Introduction and Objectives: meniscal lesions in the avascular zone are difficult to heal because of the poor biological potential of the avascular tissue. Little is known about the molecular mechanisms that develop after a meniscal lesion in this low activity zone. The purpouse of this study is to determine the levels of gene expression of five different growth factors (IGF, IL-1β; TGF-β, PDGF-β and VEGF) in the first three weeks after a meniscal lesion in the avascular zone of rabbit menisci.

Materials and Methods: 28 white female New Zealand rabbits were used in this study. Through a small arthrotomy a 5mm longitudinal lesion was performed in the avascular zone of the anterior horn of the medial meniscus of each rabbit. The rabbits were sacrificed after 0, 1, 3, 7, 14 and 21 days (4 rabbits each). After sacrifice, the zone in which the meniscal lesion was performed was disected from the rest of the mensicus. It was then divided in two parts: a peripheric vascular zone and a central avascular zone. After ARNm extraction cuantitative PRC anaylisis with Sybergreen technology was performed using specific primers for each gene.

Results: There were significant expression increases of IGF, TGF-β and PDGF-β, in the vascular zone at two weeks but no variations of note in these genes in the avasacular zone. The expression of IL-1β is increased in the first day after injury in both zones but only last up to the thrid day in the vascular zone. There is an increase in VEGF expresion in the avascular zone at two weeks that is related to a symetric decrease in the vascular zone.

Various studies have demonstrated that menisci heal in the vascular region but do not heal in the avascular area. Experimental studies of the promotion of meniscal healing in the avascular area have involved the application of fibrin clot, fibrin glue to the injured area, as well as the construction of an access chanel to the vascular regiòn, all of them with poor results. The multilineage potential of adult stem cells has been characterized extensively. The adipose tissue has been described as a useful source of adult stem cells. We try to show that the use of stem cells from the adipose tissue may promete meniscal healing in the avascular area.

Twelve New Zealand white rabbits with a mean weight of 3 kg were used. The medial meniscus of both knees was aproached, and was performed a longitudinal tear in the avascular area in the anterior horn with a mean length of 0.5 cm. All the tears were sutured with one vertical stitch of nonabsorbable suture. In each rabbit a solution with 1 00 000–1 000 000 stem cells from the fat was introduced in one of the knees, and the other one was used as a control. The rabbits were killed at 12 weeks, and a macro-microscopic study of the meniscus was done, and also a inmunohistochemistry study for the stem cells.

The incidence of healing was better in those menisci with the stem cells solution. Three total and three partial healing was obtained in the stem cells group and none in the control group. The inmunohistochemistry showed that the stem cells were in the repair zone.

We think that stem cells will be very useful in the treatment of the lesion in the avascular area of the meniscus.