Three-dimensional distribution of articular cartilage thickness in the elderly cadaveric acetabulum: a new method using three-dimensional digitizer and CT.

ABSTRACT

OBJECTIVE: The aim of this study was to evaluate the three-dimensional (3D) distribution of the acetabular articular cartilage thickness in cadaveric elderly individuals, measured using a new method with a 3D-digitizer and computed tomography (CT) and to validate this method using a thresholding technique. DESIGN: Twenty cadaveric hemipelves without fracture, previous hip surgery, or macroscopic degenerative changes were digitized by a 3D-digitizer to make 3D cartilage surface models, and scanned by 3D-CT to create 3D bone surface models. These two surface models were then merged using a surface registration method. Acetabular articular cartilage thickness was evaluated as the distance between the two surface models, and the distribution was mapped. Tests for accuracy and reproducibility were performed by comparing the cartilage thickness of five human femoral heads measured by stereomicroscopy with the distance between the cartilage and bone surface models. RESULTS: The superolateral cartilage tended to be the thickest in all acetabula. The smallest category (0-0.5 mm) of articular cartilage thickness existed at the posteroinferior lunate surface. In this new method, the mean measurement error was 0.018+/-0.044 mm for the average optimum threshold and the intraclass correlation coefficients were 0.99 in surface registration and 0.94 in data acquisition for reproducibility, indicating high accuracy and reproducibility. CONCLUSIONS: The proposed method for measuring articular cartilage using a 3D-digitizer and 3D-CT was accurate and reproducible. In the elderly individuals, acetabular articular cartilage tended to be thicker in the superolateral area and there was the thinnest category (0-0.5 mm) on the posteroinferior lunate surface of the acetabulum. The contour generated along 480 Hounsfield units (HU) was closest to the subchondral bone contour in the elderly hip.