Injury of the knee articular cartilage and osteochondral unit is a significant cause of functional limitation in which the goal of treatment is preservation of the native knee joint. There are a variety of cell-based cartilage and osteochondral unit repair methods that may be used to treat different injuries, given the limited potential for cartilage injury to heal without intervention. Restoration of hyaline-like cartilage is the ultimate goal in treatment of osteochondral unit as it offers an improved durability of repaired tissue and preferable wear characteristics. Over the years many cell-based therapies have been developed to address the need for the long-term viability of repaired tissue. Some of the techniques use mesenchymal stem cells (MSCs) as a core ingredient for tissue repair.
Microfracture, a bone marrow stimulation technique using MSCs, when used wisely and with caution in selected patients has shown good clinical results at short-term follow up. Nonetheless, deterioration of the clinical outcome may be expected after 2 -3 years post-treatment, and degenerative changes are present at long-term follow-up, with a higher rate in older patients with extensive and multiple lesions [1, 2]. Autologous Matrix-Induced Chondrogenesis (AMIC) has emerged as a modification of the microfracture technique by addition of a collagen scaffold. However both of these techniques raise a concern of the damage of the subchondral bone and the formation of microcysts, that may quicken the deterioration of the cartilage and compromise the articular surface for future procedures [3, 4]. Autologous chondrocyte implantation (ACI) consists of a two-step procedure; first, a sample of healthy cartilage is harvested from a non-weight bearing site, followed by an in vitro cell expansion. The second step is the implantation of the chondrocyte suspension into the cartilage defect. Compared to bone marrow stimulating techniques such as microfracture, ACI technique has appeared to be superior over time due to longer-lasting effects, without the concerns of destruction of the subchondral bone [5,6]. However, while techniques using autologous chondrocytes have demonstrated durable cartilage repair, these methods require the patient to undergo two surgical procedures due to the need for chondrocyte culture.
Hyaluronic acid-based scaffold with bone marrow aspirate concentrate (HA-BMAC) was developed 30 years ago, it allowed the treatment of larger cartilage defects in a one-step surgery with biologic tissue such as mesenchymal stem cells, chondrocytes, or platelet-rich plasma. This technique has provided long-term results and has proven its superiority to microfracture due to lasting effect over ten years compared to the 2-3 years with microfracture technique [2]. Moreover, it can be used even in cases of multiple compartment injury, extensive lesions, or in older patients [7-10]. This procedure provides a good source of chondrocytes, whether directly or through differentiation of multipotent precursor cells, capable of producing hyaline-like cartilage, with minimal formation of fibrocartilage tissue [10].
Lately more attention was brought to the osteochondral unit and especially the role of subchondral bone in maintaining homeostasis of the joint [4]. Bone marrow lesions (BMLs) are the focal changes in the subchondral bone and can be identified by magnetic resonance imaging (MRI). A technique using MSCs to treat BMLs, the Osteo-Core-Plasty (Marrow Cellution™) is a minimally invasive subchondral bone augmentation that offers both biologic and structural components to optimize the osteochondral environment for regeneration. This technique may also by applied in treatment of insufficiency fractures, subchondral cysts, and avascular necrosis [11, 12].
MSCs are also found in other sources than bone marrow, one of which is fat tissue. Adipose derived Mesenchymal Stem Cells (ADMSCs) are quickly becoming a viable source of MSC, not only because they are easy to harvest but also have a high concentration of progenitor cells. Primary outcomes of the use of microfragmented adipose tissue (MFAT) injection in elderly patients with knee osteoarthritis (OA) have shown good clinical results compared with the pre-treatment state and could be an alternative treatment for elderly patients 60 years or older [13, 14].
Summarizing, over 30 years of using MSCs have shown good and very good clinical outcomes in treatment of osteochondral unit lesions and OA.
References:
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