The Meniscus and Meniscal Scaffolds for Partial Meniscal Replacements

Abstract

The meniscus is the most common damaged structure of the knee, accounting for almost one million cases of knee surgeries performed annually in the United States alone. A complete meniscectomy (complete meniscus removal) was the most common procedure performed in 1889 and was the standard procedure in the next 80 years. However, follow-up radiographic studies from the late 1960s to 1980s reported a high frequency of post-meniscectomy osteoarthritis of the knee.The meniscus functions to transmit load, absorb shock, stabilize the knee joint and nourish the joint. A complete integrity of the meniscus is crucial in maintaining the normal biomechanics of the knee and preventing the onset of premature or traumatic osteoarthritis. 3D Printing of silicone allows arthroscopic replacement of damaged menisci, either totally or partially, enabling the patient to return to work and sports almost instantaneously after surgery.This review summarizes the meniscal structure, biomechanical properties, meniscal lesions, the characteristics and clinical outcomes of various biodegradable synthetic and biological meniscal scaffolds.The menisci are a pair of fibrocartilaginous cushions which sits on the tibial plateau in the knee joint. They act as knee cushions which transmit body weight evenly across the knee joints, thus minimizing contact stresses between femur and tibia and damages to the articular surfaces. Meniscal injuries predisposed the knees to developing premature osteoarthritis (Figure 1). Figure 1: Anatomy of the meniscus.The meniscus is divided into 3 zones, the outermost vascular red-red zone, middle red-white zone and the innermost avascular white-white zone. Cells are spindled-shaped in the outermost redred zone while chondrocyte-like in the innermost white-white region.The meniscus obtains its limited blood supply from the perimeniscal capillary plexus within the synovial and capsular tissues of knee. These plexus, extending for one to three millimeters over the articular surfaces of menisci, are branches of the inferior and superior branches of the lateral and medial geniculate arteries.The vascular supply to meniscus is age dependent. In adult, tears which occur at the most vascularized, peripheral 3 mm of the menisci are most amenable to repair and cellular regeneration, as opposed to the generally avascular tears, greater than 5 mm from the menisci-synovial junction, which are not reparable. For both the medial and lateral menisci, the vascular penetration is about 10-30% ( Figure 2).

Composite Zonal Scaffolds of Collagen I/II for Meniscus Regeneration

“…The mechanical properties of the scaffolds vary when the tests are conducted with dry or wet samples. Data obtained with wet scaffolds are more similar to those of the native meniscus than those obtained with dry scaffolds because the microenvironment of the meniscus is aqueous and reorganizes under stress . The mechanical evaluation of hydrated samples confirmed that the composite scaffolds were structural units because they retained their integrity until reaching the breaking point in the test.…”