Total Knee Replacement Surgery

Understanding CR, CS, and PS Joint Designs — Which Is Right for You?

When your doctor recommends Total Knee Replacement Surgery, you may assume there is just one standard procedure. In reality, there are three distinct implant designs used in total knee replacement — each with its own approach to knee stability, ligament management, and movement. These are known as:

• CR — Cruciate Retaining
• CS — Cruciate Substituting
• PS — Posterior Stabilised

Understanding the difference between these three joint designs can help you ask the right questions, feel more confident about your surgical plan, and develop realistic expectations for your recovery and outcome. This guide explains each design in plain language — and what factors guide the choice between them.

What is Total Knee Replacement Surgery?

Total Knee Replacement Surgery — also called total knee arthroplasty (TKA) — is a procedure in which the damaged surfaces of the knee joint are removed and replaced with artificial components. These components resurface the ends of the femur (thigh bone) and tibia (shin bone), and in most cases also the undersurface of the patella (kneecap), restoring a smooth, pain-free joint.
Total knee replacement is recommended for patients with advanced knee arthritis — typically osteoarthritis, rheumatoid arthritis, or post-traumatic arthritis — where damage extends across the joint and conservative treatments are no longer effective. It is one of the most successful procedures in modern medicine, consistently delivering high patient satisfaction and long-lasting outcomes.
The implant consists of three key components: a metal femoral component, a metal tibial tray, and a plastic (polyethylene) insert that sits between them — mimicking the cushioning and gliding action of healthy cartilage. The specific design of the polyethylene insert and the way the implant manages the posterior cruciate ligament (PCL) is what defines whether a procedure is CR, CS, or PS.

CR — Cruciate Retaining Total Knee Replacement

What is CR Total Knee Replacement?

In a Cruciate Retaining (CR) total knee replacement, the posterior cruciate ligament is carefully preserved throughout the procedure. The implant is designed around the assumption that the PCL remains intact and will continue to function as a stabiliser — just as it does in a healthy knee. The polyethylene insert in a CR implant is less constrained, allowing the natural roll-back motion of the femur on the tibia that the PCL normally governs.

Who is CR Most Suitable For?

• Patients with a healthy, intact posterior cruciate ligament
• Standard osteoarthritis cases without major angular deformity
• Patients without prior significant knee trauma or surgery that may have compromised the PCL
• Surgeons experienced in the precise ligament balancing that CR technique demands

Advantages

• Preserves more of the patient’s natural anatomy and proprioception (sense of joint position)
• More natural-feeling knee movement post-surgery
• Maximum bone stock preservation — no femoral box cut required
• Studies suggest slightly better long-term implant survivorship in appropriate candidates
• Avoids complications associated with the cam-post mechanism used in PS designs

Considerations

• Requires precise PCL balancing — technically more demanding than PS
• Not suitable if the PCL is damaged, absent, or insufficiently functional
• May not be ideal in severe deformity, stiff knees, or revision cases
• Improper PCL tensioning can lead to mid-flexion instability if not executed carefully

CS — Cruciate Substituting Total Knee Replacement

What is CS Total Knee Replacement?

The Cruciate Substituting (CS) design occupies a middle ground between CR and PS. In this approach, the PCL is released and removed — but instead of a mechanical cam-and-post system (as in PS), stability is achieved through a highly congruent, ultra-conforming polyethylene tibial liner. This congruent design closely matches the shape of the femoral component, providing inherent stability through surface geometry rather than through a retained ligament or a mechanical post.
The CS philosophy brings together the bone-preservation advantages of CR (no femoral box cut required) with the easier gap-balancing of PS (no need to carefully tension the PCL), making it an increasingly popular and versatile option.

Who is CS Most Suitable For?

• Patients where the PCL is insufficient, damaged, or of poor quality
• Cases with moderate knee deformity where PCL balancing would be challenging
• Surgeons transitioning from PS to a more bone-conserving approach
• Patients where a femoral box cut (required in PS) poses elevated fracture risk

Advantages

• No femoral box cut — preserves more distal femoral bone stock than PS
• Easier surgical balancing — no need to titrate PCL tension
• Ultra-congruent liner provides reliable stability without cam-post complications
• Growing evidence base supports comparable outcomes to CR and PS
• Ideal bridging option for surgeons experienced in either CR or PS technique

Considerations

• Less established long-term evidence compared to the decades-long track record of CR and PS
• Increased theoretical polyethylene wear concerns in early designs (largely addressed in modern implants)
• Femoral rollback may be marginally less than in well-balanced CR designs
• Not yet universally available at all surgical centres

PS — Posterior Stabilised Total Knee Replacement

What is PS Total Knee Replacement?

In a Posterior Stabilised (PS) total knee replacement, the PCL is removed and its function is replicated by a mechanical cam-and-post system built directly into the implant. A post on the tibial insert engages with a cam (intercondylar box) on the femoral component during knee flexion — guiding the femur to roll backwards naturally as the knee bends, mimicking the action the PCL would normally provide.
This design has been in use for several decades and has an extensive, well-documented track record of success — particularly in more complex or demanding surgical cases.

Who is PS Most Suitable For?

• Patients with PCL deficiency — whether pre-existing or anticipated during surgery
• Severe varus or valgus deformity requiring significant soft tissue release
• Severely stiff knees with significant flexion contracture
• Revision total knee replacement cases
• Patients where achieving precise PCL balance is not reliably achievable
• Cases involving previous significant knee trauma or surgery

Advantages

• Highly reliable stability provided by the cam-post mechanism — less dependent on ligament balance
• Studies show better deep flexion range of motion compared to CR in several analyses
• Technically more forgiving in complex deformities — easier gap balancing
• Decades of clinical evidence supporting excellent long-term outcomes
• Reproducible results even in challenging anatomical situations

Considerations

• Femoral box cut removes additional bone — not ideal where bone preservation is a priority
• Cam-post mechanism introduces a small risk of ‘patellar clunk syndrome’ in some implant designs
• Some studies report marginally higher mid-term revision rates compared to CR in straightforward cases
• Less natural proprioceptive feedback without the PCL

CR vs CS vs PS — Side-by-Side Comparison

Which Design is Best — And Who Decides?

This is perhaps the most important question — and the honest answer is that no single design is universally best. All three options — CR, CS, and PS — are well-established, evidence-backed approaches to total knee replacement surgery, each delivering excellent results in the right patient.
The choice of implant design depends on a carefully considered combination of factors:

• Condition of the PCL — is it intact, functional, damaged, or absent?
• Severity and type of knee deformity — varus, valgus, or neutral alignment
• Degree of stiffness or flexion contracture present pre-operatively
• Bone quality and quantity — particularly relevant in older patients or revision cases
• Patient’s age, activity level, and post-operative lifestyle goals
• Surgeon’s experience, training, and preferred surgical technique
• Whether this is a primary (first-time) or revision procedure

In straightforward cases with an intact PCL and no severe deformity, many experienced surgeons prefer CR for its natural feel and bone-preserving properties. In more complex cases — severe deformity, PCL deficiency, or revision surgery — PS or CS designs offer more reliable stability and are often the preferred choice. CS is an increasingly popular option for surgeons who want the balancing ease of PS with the bone preservation of CR.

Frequently Asked Questions

Is one implant design better?

No single design is universally superior. Clinical studies consistently show comparable pain relief, functional scores, and patient satisfaction across CR, CS, and PS designs when used in appropriately selected patients. The most important factor is correct patient-implant matching by an experienced surgeon.

Will I be able to feel the difference between CR, CS, and PS after surgery?

Most patients notice little difference in daily life between well-implanted CR, CS, and PS knees. CR designs retain the PCL and can offer a marginally more natural feel for some patients. PS designs may allow slightly better deep flexion in some cases. For the vast majority of patients, all three designs deliver an excellent, comfortable outcome.

How long do these implants last?

Modern total knee implants — across all three designs — are expected to last 15 to 20 years or more in most patients. Studies show 90%+ survivorship at 10 years for CR, CS, and PS implants. Proper patient selection, surgical technique, and post-operative physiotherapy all contribute to implant longevity.

Is Total Knee Replacement Surgery available with robotic assistance?

Yes. Dr. Manu Sharma performs total knee replacement surgery — including CR, CS, and PS implant placements — using robotic-assisted technology where appropriate, achieving sub-millimetre precision in implant positioning for optimal outcomes.

What is the recovery time after Total Knee Replacement Surgery?

Most patients begin walking within 24 to 48 hours of surgery. Return to light daily activities typically occurs within 4 to 6 weeks, with full recovery and return to higher-demand activities usually achieved within 3 to 6 months, depending on the individual’s health, age, and rehabilitation commitment.