Bone strength measurements at the proximal tibia. Penetration tests and epiphyseal compressive strength.

Three penetration tests were obtained from corresponding locations at each condyle of 19 proximal tibiae. The patterns of condylar cancellous bone strength varied little between knees. The medial condyle was the strongest with an average medial to lateral strength ratio of 1.9, and in most knees the medial condyle was strongest centrally while the lateral condyle was strongest posteriorly. The penetration strength at 5 successive 2 mm levels beneath the resected subchondral surface also showed a constant pattern of variation. Bone strength decreased significantly at first except at the posterolateral site, then tended to level off. The reduction of strength was most pronounced in the centre of the condyles. The penetration tests were good predictors of the static compressive strength of the proximal tibia. Correlation coefficients of approximately 0.90 were obtained indicating statistically highly significant correlations (p less than or equal to 0.00001). The tests were carried out with equipment developed for in vivo measurements of cancellous bone strength during total knee replacement. The findings confirm the close relationship of these investigations to conventional compression tests.