Mosaicplasty: Surgical Repair for Cartilage Damage

What is Mosaicplasty?

Mosaicplasty is a surgical procedure designed to repair localized areas of damaged articular cartilage in a joint, typically the knee, by transplanting healthy cartilage and bone plugs from a less critical area of the patient's own joint.

Understanding Articular Cartilage Damage

Articular cartilage is the smooth, glistening tissue that covers the ends of bones within a joint, allowing them to glide effortlessly against each other during movement. Unlike many other tissues, articular cartilage has a very limited capacity for self-repair due to its avascular nature (lack of blood supply). When this cartilage is damaged—whether through acute trauma, repetitive stress, or degenerative processes—it can lead to pain, swelling, stiffness, and mechanical symptoms like catching or locking. Untreated, these defects can progress to more widespread osteoarthritis.

What is Mosaicplasty? (Detailed Explanation)

Mosaicplasty, also known as an Osteochondral Autograft Transfer System (OATS), is a restorative surgical technique aimed at addressing specific, well-defined areas of full-thickness articular cartilage loss. The fundamental principle involves harvesting small, cylindrical plugs of healthy cartilage and underlying bone (osteochondral grafts) from a non-weight-bearing region of the patient's own joint (the donor site) and transplanting them into the prepared defect in the damaged, weight-bearing area (the recipient site). The term "mosaic" refers to the pattern created by placing multiple small grafts side-by-side to fill the defect, resembling a mosaic tile pattern.

How is Mosaicplasty Performed?

The procedure typically involves several key steps:

• Donor Site Selection: The surgeon identifies an area within the same joint (most commonly the knee, but also ankle or hip) that is not subject to significant weight-bearing or stress. This ensures that harvesting the plugs from this site will not compromise joint function.
• Graft Harvesting: Using specialized cylindrical coring instruments, the surgeon carefully extracts one or more osteochondral plugs from the chosen donor site. Each plug contains both healthy articular cartilage on top and a small cylinder of subchondral bone beneath.
• Recipient Site Preparation: The damaged cartilage area is meticulously prepared. The surgeon removes the unhealthy cartilage and bone to create precisely sized holes that match the harvested grafts.
• Graft Implantation: The harvested osteochondral plugs are then carefully inserted, cartilage-side up, into the prepared holes in the recipient site. The goal is to achieve a snug fit and ensure the cartilage surface of the implanted plugs is flush with the surrounding native cartilage, creating a smooth, continuous joint surface.
• Surgical Approach: Mosaicplasty can be performed through an arthroscopic (minimally invasive, using small incisions and a camera) or open (larger incision) approach, depending on the size and location of the defect.

Who is a Candidate for Mosaicplasty?

Mosaicplasty is not suitable for all cartilage defects. Ideal candidates typically meet specific criteria:

• Localized, Contained Defects: The procedure is most effective for single, well-defined cartilage lesions, usually no larger than 2-4 square centimeters. It is less effective for widespread cartilage degeneration (e.g., advanced osteoarthritis).
• Age: Generally, younger, more active individuals (under 40-50 years old) with good bone quality tend to have better outcomes, as their healing potential is greater.
• Activity Level: Candidates should be motivated to undergo a significant rehabilitation period.
• Joint Stability: The joint must be stable; any underlying ligamentous instability or meniscal issues often need to be addressed concurrently.
• Absence of Widespread Arthritis: The surrounding cartilage should be healthy.

Potential Benefits of Mosaicplasty

When successful, mosaicplasty offers several advantages:

• Uses Autologous Tissue: The procedure utilizes the patient's own healthy cartilage and bone, eliminating the risk of immune rejection associated with donor tissue.
• Provides Hyaline-like Cartilage: Unlike techniques that promote fibrocartilage formation (a less durable repair tissue), mosaicplasty transplants true hyaline cartilage, which closely matches the original tissue's properties.
• Single-Stage Procedure: Often, mosaicplasty can be completed in a single surgical session, unlike some other cartilage repair techniques that require multiple stages.
• Pain Reduction and Improved Function: Many patients experience significant reduction in pain and improvement in joint function, allowing them to return to daily activities and often sports.

Potential Risks and Complications

As with any surgical procedure, mosaicplasty carries potential risks:

• Donor Site Morbidity: Pain, stiffness, or discomfort at the site where the grafts were harvested is a common concern, though usually temporary.
• Incomplete Graft Integration: The transplanted plugs may not fully integrate with the surrounding bone and cartilage, leading to instability or failure.
• Graft Failure: The transplanted cartilage may degenerate or detach over time.
• Uneven Joint Surface: If the grafts are not perfectly flush, they can create an uneven surface that may lead to pain or accelerated wear in other areas.
• Infection, Bleeding, Stiffness, Swelling: General surgical risks.
• Nerve or Blood Vessel Damage: Rare but possible.

Recovery and Rehabilitation

Recovery from mosaicplasty is a gradual process that requires dedication to a structured rehabilitation program.

• Initial Phase (Non-Weight-Bearing): Immediately after surgery, the joint (e.g., knee) is typically protected with a brace, and weight-bearing is restricted for several weeks (often 4-8 weeks) to allow the grafts to heal and integrate.
• Progressive Weight-Bearing and Range of Motion: Under the guidance of a physical therapist, weight-bearing is gradually increased, and gentle range-of-motion exercises are introduced.
• Strengthening and Proprioception: As healing progresses, exercises focus on restoring muscle strength, balance, and proprioception (the body's awareness of its position in space).
• Return to Activity: A full return to high-impact activities or sports can take 6 months to over a year, depending on the individual, the size of the defect, and the joint involved. Adherence to the rehabilitation protocol is crucial for optimal outcomes.

Comparison with Other Cartilage Repair Techniques

Mosaicplasty is one of several surgical options for cartilage repair. Other common techniques include:

• Microfracture: Involves creating small holes in the bone beneath the defect to stimulate the formation of fibrocartilage (a less durable type of cartilage).
• Autologous Chondrocyte Implantation (ACI) / Matrix-Associated Autologous Chondrocyte Implantation (MACI): These multi-stage procedures involve harvesting cartilage cells, culturing them in a lab, and then implanting them back into the defect.
• Osteochondral Allograft Transplantation: Uses cartilage and bone from a deceased donor.

Each technique has specific indications, advantages, and disadvantages, and the choice depends on the individual patient's defect characteristics and overall health.

Conclusion

Mosaicplasty stands as a valuable surgical option for specific, localized articular cartilage defects, particularly in younger, active individuals. By transplanting healthy, native cartilage and bone, it aims to restore a smooth joint surface, reduce pain, and improve function. While it offers significant benefits, it is a complex procedure with a demanding recovery, underscoring the importance of careful patient selection and a comprehensive rehabilitation program under the guidance of experienced orthopedic surgeons and physical therapists.