Mechanical properties of subchondral cancellous bone of the radial head.

Objective: To quantify the mechanical properties of subchondral bone of the radial head, with special interest in the regional variations in bone stiffness and strength.

Design: Transverse subchondral cancellous bone slices obtained from the proximal radial head were subjected to indentation tests.

Setting: Biomechanics laboratory with a servohydraulic materials testing machine.

Specimens: Thirteen previously frozen, cadaver proximal radii of mean age 69 +/- 9 years.

Main Outcome Measurements: The mean indentation modulus and local yield strength were calculated for the anteromedial (AM), anterolateral (AL), posteromedial (PM), and posterolateral (PL) quadrants of the radial head.

Results And Conclusions: There were no differences in mean indentation modulus across all 4 quadrants (AL, 55.56 +/- 16.20 MPa; AM, 53.48 +/- 20.67 MPa; PM, 49.20 +/- 18.31 MPa; PL, 49.96 +/- 14.97 MPa) (P > 0.05). The AM quadrant had higher local yield strength than the PL and PM quadrants, as did the AL compared with the PL quadrant (AL, 24.89 +/- 8.52 Mpa; AM, 28.39 +/- 10.52 Mpa; PM, 23.01 +/- 6.99; PL, 20.62 +/- 4.83 MPa) (P < 0.05). This suggests that the high frequency of radial head fractures in the AL quadrant is likely not due to the local strength of cancellous bone. Rather, the location of fracture may be influenced by the composite strength or the mechanisms of loading at the radiocapitellar and proximal radioulnar joints. The modulus results suggest that similar screw purchase can be achieved in all areas of the radial head during internal fixation of fractures. These results may also influence implant design and fixation. This study was limited to an older population and may not be representative of a younger population.