Cancellous bone at the knee: a comparison of two methods of strength measurement.

The relation of thin-needle axial penetration tests to axial compression tests on machined specimens was examined utilizing distal femoral and proximal tibial epiphyseal cancellous bone. The penetration strength was closely related to the yield strength (r = 0.87), the ultimate strength (r = 0.86), Young's modulus (r = 0.77), the yield energy absorption (r = 0.81), and the ultimate energy absorption (r = 0.84) derived from the compression tests. Generally, femoral specimens were stronger, stiffer, and tougher than tibial specimens. Higher peak penetration strength values were obtained from the medial than from the lateral condyles. The variation of strength within compression test specimens could be expressed in terms of penetration strength; this variation differed slightly between tibial and femoral specimens, but invariably the bone deepest to the joint surface was the weakest. Accordingly, adjustments were introduced in the regression equations connecting the penetration strength to the material properties derived from the compression tests.