  Femoroacetabular impingement (FAI) cam morphology is routinely assessed using
two-dimensional alpha angles which do not provide specific data on cam size
characteristics. The purpose of this study is to implement a novel, automated
three-dimensional (3D) pipeline, CamMorph, for segmentation and measurement of
cam volume, surface area and height from magnetic resonance (MR) images in
patients with FAI. The CamMorph pipeline involves two processes: i) proximal
femur segmentation using an approach integrating 3D U-net with focused shape
modelling (FSM); ii) use of patient-specific anatomical information from 3D FSM
to simulate healthy femoral bone models and pathological region constraints to
identify cam bone mass. Agreement between manual and automated segmentation of
the proximal femur was evaluated with the Dice similarity index (DSI) and
surface distance measures. Independent t-tests or Mann-Whitney U rank tests
were used to compare the femoral head volume, cam volume, surface area and
height data between female and male patients with FAI. There was a mean DSI
value of 0.964 between manual and automated segmentation of proximal femur
volume. Compared to female FAI patients, male patients had a significantly
larger mean femoral head volume (66.12cm3 v 46.02cm3, p<0.001). Compared to
female FAI patients, male patients had a significantly larger mean cam volume
(1136.87mm3 v 337.86mm3, p<0.001), surface area (657.36mm2 v 306.93mm2 ,
p<0.001), maximum-height (3.89mm v 2.23mm, p<0.001) and average-height (1.94mm
v 1.00mm, p<0.001). Automated analyses of 3D MR images from patients with FAI
using the CamMorph pipeline showed that, in comparison with female patients,
male patients had significantly greater cam volume, surface area and height.
