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Femoral Head Asymmetry and Coxa Magna: Anatomic Study

Young, Ernest Y. MS*,†; Gebhart, Jeremy J. BS*,†; Bajwa, Navkirat BS*,†; Cooperman, Daniel R. MD*,†; Ahn, Nicholas U. MD*,†

Journal of Pediatric Orthopaedics: June 2014 - Volume 34 - Issue 4 - p 415–420
doi: 10.1097/BPO.0000000000000132

Background: Coxa magna, the asymmetrical circumferential enlargement of the femoral head, is an important sequela of pediatric disorders such as Legg-Calvé-Perthes disease. Definitions vary because of lack of controls and a scarcity of research on the distribution of the femoral head asymmetry. This study aims at defining the normal distribution of asymmetry between the left and the right femoral head and neck in the population and how demographics affect these properties. The study also looked at the distribution of side dominance (left or right).

Methods: This study measured 230 paired femurs from individuals (20 to 40 y old) distributed for sex and ethnicity. The height and weight of the individuals were also recorded. The femoral head diameter and minimal femoral neck diameter in the anteroposterior view were measured on each paired femurs. The absolute and percent differences were determined to define asymmetry.

Results: Most of the population fell within 3% of asymmetry for the femoral head and 4% for the femoral neck. The maximum head percent asymmetry was 7.4%. Absolute difference in millimeters to percent asymmetry showed a ratio of 2:1 for the femoral head and 3:1 for the femoral neck. African Americans showed greater femoral head symmetry and a bias toward left-sided femoral head and neck enlargement when compared with their white counterparts.

Conclusions: There was a high degree of symmetry between the left and right femoral heads and necks, which supports definitions found in the literature that define coxa magna above 10%. This study defines asymmetry in the femoral head in the normal population, which will help to define a quantitative definition of coxa magna.

*Department of Orthopaedics, Case Western Reserve University School of Medicine

University Hospitals Case Medical Center, Cleveland Heights, OH

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

None of the authors received financial support for this study.

The authors declare no conflicts of interest.

Reprints: Ernest Y. Young, MS, 1585 Rydalmount Rd., Cleveland Heights, OH 44118. E-mail:

© 2014 by Lippincott Williams & Wilkins