June 20, 2024

Total Knee Arthroplasty is the surgical procedure to manage the end-stage arthritis of the knee.

There are basically two types:

  1. Cruciate retaining prosthesis ( keeps PCL)
  2. Cruciate sacrificing prosthesis  (remove PCL)
Total Knee Arthroplasty
Total Knee Arthroplasty

Cruciate retaining primary TKA

Functions of Posterior Cruciate ligaments (PCL) in TKA

  • Regulates flexion stability
  • Its tension influence femoral rollback

Roll back is defined as progressive postural change in femoral tibial contact point as the knee moves into flexion

Advantages of Cruciate retaining prosthesis

  1. Bone conserving
  2. More consist of joint line restoration (keeping flexion gaps keeps flexion gap smaller)
  3. More proprioceptive feedback by keeping PCL

Disadvantages of Cruciate retaining prosthesis

  1. Harder to balance with severe deformity so avoid cruciate-retaining if varus >10° or valgus >15°
  2. A tight flexion in PCL causes increased PE wear
  3. Paradoxical forward sliding as the knee flexes (i.e. ACL removed, knee kinematics drastically altered)= PE wear ↑
  4. Late rupture of PCL will result in instability

Wear particles from polyethylene can cause osteolysis will cause disruption of PCL from bony attachments

Cruciate sacrificing Primary TKA

Indications of cruciate sacrificing TKA

  1. Past history of Patellectomy
  2. Inflammatory arthritis
  3. Trauma with PCL rupture
Anterior and Posterior Stabilized Knee

Anterior Stabilized Knee vs Posterior Stabilized Knee

Posterior Stabilized KneeAnterior Stabilized Knee
Cam will connect between 2 posterior femoral condyles.
It will engage tibial PE post during flexion
Cam and Post will control the rollback mechanism
Have more congruent PE inserts    
The tibial insert is highly congruent with raised anterior PE lip
No mechanism of rollback –
The anterior Lip resist anterior translation
Advantages
Easier balancing in a severe coronal deformity
Control flexion kinematics with cam and spine
Have less sliding wear  
Bone conserving
Operative versatility that it doesn’t have to switch to post stabilized system if PCL is lost/ over released
Disadvantages
Femoral cam can jump
The loose flexion gap needs revision
Additional bone is removed from the middle of the distal femur
The flexion gap is bigger
↑ PE surface area will ↑ risk of PE wear
Minimal rollback
Rotational instability
Anterior Stabilized Knee vs Posterior Stabilized Knee
Rollback mechanism in TKA
Rollback mechanism in TKA

Contraindications of Cruciate Sacrificing TKA

  1. Medically unfit patients with severe comorbidities
  2. Deficient extensor mechanisms
  3. Active sepsis
  4. Peripheral vascular disease
  5. Severe/prolonged neuropathy with Charcot’s joints
  6. Severely traumatized soft tissue envelop