Chronic Stress Tolerance of Human Articular Cartilage: Developmental Dysplasia of the Hip as a Model of Long Term Overloading
Sponsor: The Whitaker Foundation

Douglas R Pedersen, Ph.D.
Research Scientist, Department of Orthopaedic Surgery

Adjunct Associate Professor of Biomedical Engineering
The University of Iowa

Iowa City, IA 52242
e-mail: Doug-Pedersen@uiowa.edu

Name	Organization	Role on Project
Stuart L. Weinstein, M.D.	University of Iowa	Co-Investigator
Jose A. Morcuende, M.D.	University of Iowa	Co-Investigator
Lori A. Dolan, R.N., M.S.	University of Iowa	Co-Investigator
Thomas D. Brown, Ph.D.	University of Iowa	Co-Investigator

The objective of this proposal is to calculate three-dimensional articular cartilage stresses that may initiate the osteoarthritic process in the human hip. In the absence of trauma or surgical intervention, patients afflicted with developmental dysplasia of the hip (DDH) tend to develop osteoarthritis (OA) much earlier than the population norm. By correlating the presence of OA with cartilage stress profiles over time, the global objective is to identify a threshold of acceptable stress tolerance levels.

From the time of diagnosis and closed reduction of a congenital displaced hip in early infancy, pelvis-centered anteroposterior (AP) radiographs track the progression of hip development. Patients afflicted with DDH who have been treated conservatively since early infancy are now in their fifth decade of clinical and radiographic follow-up at the University of Iowa Hospital and Clinics. This combination of conservative treatment and long-term follow-up constitute a unique resource to study the natural history relationship between chronic cartilage stress elevation and the development of osteoarthritis, in actual human joints, without surgical intervention. Four specific aims are proposed.

Aim 1. Trace individual bone morphology histories and measure radiographic features predictive of long-term DDH outcome from standard clinical AP films.

Aim 2. Assemble bilateral three-dimensional, nonlinear contact finite element (FE) models of hips, from spiral computed tomography (CT) arthrograms taken at the time of forty-year follow-up of twenty patients afflicted with unilateral DDH.

Aim 3. Impose individual bone morphology histories on each patient’s CT geometries to extrapolate 3D nonlinear contact FE models of both hips of each patient at every available follow-up visit after skeletal maturity. Apply whole-gait-cycle loading to calculate three-dimensional articular cartilage stress histories.

Aim 4. Identify localized bony incongruity effects on acetabular and femoral articular cartilage stress patterns calculated by the time-series 3D nonlinear contact FE models of dysplastic and contralateral asymptomatic hips. Compute the value of tolerance threshold for which the time histories of supra-threshold contact stress best correlate with clinical and radiographic measures of OA.

Functional tissue engineering faces many challenges in repairing or replacing diseased or injured tissues, such as bone and articular cartilage, which serve a predominantly biomechanical function. At the conclusion of the proposed project, we will have quantified in-vivo three-dimensional chronic stress elevations in hip articular cartilage of patients with unilateral developmental dysplasia of the hip. We will have described a relationship between patient-specific three-dimensional stress histories, of normal and abnormal articular cartilage, which will provide an envelope of intrinsic mechanical thresholds that hip articular cartilage repairs and replacements will likely encounter.

Back to top