Osteochondral autograft transplantation

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Osteochondral autograft transplantation (OAT) or mosaicplasty is a tissue-based cartilage reconstruction or replacement method which is used for smaller chondral and osteochondral lesions.

History

Osteochondral autograft transplantation (OAT) or mosaicplasty was originally reported in the early 1990s and further refined in that decade .

Indications

Osteochondral autograft transplantation surgery was initially conducted in small chondral defects of the knee but has been used in multiple other joints like the hip, ankle, shoulder and elbow in the meantime. Also, smaller osteochondral defects can be treated with technique . The typical indication is active younger patients with smaller (<2-4 cm) chondral and osteochondral defects .

Contraindications

Relative contraindications of the osteochondral autograft transplantation include :

larger lesions (in particular ≥8 cm)
inflammatory arthritis
severe osteoarthritis
no appropriate donor site
noncompliance in rehabilitation

Procedure

The osteochondral autograft transplantation or mosaicplasty technique comprises the following :

debridement of the damaged cartilage for stable healthy borders
harvesting of cylindrical osteochondral plugs from non-weight bearing, low contact pressure areas (e.g. superomedial and superolateral trochlea)
creation or drilling of matching, cylindrical recipient holes
press-fit insertion of the harvested plugs into the chondral defect in a mosaic pattern, restoring the joint surface morphology
optional back-filling of the donor-site by bone graft substitute

Complications

poor graft integration (e.g. due to peripheral chondrocyte death from mechanical trauma)

osteonecrosis of the graft
overfilling of the donor site
posttraumatic arthritis at the donor site

Radiographic features

Osteochondral autograft transplantation has been evaluated with MR imaging and includes the assessment of defect filling, the peripheral integration and morphologic characteristics of the bony and cartilaginous portions of the cylindrical, osteochondral plug as well as the evaluation 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 fat-saturated T1 weighted images .

MRI

A good postoperative result presumes a complete defect fill with uniform cartilage signal intensity, without fissures or gaps at the bony and chondral interfaces of the freshly introduced osteochondral autograft .

Within the first year after osteochondral autograft transplantation bone marrow edema like signal in and around the plug is a frequent finding. This will gradually resolve afterwards .

As with other methods of cartilage repair, the MOCART scoring system can be used for evaluation .

Subchondral cyst formation or persisting bone marrow edema like-signal for more than 18 months after surgery may indicate poor graft integration .

Joint effusion and reactive synovitis may still be visible in up to 2 years .

Radiological report

The radiological report should include the description of the following features :

degree of the defect filling
signal characteristics and thickness of the graft cartilage
articular surface of the graft
border zone to the native cartilage
presence of chondral fissures and chondral delaminations
presence of chondral osteophytes
subchondral bone plate
border zone to the surrounding bone
subchondral bone (bone marrow edema, subchondral cysts, granulation tissue)

Outcomes

Osteochondral autograft transplantation was found to have better long-term results due to hyaline cartilage repair and a lower reoperation rate than microfracture at 5-10 years follow up .

Other advantages of osteochondral autograft transplantation are :

can be performed as one stage procedure
can be performed arthroscopically
coverage of the lesion with hyaline cartilage
allows earlier rehabilitation as a tissue-based therapy
few complications
relatively low cost

Disadvantages are the increased complexity of the implantation in medium-sized lesions since multiple osteochondral plugs need to be placed adjacent to each other and joint congruency should be obtained, and the fact that it cannot be performed on larger lesions due to restricted availability of donor sites .