Which parts of cartilage surgery are actually essential?

Why cartilage rarely heals on its own

Cartilage does not bleed. That single biological fact — the absence of a blood supply in articular cartilage — is what makes joint damage so stubbornly permanent. Most tissues heal because blood carries repair cells to the site of injury. Without it, damaged cartilage has almost nothing to work with: no meaningful influx of progenitor cells, no clotting cascade to initiate repair, no reliable pathway back to the smooth, load-bearing surface the joint depends upon.

For a patient in their forties or fifties with a focal chondral defect — a discrete area of damage in an otherwise functioning knee — this creates a clinical limbo. The joint is not worn out enough to justify replacement. But the body cannot mend the lesion either. Doing nothing is not a neutral choice; untreated defects tend to persist or enlarge, converting a contained problem into a wider one over time.

The PRRR framework — Preserve, Repair, Regenerate, Replace — maps this territory honestly. Between the last available regenerative tool and the decision to replace the joint entirely lies a gap that, for most patients, historically meant managed decline rather than recovery. Articular cartilage repair treatments can provide some measure of pain relief and slow damage accumulation, but no current technique perfectly restores hyaline cartilage.

That gap is not a failure of surgical will. It is a consequence of biology. And it is precisely what made the engineering question so urgent: if the body cannot repair cartilage on its own, what does surgery actually need to do — and which parts of it are genuinely necessary?

What ACI/MACI actually asks of a patient

ACI/MACI is the established surgical gold standard for focal cartilage repair — not a niche intervention but a well-evidenced technique with genuine clinical outcomes. Its effectiveness is not the issue.

The pathway runs in two distinct stages. In the first, a small portion of healthy cartilage is harvested from a low-load area of the same joint, then sent to an accredited external laboratory. There, technicians enzymatically digest the tissue, isolate the chondrocytes, and expand them over several weeks in culture. Control over this phase passes, temporarily but entirely, to the laboratory.

When the cells are ready, the patient returns for a second hospital admission. Under a second anaesthetic, the cultured cells are reimplanted into the defect — either through open surgery or arthroscopically, using a membrane-based carrier. Recovery then involves months of protected weight-bearing and graduated rehabilitation before the repaired tissue can tolerate normal loading.

For patients who qualify — typically younger adults with focal, contained lesions and the capacity to sustain this commitment — ACI/MACI offers something biologically meaningful: structured repair rather than fibrocartilage scar substitution. The two-stage burden is the price of that biology, and for the right patient it may well be worth paying.

The question that follows is deliberately narrow: does the biology itself demand all of these steps, or have some of them simply been inherited as procedural convention, never formally examined?

The engineer's question: which steps are biologically necessary?

Performing a procedure, rather than reading about it, produces a particular kind of knowledge. Professor Paul Lee spent years carrying out ACI — scrubbing in, harvesting tissue, waiting on the laboratory, returning for the second operation. That proximity is where an engineering instinct found its purchase.

Lee holds a PhD alongside his surgical qualifications (MBBCh, FRCS T&O) and serves as President of the International Association of Musculoskeletal Regeneration (I AM Regen), based at the London Cartilage Clinic on Harley Street. The engineering training instilled a working principle: a system should contain only the steps it requires. Applied to ACI, the question becomes direct — is each element present because the biology demands it, or because it was never formally examined?

That filter divides the pathway cleanly. On one side sit steps that provide irreducible biological value: the chondrogenic material, the structural environment, the signals that instruct repair. On the other sit steps that accumulated as procedural convention — theatre-based delivery, arthroscopic access, external cell expansion — embedded in the pathway from its early days and rarely interrogated since.

This is not a challenge to ACI's underlying science. The principle that autologous chondrocytes can help restore articular cartilage is not what Lee questioned. The target was the process architecture built around that science — and whether, once examined, all of it still had to be there.

What the analysis identified as removable

Two candidates emerged from that scrutiny: arthroscopy and ex-vivo cell culture.

Arthroscopy — keyhole access, theatre time, a general or regional anaesthetic — is a delivery mechanism. It places instruments inside the joint, but it contributes nothing to the chondrogenic repair environment itself. The incisions, the theatre infrastructure, the associated surgical trauma: none of these belong to the biology of cartilage regeneration. They were imported into the procedure because that was the access convention when ACI was established, and they remained, for decades, unexamined.

Ex-vivo cell culture occupies a similar position. Chondrocytes are expanded in an external laboratory because that is how the technique developed historically, not because external expansion has been shown to be biologically superior to point-of-care preparation. The weeks-long laboratory phase transfers control away from the surgeon and the patient without, in Lee's analysis, adding something the repair biology itself requires.

Remove both, and the arithmetic changes sharply. Two hospital admissions become one — or none. Two anaesthetics disappear. The weeks of laboratory waiting disappear with them. What remains is the specialist, the biological components, and the needle.

The principle that crystallised this analysis is stated plainly: 'Keep the surgeon. Keep the science. Remove the arthroscopy.' Specialist judgement is not the removable element. The operative delivery infrastructure is. The innovation, as Lee frames it, is not something added — it is the surgery taken away.

What the analysis kept: seed, scaffold, and signal

Three biological roles emerged as the irreducible remainder: a chondrogenic cellular source, a structural environment, and a growth-factor medium. These became the foundation of NanoACi™ — Professor Paul Lee's surgeon-led, non-arthroscopic, needle-delivered, one-stage autologous chondrogenic injection technique, developed at the London Cartilage Clinic.

Seed. The chondrogenic source in NanoACi is a micrograft taken from the patient's own ear cartilage. A small sample of auricular cartilage is mechanically prepared at point of care — no enzyme digestion, no external laboratory, no weeks of cell expansion. The micrografts are autologous from the first step to the last, and their preparation does not leave the clinical setting.

Scaffold. Micrografts alone need a structural home. NanoACi uses a cell-free native type I collagen matrix to provide that environment. No foreign cells are introduced; the matrix is present to support the patient's own biological activity rather than substitute for it.

Signal. The third role belongs to autologous platelet-rich fibrin (PRF), derived from the patient's own blood. PRF is a platelet-and-leukocyte fibrin matrix that provides growth-factor signalling — the biological instruction set designed to support repair and integration at the treatment site. Because it originates from the patient, no foreign material is introduced through this component.

All three — seed, scaffold, and signal — are combined at point of care and delivered via needle in a single planned sitting. The acronym states the design logic plainly: Non-Arthroscopic, Needle-delivered, One-stop Autologous Chondrogenic Injection. Needle delivery is the access route, not the whole procedure. Imaging review, case selection, tissue sampling, preparation, sequencing, delivery, and follow-up remain essential and remain specialist-led. That distinction is central to how NanoACi is described: a planned clinical technique, not a commodity injection or manufactured device.

Where the evidence stands and what it means for patients

Three levels of evidence apply to NanoACi, and keeping them distinct matters.

Each component carries its own clinical record. The cell-free collagen scaffold (ChondroFiller) has been used in more than 20,000 implantations. PRF has an established growth-factor literature with published support for its signalling role in tissue repair. Auricular cartilage micrografts have scaffold-plus-cells data including in end-stage knees. That record is real — but it describes the parts, not the assembled protocol.

The combined three-part approach — ChondroFiller, Mytocel MSK, and Arthrozheal prepared and delivered together — has not been tested in a randomised controlled trial, and no independent external validation of the combined protocol yet exists. Outcomes are being developed through NanoACi 100, a prospective study of 100 consecutive cases with pre-agreed pain, function, and imaging measures at fixed intervals; results will not be reported until the dataset is complete. This gap between component support and whole-protocol proof is the principal remaining uncertainty, and it is worth naming plainly rather than eliding.

No existing cartilage repair technique — microfracture, ACI, AMIC, or any other — perfectly restores hyaline cartilage. NanoACi is a non-arthroscopic lane for suitable patients, not a universal answer to cartilage disease; suitability depends on alignment, joint stability, the extent and pattern of damage, imaging findings, symptoms, and individual goals. A consultation and imaging review are the right starting point for anyone whose joint may benefit.

What NanoACi 100 will ultimately be asked to show is whether a protocol built from individually evidenced parts, stripped of unnecessary surgical steps, delivers meaningful outcomes across a range of patients — and whether regeneration, made simpler, can reach people earlier in the care pathway than a decade of operating-theatre convention has allowed.

1. [1] Autologous chondrocyte implantation. https://en.wikipedia.org/?curid=19074150 https://en.wikipedia.org/?curid=19074150
2. [2] Articular cartilage repair. https://en.wikipedia.org/?curid=19042351 https://en.wikipedia.org/?curid=19042351
3. [3] Microfracture surgery. https://en.wikipedia.org/?curid=8840994 https://en.wikipedia.org/?curid=8840994
4. [4] Autologous matrix-induced chondrogenesis (AMIC). https://en.wikipedia.org/?curid=29760859 https://en.wikipedia.org/?curid=29760859