What hip mosaicplasty actually does

Focal damage to the cartilage and underlying bone of the femoral head presents a specific clinical problem: the hip joint cannot repair that tissue on its own, and leaving it untreated risks progressive deterioration toward end-stage hip osteoarthritis. Mosaicplasty — also termed osteochondral autograft transfer (OATS) — is a surgical technique designed to address that problem directly while preserving the joint.

The procedure works by moving cylindrical plugs of bone and cartilage from a low-load zone of the hip — typically the non-weight-bearing periphery of the femoral head, or occasionally the ipsilateral knee — and press-fitting them into prepared tunnels at the damaged site. The result is a mosaic of plugs that reconstruct the femoral head surface with living tissue. Crucially, that tissue is true hyaline cartilage, which is mechanically superior to the fibrocartilage produced by marrow-stimulation techniques such as microfracture.

Hip cartilage defects of this kind are uncommon — they account for roughly 2% of all osteochondral lesions across the body's joints — yet they carry significant clinical weight: up to 76% of patients presenting with mechanical hip symptoms have chondral lesions visible on MRI. Causes include femoroacetabular impingement (FAI), trauma, avascular necrosis, labral tears, and hip dysplasia.

Mosaicplasty sits firmly in the category of hip joint preservation. Its goal is to restore the joint surface and, in doing so, delay or avoid the need for hip replacement — particularly in younger, active patients where early arthroplasty would be premature. It is not a permanent solution for every patient, and understanding that distinction from the outset helps set realistic expectations.

Causes of hip osteochondral defects

Several distinct hip conditions can produce the focal osteochondral damage that mosaicplasty targets. Femoroacetabular impingement (FAI) is among the most common: abnormal bony contact between the femoral head and acetabular rim generates repeated shear forces during movement, concentrating stress on a small area of cartilage and subchondral bone until a focal defect forms. Avascular necrosis (AVN) disrupts the blood supply to the femoral head, causing localised bone death and surface collapse. Direct trauma — a hip dislocation or a significant fall — can shear away a segment of cartilage immediately. Labral tears and hip dysplasia alter load distribution across the joint, predisposing certain areas to accelerated wear.

What all these causes share is a common consequence: once articular cartilage is lost beyond a superficial level, the joint cannot restore it. This limited self-repair capacity is why active intervention is considered in younger patients rather than watchful waiting.

Clinicians grade lesion severity using the ICRS (International Cartilage Repair Society) or Outerbridge classification; mosaicplasty is generally reserved for contained, full-thickness defects — Grade III or IV — where damage extends to subchondral bone. Within that group, defect size is the most clinically significant variable. Lesions smaller than 2 cm² carry a reported 12% conversion rate to hip replacement at five years; for lesions of 2 cm² or above, that figure rises to 57%. The threshold is not arbitrary — it reflects the practical limits of autograft plug supply and the biomechanical demands placed on a reconstructed surface, and it sits at the centre of any consultant assessment of suitability.

Who is a realistic candidate

The patients most likely to benefit from hip mosaicplasty share a fairly consistent profile: age under 40, physically active, low BMI, and — most critically — a small, focal, contained osteochondral defect on the femoral head. The 2 cm² lesion boundary discussed above is not a soft guideline; the difference in hip replacement conversion rates on either side of that threshold is stark enough that defect size functions as the primary gateway criterion at the point of consultant assessment.

Beyond size, the nature of the damage matters. Mosaicplasty is appropriate when the defect is focal and contained — a discrete area of full-thickness cartilage loss — rather than diffuse. Patients with widespread hip osteoarthritis, advanced joint space narrowing, or damage extending across multiple surfaces of the femoral head or acetabulum are unlikely to gain meaningful benefit from autograft transplantation. For those individuals, joint replacement planning is the more realistic conversation to have at the outset.

Age and biological activity influence graft integration. Younger patients with robust bone-healing capacity tend to achieve better outcomes; published series consistently report stronger results at the younger end of the age spectrum. This does not mean mosaicplasty is categorically excluded beyond 40, but the trade-offs sharpen with each additional decade, and individual clinical assessment is essential before any decision is made.

Donor tissue availability is a practical constraint that can change the operative plan entirely. If the non-weight-bearing periphery of the femoral head cannot supply plugs of adequate size and quality, the procedure cannot proceed as a pure autograft technique. Where the defect exceeds what available autograft volume can cover, fresh osteochondral allograft transplantation becomes the more appropriate option.

Surgeons will screen for FAI before listing a patient, since correcting any impingement at the same operation is a prerequisite for a durable repair — not an optional surgical addition.

What the outcome evidence shows

The clearest picture of long-term benefit comes from a 2025 cohort of 24 hips (mean patient age 28.7 years) followed for an average of ten years: those who did not require further surgery reported a modified Harris Hip Score of 87.2 and a WOMAC score of 84.1 — both in the good-to-excellent range. That group represented 75% of the original cohort. The remaining 25% required conversion to total hip arthroplasty at a mean of 5.1 years post-procedure, placing THA conversion squarely within the medium-term horizon rather than the distant future.

A 2023 meta-analysis drawing on 11 studies and 70 patients reported a mean Harris Hip Score gain of 32.4 points — a clinically meaningful shift — and corroborated the finding that ipsilateral donor tissue and freedom from post-operative complications were associated with superior results.

Plug survivorship data extend the picture over a longer timeline: approximately 91% of grafts remain intact at five years, declining to around 62% at ten years and 37% at twenty years. Read together, these figures describe a procedure that may reliably deliver a good-quality decade for well-selected patients, but whose durability diminishes progressively — making hip preservation more accurately understood as a joint-delaying strategy than a permanent solution for most individuals.

The evidence base underpinning these findings is modest: 70 patients across 11 studies, with overall methodological quality rated as poor. No randomised controlled trials directly compare hip mosaicplasty against alternative cartilage repair techniques. Prospective studies with larger numbers would be needed before more definitive conclusions can be drawn about where this technique sits relative to other hip preservation options.

How hip mosaicplasty compares to other cartilage repair options

Choosing between cartilage repair techniques for a hip osteochondral defect is primarily a question of defect size, available tissue, and the number of operations a patient can undergo — not a simple ranking of one procedure over another.

Microfracture has a long history as the first procedure tried for small cartilage lesions, including during arthroscopic correction of FAI. Its role has narrowed considerably, however: the fibrocartilage it produces is mechanically weaker than native hyaline cartilage, tends to deteriorate within two to three years, and can cause lasting damage to the subchondral bone plate that complicates any subsequent repair attempt. For focal hip defects where durable restoration is the goal, it is no longer considered a preferred first-line option.

Mosaicplasty fills the small-defect niche — typically lesions up to around 2 cm² — by delivering genuine hyaline cartilage in a single operative stage. AMIC (matrix-augmented microfracture) occupies an intermediate position, augmenting marrow stimulation with a scaffold to encourage better-quality tissue fill, though without transferring structural osteochondral plugs.

For defects larger than 2 cm², autograft donor supply becomes the limiting factor. Autologous chondrocyte implantation (ACI) and its matrix-assisted variant (MACI) can address these bigger areas, but both require two separate surgical stages — a biopsy to harvest and culture cells, then re-implantation. Where defects are larger still, or where autograft is simply insufficient, fresh osteochondral allograft transplantation (OCAT) is an emerging alternative, typically performed through formal surgical hip dislocation to gain adequate femoral head exposure.

No single technique suits every patient. Defect size, bone quality, donor availability, and concurrent hip pathology collectively determine which option a hip specialist would consider — underscoring why individual consultant assessment remains the essential starting point.

Planning a hip assessment and what to expect

Diagnosis begins with imaging. An MRI — ideally an MR arthrogram, in which contrast medium is injected into the hip joint to improve tissue resolution — gives a surgeon the clearest picture of defect size, depth, cartilage quality, and whether concurrent pathology such as FAI or labral tearing is present. Physical examination and a history of how symptoms developed help establish whether the focal defect is the primary driver of pain.

Surgical planning then maps lesion location on the femoral head against available donor tissue — from the non-weight-bearing periphery of the same femoral head or from the ipsilateral knee — and determines whether impingement needs to be corrected at the same time. The outcome evidence links untreated FAI with higher rates of eventual hip replacement, making concurrent treatment an important part of the operative plan.

Recovery follows a graduated path: protected, toe-touch weight-bearing for the first four to six weeks while the grafts integrate, then progressive rehabilitation to restore hip range of motion and strength. Return-to-activity timelines vary with defect complexity and individual progress.

Patients who enter this process with clear expectations tend to do best. Hip mosaicplasty is designed to deliver meaningful years of improved function and to delay deterioration — not to replace the hip joint permanently. For younger patients with small focal femoral head lesions, that is a realistic and worthwhile goal. Lincolnshire Hip is part of the MSK Doctors group and accepts patients without referral for hip assessment — a practical starting point for anyone considering whether hip preservation surgery is right for them.

1. [1] Femoral head mosaicplasty by direct anterior approach for an osteochondral impaction without performing surgical hip dislocation. (2021). https://doi.org/10.1051/sicotj/2021014 https://doi.org/10.1051/sicotj/2021014
2. [2] EP149 Hip mosaicplasty provides good-to-excellent clinical scores at 10 years in patients with small femoral osteochondral lesions. (2025). https://doi.org/10.1093/jhps/hnaf069.277 https://doi.org/10.1093/jhps/hnaf069.277
3. [3] Positive predictors of hip mosaicplasty outcomes: a systematic review and meta-analysis with knee comparison. (2023). https://doi.org/10.21037/aoj-25-10 https://doi.org/10.21037/aoj-25-10
4. [4] Editorial Commentary: Microfracture Remains a Foundational Tool for Cartilage Restoration During Hip-Preservation Procedures. (2023). https://doi.org/10.1016/j.arthro.2023.01.011 https://doi.org/10.1016/j.arthro.2023.01.011
5. [5] Hip preservation for large femoral head articular cartilage defects and irreparable acetabular labral deficiency using fresh osteochondral allograft transplantation. (2026). https://doi.org/10.1177/11207000261425923 https://doi.org/10.1177/11207000261425923
6. [6] Promising outcomes of hip mosaicplasty by minimally invasive anterior approach using osteochondral autografts from the ipsilateral femoral head. (2019). https://doi.org/10.1007/s00167-019-05442-1 https://doi.org/10.1007/s00167-019-05442-1