Tissue engineering for meniscus regeneration.

Menisci represent fundamental structures for the manteinance of knee homeostasis, playing a key role in knee biomechanics. Lesions of the meniscus are frequently observed in orthopedic practice. Injury to the meniscus is one of the most common problems in the knee joint, with a mean annual incidence of 60 to 70 per 100 000 knee injuries (Erkman et al. 1975; Hede et al. 1990; Neilson et al 1991; Renstrom P 1990; Weinand et al 2006). Injury or loss of meniscal tissue leads to pain, knee dysfunction and osteoarthritis at long term (Cook et al 2005; Wyland 2002). Studies have demonstrated that knee degeneration is inversely related to the amount of meniscal tissue resected (McDermott and Amis 2006; Rijk 2004). Unfortunately, their intrinsic regenerative potential is poor. Healing is usually limited to the vascularized areas in the outer one third of the meniscus (Arnoczky and Warren 1983; Miller 1994). When a lesion involves the avascular portion of the meniscus, the reparative process cannot occur, since it emanates from bleeding and subsequent inflammation. As a result, the standard biological healing process produces limited results. Thus, a large proportion of meniscal tears observed at arthroscopy remain irreparable, and partial, subtotal or even total meniscectomy is often necessary, regardless of the recognized consequences. Even after an only partial meniscectomy, knee mechanics are subject to dramatic changes, leading often to the development of early osteoarthritis. Therefore, menisci should be repaired whenever possible. In the last decades, tissue engineering approaches have been advocated to improve the reparative processes of joint tissues. The possibility to entirely reproduce the meniscus struscture and function is highly attractive, and some new biomaterials have been studied and applied in preclinical and clinical studies.