The disease of the knee joint caused by wear (gonarthrosis) is a widespread cause of pain, movement restrictions, and reduced quality of life – especially in older individuals, but increasingly also in active middle‑aged patients. When conservative therapies (such as physiotherapy, injections, weight reduction, orthopedic aids) have reached their limits, the option of a knee prosthesis comes into view.

However, many patients and also some Ärzt*innen think first of a Totalendoprothese, i.e., the complete exchange of all joint surfaces. In suitable indications, there is a less invasive alternative: the Teilgelenkersatz, often in the form of a Schlittenprothese (unicondylar prosthesis). While medial sled prostheses are relatively often discussed, the laterale Schlittenprothese – also the partial replacement in the outer (lateral) compartment – often overlooked or viewed skeptically.

In this article we examine why the lateral sled prosthesis is often underestimated, how it works, who it is suitable for, what risks exist, and what to consider when selecting the surgeon.

Basics: knee prosthesis, partial joint replacement and sled prosthesis

Before we go into detail, it is important to define the terms clearly and understand the basic principles, so that later the specifics of the Lateralen Schlittenprothese become clear.

What is a knee replacement?

The term knee prosthesis (also knee endoprosthesis, knee joint prosthesis) refers to an artificial implantation for the restoration or replacement of the joint surfaces in the knee. The goal is to relieve pain and regain mobility.

Depending on the extent of the disease, various options exist:

• Total knee prosthesis (TEP or TKA, total knee arthroplasty): Replacement of all joint surfaces (femoral, tibial and, if applicable, patella).
• Partial knee arthroplasty (Partial Knee Arthroplasty, UKA for a single compartment or BKA as a bicondylar partial replacement): Only the diseased compartment is replaced, while intact structures are preserved.
• Variants such as patient-specific prostheses also exist.

The advantage of a partial prosthesis is often a gentler operation, less bone substance loss, preservation of ligaments and natural structure, as well as often faster convalescence.

Total endoprosthesis vs. partial joint replacement

Benefits of partial joint replacement:

• Preservation of healthy bone material
• Preservation of ligament structures and a more physiological kinematics
• Smaller operative intervention, often shorter operation time and less blood loss
• Faster rehabilitation and better mobility in daily life
• If later needed, in many cases one can switch to a total prosthesis

Disadvantages and limitations:

• Only possible if the osteoarthritis is limited to one compartment
• Higher demands on the indication and the surgeon's expertise
• Potential for progression of osteoarthritis in other compartments
• In some scenarios (e.g., multi-compartment damage) a total prosthesis is unavoidable

For this reason, partial joint replacement – especially as a sliding prosthesis – is an attractive option when the prerequisites are met.

What is a sliding prosthesis (unicondylar prosthesis)?

The term sliding prosthesis is often used synonymously with unicondylar knee prosthesis. The name „sled“ therefore originates because the implant often glides along only one side (one condyle) and only crowns a single rim of the knee joint – like a „sled“ in the joint.

Features:

• Only one of the two condyles (medial or lateral) is replaced – only where the articular cartilage is destroyed
• The healthy parts of the knee (joint surfaces, meniscus, ligaments, other compartment) remain intact
• The operation is less invasive than a full knee prosthesis
• The movement sequences and the “natural“ knee feeling remain largely preserved

In many clinics one also speaks of a partial knee replacement – a partial replacement of a joint part – and thus the sliding prosthesis is a variant of the partial knee replacement.

Lateral vs. medial sled prosthesis

The majority of UKA procedures is performed on the medial (inner) compartment performed, because osteoarthritis occurs there more frequently. The lateral sled prosthesis (also replacement in the äußeren compartment) is rarer and technically more demanding.

Differences and challenges:

• The anatomical and biomechanical relationships in the lateral compartment differ – e.g., laxity, movement patterns, load distribution
• The indication is tendentially narrower
• The surgeon's need for experience is higher
• Design questions for implants (e.g., mobile vs. fixed bearing) are more nuanced

Precisely because of these particularities, the lateral sled prosthesis is often underestimated – many patients are referred directly to a total prosthesis, even though a partial prosthesis could be sufficient. With careful selection and an experienced surgeon, the Lateral sled prosthesis however can deliver excellent results.

Anatomy and Biomechanics of the Knee Joint

To understand why the Lateral sliding prosthesis is technically demanding – and when it is appropriate – a look at the anatomy and function of the knee joint is worthwhile.

Structure of the knee joint

The knee joint is a complex joint that encloses the joint surfaces of the femur and tibia, the patella, menisci, ligaments (cruciate ligaments, collateral ligaments) as well as soft tissues. It is primarily a rolling‑gliding joint with certain rotational components.

Important structures:

• Joint cartilage: provides low-friction movement
• Menisci (where present): contribute to load distribution
• Cruciate and collateral ligaments: ensure stability
• Joint capsule and musculature: control, guidance and stabilization
• Compartments: the knee can be divided into a medial (inner), lateral (outer) and patellofemoral (kneecap) compartment

If osteoarthritis affects only one compartment, a targeted partial replacement can often restore function very well.

Load distribution, ligaments, gliding movements

During loading, the knee joint is subjected to forces that are significantly higher than body weight (depending on the type of movement 2–3× or more). The load is transferred over the joint surfaces. Even the smallest imbalances can lead to increased wear.

Important are:

• Ligament tension: Especially the collateral ligament (e.g., the lateral collateral ligament) plays a role in gliding in the lateral compartment
• Gliding movements (translation and rotation): under load the femoral condyle slides partly backward/forward, combined with rotation
• Screw-Home mechanism: During extension, the lower leg rotates slightly – a feature that has a stronger effect in the lateral compartment

These biomechanical nuances make it necessary that a Lateral sliding prosthesis reproduces the natural movement pattern as accurately as possible.

Specifics of the lateral compartment

Some particularities of the lateral knee (compared to the medial):

1. Greater flexibility: The lateral side is generally slightly more lax than the medial – meaning it allows more movement
2. Different contact mechanisms: During flexion and extension the contact surfaces in the lateral compartment change differently than in the medial
3. Tendency to subluxation with mobile Einsätzen: With mobile bearing designs, the risk that the inlay shifts is slightly höher on the lateral side
4. Anatomical variance: The lateral femoral condyle and the tibial plateau structures können be more variable

These particularities require special care in design, implant selection, and surgical technique to ensure optimal function and longevity.

Indications and contraindications for the lateral sliding prosthesis

Not every knee osteoarthritis is suitable für a lateral partial prosthesis. An exact indication is essential für success and longevity. Here we discuss when a Lateral sliding prosthesis is appropriate and what must be considered.

When is a lateral sliding prosthesis appropriate?

In general, a lateral partial knee prosthesis is appropriate when:

• the osteoarthritis isolated or überwiegend in the lateral compartment is located (e.g., Valgus gonarthrosis)
• the medial compartment is largely intact, without significant cartilage damage
• the ligament apparatus (especially cruciate and collateral ligaments) is stable
• the leg axis (valgus deformity) is correctable or minimal
• with good mobility and without significant contractures
• the patient has good bone quality

In the literature, such indications for lateral UKA are described, e.g., for isolated lateral osteoarthritis or avascular necrosis of the lateral femoral condyle.

Advantages with appropriate indication:

• Preservation of healthy structures
• Less invasive surgery
• Better mobility and gait feeling
• Possible option to switch to a total prosthesis at a later time

Distinction: When is a Total prosthesis more appropriate?

In some situations, the path to a total prosthesis is unavoidable:

• When multiple compartments are severely affected (e.g., medial + lateral + patellofemoral osteoarthritis)
• When severe deformities, instabilities or contractures are present
• If the ligamentous apparatus is severely damaged or insufficient
• In inflammatory diseases (e.g., rheumatoid arthritis)
• In case of significant axis deviation that cannot be corrected
• If other surgeries (e.g., corrective osteotomy) have already been performed during the course and the anatomy is significantly altered

In such cases a complete knee prosthesis (total knee arthroplasty) a more stable and comprehensive solution.

Exclusion criteria and special risks

Following contraindications or risks should be considered:

• Massively damaged medial compartment or central cartilage damage (gonarthrosis in the medial area)
• Significant axis deformity (e.g., valgus > 15°), not correctable
• Instability of the collateral or cruciate ligaments, contractures > 15°, flexion capability < 100° SpringerLink
• Fractures or significant bone defects, especially in the tibial plateau
• Previous realignment surgeries, prosthesis failure, revisions
• Rheumatoid disease or other systemic joint disorders
• Infections or poor soft tissue conditions

The literature consistently emphasizes that a lack of proper indication discipline or insufficient surgical experience are the main causes of failure.

Mobile bearing vs. Fixed bearing – Advantages and disadvantages

A central design difference exists between mobile bearing (mobile inserts) and fixed bearing (fixed polyethylene) implants:

Mobile bearing (mobile inlay):

Benefits:

• Potentially lower wear, as the inlay adapts
• Gliding motion can occur more physiologically

Disadvantages:

• Higher risk for dislocation of the insert, especially with the lateral sled prosthesis.

Fixed bearing (fixed polyethylene inlay):

Benefits:

• Lower risk of inlay dislocation
• More stable positioning through a rigid design

Disadvantages:

• potentially slightly higher wear, as there is less flexibility in the adjustment
• Sliding movement may theoretically be slightly more restricted

From the literature it emerges that for lateral partial knee replacement fixed inlays are often preferred to minimize the dislocation risk. In many cases therefore Fixed bearing is recommended as the safer choice.

Rehabilitation and aftercare

A good operation is only half – the success depends heavily on rehabilitation and the aftercare concept. Here are the essential steps and recommendations for the postoperative phase after implantation of a Lateral sliding prosthesis.

Postoperative Mobilization

• Usually, early mobilization takes place already on the day of surgery or the first day thereafter
• Full weight-bearing is often allowed immediately – depending on intra‑operative stability and the surgeon’s decision
• During mobilization with walking aids (e.g., crutches) to relieve load in the first days

The goal is to promote mobility, minimize thrombosis risks, and prevent muscle loss.

Physiotherapy and load training

Physiotherapy should be carried out gradually:

1. Early phase (first week): passive/assisted exercises, muscle activation (Quadriceps, Hamstrings)
2. Mid phase (2.–6 weeks): active exercises, strength training, balance and coordination
3. Late phase (from week 6): functional training, daily activities, stair climbing, sports and leisure activities

The exact course depends on the individual healing process, muscle strength, and stability.

Sports, daily movements and long‑term behavior

• Light sports such as cycling, swimming or walking are often possible early on
• Intensive sports (e.g., tennis, handball) should only be performed after consultation and under physiotherapeutic supervision
• The load on the knee joint should be increased gradually
• Regular check-ups (clinical and radiological) are indicated
• If there are symptoms in the medial compartment, it should be clarified early whether progression is present

With good rehabilitation and appropriate loading, many patients can achieve a high activity level with the Lateral sled prosthesis achieve.

Advantages of a lateral sliding prosthesis at a glance

The lateral sliding prosthesis offers many advantages:

• Minimally invasive procedure
• Preservation of the native cruciate ligament apparatus
• Shorter rehabilitation time
• More natural feeling of movement
• High satisfaction and functionality
• Easy expandability to knee TEP if needed

Especially for active patients aged 50 to 70 with isolated lateral compartment osteoarthritis, the procedure is often the best solution, to preserve quality of life and mobility in the long term.

Frequently Asked Questions (FAQ)

Question: Is a Lateral sled prosthesis für every patient with knee osteoarthritis suitable?
Answer: No – it is only suitable when the osteoarthritis überwiegend in the lateral compartment lies, the Bänder are stable and the medial compartment is largely intact. A careful diagnosis is mandatory.

Question: How long hält a sled prosthesis?
Answer: With correct indication and surgery, studies report über Überlebensraten of 90% and more at 10 years or more. For the lateral variant data are rarer, but in ausgewählten studies 10-year Überlebensraten of 94% or more have been shown.

Question: Is there a risk that später still a Total prosthesis nötig will be?
Answer: Yes – especially if the healthy compartment degenerates. Then usually a switch to a Total prosthesis can be performed.

Question: Is the operation riskier than a Total prosthesis?
Answer: Not necessarily. As long as the operation is performed under optimal conditions (durchgeführt), the risks are comparable or even lower (as a more invasive procedure is avoided). But a misplacement or indication error erhöht the risk.

Question: How quickly is the return to everyday life possible?
Answer: With good healing and rehabilitation many patients can resume everyday activities within weeks, often faster than after a total knee replacement.

Conclusion & Outlook

The Lateral sliding prosthesis (lateral partial knee replacement) is an often underestimated, but very sensible option with carefully selected indication. It offers the chance to reduce pain and preserve mobility – with less invasive surgery and preservation of healthy structures – compared to a total knee replacement.

The key to success lies in:

• an exact indication
• high operative experience
• optimal implant design (often with fixed inlay)
• careful surgical technique
• structured rehabilitation
• Selection of a specialized knee specialist

Strategies for selecting the right specialist

A decisive factor für the success of a Lateral sled prosthesis is the selection of an experienced, specialized knee surgeon. Here are some guidelines and criteria:

What to look for in a knee surgeon

• Specialization and experience in the field of knee endoprosthetics, especially partial joint replacement
• Case numbers – the more corresponding procedures per year, the better (surgeon and clinic)
• Publications/guideline recognition – does the doctor have experience with scientific Veröffentlichungen or specialization in professional societies?
• Technical equipment – modern implant systems, navigation, planning tools
• Transparency bezüglich risks, experiences and alternatives
• Aftercare & Rehabilitation concept – comprehensive follow‑up, physiotherapy, Qualitätskontrollen
• Patient recommendations and experience histories – reports from other Patient*innen

The impact of experience and case numbers

In endoprosthetics it has been repeatedly demonstrated that clinics and surgeons with high case numbers achieve better results and fewer complications. This also applies to the complex procedure of the lateral sliding prosthesis, where the learning curve is steeper.

Studies show that at specialized centers the revision rates and complications are significantly lower. Therefore it makes sense to choose a specialist with sufficient experience in partial knee replacement.

Lateral sliding prosthesis – the underestimated option with great potential

The lateral sled prosthesis is far more than a niche solution.
It offers for selected patients with isolated lateral arthrosis a high-quality, joint-preserving and functionally superior alternative to the total prosthesis.

If the knee hurts only on one side, it is worthwhile to discuss this option with an experienced knee specialist to discuss.

At the Endoprotheticum Rhein-Main in Mainz under the leadership of Prof. Dr. Karl Philipp Kutzner patients receive a individual consultation, a precise diagnostics and a customized treatment, which meets the highest medical and functional requirements.

In Germany there are several centers that focus on knee endoprosthetics, especially partial knee replacement and sled prostheses. One of them is the Endoprotheticum Rhein-Main in Mainz  with the knee specialist Prof. Kutzner.

• A specialized center like the Endoprotheticum can generally offer state-of-the-art implant models, technical equipment, experienced teams and structured aftercare
• For patients this can mean: careful diagnostics, individually tailored surgery and optimized rehabilitation
• In cases where the lateral sled prosthesis is an option, a specialist with extensive experience is especially valuable

If you are interested: here können you can schedule an appointment  www.endoprotheticum.de