Do small changes in rotation affect measurements …

1 RESEARCH ARTICLEOpen AccessDo small changes in rotation affectmeasurements of lower extremity limbalignment?Amir A. Jamali1*, John P. Meehan2, Nathan M. Moroski3, Matthew J. Anderson4, Ramit Lamba5and Carol Parise6 AbstractBackground:The alignment of the lower extremity has important implications in the development of knee effect of incremental rotations of the limb on common parameters of alignment has not been studied. Thepurpose 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 :Eighty-seven full length CT angiography studies (49 males and 38 females, average age 66 years old) wereincluded. Three-dimensional models were created using a rendering software program and placed on a virtual image of the extremity was obtained.

2 Thirty scans were randomly selected, and those models were rotated in 3 intervals around the longitudinal axis and additional images were :In the neutral position, the mechanical lateral distal femoral articular angle (mLDFA) was , medialproximal tibial angle (MPTA) was , and mechanical tibiofemoral angle (mTFA) was . Females had amore valgus alignment with a mTFA of while males had a more varus alignment with a mTFA of .The anatomic tibiofemoral angle (aTFA) was , the anatomic lateral distal femoral angle (aLDFA) measured , and the anatomical-mechanical angle (AMA) was . The prevalence of constitutional varus was 18%.The effect of rotation on the rotated scans led to statisticallysignificant differences relative to the 0 measurement for allmeasurements.

3 These effects may be small ,and their clinical importance is :This study provides new information on standardized measures of lower extremity alignment and therelationship between discreet axial rotations ofthe entire lower extremity and these :Alignment, Lower extremity, Osteotomy, rotation , Constitutional varus, Total knee replacementBackgroundThe alignment of the lower extremity has been an areaof ongoing study for decades. Standard radiographs havebeen used to determine the normal parameters ofalignment of the lower extremity. These are prone totechnical errors based on distance from the cassette androtation of the lower extremity around the longitudinalaxis. Deviations from normal have been broadly cate-gorized at malalignment although a clear definition of normal alignment has not been established.

4 One candefine normal on a statistical basis as lying withinsome arbitrarily defined range relative to the mean or ona pathological basis according to the risk of the jointundergoing degeneration secondary to the of the native lower extremity has beenassociated in previous studies with a higher risk ofosteoarthritis [1 4]. Accurate preoperative and postoper-ative alignment parameters are required for planningand prediction of outcome for both osteotomies andtotal knee replacement [5 11]. Thus, the assessments ofboth the lower extremity alignment in native kneesand those that have undergone replacement dependon an accurate definition of native lower extremityalignment [12, 13].In spite of increased sophistication in imaging andcomputer generated reconstructions, most surgeons stilldepend on two-dimensional radiographs in planning* Preservation Institute, 2825 J Street, Suite 440, Sacramento, CA 95816, USAFull list of author information is available at the end of the article The Author(s).

5 2017 Open AccessThis article is distributed under the terms of the Creative Commons Attribution License ( ), which permits unrestricted use, distribution, andreproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link tothe Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver( ) applies to the data made available in this article, unless otherwise al. Journal of Orthopaedic Surgery and Research (2017) 12:77 DOI such as osteotomy, unicompartmental kneereplacement, or total knee objectives of this study were twofold. We soughtto (1) determine the standardized neutral position mea-surements of alignment and (2) determine the effect ofrotation on commonly used measurements of prepared three-dimensional models of the lower ex-tremity in a standardized position and rotated themodels in 3 increments in each direction, taking digitalphotographs in each total of 221 full lower extremity CT angiography stud-ies for vascular disease workup were performed at ourinstitute between July 8, 2008, and May 14, 2010.

6 Ofthese, 87 patients (49 males and 38 females) were in-cluded in the present study. The average age was 66 yearsold (range 28 91 years old) Exclusion criteria includedadvanced osteoarthritis of the hip, knee , or ankle, radio-graphic evidence of previous realignment surgery orfracture, irregular positioning in the scanner, or any typeof lower extremity joint values of coronal alignment of the lower extremitieswith the femur placed on a virtual flat tableThe first portion of the study was the determination ofthe normal values of coronal alignment of the lower ex-tremity without the effect of rotation and in a neutralposition. Three-dimensional models were created fromthe CT data using a commercially available and previ-ously validated three-dimensional rendering softwareprogram (Mimics, Materialise, Ann Arbor, MI) [14].

7 These models were then placed on a virtual flat table inthe computer environment. The femora rested with thevirtual table plane passing through the posterior mostpoint of the greater trochanter and the posterior mostpoints of both the medial and lateral femoral this neutral position, a high resolution image of thefemur and the tibia from anterior to posterior was ob-tained. Next, 30 scans were randomly selected, and usingthe software, the entire lower extremity model was ro-tated in discreet 3 intervals in both internal and exter-nal rotation around the virtual axis from the femoralhead to the center of distal femur up to 12 in each dir-ection. After each rotation , a new anterior to posteriorimage of the now rotated lower extremity was image files were then analyzed using a custommeasurement analysis program written in Matlab (Math-works, Natick, MA, USA).

8 The analysis was performedin this fashion to optimize speed and precision andminimize risk of observer bias. The independent variablewas the degree of rotation . The dependent variableswere the alignment parameters for image analysis, points, axes, and angularmeasurementsPointsThe convention used by Moreland et al. was utilizedto define the center of the femoral trochlea as thecenter point of the knee [15]. Moreland et al. had de-scribed taking a visual midpoint among a total of fivepoints to define the center of the knee . These in-cluded the center of the femoral notch (trochlea),center of tibial spines, center of femoral condyles,center of soft tissue, and center of the tibia. Theyfound that all points were within 5 mm of one an-other. Based on the high consistency of the center ofthe femoral trochlea, we chose that point as the cen-ter of the knee .

9 The center of the ankle was definedvisually as the center of the distal tibial articular sur-face. The other points selected on lower extremityimages obtained were the center of the femoral head,the most distal points of the distal medial and lateralfemoral condyles, and the most proximal point of themedial and lateral tibial proximal femoral shaft center (PFSC) was definedby selecting two lateral points and two medial points inthe subtrochanteric region of the femur and allowing thesoftware to calculate the geometric center of those fourpoints located centrally within the femoral shaft in thesubtrochanteric axesThe mechanical axis of the femur was defined as aline drawn from the center of the femoral head tothe center of the knee . The mechanical and anatom-ical axes of the tibia were both defined in an identicalfashion as the line connecting the center of the kneeand the center of the axesThe line connecting the PFSC and the center of thefemoral trochlea was used to define the anatomicalaxis of the femur.

10 The line connecting the center ofthe femoral trochlea and the center of the ankle wasused to define the anatomical and mechanical axes ofthe tibia as noted axesThe distal femoral articular axis was defined by the lineconnecting the distal most points of the medial and lat-eral femoral condyles. The proximal tibial articular axiswas defined as the line connecting the two most prox-imal points of the tibial al. Journal of Orthopaedic Surgery and Research (2017) 12:77 Page 2 of 8 Angular measurementsMechanical angle measurementsThe mechanical lateral distal femoral articular angle(mLDFA) was defined as the lateral angle between thefemoral mechanical axis and the distal femoral articularaxis [16] (Fig. 1a). The medial proximal tibial angle(MPTA) was unique among the measurements in that itwas included in both the mechanical parameters and theanatomical parameters and was defined as the medialangle between the mechanical (as well as anatomical)axis of the tibia and the proximal tibial articular axis(Fig.)