Arthroplasty and Reconstructive Surgery
Principles of Arthroplasty
Candidates must understand indications (end-stage osteoarthritis, rheumatoid arthritis, avascular necrosis, fracture) and contraindications (active infection, inadequate soft tissue envelope, neuropathic joint). Know implant selection (cemented vs uncemented, bearing surfaces: metal-on-polyethylene, ceramic-on-ceramic, dual mobility), fixation principles (cement mantle, press-fit), and complications (periprosthetic fracture, dislocation, loosening, infection, wear).
Key Concepts
- Total hip arthroplasty (THA): Approaches (posterior, direct anterior, lateral). Complications: dislocation (posterior approach higher risk), sciatic nerve injury (posterior), heterotopic ossification (lateral). Lewinnek safe zone for cup position (inclination 40°±10°, anteversion 15°±10°).
- Total knee arthroplasty (TKA): Mechanical alignment (neutral), gap balancing vs measured resection. Complications: stiffness, instability, periprosthetic joint infection (PJI), patellar complications.
- Periprosthetic joint infection (PJI): Diagnosis (MSIS criteria: clinical, labs, cultures). Treatment: debridement, antibiotics, implant retention (DAIR) for acute; two-stage exchange for chronic.
- Aseptic loosening: Most common cause of late failure; osteolysis due to particulate wear debris.
Traps
- Dislocation after THA: Most common within first 3 months; posterior approach with inadequate soft tissue repair increases risk.
- Periprosthetic fracture: Vancouver classification for THA (A: trochanteric, B: around stem (B1: well-fixed, B2: loose, B3: loose with poor bone stock), C: below stem).
- PJI diagnosis: No single test is perfect; use combined criteria. Alpha-defensin is a promising marker.
- Bearing surfaces: Metal-on-metal has higher failure due to adverse local tissue reaction (ALTR).
Worked Example
A 65-year-old woman with hip osteoarthritis undergoes THA via posterior approach. Postoperative day 2, she experiences sudden pain and inability to bear weight. X-ray shows dislocation. Rule of thumb: Posterior dislocation is most common; check for component malposition. Treatment: closed reduction under sedation, then assess stability; if recurrent, consider revision or abduction brace. Prevent with posterior soft tissue repair and patient education.