The sled prosthesis – also referred to as unicompartmental knee replacement or partial knee replacement – is a modern and tissue-sparing solution for patients with isolated osteoarthritis of the knee joint. While many patients initially consider a total knee replacement, the sled prosthesis offers a minimally invasive and functionally convincing alternative. This detailed article shows you why less is often more with the sled prosthesis. You will also learn how modern surgical techniques, new implant materials, and precise diagnostics lead to better outcomes and faster rehabilitation.

The Knee in Focus – When Every Movement Hurts

The knee joint is one of the most complex and heavily stressed joints in the human body. Millions of people suffer from osteoarthritis – a degenerative joint disease that leads to pain, limited mobility, and ultimately a significant loss of quality of life. While advanced osteoarthritis often requires a complete joint replacement, there is a significantly gentler alternative for certain patient groups: the sledge prosthesis, also known as unicondylar knee prosthesis or partial joint replacement.

What is a sled prosthesis?

The sled prosthesis is a form of artificial knee joint in which only one part of the joint is replaced - usually the inner or outer joint compartment (medial or lateral). Unlike a total knee replacement (TKR), in which all joint surfaces are replaced, the healthy structures such as the cruciate ligaments, collateral ligaments and the unaffected joint section remain in place with the sled prosthesis.

This procedure is particularly suitable for patients who suffer from unilateral osteoarthritis and have an intact remaining knee joint. The lower bone loss is also advantageous, making subsequent revision surgeries easier.

Structure of the Sled Prosthesis

• Metal components: The femoral and tibial components are typically made of high-quality titanium or cobalt-chromium.
• Polyethylene Insert: Serves as a gliding surface between the two metal components.
• Fixation: Usually cemented, in individual cases also possible without cement.

Indications for a sled prosthesis

Not every patient with knee osteoarthritis is automatically a candidate for a sled prosthesis. The ideal prerequisites are:

• Isolated medial or lateral gonarthrosis
• Preservation of the anterior and posterior cruciate ligaments
• Intact lateral or medial compartments
• No significant malalignment or instability
• Good general health and motivation for rehabilitation

Precise imaging – ideally in the form of MRI or X-ray diagnostics with stress images – is essential to assess the extent of cartilage damage and the integrity of the remaining joint structures.

When is a unicompartmental knee arthroplasty suitable?

A sledge prosthesis is particularly suitable for patients with:

• Isolated osteoarthritis: If only one part of the knee joint is affected.
• Intact ligament apparatus: The anterior cruciate ligament, in particular, should be functional.
• Good bone substance: Adequate bone density is necessary for anchoring the prosthesis.
• Active Lifestyle: Patients who wish to remain active benefit from the mobility of the sled prosthesis.

Benefits of the unicompartmental knee arthroplasty

1. Joint preservation

The sled prosthesis leaves large parts of the native knee joint intact, allowing for a more natural feeling of movement and physiological joint kinematics.

2. Less invasive procedure

The surgical approach is smaller, fewer soft tissues are damaged and blood loss is lower.

3. Faster Rehabilitation

Many patients can quickly load the operated leg again and return to everyday life and work faster.

4. Better revision options

Since only part of the joint is replaced, more bone is preserved. If further signs of wear occur, conversion to a total endoprosthesis is more easily possible.

Surgical technique of unicompartmental knee replacement – precision is crucial

The implantation is usually performed minimally invasively and with the use of modern aids such as computer navigation or robotic-assisted technology. The correct axial position and alignment of the components are crucial to achieve ideal biomechanics.

The affected compartment - medial or lateral - is smoothed, prepared, and fitted with a custom-made prosthesis. Usually, it is fixed with cement, but there are also cement-free designs.

Material selection: Modern implants for maximum durability

Current sled prostheses consist of highly cross-linked polyethylene inlays in combination with titanium or cobalt-chromium components. The sliding surfaces are extremely abrasion-resistant, which has significantly extended the lifespan of the prostheses. Long-term studies show survival rates of over 15 years with high patient satisfaction.

Postoperative care and rehabilitation with unicompartmental knee replacement

Mobilization with forearm crutches is possible on the day of surgery. Full weight-bearing is usually allowed immediately or after a few days, depending on the surgical technique. Early physiotherapeutic care aims to quickly restore mobility, muscle strength, and coordination.

Rehabilitation typically lasts 3–4 weeks and can be inpatient or outpatient. The goal is to return to daily life, work, and leisure activities as soon as possible.

Comparison between sled prosthesis and total knee replacement (TKR)

A key point in deciding for or against a unicompartmental knee arthroplasty is the comparison with total knee arthroplasty (TKA). Both procedures are used for osteoarthritis, but differ fundamentally in indication, surgical effort, recovery time and long-term outcome.

Anatomical Differences

The total knee replacement replaces the entire joint surface of the knee joint - both on the thigh and the shinbone side. The sled prosthesis, on the other hand, is limited to one of the three joint compartments (usually the medial compartment), with the remaining joint structures - in particular the cruciate ligaments, lateral joint compartment and patella - being preserved.

Extent of surgery

The operation to implant a unicompartmental knee arthroplasty is significantly smaller because only part of the joint is replaced. It is often performed minimally invasively, with smaller incisions, less soft tissue damage and a significantly reduced risk of bleeding. The intervention is therefore often shorter, less risky and better tolerated for the patient.

Functionality and sense of movement

Because the natural ligaments and bone structures are preserved with unicompartmental knee replacement, many patients feel the knee is more "natural" after surgery. The proprioceptive feedback is better, and the gait pattern is more physiological. In contrast, a total knee replacement provides more comprehensive care for advanced arthrosis but is associated with a more artificial feeling of movement.

rehabilitation duration

Rehabilitation after a unicompartmental knee replacement usually proceeds faster and more easily. Patients less frequently require longer rehabilitation stays and achieve full weight-bearing capacity earlier. Climbing stairs and engaging in sports activities also generally become easier and faster.

Complication rate

The complication rate - especially infections and thrombosis - is statistically lower with sled prostheses. Revision surgeries are also easier to perform because less bone is removed. In contrast, revision surgery for a TEP is technically more complex.

Long-term indications

TEP is indicated in cases where there is already tricompartmental osteoarthritis or ligament instability. In cases of localized osteoarthritis, the sled prosthesis is the method of choice - not least due to the potential possibility of switching to a TEP later if necessary.

When is a total endoprosthesis the better choice?

A sled prosthesis is not always sufficient. In cases of advanced osteoarthritis in multiple compartments, instabilities, or ligament injuries, a complete knee TEP is more sensible. Also, in cases of inflammatory-rheumatic underlying diseases or complex malalignments, a total endoprosthesis is the better option.

Sports and activity after sled prosthesis

Many patients can participate actively in life again after surgery. Especially joint-friendly sports such as hiking, swimming, cycling or Nordic walking are possible without problems. Golf or cross-country skiing can also be practiced - after individual consultation. High-dynamic or joint-stressing sports such as jogging or tennis should be viewed with caution.

Risks and complications of a sled prosthesis – what you should know

Although it is a comparatively gentle procedure, the unicompartmental prosthesis is also a surgical intervention with certain risks:

• Loosening of the prosthesis (rare, with overload)
• Progression of osteoarthritis in other compartments
• Pain with incorrect positioning
• Infections (very rare in aseptic conditions)

Long-term results and durability of the sled prosthesis

Current studies show that modern sled prostheses have a survival rate of over 90% after 10–15 years . The correct patient selection and precise surgical technique are crucial here.

Contrary to earlier assumptions, modern sled prostheses now show very good long-term results. Technological advances, improved materials and more precise surgical techniques contribute significantly to the extended durability.

Durability in years

Modern sled prostheses achieve service lives of 15 years or more. Studies show that over 90% of implanted partial prostheses are still fully functional after 10 years. With correct indication and precise implantation, survival rates of over 95% after ten years are not uncommon.

Factors influencing durability

• Indication: A precise selection of patients is crucial. Unicompartmental prostheses are particularly suitable for isolated medial gonarthrosis.
• Surgical experience: High case numbers and expertise of the operator are important quality factors.
• Body weight and activity level: Patients with high BMI or extreme stress on the knee joint statistically have a slightly higher revision rate.
• Implant design: Modern unicompartmental prostheses are modular, anatomically shaped, and equipped with highly wear-resistant gliding pairs, which increases the service life.

Revision options

A major advantage of the sled prosthesis is that in the event of failure, a complex revision surgery is not immediately necessary. In most cases, the sled prosthesis can be converted into a standard total endoprosthesis without the need for additional special implants.

Patient satisfaction

Patients who have received a sled prosthesis often report high satisfaction, quick return to daily activities and physical stress. Especially in younger patients, the subjective feeling of movement is usually better than after a total endoprosthesis.

Conclusion: The unicompartmental knee replacement as a modern solution for selected patients

Partial joint replacement with a sled prosthesis represents a minimally invasive and everyday suitable solution for many patients with unilateral knee arthrosis. Thanks to modern surgical techniques, precise diagnostics and high-quality materials, the natural joint feeling can often be maintained or restored. Prerequisites for success are a precise patient selection and close follow-up care.

FAQs about the sled prosthesis:

What is the difference between a unicompartmental knee replacement and a total knee replacement? A unicompartmental knee replacement replaces only part of the knee joint, whereas a total knee replacement replaces the entire joint.

How long does a sled prosthesis last? The durability is on average 15–20 years – depending on the load and implant type.

When can I resume sports after surgery? Gentle sports like cycling or swimming are often possible again after a few weeks.

Can I go hiking with a sled prosthesis? Yes, hiking is one of the recommended activities after surgery.

How big is the scar? Usually, a minimally invasive incision of approx. 8–10 cm is sufficient.

Are there any risks? As with any surgery, there are risks such as infections, thrombosis, or loosening of the prosthesis – however, these are rare.