Do small changes in rotation affect measurements of lower extremity limb alignment?
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RESEARCH ARTICLE
Open Access
Do small changes in rotation affect measurements of lower extremity limb alignment? Amir A. Jamali1*, John P. Meehan2, Nathan M. Moroski3, Matthew J. Anderson4, Ramit Lamba5 and Carol Parise6
Abstract Background: The alignment of the lower extremity has important implications in the development of knee arthritis. The effect of incremental rotations of the limb on common parameters of alignment has not been studied. The purpose of the study was to (1) determine the standardized neutral position measurements of alignment and (2) determine the effect of rotation on commonly used measurements of alignment. Methods: Eighty-seven full length CT angiography studies (49 males and 38 females, average age 66 years old) were included. Three-dimensional models were created using a rendering software program and placed on a virtual plane. An image of the extremity was obtained. Thirty scans were randomly selected, and those models were rotated in 3° intervals around the longitudinal axis and additional images were obtained. Results: In the neutral position, the mechanical lateral distal femoral articular angle (mLDFA) was 85.6 ± 2.3°, medial proximal tibial angle (MPTA) was 86.1 ± 2.8°, and mechanical tibiofemoral angle (mTFA) was −0.7 ± 3.1°. Females had a more valgus alignment with a mTFA of 0.5 ± 2.9° while males had a more varus alignment with a mTFA of −1.7 ± 2.9°. The anatomic tibiofemoral angle (aTFA) was 4.8 ± 2.6°, the anatomic lateral distal femoral angle (aLDFA) measured 80.2 ± 2.2°, and the anatomical-mechanical angle (AMA) was 5.4 ± 0.7°. The prevalence of constitutional varus was 18%. The effect of rotation on the rotated scans led to statistically significant differences relative to the 0° measurement for all measurements. These effects may be small, and their clinical importance is unknown. Conclusions: This study provides new information on standardized measures of lower extremity alignment and the relationship between discreet axial rotations of the entire lower extremity and these parameters. Keywords: Alignment, Lower extremity, Osteotomy, Rotation, Constitutional varus, Total knee replacement
Background The alignment of the lower extremity has been an area of ongoing study for decades. Standard radiographs have been used to determine the “normal” parameters of alignment of the lower extremity. These are prone to technical errors based on distance from the cassette and rotation of the lower extremity around the longitudinal axis. Deviations from “normal” have been broadly categorized at malalignment although a clear definition of “normal alignment” has not been established. One can define “normal” on a statistical basis as lying within some arbitrarily defined range relative to the mean or on * Correspondence: [email protected] 1 Joint Preservation Institute, 2825 J Street, Suite 440, Sacramento, CA 95816, USA Full list of author information is available at the end of the article
a pathological basis according to the risk of the joint undergoing degeneration secondary t
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