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What Are the Reference Values and Associated Factors for Center-edge Angle and Alpha Angle? A Population-based Study

Fischer, Cornelius Sebastian; Kühn, Jens-Peter, PhD, MD; Ittermann, Till, PhD; Schmidt, Carsten-Oliver, PhD; Gümbel, Denis, MD; Kasch, Richard, PhD, MD; Frank, Matthias, PhD, MD; Laqua, René, MD; Hinz, Peter, PhD, MD; Lange, Jörn, PhD, MD

Clinical Orthopaedics and Related Research®: November 2018 - Volume 476 - Issue 11 - p 2249–2259
doi: 10.1097/CORR.0000000000000410

Background The available evidence regarding normal ranges for the center-edge angle and the alpha angle derives from a few small studies, and associated factors such as sex and anthropometric factors have not been well evaluated. Knowing more about normal values for these parameters is critical, because this can inform decisions about when to perform elective hip preservation surgery. Population-level studies would provide considerable clarity on these issues, but to our knowledge, no such studies are available.

Questions/purposes The purposes of this study were (1) to use MRI in patients of a population-based study to establish normal values for the alpha and center-edge angles in the normal adult hip; and (2) to determine whether age, sex, or anthropometric variables were associated with differences in these values.

Methods We used MRI images (1.5 T) of 3226 participants of the Study of Health in Pomerania (SHIP). SHIP is a population-based study that started with 4308 participants in 1997. Participants were recruited randomly from official inhabitant data files as a stratified cluster sample of the population from a defined region in northeastern Germany. To ensure a representative epidemiologic cohort, stratification variables were sex, age, and city of residence. Between 2008 and 2012, 1094 of these participants underwent whole-body MRI with pelvic sequences in the second followup. In parallel, the next cohort, SHIP-Trend, started with the same protocol in which 2132 participants underwent MRI examination. Reference values were calculated by quantile regressions for the 2.5th and 97.5th percentiles. Associations with the demographic features sex, age, weight, height, body mass index (BMI), and waist circumference were analyzed by bivariate linear regression models.

Results The mean center-edge angle was 31° (± 7°) with a corresponding calculated normal range of 17° to 45°. The mean alpha angle was 55° (± 8°) with a corresponding calculated normal range between 39° and 71°. Men (30° ± 7°) had a lower center-edge angle than women (32° ± 8°) (p < 0.001, β = 1.4°; 95% confidence interval [CI], 0.9°-1.9°) and a higher alpha angle (57° ± 8° versus 52° ± 7°, p < 0.001, β = 5.7°; 95% CI, 5.2°-6.3°). Moreover, a higher center-edge angle for the left side was found (33° ± 8° versus 30° ± 8°, p < 0.001, β =3.2°; 95% CI, 3.0°-3.4°). In addition to sex, we found that age, height, waist circumference, and BMI affected both center-edge angle and alpha angle. Weight was associated with the alpha angle as well. Because of these associations, age- and sex-adjusted reference values with belonging formulas were calculated.

Conclusions The range of normal center-edge and alpha angles is quite wide. Therefore, only markedly abnormal angles may be associated with pathology. Moreover, center-edge angle and alpha angle are associated with age, sex, and anthropometric factors, which have to be taken into account for better interpretation.

Clinical Relevance The association of abnormal radiographic values with true clinical hip pathology is tenuous at best. Assuming that a patient with an abnormal radiograph requires treatment is unwise. The clinical picture has to be substantial for therapeutic decisions.

C. S. Fischer, D. Gümbel, P. Hinz, J. Lange, Clinic of Trauma, Reconstructive Surgery and Rehabilitation Medicine, University Medicine Greifswald, Greifswald, Germany

J.-P. Kühn, Institute of Diagnostic Radiology and Neuroradiology, University Medicine Greifswald, Greifswald Germany; and the Institute of Radiology, University Hospital, Carl-Gustav Carus University, Dresden, Germany

T. Ittermann, C.-O. Schmidt, Institute for Community Medicine, Ernst Moritz Arndt University of Greifswald, Greifswald, Germany

R. Kasch, Center for Orthopaedics, Trauma Surgery and Rehabilitation Medicine and Clinic and Outpatient Clinic for Orthopaedics and Orthopaedic Surgery, University Medicine Greifswald, Greifswald, Germany

M. Frank, Department of Trauma and Orthopaedic Surgery, Unfallkrankenhaus Berlin, Berlin, Germany

R. Laqua, Department of Diagnostic, Interventional and Pediatric Radiology, Bern University Hospital, Bern, Switzerland

J. Lange, Clinic of Trauma, Reconstructive Surgery and Rehabilitation Medicine, University Medicine Greifswald, Ferdinand-Sauerbruch-Straße, 17475, Greifswald, Germany, email:

Each author certifies that neither he, nor any member of his immediate family, has funding or commercial associations (consultancies, stock ownership, equity interest, patent/licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article.

All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research® editors and board members are on file with the publication and can be viewed on request.

Clinical Orthopaedics and Related Research® neither advocates nor endorses the use of any treatment, drug, or device. Readers are encouraged to always seek additional information, including FDA approval status, of any drug or device before clinical use.

Each author certifies that his institution approved the human protocol for this investigation and that all investigations were conducted in conformity with ethical principles of research.

This work was performed at University Medicine Greifswald, Greifswald, Germany.

Received January 11, 2018

Accepted June 26, 2018

© 2018 Lippincott Williams & Wilkins LWW
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