Objective: To explore the effect of osteoporosis on the stress, stability, and lumbar intervertebral disc of AIS lumbar vertebrae by finite element method. Better understand the biomechanical characteristics of osteoporotic scoliosis. Methods: Based on the CT images of normal lumbar vertebrae and lumbar vertebrae with AIS, the finite element models were established to simulate the estimated osteoporosis by changing the Young's modulus of cortical bone, cancellous bone, and endplate. Four finite element models of normal lumbar, osteoporotic lumbar, normal AIS lumbar and osteoporotic AIS lumbar were established, and the same load and boundary conditions were applied respectively. The displacement, stress, and intervertebral disc strain of the four models were compared to explore the effect of osteoporosis on the stability and injury risk of AIS. Results: After suffering from osteoporosis, under the same load, the displacement of lumbar spine increases, the stability decreases, and the stability of AIS lumbar spine decrease more obviously, especially under extension load. Suffering from osteoporosis will increase the stress of lumbar spine, AIS lumbar spine increases more obviously, and the stress is more concentrated, Osteoporotic lumbar spine only affects the strain of intervertebral disc when AIS lumbar spine bends on the concave side, resulting in greater strain behind the concave side of intervertebral disc. Conclusions: AIS patients with OP have lower lumbar stability, a higher risk of fracture of lumbar vertebrae, and spinal nerves are more likely to be compressed by intervertebral discs. OP can aggravate the scoliosis of lumbar vertebrae.

Background: The stress of foot bone can effectively evaluate the functional damage caused by foot deformity and the results of operation. In this study, the finite element method was used to investigate the degree of displacement of distal chevron osteotomy on metatarsal stress and metatarsophalangeal joint load; Methods: Four finite element models of displacement were established by using the CT images of a patient with moderate hallux valgus (hallux valgus angle and intermetatarsal angle were 26.74° and 14.09°, respectively), and the validity of the model was verified. Each finite element model consisted of bones and various cartilage structures, ligaments, and plantar fascia, as well as encapsulated soft tissue. Except for soft tissue, the material properties of other parts were isotropic linear elastic material, and the encapsulated soft tissue was set as nonlinear hyperelastic material. The mesh was tetrahedral mesh. Link elements were used in ligament and plantar fascia. A ground reaction force with a half-body weight was applied at the bottom of the floor to simulate the ground reaction when standing. The upper surfaces of the encapsulated soft tissue, distal tibia, and distal fibula were fixed. The stress distribution of metatarsals and the stress of cartilage of the first metatarsophalangeal joint were compared and analyzed; Results: Compared with the hallux valgus without osteotomy, the stress of the first metatarsals and second metatarsals of 2–4 mm decreased, and the stress of the interarticular cartilage of the first metatarsophalangeal joint with 4 mm was reduced. In the case of 6 mm, the stress value between the first metatarsal and the first metatarsophalangeal joint increased, and 4 mm was the most suitable distance; Conclusions: Compared with the hallux valgus without osteotomy, the stress of the first metatarsals and second metatarsals of 2–4 mm decreased, and the stress of the interarticular cartilage of the first metatarsophalangeal joint with 4 mm was reduced. In the case of 6 mm, the stress value between the first metatarsal and the first metatarsophalangeal joint increased, and 4 mm was the most suitable distance. For the degree of displacement of the distal chevron osteotomy, the postoperative stability and the stress distribution of metatarsal bone should be considered. Factors such as hallux valgus angle, intermetatarsal angle, patient’s age, body weight, and metatarsal width should be considered comprehensively. The factors affecting osteotomy need to be further explored. The degree of displacement of osteotomy can be evaluated by FE method before the operation, and the most suitable distance can be obtained.

(1) This study examined the impact of fatigue and unanticipated factors on knee biomechanics during sidestep cutting and lateral shuffling in female basketball players, assessing the potential for non-contact anterior cruciate ligament (ACL) injuries. (2) Twenty-four female basketball players underwent fatigue induction and unanticipated change of direction tests, and kinematic and kinetic parameters were collected before and after fatigue with a Vicon motion capture system and Kistler ground reaction force (GRF) sensor. (3) Analysis using two-way repeated-measures ANOVA showed no significant interaction between fatigue and unanticipated factors on joint kinematics and kinetics. Unanticipated conditions significantly increased the knee joint flexion and extension angle (p < 0.01), decreased the knee flexion moment under anticipated conditions, and increased the knee valgus moment after fatigue (p ≤ 0.05). One-dimensional statistical parametric mapping (SPM1d) results indicated significant differences in GRF during sidestep cutting and knee inversion and rotation moments during lateral shuffling post-fatigue. (4) Unanticipated factors had a greater impact on knee load patterns, raising ACL injury risk. Fatigue and unanticipated factors were independent risk factors and should be considered separately in training programs to prevent lower limb injuries.

This study investigated the effects of knee braces with differing stiffness on in vivo knee kinematics and neuromuscular control during single-leg lateral landings. 14 healthy males performed landings under three conditions: no brace (Control), low-stiffness (Type-1), and high-stiffness (Type-2). Kinematics were quantified via dual fluoroscopic imaging, and sEMG recorded seven lower-limb muscles. Brace mechanics were assessed via three-point bending. Statistical analysis used repeated-measures ANOVA (α = 0.05). Kinematically, neither brace restricted knee flexion. Both significantly reduced varus angle (Type-1: 27–100% stance, p = 0.043; Type-2: 60–100% stance, p = 0.033), and Type-2 also lowered peak sagittal flexion acceleration (5.0 rad/s², p = 0.013). Neuromuscularly, Type-1 enhanced multiplanar control, advancing rectus femoris (154.7 ms vs. Type-2, p = 0.005) and vastus lateralis (35.6 ms vs. Control, p = 0.046) activation without increasing rotational instability. Conversely, Type-2 demonstrated a trade-off: despite earlier vastus medialis activation (43.6 ms vs. Control, p = 0.011), it significantly delayed gluteus medius activation (23.9 ms vs. Type-1, p = 0.037) and, critically, exacerbated compensatory internal-rotation acceleration (3.3 rad/s² vs. Type-1, p = 0.006) at peak flexion. The low-stiffness brace leveraged neuromuscular coordination for multiplanar stability, whereas the high-stiffness brace improved frontal-plane protection at the cost of rotational instability. These findings provide biomechanical evidence for the synergistic optimization of mechanical support and neuromuscular adaptation in knee brace design for populations with similar characteristics to the young male athletes studied herein.

(1) Background: Scoliosis has the mechanical characteristic of asymmetric stress distribution, which is one of the reasons for the aggravation of scoliosis. Bracing therapy is the best treatment for AIS, but it is difficult and costly to operate. Is it possible to reduce pressure in the concave side by relaxing the ITL in the concave side of scoliosis, so as to improve the abnormal stress distribution of scoliosis? In this paper, a finite element method was used to simulate the effect of the relaxation of concave-side ITL on the stress of a lumbar spine with scoliosis, which provides some guidance for the treatment of scoliosis. (2) Methods: Using CT images of a patient with scoliosis whose Cobb Angle was 43° and Lordosis Angle was 45, a scoliosis lumbar was established, and Young’s modulus of the ITL of the concave-side lumbar spine was reduced by 95% to simulate ligament relaxation. By comparing the stress condition of the model vertebral body with no ligament relaxation, the effect of concave-side ITL relaxation on the mechanical characteristics of scoliosis lumbar spine was explored. (3) Results: An effective and complete model of the lumbar spine was established. The concave ITL relaxed, which only had a great impact on the bending loads. After the ligament was relaxed, the stability of the spine was reduced. Stress concentration on the concave side of vertebrae and the IVD was aggravated. Under loads on the convex side, the maximum stress on the vertebral body and the IVD increased significantly, making lumbar vertebrae more vulnerable to injury. (4) Conclusions: Laxity of the ITL on the concave side of the AIS lumbar only affects the bending load. Laxity of the concave-side ligament will reduce the stability of the lumbar, aggravate the uneven stress distribution of scoliotic lumbar vertebrae, increase the risk of IVD injury, and be unfavorable for the scoliotic lumbar spine. Relaxation of the concave ITL alone is not an effective way to treat scoliosis.