Trabecular Bone Strain Changes Associated with Subchondral Comminution of the Distal Tibia

OBJECTIVETo measure trabecular bone strain changes resulting from three increasing subchondral bone defects in the distal tibia. DESIGNCadaveric biomechanical model. SETTINGContact radiographs were made from sagittal sections of human cadaveric distal tibia under no load and loaded to 400 N. Digital images, made from contact radiographs of unloaded specimens, were compared to corresponding digital images of loaded specimens using custom software that measures trabecular deformation and calculates trabecular bone strain. INTERVENTIONTwelve specimens were initially loaded intact in compression. Testing was repeated after creating three increasing circular subchondral bone defects in the center of a sagittal cross-section of the distal tibia. Defects were 10%, 20%, and 30% of the sagittal diameter of the distal tibia. MAIN OUTCOME MEASURESMaximum shear strain, maximum principal strain, and minimum principal strain were measured in six discrete regions in the trabecular bone in the distal tibia. RESULTSSmall defects (10%) caused minimal strain elevations. Significant increases in trabecular bone strain were measured with medium (20%) and large (30%) defects. Compressive strain increases as high as 1,400 microstrain (10 strain) were measured adjacent to and proximal to the defects with medium and large defects. CONCLUSIONSSubchondral defects cause size-dependent elevations in trabecular bone strain in the distal tibia. Medium and large defects caused rapidly increasing trabecular bone deformation under load.