Knee Replacement: Everything You Need to Know About Artificial Knee Joints, Surgery, and Modern Total Knee Replacement (TKR)

A knee replacement (artificial knee joint, knee endoprosthesis) is a replacement for the knee joint. During the procedure, doctors replace part or all of the joint (total knee replacement = TKR).

Knee replacement surgery is the most commonly performed orthopedic procedure in Germany. Patients with advanced knee osteoarthritis, in particular, benefit from this procedure. It restores the knee joint’s function and significantly improves quality of life.

A knee replacement typically lasts 15 years or longer.

The most common reason for a knee replacement is osteoarthritis of the knee (gonarthrosis). Gonarthrosis is a painful, pathological wear and tear of the knee joint.

Knee osteoarthritis can develop for several reasons:

• Following bone fractures and knee injuries (to the meniscus and cruciate ligaments), without timely or adequate treatment
• Due to misalignments in the knee (such as bowlegs and knock-knees)
• As a result of conditions such as rheumatic diseases
• Due to obesity
• Due to a family history of the condition

Knee replacement surgery is recommended in the following cases:

• When other conservative and joint-preserving treatments are ineffective
• When the patient’s quality of life is impaired by increasing pain
• When limited mobility in the knee causes the patient significant distress

In rare cases, conditions other than osteoarthritis may also necessitate a knee replacement, such as:

• Hemophilia
• Gout
• Osteonecrosis and
• Inflammation

Depending on the severity of knee osteoarthritis and the patient’s needs, knee replacement specialists have several types to choose from.

In general, medical professionals in the field of endoprosthetics distinguish between:

• Total knee replacement: total knee arthroplasty (TKA), complete artificial knee joint, bicondylar surface replacement, bicondylar sled prosthesis) and
• Partial knee replacement: unicondylar sliding prosthesis, unicondylar surface replacement
• With a unicondylar sliding prosthesis, doctors replace only one part—usually the inner side of the knee joint. This often restores normal mobility.

In total knee arthroplasty (TKA), surgeons replace the entire knee joint with a surface replacement. Here, the surgeon chooses between a CR (posterior cruciate) or PS (posterior stabilized) version. The CR version is used when the posterior cruciate ligament is intact, while the PS version is used when the cruciate ligament is not intact.

In addition to the sliding prosthesis, there is also the coupled knee prosthesis, which offers more stable support in complex cases.

Furthermore, a total knee replacement can be performed as an axis-guided knee prosthesis. In this type, the components of the artificial knee joint are connected, i.e., coupled.

These systems are suitable for:

• Significant misalignments
• Loss of ligament function
• Revision surgeries

Damage to the collateral ligaments can also lead to joint wear over time.

If a patient has metal allergies, hypoallergenic implants are used instead. Patients with a nickel allergy receive a special implant made of polyethylene or other materials.

The artificial knee joint is typically anchored using a special bone cement (a fast-setting plastic containing antibiotics). The prosthesis is either cemented—that is, fixed with bone cement—or mechanically anchored in the bone.

There is also a hybrid fixation method. In this procedure, doctors secure the lower leg component with bone cement. They clamp the thigh component into place in the thigh area. Over time, the thigh component must then integrate into the bone. 

In certain cases, the cartilage on the kneecap can also be replaced by implanting a patellar component into the knee prosthesis.

A total knee replacement replaces the entire joint surface, while a partial knee replacement replaces only a portion @ Adisak /AdobeStock

Before the procedure, the doctor decides together with the patient which type of knee prosthesis and which fixation technique will be used. The choice depends on the mobility and stability of the knee joint and the patient’s individual anatomy.

Types of knee replacements include:

• Unicondylar sled
• Bicondylar sled or
• Axial-guided knee prosthesis

Knee replacement specialists perform the procedure on an inpatient basis under general or regional anesthesia.

During the procedure, the surgeon exposes the joint, removes the worn joint surfaces, and prepares the bone to fit the artificial joint.

The adaptation is achieved through:

• Preoperative planning using specialized planning software
• A custom template fabricated preoperatively, or
• Custom-made implants

Depending on the type of knee replacement, the surgery takes between 1 and 2.5 hours.

To manage postoperative pain, patients receive local infiltration anesthesia during surgery, which typically lasts 48 hours.

In addition, pain management protocols are used so that the patient can get out of bed and begin physical therapy on the day of surgery. In many cases, patients are able to bear weight with virtually no pain six months after surgery.

As with any surgery, complications can occur during knee replacement surgery. These include infections, bleeding, or, in rare cases, an allergic reaction—such as a nickel allergy. Another possible long-term complication is loosening of the prosthesis, which can lead to renewed pain. In rare cases, the prosthesis must be surgically removed years later. However, the lifespan of modern knee replacements is now 15 to 20 years or longer, depending on the level of stress placed on the joint, the quality of the materials, and the patient’s physical activity. Regular follow-up examinations with an orthopedic surgeon help identify risks early on and ensure the long-term function of the knee prosthesis. Potential complications also include thrombosis or damage to surrounding structures.

Postoperative pain is less severe thanks to pain management that begins during surgery. As a result, patients can begin their first passive range-of-motion exercises as early as the day after surgery.

Patients can then begin physical therapy exercises and take their first steps with assistance. A 6- to 10-day hospital stay is followed by 3- to 4-weeks of outpatient or inpatient rehabilitation.

Most patients are able to bear weight on the knee joint again after a few weeks. The doctor then decides whether and when the patient may resume low-impact sports. Suitable options include joint-friendly activities such as swimming or cycling, which make climbing stairs easier in daily life. However, the patient should avoid contact sports in the long term.

In most cases, full weight-bearing is permitted immediately after the procedure @ vschlichting /AdobeStock

Knee replacement specialists are typically specialists in:

• Orthopedics
• Knee surgery
• Trauma surgery, and
• Endoprosthetics

Specialized clinics for knee replacements include orthopedic treatment centers and trauma surgery clinics.

It is not possible to designate a hospital as the “best clinic” or “top clinic” for knee replacement surgery. However, there are certainly doctors and hospitals that specialize in knee replacement surgery. As a result, they have extensive experience. You can find these experts in the Leading Medicine Guide.

In the Leading Medicine Guide, you’ll find selected, highly qualified medical experts and specialists. All listed doctors possess a high level of professional expertise in the field of knee replacement surgery.