New insight on the subchondral bone and cartilage functional unit: Bone mineral density and cartilage thickness are spatially correlated in non-osteoarthritic femoral condyles

Hugo Babel; Patrick Omoumi; Thomas P Andriacchi; Brigitte M Jolles; Julien Favre

doi:10.1016/j.ocarto.2020.100079

New insight on the subchondral bone and cartilage functional unit: Bone mineral density and cartilage thickness are spatially correlated in non-osteoarthritic femoral condyles

Osteoarthr Cartil Open. 2020 Jun 4;2(3):100079. doi: 10.1016/j.ocarto.2020.100079. eCollection 2020 Sep.

Authors

Hugo Babel¹, Patrick Omoumi², Thomas P Andriacchi^{3

4

5}, Brigitte M Jolles^{1

6}, Julien Favre¹

Affiliations

¹ Lausanne University Hospital and University of Lausanne (CHUV-UNIL), Department of Musculoskeletal Medicine, Swiss BioMotion Lab, Lausanne, Switzerland.
² Lausanne University Hospital and University of Lausanne (CHUV-UNIL), Department of Diagnostic and Interventional Radiology, Lausanne, Switzerland.
³ Stanford University, Department of Mechanical Engineering, Stanford, CA, USA.
⁴ Palo Alto Veterans Affairs, Palo Alto, CA, USA.
⁵ Stanford University Medical Center, Department of Orthopaedic Surgery, Stanford, CA, USA.
⁶ Ecole Polytechnique Fédérale de Lausanne (EPFL), Institute of Microengineering, Lausanne, Switzerland.

Abstract

Objective: This study aimed to improve our understanding of the relationship between bone and cartilage by characterizing the morphological coupling between these mechanosensitive tissues exposed to the same mechanical environment within each knee. Specifically, it reanalyzed a prior dataset to test the hypothesis that the locations of thickest cartilage and densest subchondral bone are correlated in non-osteoarthritic femoral condyles.

Method: Anatomically standardized maps of cartilage thickness (CTh) and subchondral bone mineral density (sBMD) were calculated for 50 non-osteoarthritic distal femurs based on computed tomography arthrography examinations. The locations of thickest CTh and densest sBMD were identified in the load-bearing region of the medial and lateral compartments, and correlation analyses were performed to quantify the associations between these locations, with inclusion of age, gender, femoral bone size and femorotibial angle as cofounding variables. Paired Student's t-tests were also performed to compare CTh and sBMD locations.

Results: Locations of thickest CTh and densest sBMD were positively correlated along the anteroposterior direction in both compartments (r ≥ 0.45, p ≤ 0.001). Furthermore, thickest CTh was more posterior than densest sBMD in the medial (p = 0.014) and lateral (p < 0.001) compartments, and more lateral than densest sBMD in the lateral compartment (p < 0.001). On average, these location differences were of 1.3, 5.3 and 2.1% of the subchondral bone size.

Conclusion: The positive spatial relationship between the locations of thickest CTh and densest sBMD supports the idea of a functional cartilage/subchondral bone unit with morphological coupling conditioned by the individual loading pattern.

Keywords: CT arthrography; CT, computerized tomography; CTh, cartilage thickness; Knee joint; Loading; OA, osteoarthritis; Osteochondral unit; sBMD, subchondral bone mineral density.