Relationship Between the Alpha and Beta Angle in Diagnosing CAM type Femoroacetabular Impingement on Frog-leg Lateral Radiographs

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Surgery, McMaster University, Hamilton, ON, Canada (2)Hospital for Special Surgery, New York, NY, USA (3)Division of

1 Relationship Between the Alpha and Beta Angle in Diagnosing CAM type Femoroacetabular Impingement on Frog-leg Lateral Radiographs Moin Khan 1, Anil Ranawat 2, Dale Williams 1, Rajiv Gandhi 3, Hema Choudur 4, Naveen Parasu 4, Nicole Simunovic 5 and Olufemi R. Ayeni 1 Investigation performed at McMaster University, Hamilton, ON, Canada (1)Division of Orthopaedics, Department of Surgery, McMaster University, Hamilton, ON, Canada (2)Hospital for Special Surgery, New York, NY, USA (3)Division of Orthopaedic Surgery, University of Toronto, Toronto, ON, Canada (4)Department of Radiology, McMaster University, Hamilton, ON, Canada (5)Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, ON, Canada

2 Funding Disclosure *No funding affiliations to be disclosed

3 Overview of Study Purpose: To explore the relationship between alpha and beta angles on frog leg lateral hip radiographs. Method: 50 frog-leg lateral hip radiographs were evaluated by 2 orthopaedic surgeons and 2 radiologists. Each reviewer measured the alpha and beta angles on 2 separate occasions. Results: There was no significant association between positive alpha and beta angles, [kappa range (95 % CI 0.17 to 0.086) to 0.54 (95 % CI )]. Intra-observer reliability was high. Conclusion: There is no statistical or functional relationship between readings of positive alpha and beta angles. The radiographic measurements resulted in high intra-observer and fair-tomoderate inter-observer reliability. Level of Evidence: III.

4 Background Femoroacetabular impingement (FAI) - common source of hip pain in the young adult Two different types of FAI: CAM and pincer FAI causes damage to the acetabular labrum and joint cartilage Alpha angles are used to assess the sphericity of the proximal femur Beta angles are used to assess the distance between the pathologic head-neck junction and the acetabular rim

5 Background Fig. 1 Diagram demonstrating measurement of alpha angle and beta angle in FAI hip (modified from Nepple et al.) Fig. 2 Diagram demonstrating measurement of alpha angle and beta angle in normal hip

6 Research Question The aim of this study was to explore the relationship between alpha and beta angles on frog-leg lateral hip radiographs

evaluated by 2 orthopaedic surgeons and 2

7 Methods 50 frog-leg lateral view radiographs of the proximal femur were evaluated by 2 orthopaedic surgeons and 2 radiologists Determined the relationship between positive alpha and beta angles through the inter- and intraobserver reliability of these measurements Each reviewer measured the alpha and beta angles on two separate occasions

Kappa (k) range: - 0.043 (95% CI: -0.17-0.

8 Results No significant association between positive alpha and beta angles Kappa (k) range: (95% CI: ) to 0.54 (95% CI: ) Alpha angle ICC range: 0.74 (95% CI: ) to 0.99 (95% CI: ) Beta angle ICC range: 0.86 (95% CI: ) to 0.97 (95% CI: ) High Intraobserver reliability

9 Results Table 1. Correlation Between Positive Alpha Angle and Positive Beta Angle Assessor Kappa (95 % CI) Trial 1 Trial 2 Radiologist ( to 0.29) 0.14 ( to 0.32) Radiologist ( 0.17 to 0.091) ( 0.17 to 0.086) Orthopaedic surgeon ( 0.17 to 0.16) ( to 0.17) Orthopaedic surgeon (0.33 to 0.75) 0.53 (0.32 to 0.74) Table 2. Intra-Observer Reliability in Determining Alpha and Beta Angles Assessor ICC (95 % CI) Alpha angle Beta angle Radiologist ( ) 0.86 ( ) Radiologist ( ) 0.97 ( ) Orthopaedic surgeon ( ) 0.89 ( ) Orthopaedic surgeon ( ) 0.87 ( )

10 Discussion No correlation between reading a positive alpha angle and positive beta angle from the same film Presence of a CAM lesion does not necessarily imply that there is a decrease in the angular relationship between the head neck junction and acetabular rim Limitations exist for using radiographs to evaluate hip pathology Planning acetabular rim recession is not necessarily required in the setting of findings of an increased alpha angle

11 Conclusions No statistical or functional relationship between readings of positive alpha and beta angles Radiographic measurements resulted in high intra-observer and fair-tomoderate inter-observer reliability Presence of a CAM lesion on lateral radiographs does not necessitate a decrease in clearance between the femoral head and acetabular rim Relationship between a positive alpha angle and a positive beta angle may not be the best measure of functional impingement Further study is required to assess the relationship between alpha and beta angles

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