ABSTRACT
I. Introduction ............................................................................... 2
II. A Classification of Osteopenias and Osteoporoses .................. 3
III. Biological Mechanisms that Affect Bone Strength ................... 4 A. Endochondral Ossification ................................................ 4 B. Bone Modeling Drifts ........................................................ 4 C. Bone Remodeling BMUs (Basic Multicellular Units)....... 5 D. Adults and Children Compared ....................................... 7
IV. Bone Strength, Architecture, Microdamage, and Fracture Mechanics ................................................................................... 7
V. Some Vital Biomechanics ........................................................... 9 A. Modeling ............................................................................ 9 B. Remodeling ........................................................................ 9 C. Some Disuse Effects......................................................... 10 D. Some Hypervigorous Mechanical Usage Effects ........... 10 E. The Two-Stage, Tissue-Dynamic Remodeling Pattern
in Disuse .......................................................................... 10 F. The Mechanically Adapted State .................................... 11
VI. Relevance to Osteopenias and True Osteoporoses................. 12
VII. Therapeutic Objectives, Targets, Problems............................. 13 A. General Objectives........................................................... 13 B. The Ultimate Control of Bone Losses and Conservation
of Bone Strength in Adults .............................................. 13 C. To Prevent Increased Fragility ........................................ 14 D. To Correct Already Increased Fragility .......................... 14 E. On Independent Pharmacologic Control of Osteoclastic
or Osteoblastic Activity, “Antiresorption Drugs,” and the “Either-Or” Idea .............................................................. 14
F. On Photon Absorptiometry............................................. 15 G. The Promising “Bone-Anabolic” Effects of Parathyroid
Hormone and Prostaglandins ......................................... 16 H. The Mechanostat: The Main Pharmacologic Target? ..... 17
VIII. General Comments .................................................................. 18 A. On the Role of Muscle Strength in Bone Architecture
and Strength..................................................................... 18 B. Bone-Strength-Index (BSI) Standards, Mechanical Usage,
Muscle Strength ............................................................... 19 C. On Treatment Modes ....................................................... 19 D. On Differences in Vertebral Body and Long-Bone
Metaphyseal Spongiosas ................................................. 20 E. On the Cell-and Molecular-Biologic “Faces” of
Osteoporoses.................................................................... 20 F. A Self-Test ........................................................................ 20
IX. Conclusion................................................................................ 21
Acknowledgments .............................................................................. 21
References ........................................................................................... 22
Glossary .............................................................................................. 28
To understand a disease requires knowing three things: 1) Its nature (the pathology); 2) which tissue-level and other mechanisms cause the pathology (its pathogenesis); and 3) what makes the mechanisms do that (control by hormones, genes, calcium, vitamins, growth factors, drugs, mechanics, etc.). For osteoporoses, understanding of 1 and 2 improved dramatically after 1964, but mainstream skeletal thought has not accounted for this improved understanding adequately, due partly to poor interdisciplinary communication,1,2 and as others also have noted.3-6 This chapter concerns 1 and 2, since understanding 3 requires understanding them first.
