Ex Vivo Equine Medial Tibial Plateau Contact Pressure With an Intact Medial Femoral Condyle, With a Medial Femoral Condylar Defect, and After Placement of a Transcondylar Screw Through the Condylar Defect

Objective: To determine ex vivo contact data on the equine medial tibial plateau loaded by an intact medial femoral condyle (MFC), by an MFC with an osteochondral defect, and with a screw inserted in lag fashion through the MFC defect. Study Design: Ex vivo experiment. Animals: Stifles (n=6). Horses (n=4). Methods: Stifle joints were axially loaded to 1800N at 155°, 145°, and 130°, under 3 conditions: Intact, MFC with a 15mm circular osteochondral defect, and with a transcondylar screw inserted in lag fashion through the defect. An electronic pressure sensor (Tekscan®) on the medial tibial plateau recorded contact area, force, peak pressure, and contact maps. Stress load (N/cm²) was calculated for the entire medial plateau and in 3 sub-regions; cranial, caudal, and central. Significance was set at P≤.05. Results: Flexion increased force, contact area, and stress load for all conditions. An MFC defect significantly reduced force at both flexion angles and contact area at 145°. The transcondylar screw returned force to intact values at 130° and reduced contact area in extension. Intact MFC contact maps revealed pressure peaks on the central cartilage at all angles and contact pressure and area expansion and caudal movement with flexion. Contact maps with an MFC defect amplified the caudal and abaxial pressure movement during flexion, and the screw did not further change them. Conclusions: Stifle flexion increases force, contact area, and stress load on the medial tibial plateau and is most pronounced caudally. An MFC defect alters load on the medial tibial plateau, and a transcondylar screw may reverse some of those changes.