Structure
The surgical work the joint needs first: correcting relevant alignment or instability, treating associated mechanical damage and preparing a stable defect bed.
The evidence
STACi evidence: what supports Structure, Seed, Soil and Signal
A transparent look at the evidence behind each part of the surgical STACi pathway—and where component evidence stops short of proving the whole combination.
Reviewed byProfessor Paul Lee MBBch, FRCS (Tr & Orth), PhDCartilage and joint preservation expertiseQuick answer
STACi is an evidence-informed surgical framework. Published research supports addressing clinically important alignment and stability, and separately supports single-stage autologous cartilage repair, collagen scaffolds and platelet-derived biological augmentation. No claim is made that one study has validated every four-part STACi combination for every patient.
What we mean by evidence
STACi belongs to a well-studied family of treatments: autologous chondrocyte therapies, in which your own cartilage cells (chondrocytes, KON-droh-sites) are used to regrow a joint surface. The original two-stage techniques, ACi and MACi, have been studied for more than two decades. STACi is the single-stage, three-dimensional-scaffold evolution of that lineage — the laboratory step is brought into theatre so cells are harvested, processed and implanted in one operation.
The most honest way to read the evidence is in layers: first the need to create a mechanically credible joint, then the evidence for the biological components, and finally the more limited evidence for a complete combined protocol. That distinction is central to informed consent, not a weakness to hide.
The surgical RegenRepair™ pathway
Structure. Seed. Soil. Signal.
STACi is used when biology alone is not enough. The operation first creates a mechanically credible joint environment, then applies the same Seed, Soil and Signal logic used in RegenRepair™ for cartilage.
Seed
Autologous cartilage tissue is harvested and prepared during the procedure to provide the patient-derived cellular material.
Soil
A three-dimensional collagen scaffold holds the prepared tissue within the cartilage defect and supports local organisation.
Signal
A patient-derived platelet-rich fibrin preparation provides a fibrin matrix and biological signals alongside the repair.
The evidence boundary matters. Each part is supported by its own clinical or biological literature, but that does not mean the exact four-part combination has been proven as one standardised protocol for every joint and damage pattern.
Read the evidence by layer
What is established—and what is still evolving
Structure: alignment and stability
Cartilage repair does not sit apart from joint mechanics. Systematic reviews and comparative studies support assessing and, where indicated, correcting malalignment or instability alongside cartilage restoration. The exact structural procedure remains patient-specific.
Systematic review of cartilage repair with osteotomySeed: single-stage autologous cartilage
A 2023 systematic review found positive patient-reported outcomes across single-stage autologous cartilage repair studies, while also highlighting heterogeneous techniques and the need for better comparative trials.
Single-stage autologous cartilage repair reviewSoil: scaffold-supported repair
Scaffold-based cartilage repair has a clinical literature of its own. Results vary by scaffold, cell source, defect and any accompanying bone-marrow procedure, so the scaffold evidence must not be treated as proof of every combined protocol.
Single-step scaffold repair reviewSignal: platelet-derived augmentation
Laboratory and clinical literature provides a biological rationale for platelet preparations in cartilage repair, but preparation methods and outcome reporting vary. That supports a cautious component claim, not a guarantee of regenerated cartilage.
Platelet preparation and cartilage reviewDoes it grow real cartilage?
The most important question about any cartilage repair is what actually grows back. Microfracture, the simplest option, tends to fill a defect with fibrocartilage — a weaker, scar-type tissue that does not wear as well as the original. The point of cell-based regeneration is to do better: to form hyaline-like cartilage, the smooth, load-bearing surface a healthy joint is built from.
Evidence for scaffold-based autologous chondrocyte therapy reports formation of hyaline-like cartilage in the majority of treated defects, with the three-dimensional scaffold supporting growth through the full depth of the damage rather than only skinning the surface. Where biopsies and MRI have been examined, the repair tissue is described as maturing and integrating with the surrounding cartilage over the first year — consistent with the staged recovery STACi patients follow.
What the MRI shows (MOCART)
Cartilage repair is tracked on MRI using a standardised score called MOCART (Magnetic resonance Observation of Cartilage Repair Tissue), which grades how well a repair has filled the defect, how smoothly its surface sits, and how completely it has bonded to the surrounding cartilage and bone. It is the standard way researchers compare cartilage procedures objectively rather than on symptoms alone.
Single-stage scaffold cartilage therapies of STACi’s class report good defect fill and integration on MOCART assessment, improving over the first year as the tissue matures.
Pain, function and return to activity
Measured on validated knee scores
STACi is a regeneration procedure, not a quick painkiller. The measured goal is durable improvement in pain and everyday function, tracked with validated knee scores such as the IKDC (International Knee Documentation Committee) score and the KOOS (Knee injury and Osteoarthritis Outcome Score). Studies of single-stage, scaffold-based cartilage cell therapy report meaningful, lasting gains on these measures, with many patients returning to their previous activity level.
Your individual result depends on the size, depth and location of the damage, the health of the surrounding cartilage, and how closely rehabilitation is followed. We tell you, in writing at consultation, what to expect for your specific defect — and every outcome feeds our ICRS-aligned cartilage regeneration database.
Safety
Because STACi uses your own cells and your own biological augmentation, it avoids the rejection and disease-transmission concerns of donor material. The evidence for autologous chondrocyte therapies describes a safety profile comparable to, or better than, other cartilage treatments, with the main considerations being those common to any joint surgery — swelling, stiffness and the need to protect the graft while it beds in. Delivering STACi as a single operation also removes the second surgery and second anaesthetic that two-stage ACi and MACi require.
Frequently Asked Questions
Is there good evidence that STACi works?
There is evidence for the individual clinical decisions and components used in STACi: correcting important joint mechanics, single-stage autologous cartilage repair, scaffold support and platelet-derived biological augmentation. The exact Structure–Seed–Soil–Signal combination is Professor Lee's surgical framework; it should not be presented as though one trial has already tested every version of that complete pathway.
Does STACi grow real cartilage or scar tissue?
The aim, supported by the evidence, is hyaline-like cartilage — the smooth, load-bearing surface a healthy joint is built from — rather than the weaker fibrocartilage that microfracture tends to produce. The 3D scaffold supports growth through the full depth of the defect.
What is a MOCART score?
MOCART is a standardised MRI score that grades how well a cartilage repair has filled the defect, how smooth its surface is, and how completely it has integrated. It lets clinicians compare cartilage procedures objectively rather than on symptoms alone.
How long is the follow-up in the studies?
Cartilage repair is judged over years, not weeks, because the tissue matures over the first year and durability is what matters. We give you written, defect-specific expectations at consultation and record every outcome in our ICRS-aligned database.
Is STACi safe?
It uses your own cells and biological augmentation, avoiding rejection and donor-tissue risks. The evidence describes a safety profile comparable to or better than other cartilage treatments, with the usual considerations of any joint surgery. Single-stage delivery removes a second operation and anaesthetic.
How does STACi’s evidence compare to ACi and MACi?
Still have more specific concerns?
Free Discovery CallSee whether the evidence applies to your joint
The only way to know what STACi could achieve for you is an imaging review. Talk it through first on a free discovery call, or book a consultation with the surgeon who will perform the procedure.
London Cartilage Clinic
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