Prof. Dr. Murat Demirel
Orthopedics and Traumatology Specialist

Orthopedics Specialist Prof. Dr. Murat Demirel was born in Ankara in 1974. He completed his primary education at Ankara Kavaklıdere Primary School and his secondary and high school education at Ankara Atatürk Anatolian High School. Dr. Demirel graduated from Ankara University Faculty of Medicine in 1998 and completed his residency in Orthopedics and Traumatology at Ankara Numune Training and Research Hospital, 1st Orthopedics and Traumatology Clinic, in 2004.

PhD
Ankara University Institute of Health Sciences

Specialization
Ankara Numune Training and Research Hospital, 1st Orthopedics Clinic

Medical School
Ankara University Faculty of Medicine

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What Are Partial Knee Replacements and For Which Knee Problems Are They Used?

We can think of the knee joint as a house with three rooms. One of these rooms is on the inside (medial compartment), another on the outside (lateral compartment), and the third is located right behind the kneecap (patellofemoral compartment). In a young and healthy knee, the cartilage tissue covering the floor of these rooms is smooth, slippery, and flexible. This allows joint movements to occur without pain.

However, due to factors such as age, genetic predisposition, excess weight, or previous traumas, this cartilage tissue begins to wear down over time. This process of wear and tear is called “osteoarthritis.” Sometimes osteoarthritis affects all three rooms, but in many patients, it starts in only one room—usually the inner compartment that bears most of the body’s weight—and remains localized there for a long time. In such a case, instead of replacing the entire house by sacrificing the other two healthy rooms, it makes much more sense to repair only the damaged one.

Partial knee replacements are based precisely on this philosophy. Without touching the healthy parts of the knee, only the worn cartilage and bone surfaces in the compartment affected by osteoarthritis are covered with specially designed metal and polyethylene (a durable plastic) implants.

Of course, this surgery is not the first-line treatment. Conservative (non-surgical) methods are always prioritized. Partial knee replacement surgery is usually considered when these methods have been tried and are no longer sufficient to relieve the patient’s pain. Before deciding on surgery, there are fundamental approaches that should be attempted.

These non-surgical treatment methods include:

• Lifestyle changes (such as weight loss)
• Avoiding activities that strain the knee
• Physiotherapy and exercise programs
• Use of pain relievers and anti-inflammatory medications
• Supportive devices such as knee braces, canes, or walkers
• Intra-articular injections (such as cortisone or hyaluronic acid)

If, despite all these methods, pain continues to negatively affect daily life (such as walking comfortably, climbing stairs, or sleeping at night), partial knee replacement may be a permanent and effective solution for you.

What Is the Difference Between Partial Knee Replacement and Total Knee Replacement?

One of the most common questions patients have is the fundamental differences between partial and total knee replacements. These two surgeries can be compared to garden maintenance. If only one corner of the garden has dried out, it makes sense to clean up just that area and plant new grass (partial knee replacement). However, if the entire garden is neglected and dried, then it must be renewed entirely (total knee replacement).

The main difference lies in the scope of intervention. In partial knee replacement, only the worn compartment of the knee is replaced, while in total knee replacement, all three compartments of the knee (or at least two) are covered with artificial implants. This key difference brings along several other distinctions.

One of the greatest advantages of partial knee replacement is that it preserves the natural anatomy and mechanics of the knee much more. In particular, the anterior and posterior cruciate ligaments, which act as the “seat belts” of the knee, are not touched. Preserving these ligaments ensures that the knee’s position sense (proprioception)—our brain’s ability to feel the position of the knee in space—remains intact. This is why patients with partial knee replacement feel their knees much more “natural” and “like their own” compared to those with total knee replacements. Performing the operation through a smaller incision, removing less bone, and causing less soft tissue damage also directly affect the recovery process.

To summarize the main differences between the two surgeries:

Surgical Scope: In partial knee replacement, only one compartment is replaced, while in total knee replacement, the entire knee joint is replaced.

Ligament Preservation: In partial knee replacement, the anterior and posterior cruciate ligaments are preserved, while in total knee replacement, at least one is usually sacrificed.

Bone Preservation: In partial knee replacement, minimal bone loss occurs, which makes a possible future revision (replacement) surgery easier.

Recovery Speed: Recovery is generally faster in partial knee replacement.

Natural Feel: Because the natural movement mechanics of the knee are preserved, partial knee replacement provides a more natural feeling.

Eligibility: While total knee replacement can be applied to a broader patient group, partial knee replacement requires stricter criteria.

Who Is Considered a Good Candidate for Partial Knee Replacement?

The success of partial knee replacement surgery depends primarily on correct patient selection. This operation is not suitable for every patient with knee osteoarthritis. Identifying the right candidate requires a meticulous process, much like tailoring a custom suit. This involves a detailed consultation, a comprehensive physical examination, and advanced imaging methods.

The most essential criterion is that osteoarthritis should be limited to only one compartment of the knee. The pain should also be concentrated mainly in that damaged area. The patient can often point to the exact location of the pain by saying, “It hurts right here.” On physical examination, it is important that the knee has sufficient range of motion, meaning there should be no severe stiffness or flexion limitation. One of the most critical factors is that the anterior cruciate ligament should be intact and functional, since the stability of the prosthesis relies on this natural ligament.

However, certain conditions make partial knee replacement unsuitable. In these cases, total knee replacement would be a more appropriate choice.

Conditions unsuitable for partial knee replacement include:

• Inflammatory joint diseases such as rheumatoid arthritis
• Widespread osteoarthritis affecting more than one compartment of the knee
• Untreated or insufficient anterior cruciate ligament injuries
• Severe knee stiffness (restricted movement)
• Severe, difficult-to-correct deformities (leg misalignment)
• Active or past knee joint infections

Factors such as age and weight, which were once considered strict barriers, are now approached more flexibly. If all other criteria are met, both younger, active patients and older patients can benefit greatly from this surgery. Similarly, being overweight alone is not a strict obstacle, but severe obesity can increase the load on the prosthesis and negatively affect long-term outcomes. Therefore, losing weight before surgery is highly recommended.

The final decision is made after evaluating all these factors together with X-rays and especially MRI scans, which show cartilage and ligaments in detail, while also considering the patient’s expectations and lifestyle. Ultimately, the decision is shared between the patient and the surgeon.

What Are the Advantages of Partial Knee Replacement Surgery?

When applied to the right patient by an experienced surgeon, partial knee replacement surgery offers many important advantages that significantly improve quality of life. Almost all of these benefits stem from the fact that partial knee replacement is less invasive and more tissue-preserving compared to total knee replacement. The less trauma the body experiences, the faster and smoother the recovery.

The main advantages of partial knee replacement are:

• Faster recovery process
• Less postoperative pain
• Shorter hospital stay
• Less blood loss and reduced need for transfusion
• Smaller and more aesthetic surgical scar
• A much more natural knee feel and function
• Better range of motion (especially knee flexion)
• Lower risk of major complications

To expand on these: “Faster recovery” means patients often begin walking the day after surgery and can return to their daily lives within weeks, often without the need for assistive devices. “Less pain” translates into reduced reliance on pain medication and a more comfortable start to the rehabilitation process.

Perhaps the most valuable advantage is the “more natural knee feel.” Preserving the intact ligaments and other compartments of the knee allows the joint to maintain its normal mechanics and proprioception (position sense). As a result, patients feel their knees not as an artificial joint but as their own limb when walking, climbing stairs, or engaging in light physical activity. Scientific studies have also shown that patients with partial knee replacement have significantly lower risks of complications such as infections, blood clots (thrombosis), and cardiopulmonary problems compared to total knee replacement. This makes partial knee replacement a safer option, especially for elderly patients or those with other health issues.

Are There Any Possible Disadvantages or Limitations of Partial Knee Replacement?

As with any surgical procedure, partial knee replacement has potential disadvantages and limitations that need to be considered. Being transparent about these factors allows patients to make the most informed decision about their treatment. The goal is for patients to weigh the potential risks and benefits carefully before proceeding with surgery.

Possible disadvantages or limitations include:

• Risk of osteoarthritis progression in other knee compartments
• Higher likelihood of revision (repeat surgery) compared to total knee replacement
• Technically more demanding surgery
• Limited patient eligibility
• In rare cases, persistent pain after surgery

The most significant issue is the risk of osteoarthritis progression. Partial knee replacement addresses the existing problem but does not cure the underlying disease. This is similar to treating a tooth cavity with a filling—the filling saves that tooth but does not prevent other teeth from decaying. Likewise, healthy compartments of the knee may develop osteoarthritis years later. In such cases, usually 10–15 years after the first surgery, the partial knee prosthesis may need to be revised to a total knee replacement.

As a result, large national registries show that partial knee replacements have higher long-term revision rates compared to total knee replacements. However, this statistic alone can be misleading. In experienced centers and when performed by skilled surgeons, outcomes are excellent and revision rates are low. Moreover, converting a partial knee replacement to a total knee replacement is technically easier than revising an already replaced total knee prosthesis.

Finally, partial knee replacement is a technically precise surgery. Success is closely tied to the surgeon’s expertise and skill. Correct alignment and positioning of the prosthesis are critical for long-term success.

How Does the Partial Knee Replacement Surgery Process Progress?

Partial knee replacement is a process that requires careful planning and meticulous execution from start to finish. This process can be divided into three stages: preoperative, intraoperative, and postoperative.

Preoperative Preparation:

The goal in this phase is to prepare you in the safest and most optimal way for surgery. An anesthesiologist evaluates your overall health and decides the most appropriate anesthesia method (general or spinal/regional). Blood tests, chest X-ray, and ECG are performed. Consultations from other specialties (cardiology, internal medicine, etc.) may be requested if needed. Patients are advised to quit smoking, adjust blood-thinning medications under medical supervision, and maintain surgical site hygiene.

Intraoperative Stage:

On the day of surgery, a team consisting of a surgeon, anesthesiologist, and nurses welcomes you in the operating room. After anesthesia is administered, a small incision of about 7–10 cm is made at the front of the knee. The surgeon reassesses all compartments of the knee to confirm that osteoarthritis is limited to the planned area and that ligaments are intact. Using precise surgical instruments and special cutting guides, the damaged cartilage and underlying bone are carefully removed. Trial implants are placed to check joint alignment and balance. Once everything is confirmed, permanent metal and polyethylene implants are fixed using bone cement. The wound is then closed in layers after final checks.

Postoperative Recovery:

After surgery, you are taken to your room, and pain management begins. Most patients start walking with the assistance of a physiotherapist on the same day or the following day. The hospital stay typically lasts 1–3 days. During this time, basic exercises are taught. Continuing rehabilitation at home or at a physical therapy center after discharge is crucial to the long-term success of the surgery.

The main rehabilitation goals in the first weeks are:

• Controlling pain and swelling
• Achieving full knee extension
• Bending the knee at least 90–110 degrees
• Beginning to strengthen surrounding muscles
• Walking safely without assistive devices

Most patients return to the majority of daily activities within 4–6 weeks. Driving usually resumes in 4–6 weeks, while office work can be started earlier, and physically demanding jobs may require more time.

What Types of Implants Are Used for Partial Knee Replacement?

Partial knee replacement implants generally consist of three main components: a metal piece for the femur (thigh bone), a metal piece for the tibia (shin bone), and a durable polyethylene (plastic) insert that provides a smooth surface between the two. Depending on the mobility of this polyethylene insert, there are two main implant designs: fixed-bearing and mobile-bearing.

Fixed-Bearing Design: This is the more traditional design. The polyethylene insert is firmly locked into the metal base plate placed on the tibia. Similar to a simple door hinge, movement occurs only by the femoral component gliding over this fixed plastic surface. It is technically easier to implant and does not carry the risk of insert dislocation. It has been used safely for many years with excellent reported outcomes.

Mobile-Bearing Design: In this design, the polyethylene insert is not fixed to the metal base plate. During knee movements, the plastic insert can slide forward and backward and rotate slightly. The theory behind this design is to mimic the movement of the natural meniscus, spreading loads over a wider area and potentially reducing polyethylene wear. It offers the potential for more natural knee function. However, a very rare risk specific to this design is dislocation of the polyethylene insert.

Both designs have their own theoretical advantages and potential risks. When long-term results are compared, neither has been proven to be definitively superior. The surgeon’s choice of implant type depends on many factors, including the patient’s anatomy, bone quality, expected activity level, and most importantly, the surgeon’s experience and comfort with that particular implant design.

Frequently Asked Questions