Osteochondral Allografting in the Knee

Andreas H. Gomoll, Richard Kang and Brian J. Cole

• This chapter summarizes the indications for and technique and results of osteochondral allograft transplantation for the treatment of symptomatic cartilage defects of the knee.

Important Points

• Osteochondral transplants are indicated for symptomatic, full-thickness chondral defects. Osteoarthritis, with the exception of very specific circumstances, is a contraindication.

• Two techniques are presented: the dowel (Mega-OATS) technique and the less commonly used shell allograft.

Clinical and Surgical Pearls

• Ensure that the graft has been received in acceptable condition and that the size and side are correct before the patient is anesthetized.

• Adequate exposure is key to ensure perpendicular pin placement.

• Takedown of the meniscus can improve access, especially for posterior defects; this is repaired during closing.

• A positioning device can be helpful to stabilize the extremity in hyperflexion for very posterior lesions.

• Dilate the recipient site and bevel the graft edges to facilitate introduction with little force.

• It is preferable to recess the graft rather than to leave it proud.

Clinical and Surgical Pitfalls

• Do not use excessive force to seat the graft, because this results in chondrocyte death. Ideally, the graft should be seated with use of manual pressure and range of motion.

• Grafts most commonly fail through the bone, not the cartilage; make sure to keep the plug thin (6 to 8 mm) so that only little bone has to be incorporated.

• Avoid excessive impact activities during the first year. The subchondral bone is only slowly substituted and is at its weakest several months after the operation.

Osteochondral allografting in the knee has been used for more than 20 years to reconstruct osteochondral defects resulting from trauma, malignant disease, and developmental disorders.¹⁴ In current practice, osteochondral allografts are most commonly used for the treatment of symptomatic osteochondritis dissecans and other chondral lesions that have failed primary treatment, such as internal fixation of osteochondritis dissecans fragments, marrow stimulation, mosaicplasty, and autologous chondrocyte implantation. Increasingly, allografts are now also being used as the primary treatment in situations in which other restorative procedures have demonstrated limited success, such as in the very large or uncontained defect and in the older population of patients. Although use of the procedure was initially limited by the low number of available grafts, fresh allograft tissue is becoming increasingly available as a result of improved harvesting and storage protocols, but the supply is still outpaced by a rapidly increasing demand.

Preoperative Considerations

History

Osteochondral allografting is indicated in patients with osteochondral or, less frequently, isolated chondral or osseous defects. Patients with osteochondritis dissecans often report a history of failure of other treatment modalities, such as immobilization, open reduction and fixation of the fragment, and simple excision. The onset of symptoms is mostly insidious, with no distinctive trauma. Conversely, chondral defects often result from athletic injuries that lead to tears of the anterior cruciate ligament or the meniscus, which in turn result in acute or secondary damage to the articular surface. Lastly, young patients with osteonecrosis and secondary articular collapse can be amenable to osteochondral allografting in an attempt to avoid joint replacement surgery.

Figure 63-1 illustrates the following radiographic positions:

Figure 63-1 Anteroposterior and lateral radiographs of an osteochondral lesion of the medial femoral condyle. The patient had previously been treated with pinning of an osteochondritis dissecans lesion, then underwent bone grafting because of failure of the initial procedure.

• Standing anteroposterior view with knee in full extension

• Standing posteroanterior view with knee in 30 to 60 degrees of flexion (notch, tunnel or Rosenberg view)

• Lateral view

• Patellar sunrise view

• Bilateral long-leg alignment views

Magnetic Resonance Imaging

Magnetic resonance imaging is the “gold standard” for osteochondral lesions. Fluid or edema behind the lesion is suggestive of an unstable fragment.

Evaluate the extent and depth of osseous involvement. Beware of high sensitivity for subchondral edema, which leads to false positives for osseous disease. Computed tomography (CT) scan, especially when combined with arthrography, can provide very high resolution for both cartilage and subchondral bone (Fig. 63-2). This can be particularly helpful to evaluate for subchondral sclerosis and cysts that might have to be addressed by bone grafting.

Figure 63-2 Coronal and sagittal computed tomography images show an osteochondral defect of the medial femoral condyle without cartilage cover.

Indications and Contraindications

The typical candidate for osteochondral allografting has a large full-thickness chondral or osteochondral defect; prior procedures, such as the repair of an unstable osteochondritis dissecans lesion, microfracture, osteochondral autograft transfer, and autologous chondrocyte implantation, have failed. Some lesions preclude the use of other cartilage repair procedures because of their large size, specific location, or associated deep osseous defects. Localized unipolar lesions larger than 2 to 3 cm² provide an optimal environment for osteochondral grafting.1,8,9,12

Comorbidities that must be addressed either before or at the time of the osteochondral allografting procedure include malalignment, ligament deficiency, and meniscal insufficiency. Bipolar lesions are a relative contraindication and result in less predictable outcomes. Both lesions should be treated concomitantly; the larger and deeper defect is commonly allografted, and the kissing lesion is often amenable to microfracture.

Allograft Preservation and Graft Sizing

Traditionally, grafts were retrieved and reimplanted fresh within 24 to 48 hours. Current standard clinical practice ¹⁹ uses prolonged fresh osteochondral allografts that are stored for 2 to 4 weeks at approximately 4° C. The extended storage time allows for bacterial and viral testing before release, and also facilitates scheduling. Grafts are generally size, side, and compartment specific—for example, a left medial femoral condyle defect is treated with use of a left medial femoral hemicondyle graft. Given the popularity of the procedure, wait times for suitable grafts have increased, and the use of contralateral side and compartment grafts has become more common—for example, use of the right lateral hemicondyle to treat aforementioned left medial femoral condyle defect. Graft size is determined on preoperative MRI or CT scans, or AP and lateral radiographs obtained with sizing markers for correction of magnification. In general, size mismatch is more acceptable when the graft is larger rather than smaller than the recipient condyle. The tissue banks usually require the width of the tibial plateau, as well as the width and length of the hemicondyle. Also, it is helpful to relate the size of the defect and likely required dowel size. Although no consensus exists, we accept grafts that are smaller by 1 to 2 mm or larger by up to 5 mm.