Meniscal Allograft Transplantation

Courtesy: Alberto Grassi MD, Associate Professor, Rizzoli Orthopaedic Institute, Bologna, Italy

Introduction

• A webinar session featured an orthopedic surgeon specializing in knee ligament injuries, meniscal disorders, and sports traumatology.
• The speaker has extensive clinical and research experience in knee surgery and sports medicine, with numerous peer-reviewed publications and academic contributions.
• The presentation focused on meniscal allograft transplantation, including its indications, surgical principles, and clinical outcomes.

Importance of the Meniscus

• The meniscus is a critical structure within the knee joint.
• Historically, it was considered nonessential and frequently removed even for minor injuries.
• Athletes often performed well immediately after meniscectomy, which reinforced the belief that the meniscus was not necessary.
• Long-term follow-up later demonstrated that removal of meniscal tissue leads to significant degenerative changes in the knee joint.

Biomechanical Functions

• Distributes load across the knee joint.
• Increases contact area between the femur and tibia.
• Reduces stress on articular cartilage.
• Provides stability to the knee joint.
• Contributes to control of anterior tibial translation and rotational stability.

Consequences of Meniscectomy

Removal of meniscal tissue can lead to several biomechanical changes:

• Increased contact pressure on articular cartilage.
• Reduced contact area between the femoral condyle and tibial plateau.
• Increased shear stress within the joint.
• Increased anterior tibial translation.
• Reduced rotational stability, particularly after lateral meniscus removal.

Long-Term Effects

• Degenerative joint changes may occur over time.
• Studies show:
  • Approximately 22% risk of osteoarthritis within 10 years after medial meniscectomy.
  • Nearly 40% risk after lateral meniscectomy during the same period.
• After 20 years, almost 50% of patients with lateral meniscectomy may develop osteoarthritis.

Clinical Impact

• Young athletes who undergo meniscectomy early in life may develop premature degenerative knee disease.

Meniscus and Knee Stability

• The medial meniscus plays an important role in controlling anteroposterior knee stability.
• Removal of the medial meniscus can increase anterior tibial translation similar to that seen in anterior cruciate ligament deficiency.
• Meniscal deficiency may contribute to instability even after ligament reconstruction.

Clinical Evidence

• Studies using navigated knee evaluation showed increased anteroposterior laxity in patients with medial meniscus removal.
• This highlights the stabilizing function of the meniscus.

Shift Toward Meniscal Preservation

Modern orthopedic practice emphasizes preserving the meniscus whenever possible.

Strategies include:

• Meniscal repair techniques.
• Partial meniscus reconstruction.
• Meniscal scaffold implantation.
• Meniscal allograft transplantation.

The goal is to restore knee biomechanics and prevent long-term joint degeneration.

Meniscal Scaffold

• Used when there is partial loss of meniscal tissue.
• Requires intact anterior and posterior meniscal horns.
• Indications are limited because many patients have more extensive meniscal deficiency.
• Suitable mainly for younger patients with partial meniscal defects.

Meniscal Allograft Transplantation

Background

• Meniscal transplantation has been performed for nearly three decades.
• Early procedures involved open surgery with large incisions and complex techniques.
• Advances in arthroscopy have made the procedure less invasive and more standardized.

Evolution of Graft Preservation

Different preservation methods have been used over time:

• Lyophilized grafts
• Cryopreserved grafts
• Fresh frozen grafts

Currently, fresh frozen grafts are widely used because they preserve structural properties while being easier to store.

Biological Integration of the Graft

Research studies have demonstrated:

• Peripheral healing and revascularization of the transplanted meniscus.
• Increase in cellularity within the graft over time.
• Repopulation of the graft by recipient cells.

Immunological Response

• Approximately 90% of cells in the transplanted meniscus originate from the recipient.
• Because of this cellular replacement, immunosuppressive therapy is not required.
• Immune rejection is extremely rare.

Biomechanical Effects of Transplantation

Meniscal transplantation helps restore knee biomechanics by:

• Increasing joint contact area.
• Reducing peak pressure on articular cartilage.
• Improving load distribution.
• Restoring joint stability.

Proper fixation of the anterior and posterior horns is essential for maintaining the structural integrity of the graft.

Indications for Meniscal Transplantation

Primary indications include:

• Persistent compartmental knee pain after subtotal or total meniscectomy.
• Meniscal deficiency contributing to failure or instability after ligament reconstruction.
• Combined procedures with cartilage repair or corrective osteotomy in meniscus-deficient knees.

Situations Where Transplantation Is Not Recommended

Meniscal transplantation is not typically performed in:

• Asymptomatic patients without pain or functional limitation.
• Advanced degenerative joint disease.
• Severe obesity.
• Inflammatory joint disorders.
• Significant malalignment or instability that has not been corrected.

Graft Sizing and Matching

Accurate graft size is essential for successful transplantation.

Methods used to determine graft size include:

• Radiographic measurements
• Magnetic resonance imaging
• Computed tomography analysis
• Anthropometric measurements based on height, weight, and sex

Availability of appropriate graft sizes from tissue banks can also influence graft selection.

Surgical Fixation Techniques

Two main methods are commonly used:

• Bone plug fixation
• Soft tissue fixation

Key Principles

• Secure fixation of meniscal horns is critical.
• Both fixation techniques have shown comparable short-term clinical outcomes.

Graft Extrusion

• Some degree of graft extrusion may occur after transplantation.
• Although mild extrusion is often tolerated, excessive extrusion may be associated with joint degeneration over time.

Rehabilitation and Return to Activity

Postoperative rehabilitation typically includes:

• Partial or minimal weight-bearing for 4 to 6 weeks.
• Gradual range-of-motion exercises starting within 1 to 2 weeks.
• Progressive strengthening over several months.

Return to Sports

• Most patients resume sports activities after about 9 months.
• Low-impact activities are preferred.
• High-impact sports are generally limited to selected cases.

Clinical Outcomes

Evidence from clinical studies indicates:

• Significant improvement in pain and knee function after transplantation.
• Mean functional scores show good results in many patients.
• Mid-term failure rates are relatively low.

Long-Term Results

• Approximately 73% graft survival at 10 years.
• Around 70% survival at 15 years.
• Average functional survival ranges from 11 to 13 years.

Predictors of Outcome

Factors associated with better results include:

• Younger patient age.
• Minimal cartilage damage.
• Stable knee alignment.
• Early transplantation after meniscal loss.

Factors associated with poorer outcomes include:

• Advanced cartilage degeneration.
• Knee malalignment.
• Uncorrected ligament instability.

Return to Sports

• Around 70% of patients return to sports activities.
• Most return to low-impact activities rather than high-impact competitive sports.
• Some studies in military populations report return to active duty in a majority of patients.

Institutional Clinical Experience

• Over several years, hundreds of meniscal transplant procedures have been performed.
• Many cases involved isolated transplantation, while others required additional procedures such as ligament reconstruction or corrective osteotomy.
• Clinical follow-up demonstrated functional improvement and pain relief in most patients.