Current surgical options for articular cartilage repair and future perspectives

INTRODUCTION The repair of chondral or osteochondral lesions still represents a big challenge for the orthopaedic surgeon. Many efforts have been done and are currently part of research and clinical programs to try to find the solution for this issue. Generally, the surgical options for articular cartilage repair can be divided into three groups: techniques without transplant of cells or tissues; techniques based on the transplantation of tissues; the tissue engineering techniques. SURGICAL TECHNIQUES WHICH DO NOT REQUIRE CELL OR TISSUE TRANSPLANT Several procedures were developed with the attempt of inducing bleeding from the bone marrow and, consequently, the migration of growth factors and stem cells into the lesion site. These techniques are simple and are performed arthroscopically, but present the limit of generating fibro-cartilaginous tissue. SURGICAL TECHNIQUES WHICH REQUIRE TISSUE TRANSPLANT A different approach for the repair of a chondral lesion consists in the transplantation to the lesion site of a mature osteocartilaginous tissue. In this procedure, healthy osteochondral cylinders are taken from low bearing areas of the joint and transplanted to the defect site. This procedure has the disadvantage of the creation of one or more iatrogenic lesions having overall the same dimension of that to be repaired. TISSUE ENGINEERING TECHNIQUES FOR CHONDRAL REGENERATION The current tissue engineering techniques for chondral regeneration can be divided into three groups: first, the transplantation of chondrocytes or other cells in solution; second, the transplantation of cells previously seeded onto a scaffold; third, the implantation of acellular scaffold capable of the recruitment of nucleated mesenchymal stem cells from the bone marrow and the blood of the sub-chondral bone. Eventually, these scaffolds should also provide the proper stimuli for the correct differentiation of the reparative cells. The original technique was proposed by Brittberg in the 1994 and was called A.C.I. (Autologous Chondrocyte Implantation). This procedure requires two surgical steps; during the first step, a cartilage biopsy is taken from an area of healthy cartilage and then transferred in a laboratory for cells’ isolation and expansion. Cells are expanded in a monolayer culture until they reach the sufficient number to fill the defect. During the second step, the patient undergoes a second surgery; at this time, a periosteal flap is sutured at the boundaries of the lesion and the cells are injected in solution under the flap. In the following years, some authors have proposed to seed the cells onto biocompatible scaffolds. The materials employed as cell carriers are different. These techniques still require two surgical steps and several new materials have been developed. Beside these techniques that involve the transplantation of cells, others approaches are currently used, based on the employment of non-seeded membrane. These products are based on the natural healing potential of full thickness acute lesions of the articular cartilage, as bone marrow-stimulation techniques do. FUTURE PERSPECTIVES The research in the field of cartilage repair is becoming more and more active and involves the use of different biomaterials, growth factors, isolated or incorporated in their structure, able to induce or maintain the cartilaginous phenotype of the reparative cells. Our group has being studying the use of fresh or expanded cells for the development of engineered substitute in combinations with hydrogel and open matrix collagen scaffolds. The coupling of such a materials with bone compatible material brought to interesting results in the repair of osteocartilaginous lesion in pre-clinical models. Moreover, thanks to the evolution of the research in the material science and in the imaging, it will be soon possible to create a custom-made scaffold, based on the dimension and size of the patient’s lesion. CONCLUSIONS In the past years, a lot of efforts have been done by studying the lesions’ biology and trying to improve the natural healing potential of the articular cartilage. All the bone marrow-stimulation techniques are based on this principle, but have the limit of the low quality of the newly formed tissue. In order to improve the biomechanical properties of the neo-tissue, many different procedures based on tissue engineering methodologies were proposed that can potentially reproduce a hyaline cartilage by more complex and expensive procedure. Nowadays, none of the techniques described can completely and systematically restore the injured cartilaginous tissue. On the other hand, important future perspective are originating from the research activity in a multidisciplinary scenario, involving cells, biomaterials, gene-based therapies and the use of novel stimulating factors.