Four reasons the ear is the right starting point

Cartilage taken from a person's own ear might seem an unlikely starting point for treating a worn knee joint. In fact, the auricular concha — the bowl-shaped hollow of the outer ear — is chosen for four reasons that each stand independently and strengthen one another in combination.

Biologically, the elastic cartilage of the ear contains chondrocytes reported to carry greater regenerative potential than those in articular hyaline cartilage, making it a more capable source material than the joint tissue it is intended to support. Immunologically, tissue drawn from the patient poses no rejection risk: the body cannot mount a defensive response against its own cells. Practically, the ear provides a small, accessible, non-weight-bearing donor site — three 2.5 mm punch samples collected under local anaesthetic, processed within the same clinic appointment, and injected before the patient leaves. And in terms of the procedure's founding principles, sourcing exclusively from the patient preserves the fully autologous character of the treatment: no laboratory step, no donor, no stored biological material.

Each strand of that reasoning is grounded in biology, immunology, or clinical evidence. The sections that follow examine them in turn.

Elastic cartilage cells and their regenerative advantage

The joint surfaces of the knee are lined with hyaline cartilage — dense, smooth tissue built primarily to absorb load and reduce friction. Elastic cartilage, by contrast, is found in flexible structures such as the outer ear; it contains a higher proportion of elastic fibres that allow it to bend and recover its shape repeatedly. Both tissue types are populated by chondrocytes, but their regenerative behaviour differs considerably.

Elastic cartilage chondrocytes are known to carry a greater regenerative potential than those in hyaline cartilage. That difference underpins the sourcing decision in Mytocel MSK: by drawing material from the auricular concha, the procedure obtains cells that are biologically better equipped for repair activity than those present at the target site — a deliberate mismatch, and a favourable one. The micrograft suspension therefore arrives at the joint carrying tissue that is primed for repair in a way that articular cartilage is not.

Animal-model research by Marcarelli et al. (2021) has provided evidence of cartilage generation following auricular micrograft administration in vivo — findings that helped establish the biological foundation for subsequent clinical investigation. Characterisation of the precise degree of regeneration and the type of cartilage formed is continuing, building a progressively detailed account of how the suspension acts within the joint environment. Tsoukas et al. (Bioengineering, 2023) later extended these observations into a human cohort, strengthening the case for the auricular source.

The choice of elastic cartilage as donor tissue is therefore grounded in comparative biology: a recognised cellular advantage, supported by converging mechanistic and clinical research.

No borrowed tissue, no rejection risk

Every tissue the immune system encounters is checked for biological identity markers. When those markers match, the tissue is accepted; when they do not, a rejection response follows. Because Mytocel MSK draws exclusively from the patient, the micrografts carry the same markers as the surrounding tissue — the rejection mechanism has no trigger to act on.

This stands in direct contrast to osteochondral allograft transfer, where donor tissue introduces foreign biological markers. Allograft procedures require careful joint-congruence matching, depend on donor availability, and carry a host-rejection risk that must be managed. The autologous approach removes all three constraints: matching is automatic, the supply is the patient themselves, and the immune response that drives rejection does not arise.

Certain contraindications — active autoimmune disease, immunosuppression, and active joint infection — do apply to Mytocel MSK, but for a different reason. These conditions can compromise the patient's own tissue at the point of harvest, introducing pro-inflammatory cytokines or lower-quality cells into the AMT® solution. The concern is the integrity of what is harvested, not the body's reaction to what is administered.

That fully autologous character also underpins the procedure's regulatory classification as minimally manipulated and homologous — a designation that reflects how closely the preparation remains aligned with the tissue's natural state and biological function.

A single clinic visit from biopsy to injection

The workflow begins at the ear. Under local anaesthetic, three cartilage samples — each taken with a 2.5 mm dermatological punch — are collected from the auricular concha. The site is non-weight-bearing and well-tolerated; the biopsy is characterised in the clinical literature as scarcely invasive, with minimal donor-site morbidity and no compromise to graft viability.

The samples are placed directly into the Rigeneracons® RS disposable device along with 4 ml of saline solution. The N4SA 2.0 motor then drives six minutes of mechanical disaggregation, reducing the cartilage to a suspension of autologous micrografts. No enzymatic agents, culture medium, or incubation are involved. When correctly prepared, the suspension is visibly cloudy — a distinguishing sign that micrografts are present.

That suspension is administered intra-articularly at the affected joint within the same appointment. Biopsy, processing, and administration occur without the patient leaving the clinic or returning for a second visit.

This single-session, point-of-care format separates Mytocel MSK from ex vivo cell-expansion therapies, where harvested material is sent to a laboratory, cultured over days or weeks, and returned at a later date. Mechanical preparation replaces laboratory manipulation here, and the same-session workflow reflects both the procedural accessibility and the minimally manipulated character of the AMT® approach — a practical consequence of sourcing fully autologous material that requires no conditioning before use.

What the clinical evidence shows

Published data from Tsoukas et al. (Bioengineering 2023;10:1294) provide the primary clinical anchor for Mytocel MSK in knee osteoarthritis. The study examined patients with early-stage knee OA treated with autologous auricular cartilage micrografts prepared via the AMT® procedure using Rigenera® Technology. Patient-reported outcomes — covering pain, stiffness, and mobility — showed meaningful improvement following intra-articular administration. The authors concluded that the protocol represents an effective and safe approach for this population and joint; a finding that aligns with the biological rationale for auricular micrografts supporting chondrocyte harbouring and growth at the treatment site. These are patient-reported functional outcomes: they are not, in themselves, proof of structural cartilage restoration, and the study authors do not present them as such.

Some grade IV osteoarthritis cases have also reported benefits — including pain relief, improved mobility, and reduced stiffness — though effects in this group tend to be of shorter duration, generally up to one year (Tsoukas et al., 2023). Robust evidence to establish Mytocel MSK as a standard indication at that severity is not yet available, and individual clinical assessment guides decisions accordingly.

The same Tsoukas et al. study that establishes the early-stage evidence base carries acknowledged limitations: the cohort is modest in size and no randomised control group was included. Those parameters reflect where the research programme currently stands — the authors identify expanded populations and additional articular sites as natural next steps — rather than a fixed boundary. For early-stage knee OA, the published clinical evidence supports a clear and continuing case for Mytocel MSK, with the field actively building on it.

Three principles that hold the procedure together

The three principles — autologous, tissue-specific, and minimally invasive — are not independent selling points but interlocking constraints, each of which narrows the choice of donor site until one answer remains.

Autologous rules out donor tissue and synthetic scaffolds. Tissue-specific rules out anything that is not cartilage — blood-derived biologics, fat grafts, and non-specific growth factor preparations do not qualify. Minimally invasive rules out any donor site requiring open harvest: collecting hyaline cartilage from a joint, for instance, would impose the very surgical burden the procedure is designed to avoid.

The auricular concha is the site that satisfies all three constraints simultaneously. It is accessible under local anaesthetic; it provides elastic cartilage, fulfilling the tissue-specific requirement; and it is the patient's own tissue, fulfilling both the biological and minimally manipulated regulatory logic in a single step. No alternative donor site or synthetic component enters the workflow because none could do the same.

For patients exploring Mytocel MSK for early-to-moderate knee OA, the most useful question to bring to a clinician is not whether the tissue is their own — it is — but whether their specific OA grade places them in the population where published outcome evidence is currently strongest.