What happens to injected cells
Researchers have labelled MSCs with tracers and followed them after injection in animals and, in a few studies, in humans:
- Intravenous: the majority lodge in the lung capillaries within minutes (the "pulmonary first-pass effect"). Most are gone within 24 to 72 hours. Almost none reach a distant joint, the brain, or the spinal cord.
- Intra-articular: cells persist in the joint for days to a few weeks, declining steadily. Long-term engraftment into cartilage is rare, and where it has been reported it is a tiny fraction of the injected dose.
- Intrathecal: cells distribute along the spinal fluid and are cleared over days.
- Surgical implantation on a scaffold (the Medipost-style approach): better retention at the site, which is one reason those trials show structural effects that injections do not.
Why the cells still seem to do something
Trials of intra-articular MSCs report pain and function improvement even though the cells are gone. The dominant explanation, now broadly accepted, is paracrine: while alive, the cells secrete growth factors, cytokines and extracellular vesicles (exosomes) that dampen inflammation, reduce cartilage-degrading enzyme activity, and stimulate resident cells. The injected cells are a short-lived drug factory, not a building material.
This reframing has consequences:
| Old model (cells become tissue) | Paracrine model (cells signal, then die) |
|---|---|
| More cells is better | Dose matters, but viability and secretory activity matter more; see viability |
| IV cells "home" to injury | IV cells mostly go to the lungs; local delivery is essential for local effect |
| Regeneration of cartilage or neurons | Symptom modification; structural repair unproven for injections |
| One treatment is permanent | Effects fade; repeat treatments are the honest expectation; see repeat frequency |
| Live cells required | Cell-free products (secretome, exosomes) might reproduce the effect, which is why that market exploded; see secretome explained |
How this exposes marketing
- "Cells migrate to the damaged area" after an IV infusion: contradicted by tracking data
- "Regrows cartilage": not demonstrated for injected cells in controlled trials
- "Permanent results": inconsistent with cells that live days and effects measured in months
- "100 million cells": the number is less informative than viability, potency and delivery site
What it means for choosing a treatment
Local, imaging-guided delivery into the target tissue is the only route consistent with the mechanism; see imaging guidance. Anti-inflammatory and trophic effects are real but bounded, so mild-to-moderate disease is the reasonable target and end-stage disease is not. And because the mechanism is signalling, PRP, which delivers growth factors without cells, is a legitimate cheaper comparator for many indications; see the orthobiologic ladder.
What Colombian clinics should say
A clinic that explains the paracrine model, sets expectations of symptom improvement rather than regeneration, and recommends local delivery over IV drips for orthopedic problems is telling you the truth. A clinic describing cells homing to your knee from an arm vein is not.
Regulatory status: FDA vs INVIMA
United States (FDA): No stem cell product is FDA-approved for orthopedic, neurologic, or systemic use. Minimally manipulated same-day autologous procedures are marketed under a narrow exemption; culture-expanded cells and most umbilical products are unapproved biologics and the FDA's authority over them was reaffirmed in federal court in 2024. Florida's 2025 law permits certain treatments under state rules but does not create FDA approval.
Colombia (INVIMA): Cell therapies are regulated as advanced-therapy products. Clinics require INVIMA habilitation for the facility and, for laboratory-processed products, product-level authorization or an approved research protocol. Ask to see the INVIMA registration number and verify the treating physician on ReTHUS. "INVIMA registered" for the clinic is not the same as an authorized product.
Frequently asked questions
Do stem cells become new cartilage after injection?
Rarely and minimally. Tracking studies show injected cells die within days to weeks; benefits are attributed to secreted signals.
If the cells die, why does the treatment work at all?
Through paracrine signalling: growth factors and vesicles released while the cells are alive modulate inflammation and stimulate resident cells.
Does this mean exosomes are as good as cells?
Possibly for some effects, but exosome products are unstandardized and unapproved, and the evidence is earlier than for cells.
Want a clinic that explains the science honestly?
Tell us your condition. We will refer you to Colombian clinics that set paracrine-model expectations and deliver locally under imaging.
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