OPBSInfectionBiomaterials
Must Know
- Treatment combines aggressive surgery with antimicrobials chosen by organism, susceptibility, toxicity and host health.
- Local delivery (beads, powder, spacers) gives high concentrations to kill planktonic and biofilm bacteria.
- Choose antibiotics with good bone and soft tissue penetration and activity against biofilm.
- Bioavailability describes the rate and the extent of absorption of a nonintravenous drug into the circulation.
- Quality of débridement is the strongest determinant of success in acute or chronic infection.
- A margin over 5 mm cleared almost all chronic osteomyelitis.
- Fracture risk is low with 70 percent or more of cortex intact at the débridement level.
Antibiotic Cement
- Elution depends on antibiotic type, amount and number, cement porosity and type, and surface area.
- Suggested load is at least 3.6 g tobramycin with 1 g vancomycin per 40 g PMMA.
- Tobramycin stayed at effective levels at 4 months. Vancomycin did not.
- Tobramycin and vancomycin together elute better than either alone. Do not use vancomycin alone.
- Hand mixing gives uneven distribution and lower elution than commercial premixed cement.
- Vacuum mixing lowers porosity and so lowers elution.
- 40 percent more surface area raised vancomycin elution by 20 percent.
- Adding 25 percent dextran raised 48 hour antibiotic release about fourfold.
Septic Arthritis and Osteomyelitis
- Proteolytic enzymes from synovial cells destroy cartilage. IL-1 triggers protease release from chondrocytes and synoviocytes.
- Cartilage damage begins by 8 hours. Proteoglycan is lost by 5 days and collagen by 9 days.
- Antibiotics within 24 hours still do not prevent glycosaminoglycan and collagen damage.
- In children acute haematogenous spread is commonest, with the long bone metaphysis most affected.
- Thin cortex, loose periosteum and vessels crossing to the epiphysis aid spread in children.
- Intracapsular metaphysis at shoulder, elbow, hip and ankle lets osteomyelitis enter the joint.
- About 85 percent of adult septic arthritis is monoarticular, the knee most often.
- Chronic osteomyelitis shows sequestrum (dead bone) and involucrum (periosteal new bone), mostly after open injury.
- Osteomyelitis usually gets 4 to 6 weeks of antibiotics.
- Arthroscopic washout is effective. Open drainage was the historical benchmark.
| Kocher predictor (one point each) | Predictors present | Probability of septic hip |
|---|---|---|
| Non-weight-bearing | 0 | 2.0 percent |
| Temperature over 38.5 °C | 1 | 9.5 percent |
| ESR over 40 mm/h | 2 | 35.0 percent |
| WCC over 12,000 cells/mm3 | 3 | 72.8 percent |
| 4 | 93.0 percent |
Periprosthetic Joint Infection
- 2018 scoring definition had sensitivity 97.7 percent against MSIS 79.3 and ICM 86.9, specificity 99.5 percent.
- Preoperative score 6 or more means infected. Score 2 to 5 needs intraoperative findings.
- Blood leucocyte count is neither sensitive nor specific. Synovial count and differential are rapid and accurate.
- After surgery CRP normalises by 3 weeks. ESR takes up to 6 weeks.
- Low virulence organisms (coagulase-negative staphylococci, Cutibacterium acnes) can give falsely normal ESR and CRP.
- Alpha defensin is an innate antimicrobial peptide unaffected by prior antibiotics, accurate but costly.
- Serum IL-6 comes from monocytes and macrophages.
- Next-generation sequencing may identify culture-negative organisms. It needs validation.
| PJI marker (2018 definition) | Threshold |
|---|---|
| Serum CRP | Over 1 mg/dL |
| ESR | Over 30 mm/h |
| Synovial WCC, chronic | Over 3,000 cells/µL |
| Synovial PMN | Acute over 90 percent, chronic over 80 percent |
| Alpha defensin | Signal to cutoff ratio over 1 |
| Leucocyte esterase | ++ |
| Synovial CRP | 6.9 mg/L |
| Serum IL-6 | Over 10 pg/mL |
| Option | When |
|---|---|
| Suppressive antibiotics | Unfit for surgery, low virulence, well-fixed implant, oral drug available. Success 18 to 86 percent |
| DAIR | Acute PJI within 4 weeks of surgery or acute haematogenous, stable implant, susceptible organism |
| One-stage exchange | Favoured by most European surgeons |
| Two-stage exchange | Traditional US choice. Chronic or late PJI. Eradication checked off antibiotics before reimplantation |
| Arthrodesis | Most functional salvage. Multiple failures, resistant organisms, lost extensor mechanism |
| Resection arthroplasty | Low demand or medically complex. Sitting easier than after fusion |
| Amputation | Massive bone or soft tissue loss, vascular injury, necrotising fasciitis, life-threatening sepsis |
- Another uninfected implant or mechanical heart valve is a relative contraindication to suppression.
- Remove implants for loose components, chronic late infection or sepsis.
- Articulating spacers give better motion and knee scores without more infection or bone loss.
- Static spacers limit motion and risk quadriceps or abductor shortening.
- Knee fusion is a poor choice with contralateral limb, ipsilateral hip or ankle dysfunction.
Spine Infection
- S aureus is the commonest pyogenic cause. Granulomatous infection is tuberculosis or, rarely, fungal.
- Antibiotics for about 6 weeks, monitored by serial ESR and CRP.
- Decompress promptly for new deficit, sepsis, epidural abscess, instability or deformity.
- Poor outcome follows deficit over 36 hours before surgery, age over 60 and multiple comorbidities.
- Spinal TB stages are implantation, early destruction, advanced destruction, neurological involvement and residual deformity.
- Kyphosis grades K1 under 10 degrees, K2 11 to 60 degrees, K3 gibbus over 60 degrees.
- TB paraplegia is graded 1 to 4. Grade 2 walks with support. Grade 3 cannot walk.
- Medical treatment is RIPE (rifampicin, isoniazid, pyrazinamide, ethambutol).
More on spine SSI risk
- Risks include blood loss over 1 L, previous SSI, obesity, surgery over 5 hours, smoking and ASA 3 or more.
- Others are dependent status, perioperative hyperglycaemia, poor antibiotic timing and two or more residents operating.
- Cancer is a risk factor specific to thoracolumbar surgery.
- Surgical options in TB include combined anterior and posterior stabilisation, extrapleural anterior stabilisation and VATS.
Fracture-Related Infection and Infected Nonunion
- Confirmatory FRI criteria are fistula, sinus or wound breakdown, pus, two matching deep cultures and organisms on histology.
- A single positive deep culture, raised markers, new effusion and radiological signs are suggestive only.
- Type A infected nonunion is quiescent. Type B is draining. Subtype 1 gap under 4 cm, subtype 2 over 4 cm.
- A1 gets single-stage débridement, grafting and fixation. B1 gets débridement, fixation then delayed grafting.
- A2 and B2 are treated by distraction histiogenesis.
More on outcomes and definitions
- Intravenous dosing avoids the unknown absorbed fraction of oral dosing.
- Dead space is managed with myoplasty, free tissue transfer or antibiotic beads.
- Raised capsular pressure and vessel thrombosis add to septic cartilage injury.
- Deep infection after open fracture is about 23 percent, with 6 percent progressing to osteomyelitis.
- Host-dependent open fracture infection ranges from 4 to 30 percent.
- Infected nonunion risks include bone exposed without vascular periosteum for over 6 weeks and empty lacunae on histology.
- Suppression is often stopped after a mean 23 months due to drug reactions.
Related pages. Antibiotics, Antibiotic Therapy for Musculoskeletal Infections, Chronic Osteomyelitis, Septic Arthritis, Periprosthetic Infections, Pyogenic Spinal Infection, Surgical Site Infection
Source
Cooper AM, Goswami K, Parvizi J. Treatment of Skeletal Infections. 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.