Douglas Preston Beall MD, Presenter: Research support, Spineology, Inc, Minneapolis, MN Stock options, Spineology, Inc, Minneapolis, MN Consultant, Spineology, Inc, Minneapolis, MN Stock options, AOI Medical, Orlando, FL Consultant, Medtronic, Inc, Memphis, TN

To compare the sensitivity of an increased alpha angle measurement to that of physical exam findings in patients with surgical confirmation of femoroacetabular impingement (FAI).

Magnetic Resonance (MR) imaging results were compared with physical examination data and surgical findings in 44 patients from July 2005 to April 1, 2006. The physical exam findings and surgical findings were recorded prospectively by an Orthopedic surgeon specializing in hip disorders. The MR imaging examinations were subsequently viewed by 2 musculoskeletal radiologists and the alpha angle was recorded along with the other associated findings. Following the recording of the data, the sensitivity, specificity and accuracy was calculated for alpha angle measurements and for the physical examination finding most characteristic of FAI.

Surgical evidence of FAI was found in 88.6% of the patients (39 of 44 patients). The primary physical examination finding consistent with FAI (flexion adduction internal rotation or FADDIR) was found in 68.2% of the patients (30 of 44 patients) and an increased alpha angle ≥55 degrees was seen on MR imaging in 31.4% of the patients (14 of 44). The sensitivity, specificity and accuracy of a positive FADDIR test in detecting FAI was 70.0%, 50.0% and 68.2% respectively. The sensitivity, specificity and accuracy of an increased alpha angle seen on MR imaging for detecting FAI was 32.5%, 75.0% and 36.4% respectively.

An abnormally increased alpha angle is less accurate than the physical exam in identifying patients with FAI and identified less than one third of the patients with FAI in our patient population.

This information illustrates the limited utility of the alpha angle measurement in identifying patients with femoroacetabular impingement and supports the value of physical exam in these patients.

Beall, D, Sensitivity of an Increased Alpha Angle Measurements as Compared to Physical Examination Findings in Detecting Patients with Surgical Confirmation of the Presence of Femoroacetabular Impingement.  Radiological Society of North America 2008 Scientific Assembly and Annual Meeting, February 18 - February 20, 2008 ,Chicago IL. http://archive.rsna.org/2008/6013691.html