Table 1. Summary of the augmentation procedures for meniscal repair.

Augmentation procedure	Surgical technique	Preclinical evidence	Clinical evidence
Mechanical stimulation	Vascular access channels: a core of the tissue from the periphery of the meniscus (red zone) to the tear is removed, thus creating a transverse tear connecting the peripheral vasculature with the avascular portion (white zone)	Few preclinical studies with limited results	Limited clinical application due to the negative effects on the biomechanics and function of meniscus
	Trephinations: multiple holes are made with a spinal needle through the peripheral aspect of the meniscus rim to make a series of bleeding puncture sites promoting bleeding	Few preclinical studies with promising results	Controversial clinical results in particular when the procedure is performed alone
	Abrasions: the meniscal surface and the synovium adjacent to the meniscal tear are abraded	Promising preclinical results	Promising preliminary clinical findings but limited evidence
Synovial flap	A pedunculated and vascularized synovial flap is applied to cover the meniscal tear and then sutured	Procedure extensively tested in the animal model, with positive results in terms of meniscal healing improvement	Despite the promising preclinical findings, currently there is a lack of clinical reports
Fibrin clot augmentation	A fibrin clot in applied in a stable tear within the avascular zone of the meniscus, providing both a chemotactic and mitogenic stimulus to the reparative process	Several preclinical studies showing promising results	Controversial clinical results also conditioned by limitations technique-related
PRP augmentation	The platelet concentrate can be obtained as a sticky gel to deliver into the repair meniscal site before the suture procedure, and able to release different growth factors	Some animal studies have confirmed the positive effects of PRP augmentation in terms of meniscal tissue regeneration	The evidences remain limited, with still few studies and with an overall low quality. High heterogeneity in PRP composition and preparation/administration methods
MSC augmentation	Progenitor cells, such as MSCs, previously isolated from various sources (bone marrow, adipose tissue, muscle and synovium) and opportunely expanded without losing their differentiation, are applied with an intra-articular injection	Some studies on animal models suggested the potential of MSCs to promote meniscus healing, with the regenerative effects of intra-articular injections	Very few data on the application of MSCs in meniscal defects

PRP, platelet-rich plasma; MSCs, mesenchymal stem/stromal cells.