Ligament Status After Total Knee Arthroplasty
The ligaments of the knee do NOT remain intact after most total knee arthroplasty (TKR) procedures—the anterior cruciate ligament (ACL) is typically sacrificed during surgery, while the posterior cruciate ligament (PCL) may be retained or removed depending on the implant design used.
What Happens to Each Ligament
Anterior Cruciate Ligament (ACL)
- The ACL is routinely removed in the vast majority of modern TKA designs
- Even when surgeons attempt preservation, the ACL is often already degenerated from the underlying osteoarthritis
- Research shows that in patients requiring TKA, approximately 78% have an intact ACL at the time of surgery 1, but this ligament is typically sacrificed during the procedure regardless of its condition
Posterior Cruciate Ligament (PCL)
- The PCL may be retained or sacrificed depending on the prosthesis design:
- PCL-retaining designs: Keep the PCL intact to help with knee kinematics
- PCL-substituting designs: Remove the PCL and rely on the implant's cam-post mechanism for stability
- Studies show 98% of TKA patients have an intact PCL preoperatively 1, but surgical decision determines final status
- When using highly congruent polyethylene inserts, PCL sacrifice versus retention shows no significant difference in range of motion or stability 2
Collateral Ligaments (MCL and LCL)
- These ligaments are preserved during TKA and remain intact
- The MCL is particularly important for stability, and proper surgical technique aims to maintain native ligament strain
- Kinematically aligned TKA better restores native MCL strain compared to mechanically aligned techniques 3
- Osteolysis can occur near collateral ligament attachments on the femoral condyles, but the ligaments themselves remain 4
Clinical Implications
Ligamentous balance/imbalance plays a role in joint instability post-TKA, but it is not the only factor accounting for stability 4. The prosthesis design, surgical alignment, and soft tissue balancing all contribute to overall knee stability.
Key Points:
- Instability after TKA accounts for 7.5% of prosthesis failures and typically requires revision surgery around 4 years post-operatively 4
- Even torn or reconstructed ACLs do not adversely affect outcomes when using appropriate surgical techniques (PCL retention with intermediate medial conforming inserts) 5
- Bi-cruciate retaining designs (preserving both ACL and PCL) can achieve 95% survival rates at 10 years with excellent anteroposterior stability 6, though these designs are rarely used in modern practice
Bottom Line
Ligaments are not "restored" by TKR—the ACL is removed, the PCL status depends on implant choice, and the collateral ligaments are preserved but not regenerated. Stability after TKA comes from the prosthesis design, proper alignment, and balanced soft tissues, not from intact or restored cruciate ligaments.