Arthroplasty and Adult Reconstructive Surgery
What this domain tests
Indications and timing, fixation and bearing choices, wear and osteolysis, periprosthetic joint infection (PJI) diagnosis, instability, and revision strategy for hip, knee, and shoulder arthroplasty.
Core rules
- Cemented femoral fixation remains excellent in older, lower-demand patients; cementless stems suit younger bone. Highly cross-linked polyethylene has substantially reduced wear; metal-on-metal bearings have been abandoned because of adverse reaction to metal debris.
- Aseptic loosening is a late, progressive radiolucent line with implant migration; PJI may present identically but earlier and with systemic or wound signs.
- ICM 2018 criteria: two major criteria (sinus tract communicating with the prosthesis; two positive cultures with the same organism) are diagnostic. Minor criteria score CRP, ESR, synovial white cell count, polymorphonuclear percentage, alpha-defensin, leukocyte esterase, single positive culture, and histology. A score of 6 or more is infected, 2-5 inconclusive, 1 or less not infected. Aspirate after at least two weeks off antibiotics.
- Hip precautions and component positioning matter: combined anteversion near 35-40°, cup inclination near 40°, and restoration of offset and leg length reduce dislocation.
Worked example
A knee arthroplasty at 10 days with persistent drainage: CRP 22 mg/L, ESR 44 mm/h, synovial white cells 3,200/µL, 78% polymorphonuclear, one positive culture. Score: CRP 2 + ESR 1 + white cells 3 + 78% PMN 2 + single culture 2 = 10, so infected. Within four weeks of implantation, with a stable implant and a susceptible organism, debridement with modular exchange and antibiotic suppression is reasonable; later presentations need staged revision.
Traps that cost marks
- Aspirating or culturing while the patient is on antibiotics.
- Treating a chronic PJI as aseptic loosening because cultures were negative.
- Forgetting that normal inflammatory markers do not exclude infection in low-virulence organisms.