Context: Accurate, efficient, and reliable measurement methods are essential to prospectively identify risk factors for knee injuries in large cohorts.Objective: To determine tester reliability using digital photographs for the measurement of static lower extremity alignment (LEA) and whether values quantified with an electromagnetic motion-tracking system are in agreement with those quantified with clinical methods and digital photographs.Design: Descriptive laboratory study. Setting: Laboratory.Patients or Other Participants: Thirty-three individuals participated and included 17 (10 women, 7 men; age ¼ 21.7 6 2.7 years, height ¼ 163.4 6 6.4 cm, mass ¼ 59.7 6 7.8 kg, body mass index ¼ 23.7 6 2.6 kg/m 2 ) in study 1, in which we examined the reliability between clinical measures and digital photographs in 1 trained and 1 novice investigator, and 16 (11 women, 5 men; age ¼ 22.3 6 1.6 years, height ¼ 170.3 6 6.9 cm, mass ¼ 72.9 6 16.4 kg, body mass index ¼ 25.2 6 5.4 kg/ m 2 ) in study 2, in which we examined the agreement among clinical measures, digital photographs, and an electromagnetic tracking system. Intervention(s): We evaluated measures of pelvic angle, quadriceps angle, tibiofemoral angle, genu recurvatum, femur length, and tibia length. Clinical measures were assessed using clinically accepted methods. Frontal-and sagittal-plane digital images were captured and imported into a computer software program. Anatomic landmarks were digitized using an electromagnetic tracking system to calculate static LEA.Main Outcome Measure(s): Intraclass correlation coefficients and standard errors of measurement were calculated to examine tester reliability. We calculated 95% limits of agreement and used Bland-Altman plots to examine agreement among clinical measures, digital photographs, and an electromagnetic tracking system.Results: Using digital photographs, fair to excellent intratester (intraclass correlation coefficient range ¼ 0.70-0.99) and intertester (intraclass correlation coefficient range ¼ 0.75-0.97) reliability were observed for static knee alignment and limblength measures. An acceptable level of agreement was observed between clinical measures and digital pictures for limb-length measures. When comparing clinical measures and digital photographs with the electromagnetic tracking system, an acceptable level of agreement was observed in measures of static knee angles and limb-length measures.Conclusions: The use of digital photographs and an electromagnetic tracking system appears to be an efficient and reliable method to assess static knee alignment and limb-length measurements.Key Words: posture, risk factor assessment, digital photographs Key PointsDigital photographs are a reliable tool to assess static knee alignment and limb-length measurements. An electromagnetic tracking system is an efficient and acceptable method to assess static frontal-plane knee alignment and limb-length measures. Incorporating measures of static lower extremity alignment in prospective study designs will help researchers ide...