Femoral neck fractures in young patients are usually caused by a high-energy trauma, which results in a perpendicular fracture. Although efforts are focused on preserving the femoral head in young patients, vertical femoral neck fracture is a problematic orthopedic injury due to the domination of shear forces. Due to controversy regarding which fixation method is the best choice, the purpose of this study was to find the most stable fixation method for this kind of fracture. This study includes experimental testing on cadaveric bone samples and finite element analysis (FEA) for three fracture fixation techniques, namely cannulated screws (CSs), dynamic hip screw with derotational screw (DHS + DS), and proximal femoral locking plate (PFLP). Experimental results of bone-implant stiffness, average femoral head displacement, failure load, failure energy, and relative position of the fractured fragments indicate that DHS + DS offers the strongest structure for stabilizing a vertical femoral neck fracture. Experimental data and FEA results both indicate that under static loading, the DHS + DS method of fixation produces the lowest femoral head displacement and interfragmentary movement, followed by PFLP and then CSs. The results of this research suggest that, based on the clinical assumption that a restricted weight-bearing regimen is recommended in the postoperative rehabilitation protocol, the DHS + DS method of fixation is a better choice compared to CSs and PFLP for a vertical femoral neck fracture fixation in young adults.

Background: Cam femoroacetabular impingement (FAI) can impose elevated mechanical loading in the hip, potentially leading to an eventual mechanical failure of the joint. Since in vivo data on the pathomechanisms of FAI are limited, it is still unclear how this deformity leads to osteoarthritis. Purpose: The purpose of this study was to examine the effects of cam FAI on hip joint mechanical loading using finite element analysis, by incorporating subject-specific geometries, kinematics, and kinetics. Questions: The research objectives were to address and determine: (1) if hips with cam FAI demonstrate higher maximum shear stresses, in comparison with control hips; (2) the magnitude of the peak maximum shear stresses; and (3) the locations of the peak maximum shear stresses. Methods: Using finite element analysis, two patient models were control-matched and simulated during quasistatic positions from standing to squatting. Intersegmental hip forces, from a previous study, were applied to the subjectspecific hip geometries, segmented from CT data, to evaluate the maximum shear stresses on the acetabular cartilage and underlying bone. Results: Peak maximum shear stresses were found at the anterosuperior region of the underlying bone during squatting. The peaks at the anterosuperior acetabulum were substantially higher for the patients (15.2±1.8 MPa) in comparison with the controls (4.5±0.1 MPa). Conclusions: Peaks were not situated on the cartilage, but instead located on the underlying bone. The results correspond with the locations of initial cartilage degradation observed during surgical treatment and from MRI. Clinical Relevance: These findings support the pathomechanism of cam FAI. Changes may originate from the underlying subchondral bone properties rather than direct shear stresses to the articular cartilage.

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Based on the clinical assumption that restricted weight-bearing regimen is recommended in the postoperative rehabilitation protocol, the results of this study suggest that the priority order of selection for the stable fixation implant of vertical femoral neck fracture in young patients is DHS+DS, then PFLP, and finally CSs.

There is a lack of studies investigating gender differences in whole-body kinematics during single-leg landings from increasing vertical heights and horizontal distances. This study determined the main effects and interactions of gender, vertical height, and horizontal distance on whole-body joint kinematics during single-leg landings, and established whether these findings could explain the gender disparity in non-contact anterior cruciate ligament (ACL) injury rate. Recreationally active males (n=6) and females (n=6) performed single-leg landings from a takeoff deck of vertical height of 20, 40, and 60 cm placed at a horizontal distance of 30, 50 and 70 cm from the edge of a force platform, while 3D kinematics and kinetics were simultaneously measured. It was determined that peak vertical ground reaction force (VGRF) and the ankle flexion angle exhibited significant gender differences (p=0.028, partial η 2 =0.40 and p=0.035, partial η 2 =0.37, respectively). Peak VGRF was significantly correlated to the ankle flexion angle (r= −0.59, p=0.04), hip flexion angle (r= −0.74, p=0.006), and trunk flexion angle (r= −0.59, p=0.045). Peak posterior ground reaction force (PGRF) was significantly correlated to the ankle flexion angle (r= −0.56, p=0.035), while peak knee abduction moment was significantly correlated to the knee flexion angle (r= −0.64, p=0.03). Rearfoot landings may explain the higher ACL injury rate among females. Higher plantar-flexed ankle, hip, and trunk flexion angles were associated with lower peak ground reaction forces, while higher knee flexion angle was associated with lower peak knee abduction moment, and these kinematics implicate reduced risk of non-contact ACL injury.

The central tenet of this study was to develop, validate and apply various individualised 3D musculoskeletal models of the human body for application to single-leg landings over increasing vertical heights and horizontal distances. While contributing to an understanding of whether gender differences explain the higher rate of non-contact anterior cruciate ligament (ACL) injuries among females, this study also correlated various musculoskeletal variables significantly impacted by gender, height and/or distance and their interactions with two ACL injury-risk predictor variables; peak vertical ground reaction force (VGRF) and peak proximal tibia anterior shear force (PTASF). Kinematic, kinetic and electromyography data of three male and three female subjects were measured. Results revealed no significant gender differences in the musculoskeletal variables tested except peak VGRF (p = 0.039) and hip axial compressive force (p = 0.032). The quadriceps and the gastrocnemius muscle forces had significant correlations with peak PTASF (r = 0.85, p < 0.05 and r = - 0.88, p < 0.05, respectively). Furthermore, hamstring muscle force was significantly correlated with peak VGRF (r = - 0.90, p < 0.05). The ankle flexion angle was significantly correlated with peak PTASF (r = - 0.82, p < 0.05). Our findings indicate that compared to males, females did not exhibit significantly different muscle forces, or ankle, knee and hip flexion angles during single-leg landings that would explain the gender bias in non-contact ACL injury rate. Our results also suggest that higher quadriceps muscle force increases the risk, while higher hamstring and gastrocnemius muscle forces as well as ankle flexion angle reduce the risk of non-contact ACL injury.

The increasing rate of osteoporosis in an aging population calls for a greater understanding of the cellular mechanism of bone resorption. We propose a biphasic mixture model. The solid phase (matrix) is assumed to be elastic and isotropic, and the fluid phase is assumed to be a linear viscous fluid. We give conservation equations for each constituent and for the whole mixture, and write new constitutive equations for the system. The rate of mass supply to constituents, caused by chemical reactions, is taken from an empirical relation of dissolution kinetics. We derive the biochemomechanical affinity in terms of biological, chemical, and mechanical factors. The strain energy density, hydrostatic pressure, and concentration of different ions present in the mixture are shown to affect the rate of bone resorption.