Meniscus substitution: The European perspective on scaffolds, allografts, and prosthetic implants

OVERVIEW

Chapter synopsis

In this chapter, the different options for meniscus substitution are discussed and elaborated. Specific attention is paid to the important differences in indication and surgical technique. Although a number of these therapeutic options have already proven their clinical benefit in multicenter European trials, many of them have not yet been made available outside of Europe—hence the scope of this chapter.

Important points

Meniscus scaffolds are indicated for partial meniscus defects (ideally less than 5 cm), whereas meniscus allografts are indicated in larger defects. Prosthetic meniscus implants are a promising new tool for meniscus deficiency.

Clinical and surgical pearls

Meniscus substitution is a treatment option for nonarthritic, well-aligned, stable knees.

Clinical and surgical pitfalls

Significant osteophytes or flattening of the femoral condyle, often observed in chronic meniscectomy, eliminates the possibility of meniscus substitution.

Treatment of meniscal lesions is the most common surgical intervention performed by orthopedic surgeons today, with more than 1 million surgical interventions involving the meniscus performed annually in the United States and approximately 400,000 in Europe. The meniscus, a semilunar, fibrocartilaginous structure, preserves a pain-free functional knee and plays an important role in the biomechanical functions of the knee, including load bearing, load and force distribution between the femoral condyles and tibial plateau, joint stabilization, lubrication, and proprioception. Over the last few decades, the understanding of meniscal functions and consequently the management of meniscal injuries has continued to evolve, with increasing commitment among physicians to preserve the meniscus whenever possible. The natural history of a meniscus-deficient knee has been shown to involve poor clinical and radiologic outcomes over time, including disruption of load-sharing and shock absorption, diminution of joint stability, and deterioration of articular cartilage with progression to arthrosis. It is now accepted that loss of all or part of the meniscus leads to long-term degenerative changes owing to higher peak stresses on the articular cartilage in the meniscectomized compartment as a result of the decreased contact area. Thus, it seems logical to regenerate or substitute lost meniscus tissue with a scaffold, allograft, or implant to restore the function of the knee joint and to possibly prevent further joint degeneration.

In this chapter, the different options for meniscus substitution are discussed and elaborated. Specific attention is paid to the important differences in indication and surgical technique. Although a number of these therapeutic options have already been proven to be of clinical benefit in multicenter European trials, many of them have not yet been made available outside of Europe—hence the scope of this chapter.

Meniscus scaffolds for the treatment of partial meniscus defects

Meniscal regeneration appears to require the physical presence of a scaffold to encourage successful migration and colonization with precursor cells and vessels, eventually leading to the formation of organized meniscal tissue. ^,

In Europe, two scaffolds for the treatment of partial meniscus defects are available: polyurethane and collagen meniscus scaffolds. We have acquired extensive experience with a novel, biodegradable, synthetic, acellular scaffold composed of aliphatic polyurethane (Actifit, Orteq, London, United Kingdom), which was designed to fill an unmet clinical need in the treatment of patients with irreparable partial meniscal tissue lesions. The treatment objective of the scaffold is to provide pain relief and restore lost meniscus functionality.

The scaffold comes in two configurations: one for the medial indication and one for the lateral. Design criteria were biocompatibility, strength, flexibility and ease of handling (insertion and suturing with standard arthroscopic techniques), high and interconnected porosity to support tissue ingrowth, and degradation over a suitable time as new tissue forms and matures. The scaffold is highly porous, with approximately 20% of the structure being composed of biodegradable aliphatic polyurethane and the remaining 80% being the pores.

When implanted into the void created in the meniscal tissue after a standard arthroscopic partial meniscectomy and connected to the vascularized portion of the meniscus, the scaffold provides a three-dimensional matrix of interconnected pores for vascular ingrowth.

Indications

Meniscus scaffold implantation represents a novel biologic solution for the treatment of patients with symptomatic partial meniscus defects and limited signs of cartilage degeneration. Because the negative impact of meniscectomy in knees with an anterior cruciate ligament (ACL) injury on long-term cartilage degeneration has recently been established, prophylactic meniscus reconstruction with use of a scaffold in the ACL-reconstructed knee with partial meniscectomy could be another indication.

The key inclusion criteria are as follows:

1.
Irreparable medial or lateral meniscal tear or partial meniscus loss with intact rim. Most important, the synthetic meniscus substitute is not intended for the treatment of total or subtotal meniscus defects; ideally, the defect length should be limited to 5 to 6 cm.
2.
Skeletally mature male or female patients.
3.
Patients aged 16 to 50 years.
4.
Stable knee joint or knee joint stabilization procedure within 12 weeks of index procedure.
5.
International Cartilage Repair Society (ICRS) classification of 3 or lower.
6.
Patient willing and able to give consent to participate in the clinical study, follow rehabilitation protocol, and attend or undergo all follow-up visits and procedures.

The key exclusion criteria are as follows:

1.
Total meniscus loss or unstable segmental rim defect.
2.
Multiple areas of partial meniscus loss that could not be treated by a single scaffold.
3.
Any significant malalignment (varus or valgus).
4.
ICRS classification of greater than 3.
5.
Body mass index of 35 or higher.

Surgical technique

Anesthesia and positioning

The Actifit meniscal scaffold is placed in the subject’s knee using a standard arthroscopic surgery procedure and standard equipment. Implantation is usually performed with use of spinal or general anesthesia at the discretion of the orthopedic surgeon. The use of a tourniquet is optional. The surgeon may prefer thigh fixation to achieve appropriate valgus or varus stress positioning.

Examination

Verification of cartilage status as well as the integrity of the meniscal rim and both the anterior and posterior horns should be performed. In the case of a tight medial compartment, distending the medial collateral ligament using the outside-in puncture method (several passes with a spinal needle from outside in) or the inside-out pie-crusting release technique described by Steadman allows the surgeon to adequately visualize both the femoral and the tibial cartilage status and create an optimal working space for meniscus reconstructive surgery.

Portals

The implantation requires the usual small incisions for anteromedial and anterolateral portals, with an optional central trans-patellar tendon portal. To allow for easy insertion of the scaffold, an enlargement of the portal used for insertion of the device may be required (the size of the little finger is typically sufficient). In addition, a posteromedial or posterolateral incision may be required if an inside-out meniscal fixation technique is used. Additional small incisions are made around the joint line if an outside-in technique is used.

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