Our mothers always told us to eat more oats. A simple surgical procedure for osteochondral defects (osteochondritis dissecans) is easier to swallow than the bland carbs thrust at us as children every morning before school. Here is a quick synopsis of the Osteoarticular Transfer System (OATS), otherwise known as the Osteochondral Autograft Transfer System procedure I employ using the Arthrex system.
The OATS procedure is a fantastic procedure for an arthritic defect within the joint. The use of this procedure is limited to focal arthritic defects. Patients with diffuse arthritis (like one would see in degenerative joint disease or osteoarthritis) are not viable candidates for the OATS procedure. Some debate the size at which subchondral drilling microfracture surgery is indicated. Most literature has any lesion over 10-15 mm requiring more than just microfracture surgery.1-3
When examining osteochondritis dissecans with the Berndt-Hardy classification system, one should generally treat stage I and II lesions conservatively. Canale and Belding recommended surgery for all stage III lateral transchondral lesions but believed that stage III medial lesions should receive conservative treatment with casts, patellar braces, ankle corsets or arch supports.1 Patients with stage III and IV osteochondritis dissecans are more likely to be surgical candidates. Many investigators seem to agree that both medial and lateral stage IV lesions should have surgical treatment.1-3 Most osteochondritis dissecans of the talus occurs anterolaterally but can also occur rarely on the medial side.2
My preference is the Arthrex system, which makes it simple for stage 3 and 4 lesions. I will attempt to give step-by-step guidance on how to perform the procedure.4
When making the incision, avoid severing the deltoids completely as they provide stability and vascularity to the medial malleolus.
For posteromedial lesions, make a curved longitudinal incision over the medial malleolus so you can visualize the anterior medial talar dome. Protect the neurovascular bundle with retractors. If the lesion is accessible, then no medial malleolar osteotomy is necessary.
Lateral lesions require release of the anterior talofibular ligament. This provides adequate lateral talar exposure when one plantarflexes and performs forcible subluxation of the foot.
When using a malleolar osteotomy for lateral lesions, you may need to direct the cut laterally. Pre-drill the medial malleolar with two 0.045-inch pins slightly divergent to prevent proximal slippage of the medial malleolus during screw insertion.
Use intraoperative fluoroscopy and create a 45-degree osteotomy cut from the superior medial malleolus down to the junction of the tibial plafond and medial colliculus. After the procedure, replace the medial malleolus.
Insert two 0.045-inch wires into the cannulated holes. Insert two cannulated, 4.5 mm screws into the holes while reducing the malleolus anatomically.
When performing a mosaicplasty, inspect the lesion and drill it centrally with a guide pin. Overdrill the guide pin with appropriate size and depth of about 15 to 20 mm. Insert the OATS alignment rod and tap it for depth measurement. The appropriate diameter is based on the size of the overdrilled osteochondritis dissecans site.
Surgeons can opt for the allograft of their choosing. To avoid having to call in another surgeon to harvest a graft outside of the foot, the talar neck offers an easily accessible location. Typically, one can harvest the graft from the dorsal medial talar head proximal dorsal to the articular surface. This is a simple procedure in which one uses a harvesting tube.
One can visualize the graft size through the donor harvesting tube. If necessary, the surgeon can use a rongeur on any excess cancellous graft.
At this point, set the plug into the recipient hole in the talus. If the graft is proud, use a tamp until the graft is flush with the articular surface of the talar dome.
There are many adaptations to this procedure but I find that this is a simple, open, one-incision technique that yields good results.
1. Canale ST, Belding RH. Osteochondral lesions of the talus. J Bone Joint Surg Am 1980; 62(1):97–102.
2. Fallat LM, Christensen JC, Hord JA. Osteochondroses of the foot and ankle. In: Southerland JT (ed): McGlamry's Comprehensive Textbook of Foot and Ankle Surgery, fourth edition, Ch. 54, Lippincott, Williams and Wilkins, 2012, pp. 780-800.
3. McNickle AG, Provencher MT, Cole BJ. Overview of existing cartilage repair technology. Sports Med Arthrosc. 2008;16(4):196-201.
4. Available at http://www.arthrex.com/foot-ankle/oats-technique  .
For more information on this blog, please contact Dr. Bowman at
www.houstonfootspecialists.com  .