Mechanical properties of cancellous bone of the distal humerus.

BACKGROUND The objectives of this study were to quantify the indentation strength and modulus of distal humeral cancellous bone, and to identify regional variations. The motivations were to assist in prosthesis development and to optimize screw placement. METHODS Three consecutive 3mm transverse slices were sectioned from the distal ends of seven fresh-frozen cadaveric specimens. A 3 x 3mm grid was drawn on each slice, providing locations for indentation using a flat cylindrical indenter (diameter=1.6mm) attached to a materials testing machine. The mean indentation modulus and local yield strength were calculated for each site, and pooled into nine anatomically defined regions. FINDINGS Indentation modulus was found to range from 2.9 to 1041.7 MPa with a mean of 309.8 (242.0)MPa. Local yield strength was found to range from 0.6 to 16.3 MPa, with a mean value of 4.4 (2.5)MPa. The most distal slice had higher modulus values (P<0.05), and the posterior lateral region had lower modulus values (P<0.05). There were no slice or regional differences in strength. INTERPRETATION The influence of slice depth emphasizes the importance of minimizing the amount of bone removed during prosthetic replacement. Regional variations in indentation modulus suggest that the posterior lateral region should be avoided during fixation of implants or placement of screws. A comparison with proximal tibial cancellous bone properties suggests the distal humerus may carry loads approaching 45% of those at the knee, assuming that bone adapts to stress magnitudes.