Comparison of bone screw holding strength in healthy bovine and osteoporotic human cancellous bone.

Pushout tests were carried out on two different diameter, self-tapping, cancellous bone screws (4 mm and 6.4 mm) inserted in bovine cancellous bone sections taken perpendicular and at 45 degrees to the long axis of the bone. Comparison was made with the same type of screws inserted into sections taken from osteoporotic and/or osteoarthritic human femoral heads. The results showed no significant difference in the holding strength of different diameter screws in bovine bone sections of given orientation but significant differences when the trabecular orientation of the section was changed. By comparison, the holding strengths of the same screws in diseased femoral heads were found to be both significantly different from each other and significantly lower than for the same screws inserted in healthy bovine bone. The screw diameter, trabecular orientation, mineral content and the health of the bone all need to be considered in order to optimise the holding strength of the screws in cancellous bone.