Effects of Thigh and Leg Rotation on Sagittal Knee Angle During Static Assessment

Background: The femur and tibia can suffer changes in rotation, mainly in the orthostatic position, causing errors in measurements when two-dimensional instruments are utilized. Objectives: To test the effects of thigh and leg rotation on sagittal knee angle measurement. Methods: A physical model simulating the right lower limb was constructed using two wooden rafters and a plastic protractor between the rafters. The thigh rotation and leg rotation were measured, ranging from 50° of internal rotation to 50° of external rotation. The sagittal knee angle was measured using the three-dimensional kinematics via three protocols (femoral condyle angle, head of fibula angle, and four points angle) with points marked on the model corresponding to the greater trochanter of the femur, lateral condyle of the femur, head of the fibula, and lateral malleolus. Results: During the internal rotation of the thigh and leg, the sagittal knee angle increased (varying from 3.1° to 6.3° for thing, and 0.9° to 3.6° for leg), whereas it decreased during the external rotation of the thigh and leg (varying from -5.2° to -7.8° for thing, and 0.1° to -5.5° for leg). Conclusions: Thigh rotation and leg rotation affect sagittal knee measurement and can lead to erroneous assessments if not considered.