Do all PFFD cases look the same? No. [Mc Cormack, 2001] There is a spectrum of severity in PFFD. There are some typical features of a child born with PFFD. The thigh is abnormally short, when the leg is relaxed it is held in flexion (bent), abduction (moved to the side), and external rotation.[Westin, 1969] Some have described the leg as an upside down L-shape or resembling a ship's funnel. The foot of the affected leg is frequently at the level of the opposite knee.
There may be significant anteroposterior (front to back) instability of the knee joint due to deficient or missing cruciate ligaments.[Westin, 1969] 70-80 percent of the cases also experience fibula (smaller bone of lower leg) defects - ranging from mild tissue defects to complete absence of the fibula and a deformed foot.[Westin, 1969] Some people with fibular hemimelia have reported seeing a small indent or dimple on the front of the leg at shin level.
Presence or absence of a foot deformity, presence or absence of fibular hemimelia (shortening of the fibia), and knee structure affects treatment options. 50 percent of patients also experience defects in other limbs.[Krajbich,1991],[Westin, 1969] Approximately 15 percent of PFFD cases are bilateral (both legs), with those cases frequently having the more severe fibula and foot defects.[Westin, 1969]
Diagnosis is almost always possible on the first physical examination due to the typical PFFD characteristics. However, the physical exam is of little value for determining the severity of the defect. An X-ray or MRI will be required to determine severity and classification.
An X-ray has the advantage no sedation is required and takes much less time than an MRI, however in the first few months the hip is mostly cartelage and does not display well.
Also the X-ray technician may not have the PFFD leg perfectly parallel to image plate leading to an image with poor value. An MRI has the advantage that you can view much more structure (arteries, cartelage, fat, bone, muscle) and the image is in 3D, but an MRI is typically an hour long affair where the subject must remain absolutely still in an extremely loud environment (imagine a very noisy old-style, humming-clanking elevator).
[Update] A study of the efficacy of MRI vs X-Ray for classifying PFFD found that radiographic evaluation tends to overestimate the degree of deficiency and that, therefore, MRI is better than X-Ray for a good classification. Maldjian et. al, 2007
If an infant is going to get an MRI it should be fed only breast milk or water (breast milk does not interfere with an MRI) and will probably either be given a suppository or oral sedative to make it sleep and not move while sleeping. After the baby falls asleep it will be transferred to the MRI room.
If you decide on an MRI - it is important for at least one parent to be in the MRI room at the moment your baby is moved from the table it was sleeping on to the MRI platform. This is because if the baby wakes up from the jostling, now in a strange environment with strange people, he or she probably will not want to go to sleep again without a moment of cuddling from Mommy and/or Daddy.
This was the case for us. Our one-year-old woke up, was scared, and wouldn't go back to sleep. The nurses wanted to give even more sedative, even though the maximum recommended level had already been given. Fortunately one of us was a medical professional and knew this and also was able to persudade the nurses to let us try a daddy-lullaby first. Thirty seconds into a quiet hum from daddy and our daughter was asleep and ready for the MRI.