OPBSPathologyMusculoskeletal
Must Know
- Aseptic loosening is still the leading cause of arthroplasty failure, ahead of infection, instability and breakage.
- Highly cross-linked polyethylene has reduced particulate wear and osteolysis.
- Wear is loss of material volume, with particle generation, from motion between opposed surfaces.
- Foreign body reaction runs from injury and haematoma to cell recruitment, acute then chronic inflammation, then fibrosis or granuloma.
- Early bone loss raises strain and micromotion. Cyclic micromotion pumps particles along the interfaces.
- Osteolysis now accounts for about 21.8 percent of hip revisions, against about 40 percent decades ago.
- Wear above 0.1 mm per year carries high osteolysis risk.
More on history
- Charnley’s original Teflon bearing (1959 to 1962) failed in 95 percent, mostly from osteolysis and loosening.
- Willert and Harris separately described macrophage-driven lysis around loose implants.
- Jones and Hungerford named it cement disease in 1987. Uncemented hips followed in the 1980s, yet osteolysis persisted.
- The term particle disease has replaced cement disease.
- The original Charnley hip showed 85 percent survival at 25 years.
- Modern polyethylene shows no radiographic penetration at 10 years in early data.
Phases of Particle Disease
- Immune activation. Chronic cellular and cytokine response to debris.
- Tissue breakdown. More macrophages, fibroblasts and osteoclasts disrupt periprosthetic bone.
- Failed regeneration. Direct cytotoxic effect on mesenchymal osteoprogenitors impairs remodelling.
Particle Size and Cell Response
| Particle | Main handling | Response |
|---|---|---|
| 0.2 to 10 µm (polyethylene, cement) | Macrophage phagocytosis | Macrophage driven foreign body reaction |
| 0.3 to 1.0 µm | Most potent stimulus of mononuclear phagocytes | Strongest inflammation |
| Below 0.3 µm | Pinocytosis | Much less inflammatory, no receptor mediated response |
| Metal, about 50 nm | Lymphocyte response | ALVAL and pseudotumour |
- Cytokine release depends on dose, particle size, concentration and surface area.
- Direct particle contact with cells, without phagocytosis, can activate osteoclastogenic pathways.
- Within 48 hours macrophages enlarge from 10 to 20 µm to 40 to 50 µm.
- Activated macrophages release TNF-α, MCP-1 and MIP-1α. MCP-1 recruits more monocytes and osteoclast precursors.
Bearings and Debris
| Bearing | Wear | Debris problem |
|---|---|---|
| Polyethylene in the hip | Adhesion and abrasion from cyclic motion | Small particles, macrophage response. Backside wear uncommon |
| Polyethylene in the knee | Delamination, pitting, fatigue from sliding, rolling and rotation | Large debris, smaller macrophage response. Backside wear matters |
| Ceramic on ceramic | Lowest of all, under 0.5 to 2.5 µm per year | Narrow positioning window, squeak, fracture with severe debris |
| Ceramic on polyethylene | Results similar to metal on polyethylene | Stripe and lead pencil head wear raises roughness and fracture risk |
| Metal on metal | Under 5 µm per year | About 50 nm particles up to 500 times more numerous. ALVAL, pseudotumour, systemic ions |
- Knee osteolysis prevalence is 5 to 20 percent at 15 years.
- A broken ceramic liner must be revised to ceramic because polyethylene fails rapidly against ceramic debris.
- Overabducted MOM cups give higher serum ion levels.
- Fretting corrosion now occurs at modular dual taper necks and trunnions.
- Gamma sterilisation in air oxidised conventional polyethylene, raising wear.
- Latest polyethylenes use refined irradiation, annealing and vitamin E to reduce free radicals.
- Cross-linked polyethylene particles are fewer, but each can be up to 100 times more inflammatory.
More on MOM tissue findings
- Reactions include tissue necrosis, metal laden macrophages, granulomas, perivascular lymphocytes, lymphoid neogenesis and large invasive fluid collections.
- Invasion of nearby vessels and nerves has been described.
- Some small head MOM bearings did well beyond 20 years. Large head designs failed and some were recalled.
Biology of Osteolysis
- Osteolysis reflects imbalance between debris production and clearance.
- Early stages resemble healing, with fluid and a synovial-like membrane forming an effective joint space.
- Unlike healing, inflammation escalates to osteoclastogenesis and bone loss.
- Osteoclasts are multinucleated cells of the monocyte macrophage lineage.
- Osteoclast precursors activate on contact with osteoblasts or marrow stromal cells.
- Synovial fibroblast-like cells secrete RANKL in response to PGE2.
- RANKL binding RANK activates IKK, which phosphorylates IκB, freeing NF-κB to enter the nucleus.
- OPG is a soluble decoy receptor for RANKL. Mice overexpressing OPG develop osteopetrosis.
- Innate immunity dominates. Osteoclasts are the final effector.
- TNF-α, IL-1, IL-6, PGE2 and MMPs mark a nonspecific inflammatory process.
- Loose implants without osteolysis show mainly fibrous tissue.
- T lymphocytes may make up 10 percent of interface cells but are not activated.
- TNF-α or RANKL knockout mice do not develop osteolysis from cement particles.
- Particles can also signal osteoclasts directly through c-src, MAPK, JNK and NF-κB. Blocking NF-κB inhibits osteolysis.
More on tissue and cell interactions
- Classic macrophage activation is driven by Th1 cytokines, especially interferon gamma.
- Alternative activation is driven by Th2 cytokines IL-4 and IL-13.
- Cytokine and transcription responses rise linearly with particle volume.
- Periprosthetic tissue holds histiocytes, macrophages, giant cells, fibroblasts, osteoblasts, osteoclasts, synovial and endothelial cells.
- Fibroblasts trigger giant cell formation and release stromelysin and collagenase, especially with titanium particles.
- Endotoxin may concentrate on particle surfaces. Immunoglobulin bound polyethylene can fix complement.
- Retrieved T cells lack IL-2, IL-2R, interferon gamma and TNF-β expression.
- Mouse calvarial models show pitting and bone loss after subperiosteal polyethylene.
Interface Membrane Pathology
- Micromotion leads to fibrous tissue instead of osseous anchorage, forming a membrane like a pseudarthrosis.
- The membrane may develop a synovial-like lining.
- At autopsy, well-fixed cemented hips pass through necrosis, then fibroblastic repair, then an acellular fibrous membrane.
- Histiocytes reacting to polyethylene increase with time at different rates in different patients.
- In late loosening of cemented hips the membrane has a pseudosynovial layer next to cement, then foamy histiocytes with cement pearls.
- Some membrane cells contain contractile filaments, like myofibroblasts.
- Membrane fibroblasts can drive monocytes to become osteoclasts through RANKL and TNF-alpha.
- Cobalt debris is toxic to fibroblasts. Titanium and chromium particles stimulate fibroblast proliferation.
Radiolucent Lines
- A radiolucent line usually corresponds to a fibrous membrane.
- A few lucencies reflect endosteal cortical resorption.
- Acetabular lucencies mostly show fibrous membrane. Femoral lucencies mostly show endosteal remodelling.
- Radiolucency does not always mean clinical loosening.
- In a cadaver model MRI detected 95.4 percent of osteolytic lesions against 51.7 percent for CT.
- Hip osteolysis usually appears about 4 years after surgery. About 60 percent of lesions progress, at about 0.89 mm per year.
Causes of Osteolysis
- Wear particle activation of macrophages.
- Raised intracapsular pressure pumping fluid and debris along interfaces.
- Micromotion.
- Possibly hypersensitivity, with metal ions acting as haptens.
- Bacterial endotoxin or lipoteichoic acid bound to particles may amplify the response.
- Macrophages release IL-1, IL-6, IL-18, TNF-alpha, PGE2 and RANKL. NALP3 cleaves pro-IL-1 beta.
- Interface cathepsin levels exceed those in rheumatoid synovium.
- No serum marker reliably diagnoses aseptic loosening. Diagnosis is clinical and radiological.
| Reason for hip revision in Sweden 1979 to 2003 | Share |
|---|---|
| Aseptic loosening | 73.9 percent |
| Infection | 7.9 percent |
| Dislocation | 7.5 percent |
| Periprosthetic fracture | 5.7 percent |
Implant Sarcoma
- Only about two dozen sarcomas after arthroplasty are reported.
- Estimated osteosarcoma risk is under 12 per million implants per year, against 20 per million from background radiation.
- Pleomorphic sarcoma (malignant fibrous histiocytoma) is the most frequent type, then osteosarcoma.
- Mean latency is 5 to 8 years, occasionally up to 30.
- Proposed mechanisms are osteonecrosis from surgery or cement heat and chronic particle-driven proliferation.
- Lymphomas near implants are Epstein-Barr virus-associated large B-cell lymphomas of chronic inflammation.
- Cobalt-chrome debris causes more chromosome translocations. Titanium alloy debris causes more aneuploidy.
Source
Vigorita VJ, Ghelman B, Mintz D. Joint Arthroplasty Pathology. In. Vigorita VJ, Ghelman B, Mintz D. Orthopaedic Pathology. 3rd ed. Philadelphia, Wolters Kluwer, 2016.
Potential Therapies
| Approach | Agent | Evidence |
|---|---|---|
| Cytokine modulation | cAMP analogues, PGE1, PGE2 | Raise IL-6 but inhibit TNF-α |
| NSAID | Indomethacin | Paradoxically increases TNF-α activity |
| Macrophage recruitment | Mutant MCP-1 coating on implants | Good experimental results |
| Osteoclast formation | SHP-2 inhibitor SHP099 | Inhibits osteoclasts, local implant delivery proposed |
| Chelation and antioxidant | N-acetylcysteine | Cut cobalt from 16 to 20 to under 7 mcg/L, with rebound. Bone effects conflict |
| Statins | Cholesterol lowering | Revision RR 0.34, femoral osteolysis RR 0.38. Not yet recommended |
| Bisphosphonates | Alendronate, pamidronate, neridronate | Inhibit or reverse particle bone loss. Neridronate halted osteolysis at 1 year |
- Bisphosphonates bind hydroxyapatite and block osteoclast ruffled border, adhesion and proton production.
- They promote osteoclast apoptosis but prevent osteoblast and osteocyte apoptosis.
- Blocking one cytokine pathway may amplify others.
More on drug detail
- Other metal chelators reported are EDTA, sodium 2,3-dimercaptopropane sulfonate and dimercaprol.
- NAC is a glutathione precursor. Glutathione suppresses RANKL signalling in some studies but enhanced osteoclasts fivefold in another.
- The statin revision benefit (4698 THA patients) covered infection, aseptic loosening and other causes.
- Neridronate was given intramuscularly fortnightly for 3 months, then monthly, raising periprosthetic BMD on DEXA.
- Coupling of osteoclasts and osteoblasts means osteoclast blockade could impair remodelling, though knockout mice showed normal osteoblasts.
Numbers to Remember
- Osteolysis threshold. Wear above 0.1 mm per year.
- Hip revisions for osteolysis. 21.8 percent now, 40 percent previously.
- Knee osteolysis. 5 to 20 percent at 15 years.
- Macrophage particles. 0.2 to 10 µm, most potent 0.3 to 1.0 µm.
- Pinocytosis. Below 0.3 µm.
- MOM. About 50 nm particles, up to 500 times more, wear under 5 µm per year.
- Macrophage size. 10 to 20 µm rising to 40 to 50 µm in 48 hours.
- Interface T cells. Up to 10 percent.
Memory Aids
- Big knee, small hip. Knee debris is large from delamination. Hip debris is small from adhesion and abrasion.
- Micro to macrophage, nano to lymphocyte. Micron particles drive macrophages. Nanometre metal drives lymphocytes and ALVAL.
- Three phases ABC. Activation, Breakdown, Crippled regeneration.
Exam Traps
- Particles under 0.3 µm are taken up by pinocytosis, which is less inflammatory.
- Fewer cross-linked polyethylene particles does not mean less inflammation per particle.
- Indomethacin increases TNF-α activity.
- Interface T cells are present but not activated.
Related pages. Bearing Surfaces and Wear, Modern Metal-on-Metal Implants in Hip Surgery, Squeaking Hip Implants
Source
Antoci V Jr, Garcia DR, Glasser JL, Shukla A. Osteolysis and Implant Loosening. In. Aaron RK, editor. Orthopaedic Basic Science. Foundations of Clinical Practice. 5th ed. Philadelphia, Wolters Kluwer, 2021.
Practise Type X questions on this topic
Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 17 October 2026.