Joint replacement basics (hip

🔩 Core concept - Hip Hardware 101

• Total Hip Arthroplasty (THA) Components:
  • Acetabular Cup: Replaces socket; typically titanium, porous-coated for bone ingrowth.
  • Liner: Fits inside cup; common material is ultra-high-molecular-weight polyethylene (UHMWPE).
  • Femoral Head: Replaces ball; usually ceramic or cobalt-chrome.
  • Femoral Stem: Inserts into femur; titanium or cobalt-chrome alloy.

• Fixation Methods:
  • Cementless (Press-fit): Relies on bone ingrowth; preferred in younger patients with good bone.
  • Cemented (PMMA): For immediate fixation; used in older patients or poor bone quality.

⭐ Bearing Surfaces: The head-liner articulation is critical. Ceramic-on-polyethylene offers low wear rates, reducing the risk of periprosthetic osteolysis from wear debris-a major cause of long-term failure.

🤕 Clinical Manifestations - The Failing Hip

• Pain: Primary symptom, typically a dull, aching groin pain.
  • May radiate to the buttock, anterior thigh, or knee.
  • Worsens with activity and weight-bearing; can progress to rest/night pain.
• Stiffness & Functional Decline:
  • ↓ range of motion, especially internal rotation.
  • Difficulty with ADLs (e.g., putting on socks, tying shoes).
  • Antalgic gait (limp) and reduced walking distance.
• Physical Exam:
  • Pain with passive hip motion.
  • Possible Trendelenburg sign (abductor weakness).

⭐ Pearl: Hip pathology often presents as isolated knee pain via the obturator nerve (L2-L4). Always examine the hip in patients with knee pain.

🔎 Diagnosis - Spotting the Damage

• History & Physical: Insidious-onset groin/thigh pain, morning stiffness < 30 minutes, pain worsened by activity. A key physical exam finding is decreased internal rotation of the hip.
• Imaging: Weight-bearing Anteroposterior (AP) Pelvis and lateral hip X-rays are the primary diagnostic tools.

⭐ Radiographic findings are paramount for diagnosis. 📌 Mnemonic: JSN-OSS (Joint Space Narrowing, Osteophytes, Subchondral Sclerosis, Subchondral Cysts).

🔩 Management - The Surgical Fix

• Total Hip Arthroplasty (THA): Replaces the damaged femoral head and acetabulum with prosthetic components.

• Components & Fixation:
  • Cementless: Press-fit for bone ingrowth; used in younger, active patients with good bone stock.
  • Cemented: Uses bone cement for immediate fixation; common in older patients or those with osteoporosis.
• Bearing Surfaces:
  • Metal-on-Polyethylene: Most common standard.
  • Ceramic-on-Polyethylene/Ceramic: Lower wear rates, often for younger patients.

⭐ Posterior Approach: Most common surgical approach. Carries the highest risk of posterior hip dislocation and sciatic nerve injury. Post-op precautions include avoiding hip flexion >90°, adduction, and internal rotation.

⚠️ Complications - Post-Op Pitfalls

• Dislocation: Most common early complication.
  • Posterior approach: ↑ risk. Presents as shortened, internally rotated leg.
  • Anterior approach: ↓ risk.
• Infection:
  • Acute (<3 mo): S. aureus, Strep.
  • Chronic (>3 mo): S. epidermidis (biofilm).
• VTE (DVT/PE): Major cause of morbidity/mortality; requires prophylaxis.
• Nerve Injury: Sciatic (posterior approach), Femoral (anterior approach).
• Late Failure:
  • Aseptic Loosening: Most common cause. Polyethylene wear debris → osteolysis.
  • Periprosthetic fracture.

⭐ A patient with a recent posterior approach hip arthroplasty presenting with sudden hip pain, a shortened, and internally rotated limb likely has a prosthesis dislocation.

⚡ Biggest Takeaways

• Severe osteoarthritis is the leading indication for total hip arthroplasty (THA).
• The posterior surgical approach is most common but carries a higher risk of sciatic nerve injury and posterior dislocation.
• Hip dislocation is the most frequent early complication, presenting with a shortened, internally rotated leg.
• Aseptic loosening, caused by polyethylene wear debris, is the most common reason for late implant failure.
• Prosthetic joint infection is a devastating complication; suspect S. aureus early and S. epidermidis late.
• Venous thromboembolism (VTE) is a major risk requiring routine pharmacologic prophylaxis.