Subchondral Bone Density Distribution in Cam Type Femoroacetabular Impingement Hips Nozomu Inoue MD, PhD Simon Lee MPH Shane J. Nho MD, MS Department of Orthopedic Surgery Rush University Medical Center Chicago, U.S.A. 2007 RUSH University Medical Center
Disclosure Nozomu Inoue MD, PhD Financially supported by NIH/NCCAM 1R01AT006692-01A2 Simon Lee MPH No Disclosures Shane J. Nho MD, MS Allosource, Arthrex Inc., Athletico, DJ Orthopaedics, Journal of Bone and Joint Surgery, Linvatec, Miomed, Ossur, Pivot Medical, Smith & Nephew, Stryker
Introduction Current 3D imaging techniques allow visualization of geometrical abnormality of the femoral head associated with cam type FAI. However, assessment of abnormal load distribution caused by cam deformity, which may cause osteoarthritis, is difficult using the current clinical imaging modality. It has been hypothesized that subchondral bone density (SBD) distribution reflects the long-term distribution of stress acting on the joints.
Objective CT osteoabsoptiomery (CT-OAM) is a method to measure SBD distribution at different depths from the joint surface. The objective of this study was to analyze the SBD the femoral head by means of CT-OAM in cam type FAI subjects.
Materials and Methods 8 patients (mean 39.7 y.o., range 20.5-61.6 y.o.) diagnosed as cam type FAI (IRB approved). CT scanning and 3D modeling. Determination of surface geometry. Determination of ROIs at cam lesion and adjacent regions on the atlas of the femoral head. Measurement of subchondral bone density at 0.5mm intervals from the femoral head surface. Measurement of the mean Hounsfield Units (HU) within the ROI at each depth. Comparison between cam vs. adjacent region.
Determination of 3D Surface Geometry of Femoral Head -3 mm +3 mm 3D surface geometry was determined by the distances between each surface point and the centroid of the femoral head and presented by deviation from the radius of the femoral head to characterize deformity surfaces
Determination of 3D Surface Geometry of Femoral Head 12 o clock 3 o clock 6 o clock 9 o clock 12 o clock Equator Superior Anterior Inferior Posterior Superior -3 mm +3 mm An atlas of the surface geometry was created by a planar projection of the femoral head surface, and the cam deformity and adjacent region were interactively segmented on the atlas
Measurement of Subchondral Bone Density of Femoral Head Surface 0.5 mm 1.0 mm 1.5 mm 2.0 mm 2.5 mm 3.0 mm 3.5 mm 4.0 mm 4.5 mm 5.0 mm 0 HU 1200 HU
3D Surface Geometry vs. Subchondral Bone Density of Femoral Head -3 mm +3 mm 0 HU 1200 HU Surface height distribution Subchondral bone density distribution (2.0 mm under the surface)
Results Mean height of the deformity (mean ± SD) Cam; 1.64 ± 1.56 mm Adjacent region; -0.29 ± 0.74 mm Subchondral bone density (The highest mean HU within each ROI from the surface to the depth of 5.0mm) Cam; 631.0 ± 213.1 HU Adjacent region; 458.4 ± 289.4 HU (p < 0.0001)
Discussion This study was able to precisely investigate SBD under cam type FAI at different depth from the surface of the femoral head. The results of the study showed higher SBD under cam type FAI quantitatively determined by the deformity height as compared to the surrounding adjacent region.
Discussion This finding indicates the cam deformities have been exposed in the higher loading due to the repetitive impaction. Combination of the quantitative analysis of the 3D geometry and SBD distribution may be useful to evaluate if the impacted deformity causes impingement without using dynamic imaging which is limited in accessibility in the current clinical setting.
Discussion Future study includes the relationship between the high SBD area and cartilage degeneration as evaluated under arthroscopy. REFERENCE: Kang KW, Yanke AB, Orias AE, Inoue N, Nho SJ. Emerging ideas: Novel 3-D quantification and classification of cam lesions in patients with femoroacetabular impingement. Clin Orthop Relat Res.471(2):358-62.2013.