Historical Background of Autologous Chondrocyte Implantation (Transplantation)

In 1965, Smith was successful in isolating and growing chondrocytes in culture for the first time.¹¹ Epiphyseal chondrocytes grown in culture were injected into tibial articular defects in the rabbit knee but did not show any significant repair.

In 1982, experimental work was begun at the Hospital for Joint Diseases–Orthopedic Institute in New York to design an experimental rabbit model using articular chondrocytes isolated and grown in culture for implantation into a defect made in the patella and covered with a periosteal flap. The idea was to use articular chondrocytes because they are the only cells committed to form hyaline cartilage.

Initial results of ACI in this rabbit model were presented in 1984 and showed hyaline-like cartilage filling 80% of the patellar defect. No significant filling was seen in the control side, where the defect was treated with periosteal cover but no cells.

Since 1984, extensive animal studies have been ongoing at the University of Göteborg, Sweden. The results from New York have been confirmed and improved.

In 1985, work started on transferring the cell-culturing technique to human chondrocytes, and in 1987 the first ACI (or transplantation, as first named) was performed in the human knee at the Department of Orthopaedics, University of Göteborg, after approval by the Ethical Committee of the Medical Faculty of the University of Göteborg (Fig. 22-1).

Figure 22-1 Diagram of the autologous chondrocyte implantation procedure.

A pilot study of 23 patients with 39 months’ follow-up reported in the New England Journal of Medicine in October 1994 showed that of 16 patients who underwent femoral condyle procedures, 14 had a good or excellent result. Eleven of 15 biopsy specimens showed hyaline-like cartilage. Among seven patients who underwent ACI of the patella, however, only two good or excellent results were achieved, and one biopsy specimen showed hyaline-like cartilage.⁵

Since 1987, more than 1800 patients have been operated on in Göteborg, Sweden, and since 1995, more than 400 surgeons have performed ACI on more than 30,000 patients outside Sweden.

Clinical results from Sweden were reported at the American Academy of Orthopaedic Surgeons in 1996, 1997, 1998, 2000, 2001, 2002, 2003, and 2004, and long-term results obtained 10 to 20 years after the ACI were first presented at the International Cartilage Research Society meeting in 2009.^29,34

Indications for Autologous Chondrocyte Implantation

Autologous chondrocyte implantation is indicated in patients between 15 and 55 years old with symptomatic, full-thickness Outerbridge or International Cartilage Repair Society (ICRS) grade III to IV cartilage injuries of the knee with a diameter larger than 10 mm up to an area of 10 to 16 cm² (Fig. 22-2). The defect should be located on the femoral or patellar articular surface and should be accessible for implantation via open arthrotomy. Only grade I to II Outerbridge or ICRS classification changes on the reciprocal articular surface should be included.

Figure 22-2 Arthroscopic view of a chondral injury down to bone on the medial femoral condyle, an indication for autologous chondrocyte implantation.

Osteochondritis dissecans of the medial or lateral femoral condyles with an unstable fragment, a separated but attached flap, or an empty bed is another indication for ACI (Fig. 22-3).

Figure 22-3 A, Arthrotomy of a right knee with osteochondritis dissecans of the lateral femoral condyle and an avulsed but attached flap, an indication for autologous chondrocyte implantation. B, Magnetic resonance image showing a deep osseous defect on the lateral femoral condyle.

Bipolar chondral injuries (i.e., osteoarthritis) are undergoing investigational study and at present could be considered as requiring a salvage procedure or as a relative indication. A recent long-term follow-up study described very good results 10 to 20 years after implantation, even for large bipolar lesions, for which ACI had been performed as a salvage procedure.^29,34 Evidence supports that ACI is indicated even for large bipolar lesions, delaying total knee arthroplasty. A definite decision regarding the indication is made during arthroscopic evaluation.

Clinical Evaluation

A thorough history of symptoms, trauma, or repetitive loading is important, as is a careful record of previous surgeries. Clinical examination, including assessment of signs of local tenderness, swelling, range of motion, and crepitation, is performed.

Varus and valgus deformities are assessed, and patellar malalignment, maltracking, or instability is evaluated. Ligament instability is clinically tested.

Background Factors to Consider

An understanding of the optimal environment for survival of repair tissue in the short or long term is of utmost importance. Varus or valgus malalignment should be evaluated on standing x-ray films of the knee in the extended position and in 45 degrees of knee flexion. Additional information could be gathered by examining the hip, knee, and ankle axis on long, standing x-ray films. Varus or valgus deformity should be corrected. Magnetic resonance imaging (MRI) could be helpful in evaluating articular cartilage injury and the condition of the subchondral bone in greater detail, as well as the status of the menisci. Previous meniscal surgery should be assessed, and after total or subtotal meniscectomy, meniscal transplantation should be considered.

Instability should be evaluated clinically, and any instability noted should be corrected. Osseous defects deeper than 8 to 10 mm should be considered for autologous bone grafting and chondrocyte implantation. MRI could be a helpful tool in evaluating bone pathology.

Arthroscopic Evaluation—Cartilage Retrieval

Under general or spinal anesthesia, complete stability testing of the knee is performed, and results are compared with those on the healthy side. Complete examination of the knee joint should be performed, including visualization and probing of articular cartilage surfaces, synovial lining, menisci, and cruciate ligaments, and the presence of any fragment or loose body should be identified. Undiagnosed pathology may be critical to the outcome of surgery. The cartilage injury is visualized, probed, and assessed for depth, size, and location. The opposing articular surface should be assessed and should be normal or should have only fibrillation or superficial fissuring, Outerbridge or ICRS grade I to grade II. The defect should be evaluated regarding containment and shouldering. An uncontained lesion extends into the synovial lining of the joint. It may be unilateral or bilateral, for example, extending from the synovial lining of the articular surface of the medial femoral condyle into the synovial lining of the intercondylar notch (Fig. 22-4).

Figure 22-4 Schematic drawing showing containment of defects. The left drawing shows contained defects; the middle drawing, unilateral uncontained defects extending to the synovial lining; and the right drawing, bilateral uncontained defects.

A shouldered defect is a defect surrounded by normal cartilage in which the bone in the center of the defect is not in contact with the opposing articular surface. An unshouldered defect is so large that in a weight-bearing position, the subchondral bone in the center of the defect is in contact with the opposing articular surface (Fig. 22-5). During arthroscopy, the proposed implantation is evaluated regarding different possibilities for the surgical approach, the intended amount of débridement, the extent of shouldering, containment of the defect, and so forth.

Figure 22-5 A, Shouldered defects are usually smaller than 10 mm and are contained. B, Unshouldered defects are larger. During weight bearing, the center of the defect is in contact with the opposing articular surface.

Meniscal lesions should be treated at this time, but only after cartilage has been harvested for cell culture. Cartilage fragments and loose bodies should be removed before the cartilage is harvested.

Only gentle or no débridement of the injury should be performed at this time. When the specifics of the indication have been fulfilled, cartilage is harvested from the upper medial or upper lateral femoral condyle on minor weight-bearing areas (Fig. 22-6). It can also be harvested from the intercondylar notch. In 98% of our cases, cartilage is harvested from the upper medial femoral condyle. With a curette, three to four slices of cartilage 3 to 4 mm wide by 10 mm long should be taken down to subchondral bone on the upper medial femoral condyle.⁶ Approximately 200 to 300 mg of articular cartilage is required for enzymatic digestion and cell culturing. The harvesting area should extend to the synovial lining to allow fibrous and synovial ingrowth to cover the harvest area. In more than 1600 patients who have had cartilage removed for cell culturing, no complications or late symptoms from the donor site have occurred. Optimal harvesting of cartilage is of greatest importance for the success of cell culturing, and optimal cell quality is necessary for the best possible result of this procedure.

Figure 22-6 Arthroscopic views show harvesting of articular cartilage from the upper medial femoral condyle with a grasper (left picture) and a ring curette (right picture).

Cell Culturing

The retrieved cartilage is transferred to the cell culture laboratory in a sterile tube containing 0.9% NaCl. Upon arrival, the cartilage is mechanically minced into smaller pieces (1 mm of diameter) and washed in medium supplemented with antibiotics (gentamicin sulfate, amphotericin B, L-ascorbic acid, and glutamine). Then it is subjected to overnight collagenase digestion, allowing isolation of the chondrocytes. The chondrocytes are then cultured in DMEM/F12 with 10% autologous serum supplement and antibiotics. Primary cultures are performed in 25-cm² flasks incubated in 7% CO₂ in air at 37° C. After 1 week, the cells are trypsinized and passed into bigger culture flasks (75 cm²), where they are cultured for an additional week. Two weeks after the culture begins, the cells are trypsinized again, washed, counted, and resuspended in 0.3 to 0.4 mL of implantation medium, in a tuberculin syringe, to a treatment density of 30 million cells/mL. A second surgery is performed for implantation of cells into the cartilage defect area.

Surgical Procedure—Chondrocyte Implantation

Chondral Lesions

The patient is placed under general or spinal anesthesia. With a tourniquet-controlled bloodless field, a minor parapatellar incision is made. The joint is opened and the injury assessed. For good surgical technique, it is important to obtain good access to the defect, and the arthrotomy might need to be adjusted accordingly (Fig. 22-7). The patella may have to be dislocated in the case of implantation to multiple femoral or patellar lesions.

Figure 22-7 The arthrotomy is adjusted for good exposure of the defect.

Clinical and radiologic assessment has to be performed before surgery is undertaken, revealing a potential indication for a realignment procedure. A realignment procedure is then scheduled in patients with patellar lesions and patellofemoral malalignment or instability. Tibial or femoral osteotomies are performed when needed, in cases of excessive varus or valgus deformity, for protection of the implanted area. Corrective operations (osteotomy, reconstruction of extensor mechanism, ACL reconstruction) are performed before the cells are implanted. In tibial osteotomy, medial transfer of the tibial tuberosity, or ACL reconstruction, fixation is performed at the end of the procedure before the cells are implanted.

Excision and Débridement of the Lesion

The cartilage lesion area is assessed, incised, and débrided with a curette down to the subchondral bone and until healthy cartilage is reached in the periphery of the defect. Radical excision is the key to success. Resulting lesions should be as circular or as oval as possible. If the lesion is not contained by healthy cartilage, it is better to leave a 3- to 4-mm rim of acceptable cartilage than to have the lesion border bone or synovium. Gentle débridement of the excised area is performed down to subchondral bone without causing any bleeding. If bleeding occurs, an epinephrine sponge or a drop of fibrin glue can stop it. The excised defect is then measured in its longest diameter and longest perpendicular diameter. The defect should be shaped as geometrically as possible. A template of sterile aluminum foil or paper is used to model the exact size of the defect (Fig. 22-8).

Figure 22-8 All damaged or undermined cartilage is excised (A) and carefully débrided (B). A template of the defect is made from sterile aluminum foil (C).

Harvesting of the Periosteal Flap

Through a separate incision on the upper medial aspect of the tibia, the periosteum is dissected free of fascia, fat, and fibrous tissue. Even passing vessels should be dissected off the flap. Measure the intended periosteal flap, or use the template to create the exact size and form. Oversize the periosteal flap by adding 1 to 2 mm to the periphery of the intended flap. Incise the periosteum and use a sharp elevator to remove the periosteal flap. Use small movements to avoid rifts in the periosteum (Fig. 22-9). Mark the side of the periosteum to allow identification of the cambium layer. Saline is used to keep the periosteal flap moist. The periosteal flap should be as thin as possible and transparent to achieve more volume in the defect and to allow the cells to spread and expand. The thinner the periosteal flap, the less is the risk for hypertrophy, fibrillation, or other complications.

Figure 22-9 A, Careful dissection to gain access to good-quality periosteum. B, The template is used to determine the correct size and form of the periosteal flap. C, With careful technique, the flap is removed.

Suturing of the Periosteal Flap

Anchor the periosteal flap in four corners with the cambium layer facing the inside of the bone of the defect. Then adapt the periosteum to the surrounding cartilage by placing 6-0 resorbable suture at 4- to 6-mm intervals. Insert the suture to a depth of at least 5 to 6 mm to avoid cutting through the cartilage. Intervals between sutures are sealed with fibrin glue. An opening in the upper part of the defect is left for injection of the cells.

Before injecting the cells, check that there is no leakage by introducing a soft catheter with a syringe into the defect. Inject saline slowly into the defect and check for any leakage. Then aspirate the saline and inject the cells into the defect, starting distally and withdrawing the syringe proximally as the cells are injected. Close the injection site with suture and fibrin glue (Fig. 22-10).

Figure 22-10 A, The periosteal flap is first anchored with a suture in each corner. B, The flap is then sutured to the cartilage rim. C, The integrity of the chamber under the flap is tested with an injection of saline.

Osteochondral Lesions (Osteochondritis Dissecans)

When osteochondritis dissecans is treated by ACI, attention must be paid to the depth of the defect. If the bony defect is shallower than 6 to 8 mm, the lesion is treated the same way as a chondral lesion. Gently débride the sclerotic bottom of the defect, but be careful to not cause bleeding. The cartilage is incised and débrided to vertical edges of healthy cartilage. Cover the defect with a periosteal flap, seal, and check for leakage. Then implant the chondrocytes and close the last opening.

If the bony defect is deeper than 6 to 8 mm, ACI is not enough, and concomitant autologous bone grafting is needed (“sandwich technique”). Start by abrading the sclerotic bottom of the defect to spongy bone and undercut the subchondral bone plate. Use a 2-mm bur and drill multiple holes into the spongy bone. The cartilage is débrided to healthy cartilage with vertical edges. Then harvest cancellous bone for grafting of the bony defect. If the bony defect is small, use bone from the tibial or femoral condyle, but if the defect is larger, bone has to be harvested from the iliac crest. Pack the bone from the bottom up and try to shape the bone graft to the contour of the condyle.

Harvest a periosteal flap to cover the bone graft at the level of subchondral bone, with the cambium layer facing the joint. Anchor it with horizontal or mattress sutures placed into the cartilage or through small drill holes in the subchondral bone plate, and use fibrin glue under the flap for fixation to the bone graft. This technique will avoid bleeding into the cartilage defect. Another periosteal flap is harvested and sutured to the cartilage edges, with the cambium layer facing the defect. Use fibrin glue to seal the intervals between sutures. Test for a watertight seal with a gentle saline injection. If no leakage is present, aspirate the saline and inject the chondrocytes. Close the last opening and seal with fibrin glue (Fig. 22-11).

Figure 22-11 Schematic drawing of the sandwich procedure with layers of transplanted bone, periosteal flap, chondrocytes, and periosteal flap.

The Concept of Optimal Environmental Conditions for the Short- and Long-Term Survival of Repair Tissue

Over the years, it has become obvious that for ACI and concomitant procedures, it is mandatory to create optimal local environmental conditions for the short- and long-term survival of the repair. Malalignment and instability will need corrective surgery for a good result. Procedures such as anterior cruciate ligament (ACL) reconstruction or high tibial osteotomy may be performed at the same time that the biopsy specimen is harvested. Otherwise, they could be done concomitant with the implantation. Pathologic mechanics in the joint reduces the chance of successful repair. Patellar lesions are often related to a maltracking or unstable patella; the patella must thus be realigned or stabilized for good healing. Stabilizing procedures may include anteromedialization of the tibial tuberosity, lateral release, proximal medial soft tissue shortening, and trochlear grooveplasty (if it is dysplastic). In patients with trochlear and patellar lesions, especially large and uncontained ones, unloading with ventralization of the tibial tuberosity should be considered. A torn ACL is reconstructed after the cartilage lesion is débrided and covered with periosteum, but before the chondrocytes are injected. To unload the transplanted area when a varus or valgus deformity is present, a high tibial or distal femoral osteotomy is performed. When these corrective surgeries are performed, a brace-limiting range of motion of 0 to 60 degrees is used postoperatively for 3 weeks, and for the following 3 weeks, range of motion is limited to 0 to 90 to 120 degrees. In patients with previous total or subtotal meniscectomy, meniscus allograft implantation should be considered.