Effects of Proud Large Osteochondral Plugs on Contact Forces and Knee Kinematics: A Robotic Study

Document Type


Publication Date

May 2018




BACKGROUND: Osteochondral allograft (OCA) transplantation is used to treat large focal femoral condylar articular cartilage defects. A proud plug could affect graft survival by altering contact forces (CFs) and knee kinematics. HYPOTHESIS: A proud OCA plug will significantly increase CF and significantly alter knee kinematics throughout controlled knee flexion. STUDY DESIGN: Controlled laboratory study. METHODS: Human cadaver knees had miniature load cells, each with a 20-mm-diameter cylinder of native bone/cartilage attached at its exact anatomic position, installed in both femoral condyles at standardized locations representative of clinical defects. Spacers were inserted to create proud plug conditions of +0.5, +1.0, and +1.5 mm. CFs and knee kinematics were recorded as a robot flexed the knee continuously from 0 degrees to 50 degrees under 1000 N of tibiofemoral compression. RESULTS: CFs were increased significantly (vs flush) for all proudness conditions between 0 degrees and 45 degrees of flexion (medial) and 0 degrees to 50 degrees of flexion (lateral). At 20 degrees , the average increases in medial CF for +0.5-mm, +1-mm, and +1.5-mm proudness were +80 N (+36%), +155 N (+70%), and +193 N (+87%), respectively. Corresponding increases with proud lateral plugs were +44 N (+14%), +90 N (+29%), and +118 N (+38%). CF increases for medial plugs at 20 degrees of flexion were significantly greater than those for lateral plugs at all proudness conditions. At 50 degrees , a 1-mm proud lateral plug significantly decreased internal tibial rotation by 15.4 degrees and decreased valgus rotation by 2.5 degrees . CONCLUSION: A proud medial or lateral plug significantly increased CF between 0 degrees and 45 degrees of flexion. Our results suggest that a medial plug at 20 degrees may be more sensitive to graft incongruity than a lateral plug. The changes in rotational kinematics with proud lateral plugs were attributed to earlier contact between the proud plug's surface and the lateral meniscus, leading to rim impingement with decreased tibial rotation. CLINICAL RELEVANCE: Increased CF and altered knee kinematics from a proud femoral plug could affect graft viability. Plug proudness of only 0.5 mm produced significant changes in CF and knee kinematics, and the clinically accepted 1-mm tolerance may need to be reexamined in view of our findings.