Basic Sciences Applied to Orthopedics
Core principles
- Bone remodelling couples osteoclast resorption (RANK–RANKL signalling, restrained by osteoprotegerin) with osteoblast formation; bisphosphonates promote osteoclast apoptosis, whereas teriparatide is anabolic.
- Articular cartilage is avascular, aneural and alymphatic, so superficial lesions rarely heal and deep lesions expose subchondral bone.
- Biomechanics uses load–deformation, stiffness, creep and fatigue concepts; cortical bone is strongest in compression, weakest in shear, and fixation should neutralize the weakest loading mode.
- Staphylococcus aureus is the commonest cause of bone and joint infection; biofilm reduces antibiotic efficacy and requires debridement.
- Aminoglycosides are concentration-dependent and nephrotoxic; vancomycin needs trough or AUC monitoring; NSAIDs inhibit COX and may impair fracture healing in animal models, although human evidence is less clear.
Worked example
A 72-year-old woman with CKD stage 4 and atrial fibrillation on warfarin sustains a low-energy distal radius fracture. Osteoporotic trabeculae lose connectivity, so the bone fails under compression and tension. Her anticoagulation affects surgical timing and haematoma risk, and CKD alters analgesic and antibiotic dosing. Reasoning: correct modifiable coagulopathy, choose load-sharing fixation, avoid nephrotoxic drugs, and assess falls plus osteoporosis treatment.
Traps
Do not attribute every postoperative infection to contamination without sampling. Do not confuse osteoclast inhibition with osteoblast stimulation. Do not ignore mechanical environment when choosing implants.
Key points are listed separately.