Open Osteochondral Autograft Transfer System (OATS)/Mosaicplasty for Osteochondral Lesions of the Knee
Thomas J. Gill
Indications
• Symptomatic grade III-IV femoral condyle defect 1-4 cm2
• MRI demonstrates focal osteochondral defect of the weight-bearing femoral condyle, with mild associated subchondral femoral condylar edema as seen on sagittal image (Fig. 57-1).
• Cartilage fragment displaced toward intercondylar notch.
• First- or second-line treatment
• High physical demand patient
Equipment
• Standard operating room table
• Lateral post at level of distal femoral metaphysis
• Tourniquet (usually 34″ cuff)
• U-drape 1015
• Bovie
• Disposable OATS kit (plugs come in 6, 8, and 10 mm)
• Z retractors
• Rongeur
• Curette
• Microfracture pick set
• Open knee retractor kit
Prep/Drape
1. Well-padded thigh tourniquet as high as possible, 1015 U-drape (Fig. 57-2A).
2. Supine with lateral leg post (Fig. 57-2B).
3. Horizontal post or “bump” at the level of the mid-tibial diaphysis to hold the knee in hyperflexion (more than 90 degrees) when the knee is flexed after draping and the foot placed just proximal to the post (Fig. 57-2C).
4. Prepare thigh, knee, and ankle.
5. Draping: half sheet down, half sheet up, and blue U-drape. Foot in blue impervious stockinette. Leg wrapped with Coban (3M, St. Paul, MN). Lower extremity drape.
 Figure 57-1 | A. Coronal T2-weighted fat-suppressed. B. Sagittal T2-weighted fat-suppressed. |
 Figure 57-2 | A. Well-padded thigh tourniquet as high as possible, 1015 U-drape. B. Supine with lateral leg post. C. Horizontal post or “bump” at the level of the mid-tibial diaphysis to hold the knee in hyperflexion (more than 90 degrees) when the knee is flexed after draping and the foot placed just proximal to the post. |
Technique
Surgical Approach
• Knee arthroscopy is performed first to evaluate the chondral lesion, confirm planned method of treatment, and treat associated pathology such as a meniscus tear or removal of a loose body (Fig. 57-3).
• Decision is made whether to perform the OATS procedure arthroscopically vs open technique.
• My preference for any lesion over 8 mm is to perform an open approach. The surgical outcome is highly dependent on a near-perfect reconstruction of the convex surface of the femoral condyle and articular surface, and I believe this is best accomplished with an open approach.
• After arthroscopy is complete, the limb is exsanguinated, and the thigh tourniquet is inflated to 280 mm Hg.
• Knee is placed in 90-100 degrees of flexion.
• A 3- to 4-cm incision is made for a medial parapatellar approach (medial inferior pole of the patella coursing distally) with a no. 15 blade. Care is taken to maintain well-vascularized skin flaps.
 Figure 57-3 | Knee arthroscopy is performed first to evaluate the chondral lesion, confirm planned method of treatment, and treat associated pathology such as a meniscus tear or removal of a loose body.
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