Effect of Foot Orthoses on Kneecap Position in Adults With Flexible Flatfoot

Lateral patellar tilt will be measured in degrees on standardized weight-bearing cone beam CT images. The measure describes the sideways tilt of the kneecap in relation to the thigh bone. It is defined as the angle between the transverse axis of the patella and the posterior condylar axis of the femur. Measurements will be performed for each foot posture condition: natural foot posture, barefoot correction with foot orthoses, and correction with foot orthoses inside a neutral running shoe. Measurements will be assessed at both 0 and 20 degrees of knee flexion. Change will be reported as the within-participant difference between foot posture conditions.

Bisect offset will be measured as a percentage on standardized weight-bearing cone beam CT images. The measure describes the sideways position of the kneecap in relation to the groove of the thigh bone. It is defined as the percentage of lateral displacement of the midpoint of the patella from the midpoint of the trochlear groove. Higher percentages indicate greater lateral displacement of the kneecap. Measurements will be performed for each foot posture condition: natural foot posture, barefoot correction with foot orthoses, and correction with foot orthoses inside a neutral running shoe. Measurements will be assessed at both 0 and 20 degrees of knee flexion. Change will be reported as the within-participant difference between foot posture conditions.

Tibial tuberosity-trochlear groove distance will be measured on standardized weight-bearing cone beam CT images and reported in millimeters. The measure describes the side-to-side distance between the tibial tuberosity, where the patellar tendon attaches on the shin bone, and the center of the trochlear groove of the thigh bone, where the kneecap moves. Measurements will be performed for each foot posture condition: natural foot posture, barefoot correction with foot orthoses, and correction with foot orthoses inside a neutral running shoe. Measurements will be assessed at both 0 and 20 degrees of knee flexion. Change will be reported as the within-participant difference between foot posture conditions.

Transmalleolar rotation will be measured in degrees on standardized weight-bearing cone beam CT images. The measure describes the rotation of the ankle axis in relation to the long axis of the foot. The ankle axis is defined as a line through the medial and lateral malleoli. The foot axis is defined by an adjusted sagittal foot reference plane derived from calcaneal and metatarsal head landmarks on cone beam CT. Transmalleolar rotation is calculated as the angle between the malleolar line and this foot axis. Positive values indicate external rotation relative to the foot axis, and negative values indicate internal rotation. Measurements will be performed for each foot posture condition at 0 and 20 degrees of knee flexion.

Tibial rotation will be measured in degrees on standardized weight-bearing cone beam CT images. The measure describes the rotation of the shin bone in relation to the long axis of the foot. It is defined as the angle between a line tangent to the posterior surface of the proximal tibia and the foot axial rotation reference. The foot axial rotation reference is an adjusted sagittal foot plane derived from calcaneal and metatarsal head landmarks on cone beam CT. Positive values indicate external rotation relative to the foot axis, and negative values indicate internal rotation. Measurements will be performed for each foot posture condition at 0 and 20 degrees of knee flexion. Change will be reported as the within-participant difference between foot posture conditions.

Femoral rotation will be measured in degrees on standardized weight-bearing cone beam CT images. The measure describes the rotation of the thigh bone in relation to the long axis of the foot. It is defined as the angle between a line tangent to the posterior femoral condyles and the foot axial rotation reference. The foot axial rotation reference is an adjusted sagittal foot plane derived from calcaneal and metatarsal head landmarks on cone beam CT. Positive values indicate external rotation relative to the foot axis, and negative values indicate internal rotation. Measurements will be performed for each foot posture condition at 0 and 20 degrees of knee flexion. Change will be reported as the within-participant difference between foot posture conditions.

Patellar rotation will be measured in degrees on standardized weight-bearing cone beam CT images. The measure describes the rotation of the kneecap in relation to the long axis of the foot. It is defined as the angle between the transverse axis of the patella and the foot axial rotation reference. The foot axial rotation reference is an adjusted sagittal foot plane derived from calcaneal and metatarsal head landmarks on cone beam CT. Positive values indicate external rotation relative to the foot axis, and negative values indicate internal rotation. Measurements will be performed for each foot posture condition at 0 and 20 degrees of knee flexion. Change will be reported as the within-participant difference between foot posture conditions.

Navicular plantar position will be measured in millimeters on standardized weight-bearing cone beam CT images. The measure describes the vertical position of the navicular bone, which is a bone on the inner side of the midfoot and an indicator of medial arch position. It is defined as the perpendicular distance between the lowest point of the navicular bone and the tripod-adjusted axial foot plane. This reference plane is based on the plantar support points of the foot. Greater values indicate that the navicular bone is positioned farther from the plantar reference plane. Measurements will be performed for each foot posture condition at 0 and 20 degrees of knee flexion. Change will be reported as the within-participant difference between foot posture conditions.

Navicular medial displacement will be measured in millimeters on standardized weight-bearing cone beam CT images. The measure describes the side-to-side position of the navicular bone, which is a bone on the inner side of the midfoot and an indicator of foot pronation and medial arch position. It is defined as the perpendicular distance from the most medial point of the navicular bone to the adjusted sagittal foot reference plane. This reference plane is derived from calcaneal and metatarsal head landmarks on cone beam CT and approximates the long axis of the foot. Greater values indicate that the navicular bone is positioned farther medially relative to the foot reference plane. Measurements will be performed for each foot posture condition at 0 and 20 degrees of knee flexion. Change will be reported as the within-participant difference between foot posture conditions.

Foot axial rotation will be measured in degrees on standardized weight-bearing cone beam CT images. The measure describes the toe-in or toe-out orientation of the foot. It is defined as the angle between the adjusted sagittal foot reference plane and the global sagittal plane. The adjusted sagittal foot reference plane is derived from calcaneal and metatarsal head landmarks and approximates the long axis of the foot. Positive values indicate external rotation, or toe-out, and negative values indicate internal rotation, or toe-in. Measurements will be performed for each foot posture condition at 0 and 20 degrees of knee flexion. Change will be reported as the within-participant difference between foot posture conditions.

Femoral anteversion will be measured in degrees on the baseline weight-bearing cone beam CT scan. The measure describes the forward rotation of the femoral neck in relation to the distal femur. It is defined as the angle between the femoral neck axis and the posterior condylar axis of the distal femur. The femoral neck axis is defined as a line connecting the center of the femoral head and the center of the femoral neck. The posterior condylar axis is defined as a line tangential to the most posterior aspects of the medial and lateral femoral condyles. Positive values indicate increased femoral anteversion. This measure will be used to describe baseline femoral morphology and to account for anatomical variation that may influence lower-limb rotational alignment.

Foot Posture Index will be assessed at baseline by a trained examiner during standing. The measure describes the participant's static foot posture, including the degree of pronation or supination. The Foot Posture Index is a clinical scoring tool with six items, each scored from -2 to +2, giving a total score from -12 to +12. Lower scores indicate a more supinated foot posture, and higher scores indicate a more pronated foot posture. In this study, baseline pronated foot posture is defined as a Foot Posture Index score of +6 or higher, including a calcaneal frontal-plane position sub-score of +2. Inclusion is based on the right foot.

Calcaneal frontal-plane angle will be measured in degrees at baseline during standing. The measure describes the frontal-plane position of the heel bone in relation to the lower leg and reflects the degree of rearfoot valgus or varus. It is defined as the angle between a posterior calcaneal bisection line and a vertical tibial reference line. The posterior calcaneal bisection line is established using markers on the proximal and distal thirds of the posterior calcaneus. The tibial reference line is defined by the vertical midline of the distal third of the tibia. If used in the dataset coding, positive values will indicate calcaneal valgus and negative values will indicate calcaneal varus.

Perceived comfort of the selected foot orthosis will be assessed immediately after completion of the imaging protocol using a 10-point numeric rating scale. Participants will be asked to rate how comfortable the selected foot orthosis felt during the scan conditions. The scale ranges from 1 to 10, where 1 indicates "not comfortable at all" and 10 indicates "maximally comfortable." Higher scores indicate greater perceived comfort of the orthosis.

Patellar height will be assessed at baseline using patellar articular overlap on weight-bearing cone beam CT images. Patellar articular overlap describes the proportion of the kneecap joint surface that overlaps with, or is positioned within, the trochlear groove of the thigh bone. It will be expressed as a percentage. Higher percentages indicate greater overlap between the patellar articular surface and the trochlear groove, while lower percentages indicate less overlap. This measure will be used to describe baseline patellofemoral morphology and alignment.

Lateral trochlear inclination will be measured in degrees on the baseline weight-bearing cone beam CT scan. The measure describes the slope of the outer part of the trochlear groove, which is the groove of the thigh bone where the kneecap moves. It is defined as the angle of the lateral trochlear facet in relation to the posterior condylar line of the femur. This measure will be used to describe baseline trochlear morphology and patellofemoral anatomy.

Sulcus angle will be measured in degrees on the baseline weight-bearing cone beam CT scan. The measure describes the shape and depth of the trochlear groove, which is the groove of the thigh bone where the kneecap moves. It is defined as the angle formed by three points: the highest point of the medial trochlear facet, the deepest point of the trochlear groove, and the highest point of the lateral trochlear facet. A larger sulcus angle generally indicates a flatter or shallower trochlear groove, while a smaller angle indicates a deeper groove. This measure will be used to describe baseline trochlear morphology and patellofemoral anatomy.