Rearfoot varus When viewed in a non-weightbearing position with the subtalar joint in neutral, a rearfoot varus mimics a forefoot varus in that the plantar surface is “elevated” medially compared to the lateral surface (Biomechanical Assessment of Foot and Ankle, 2023). When weightbearing, a foot with a rearfoot varus in non-weightbearing will exhibit an everted calcaneus in weightbearing (see “Heel Position” in “Running Biomechanics” above). This leads to increased pronation at the subtalar joint (Araújo). Navicular drop test The navicular drop test is used to assess subtalar joint pronation during standing. It measures the vertical difference of the navicular tuberosity in standing with the subtalar joint in neutral versus the navicular tuberosity in relaxed standing (Navicular Drop Test, 2022). To complete this test, the client is positioned in standing, and the most prominent aspect of the navicular tuberosity is marked. The foot is placed in subtalar joint neutral, and the distance from the navicular tuberosity to the floor is measured. Now the client relaxes the foot out of subtalar joint neutral, and the distance between the navicular tuberosity and the floor is measured again. A greater amount of subtalar joint pronation in weightbearing will result in a greater difference between the position of the navicular tuberosity in the subtalar joint neutral position versus the relaxed position (Navicular Drop Test, 2022). If the navicular drop measurement is equal to or less than 5 mm, the foot is classified as supinated; measurements between 6 to 9 mm typify a neutral foot; and measurements equal to or greater than 10 mm typical a pronated foot (Navicular Drop Test, 2022). Self-Assessment Quiz Question #1 The foot will compensate for both forefoot and rearfoot varus during running with: The alignment of the tibia may be a relevant biomechanical factor for runners, as it affects the manner in which the foot presents to the ground with each step. External tibial torsion Tibial torsion refers to any twisting of the tibia along its longitudinal axis, which changes the alignment between the proximal alignment of the tibia with the knee and the distal alignment of the tibia with the ankle/foot (Snow, 2021). A certain degree of external tibial torsion is normal, but increased external tibial torsion leads to a toe-out position of the foot. This, in turn, leads to compensatory or induced gait/running mechanics abnormalities. A common compensation for excess external tibial torsion is increased hip internal rotation. However, this compensatory mechanism causes a “knee in” alignment, which creates a dynamic knee valgus that can affect patellofemoral mechanics (Snow, 2021). a. Pronation. b. Supination. c. Early heel lift. d. Decreased vertical displacement. Tibial alignment If excess external tibial torsion is not compensated for at the hip, the runner will demonstrate a toe-out position of the foot. This creates an abnormal foot progression angle, where there is a difference between the axis of the foot and the direction of progression of the body. This can lead to increased subtalar joint pronation as the runner pushes off along the medial foot instead of rolling onto the toes for push-off (Snow, 2021).
Measuring tibial torsion can be difficult, and some state that reliable assessment requires computerized tomography (CT) and/or magnetic resonance imaging (MRI) (Stephen et al., 2021). However, Hawi et al. (2022) describe a clinical assessment that has been shown to be reliable. This involves having the client kneel on the examination table with the feet hanging over the edge. The knee is flexed 90 degrees, and the hip is in neutral abduction/adduction with the back straight. The axis of the thigh is compared with an axis through the second ray of the foot. The difference between these two axes reflects the amount of tibial torsion (Hawi et al., 2022). Normal external tibial torsion is 20 to 30 degrees (Mercier, 2008). When tibial torsion is greater than normal, its effect on gait and running mechanics should be assessed for its possible influence on a runner’s injury. Tibial varum Tibial varum is a condition where the tibia displays a bowing deformity. Specifically, this is a frontal plane deformity where the distal third of the tibia is angled medially relative to the proximal tibia. This alignment angles the medial aspect of the foot further from the ground, which causes accelerated pronation and an increased demand on the muscle that function as pronation decelerators. Burke et al. (2022) suggest that the rate of loading of tissues is a relevant factor in injury onset in runners. Tibial varum correlates with increased subtalar joint pronation, which correlates with overuse injuries in runners (Raissi et al., 2009). Genu valgum Genu valgum is a frontal plane deformity where the knee is adducted and is defined as the angle formed by a line connecting the anterior superior iliac spine (ASIS) and the midpoint of the patella and a line from the midpoint of the patella and the tibial tubercle. It represents the frontal plane resultant vector of the force of quadriceps muscles and the force of the patellar tendon acting on the patella (Skouras et al., 2022). Normal genu valgus in adults is 5 to 7 degrees (Lee et al., 2009). Genu valgus has been associated with iliotibial band syndrome and patellofemoral pain syndrome in runners (Willwacher et al., 2022). Genu varum Genu varum involves outward bowing of the knee so that the axis of the lower leg is angled medially compared with the axis of the thigh. Genu varum changes the alignment of the line of gravity to the base of support (Letafatkar et al., 2018). Like tibial varum, genu varus angles the medial aspect of the foot further from the ground, which causes accelerated pronation and an increased demand on the muscle that function as pronation decelerators. Genu varum has shown an association with onset and severity of Achilles tendinopathy in runners (Aiyegbusi et al., 2020). Femoral anteversion Femoral neck anteversion (also known as femoral torsion or femoral version) is the angle between two lines in the axial plane perpendicular to the femoral shaft: one line goes through the proximal femoral neck, and the second line goes through the distal femoral condyles. Comparing these two lines allows for assessment of the “twist” in the femur (Scorcelletti et al., 202). Normal femoral anteversion is approximately 15 degrees (Cibulka, 2004). Increased femoral anteversion usually results in a “knee in” position and/or a toe-in position of the foot. This typically results in dynamic knee valgus during stance, a heel whip during the swing phase of running, and increased hip internal rotation range of motion. Femoral anteversion has been correlated with patellofemoral problems in runners (Apti et al., 2023).
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