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Knee Endoprosthesis: Knee Replacement Explained

A knee endoprosthesis is an artificial knee joint implanted to replace a severely damaged natural joint, relieving chronic pain and restoring mobility in patients with advanced arthritis.

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Things worth knowing about "Knee endoprosthesis"

A knee endoprosthesis is an artificial knee joint implanted to replace a severely damaged natural joint, relieving chronic pain and restoring mobility in patients with advanced arthritis.

What is a Knee Endoprosthesis?

A knee endoprosthesis – commonly referred to as a knee replacement or total knee arthroplasty (TKA) – is a surgical implant that replaces the damaged surfaces of the knee joint, either partially or entirely. The implant typically consists of metal alloy components that resurface the femur (thighbone) and tibia (shinbone), combined with a high-density polyethylene spacer that acts as a smooth gliding surface. The primary goals of the procedure are to eliminate persistent knee pain, restore joint function, and significantly improve the patient's quality of life.

Indications: When is a Knee Replacement Needed?

The most common reason for knee replacement surgery is osteoarthritis of the knee (gonarthrosis), a degenerative joint disease in which the protective cartilage gradually wears away. Other indications include:

Rheumatoid arthritis: An autoimmune disease causing chronic inflammation and joint destruction
Post-traumatic arthritis: Joint degeneration following a knee injury or fracture
Avascular necrosis: Death of bone tissue due to reduced blood supply
Severe knee deformities that cannot be adequately managed with non-surgical treatments

Surgery is generally considered only after conservative treatments such as physiotherapy, pain medications, and intra-articular injections have been exhausted.

Types of Knee Endoprosthesis

Total Knee Replacement (TKR)

In a total knee replacement, all three compartments of the knee joint are resurfaced: the medial (inner), lateral (outer), and patellofemoral (kneecap) compartments. This is the most common type, used when damage is widespread throughout the joint.

Unicompartmental (Partial) Knee Replacement

A unicompartmental or partial knee replacement resurfaces only the damaged portion of the knee – most often the medial compartment. It is a less invasive option for patients with isolated, single-compartment arthritis and preserved ligament function.

Patellofemoral Resurfacing

In selected cases, the back surface of the kneecap (patella) is additionally replaced with a polyethylene component, particularly when significant patellofemoral arthritis is present.

The Surgical Procedure

Knee replacement surgery is typically performed under general anesthesia or spinal anesthesia and takes approximately one to two hours. The surgeon removes the damaged cartilage and bone from the joint surfaces and attaches the prosthetic components either using bone cement (cemented fixation) or by allowing the bone to grow into a specially textured implant surface (cementless fixation). Both techniques have their own advantages, and the choice depends on the individual patient's bone quality and age.

Rehabilitation and Recovery

Post-operative rehabilitation typically begins within the first one to two days after surgery. Physiotherapy is essential for building muscle strength around the knee, regaining range of motion, and restoring normal walking patterns. The recovery process generally involves:

Early mobilization in the hospital (approximately 5–10 days inpatient stay)
Inpatient or outpatient rehabilitation program (3–6 weeks)
Ongoing outpatient physiotherapy over several months
Regular follow-up appointments for implant monitoring

Full recovery and optimal joint function are typically achieved within 6 to 12 months following surgery.

Risks and Possible Complications

As with any surgical procedure, knee replacement carries certain risks that patients should be aware of:

Deep vein thrombosis and pulmonary embolism: Blood clot formation, routinely prevented with anticoagulant medications
Infection: Bacterial infection of the implant, which may rarely require revision surgery
Implant loosening: Long-term loosening of the prosthesis from the bone
Nerve or vessel injury: Temporary or permanent numbness or weakness around the knee
Stiffness: Reduced range of motion, particularly in terms of knee flexion

Longevity and Long-Term Outcomes

Modern knee endoprostheses have an average lifespan of 15 to 20 years, with many lasting even longer. Clinical data show that more than 90% of patients report good to excellent outcomes 10 years after surgery. Factors such as body weight, physical activity level, and adherence to rehabilitation significantly influence implant longevity. If the prosthesis wears out or loosens, a revision surgery (implant exchange) can be performed.

References

Carr AJ et al. – Knee replacement. The Lancet, 379(9823):1331–1340 (2012). PubMed PMID: 22398175.
National Institute for Health and Care Excellence (NICE): Joint replacement (primary): hip, knee and shoulder. NICE Guideline NG157 (2020). Available at: nice.org.uk.
Endoprothesenregister Deutschland (EPRD): Annual Report 2023. German Institute for Orthopaedic Research, Berlin.

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