Total Hip Arthroplasty

THA Basics - Hip Hits Reset

Total Hip Arthroplasty (THA) replaces a damaged hip joint with a prosthesis, aiming for pain relief & function restoration.

Key Indications:

• Osteoarthritis (OA) - most common
• Avascular Necrosis (AVN) - femoral head
• Displaced Neck of Femur Fracture (#NOF) - elderly, active
• Rheumatoid Arthritis (RA) - severe joint damage
• Developmental Dysplasia of Hip (DDH) - secondary OA

Contraindications:

• Absolute:
  • Active sepsis
  • Severe medical comorbidities (prohibitive surgical risk)
• Relative:
  • Neuromuscular compromise affecting stability
  • Skeletal immaturity
  • Charcot joint (neuroarthropathy)

⭐ Primary osteoarthritis is the most common indication for THA.

THA Blueprint - Plan & Pathways

Pre-operative Evaluation:

• Hx: Pain, functional limitation. P/E: Harris Hip Score (HHS: <70 Poor, 70-79 Fair, 80-89 Good, 90-100 Excellent), abductor strength (Trendelenburg).
• Investigations: X-rays (AP Pelvis, Lat Hip), ESR/CRP (infection screen).
• Medical Fitness: Optimize co-morbidities (cardiac, diabetes).

Templating Goals (Digital/Analog):

• Restore biomechanical hip center of rotation.
• Achieve leg length equality.
• Optimize femoral offset & version for stability.

Surgical Approaches Overview:

• Posterior (Moore): Most common. Risk: Sciatic n., ↑early dislocation.
• Lateral (Hardinge): Transgluteal. Risk: Sup. gluteal n., abductor weakness.
• Anterolateral (Watson-Jones): Interval: TFL & Gluteus Medius.
• Anterior (DAA): Internervous. Risk: LFCN. Potential faster early recovery.

⭐ The posterior approach is the most commonly used worldwide but carries a higher risk of early dislocation.

THA Hardware - Parts & Performance

• Components:

  • Acetabular Cup: Ti/Co-Cr alloy; porous coating (uncemented).
  • Liner: UHMWPE, Ceramic; locking mechanism.
  • Femoral Stem: Ti/Co-Cr alloy; designs: tapered wedge, CPT (Collarless Polished Taper).
  • Femoral Head: Ceramic (e.g., Biolox delta), Co-Cr; sizes: 28mm, 32mm, 36mm.

• Fixation Methods:

  • Cemented: Polymethylmethacrylate (PMMA). Indications: older patients, poor bone stock, irradiated bone.
  • Uncemented (Press-fit): Relies on bony ingrowth. Indications: younger patients, good bone stock.

• Bearing Surfaces: Choice impacts wear & longevity.

  Surface	Wear Rate	Pros	Cons
  Metal-on-Poly (MoP)	Moderate	Cost-effective, historical standard	Polyethylene wear, osteolysis
  Ceramic-on-Poly (CoP)	Low	↓Wear vs MoP, good biocompatibility	Higher cost than MoP
  Ceramic-on-Ceramic (CoC)	Lowest	↓↓Wear, inert, scratch-resistant	Risk of fracture, squeaking, expensive
  Metal-on-Metal (MoM)	Variable (Concerns)	Allowed large heads; (Largely abandoned)	Adverse Reactions to Metal Debris (ARMD), pseudotumors

⭐ Charnley's concept of low-friction arthroplasty revolutionized THA, using a small femoral head (22.225mm) and UHMWPE acetabular component, significantly reducing wear compared to previous designs.

THA Pitfalls & Fixes - Dodging Disasters

• Intra-op: Femoral/acetabular fracture, Leg Length Discrepancy (LLD), Nerve palsy (sciatic, femoral, sup. gluteal), Vascular injury, Implant malposition.
• Early Post-op (<6 wks):
  • DVT/PE: Prophylaxis essential.
  • PJI: Dx (MSIS criteria). Class (TSAI/Coventry). Mgmt: DAIR (acute), 1/2-stage revision (chronic).

*   Dislocation: Posterior commonest. Risk factors: surgical approach, component malposition, patient factors. Closed/open reduction.

• Late Post-op (>6 wks):
  • Aseptic Loosening: Most common late revision cause. Mechanisms: particle-induced osteolysis. Radiographic signs: radiolucent lines, component migration.
  • Osteolysis; Implant wear/failure.
  • Heterotopic Ossification (HO): Risk factors. Prophylaxis (NSAIDs, XRT). Brooker Stages I-IV.
  • Periprosthetic Fracture: Vancouver Classification Types A, B1-B3, C.

⭐ Aseptic loosening is the most common cause for late revision of total hip arthroplasty.

High‑Yield Points - ⚡ Biggest Takeaways

• Primary osteoarthritis is the most common indication for THA.
• Posterior approach: most common, ↑ dislocation risk; Anterolateral: ↓ dislocation, potential abductor lurch.
• Components: acetabular cup, femoral stem & head, liner. Polyethylene wear is a key long-term issue.
• Cemented THA for older patients/poor bone stock; uncemented for younger/active individuals.
• Complications: dislocation (early), infection, periprosthetic fracture, aseptic loosening (late).
• Charnley: pioneer of low-friction arthroplasty (metal-on-polyethylene).
• Metal-on-metal bearings: risk of pseudotumors and metallosis due to ion release.