Contact pressure distribution of osteochondral defects of the knee: effects of non-vertical walls

CONTACT PRESSURE PROPERTIES OF OSTEOCHONDRAL DEFECTS OFTHE KNEE: THE EFFECT OF NON-VERTICAL WALLSbySCOTT ENSMINGERDecember 2012Advisor: Dr. King-Hay YangMajor: Mechanical EngineeringDegree: Master of SciencePurpose: To examine the relationship between well-shouldered osteochondraldefects and defects of different geometries by studying their effects on rim stressconcentration and load redistribution in the human knee.Methods: Ten fresh-frozen cadaveric knees were mounted at 30° of flexion in amaterials testing machine. Digital electronic pressure sensors were placed in the medialand lateral compartments of the knee. Dynamic pressure readings were recordedthroughout the loading and holding phases as each knee was loaded to 700N and held for5 seconds. Artificial defects were created in each knee to simulate well-shouldered defects and beveled-defects. Loading was repeated for well-shouldered and beveledosteochondral defects sized 6, 8, 10, 12, 14, 16, 18 and 20 mm.Results: Stress concentrations around rims of defects were shown to act similarly to a previous study by Guettler et al. As defect size increased, a rim of peak pressures formed on the adjacent cartilage with distance from defect center to rim of peak pressuresincreasing as defect size increased (p<0.05). Average radius from the center to the rim ofpeak pressure was found to be higher among beveled defects although this was not found