Currently, there is a significant increase in the number of studies devoted to articular cartilage regeneration. A variety of surgical methods are used for regeneration, including tunneling, microfracturing, and arthroplasty. Recently, the replacement of cartilage defects with cultured autologous chondrocytes has begun to be used for this purpose. Expensive tissue and genetic engineering techniques are used to culture and grow cartilage tissue outside the body for subsequent transplantation. The keynote of this work on creating cartilage and replacing its defect is the minimally invasive nature of the replacement process itself. Tissue transplantation is impossible without the use of arthroscopic techniques. The arthroscope [https://eleps.ru/katalog/artroskopiya-optika/] is becoming the primary surgical instrument for new, high-tech treatments for joint pathologies. The most widely used method for cartilage transplantation is a suspension of cultured autologous chondrocytes, called Carticel. The drug and method were developed by Genzyme, a Massachusetts-based company (Genzyme Tissue Repair). Research on this drug is being conducted simultaneously in the United States, Sweden, and Germany. According to published data, the cost of cartilage replacement surgery is $30 million annually. These figures are based on the following: 500,000 joint surgeries are performed in the United States each year. Of these, 95,000 are knee replacements and 41,000 are various types of arthroplasty. If the proposed restoration of knee cartilage in the early stages of degeneration proves effective and can prevent the development of degenerative osteoarthritis, the need for total joint replacement will gradually disappear. Traditional principles of surgical treatment. Until recently, joint lavage and debridement of the articular surface remained the main principles of treating knee cartilage defects. Since the first use of arthroscopy, the idea of ??clearing joints of non-viable cartilage fragments, loose intra-articular bodies, and synovial fluid containing dissolved lytic enzymes has become firmly established. Approximately two-thirds of patients experienced improvement over three years after such procedures. In patients with deforming arthrosis, 52% of cases showed improvement, but after three years, this figure dropped to 44%. Some studies have observed good results in two-thirds of patients five years after arthroscopy. Joint debridement has been shown to be more effective than lavage. In osteoarthritis, in cases of complete cartilage degeneration, even to the point of exposing the subchondral bone, arthroscopic lavage and debridement have proven ineffective treatment methods. Filling the cartilage defect with fibrin has been proposed as a method of filling the defect. To achieve this, cartilage abrasion, tunneling, and microfracturing of the subchondral bone were performed during arthroscopy. During these procedures, joint debridement was performed to clean the defect surface to improve fibrin contact with the underlying bone. Abrasive arthroplasty involved preparing the bone with an arthroscopic bur until petechial bleeding from the subchondral bone layer occurred. Multiple bone reaming resulted in bone marrow elements emerging on the defect surface, forming a fibrous clot. Similar goals were achieved by preparing the bone with a special perforator, resulting in multiple microfractures of the bone surface. All these techniques were based on the idea of ??disrupting the integrity of the bone to allow bone marrow elements to access the defect surface from deep within the spongy bone. As a result, repeat arthroscopy revealed fibrous tissue or fibrocartilage in the defect area. Unfortunately, the newly formed tissue was inferior in mechanical properties to hyaline cartilage and could not withstand the loads placed on the knee joint. Attempts to stimulate cartilage growth resulted in the new fibrocartilage not being strong enough and wearing out quickly. Numerous studies have shown a deterioration in patients' condition shortly after this procedure. In patients over 40, pain persisted in 66% of cases, and only 12% reported no complaints. There were reports that, five years after abrasive arthroplasty, relatively better results were observed in younger patients. Postoperative care was crucial for treatment outcomes. Repeat arthroscopy revealed that the appearance of newly formed cartilage was better in the group of patients who regularly exercised their knees compared to those who did not. Biological restoration of cartilage using autologous tissue. In 1990, a report appeared on an attempt to restore knee cartilage using costal autologous cartilage grafting. Grade 3-4 cartilage defects were closed using perichondral grafts, which were fixed with fibrin glue. Arthroscopic examination after one year revealed that the cartilage defect was 90% filled, and the patients themselves reported an improvement in their condition. An eight-year follow-up study revealed that 20% of the transplanted cartilage had undergone endochondral ossification, which resulted in a deterioration in 60% of patients. Closure of the cartilage defect using periosteum was initially used experimentally and then clinically. The periosteum was placed with its cambial layer on the bone surface after debridement and treatment until petechial bleeding occurred. A follow-up examination revealed neither good nor excellent results in all patients, but only satisfactory and unsatisfactory results. In young patients with osteochondritis dissecans in the femoral condyles, good results were observed in 80% of cases one year after periosteoplasty. However, after 8 years, unsatisfactory results were observed in 75% of patients, and progression of deforming arthrosis was observed in 50%. Late post-procedure arthroscopic examination and biopsy revealed no hyaline cartilage formation at the site of periosteoplasty. Osteochondral grafts were transplanted from sites with intact cartilage. According to the technique, intact cartilage was taken from the intercondylar notch or the lateral femoral condyle. Arthroscopic examination after 2 years revealed closure of a 15 mm cartilage defect. Histological examination revealed the formation of a fusion between the transplanted cartilage and the cartilage at the defect margin. A number of studies have reported an 80% success rate. This technique was used to treat defects smaller than 2 square centimeters, but its long-term results remained unknown. Autologous Chondrocyte Transplantation. In 1987, clinical trials began on transplanting cultured autologous chondrocytes for cartilage defect closure. The technique of autologous chondrocyte transplantation, known as Carticel, was developed by Genzyme. Transplantation is performed only for knee cartilage defects. Articular cartilage defects can be detected in various clinical situations. They can be identified during initial arthroscopy, which is performed due to joint trauma, or can be an incidental finding during arthroscopy for damage to the menisci and ligaments of the joint. If a cartilage defect is detected, indications for the use of Carticel are considered. If indicated, a biopsy of intact cartilage is performed, usually from the superior margin of the medial or lateral femoral condyle or the intercondylar notch. Cartilage can be taken from two or three sites across its entire depth. The total biopsy weight is 200-300 mg. The cartilage is placed in a special vessel and sent to Genzyme for culture. The culture process lasts at least three weeks. During this time, the number of autologous chondrocytes increases 10-12-fold, reaching 12 million cells. The transplant volume is typically 0.2-0.3 cubic centimeters. Chondrocyte transplantation requires a repeat surgery—arthrotomy of the knee joint. During the arthrotomy, the cartilage defect is debridement down to healthy cartilage. Scars are removed, and the subchondral bone, which must be intact and not bleeding, is exposed. A section of tibial periosteum slightly larger than the cartilage defect is harvested from a separate incision along the anteromedial surface of the leg. The cartilage defect is covered with periosteum, with its cambium layer facing the defect. The periosteum is sutured to the defect edges using 6-0 absorbable sutures. The suture is then covered with fibrin glue, which is made from the patient's tissue. A small opening is left for a catheter. The chondrocyte suspension from the vessel is drawn into a syringe and injected through the catheter under the periosteum onto the cartilage defect. The remaining opening is sealed with fibrin glue. The surgical wound is closed using the traditional method. The surgery has a chance of success if a number of requirements are met: the cartilage defect is located in the femoral condyle area, is localized, extends throughout the entire depth of the cartilage layer, joint biomechanics are normal, the joint is stable, not deformed, the range of motion in the joint is preserved, and the patella is in the correct position. Contraindications to chondrocyte transplantation include joint inflammation, arthritis, moderate to severe joint degeneration, and deforming arthrosis. Rehabilitation after chondrocyte transplantation. Period I (weeks 1 to 6) — Walking with crutches. — Complete immobility of the knee joint when walking. — Sleeping in a splint for up to 4 weeks. — Complete absence of weight-bearing on the leg for 2 weeks, walking on the toes for up to 4 weeks, walking on the entire foot from the 5th week. — Passive joint movements up to 90 degrees. Period II (6 to 12 weeks). — Walking with crutches up to 8-9 weeks. — Load on the affected leg no more than half of body weight. — Intermittent wearing of a knee brace. — Passive joint extension and flexion up to 125 degrees. — Stimulation of the thigh and lower leg muscles. Period III (12 to 26 weeks). — Free walking up to 3 km per day, jogging from the 20th week. — Joint flexion up to 135 degrees. Period IV (26 to 52 weeks). — Unrestricted knee joint movements. — Sports: skating and rollerblading, cycling from 6 months, aerobics and running from 8 months, team sports from 12 months.