Knee Surg Sports Traumatol Arthrosc DOI 10.1007/s00167-014-3182-3
Hip
Relationship between the alpha and beta angles in diagnosing CAM‑type femoroacetabular impingement on frog‑leg lateral radiographs Moin Khan · Anil Ranawat · Dale Williams · Rajiv Gandhi · Hema Choudur · Naveen Parasu · Nicole Simunovic · Olufemi R. Ayeni
Received: 26 March 2014 / Accepted: 9 July 2014 © Springer-Verlag Berlin Heidelberg 2014
Abstract Purpose Alpha and beta angles are commonly used radiographic measures to assess the sphericity of the proximal femur and distance between the pathologic head–neck junction and the acetabular rim, respectively. The aim of this study was to explore the relationship between these two measurements on frog-leg lateral hip radiographs. Methods Fifty frog-leg lateral hip radiographs were evaluated by two orthopaedic surgeons and two radiologists. Each reviewer measured the alpha and beta angles on two separate occasions to determine the relationship between positive alpha and beta angles and the inter- and intraobserver reliability of these measurements. Results There was no significant association between positive alpha and beta angles, [kappa range −0.043 (95 % CI −0.17 to 0.086) to 0.54 (95 % CI 0.33–0.75)]. Intraobserver reliability was high [alpha angle intra-class correlation coefficient (ICC) range 0.74 (95 % CI 0.58–0.84)
to 0.99 (95 % CI 0.98–0.99) and beta angle ICC range 0.86 (95 % CI 0.76–0.92) to 0.97 (95 % CI 0.95–0.98)]. Conclusions There is no statistical or functional relationship between readings of positive alpha and beta angles. The radiographic measurements resulted in high intraobserver and fair-to-moderate inter-observer reliability. Results of this study suggest that the presence of a CAM lesion on lateral radiographs as suggested by a positive alpha angle does not necessitate a decrease in clearance between the femoral head and acetabular rim as measured by the beta angle and thus may not be the best measure of functional impingement. Understanding the relationship between these two aspects of femoroacetabular impingement improves a surgeon’s ability to anticipate potential operative management. Level of evidence III.
M. Khan · D. Williams · O. R. Ayeni (*) Division of Orthopaedics, Department of Surgery, McMaster University, Hamilton, ON, Canada e-mail: [email protected]
H. Choudur · N. Parasu Department of Radiology, McMaster University, Hamilton, ON, Canada e-mail: [email protected]
M. Khan e-mail: [email protected]
N. Parasu e-mail: [email protected]
D. Williams e-mail: [email protected] A. Ranawat Hospital for Special Surgery, New York, NY, USA e-mail: [email protected]
Keywords Alpha angle · Beta angle · Relationship · FAI
N. Simunovic Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, ON, Canada e-mail: [email protected]
R. Gandhi Division of Orthopaedic Surgery, University of Toronto, Toronto, ON, Canada e-mail: [email protected]
13
Introduction Femoroacetabular impingement (FAI) is increasingly being recognized as a cause of hip pain and a possible cause of early osteoarthritis in young adults [16]. In CAM-type FAI, the radius of curvature of the femoral head or neck profile exceeds the radius of curvature of the acetabulum [3, 16]. This deformity is thought to be due to a lack of offset or absence of concavity on the anterolateral aspect of the femoral head–neck junction. The degree of this deformity has been defined by various measurements including offset ratio, alpha and beta angles on radiographs, CT or MRI [2]. To radiographically quantify femoral head asphericity, the angle where the femoral head–neck leaves sphericity is described as the alpha angle, which was initially proposed by Notzli et al. [33] (Figs. 1, 2). Several plain radiological techniques have been proposed to project the anterior and anterior superior aspect of the femoral neck to determine the alpha angle, such as the cross-table lateral view, the 45° and 90° Dunn views, and the frog-leg lateral view [14]. Studies have shown the Dunn view and frog-leg lateral view [11] to be sensitive in diagnosing CAM-type lesions on the anterior femoral neck [1]. The alpha angle has been shown to be the most frequently reported postoperative radiographic outcome measure, and high angles have been correlated with labral injuries, chondral damage and decreased range of movement [20, 22]. The beta angle is a radiological tool for measuring the distance between the pathologic head–neck junction and the acetabular rim [7] (Figs. 1, 2). The beta angle has been validated as an accurate measure of overall clearance between the femoral neck and the acetabular rim [4] and provides a reliable assessment of functional range of motion improvement independent of the specific femoral
Fig. 1 Diagram demonstrating measurement of alpha angle and beta angle in FAI hip (modified from Nepple et al. [31])
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Knee Surg Sports Traumatol Arthrosc
or acetabular impingement lesions [7]. The beta angle has been shown to be significantly higher in asymptomatic patients compared with those with symptomatic FAI [7]. A number of studies have demonstrated a positive alpha angle (>50°) [22, 31, 34] to be associated with FAI; however, few papers have explored the relationship between symptomatic FAI and a positive beta angle (50°) [2, 22, 33] and a positive beta angle (50° [2, 22, 33, 37]. A positive beta angle was classified as an angle
Hip
Relationship between the alpha and beta angles in diagnosing CAM‑type femoroacetabular impingement on frog‑leg lateral radiographs Moin Khan · Anil Ranawat · Dale Williams · Rajiv Gandhi · Hema Choudur · Naveen Parasu · Nicole Simunovic · Olufemi R. Ayeni
Received: 26 March 2014 / Accepted: 9 July 2014 © Springer-Verlag Berlin Heidelberg 2014
Abstract Purpose Alpha and beta angles are commonly used radiographic measures to assess the sphericity of the proximal femur and distance between the pathologic head–neck junction and the acetabular rim, respectively. The aim of this study was to explore the relationship between these two measurements on frog-leg lateral hip radiographs. Methods Fifty frog-leg lateral hip radiographs were evaluated by two orthopaedic surgeons and two radiologists. Each reviewer measured the alpha and beta angles on two separate occasions to determine the relationship between positive alpha and beta angles and the inter- and intraobserver reliability of these measurements. Results There was no significant association between positive alpha and beta angles, [kappa range −0.043 (95 % CI −0.17 to 0.086) to 0.54 (95 % CI 0.33–0.75)]. Intraobserver reliability was high [alpha angle intra-class correlation coefficient (ICC) range 0.74 (95 % CI 0.58–0.84)
to 0.99 (95 % CI 0.98–0.99) and beta angle ICC range 0.86 (95 % CI 0.76–0.92) to 0.97 (95 % CI 0.95–0.98)]. Conclusions There is no statistical or functional relationship between readings of positive alpha and beta angles. The radiographic measurements resulted in high intraobserver and fair-to-moderate inter-observer reliability. Results of this study suggest that the presence of a CAM lesion on lateral radiographs as suggested by a positive alpha angle does not necessitate a decrease in clearance between the femoral head and acetabular rim as measured by the beta angle and thus may not be the best measure of functional impingement. Understanding the relationship between these two aspects of femoroacetabular impingement improves a surgeon’s ability to anticipate potential operative management. Level of evidence III.
M. Khan · D. Williams · O. R. Ayeni (*) Division of Orthopaedics, Department of Surgery, McMaster University, Hamilton, ON, Canada e-mail: [email protected]
H. Choudur · N. Parasu Department of Radiology, McMaster University, Hamilton, ON, Canada e-mail: [email protected]
M. Khan e-mail: [email protected]
N. Parasu e-mail: [email protected]
D. Williams e-mail: [email protected] A. Ranawat Hospital for Special Surgery, New York, NY, USA e-mail: [email protected]
Keywords Alpha angle · Beta angle · Relationship · FAI
N. Simunovic Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, ON, Canada e-mail: [email protected]
R. Gandhi Division of Orthopaedic Surgery, University of Toronto, Toronto, ON, Canada e-mail: [email protected]
13
Introduction Femoroacetabular impingement (FAI) is increasingly being recognized as a cause of hip pain and a possible cause of early osteoarthritis in young adults [16]. In CAM-type FAI, the radius of curvature of the femoral head or neck profile exceeds the radius of curvature of the acetabulum [3, 16]. This deformity is thought to be due to a lack of offset or absence of concavity on the anterolateral aspect of the femoral head–neck junction. The degree of this deformity has been defined by various measurements including offset ratio, alpha and beta angles on radiographs, CT or MRI [2]. To radiographically quantify femoral head asphericity, the angle where the femoral head–neck leaves sphericity is described as the alpha angle, which was initially proposed by Notzli et al. [33] (Figs. 1, 2). Several plain radiological techniques have been proposed to project the anterior and anterior superior aspect of the femoral neck to determine the alpha angle, such as the cross-table lateral view, the 45° and 90° Dunn views, and the frog-leg lateral view [14]. Studies have shown the Dunn view and frog-leg lateral view [11] to be sensitive in diagnosing CAM-type lesions on the anterior femoral neck [1]. The alpha angle has been shown to be the most frequently reported postoperative radiographic outcome measure, and high angles have been correlated with labral injuries, chondral damage and decreased range of movement [20, 22]. The beta angle is a radiological tool for measuring the distance between the pathologic head–neck junction and the acetabular rim [7] (Figs. 1, 2). The beta angle has been validated as an accurate measure of overall clearance between the femoral neck and the acetabular rim [4] and provides a reliable assessment of functional range of motion improvement independent of the specific femoral
Fig. 1 Diagram demonstrating measurement of alpha angle and beta angle in FAI hip (modified from Nepple et al. [31])
13
Knee Surg Sports Traumatol Arthrosc
or acetabular impingement lesions [7]. The beta angle has been shown to be significantly higher in asymptomatic patients compared with those with symptomatic FAI [7]. A number of studies have demonstrated a positive alpha angle (>50°) [22, 31, 34] to be associated with FAI; however, few papers have explored the relationship between symptomatic FAI and a positive beta angle (50°) [2, 22, 33] and a positive beta angle (50° [2, 22, 33, 37]. A positive beta angle was classified as an angle
