What microfracture does — and why it was used first

If your surgeon has suggested something other than microfracture for a hip cartilage problem, you are likely wondering what changed — and why a technique that was once standard is now so often replaced.

Microfracture works by piercing the subchondral bone plate beneath a cartilage defect, using a small drill or awl, to release marrow contents — stem cells, blood, and growth factors — into the defect space. These form a clot that gradually matures into repair tissue. The procedure is single-stage, delivered arthroscopically, and technically straightforward compared with cell-based alternatives, which explains why it was widely adopted as the first-line option for small focal defects, historically those smaller than roughly 2 cm².

The hip joint makes this matter more than it might elsewhere. It is a deeply enclosed, load-bearing ball-and-socket joint lined with hyaline articular cartilage that has almost no intrinsic capacity for self-repair. When cartilage is lost, the joint depends entirely on surgical intervention to restore a functioning surface.

Microfracture's appeal was always its simplicity. The limitation, as evidence has since established, lies in the quality of tissue it produces — and that distinction is where the current clinical picture begins.

Fibrocartilage versus hyaline cartilage: the core durability gap

The repair tissue microfracture produces is the heart of its limitation. Rather than regenerating the hyaline articular cartilage that originally lined the joint, the marrow clot matures into fibrocartilage — a tissue the American Academy of Orthopaedic Surgeons describes as 'a different and somewhat less durable form of cartilage'. Think of it as a temporary patch: functional in the short term, but lacking the organised architecture of the material it is meant to replace.

That distinction matters most in the hip, which sustains forces several times body weight during ordinary walking, and considerably more during sport or heavy work. Hyaline cartilage handles these loads through a precisely organised extracellular matrix of type II collagen and proteoglycans — components that fibrocartilage lacks. Under sustained load, fibrocartilage repair tissue tends to soften, fissure, and degrade rather than remodel into something durable.

Published evidence places this degradation window at roughly two to three years post-procedure, particularly in defects larger than 2 cm². By that point, many patients experience a return of symptoms that initially appeared to have settled after surgery — a pattern that has driven clinicians away from standalone microfracture as a definitive solution for hip cartilage defects.

Scaffold-augmented and cell-based techniques — among them AMIC, ACI, and MACI — were developed specifically to address this gap. Rather than relying on the marrow clot alone, they direct repair towards hyaline-like tissue: a mechanically appropriate surface for a joint that offers no tolerance for inferior repair quality.

Hip-specific challenges that worsen microfracture's track record

Beyond the biology, the hip joint itself creates conditions that actively work against standalone microfracture in ways that do not apply to more accessible joints.

Access is the first constraint. The hip is a deep, enclosed ball-and-socket joint — arthroscopic instruments must navigate a confined space under traction, limiting the surgeon's ability to cover a defect with the precision and consistency that marrow stimulation requires. That technical difficulty is reflected in clinical cost uplifts of around 30% for non-knee joints, which exist precisely because access and reconstruction are more demanding. In practice, this narrows how reliably microfracture alone can address a hip cartilage lesion compared with scaffold-based implantation techniques that can be placed more precisely.

Clot stability is a second, less obvious problem. Microfracture depends on the marrow clot adhering to the defect and differentiating steadily into repair tissue. In the hip, joint fluid movement and positioning after surgery can physically displace this clot before it consolidates. Scaffold membranes used in AMIC and related techniques hold the clot in place and concentrate growth factors at the defect site — a mechanical advantage that standalone microfracture cannot replicate.

The most clinically significant hip-specific factor, however, is femoroacetabular impingement. FAI — an abnormal bone shape around the hip joint — is a leading cause of focal cartilage damage in active adults. When abnormal bony contact repeatedly loads one area of the cartilage surface, a focal defect develops. Microfracture can address that defect, but it leaves the bony impingement entirely untreated. Repairing the cartilage without correcting the impingement is, in practical terms, like patching a damaged surface while the cause of the damage remains unchanged — the repair tissue faces the same abnormal stress that destroyed the original cartilage. Current practice accordingly requires concurrent FAI correction for any durable cartilage repair in the hip; microfracture performed in isolation, without bony correction, carries predictably poorer outcomes as a result.

Subchondral bone damage: the hidden cost that limits future options

Choosing microfracture is not a neutral first step — it carries downstream consequences that can narrow what is available later if the initial repair fails.

The subchondral bone layer sits immediately beneath articular cartilage, providing mechanical support and contributing to the nutrient supply that repair tissue depends on. When microfracture perforates this layer, the disruption is not always confined neatly to the defect site. Research by Chen et al. (Am J Sports Med, 2011) characterised subchondral bone changes following marrow stimulation and found that the repair process can alter bone architecture in ways that degrade the quality of any subsequent cartilage resurfacing attempt. The recognised sequelae — subchondral cyst formation and sclerosis, a progressive hardening of the bone — reduce its capacity to support new tissue and change the mechanical conditions at the joint surface. Think of it as damaging the foundations: whatever is built above them becomes less stable as a result.

These changes have direct implications for revision surgery. Cell-based procedures such as ACI and MACI are associated with higher failure rates in patients who have previously undergone microfracture, because the altered subchondral surface is a less predictable base for re-implantation.

For hip cartilage defects — where the joint loading is considerable and the surgical margin for error is narrow — this matters. Selecting microfracture for a defect that may eventually require scaffold-augmented or cell-based repair can reduce the effectiveness of those techniques when they are needed most. The initial choice carries more consequence than it may appear.

What the evidence now supports for hip cartilage defects

Surgeons now work through a graduated menu of options, matched principally to defect size and the patient's individual circumstances.

For the smallest focal defects — typically 1–2 cm² — mosaicplasty (osteochondral autograft transfer, or OATS) transfers small cylinders of healthy bone and cartilage from a low-load area of the hip into the defect. Because the graft brings both the cartilage surface and its underlying bone together, it sidesteps the fibrocartilage problem altogether.

For defects larger than roughly 2 cm², AMIC (autologous matrix-induced chondrogenesis) represents the most direct evolution from microfracture: the same marrow stimulation is performed, but a collagen membrane is placed over the site to stabilise the clot and retain growth factors that would otherwise disperse — precisely the mechanism addressed in the previous section. Seven-year follow-up data in 21 patients showed significantly reduced pain and improved function for full-thickness defects larger than 2 cm², a durability benchmark that standalone microfracture does not match at comparable defect sizes.

Larger defects — broadly in the 2–10 cm² range — are the domain of MACI (matrix-induced autologous chondrocyte implantation). A two-stage procedure involving cartilage biopsy, laboratory cell culture, and reimplantation on a collagen scaffold, MACI produces hyaline-like repair tissue. The SUMMIT trial established that for defects of 3 cm² or greater, MACI produced better pain and function scores than microfracture at both two and five years.

Beyond roughly 10 cm², or where post-traumatic destruction is too extensive for autograft, fresh osteochondral allograft — donor cartilage and bone in a single composite graft — is the only viable reconstructive option. Microfracture has no meaningful role at this scale.

Across all categories, technique selection is individualised by defect size, patient age, and activity level. Where microfracture now fits most appropriately is as a preparatory step within a scaffold-augmented procedure — not as a standalone first-line treatment in its own right.

What this means for your hip cartilage assessment

Deciding between these techniques requires a structured assessment rather than a single measurement. Defect size matters, but so does the condition of the surrounding cartilage, the state of the subchondral bone, the patient's age, and what they need the joint to do. MRI is the necessary starting point: it characterises defect depth, subchondral architecture, and any cystic change that would shift the repair strategy — including changes that, as the previous section describes, can narrow the options available if a first repair fails.

Patients referred with a suggestion of microfracture are entitled to ask whether scaffold augmentation or a cell-based procedure has been considered — especially for defects of 2 cm² or larger, where current evidence consistently favours more advanced options. That is not an adversarial question; it reflects where the clinical consensus has moved.

Lincolnshire Hip, part of the MSK Doctors group, offers specialist hip cartilage assessment and accepts patients without a GP referral, with consultations available from Sleaford and Grantham. A specialist opinion — grounded in imaging and an individualised discussion of technique options — is the practical next step, because the initial repair choice shapes what remains possible should revision ever become necessary.