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Caton-Deschamps Index: Definition & Normal Values

The Caton-Deschamps Index is a radiological measurement used to assess the vertical position of the patella (kneecap) relative to the knee joint.

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Things worth knowing about "Caton-Deschamps Index"

The Caton-Deschamps Index is a radiological measurement used to assess the vertical position of the patella (kneecap) relative to the knee joint.

What is the Caton-Deschamps Index?

The Caton-Deschamps Index (CDI) is a widely used radiological measurement in orthopedic and diagnostic imaging practice. It quantifies the vertical height of the patella (kneecap) relative to the tibial plateau, as seen on a lateral X-ray of the knee. Proper patellar positioning is essential for normal knee mechanics. When the patella sits too high (patella alta) or too low (patella baja), it can lead to pain, instability, and reduced joint function.

How is the Caton-Deschamps Index Measured?

The measurement is performed on a lateral radiograph of the knee taken at approximately 30 degrees of flexion. Two distances are identified:

AT: The distance from the inferior articular surface of the patella to the anterosuperior edge of the tibial plateau
AP: The length of the articular surface of the patella

The index is calculated by dividing these two values: CDI = AT / AP

Normal Values and Interpretation

The resulting ratio is interpreted using the following reference values:

Normal: CDI between 0.6 and 1.3
Patella alta (high-riding patella): CDI greater than 1.3
Patella baja (low-riding patella): CDI less than 0.6

Patella alta is frequently associated with patellar instability, an increased risk of dislocation, and patellofemoral pain syndrome. Patella baja may occur following knee surgery or in the context of inflammatory joint diseases and is often linked to restricted range of motion.

Clinical Relevance and Applications

The Caton-Deschamps Index is applied in a variety of clinical scenarios, including:

Evaluation of knee pain and patellofemoral complaints
Diagnosis of patellar instability or recurrent patellar dislocations
Preoperative planning for procedures such as trochleoplasty or tibial tubercle osteotomy
Postoperative follow-up after knee surgery
Assessment of growth-related patellar position changes in children and adolescents

Advantages of the Caton-Deschamps Index

Compared to other patellar height indices – such as the Insall-Salvati Index or the Blackburne-Peel Index – the Caton-Deschamps Index is considered particularly reliable because it uses only the articular (cartilage-bearing) surface of the patella for its calculation. This makes it independent of variations in the shape of the inferior patellar pole and therefore less susceptible to anatomical variability between patients. It is also highly reproducible and widely used in European orthopedic practice.

Limitations

Like all radiological indices, the Caton-Deschamps Index depends on correct patient positioning and standardized imaging technique. Even small deviations in the degree of knee flexion can affect the measured values. In ambiguous cases or where complex anatomy is suspected, supplementary imaging with MRI (magnetic resonance imaging) may be advisable to gain a more comprehensive assessment.

References

Caton J, Deschamps G, Chambat P et al. - Patella infera: a propos de 128 observations (1982). Revue de Chirurgie Orthopedique.
Dejour D, Le Coultre B - Osteotomies in patello-femoral instabilities. Sports Medicine and Arthroscopy Review, 2007.
Neyret P, Robinson AH, Le Coultre B, Lapra C, Chambat P - Patellar tendon length - the factor in patellar instability? Knee, 2002.

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