Adult Reconstruction
Core concepts
Adult reconstruction questions reward a systematic approach: define the failing joint, the mode of failure, and the host. Know the indications and survivorship of primary total hip and knee arthroplasty, bearing surface choices (highly crosslinked polyethylene, ceramic-on-ceramic, metal-on-metal pitfalls), and fixation philosophy (cemented vs cementless). For revision, master the classification of periprosthetic osteolysis, the workup of the painful arthroplasty (infection first), and the principles of acetabular and femoral reconstruction in bone loss. Periprosthetic joint infection dominates: understand the MSIS/ICM criteria, the value and limits of ESR/CRP, synovial fluid WBC and alpha-defensin, and when to choose debridement with implant retention versus one- or two-stage exchange. Also know periprosthetic fracture classification (Vancouver for femur, Unified for acetabulum) and the timing of fixation versus revision.
Traps
Questions love the "normal CRP" patient with a chronic infection, the metal-on-metal patient with an adverse local tissue reaction, and the stiff knee where the examiner wants you to distinguish arthrofibrosis from low-grade infection. Another trap is component positioning: cup inclination/anteversion and the safe zone, and femoral stem version causing instability. Do not forget the osteoporotic host and the value of metaphyseal cones or sleeves in revision.
Rule of thumb
For any painful arthroplasty, exclude infection before calling it aseptic loosening. A useful heuristic: if the aspiration is equivocal, treat the joint as infected until proven otherwise.
Worked example
A 68-year-old with a well-fixed THA, groin pain, and a pseudotumor on MRI after a metal-on-metal bearing: the answer is adverse local tissue reaction; plan revision with bearing exchange and thorough debridement, not simple observation.