Bone & fracture healing

What actually decides this outcome, in order of size

A fracture heals by a sequence that is mostly decided before any molecule is involved: hematoma, soft callus of type II collagen and cartilage, mineralized hard callus, then remodeling that can run for a year. What determines the outcome, in order:

1. Mechanical stability, and a strain window measured in percent. Micromotion at the fracture line above a few percent strain produces fibrous tissue instead of bone, and that is a surgical variable, not a nutritional one. Nothing on this page has an effect size within 10 fold of getting the fixation right.
2. Local blood supply, which smoking removes within minutes of a cigarette. Nicotine is a vasoconstrictor and carbon monoxide displaces oxygen from hemoglobin; the callus is an obligate aerobic construction site, and the association between smoking and nonunion is among the largest modifiable effects in the orthopedic literature. Stopping is free, and carbon monoxide clears with a half-life of about 4 hours once it does.
3. Whether the drug builds bone or stops losing it, which is a difference in the osteoclast rather than in the marketing. This is the distinction the pathway names, and it decides everything downstream of a 3 to 4 month remodeling cycle. Teriparatide, given intermittently, drives osteoblast activity through the PTH1 receptor: in 1,637 postmenopausal women followed a median of 21 months, new vertebral fractures occurred in 14% on placebo against 5% on 20 µg, a relative risk of 0.35 (95% CI 0.22 to 0.55) Neer 2001. Abaloparatide, a PTHrP analog with a different receptor-conformation preference, reproduced that shape in its own phase 3 Miller 2016. Anti-resorptives do the opposite thing: they reduce remodeling, which preserves existing bone and is not the same intervention.
4. Substrate, which has a floor at adequacy and no ceiling worth chasing above 30 ng/mL. Calcium and vitamin D matter enormously when either is deficient and almost not at all when neither is: across 33 randomized trials in 51,145 community-dwelling adults, supplementation was not associated with lower fracture incidence Zhao 2017. Adequacy, then stop.
5. The endocrine background, because a fracture at 55 years is sometimes the presentation of something else. Hypogonadism, hyperparathyroidism and untreated celiac disease all present as a fragility fracture in somebody who thought they had an accident. The male half of that is a morning total testosterone measured twice, which is the diagnostic standard rather than a one-off number Bhasin 2018.

The order to run these in, and what has to be true first

The order here is unusual for this site, because two of the items are prescription drugs with fracture end points and the rest are substrate. Sorting by what is buyable would invert it, and the two prescriptions carry the only fracture end points on the page.

1. Establish which problem this is. An acute fracture in a healthy 30-year-old and a fragility fracture in a 70-year-old are different pages wearing the same word. The second one needs Parathyroid Hormone & Calcium, Vitamin D (25-Hydroxy), Comprehensive Metabolic Panel (CMP) and, in men, Total Testosterone before anything is decided, because the fracture was the symptom.
2. Correct the two deficiencies that gate mineralization, both of which are measured in ng/mL. Vitamin D where 25(OH)D is low, because 1,25-dihydroxyvitamin D is what drives intestinal calcium absorption through TRPV6 and calbindin, and Calcium & Magnesium to the point of adequacy rather than beyond it. Magnesium belongs in the same tablet because it is a cofactor for the 1-alpha-hydroxylase step.
3. Vitamin K2 Complex runs alongside, and its job is a carboxylase step rather than an absorption one. Gamma-glutamyl carboxylase uses vitamin K as a cofactor to carboxylate osteocalcin and matrix Gla protein; uncarboxylated osteocalcin cannot bind hydroxyapatite. That step decides whether the 300 to 400 mg of calcium absorbed each day is deposited in the callus or in an arterial wall.
4. Then protein and collagen substrate, where the daily intake matters more than the 10 g scoop does. Collagen and Silica supply glycine, proline and a silicon source for the organic phase; the hydroxylation of proline to hydroxyproline is ascorbate-dependent, which is why vitamin C sits on the sibling pathway Collagen & matrix synthesis rather than here.
5. Boron and Strontium are the two most misread items on the list, and one of them breaks a scan. Boron alters the clearance of vitamin D and of steroid hormones at intakes of 3 to 10 mg. Strontium is a group 2 metal that substitutes for calcium in hydroxyapatite, which is the source of both its claim and its measurement problem below.
6. Teriparatide and Abaloparatide are prescription anabolic agents with fracture end points, not supplements, and their place in a sequence is a clinical decision taken over 18 to 24 months. The osteosarcoma boxed warning that shaped a decade of practice was removed after the accumulated human data failed to support it Krege 2022, which is worth knowing precisely because the fear outlived the label.
7. Cartalax and Sigumir are bioregulator peptides with essentially no human fracture data, and they belong at the end of the list for that reason rather than for a safety one. Vascular, cardiac & structural is where that class is argued on its own terms.

What gets bought for this that cannot move it

An anti-resorptive is the wrong drug for an acute fracture, and it is the commonest category error here. Bisphosphonates bind hydroxyapatite and are internalized by osteoclasts, where they inhibit farnesyl pyrophosphate synthase and shut the cell down. Callus is remodeled by osteoclasts over 3 to 4 months; suppressing them enlarges the callus and delays its conversion to lamellar bone. That is the mechanism, and it is the reason the anabolic and anti-resorptive distinction is not a marketing one.

Anti-inflammatories interrupt the signal that starts the repair, at the cyclooxygenase step. Prostaglandin E2 acting at EP2 and EP4 receptors is part of how mesenchymal cells are recruited to a fracture, and cyclooxygenase inhibition removes it. The sibling pathway Inflammation resolution (not suppression) is the whole argument, and bone is where the animal data is strongest.

Strontium raises a scan by up to 10% without raising the bone underneath it. Strontium has atomic number 38 against calcium's 20 and attenuates X-rays far more, so a dual-energy absorptiometry scan reads incorporated strontium as extra mineral and reports a bone density that has not been achieved. A reader taking it and tracking DXA every 24 months is measuring their supplement.

And if there is no fracture, this is the wrong page by about a decade. Somebody with a low T-score and no break is deciding between building and preserving over a decade, not accelerating a callus over twelve weeks, and that is Bone remodeling — building vs preserving. Somebody whose problem is a tendon rather than a bone is on Angiogenesis & cytoprotection, because tendon does not regenerate the way bone does and the compounds are not interchangeable.

How you would know it was working, on a real read-out and a real timescale

Bone gives you two independent read-outs, one biochemical and one radiographic, and they answer different questions on different clocks. The prediction this page makes: if the substrate half was the limiting step, the mineralization markers move inside one remodeling cycle of roughly 3 to 4 months, and if they do not, the limit was mechanical.

• Vitamin D (25-Hydroxy) at 8 to 12 weeks. Circulating 25(OH)D has a half-life around 2 to 3 weeks, so steady state on a new intake needs four to five of those. A retest at 4 weeks reads as failure when it is an unfinished titration.
• Parathyroid Hormone & Calcium as a pair, never either one alone, because the receptor reads them together. Parathyroid hormone and calcium are only interpretable against each other: a high PTH with a low-normal calcium is a secondary response to insufficient vitamin D, and a high PTH with a high calcium is a different diagnosis entirely. Reading calcium by itself is how primary hyperparathyroidism gets missed for 5 to 10 years.
• Osteocalcin as the formation marker, on a fasting morning draw, with a swing of 30% across the day. Osteocalcin is secreted by osteoblasts and has a marked circadian rhythm with a nocturnal peak, so time of day is a larger source of variation than most interventions are. Expect it to rise over 6 to 12 weeks while formation is running, and expect it to be uninterpretable if the sample was drawn in the afternoon.
• Alkaline phosphatase on the Comprehensive Metabolic Panel (CMP), read as a trend. The bone isoenzyme rises during active callus mineralization and falls as remodeling completes, which makes a serial value more informative than a single one. A rise with a normal GGT (Gamma-Glutamyl Transferase) points at bone rather than at the biliary tree, and that pairing is the cheapest way to tell the two sources apart.
• Total Testosterone in men, twice, on separate mornings before 10 am. The guideline standard is two unequivocally low morning values, because a single number moves with sleep, illness and the assay Bhasin 2018. A fragility fracture in a man under 70 years is a reason the question gets asked at all.

What will fool you. Radiographic union lags biological union, so a film at 6 weeks understates progress and a film at 6 months overstates it. Serial DXA on a strontium-containing product is not a measurement of your bone, because attenuation scales with atomic number. And a callus that looks large on X-ray is not evidence of a strong union, since the enlarged callus of impaired remodeling looks like more bone and is weaker.

Sources read for these sections

• Neer RM. Effect of parathyroid hormone (1-34) on fractures and bone mineral density in postmenopausal women with osteoporosis. New England Journal of Medicine 2001;344(19):1434-41 · PMID 11346808
• Miller PD. Effect of Abaloparatide vs Placebo on New Vertebral Fractures in Postmenopausal Women With Osteoporosis: A Randomized Clinical Trial.. JAMA 2016 · PMID 27533157
• Krege JH. Teriparatide and Osteosarcoma Risk: History, Science, Elimination of Boxed Warning, and Other Label Updates.. JBMR Plus 2022 · PMID 36111201
• Zhao JG, et al. Association Between Calcium or Vitamin D Supplementation and Fracture Incidence in Community-Dwelling Older Adults: A Systematic Review and Meta-analysis. JAMA, 2017 · PMID 29279934
• Bhasin S. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. Journal of Clinical Endocrinology and Metabolism 2018;103(5):1715-1744 · PMID 29562364