Tiffanie Didonato grew 14 inches with distraction osteogenesis but the limit for a normal person is about six inches. Why?

Looking at her instagram she seems to be doing fine.

According to Paley’s FAQ on limb lengthening surgery, “The total height gain with two lengthenings is up to 13cm (8cm in the femurs and 5 cm in the tibias. (8cm is not well tolerated in the lower leg (tibia) and
exceeding 5cm can lead to more serious complications such as equinus contracture [ballerina foot]). Most
patients will not tolerate more than 5cm in the tibias. Of course the cost of two lengthenings is nearly twice that of one lengthening. Although the Precice can lengthen up to 8cm, not every patient can safely achieve this much even in the femurs. We will only allow lengthening to the tolerance of the patient’s bone and soft tissues. SAFETY first. We will not risk a loss of function to gain one more cm. To get the full 8cm from both femurs and both tibias requires three lengthening surgeries (see option 5 below).”

Option five as mentioned is “Combined tibia (up to 4cm) and femur (up to 4cm) lengthening three
weeks apart: total 8cm followed by re-breaking femur and tibia with same nail in place and repeating up to 4cm femur and up to 4cm tibia lengthening one year or more later (up to total 16cm; 6.3 in.)”

So normal person can gain 6.3 inches but someone with achondroplasia can gain 14 inches. The answer may involve the ligaments.

According to the chandler project, “When we stretch the bones were also stretching the muscles, and the ligaments and the nerves in the blood vessels around it and some of those get tight, and when they get tight there can be other problems that come up” But for dwarfism, “[dwarves have] all the skin in the ligaments and everything like that to be average height, but her bones are shorter, and they just don’t get the signals to grow,” Lisa explained.”

So the reason that people with achondroplasia can grow taller with Limb Lengthening Surgery than people without it is because they have the ligaments etc of an average height person thus their muscles etc don’t stretch.

But why is the soft tissue such as problem in the first place with limb lengthening surgery?

Well the ligaments normally attach at the enthesis, and the enthesis is attached near the growth plate. It’s very likely that ligament and bone growth are connected in this way so that the ligaments can grow as needed to support longitudinal bone growth. ““Entheses are fibrocartilaginous organs that bridge ligament with bone at their interface” More info about the enthesis here.

So it’s likely that a superior option to limb lengthening surgery will develop that involves stimulating enthesis development as well.