Clinical calculator
Caton-Deschamps Calculator
Caton-Deschamps Index
The Caton-Deschamps index is the ratio of the distance from the inferior pole of the patellar articular surface to the anterosuperior corner of the tibial plateau, divided by the length of the patellar articular surface, where 0.6 to 1.2 is normal, above 1.2 is patella alta and below 0.6 is patella baja.
What the Caton-Deschamps score means
Caton-Deschamps scores run from 0 to 2, where a higher score is better. The bands below are conventional reporting categories, not diagnostic cut-offs.
- Patella baja (infera)0–0.59
The patella sits lower than expected. Seen after patellar tendon shortening or scarring, following tibial tubercle distalisation, and after knee arthroplasty.
- Normal patellar height0.6–1.2
Within the normal range. The Caton-Deschamps index is unaffected by the position of the tibial tubercle, which is why it remains valid after tubercle surgery.
- Patella alta1.21–99
The patella sits higher than expected — a recognised risk factor for patellar instability and a common indication for tibial tubercle distalisation when it exceeds roughly 1.3.
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 | > 1.2 defines patella alta | — | Adults, lateral radiograph at 30° flexion | — | Caton J 1982 |
| Criterion | < 0.6 defines patella baja | — | Adults, lateral radiograph at 30° flexion | — | Caton J 1982 |
| Criterion | ≥ 1.3 commonly used as the threshold for considering tibial tubercle distalisation | — | Patellar instability surgical planning | — | Dejour D 2007 |
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.
Caton-Deschamps index = AT ÷ AP, where AT is the distance from the inferior pole of the patellar articular surface to the anterosuperior corner of the tibial plateau, and AP is the length of the patellar articular surface. Because both are measured on the same image the ratio is independent of radiographic magnification. Because the reference point is the tibial plateau rather than the tibial tubercle, the index remains valid after tibial tubercle surgery, which is its principal advantage over the Insall-Salvati ratio.
Instrument profile
- Developer
- Jacques Caton, Gilles Deschamps and colleagues
- Institution
- Lyon, France
- First published
- 1982
- Items
- 2
- Response format
- Two linear measurements in millimetres
- Score range
- 0 to 2
- Direction
- Higher score = better
- Completion time
- About 1 minutes
- Age range
- Adults and adolescents
- Regions
- Knee
- Conditions
- Patellar instability, Patella alta, Patella baja, Patellofemoral pain
- Procedures
- Tibial tubercle osteotomy, Tibial tubercle distalisation, MPFL reconstruction
- Observer agreement
- Interobserver ICC typically 0.88–0.96, comparable to or better than Insall-Salvati
- Validity
- Correlates with patellar instability and is the index of choice when the tibial tubercle position has been surgically altered.
- Reliability
- The main source of measurement error is identifying the inferior pole of the articular surface, which is distinct from the inferior pole of the patella itself — a distinction that is easy to miss and shifts the ratio systematically.
Normative values
Reference values from published cohorts, for comparison against the score you calculated.
| Population | Age | Mean | SD |
|---|---|---|---|
| Asymptomatic adults | — | 0.96 | 0.13 |
| Recurrent patellar dislocation | — | 1.20–1.30 | — |
When to use the Caton-Deschamps
Well suited to
- Assessing patellar height when the tibial tubercle has been moved, or the patellar tendon repaired, which invalidates the Insall-Salvati ratio.
- Pre-operative planning for tibial tubercle distalisation in patellar instability.
- Post-arthroplasty assessment of patella baja.
Limitations and poor fits
- When the patellar articular surface cannot be clearly distinguished on the lateral radiograph.
- At extremes of knee flexion outside roughly 10° to 80°, where the index becomes less stable.
- As a sole determinant of surgery — trochlear dysplasia, TT-TG distance and rotational profile all bear on patellar instability.
Caton-Deschamps compared with other instruments
Instruments measuring a related construct, with the practical difference between them.
| Instrument | Items | Range | What it adds |
|---|---|---|---|
| Insall-Salvati | 2 | 0–3 | The Insall-Salvati index is the ratio of patellar tendon length to patellar length measured on a lateral knee radiograph; a ratio between 0.8 and 1.2 is normal, above 1.2 indicates patella alta, and below 0.8 indicates patella baja. |
| KOOS | 42 | 0–100 | The KOOS is a 42-item patient-reported questionnaire that scores knee function as five separate subscales — Symptoms, Pain, Activities of Daily Living, Sport and Recreation, and Quality of Life — each from 0 (extreme problems) to 100 (no problems). |
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 measurement method. Freely reproducible; no licence is required.
References
- Caton J, Deschamps G, Chambat P, Lerat JL, Dejour H. Patella infera. Apropos of 128 cases. Revue de Chirurgie Orthopédique et Réparatrice de l’Appareil Moteur. 1982.PMID 6216535
- Dejour D, Le Coultre B. Osteotomies in patello-femoral instabilities. Sports Medicine and Arthroscopy Review. 2007.PMID 17301705
- Seil R, Müller B, Georg T, Kohn D, Rupp S. Reliability and interobserver variability in radiological patellar height ratios. Knee Surgery, Sports Traumatology, Arthroscopy. 2000.PMID 11061294
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.