Femoroacetabular Impingement: Can the Alpha Angle Be Estimated?

Nouh, Mohamed Ragab; Schweitzer, Mark E.; Rybak, Leon; Cohen, Jodi

doi:10.2214/ajr.07.3258

Cited by 66 publications

(42 citation statements)

References 10 publications

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“…Defining who is at risk of impingement and cartilage damage has been mainly based on the size and location of the cam deformity, which has been traditionally quantified by the alpha angle on multiplane imaging [3,7,36,37,39,43,45]. Several authors have shown that the severity of the cam deformity (that is, a higher alpha angle) is associated with an increased risk of hip pain and joint degeneration [7,28,33].…”

Section: Introductionmentioning

confidence: 99%

“…Several authors have shown that the severity of the cam deformity (that is, a higher alpha angle) is associated with an increased risk of hip pain and joint degeneration [7,28,33]. Typically, a cam deformity is indicated by an alpha angle greater than 50.5°and 60°in the oblique-axial and radial plane, respectively [7,36,37,39]. However, the accuracy and sensitivity of the alpha angle in determining the risk of developing symptomatic FAI is inconsistent [6,30,34,37,43].…”

Section: Introductionmentioning

confidence: 99%

“…Typically, a cam deformity is indicated by an alpha angle greater than 50.5°and 60°in the oblique-axial and radial plane, respectively [7,36,37,39]. However, the accuracy and sensitivity of the alpha angle in determining the risk of developing symptomatic FAI is inconsistent [6,30,34,37,43]. Moreover, other common radiographic measures of the femoral head and neck and acetabulum have been associated with symptomatic FAI [5,10,26,40], but it remains unclear as to which combination of parameters plays a role in identifying patients at risk of developing symptoms.…”

Section: Introductionmentioning

confidence: 99%

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Patient-Specific Anatomical and Functional Parameters Provide New Insights into the Pathomechanism of Cam FAI

Lamontagne

Adamczyk

et al. 2015

Clinical Orthopaedics &Amp; Related Research

103

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Background Femoroacetabular impingement (FAI) represents a constellation of anatomical and clinical features, but definitive diagnosis is often difficult. The high prevalence of cam deformity of the femoral head in the asymptomatic population as well as clinical factors leading to the onset of symptoms raises questions as to what other factors increase the risk of cartilage damage and hip pain.Questions/purposes The purpose was to identify any differences in anatomical parameters and squat kinematics among symptomatic, asymptomatic, and control individuals and if these parameters can determine individuals at risk of developing symptoms of cam FAI. Methods Forty-three participants (n = 43) were recruited and divided into three groups: symptomatic (12), asymptomatic (17), and control (14). Symptomatic participants presented a cam deformity (identified by an elevated alpha angle on CT images), pain symptoms, clinical signs, and were scheduled for surgery. The other recruited volunteers were blinded and unaware whether they had a cam deformity. After the CT data were assessed for an elevated alpha angle, participants with a cam deformity but who did not demonstrate any clinical signs or symptoms were considered asymptomatic, whereas participants without a cam deformity and without clinical signs or symptoms were considered healthy control subjects. For each participant, anatomical CT parameters (axial alpha angle, radial alpha angle, femoral head-neck offset, femoral neck-shaft angle, medial proximal femoral angle, femoral torsion, acetabular version) were evaluated. Functional squat parameters (maximal squat depth, pelvic range of motion) were determined using a motion capture system. A stepwise discriminant function analysis was used to determine

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Patient-Specific Anatomical and Functional Parameters Provide New Insights into the Pathomechanism of Cam FAI

Lamontagne

Adamczyk

et al. 2015

Clinical Orthopaedics &Amp; Related Research

103

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“…This suggests that the level of disparity between the current results and those of Nötzli and Kassarjian cannot be simply explained on the basis of selection bias alone. In a more recent study performed by Nouh et al the authors found significant intra-reader variation in alpha angle measurement, while also determining that subjective estimation of the alpha angle was a poor surrogate for direct measurement [8].…”

Section: Discussionmentioning

confidence: 96%

Cam-type femoral-acetabular impingement: is the alpha angle the best MR arthrography has to offer?

et al. 2009

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Introduction In our institutional experience, determination of the alpha (α) angle at MR arthrography as an indicator of the likelihood of cam-type femoroacetabular impingement (FAI) is fraught with inconsistency. The aims of this study were to quantify the degree of variability in and calculate the diagnostic accuracy of the α angle in suggesting a diagnosis of cam impingement, to determine the accuracy of a positive clinical impingement test, and to suggest alternative MR arthrographic measures of femoral head-neck overgrowth and determine their diagnostic utilities. Materials and methods We carried out a retrospective analysis of MR arthrographic studies performed during a 4-year period, combined with chart analysis, which allowed identification of 78 patients in whom surgical correlation was also available. The status of a preoperative clinical impingement test was also noted. Patients were designated as having cam-type FAI (Group A, n= 39) if intra-operative femoral head-neck junction bony osteochondroplasty/arthoscopic femoral debridement was performed. Group B (n=39) acted as controls. Three radiologists independently and blindly performed a series of measurements (α angle and two newly proposed measurements) in each patient on two separate occasions. An α angle of greater than 55°was considered indicative of the presence of cam-type FAI.Results Performance values for α angle measurement were poor for each observer. There was considerable (up to 30% of the mean value) intra-observer variability between the first and second α angle measurements for each subject. Binary logistic regression analysis confirmed that the α angle is of no value in predicting the presence or absence of cam-FAI. A statistically significant difference existed between Groups A and B with regard to the newly proposed anterior femoral distance (AFD; p=0.004). Using an AFD value of 3.60 mm or greater as being indicative of the presence of cam-FAI yields a 0.67 performance measure (95% confidence interval 0.55-0.79). The second proposed parameter (femoral neck ratio) was of no value in suggesting the presence or absence of this condition. The sensitivity, specificity, and positive and negative predictive values of the clinical impingement test were 76.9%, 87.2%, 85.7% and 79.1% respectively. Conclusions Femoral α angle measurement is associated with considerable variability. This index performed poorly in our patient population and was statistically of no value in suggesting the presence or absence of cam-FAI. One of our proposed measures, the AFD, outperformed the α angle, though to an insufficient degree to suggest its routine incorporation into clinical practice. Our experience suggests that the clinical impingement test remains the most reliable predictor of the presence of this condition.

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“…In a study of 50 patients, some degree of cam-type deformity was found in 74% of asymptomatic patients in at least one plane of the reconstructed CT data set with (4) found up to 30% intraobserver difference for AA measurements. In a study by Nouh et al (15) for the validation of AA measurements, moderate reproducibility was found after repeated assessments by the same reader (15). In some studies, interobserver agreement and reproducibility for AA measurements were reported to be moderate-to-good with intraclass coefficient constant values ranging from 0.50 to 0.79 (8,9,14).…”

Section: Discussionmentioning

confidence: 96%

CT assessment of asymptomatic hip joints for the background of femoroacetabular impingement morphology

Ergen

Vudali²,

Sanverdi³

et al. 2014

Diagn Interv Radiol

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ORIGINAL ARTICLE PURPOSE The purposes of this study were to assess the presence of cam and pincer morphology in asymptomatic individuals with a negative femoroacetabular impingement test, and to determine and compare the ranges of alpha angle using two measurement methods. MATERIALS AND METHODSIn total, 68 consecutive patients who underwent abdominopelvic computed tomography (CT) for reasons other than hip problems were the patient population. Patients who had a positive femoroacetabular impingement test were excluded. Alpha angle measurements from axial oblique (A N ) and radial reformat-based images (A R ) from the anterior through the superior portion of the femoral head-neck junction, as well as femoral head-neck offset, center-edge angle, acetabular version angle measurements, and acetabular crossover sign assessment, were made. RESULTSOverall prevalences of cam (increased alpha angle, decreased femoral head-neck offset) and pincer morphology (increased center-edge angle, decreased acetabular version) were 20.0%, 26.8%, 25.8%, and 10.2% of the hips, respectively. The mean A R ranged from 41.64°±4.23° to 48.13°±4.63°, whereas A N was 41.10°±4.44°. The values of A R were higher than A N , and the difference was statistically significant (P < 0.001). The highest A R values were measured on images from the anterosuperior section of femoral head-neck junction. CONCLUSIONIn asymptomatic subjects, higher alpha angle values were obtained from radial reformatted images, specifically from the anterosuperior portion of the femoral head-neck junction compared with the axial oblique CT images. Other measurements used for the assessment of cam and pincer morphology can also be beyond the ranges that are considered normal in the general population. F emoroacetabular impingement (FAI) is a recognized risk factor for the development of osteoarthritis (1, 2). Morphological abnormalities of the proximal femur and/or acetabulum result in abnormal contact between the femur and acetabulum during hip motion, especially during flexion and internal rotation. The resulting abnormal stress on the acetabular labrum and articular cartilage can cause degeneration and tearing of the labrum, damage the adjacent acetabular cartilage, and eventually lead to osteoarthritis (1).Morphological variations and measurements demonstrating such alterations in the proximal femoral head and acetabulum that might be responsible for the development of FAI have become a research focus (2-7). The alpha angle (AA) is a parameter that demonstrates the degree of focal femoral epiphyseal overgrowth and reflects insufficiency of the anterolateral femoral head-neck offset and asphericity of the femoral head (5, 7). Since the concept of FAI was proposed, the AA measurement has become a widely used method to quantify osseous deformity at the femoral head-neck junction (5). However, there has been some controversy regarding its validity in clinical use, because of the substantial overlap in AA measurements between volunteers and symptomatic patients with cam-type ...

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Femoroacetabular Impingement: Can the Alpha Angle Be Estimated?

Abstract: Subjective assessment of alpha angles is suboptimal unless one is quite confident of a bone abnormality.

Cited by 66 publications

References 10 publications

Patient-Specific Anatomical and Functional Parameters Provide New Insights into the Pathomechanism of Cam FAI

Patient-Specific Anatomical and Functional Parameters Provide New Insights into the Pathomechanism of Cam FAI

Cam-type femoral-acetabular impingement: is the alpha angle the best MR arthrography has to offer?

CT assessment of asymptomatic hip joints for the background of femoroacetabular impingement morphology

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