Introduction

Large osteochondral defects in the weight-bearing zone of the medial or lateral femoral condyle, especially in young patients, create a challenge for orthopaedic surgeons. Addressing both the cartilaginous and the osseous defect, mosaicplasty represents a modified technique of the conventional osteochondral autologous transplantation system (OATS) technique by transplantation of multiple OATS plugs into the defect area.^1,² However, this technique is limited because of the availability of the plugs at the donor site. Additionally, a primary stability of multiple plugs as well as restoration of the anatomical congruence at the cartilaginous surface level is technically demanding and often infeasible.

In the 1960s and 1970s, the posterior femoral condyle of the knee was already recognized as a potential donor site for osteochondral tissue.^3,⁴ The transfer of the posterior femoral condyle using an anterior approach was started in the 1990s at our department at klinikum Rechts der Isar in Munich, Germany. The autologous Mega-OATS procedure is a technical advancement of the posterior femoral condyle transfer.^5,⁶ Contrarily, the allogenic Mega-OATS technique illustrates an alternative procedure sparing the posterior femoral condyle as the donor site.⁷ In both autologous and allogenic Mega-OATS techniques, an almost anatomical restoration of the condyle curvature as well as an optimal congruence to the adjacent cartilaginous surface can be achieved. Nevertheless, comorbidities such as malalignment and ligamentous instabilities must be addressed before or ideally simultaneously with the Mega-OATS procedure.

Isolated Mega-OATS procedures as well as Mega-OATS procedures combined with additional procedures (malalignment correction, ligamentous stabilization, meniscus surgery, etc.) were clinically and imaging based (radiological, MRI) reevaluated in the short- and mid-term follow-up. Overall, the reevaluations demonstrated a considerable improvement regarding function, pain reduction, and swelling as well as resumption of sporting activities compared to preoperatively.^5,^6,^8,⁹

Indications

The indication criteria for the Mega-OATS technique are similar to the OATS procedure. However, because of the size of the osteochondral lesion, a conventional single plug OATS technique or a press-fit technique of a limited number of osteochondral cylinders is insufficient for adequate coverage of the defect. Therefore, the Mega-OATS technique is an alternative procedure to the mosaicplasty in which multiple osteochondral plugs are transplanted.

The indication criteria of the Mega-OATS procedure include the following:

• Large traumatic or posttraumatic osteochondral lesions

• Large osteochondritis dissecans with partial (Grade 3B according to König and Imhoff)¹⁰, or complete detachment (Grade 4B according to König and Imhoff)¹⁰ and evidence of avital areas of the osteochondral fragment detected by intravenous fluid-enhanced MRI

• Focal osteonecrosis combined with limited cartilage defect