J Orthop Sci (2010) 15:64–70 DOI 10.1007/s00776-009-1414-z Original article Three-dimensional lower extremity alignment in the weight-bearing standing position in healthy elderly subjects AKIHIRO ARIUMI 1,2 , TAKASHI SATO 1 , KOICHI KOBAYASHI 3 , YOSHIO KOGA 1 , GO OMORI 4 , IZUMI MINATO 5 , and NAOTO ENDO 2 1 Department of Orthopaedic Surgery, Niigata Kobari Hospital, 3-27-11 Kobari, Niigata 950-2022, Japan 2 Division of Orthopaedic Surgery, Department of Regenerative and Transplant Medicine, Niigata University Graduate School of Medicine and Dental Science, Niigata, Japan 3 Department of Health Sciences, Niigata University School of Medicine, Niigata, Japan 4 Center of Transdisciplinary Research, Niigata University, Niigata, Japan 5 Department of Orthopaedic Surgery, Niigata Rinko Hospital, Niigata, Japan Abstract Background. Although assessment of lower extremity align- ment is important for the treatment and evaluation of diseases that present with malalignment of the lower extremity, it has generally been performed using only plain radiographs seen in two dimensions (2D). In addition, there is no consensus regarding the criteria for quantitative three-dimensional (3D) evaluation of the relative angle between the femur and tibia. The purpose of this study was to establish assessment methods and criteria for quantitatively evaluating lower extremity alignment in 3D and to obtain reference data from normal elderly subjects. Methods. The normal alignment of 82 limbs of 45 healthy elderly subjects (24 women, 21 men; mean age 65 years, range 60–81 years) was analyzed in 3D with regard to flexion, adduc- tion–abduction, and rotational angle of the knee in the weight- bearing, standing position.The obtained computed tomography (CT) and biplanar computed radiography (CR) data were used to define several anatomical axes of the femur and tibia as references. Results. In the sagittal plane, the mean extension–flexion angle was significantly more recurvatum in women than in men. In the coronal plane, the mean 3D hip-knee-ankle angle was more varus by several degrees in this Japanese series than that in a Caucasian series reported previously. Regarding rotational alignment, the mean angle between the anteropos- terior axis of the tibia and the transepicondylar axis of the femur in this series was slightly larger (externally rotated) than that of previously reported Japanese series examined in the supine position. Conclusions. These data are believed to represent important references for 3D evaluation of morbid lower extremity align- ment in the weight-bearing, standing position and are impor- tant for biomechanical research (e.g., 3D analyses of knee kinematics) because the relative angles between the femur and tibia are assessed three-dimensionally. Introduction Lower extremity alignment is determined by both the spatial relation between the femur and tibia and by the geometry of these bones. Assessment of lower extrem- ity alignment is important when determining and evalu- ating treatment for diseases that present with abnormal alignment in the lower extremities, such as knee and hip arthritis, patellar dislocation, and congenital malalign- ment. 1–13 In the field of orthopedic surgery, lower extremity alignment is generally assessed two-dimen- sionally (2D) on plain radiographs using the hip-knee- ankle angle or the tibiofemoral angle in the coronal plane alone. 11,14,15 However, 2D radiographic measure- ments are affected by the position of the radiation source and the orientation of the subject’s pelvis and lower extremities. 16 Therefore, the accuracy and repro- ducibility of this method are insufficient for detailed investigations. In addition, rotational alignment cannot be assessed on plain radiographs. Despite remarkable recent developments in medical imaging technologies that enable visualization of the three-dimensional (3D) geometry of bone and align- ment of the lower extremity, few studies have reported quantitative 3D evaluations of lower extremity align- ment in the weight-bearing, standing position using 3D digital bone models. In addition, there remains a lack of consensus regarding the criteria for quantitative 3D assessment. As previously reported, we developed a method for assessing 3D lower extremity alignment in the standing position using 3D digital bone models; this system has been in clinical use since 2002. 17,18 To evaluate morbid alignment in the lower extremities of patients with hip and knee arthritis and other diseases, it is vital to obtain normal data of lower extremity alignment from healthy subjects as a reference. One of the purposes of this study was to obtain these reference data by Offprint requests to: T. Sato Received: January 8, 2009 / Accepted: September 13, 2009