5.Histopathological examination of retrieved periprosthetic soft tissue demonstrated characteristic extensive tissue necrosis with perivascular lymphocytic cuffs and plasma cell infiltration, indicative of a delayed-type (type IV) hypersensitivity response (ALVAL).
- 6.Microbiological cultures, fungal stains, and cytological workups were uniformly negative for infection and neoplastic pathology.
- 7.Revision to conventional metal-on-polyethylene total hip arthroplasty resolved symptoms in most cases, but technical complexity was markedly elevated due to abductor deficiency and extensive tissue necrosis.
Background
During the early 2000s, metal-on-metal (MoM) hip resurfacing arthroplasty gained widespread popularity as a bone-preserving option for young, active patients, offering low volumetric wear and minimal dislocation risk. However, concerns emerged as patients began presenting with groin discomfort, unexplained soft-tissue masses, extensive periarticular soft-tissue destruction, and implant failure without infection or frank mechanical loosening. This study sought to characterise the clinicopathological entity termed 'pseudotumours', determine its incidence in a large consecutive single-centre cohort, identify potential risk factors, and describe its pathological and imaging features.
Methods
The authors reviewed a consecutive cohort of 1,300 metal-on-metal hip resurfacing arthroplasties (primarily Birmingham Hip Resurfacing) performed at the Nuffield Orthopaedic Centre in Oxford. Patients presenting with groin pain, palpable masses, compressive symptoms, or mechanical dysfunction were investigated using ultrasonography, computed tomography (CT), or magnetic resonance imaging (MRI). Revision surgery was performed when conservative measures failed or soft-tissue destruction was evident. Intraoperative findings, implant orientation, synovial fluid aspirates, and histological specimens were systematically analysed to exclude infection and malignant processes.
Clinical implications
This landmark study triggered global awareness and regulatory warnings regarding adverse local tissue reactions (ALTR) / adverse reactions to metal debris (ARMD) in metal-on-metal hips. It fundamentally transformed follow-up protocols, introducing cross-sectional screening (MARS-MRI and ultrasound) and blood cobalt/chromium ion surveillance. It also prompted surgeon caution and eventual decline in MoM resurfacing, especially in female patients and smaller anatomical hip sizes.
Critical appraisal
A major strength is the large single-centre cohort (1,300 consecutive resurfacings) with detailed multimodal evaluation, rigorous histological analysis, and thorough exclusion of infection. Limitations include its retrospective design, the fact that only symptomatic patients were systematically imaged (thereby underestimating true pseudotumour prevalence by missing asymptomatic masses), and the absence of routine cross-sectional metal ion correlation in all early cohorts.
Teaching note
For fellowship and exit examinations, candidates must associate Pandit et al. (2008) with coining/popularising the term 'pseudotumour' in MoM hip resurfacing. Candidates must know the classic patient profile (young female with smaller component sizes), the histological triad of ALVAL (lymphocytic perivascular cuffs, macrophages, tissue necrosis), and the clinical imperative to investigate unexplained groin pain or abductor dysfunction with MARS-MRI/ultrasound and whole blood metal ion levels.
Exam-tested points
- ›Definition: Non-neoplastic, non-infective cystic or solid periprosthetic soft-tissue masses linked to metal-on-metal (MoM) hip wear and hypersensitivity.
- ›Prevalence: Reported initially as ~1% at 5 years overall, but substantially higher in female cohorts (~5–8x relative risk).
- ›Pathophysiology: Multifactorial combining high volumetric cobalt-chromium wear debris and an immunological delayed-type (type IV) hypersensitivity reaction (ALVAL).
- ›Histology: Extensive coagulative necrosis, diffuse histiocytic sheets containing fine metallic pigment, and dense perivascular lymphocytic aggregates (lymphocytic cuffing).
- ›Clinical Presentation: Groin/thigh pain, swelling/palpable mass, abductor weakness, instability/dislocation, or compression neuropathies (femoral/sciatic).
- ›Workup: Plain radiographs (evaluating steep cup inclination >50°), MARS-MRI (evaluating abductor disruption and capsular dehiscence), serum/blood cobalt and chromium ion levels, and joint aspiration to exclude PJI.
- ›Surgical challenges: High post-revision complication rates (notably instability and dislocation) secondary to severe destruction of the abductor mechanism and joint capsule.
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