Objective To investigate the effect of postoperative reduction quality in femoral neck fracture internal fixation on the mechanical properties of the femoral head from the perspective of trabecular bone biomechanics, providing a certain experimental basis for clinical treatment and rehabilitation.Methods From patients who underwent hip replacement surgery for femoral neck fractures, 13 femoral heads meeting the research criteria were selected. Each femoral head was cut into 2 slices along the coronal plane, approximately 1 cm thick, resulting in a total of 26 femoral head slice specimens. The central axis of the primary compressive trabeculae was defined as the 0° group, with the intersection point of the primary compressive trabeculae and the femoral calcar serving as the center. By rotating the specimens to simulate different reduction angles, the cut femoral head slice specimens were randomly divided into five groups: -10°, -5°, 0°, 5°, and 10°, representing femoral heads with varying reduction qualities. Each group consisted of 5 specimens, with 1 remaining femoral head slice specimen reserved as a backup.Before the experiment, all specimens underwent high-resolution X-ray examination to obtain clear images of trabecular arrangement. The specimens were embedded in base resin and tested using the Bose Electroforce dynamic mechanical testing system for single-compression load tests and fatigue load tests. The load was set from 70N to 1400N, at a frequency of 1Hz, with 10,000 cycles. Parameters measured included axial stiffness, displacement, and the number of collapse cycles, to compare the biomechanical properties of femoral head specimens under different reduction qualities.Results There were differences in the axial stiffness, displacement, and number of collapse cycles among the femoral head specimens in different groups. At 800N, the axial stiffness of the 0° group (553.85±243.98N/mm) was significantly greater than that of the 10° group (146.2±64.2N/mm) and the -10° group (210.6±151.58N/mm), with statistically significant differences (P<005). The axial stiffness of the 0° group was also greater than that of the 5° group (343.7±104.77N/mm) and the -5° group (442.22±169.34N/mm), but the differences were not statistically significant (P>0.05). Additionally, the axial stiffness of the 5° and -5° groups was greater than that of the 10° and -10° groups, with statistically significant differences (P<0.05).Regarding displacement, the 0° group (3.37±1.92mm) had lower displacement than the 5° group (7.16±4.31mm), -5° group (6.22±2.74mm), 10° group (10.96±3.2mm), and -10° group (11.44±3.16mm). However, the differences in displacement between the 0° group and the 5° or -5° groups were not statistically significant (P>0.05), while the differences between the 0° group and the 10° or -10° groups were statistically significant (P<0.05). The differences in displacement between the 5°, -5°, 10°, and -10° groups were also statistically significant (P<0.05).The results of the number of collapse cycles showed that the 0° group (9416±1165.5 cycles) had a significantly higher number of collapse cycles than the 10° group (1489±1682.62 cycles) and the -10° group (2088±2420.31cycles), cycles with statistically significant differences (P<0.05). The number of collapse cycles in the 0° group was also higher than that in the 5° group (7191.75±1890.43 cycles) and the -5° group (7289±3447.97 cycles), but the differences were not statistically significant (P>0.05). The number of collapse cycles in the 5° and -5° groups was significantly higher than that in the 10° and -10° groups, with statistically significant differences (P<0.05).Conclusions The quality of reduction after internal fixation of femoral neck fractures has a significant impact on the biomechanical properties of the femoral head. The results of this study provide a scientific basis for optimizing the treatment and postoperative management of femoral neck fractures, which can help improve clinical outcomes and the quality of life for patients.