Access Type

Open Access Thesis

Date of Award

January 2012

Degree Type

Thesis

Degree Name

M.S.

Department

Mechanical Engineering

First Advisor

King-Hay Yang

Abstract

Purpose: To examine the relationship between well-shouldered osteochondral defects and

defects of different geometries by studying their effects on rim stress concentration and

load redistribution in the human knee.

Methods: Ten fresh-frozen cadaveric knees were mounted at 30° of flexion in a materials

testing machine. Digital electronic pressure sensors were placed in the medial and lateral

compartments of the knee. Dynamic pressure readings were recorded throughout the

loading and holding phases as each knee was loaded to 700N and held for 5 seconds.

Artificial defects were created in each knee to simulate well-shouldered defects and

beveled-defects. Loading was repeated for well-shouldered and beveled osteochondral

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 pressures increasing as defect size increased (p<0.05). Average radius from the center to the rim of

peak pressure was found to be higher among beveled defects although this was not found

to be statistically significant. Peak pressure values did not increase significantly as

defects were enlarged.

Conclusions: Beveled defects were found to affect rim stress concentrations over their

well-shouldered counterparts. Although this result was not statistically significant,

multiple studies point to a link between osteochondral defects and degeneration of

surrounding articular cartilage. Based on this finding, it would be prudent when using a

size criterion in assessing severity of an osteochondral defect, to use the outermost border

of the defect as a measure of defect size.

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