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Predicting Hip Impingement


The diagnosis of hip pain and impairment is increasing. The reasoning for the increased diagnosis is not well established and may simply be from an increase in diagnosis, not an increase in actual injury occurrence. These semantics are fine and dandy, but provide little help for improving those with hip pain. It also doesn’t help predict who will have pain or injury.

Cam-type femoralacetabular impingement (FAI) is characterized by an enlarged, asperhical deformity of the femoral head and neck. During hip motion, the femoral head comes into contact with the lateral aspects of the anterosuperior labrum and acetablum. More or less, the head of the thigh bone, runs into areas of the pelvis bone. An interesting note is that simply having a FAI, does not necessarily mean one has pain or symptoms. Many individuals with Cam FAI do not have pain and are asymptomatic. Therefore, understanding more about what causes pain during FAI will help remove these pain mechanisms and decrease pain! As a physical therapist, I frequently see patients who have pain a FAI from a diagnostic image, but this does not always mean the FAI is driving the symptoms, they may just be correlated.
Imaging provides insight into the structures, but function and movement are more helpful for patients. Many would agree, they would rather move without pain, then with pain, even if it means having a FAI or some imaging defect.
One functional test for FAI is squatting depth. Squat depth and diagnostic imagine (CT scan or x-ray) are applicable measures for predicting a painful or nonpainful FAI. Overall, differences exist between those with a Cam FAI and controls (Ng 2014):
  1. Higher axial alpha angles
  2. Higher radial alpha angles
  3. Lower femoral head-neck offsets
Comparing the asymptomatic with the symptomatic group, the following occur:
  1. Higher femoral neck-shaft angle in the asymptomatic group
  2. Reduced squat depth and pelvic ROM in the symptomatic group
For classifying groups, the following are the best predictors for FAI symptoms:
  1. Radial alpha angle
  2. Femoral neck-shaft angle
  3. Pelvic range of motion
This information is helpful, but still limited for predicting Cam FAI, as research using 3-D imaging likely provides more insight.
Also, this research was solely in men, making conclusions for females questionable. Women have wider pelvises and likely varying femoral angles.
Overall, if a patient is having symptoms in the hip, an FAI may cause the pain. However, just because someone has a FAI, it doesn’t mean that is the cause of their symptoms. Taking their function and movement into account is key when working with patients with hip pain and FAI-like symptoms.

Ng KC, Lamontagne M, Adamczyk AP, Rahkra KS, Beaulé PE. Patient-Specific Anatomical and Functional Parameters Provide New Insights into the Pathomechanism of Cam FAI. Clin Orthop Relat Res. 2014 Jul 22. [Epub ahead of print]

Written by John Mullen, DPT, CSCS