ABSTRACT

Fractures at the femoral neck play an important role in morbidity and mortality among older adults. Understanding the loading environment is a crucial factor for reducing the incidence of fracture at this site. In this study, the stresses on the femoral neck during stair ascent and descent were estimated. These femoral neck stresses were also compared to the peak loading from internal hip moments. Five male and five female adult subjects performed 5 successful trials of stair ascent and the same number trials of descent with a 3-step staircase. Motion and force data were collected. Inverse dynamics was used to calculate 3-D joint moments and reaction forces at the hip, knee and ankle joints of the right leg. Musculoskeletal model and static optimization were used and muscle forces, joint reaction forces and moments were used to estimate the 3-D moments and forces at the midpoint of the femoral neck. A standardized elliptical model of the bone structure was used to estimate the stresses of the model. Differences in peak stresses and moments were assessed by dependent t-tests (p < .05).

The peak hip extensor moment was significantly greater during ascent as compared to descent (p = .001). The 1st peak tensile stress was significantly increased at the superior site during the descent condition (p = 0.005), but the 2nd peak showed no significant difference between stair ascent and descent (p = .098). Both peak compressive stresses at the inferior site during showed no significant differences between stair ascent and descent (1st peak: p =.105; 2nd peak: p = .071). Conclusions concerning the loading of the proximal femur were contradictory depending on if loading was assessed via hip joint moments or from femoral neck stresses. The results of this study indicate that researchers may benefit from a more comprehensive evaluation of the loading environment by estimating bone stresses as well as joint moments during stair ascent and descent.