Total Knee Arthroplasty (TKA)

Indications

• end-stage degenerative joint disease of the knee (>2 compartments), which may result from 1º or 2º OA, AVN and inflammatory arthropathies such as RA

TKA Primary Goals
1) Relief of pain 2) Restoration of function 3) Achievement of intrinsic stability 4) Creation of durable reconstruction

Standard Surgical Approach

• medial parapatellar capsular arthrotomy
• no true internervous plane
• superior dissection between vastus medialis & quadriceps tendon & extends inferiorly between patellar retinaculum & patellar ligament
• medial & lateral collateral ligaments must be protected throughout the procedure

Prosthesis Design

• all components are cemented (to reduce complications with loosening)
• consists of a polyethylene tibial tray insert between a metallic femoral condylar & tibial component
• cement – polymethylmethacralate (PMMA)
• two common prosthesis for primary TKA

1.) Posterior Cruciate Retaining (CR)

• preserves the posterior cruciate ligament (PCL)
• achieves better flexion by allowing femoral rollback

2.) Posterior Stabilized (PS) (most common)

• sacrifices the PCL, replacing it with a tibial post that prevents anterior translation
• balancing of flexion gap is very important to prevent dislocation

• PS prosthesis is always preferred in patients with:
  • previous patellectomy
  • inflammatory changes
  • prior trauma with PCL rupture or attenuation

PEARL the alignment of the distal femoral condyles with respect to the femoral axis is ~ 9º valgus & tibial plateau to the tibial axis ~ 3º varus, for a mechanical axis of 6º valgus

Technical Goals

• restoration of mechanical alignment (femoral head ? medial tibial spine ? centre of ankle)
• preservation of the joint line
• balanced ligaments (medial vs. lateral release)
• maintaining or restoring normal Q-angle

PEARL Flexion Gap = distance between the posterior femoral cut and the tibial cut Extension Gap = distance between distal femoral cut and tibial cut

Complications

• Immediate:
  • extensor mechanism dysfunction: “overstuffing” of the patellofemoral articulation
  • peroneal nerve palsy: most common in knees with severe valgus deformity
  • infection: rare, rates vary (1 – 2.5%) according to centre
• Long-term:
  • decreased ROM (usually from inadequate postoperative physical therapy)
  • aseptic loosening of components ? polyethylene wear
  • septic loosening of components ? joint infection
  • periprosthetic fracture
  • arthrofibrosis

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