From Wolff's law to the Utah paradigm: Insights about bone physiology and its clinical applications

Efforts to understand our anatomy and physiology can involve four often ove rlapping phases. We study what occurs, then how, then ask why, and then see k clinical applications. In that regard, in 1960 views, bone's effector cel ls (osteoblasts and osteoclasts) worked chiefly to maintain homeostasis und er the control of nonmechanical agents, and that physiology had little to d o with anatomy, biomechanics, tissue-level things, muscle, and other clinic al applications. But it seems later-discovered tissue-level mechanisms and functions (including biomechanical ones, plus muscle) are the true key play ers in bone physiology, and homeostasis ranks below the mechanical function s. Adding that information to earlier views led to the Utah paradigm of ske letal physiology that combines varied anatomical, clinical, pathological, a nd basic science evidence and ideas. While it explains in a general way how strong muscles make strong bones and chronically weak muscles make weak on es, and while many anatomists know about the physiology that fact depends o n, poor interdisciplinary communication left people in many other specialti es unaware of it and its applications. Those applications concern 1.) heali ng of fractures, osteotomies, and arthrodeses; 2.) criteria that distinguis h mechanically competent from incompetent bones; 3.) design criteria that s hould let load-bearing implants endure; 4.) how to increase bone strength d uring growth, and how to maintain it afterwards on Earth and in microgravit y situations in space; 5.) how and why healthy women only lose bone next to marrow during menopause; 6.) why normal bone functions can cause osteopeni as; 7.) why whole-bone strength and bone health are different matters; 8.) why falls can cause metaphyseal and diaphyseal fractures of the radius in c hildren, but mainly metaphyseal fractures of that bone in aged adults; 9.) which methods could best evaluate whole-bone strength, "osteopenias" and "o steoporoses"; 10.) and why most "osteoporoses" should not have bone-genetic causes and some could have extraosseous genetic causes. Clinical specialti es that currently require this information include orthopaedics, endocrinol ogy, radiology, rheumatology, pediatrics, neurology, nutrition, dentistry, and physical, space and sports medicine. Basic science specialties include absorptiometry, anatomy, anthropology, biochemistry, biomechanics, biophysi cs, genetics, histology, pathology, pharmacology, and cell and molecular bi ology. This article reviews our present general understanding of this new b one physiology and some of its clinical applications and implications. It m ust leave to other times, places, and people the resolution of questions ab out that new physiology, and to understand the many devils that should lie in its details. (Thompson D'Arcy, 1917). Anat Rec 262: 398-419, 2001. (C) 2 001 Wiley-Liss, Inc.