Should OATS Be Proud?
Abstract & Commentary
Synopsis: Two osteochondral autograft techniques were compared—1 leaving the plugs 2-mm proud and the other flush with the surrounding cartilage. The specimens were studied 3 months postoperatively, and the grafts placed proud were associated with complications.
Source: Pearce SG, et al. An investigation of 2 techniques for optimizing joint surface congruency using multiple cylindrical osteochondral autografts. Arthroscopy. 2001;17(1):50-55.
Osteochondral autografting, commonly referred to as "OATS" (so named for one of three commercially available systems [Osteochondral Autograft Transfer System, Arthrex, Inc—Naples, Fla]) is becoming a popular method for treating isolated focal chondral injuries in the knee. Although original animal studies demonstrated that these grafts can successfully incorporate, there have not been any studies comparing different techniques for plug insertion.1,2 Some anecdotal reports have suggested that these grafts should be placed proud, which would theoretically allow them to "seat" with knee range of motion and weight bearing. This study was designed to study that issue.
Full-thickness chondral defects were created on the weight-bearing surface of the medial femoral condyle (the most common clinical location for chondral defects) in 13 adult sheep. Three 4.5 ´ 10 mm plugs were inserted in a triangular pattern into 14 mm deep recipient sites. The MosaicPlasty technique and instrumentation (Acufex, Smith & Nephew Endoscopy—Mansfield, Mass) was used in this study. In 6 animals, the plugs were placed 2-mm proud, and in the remaining 7 animals, the plugs were placed flush with the surrounding articular surface. The animals were evaluated 3 months postoperatively, and the condyles were evaluated grossly, radiographically, and histologically. The proud grafts did reposition with weight bearing but were associated with fissuring and subchondral cavitation. Pearce and colleagues concluded that grafts should be delivered flush with the joint surface to avoid these complications.
Comment by Mark D. Miller, MD
Although this animal study provides some important insight into proper technique for osteochondral "plug" transfers, 2 important variables were introduced in this study that may differ from clinical application. First, the plugs were inserted into recipient sites that were 4 mm deeper than the plugs themselves. Therefore, the plugs were required to rely on sidewall friction alone for stabilization. Second, the animals were allowed to weight-bear immediately postoperatively. Most protocols for this procedure allow an initial period of protected weight-bearing. Additional studies may provide further insight into these issues. For now, however, Pearce et al’s recommendations that the plugs be inserted flush with the adjacent articular surface (as the manufacturers recommend) should be followed. It is also critical, in my opinion, to both harvest and deliver these plugs with a precise technique. Plug harvest and delivery requires perpendicular orientation of the instruments that may not be possible with arthroscopic techniques alone. Arthrotomies (or at least mini-arthrotomies) should be used whenever this principle is at risk for compromise.
References
1. Hangody L, et al. Autogenous osteochondral graft technique for replacing knee cartilage defects in dogs. Orthop Int. 1997;5(3):175-181.
2. Hangody L, et al. Osteochondral plugs: Autogenous osteochondral mosaicplasty for the treatment of focal chondral and osteochondral defects. Op Tech Orthop. 1997;7(4):312-322.
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