Does your skeleton really replace itself? Yes, about 10 percent of it every year.

• ✓Parfitt AM, Bone remodeling and bone loss (1984), various bone physiology textbooks
• ✓Seeman E & Delmas PD, Bone quality — the material and structural basis of bone strength and fragility, NEJM 2006
• ✓Clarke B, Normal bone anatomy and physiology, Clinical Journal of the American Society of Nephrology 2008
• ✓Eriksen EF, Cellular mechanisms of bone remodeling, Reviews in Endocrine and Metabolic Disorders 2010

Your skeleton is not the fixed, permanent frame it appears to be. Every single year, your body silently replaces roughly ten percent of your skeleton through a process called bone remodelling. Microscopic cells called osteoclasts dissolve tiny pockets of old or damaged bone — then a second crew, osteoblasts, fill those same pockets with fresh bone tissue. The spongy bone inside your vertebrae, packed with tiny lattice-like struts, can completely renew in as little as three to four years. The dense outer shell of your thigh bone works on a far slower schedule, taking several decades to fully cycle through. Together, these two cell types maintain a precise balance that keeps bones strong and repairs microscopic stress fractures before they become real injuries. Without this constant remodelling, your skeleton would gradually accumulate damage until it failed under ordinary daily load. Follow for a fact every day.