It is not always easy to decide the exact points of the lines because the patella is slightly different in shape in each person.
Caton-Deschamps Index and patella alta
The index is of value in determining whether or not there is patella alta (high riding kneeap). It is a ratio of the distance between:
- the lower point of the part of the patella that makes contact with the femur to the top of the tibial plateau
- the length of the part of the back of the patella that makes contact with the femur
The normal range is 0.8-1.2. A ratio higher than 1.3 is suggestive of patella alta.