Trabecular bone strain changes associated with subchondral bone defects of the tibial plateau

Objective: To measure trabecular bone strain changes resulting from three increasing subchondral bone defects in the medial tibial plateau. Design: Cadaveric biomechanical model. Setting: Contact radiographs were made from coronal sections of human cadaveric proximal tibia under no load and loaded to 400 newtons (N). Digital images made from contact radiographs of unloaded specimens were compared to corresponding digital images of loaded specimens using in-house software that detects trabecular deformation and measure trabecular bone strain. Intervention: Ten specimens were loaded intact and with three increasing circular subchondral bone defects and centered under the subchondral plates in the medial tibial plateau that were 10%, 20%, and 30% of the coronal width of the medial plateau. Main Outcome Measure: Maximum shear strain and mini- mum principal strain were measured at approximately 2,600 discrete points in the trabecular bone in the medial tibial plateau. Results: Trabecular strain increased most dramatically as defects increased from the medium (20%) to the large (30%) defect. The regions of greatest strain elevation were between the physeal scar and joint line near the medial cortex. Small (10%) and medium (20%) defects resulted in modest strain elevations. Conclusions: Subchondral defects cause size-dependent elevations in trabecular bone strain in the medial tibial plateau. A size threshold may exist, above which the trabecular bone is subjected to rapidly increasing deformation under load.