What happens to your ACL and PCL during knee replacement surgery? Understanding how knee ligaments are managed during surgery is a common concern for patients facing total knee replacement (Total Knee Arthroplasty, or TKA). In a standard knee replacement, the anterior cruciate ligament (ACL) is typically removed to allow precise implant positioning, since it is often already degraded by arthritis. Depending on the implant design, cruciate-retaining or posterior-stabilized, the posterior cruciate ligament (PCL) may be preserved or replaced by a mechanical post-and-cam system. By balancing the medial collateral ligament (MCL) and lateral collateral ligament (LCL), surgeons use modern implant geometry to restore stability and natural motion.
If you are facing knee replacement surgery, you are likely wondering what happens to the natural structures in your knee, especially your ligaments. Here is what I tell my patients: far more is kept than is removed. Understanding how your surgeon manages these stabilizing structures during total knee arthroplasty can help you feel prepared and confident going in.
Understanding Your Knee Ligaments: Basic Knee Anatomy
Before we get into what happens during surgery, it helps to know the main ligaments in your knee and what each one does. These are the structures we plan around.
- Anterior Cruciate Ligament (ACL): controls forward movement and rotation of the shinbone
- Posterior Cruciate Ligament (PCL): prevents the thighbone from sliding backward
- Medial Collateral Ligament (MCL): provides inner-side stability
- Lateral Collateral Ligament (LCL): provides outer-side stability
- Medial Patellofemoral Ligament (MPFL): helps stabilize the kneecap
What Happens to the ACL During Knee Replacement Surgery
Why the ACL is Removed
The anterior cruciate ligament is routinely removed during knee replacement surgery. That can sound alarming, but there are clear reasons behind it. Dr. Calendine explains the reasoning in a short video on ACL removal.
- Pre-existing damage: in patients with arthritis severe enough to need a replacement, the ACL is usually already torn, frayed, or significantly degraded.
- Surgical access: removing the ACL gives the surgeon a clear path to position the implant components accurately.
- More predictable results: ACL removal leads to more reliable implant alignment and a more consistent outcome.
How Stability is Maintained
You do not lose stability when the ACL comes out. Modern knee replacement implants are engineered specifically to compensate for its absence. The shape and geometry of the implant take over the job the ACL once did, which is why patients feel secure on the new knee.
In the small number of cases where the natural ligaments are too weak or damaged to stabilize the joint on their own, your surgeon can select a more constrained implant whose components link together for added support. That decision is made in the operating room based on what your knee actually needs.
The Posterior Cruciate Ligament (PCL): Keep or Remove?
Cruciate-Retaining vs. Posterior-Stabilized Implants
The fate of your PCL depends on the type of implant your surgeon chooses. Both paths have decades of strong track record behind them.
Cruciate-Retaining Implants
- The PCL is preserved when it is healthy enough to keep providing stability.
- These implants rely on your natural PCL for part of the knee’s mechanics.
- The ACL is still removed, even in cruciate-retaining designs.
Posterior-Stabilized Implants
- Both the ACL and PCL are removed.
- A built-in post-and-cam mechanism takes over the PCL’s role.
- Stability comes from the implant’s engineering rather than from natural ligaments.
Which Approach is Better?
Here is the honest answer I give patients: neither is clearly superior for most people. Current research, including a Cochrane review of cruciate-retaining versus posterior-stabilized designs, shows no meaningful difference in implant longevity or function between the two. Your surgeon chooses based on your specific anatomy and the condition of your PCL, not on a one-size-fits-all rule.
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Collateral Ligaments: The Keepers in Knee Replacement Surgery
Why These Ligaments Stay
The medial and lateral collateral ligaments are almost always preserved during knee replacement surgery. They are the side-to-side anchors of the knee, and keeping them is central to a stable result. We keep them because they:
- provide essential side-to-side stability,
- are usually less affected by arthritis than the cruciates,
- do not interfere with implant placement, and
- can be fine-tuned, or balanced, during surgery for optimal alignment.
Ligament Balancing Process
Balancing is one of the most important things I do during a knee replacement, and it is where surgical experience shows. By carefully adjusting the tension on the preserved collateral ligaments, I work toward:
- equal tension on the inner and outer sides of the knee,
- proper alignment and smooth movement, and
- biomechanics that match your new implant.
A well-balanced knee feels stable and natural. A poorly balanced one can feel loose or stiff, which is why this step deserves real attention rather than a quick check.
The MPFL: Release and Potential Repair
Why the MPFL is Released
The medial patellofemoral ligament is usually released, or temporarily detached, during total knee replacement to:
- provide surgical access to the joint,
- allow proper positioning of the implant components, and
- let the surgeon see and assess the patella (kneecap).
When MPFL Repair is Necessary
If you have a history of patellar instability, your surgeon may perform MPFL reconstruction or repair, either during the same operation as your knee replacement or in a later procedure if instability develops afterward.
MPFL Reconstruction Process
When MPFL repair is needed, the surgeon may reconstruct the ligament with graft material, augment the existing ligament to improve kneecap tracking, or use tissue from your own body (autograft) or a donor (allograft).
Other Structures: What About the Meniscus?
While the menisci are not technically ligaments, they are always removed during total knee replacement. These C-shaped cartilage cushions are replaced by the plastic spacer in your implant, which provides a similar shock-absorbing function between the metal surfaces.
Advanced Techniques: Bicruciate-Retaining Surgery
Experimental Approaches
Because roughly 15 to 20 percent of total knee replacement patients report some dissatisfaction with how natural the knee feels, some surgeons are studying bicruciate-retaining techniques that preserve both the ACL and PCL in an effort to better reproduce normal knee motion. A few points are worth knowing:
- It is a technically demanding procedure with a narrow margin for error.
- The benefits over standard designs remain unproven in large studies.
- It is not yet widely adopted, and early designs historically struggled with loosening.
For the vast majority of patients, a well-balanced cruciate-retaining or posterior-stabilized knee remains the proven, reliable choice.
Recovery and Long-Term Outcomes
What This Means for Your Recovery
Understanding how your ligaments are managed explains a lot about recovery. Because the implant and the preserved collateral ligaments do the stabilizing work, physical therapy focuses on:
- strengthening the muscles around the knee,
- retraining balance and proprioception (your sense of joint position), and
- restoring range of motion at a pace that fits which ligaments were preserved.
Functional Expectations
With sound ligament management during surgery, most patients can expect restored knee stability, a return to low-impact activities like walking, swimming, and cycling, less pain, and improved quality of life. Modern implants are durable, and most last 15 to 20 years.
Choosing the Right Surgeon and Approach
The decisions about your ligaments are made by your surgeon, so the surgeon you choose matters. When you meet for a consultation, it is fair to ask:
- Which ligaments will be preserved in my case?
- What type of implant do you plan to use, and why?
- Will any kneecap or MPFL issues need to be addressed?
- What recovery timeline should I expect based on the approach?
A surgeon who can answer these clearly is one who is planning around your individual anatomy rather than a default routine.
Conclusion
Knee replacement surgery is, at its core, an exercise in managing your knee’s natural ligaments with precision. The ACL is routinely removed because arthritis has usually already compromised it. The PCL is either preserved or substituted, depending on whether a cruciate-retaining or posterior-stabilized implant fits your knee best. The collateral ligaments are protected and balanced to anchor side-to-side stability, and the MPFL is released and, when needed, repaired. None of this is improvised. Each decision follows a deliberate plan built around your anatomy, your activity goals, and an implant designed to restore confident, pain-free movement.
What this means for you is reassurance. Modern surgical technique and implant engineering are designed to deliver a stable, durable, natural-feeling knee even after the ACL is removed and other structures are adjusted. The right approach is the one matched to your specific knee, and that judgment is exactly what an experienced, fellowship-trained joint replacement surgeon brings to your care.
Dr. Cory Calendine is a board-certified, fellowship-trained orthopaedic surgeon at the Bone and Joint Institute of Tennessee in Franklin, performing more than 700 hip and knee replacements each year and serving as a consultant to Stryker on the Mako® robotic platform. If you are weighing knee replacement, the most valuable next step is a conversation about your individual anatomy, your ligaments, and which surgical approach will give you the best long-term result. Dr. Calendine sees patients from across Middle Tennessee, including Nashville, Brentwood, and Murfreesboro, and is currently accepting new patients. You can schedule a consultation or call (615) 791-2630. No referral is required.
This article is for educational purposes only and is not a substitute for professional medical advice. Always consult your own surgeon about decisions for your individual knee.
- Parcells BW, Tria AJ Jr. The Cruciate Ligaments in Total Knee Arthroplasty. Am J Orthop (Belle Mead NJ). 2016;45(4):E153-E160.
- Verra WC, van den Boom LGH, Jacobs W, et al. Retention versus sacrifice of the posterior cruciate ligament in total knee arthroplasty for treating osteoarthritis. Cochrane Database Syst Rev. 2013;(10):CD004803.
- American Academy of Orthopaedic Surgeons (OrthoInfo). Knee Replacement Implants. AAOS; 2024.
- American Academy of Orthopaedic Surgeons (OrthoInfo). Total Knee Replacement. AAOS; 2023.
- Mayo Clinic. Knee replacement. Mayo Foundation for Medical Education and Research; 2024.
