Total Knee Arthroplasty

Indications & Contraindications - Gatekeeping TKA

Indications:

• Severe knee pain (often >6/10 VAS) with functional limitation, refractory to conservative treatment.
  • Primary Osteoarthritis (most common)
  • Rheumatoid Arthritis
  • Post-traumatic Arthritis
  • Avascular Necrosis (AVN) of knee
  • Failed conservative measures (analgesia, physiotherapy, intra-articular injections, unicompartmental knee arthroplasty)
• Significant deformity (varus/valgus >15-20°)
• Radiographic evidence of advanced arthritis (e.g., Kellgren-Lawrence Grade 3-4)

Contraindications:

• Absolute:
  • Active knee sepsis or systemic infection
  • Extensor mechanism dysfunction (e.g., patellar tendon rupture)
  • Severe vascular disease (PVD)
  • Neuropathic joint (Charcot knee) - relative to absolute depending on severity & stability
  • Recurvatum deformity due to muscular weakness
• Relative:
  • Medical instability (uncontrolled comorbidities)
  • Obesity (BMI >40 kg/m²)
  • Young age (<50-55 years) - risk of earlier revision
  • Non-compliance with rehabilitation
  • Skin conditions over the knee (e.g., psoriasis)

⭐ Exam Favourite: Active infection in the knee joint is an absolute contraindication to TKA due to the high risk of prosthetic joint infection (PJI), a devastating complication requiring prolonged antibiotics and often multiple revision surgeries.

Pre-op Planning & Biomechanics - Blueprint & Balance

• Pre-operative Assessment:
  • History: Pain, functional limitation, patient expectations.
  • Examination: ROM, deformity (varus/valgus), ligamentous stability, neurovascular status.
  • Optimize co-morbidities.
• Radiographic Planning:
  • Essential X-rays: AP, Lateral, Skyline views.
  • Long leg films (scanogram): Crucial for mechanical axis & deformity assessment.
  • Templating: Component sizing, alignment, bone resection levels.
• Biomechanical Goals:
  • Mechanical Axis: Restore to $\mathbf{0}^\circ \pm \mathbf{3}^\circ$ (Hip → Knee → Ankle).
  • Anatomical-Mechanical Angle: Femur approx. $\mathbf{6}^\circ$ valgus.
  • Joint Line Restoration: Critical for patellar tracking & mid-flexion stability.
  • Gap Balancing: Symmetrical, rectangular flexion & extension gaps.
  • Femoral Rollback: Ensure posterior femoral translation in flexion.

⭐ Deviation from the target mechanical axis (neutral plus or minus three degrees) significantly increases polyethylene wear and risk of aseptic loosening.

Implant Design & Surgical Steps - Nuts, Bolts & Action

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Post-op Care & Complications - Recovery & Roadblocks

• Immediate Post-op:
  • Mobilization: Weight bearing as tolerated (WBAT) from Day 0/1.
  • DVT Prophylaxis: LMWH/DOACs for 10-35 days. Intermittent Pneumatic Compression (IPC).
  • Pain Control: Multimodal analgesia (opioids, NSAIDs, regional nerve blocks).
  • Wound Care: Sutures/staples out at 10-14 days; monitor for discharge/erythema.
• Rehabilitation:
  • Physiotherapy: Key for Range of Motion (ROM; target 0-120° flexion), quadriceps & hamstring strengthening.
  • Continuous Passive Motion (CPM): Use debated; may offer early ROM benefits.
• Complications:
  • Early (<3 months):
    • Infection (Superficial Site Infection [SSI], Periprosthetic Joint Infection [PJI])
    • Deep Vein Thrombosis (DVT)/Pulmonary Embolism (PE)
    • Stiffness (Arthrofibrosis) - consider Manipulation Under Anesthesia (MUA) if <90° flexion by 6-12 weeks.
    • Periprosthetic fracture
    • Wound dehiscence/hematoma
  • Late (>3 months):
    • Aseptic Loosening (Most common cause of late failure)
    • Polyethylene Wear & Osteolysis
    • Late PJI
    • Instability
    • Patellofemoral pain/tracking issues

⭐ Mechanical axis alignment post-TKA within ±3° of neutral is critical for long-term implant survival and optimal function.

High‑Yield Points - ⚡ Biggest Takeaways

• Osteoarthritis (severe, tricompartmental) is the most common indication for TKA.
• Active knee sepsis and extensor mechanism dysfunction are key contraindications.
• Femoral rollback is vital for deep flexion, facilitated by PS or CR designs.
• Aim for neutral mechanical axis alignment (0°) for implant longevity.
• Patellar resurfacing is considered for anterior knee pain or patellofemoral arthritis.
• Aseptic loosening is the most common long-term complication; PJI is a serious early one.
• Cemented fixation is the gold standard, especially in older patients.