Classification system
Ficat-Arlet Classification
Ficat and Arlet Classification of Osteonecrosis of the Femoral Head
The Ficat and Arlet classification stages osteonecrosis of the femoral head from 0 to IV by the most advanced imaging finding present — normal imaging, an abnormal MRI with a normal radiograph, sclerosis or cysts with a round head, subchondral collapse, and finally joint space narrowing — with stage III marking the point at which the head has collapsed and head-preserving surgery stops working.
What the Ficat-Arlet category means
Ficat-Arlet scores run from 0 to 4, where a lower score is better. The bands below are conventional reporting categories, not diagnostic cut-offs.
- Pre-collapse (stages 0–II)0–2
The articular surface is intact. Head-preserving options remain, and their success depends mainly on lesion size and location — neither of which this system records.
- Post-collapse (stages III–IV)3–4
The subchondral bone has failed. Head preservation is no longer reliable and the discussion becomes an arthroplasty discussion.
Published criteria and reliability
The published cut-offs that define this instrument, and the measured agreement between observers using it. Each is reported with the population it was derived in.
| Type | Value | Subscale | Population | Follow-up | Source |
|---|---|---|---|---|---|
| Criterion | Crescent sign (subchondral fracture) or head flattening — stage III, the pre-collapse to post-collapse boundary | — | Adults with osteonecrosis of the femoral head on plain radiographs | — | Ficat RP 1985 |
| Criterion | Joint space narrowing with acetabular involvement — stage IV | — | Adults with osteonecrosis of the femoral head on plain radiographs | — | Ficat RP 1985 |
| Criterion | Lesion size and location, which Ficat and Arlet does not record, are the strongest predictors of collapse and are quantified in the revised ARCO staging | — | Adults with pre-collapse osteonecrosis of the femoral head | — | Yoon BH 2020 |
Criterion is a published cut-off, definition or performance figure belonging to a classification or decision rule — it is not a change score and should not be read as one.
How the score is calculated
Stated in full so the calculation can be independently checked, and reproduced by hand if needed.
The hip is assigned the stage of the most advanced finding present. Stage 0 is the preclinical hip with no symptoms and normal radiographs and MRI, recognised only in a patient at risk or with disease in the other hip; it was added after Ficat’s original four-stage description. Stage I is a symptomatic hip with a normal radiograph and an abnormal MRI or bone scan. Stage II is radiographic change without deformity: mixed osteopenia, sclerosis and cystic change with a spherical head and a normal joint space. Stage III is subchondral collapse — the crescent sign, which is a subchondral fracture — with or without flattening of the head, the joint space still preserved. Stage IV is secondary osteoarthritis with joint space narrowing and acetabular change. The single decision the staging drives is whether the articular surface has collapsed: stages 0 to II are pre-collapse and stages III and IV are post-collapse. Versions of the system differ over whether a subchondral fracture without flattening belongs in a transitional stage, in stage II or in stage III, so the convention used should be stated when a series is reported.
Missing data
Both the imaging finding and the symptom status are required, because stages 0 and I are distinguished clinically rather than radiographically. Where the radiograph is normal, the stage cannot be settled without MRI — a normal radiograph does not exclude osteonecrosis, and staging on radiographs alone systematically under-stages early disease.
Instrument profile
- Developer
- Raymond P. Ficat and Jacques Arlet
- Institution
- Toulouse, France
- First published
- 1980
- Custodian
- Largely superseded for research reporting by the Association Research Circulation Osseous (ARCO) system, revised in 2019, which adds lesion size and location
- Items
- 2
- Response format
- Most advanced imaging finding, plus the presence of symptoms
- Score range
- 0 to 4
- Direction
- Lower score = better
- Completion time
- About 1 minutes
- Age range
- Adults
- Regions
- Hip
- Conditions
- Osteonecrosis of the femoral head, Avascular necrosis of the hip, Secondary hip osteoarthritis, Corticosteroid-associated osteonecrosis
- Procedures
- Core decompression, Vascularised fibular grafting, Proximal femoral osteotomy, Total hip arthroplasty
- Validity
- The pre-collapse versus post-collapse split is clinically decisive and has held since the system was described. Within the pre-collapse stages the system predicts poorly, because outcome depends on the volume and location of the necrotic segment rather than on the presence of sclerosis.
- Reliability
- Agreement is reasonable for the collapsed stages and weakest at the II–III boundary, where a small subchondral fracture on the frog-leg lateral is easy to miss and the published versions of the system disagree about where it belongs.
When to use the Ficat-Arlet
Well suited to
- Staging osteonecrosis of the femoral head in routine practice, where the pre-collapse versus post-collapse question is what the clinic decision turns on.
- Reading the older osteonecrosis literature, most of which reports results by Ficat stage.
- Communicating quickly with a colleague about whether a hip has collapsed.
Limitations and poor fits
- Reporting a research series or selecting patients for a trial of head-preserving surgery, where lesion size matters and ARCO or a quantified necrotic angle should be used instead.
- Staging on plain radiographs alone in a symptomatic hip — that is how stage I disease is called normal.
- Predicting whether a specific pre-collapse hip will collapse: the stage does not carry the information needed to answer that.
- Osteonecrosis at other sites, such as the knee, shoulder or talus, which have their own staging systems.
Ficat-Arlet compared with other instruments
Instruments measuring a related construct, with the practical difference between them.
| Instrument | Items | Range | What it adds |
|---|---|---|---|
| Kellgren-Lawrence | 1 | 0–4 | The Kellgren-Lawrence classification grades radiographic osteoarthritis from 0 to 4 based on osteophyte formation, joint space narrowing, subchondral sclerosis and bone contour deformity, with grade 2 conventionally taken as the threshold for definite radiographic osteoarthritis. |
| Harris Hip Score | — | 0–100 | The Harris Hip Score is a 100-point clinician-administered hip assessment combining 44 points for pain, 47 for function, 4 for absence of deformity and 5 for range of motion, where 90 or above is graded excellent and below 70 poor. |
| Crowe | 2 | 1–4 | The Crowe classification grades developmental dysplasia of the hip in adults by how far the femoral head has migrated proximally, expressed as a percentage of the femoral head height and estimated from the pelvic height, giving four types: under 50%, 50–75%, 75–100% and over 100% subluxation. |
| Outerbridge | 1 | 0–4 | The Outerbridge classification grades articular cartilage damage from 0 to IV at arthroscopy, progressing from normal cartilage through softening, fissuring under and over 1.3 centimetres in diameter, to full-thickness erosion exposing subchondral bone. |
Copyright and permitted use
Published openly because it is the question every clinician and researcher asks before using an instrument, and almost nobody answers it.
A published radiographic staging system. No licence is required.
References
- Ficat RP. Idiopathic bone necrosis of the femoral head: early diagnosis and treatment. Journal of Bone and Joint Surgery (British Volume). 1985.
- Ficat RP, Arlet J. Ischemia and Necroses of Bone (Hungerford DS, ed. and trans.). Williams and Wilkins, Baltimore (book). 1980.
- Yoon BH, Mont MA, Koo KH, et al.. The 2019 revised version of Association Research Circulation Osseous staging system of osteonecrosis of the femoral head. Journal of Arthroplasty. 2020.
Editorial status
This page has not yet been signed off by a named clinical reviewer. The scoring logic is stated in full above so it can be independently verified, and every threshold is traceable to its source. See our editorial methodology.