It is very difficult to describe what exactly "knuckling" is, as it, rather than an "orthopedic issue" which has a clear definition, seems to be an individual situation when practising ballet.
In the case of "knuckling" the toes are so flexible that the current strength of the foot cannot support them, so the foot isn't stretched by the metatarsal but it only bends its toes. This way, you will see something like a "sharp angle" of bones between the metatarsal and the toes. So, a ballerina who stretches her feet has to do the stretching in the metatarsal, while dancers or ballet teachers who experience "knuckling" describe it as the very bending of the TOES when trying to stretch the foot - I always imagine a predator that catches its victim with its nails! (Except the animal stretches and bends its whole foot).
As in hyperextension, when flexibility (here concerning the toes) is more than the strength, the dancer experiences "knuckling". Of course you have to gain more strength and especially CONTROL over your toes. Ballet teacher, Sarah Arnold, proposes great exercises for this case that help a lot! In her website https://theaccidentalartist.me/ you can be informed of many issues concerning ballet, and also discover many helpful ballet exercises.
From the above we conclude that the reason for "knuckling" is very individual for each dancer and we mostly find it in dancers who have shoes that are too hard for them, so instead of bending the whole shoe (from the arch of the foot) they only bend their toes and sink a bit backwards. Also, students with pretty strong feet sometimes do the "knuckling" because they are trying to hold back.
"Knuckling" can be a matter of the shoe, too. "Dead" pointes haven't anymore their initial hardness in the box, and "knuckling" is the result of the softer box, while its treatment requires a harder one. Let's see the most suitable characteristics of a pointe shoe if one experiences "knuckling":
1. Make sure the upper part of the box of the shoe is hard enough.
2. We've noticed that the support provided from a V-cut shoe works better than the U-cut
3. Harder wings of the box
4. Plastic supportive shanks
Feel also free to fill out our questionnaire if you need our opinion about your own pointe shoe sizing and models and let’s get fitted!