Autologous chondrocyte implantation
Autologous chondrocyte implantation (ACI) is a cell-based cartilage reconstruction or replacement method where hyaline articular cartilage is directly administered and retained. It can be used for larger chondral lesions, where the subchondral bone plate remains intact.
Autologous chondrocyte implantation was first described by Brittberg and his colleagues in 1994 1,2.
Indications for autologous chondrocyte implantation include larger full-thickness defects (e.g. 2-10 cm2) in younger patients 2,3. It can be used to treat injuries that have failed debridement or other cartilage repairs 2. It also can be performed after a preceding bone graft for deeper lesions 3.
Contraindications of the autologous chondrocyte implantation include:
- inflammatory arthritis
- kissing lesions (in particular, Outerbridge grade 3-4 on the opposing surface)
- reluctance to cooperate with postoperative rehabilitation
Autologous chondrocyte implantation is a two-step procedure comprises the following 1-6:
- arthroscopic harvesting of chondrocytes usually from non-weight bearing, low contact pressure areas (e.g. lateral margins of the intercondylar notch)
- culture and multiplication ex vivo typically for 4-8 weeks
- thorough debridement of cartilage margins in a circular or oval shape
- removal of the calcified cartilage
- chondrocyte implantation
- sealing with fibrin glue and coverage with a periosteal flap (1st generation)
- sealing with a synthetic collagen membrane (2nd generation)
- within a biodegradable scaffold (3rd generation)
Complications of autologous chondrocyte implantation include the following 2,5:
- poor integration with the subchondral bone
- periosteal cover hypertrophy (1st generation)
As with other chondral repair and reconstruction techniques, autologous chondrocyte implantation can be assessed with MR imaging and includes the evaluation of defect filling, the peripheral integration and morphologic characteristics of cartilage and subchondral bone as well as the assessment of the donor site. MRI sequences most commonly used for the evaluation of cartilage are proton density-weighted, intermediate weighted images and T2 weighted images with and without fat saturation and 3D images 4,5.
The demonstration of a complete filling of the chondral defect to the level of adjacent native articular cartilage in the postoperative period indicates a complete integration.
The MOCART scoring system can be used for the evaluation.
MRI can demonstrate underfilling of the defect or complications such as delamination, periosteal cover hypertrophy, and poor integration with the subchondral bone 5.
Fluid equivalent signal intensity at bone or cartilage interface indicates delamination. Persistent or increasing subchondral bone marrow edema suggests poor or integration with the subchondral bone 5.
The radiological report should include the description of the following features 5:
- degree of defect filling
- the cartilaginous and subchondral border zone
- signal characteristics, structure and thickness of the graft cartilage
- the articular surface of the graft
- subchondral bone plate and subchondral bone (bone marrow edema, subchondral cysts, granulation tissue)
- presence of chondral osteophytes
Autologous chondrocyte implantation has shown satisfactory clinical results with improvement of pain, function and mobility over a long-term follow up of 10 years on average 5.
Advantages include good long term results, it can be used to treat multifocal cartilage injuries and less donor donor-site complications or discomfort than e.g. osteochondral autograft transplantation (OAT) 2,3.
Disadvantages are the two-stage procedure, increased failure rate if performed as a salvage procedure of microfracture, and a long course of postoperative rehabilitation not permitting a return to sports for up to 12-18 months 2,3.
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