Arthroplasty and Adult Reconstruction
What you must understand
Know indications, contraindications, and survivorship of total hip and knee arthroplasty. Understand bearing surfaces (metal-on-polyethylene, ceramic, dual mobility), fixation (cemented versus cementless), and the biomechanics of implant alignment and offset restoration. For the hip, understand the direct anterior, lateral, and posterior approaches and their neurovascular risks. For the knee, understand gap balancing and mechanical alignment. Recognize periprosthetic joint infection (PJI) criteria (MSIS/ICM), aseptic loosening, instability, and periprosthetic fracture.
Traps in questions
- Aseptic loosening is the most common long-term cause of revision; infection is the most common early catastrophic cause.
- PJI diagnosis requires a combination of clinical, serologic (CRP, ESR), synovial (WBC, PMN%, alpha-defensin), and microbiologic criteria - no single test is definitive.
- Sciatic nerve injury is associated with the posterior hip approach; superior gluteal nerve with the lateral approach; lateral femoral cutaneous nerve with the anterior approach.
- Metal-on-metal implants risk adverse local tissue reaction (ALTR) and elevated cobalt/chromium.
Worked rule of thumb
For a painful arthroplasty, first exclude infection (aspirate if CRP/ESR elevated), then assess fixation and alignment on radiographs, then consider instability or wear. Never revise for presumed loosening without ruling out infection.
Exam strategy
Questions often hinge on timing: early pain suggests infection or instability; late pain suggests loosening or wear.