The disease of the knee joint due to wear (gonarthrosis) is a widespread cause of pain, movement restrictions and reduced quality of life – especially in older people, 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 knee prosthesis comes into view.

But many patients and also some physicians think first of a Total knee arthroplasty, i.e., the complete replacement of all joint surfaces. In suitable indications there is a less invasive alternative: the partial knee replacement, often in the form of a sliding prosthesis (unicondylar prosthesis). While medial sliding prostheses are relatively often discussed, the lateral sliding prosthesis – i.e., the partial replacement of the outer (lateral) compartment – is 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 Lateral sled prosthesis become clear.

What is a knee replacement?

The term Knee prosthesis (also knee endoprosthesis, knee joint prosthesis) refers to an artificial implantation to restore or replace 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 possibly patella).
• Partial knee replacement (Partial Knee Arthroplasty, UKA for only one 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“ comes from the fact that the implant often glides along only one side (a condyle) and only crowns a single facet of the knee joint roll– 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 sled prosthesis is a variant of the partial knee replacement.

Lateral vs. medial sled prosthesis

The majority of UKA procedures are performed on the medial (inner) compartment, because osteoarthritis occurs there more frequently. The lateral sled prosthesis (also replacement of the outer compartment) is less common 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 – it is worthwhile to look at the anatomy and function of the knee joint.

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:

• Articular 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 is more pronounced 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 looser 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 compartment
3. Tendency towards subluxation in mobile applications: With mobile bearing designs, the risk of the inlay shifting on the lateral side is slightly higher
4. Anatomical variance: The lateral femoral condyle and the tibial plateau structures can 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 for a lateral partial knee prosthesis. An exact indication is essential for 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 predominantly 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:

• If multiple compartments are severely affected (e.g., medial + lateral + patellofemoral osteoarthritis)
• If 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) provides 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 (medial knee osteoarthritis)
• 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 of dislocation (dislocation) of the inlay, especially in the lateral sliding 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

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

Rehabilitation and aftercare

A good operation is only half the battle – the success depends heavily on rehabilitation and the aftercare concept. Here are the essential steps and recommendations for the postoperative phase after implanting 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 movement exercises, muscle activation (quadriceps, hamstrings)
2. Mid phase (weeks 2–6): active movement exercises, strength training, balance and coordination
3. Late phase (from week 6): functional training, daily movements, 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 rehab and appropriate loading, many patients can achieve a high activity level long-term with the Lateral sliding 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 arthrosis, the procedure is often the best solution, to secure quality of life and mobility in the long term.

Frequently Asked Questions (FAQ)

Question: Is a Lateral sliding prosthesis suitable for every patient with knee osteoarthritis?
Answer: No – it is only suitable when the osteoarthritis is predominantly in the lateral compartment, the ligaments are stable and the medial compartment is largely intact. Careful diagnostics are essential.

Question: How long does a sled prosthesis last?
Answer: With proper indication and surgery, studies report survival rates of 90% or more at 10 years or more. For the lateral variant, data are rarer, but selected studies have shown 10‑year survival rates of 94% or higher.

Question: Is there a risk that a total prosthesis will later be needed?
Answer: Yes – especially if the healthy compartment degenerates. Then a switch to a total prosthesis is usually possible.

Question: Is the operation riskier than a total knee replacement?
Answer: Not necessarily. As long as the operation is performed under optimal conditions, the risks are comparable or even lower (since a more invasive procedure is avoided). However, a misplacement or indication error increases the risk.

Question: How quickly can one return to daily life?
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 joint replacement of the knee) is an often underestimated, but very sensible option when 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 prosthesis.

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 for the success of a Lateral sliding 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 knee arthroplasty, especially partial knee replacement
• Case volume – the more relevant procedures per year, the better (surgeon and clinic)
• Publications/Guideline recognition – does the doctor have experience with scientific publications or specialization in professional societies?
• Technical equipment – modern implant systems, navigation, planning tools
• Transparency regarding risks, experiences and alternatives
• Aftercare & Rehabilitation concept – comprehensive follow-up care, physiotherapy, quality controls
• Patient recommendations and course experiences – reports from other patients

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

Wenn das Knie nur auf einer Seite schmerzt, lohnt es sich, diese Option mit einem erfahrenen Kniespezialisten zu besprechen.

Im Endoprotheticum Rhein-Main in Mainz unter der Leitung von Prof. Dr. Karl Philipp Kutzner erhalten Patient:innen eine individuelle Beratung, eine präzise Diagnostik und eine maßgeschneiderte Behandlung, die sowohl medizinisch als auch funktionell höchste Ansprüche erfüllt.

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: you can schedule an appointment here www.endoprotheticum.de