Is ACI an option for a talar cartilage defect?

For most patients with a cartilage lesion on the talar dome, the opening treatment steps will be conservative, and any surgery is likely to begin with marrow stimulation or a small osteochondral graft. ACI sits above these options in the repair hierarchy — an escalation choice, not a default first step.

That said, ACI is a recognised treatment for osteochondral lesions of the talus (OLT). Procedural feasibility has been established in published surgical literature: studies have confirmed that cells can be sourced directly from the detached osteochondral fragment itself, removing the need for a separate harvest operation at another joint site. The specific surgical technique of autologous chondrocyte transplantation at the talus has been described and replicated in peer-reviewed work. In terms of eligibility, the threshold broadly mirrors the knee: defects larger than approximately 2 cm², or lesions that have not responded to a prior repair attempt, are the typical entry point.

The talar dome presents particular technical considerations compared with the knee. The cartilage layer is significantly thinner — roughly 1 mm at the talus versus approximately 2.5 mm at the knee — which places higher demands on the implantation step.

The evidence base is real but not yet consolidated. Published case series report meaningful clinical benefit, but no randomised controlled trial has been completed specifically for ankle ACI. Defect size, lesion history, and anatomical position each shape whether ACI is the most appropriate escalation for an individual patient.

What an osteochondral lesion of the talus actually is

The talar dome is the rounded upper surface of the talus — the bone that sits between the heel and the lower leg, bearing the full load of the body during standing, walking, and impact. An osteochondral lesion of the talus (OLT) is a focal area of damage affecting both the cartilage surface and the bone immediately beneath it; 'osteochondral' simply means the injury reaches through the cartilage layer and into the subchondral bone.

Causes span a spectrum. A single acute ankle injury — typically a forceful sprain or twist — is the most common trigger. In athletes and active workers, repetitive microtrauma can accumulate over months or years without a single identifiable event. A smaller group of patients develop osteochondral disease that disrupts the blood supply to the underlying bone, leading to focal cartilage loss without any clear preceding injury.

Lesions occur most often on the medial (inner) aspect or centrally on the talar dome, positions that sit deep within the joint and complicate surgical access. Left untreated, a focal defect tends to enlarge progressively, causing worsening pain, intermittent swelling, and mechanical symptoms such as locking or giving way. This trajectory of functional deterioration — quite distinct from the diffuse joint-space loss of established ankle arthritis — is what places focal OLTs within the scope of cartilage repair rather than joint replacement.

How defect size and treatment history shape the decision

Three broad bands of defect size shape the repair pathway for talar osteochondral lesions — and treatment history adds a second, equally important layer on top.

Lesions smaller than approximately 2 cm² are generally addressed first with single-stage procedures. Osteochondral autograft transfer — OATS or mosaicplasty — transplants healthy bone-and-cartilage plugs from a non-weight-bearing donor site and suits this size range well. Marrow stimulation via microfracture is another option at this band, though it carries a recognised limitation worth weighing from the outset: the fibrocartilage it produces tends to break down by two to three years, and the drilling can compromise the subchondral bone plate in ways that narrow future repair options. For that reason, microfracture is not a default recommendation in larger or more complex lesions, and its historical role as a first-line choice is giving way to more durable alternatives.

Lesions in the 2–4 cm² range, or any defect where a prior repair has already failed, are where cell-based repair — ACI or matrix-associated ACI (MACI) — enters the picture. Prior failed microfracture is itself a specific escalation trigger: if marrow stimulation proved insufficient, it indicates that a more regenerative approach is needed rather than a repeat of the same intervention.

The clearest evidence linking defect size to the superiority of MACI over microfracture comes from knee cartilage trials; the SUMMIT trial is the most cited, and its findings are examined in a later section. No equivalent randomised trial exists for the ankle, so the size threshold is applied by clinical analogy. That evidence gap does not invalidate the principle — it is the best available framework for decision-making — but it does mean individual cases require specialist assessment rather than strict protocol application.

What the ACI procedure involves at the ankle

Conventional ACI unfolds in two distinct operations separated by several weeks. During the first, a small amount of healthy cartilage is harvested — at the ankle, the detached osteochondral fragment itself can serve as the cell source, which means a separate donor-site harvest is not always required, a technique established in the ankle ACI literature by Giannini et al. in 2005. Those harvested cells are sent to a specialist laboratory where they are cultured and expanded before the second operation, at which point the expanded cells are implanted into the defect, traditionally held in place by a periosteal flap stitched over the repair site.

Access creates the most significant procedural difference from knee ACI. Medial and central talar dome lesions sit deep within the joint, and the surrounding anatomy makes them difficult to reach directly. A medial malleolar osteotomy — a controlled, deliberate cut through the inner ankle bone — is commonly used to hinge the joint open and expose the defect adequately. This step is absent in knee ACI, and it adds both surgical complexity and recovery time: the cut bone must heal, which extends the rehabilitation period beyond what the cartilage repair alone would require.

The two-stage structure also means two separate anaesthetics and a laboratory interval of several weeks, a practical burden that is worth factoring into any decision about timing and planning.

Scaffold-based and single-stage evolutions

STACi — scaffold-based ACI — replaces the periosteal flap with a 3D scaffold and, in many cases, can be completed as a single operation. It is applicable at the ankle alongside the knee, hip, and shoulder, and suits patients whose defect size or complexity would have placed them outside conventional ACI criteria. NanoACi, a needle-delivered, non-arthroscopic concept that would eliminate both the theatre stage and the laboratory expansion step, is at an earlier stage still. Both represent next-generation directions rather than established standard-of-care pathways, and the evidence trail for each remains limited compared with two-stage ACI.

AMIC, MACI, and OATS as alternatives for OLT

Three techniques sit alongside ACI in the talar repair hierarchy, each with a distinct trade-off between surgical staging, donor-site risk, and depth of ankle-specific evidence.

AMIC — autologous matrix-induced chondrogenesis is the most specifically evidenced of the three for the talus. A single-stage procedure, it combines marrow stimulation with the immediate placement of a collagen matrix over the drilled lesion, allowing the patient's own progenitor cells to populate the scaffold rather than relying solely on the fibrocartilage clot that marrow stimulation alone produces. Weigelt et al. (2019, American Journal of Sports Medicine) reported clinical and radiological outcomes across a 2–8 year follow-up in patients with talar osteochondral lesions — one of the few ankle series with medium-term data. Because AMIC avoids laboratory cell culture and a second anaesthetic, it carries a practical advantage over two-stage ACI; arthroscopic LDFF occupies similar territory for primary talar defects alongside it, targeting the lower end of the repair range.

MACI seeds expanded chondrocytes on to a Type I/III collagen membrane rather than using a periosteal flap, which simplifies fixation and removes one of first-generation ACI's recognised technical drawbacks. Its mid-term knee evidence is substantial — as the SUMMIT trial data discussed in the previous section reflect — but dedicated randomised ankle data are absent. MACI is performed at the talar dome in specialist centres, and available series suggest it is technically feasible, though the evidence level is lower than for the knee.

OATS and mosaicplasty transfer intact osteochondral plugs from a non-weight-bearing donor site, most often at the knee. Suitable for lesions up to around 2 cm² (single plug) or approximately 4 cm² in mosaic form, their primary trade-off is donor-site morbidity: the secondary defect at the harvest site can cause persistent discomfort in some patients — a factor that does not arise with AMIC or cell-based repair.

No head-to-head randomised trial has compared these approaches specifically at the ankle. That gap means the choice between AMIC, MACI, OATS, and ACI rests on specialist assessment of defect size, prior surgical history, and individual patient circumstances rather than a direct evidence hierarchy.

Accessing ankle cartilage repair in the UK

NHS provision for ankle ACI follows the same eligibility threshold as for the knee: a defect typically larger than 2 cm², with no prior cell-based repair at the site. Referral ordinarily begins with a GP requesting weight-bearing radiographs and MRI; CT is often added when ACI is under consideration, to assess the subchondral bone alongside the cartilage loss. Specialist centres with the infrastructure for talar ACI are fewer than for the knee — the demands of deep joint access, including the possible need for a malleolar osteotomy, concentrate the procedure at a small number of dedicated units.

Private access broadens geographic reach. Ankle cartilage procedures carry roughly a 30% cost uplift over equivalent knee work in private settings — additional surgical complexity is the driver — and that applies across the repair hierarchy, not only to cell-based techniques.

Search MSK lists UK specialists in osteochondral lesion management and ankle cartilage repair; filter by region and specialty to find one near you. Worth raising at a first appointment: whether the defect and any subchondral involvement suit a single-stage or two-stage approach, and whether the centre manages ankle lesions routinely rather than as an occasional extension of knee practice. Matching technique to defect size, surgical history, and individual priorities requires a specialist practised in the full ankle repair toolkit — and that assessment is what shapes every decision that follows.