An approach to estimating bone and joint loads and muscle strength in living subjects and skeletal remains

Skeletal physiology that clarified after 1990 shows that bone modeling norm ally makes a bone strong enough to keep its loads from causing strains abov e a "modeling threshold". That arrangement adapts bone strength to the larg est loads on a bone, which are usually brief and infrequent. Accordingly, i n bone adapted chiefly to uniaxial compression loads, the modeling threshol d's value and the cross-sectional amount of that bone could suggest the siz e of those loads. Bone loaded in that way does support the articular surfac es of synovial joints as their "supporting bone", so its amount could sugge st the size of the loads it had adapted to, and therefore the loads on the joint that it supports. During growth a joint's size is proportional, directly but not linearly, to the size of its total loads, so that its size at skeletal maturity could b e an index of those loads at that time. Joints cannot decrease in size. Yet throughout life their supporting bone can decrease or increase in strength and "mass" to adapt to changes in a joint's loads. Thus, an adult joint's size could suggest the size of the loads it adapted to by skeletal maturity , while the cross-sectional amount of its supporting bone at any later age could reveal the size of those loads at that later age, and thus suggest an y change in those loads that might have occurred after skeletal maturity. S ince the bone modeling threshold, and the relationships between bone strain , stress, and unit loads are now known, it is possible with this procedure to estimate the total loads on joints, and how body weight and muscle stren gth contribute to those loads in both living subjects and skeletal remains. To make a reliable technology of the idea involves some problems which thi s paper identifies and suggests how to resolve. (C) 1999 Wiley-Liss, Inc.