Osteochondral allograft transplantation (OCA) is a tissue-based cartilage reconstruction or replacement method which can be also performed for chondral and osteochondral lesions of larger size.
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History
Allograft replacement of osteochondral lesions was first described back in 1908 1.
Indications
Osteochondral allograft transplantation can be performed irrespective of the size of the lesion and is not dependent on the donor site. It can be used to treat larger lesions ≥10 cm2. Typical indications include the following 1,2:
- post-traumatic osteoarthritis with large cartilage or subchondral defects
- osteochondritis dissecans
- focal avascular necrosis
Contraindications
Contraindications of the osteochondral allograft transplantation include 2:
- inflammatory arthritis
- moderate to severe degenerative osteoarthritis
- steroid-induced osteonecrosis
Procedure
Osteochondral allograft transplantation comprises the preparation of the cartilage defect including the debridement of the damaged cartilage for stable healthy borders and the fitting and implantation of the osteochondral allograft 1,2.
There are shell type and deep type allografts with different depths of subchondral bone.
Different graft preservation methods are available with different advantages and disadvantages.
Complications
Complications of osteochondral allograft transplantation include the following 2:
- poor graft integration (e.g. due to peripheral chondrocyte death from mechanical trauma)
- osteonecrosis of the graft
- immune rejection response
- disease transmission
Radiographic features
Similar to other cartilage repair and reconstruction techniques, postoperative results in graft integration and complications of osteochondral allograft transplantation can be evaluated with MR imaging. This includes the assessment of defect filling, the peripheral integration and morphologic characteristics of the bony and cartilaginous portions of the osteochondral allograft. 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 4,5.
MRI
Bone marrow oedema like-signal of the osteochondral allograft is seen in the early postoperative period, which should decrease after 3-6 months 4.
Bone marrow oedema like signal persisting more than 12 months, fluid-signal intensity, fissure or subchondral cyst formation as well as articular surface collapse may indicate poor graft integration.
Abnormal bone marrow within the native bone and the graft and thick host-graft border zone may indicate a potential immune response or graft rejection 5.
Similar to other cartilage repair or reconstruction methods the MOCART scoring system can be applied for postoperative imaging evaluation and follow-up 4,5.
Radiological report
The radiological report should include the description of the following features 4,5:
- degree of the defect filling
- signal characteristics and thickness of the graft cartilage
- the articular surface of the graft
- border zone to the native articular 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 oedema, subchondral cysts, granulation tissue)
Outcomes
Osteochondral allograft transplantation is a viable option for large, full-thickness chondral defects 2,3 6.
Additional advantages include immediate articular surface restoration and the option to replace subchondral bony tissue and no donor site morbidity 3.
Disadvantages are restricted graft availability, the possibility of disease transmission and logistical factors in respect to a narrow time window, if there is an aim to optimise cell viability 3.
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