Does the bone need repair — or just the cartilage?

The right treatment for a post-traumatic cartilage defect depends less on how much it hurts and more on what, precisely, has been damaged beneath the joint surface.

Cartilage sits on top of a layer of bone called the subchondral plate. When an injury damages only the cartilage surface — leaving the bone bed intact — this is called a chondral defect. When the damage extends into the bone itself, it becomes an osteochondral defect. These two scenarios are not interchangeable: a treatment that works well for one may be entirely unsuitable for the other.

Injury mechanism offers a first clue. High-energy events — fractures, dislocations, or direct impaction — are more likely to involve the subchondral bone. Lower-energy twisting or shear forces more commonly produce isolated chondral damage, leaving the bone bed undisturbed.

Defect size adds a second dimension. The clinical literature consistently places a meaningful treatment threshold at 2–4 cm², with bone involvement being the more decisive of the two variables. The condition of the surrounding cartilage border also matters: a well-contained focal lesion with healthy edges behaves very differently from a defect that is diffuse or open at its margins.

None of this can be determined from symptoms alone. A cartilage-protocol MRI — ideally 3-Tesla — together with specialist clinical assessment is needed to classify the defect accurately before any treatment pathway is considered.

What ChondroFiller injection involves

Delivered as an outpatient appointment at the London Cartilage Clinic on Harley Street, ChondroFiller injection requires no general anaesthetic, no operating theatre, and no surgical incision. The procedure uses ultrasound guidance to place an injectable Type I collagen scaffold precisely into the cartilage defect.

Once in position, the scaffold gels within the defect in three to five minutes. It then acts as a chemotactic matrix, recruiting the patient's own progenitor cells into the damaged area to lay down new cartilage tissue. This process — matrix-induced chondrogenesis — relies entirely on the body's endogenous repair cells rather than donor tissue or laboratory-grown material. The scaffold itself is acellular; no bone drilling and no harvesting of donor material is required at any stage.

Suitability depends on the structural condition of the defect. ChondroFiller injection is indicated for focal chondral lesions — damage confined to the cartilage layer, with an intact subchondral bone base beneath — typically up to 3 cm², extendable to 6 cm² where the surrounding cartilage border is sound and the bone bed undisturbed. The single-stage, outpatient nature of the procedure also preserves future repair options: because the subchondral plate is not drilled or disrupted, the bone architecture remains intact should further treatment ever be needed.

Where subchondral bone has been damaged or lost, the scaffold lacks the structural foundation the regenerative process depends on. In that scenario, ChondroFiller injection falls outside its indicated use, and a bone-restoring intervention becomes the clinically appropriate direction.

What osteochondral allograft transplantation involves

OCA is a fundamentally different category of intervention — not a more intensive version of scaffold injection, but a surgical procedure designed for a distinct biological problem.

The operation removes the damaged section of bone and cartilage and replaces it with a precisely size-matched plug of fresh donor tissue — bone and cartilage together — taken from an allograft. This restores both the joint surface and the structural bone beneath it simultaneously, which no scaffold or cell-based technique achieves. It is performed under general or regional anaesthesia, typically as an inpatient procedure.

Donor matching introduces a practical consideration: the graft must correspond closely to the patient's joint anatomy, and availability is not guaranteed. This can mean a waiting period before surgery. There is also a small but non-zero risk of immune response or disease transmission from the allograft tissue — factors that inform the pre-operative consent process.

NHS England commissions OCA for younger adults with osteochondral lesions, with joint preservation — delaying or avoiding arthroplasty — as the primary rationale. In practice, access is constrained by graft availability as much as by clinical criteria.

Post-operative recovery is more demanding than outpatient alternatives. Published protocols require 4–6 weeks of non-weight bearing and a phased rehabilitation, with full functional recovery typically taking 9–12 months. Around 39–43% of patients require a secondary procedure, though most are minor (debridement or hardware removal), and approximately 16% eventually need joint replacement. Haikal et al.'s 2023 systematic review documents graft survivorship of 86.7% at five years, declining to 67.5% at twenty years — a long-term track record that reflects OCA's role in treating some of the most structurally complex post-traumatic defects.

What the outcomes data actually shows

Placing both options' published results side by side requires an upfront qualification: the two datasets were not drawn from the same patient population, and no randomised controlled trial has compared ChondroFiller injection directly to OCA. What follows is honest accounting of what each body of evidence does — and does not — establish.

ChondroFiller injection

Across knee and ankle studies, IKDC scores improve by approximately 30 points from a baseline of around 47.6 to roughly 80 at 36 months. MOCART scores of 81–84 indicate that more than 80% of the defect is filled and integrating with surrounding tissue on MRI. The reoperation rate sits at 3–8%, markedly lower than microfracture (up to 41%) or ACI/MACI (up to 37%). Demmer et al.'s 2025 prospective study in post-traumatic wrist injury adds objective confirmation at follow-up: treated patients showed significantly better cartilage quality than controls — median Outerbridge score 1.5 versus 3 (P=0.006), ICRS score 1 versus 3 (P=0.002). The ceiling is time: follow-up beyond three to five years remains limited, and longer-term durability data is still emerging.

OCA

Functional and satisfaction data here operates at a different timescale. Chahal et al.'s cohort of 110 patients recorded 86% overall satisfaction, with 65% showing little or no arthritis at final follow-up and return to sport reaching 75–82%. Decades of survivorship follow-up represent a genuine evidence strength that ChondroFiller injection's shorter track record cannot yet match — a meaningful consideration for a patient weighing a 20-year horizon.

The populations behind these figures matter as much as the numbers themselves. OCA studies predominantly enrol patients with larger, deeper, bone-involved defects — precisely the cases outside ChondroFiller injection's indication. A patient comparing these outcome sets may, in effect, be comparing results from different clinical problems rather than competing solutions to the same one.

Recovery, return to sport, and daily life

For a parent managing school runs, a teacher on their feet all day, or a weekend runner mid-season, the difference between these two pathways is not merely clinical — it is logistical.

ChondroFiller injection is delivered as an outpatient appointment at the London Cartilage Clinic. There is no hospital admission, no general anaesthetic, and no period of strict non-weight bearing. Most patients return to ordinary daily activity within days. Structured return to low-impact exercise typically follows within a few weeks, with the full timeline for sport calibrated to defect size and the treating clinician's guidance. Critically, a shorter recovery arc does not mean no recovery protocol: the injectable collagen scaffold relies on appropriate mechanical conditions to support cell recruitment, and rehabilitation remains part of the process.

OCA's recovery demands are substantial and should be planned for honestly. The post-surgical non-weight-bearing period and the 9–12 month trajectory to full function carry real domestic and occupational weight — particularly for patients who cannot readily take extended leave, rely on physical capacity at work, or care for dependants. These are legitimate factors in treatment choice, not merely preferences.

Return-to-sport rates after OCA are well documented at 75–82% in published series. Comparable data for ChondroFiller injection across multiple studies is less comprehensively reported, and patients should note that gap when weighing the evidence. Neither route guarantees a return to previous activity levels; both require sustained rehabilitation commitment to achieve the best outcome.

Access, cost, and booking an assessment

OCA is commissioned by NHS England as a joint-preservation strategy for younger adults, but graft availability creates a real practical constraint: a size-matched donor plug must be sourced before surgery can proceed, and that timeline sits outside the clinical team's control. Patients accepted onto the NHS pathway may wait several months before the procedure takes place, which adds meaningfully to the total treatment timeline.

ChondroFiller injection is currently available privately in the UK and is not NHS-funded — a material consideration for patients without private health cover, who should factor that cost into any comparison with the commissioned OCA pathway.

For patients whose defect is chondral only — bone bed intact — the practical contrast sharpens further. An outpatient injectable scaffold pathway at the London Cartilage Clinic carries no surgical waiting list and removes the general-anaesthetic requirement that OCA involves by definition. For patients whose defect extends into the subchondral bone, OCA remains the appropriate clinical direction regardless of access preference.

The navigating question, in practice, comes down to this: does the MRI confirm bone involvement? Where it does not, an outpatient collagen scaffold pathway is worth discussing with a specialist before committing to reconstruction surgery. Where it does, the structural restoration that only OCA provides becomes the clinical priority — and the NHS-commissioned route, delays notwithstanding, represents the appropriate starting point.

Liquid Cartilage™ (ChondroFiller injection) is delivered in the UK at the London Cartilage Clinic on Harley Street, where Professor Paul Y. F. Lee leads the programme. Assessments can be booked at londoncartilage.com.