In Class A the head of the femur is present, together with an adequate acetabulum
(hip socket) and a very short femoral shaft. Initially, there is no bony
connection between the femoral shaft and the head of the femur. At skeletal
maturity a bony connection will be present between the femur head and shaft.
4
In Class B the acetabulum and head of the femur are present, but the femur
head may not be visible due to delayed ossification (formation of bone).
Based on the presence of the acetabulum, Dr King's theory can be used to
deduce that the femur head will develop. No bony connection exists between
the femoral shaft and head, and the upper end of the femoral shaft usually
has a small bony tuft. Unlike Class A, at skeletal maturity a bony connection
will not exist between the femur head and shaft. Studies show that the head
and shaft do not move together, and , therefore it is believed that there
is no cartilaginous connection between the shaft and head.4
In Class C the acetabulum is severely dysplastic (abnormally developed) and
the head of the femur never develops. The shaft of the femur is short with
a small bony tuft on the upper end.
Class D is characterized by the absence of both the acetabulum and femoral
head.4 The femoral shaft is extremely short and the upper end
is pointed.1 In the most severe cases only a small part of the
lower femur is present, with marked knee abnormality.1