Arthroscopic autologous osteochondral autografting is one of the many tools available to treat cartilage injuries. Osteochondral grafting involves transplanting a healthy peg containing articular cartilage, cartilage tide markers, and subchondral bone into a size-matched area of the injury. The advantages of this technique include the use of articular hyaline cartilage rather than fibrocartilage to repair the defect and maintain the height and shape of the joint. Arthroscopic autologous osteochondral grafting can be done in a single procedure, at low cost, even on an outpatient basis. The alloscopic procedure is technically challenging, and it is not yet possible to completely treat large cartilage defects with this technique due to the limitations of the retrieved material.
Figure 1 Indications for arthroscopic autologous bone cartilage grafting
Figure 2 Large defects with a diameter of more than 2.5 mm have poorer outcomes.
It is a single, full-layered cartilage injury in the range of 1 to 2.5 mm.
Indications and contraindications for surgery
Indications for autologous cartilage grafting include a single, full-layered cartilage defect with a diameter of 1 to 2.5 cm (Figure 1). Large defects (greater than 2.5 cm in diameter) are less effective (Figure 2). In addition, this technique is generally limited to cartilage injuries with subchondral bone defects up to 6 mm in depth (Figure 3). Autologous cartilage grafting is also not suitable for knees with damage to all adjacent articular cartilage (equivalent to tibial cartilage type IV injury), multiple type IV cartilage injuries, and unstable or poorly aligned knees. Expected results are compromised in patients older than 35 years of age, and some authors consider this technique contraindicated in patients older than 50 years of age. Other contraindications include a history of knee infection, intra-articular fractures, rheumatoid arthritis, and extensive degenerative arthritis (Figure 4). Meniscal tears and ligament instability are not absolute contraindications, but such conditions must be addressed at the time of cartilage grafting. Autologous cartilage grafts are most commonly used in the femoral condyle, although there are reports of tibial plateau, talus, and patellar lesions using autologous grafts.
Figure 3 Arthroscopic autologous osteochondral grafting is limited to subchondral bone defects up to 6 mm in depth
Contraindications include joint infection, intra-articular fractures, rheumatoid arthritis, and extensive osteoarthrosis
Instrumentation
The osteochondral graft (COR) system allows for precise extraction of the osteochondral pegs for implantation into the same size defective area drilled. This bit makes it easier to keep the recipient zone hole perpendicular to the adjacent articular cartilage surface, allowing for a better match between the recipient and donor zone retrieval sizes.
Figure 5 COR retrieval cutter teeth allow for depth-accurate cutting
Figure 6 Drilling of the lesioned recipient area with the drill bit
Technique
A thorough arthroscopic exploration of the knee is first performed for evaluation. When a limited, total cartilage defect is found, it is important to explore all areas of the knee, including the posterior lateral saphenous fossa and the lower meniscus to find and remove any mobile cartilage fragments (Figure 7). Arthroscopic grafting is indicated for most defective lesions; however, large and more posterior defects require extreme knee flexion to achieve an angle perpendicular to the articular cartilage, sometimes requiring limited dissection of the joint to achieve this angle. A lumbar puncture needle is used to determine the optimal angle of access, ensuring that the access is perpendicular to both the recipient and donor areas. Arthroscopic autologous cartilage grafting is accomplished in four steps: 1. assessment and preparation of the defective area; 2. determination of the number of grafts; 3. harvesting; and 4. preparation of the implantation area and implantation of the autologous peg.
Figure 7 It is important to visualize all areas of the knee, including the posterior lateral saphenous fossa and the underside of the meniscus, to remove all mobile cartilage fragments.
Figure 8 Preparation of the lesion area includes removal of loose cartilage fragments and scraping a vertical edge of the defect with a spatula.
Evaluation and preparation of the defect area
The knee and defect area should be carefully evaluated to determine that the selection criteria are met and that there are no contraindications to this procedure. Preparation of the defect area includes removal of all free articular cartilage debris and creation of a vertical cartilage wall at the defect edge using a spatula (Figure 8) or an arthroscopic knife. Remaining articular cartilage on the subchondral bone surface is removed, but extensive bleeding of the bone surface should be avoided. For better planning of the bone graft, the initially implanted peg should be placed in the most anterior part of the defect area immediately adjacent to the articular cartilage.
Figure 9 Estimation of the number of grafts needed with a probe or retriever
Figure 10 Determining the number of bone implants for cases with significant bone defects using different depths of retrievers
Once the defect boundary is determined, the number of bone grafts needed can be estimated with a probe (Figure 9) or the defect size and depth can be measured with a retrieval cannula to determine which shape of peg is best for the defect area. The depth of the defect area can be estimated using the COR system, i.e., measured with a single probe or a measuring tape on the side of the retrieval cannula. In general, a series of 6-mm diameter graft pins can be implanted arthroscopically and filled into the defect area. Larger pins can be obtained, but they often require a small incision for implantation and tend to involve the high-weight-bearing cartilage of the donor area.
The depth of the defect area should also be analyzed. Most defects do not have a significant bone defect. In these cases, a standard 8 mm retrieval cannula depth is sufficient to fill the defect area. However, some defects (especially those with exfoliative chondromalacia) have significant bone defects that must be addressed. Such cases can be treated with bone grafting in the bone defect area in a single procedure with subsequent cartilage grafting, or by obtaining a longer bolus using a different depth of retrieval cannula and placing the graft in position so that its cartilage surface is level with the surrounding cartilage surface, but exposing the cancellous bone beneath the bolus cartilage to the base of the bone depression (Figure 10).
Evaluation of the shape of the donor and recipient articular cartilage is also important in the graft, which allows the cartilage surfaces to achieve the best possible match. For large defects, the use of multiple peg posts can be effective in reconstructing the original shape of the condyle. Although the use of smaller pins may provide a better reconstruction of the shape, the reduced strength and stability of the graft pins can offset its benefits and increase the number of surgical steps.