Mechanical Loading of the Femoral Neck in Human Locomotion

Abstract

Advancing age and reduced loading are associated with a reduction in bone formation. Conversely, loading increases periosteal apposition and may reduce remodeling imbalance and slow age-related bone loss, an important outcome for the proximal femur, which is a common site of fracture. The ability to take advantage of bone's adaptive response to increase bone strength has been hampered by a lack of knowledge of which exercises and specific leg muscles load the superior femoral neck: a common region of microcrack initiation and progression following a sideways fall. We used an in vivo method of quantifying focal strains within the femoral neck in postmenopausal women during walking, stair ambulation, and jumping. Relative to walking, stair ambulation and jumping induced significantly higher strains in the anterior and superior aspects of the femoral neck, common regions of microcrack initiation and progression following a fall. The gluteus maximus, a hip extensor muscle, induced strains in the femoral neck during stair ambulation and jumping, in contrast to walking which induced strains via the iliopsoas, a hip flexor. The ground reaction force was closely associated with the level of strain during each task, providing a surrogate indicator of the potential for a given exercise to load the femoral neck. The gluteal muscles combined with an increased ground reaction force relative to walking induce high focal strains within the anterosuperior region of the femoral neck and therefore provide a target for exercise regimens designed to slow bone loss and maintain or improve microstructural strength. Model files used for calculating femoral neck strains are available at uitbl.mechse.illinois.edu/downloads © 2018 American Society for Bone and Mineral Research.

Heterogeneous Spatial and Strength Adaptation of the Proximal Femur to Physical Activity: A Within-Subject Controlled Cross-Sectional Study

“…The adapted sites within the femoral neck correspond with the primary compressive trabecular network and inferior cortex, regions thought to support and transmit weight-bearing directed loads. (8)(9)(10) Accordingly, the adaptation observed in pitchers resulted in increased predicted strength of the proximal femur to loading in the direction of single-leg stance. In contrast, there was a lack of any appreciable tissue adaptation in the superior femoral neck region.…”

“…It is possible that hip position during loading is important for targeting the superior femoral neck. We recently used a subject‐specific musculoskeletal model of the lower extremity and CT‐based FE model of the proximal femur to show weight‐bearing loading with the hip in flexion (eg, during stair ascent) engendered greatest strain within the superior femoral neck in postmenopausal women . An alternative research group suggested stair descent loaded the superior femoral neck more so than stair ascent, but the study applied forces to a generic elliptical femoral neck cross‐sectional model as opposed to a subject‐specific FE proximal femur model, raising concerns regarding model accuracy .…”

“…We recently used a subject-specific musculoskeletal model of the lower extremity and CT-based FE model of the proximal femur to show weightbearing loading with the hip in flexion (eg, during stair ascent) engendered greatest strain within the superior femoral neck in postmenopausal women. (8) An alternative research group suggested stair descent loaded the superior femoral neck more so than stair ascent, but the study applied forces to a generic elliptical femoral neck cross-sectional model as opposed to a subject-specific FE proximal femur model, raising concerns regarding model accuracy. (51) Martelli and colleagues (52) produced data suggesting maximal hip extension and knee flexion exercises maximally loaded the thinnest region of the superior femoral neck; however, data were limited to the study of a single individual and the application of musculoskeletal loads calculated from a young volunteer to an FE model of the proximal femur from an older individual.…”

“…The heightened fracture risk during a fall onto the greater trochanter partly results from the heterogeneous structure of the femoral neck, whose design reflects adaptation to stereotypical locomotor‐related forces . The femoral neck experiences maximum compressive stresses inferiorly and smaller tensile stresses superiorly during gait . To accommodate this habitual asymmetrical loading, the femoral neck possesses a much thicker inferior than superior cortex and an associated trabecular network positioned to resist and transmit weight‐bearing directed loads …”

“…(7) The femoral neck experiences maximum compressive stresses inferiorly and smaller tensile stresses superiorly during gait. (8)(9)(10) To accommodate this habitual asymmetrical loading, the femoral neck possesses a much thicker inferior than superior cortex and an associated trabecular network positioned to resist and transmit weight-bearing directed loads. (11) In contrast to during gait, the stress pattern within the femoral neck is reversed during a fall onto the greater trochanter.…”