Total Knee Arthroplasty (TKA) - Comprehensive Overview

1. Epidemiology & Background

2. Indications

1. Debilitating pain affecting activities of daily living
2. Pain not well controlled by conservative measures (physiotherapy, NSAIDs, intra-articular injections, walking aids)
3. Medical fitness for surgery
4. No active infection - anywhere in the body

3. Contraindications

• Active joint or systemic infection
• Absent or non-functional extensor mechanism
• Severe peripheral vascular disease compromising wound healing
• Neuropathic arthropathy (relative - higher failure rates)

• Morbid obesity (BMI >40 - increased infection, implant failure, complications)
• Poorly controlled diabetes (elevated HbA1c or fructosamine)
• Active immunosuppression (requires perioperative medication management)

4. Types of Knee Replacement

By Extent

By Posterior Cruciate Ligament (PCL) Management

By Fixation

• Cemented: Gold standard. Uses polymethylmethacrylate (PMMA) cement. Best long-term data.
• Uncemented (cementless): Bioactive surfaces (hydroxyapatite) allow bony ingrowth. Promising mid-term results; preferred in younger, more active patients.
• Hybrid: Cemented tibia + uncemented femur (or vice versa).

By Bearing Surface

• Fixed-bearing polyethylene: Standard; polyethylene is fixed to tibial tray
• Mobile-bearing (rotating platform): Polyethylene can rotate; theoretically reduces wear but no proven clinical superiority

5. Implant Materials

6. Surgical Technique Overview

Positioning & Approach

• Supine position, tourniquet applied to thigh
• Standard approach: medial parapatellar arthrotomy (most common)
• Patella is everted (or subluxed) to expose the joint
• Anesthesia: regional (spinal/epidural) preferred; equivalent outcomes to GA

Bone Cuts - "Gap Balancing"

1. Distal femoral cut - perpendicular to the mechanical axis of femur (creates the extension gap)
2. Proximal tibial cut - perpendicular to tibial mechanical axis (usually with 3-7° posterior slope)
3. Anterior/posterior femoral cuts - define the flexion gap; size the femoral component
4. Chamfer cuts - bevel the femur to match component geometry
5. Patellar resurfacing (optional, controversial)

Alignment Philosophies

Ligament Balancing - Key Principle

7. Perioperative Management

Pre-operative Risk Reduction (High-Yield for Exams)

• Avoid intra-articular corticosteroid injection within 2 weeks before TKA (significantly increases infection risk)
• Optimize nutrition: check albumin and prealbumin; supplement as needed
• Glycemic control: check HbA1c or serum fructosamine
• Perioperative management of antirheumatic medications per ACR/AAHKS guidelines:
  • Continue through surgery: Methotrexate, hydroxychloroquine, sulfasalazine, leflunomide
  • Hold biologics (TNF inhibitors, IL-6, etc.): Hold for one dosing interval before surgery (e.g., adalimumab every 2 weeks - hold until week 3)
  • JAK inhibitors (tofacitinib, baricitinib, upadacitinib): Hold 3 days prior

Anesthesia & Analgesia

• Multimodal analgesia is the standard: combines regional blocks + NSAIDs + acetaminophen +/- opioids
• NSAIDs (including IV ketorolac within 24h) reduce pain and opioid consumption
• Pregabalin reduces opioid consumption after discharge; gabapentinoids do NOT reduce postoperative pain in the perioperative period
• Nerve blocks:
  • Femoral nerve block (FNB): Motor + sensory block; good analgesia but causes quadriceps weakness → fall risk → requires knee immobilizer
  • Adductor canal block (ACB): Sensory-only block; preserves quad function; allows earlier ambulation; equivalent analgesia to FNB. ACB + periarticular block (PAB) provides additive benefit
  • iPACK block: Targets posterior capsule; fills posterior knee coverage gap left by ACB/FNB

VTE Prophylaxis

• DVT is the most common systemic complication
• Chemoprophylaxis (LMWH, aspirin, direct oral anticoagulants) plus mechanical (sequential compression devices) started immediately

8. Complications

Intraoperative

Postoperative

9. Postoperative Rehabilitation

10. Outcomes & Implant Survivorship

• TKA is highly effective: 85-90%+ survivorship at 15-20 years for cemented designs
• Patient satisfaction: ~80-85% of patients are satisfied (about 15-20% report dissatisfaction, often due to persistent pain, stiffness, or unmet expectations)
• Robotic-assisted TKA is an emerging technology; recent meta-analyses (PMID 38133653, 39052153) show improved component positioning accuracy but no definitive long-term functional superiority over conventional TKA yet

Causes of Revision (Know These)

1. Aseptic loosening (most common, especially tibial component)
2. Infection / PJI
3. Instability
4. Polyethylene wear / osteolysis
5. Periprosthetic fracture
6. Stiffness / arthrofibrosis
7. Extensor mechanism failure

Key Exam Points (High-Yield Summary)

• #1 indication: Debilitating OA pain failing conservative therapy
• Corticosteroid injection within 2 weeks of surgery = highest infection risk
• PS vs CR design: PS sacrifices PCL; PS notches femur → higher condylar fracture risk
• Varus deformity → medial release; Valgus → lateral release (ITB is key lateral structure)
• Peroneal palsy → first: flex knee + remove dressings. No surgery unless no recovery at 3 months
• Patellar fracture with minimal lag (<10°) + stable TKA → treat conservatively (cast/brace; NO therapy!)
• Arthrofibrosis → manipulation at 6-8 weeks; late manipulation risks femur fracture
• MCL injury intraoperatively → constrained revision prosthesis
• ACB preferred over FNB for early ambulation (no quad weakness)
• Hold biologics one dosing interval before surgery; JAK inhibitors 3 days before; continue MTX/HCQ