Compressive strength of tibial cancellous bone. Instron and osteopenetrometer measurements in an autopsy material

The topographic variation of proximal tibial cancellous bone strength was investigated in 12 knees from routine autopsies. Samples from eight knees were tested to compressive failure in an Instron material testing machine, and four knees were tested with the osteopenetrometer, an instrument developed for intraoperative measurement of bone strength. Ultimate stress, elastic modulus and energy absorption of the bone were calculated from the Instron-curves. Mechanical properties varied considerably from knee to knee, but the topographic patterns were remarkably constant. The medial condyle showed the highest strength, the intercondylar area the lowest. On the medial side the bone was strongest at the front, while on the lateral side the reverse was true. The two horizontal levels tested did not differ significantly. The osteopenetrometer measurements closely modelled the pattern of ultimate stress.