Objective: Restoration or preservation of the loading tolerance of the knee joint. Delay of the development of degenerative arthrosis.
Indications: Extensive osteochondral defects (traumatic, posttraumatic, osteochondrosis dissecans, focal osteochondronecrosis) within the weight-bearing zone of the femoral condyle. Comorbidities such as malalignment and ligament instabilities should be addressed prior to or, ideally, simultaneously with the Mega-OATS intervention.
Contraindications: Delocalized uni- and multicompartmental osteochondral lesions of the knee. Tricompartmental knee arthrosis. Acute and chronic arthritis or infection of the knee. Chondrocalcinosis. Not simultaneously corrected or noncorrectable malalignment or ligamentous instabilities. Patient's age > 55 years. Postoperative continuation of activities with high loading stresses at high knee flexion angles, e.g. pavior, downhill ski racer.
Surgical technique: Anteromedial or anterolateral arthrotomy. Exposure and measurement of the affected osteochondral area. Reaming of the defect until attainment of a vital bed of the defect. Measurement of the depths of the prepared defect. Removal of the medial posterior femoral condyle. Preparation of the cylinder of the transplant harvested from the removed posterior femoral condyle using a specially designed Mega-OATS workstation (diameter between 20 and 35 mm). Placement of the Mega-OATS cylinder in press-fit technique.
Postoperative management: Initial continuous passive motion therapy, active range of motion 90 degrees -0 degrees -0 degrees , and unloading for 6 weeks postoperatively using crutches, followed by progressive weight bearing with 20 kg per week until full weight bearing. Free active range of motion as tolerated from 7th week. Four-point hard-frame knee orthosis for 6 weeks. Concomitant intensive muscle and proprioceptive training from 3rd to 6th month. Specific sports rehabilitation program starting 7th month.
Results: The initial 17 and 16 patients following Mega-OATS procedure due to a large osteochondral defect (average size 6 cm2, range 4-9 cm2) of the femoral condyle were clinically examined including an image-guided evaluation protocol at an average follow-up of 12 and 55 months, respectively. In the Lysholm Score, there was a significant increase from 62 +/- 4 points (mean +/- SEM [standard error of the mean]) preoperatively to 85 +/- 7 points at 12 months and 81 +/- 4 points at 55 months postoperatively. In nine patients with varus malalignment, a simultaneous high tibial osteotomy was performed. However, a significant difference in the Lysholm Score between the subgroup with and without simultaneous high tibial osteotomy could not be found. In more than 90% of the patients, a high subjective satisfaction rate was noted. Randomized magnetic resonance images revealed a good viability of the Mega-OATS graft as well as an intact posterior horn of the ipsilateral meniscus.