Abstract
Background
Rehabilitation exercise plays a key role in bone fracture healing. Although traditional clinical experiments and observations are adopted to evaluate the effect of rehabilitation exercise, the biomechanical mechanism is still unclear. There are few reports on the mechanical analysis model of elbow flexion rehabilitation exercise of the complete upper limb model previously. Because the upper limb structure is complex, the previous model is so simplified that soft tissue structure is not considered. It cannot reflect the change and distribution of the stress and stress state during elbow flexion exercise.
Methods
From the perspective of biomechanics, based on the CT scanning images of forearm for an aged female volunteer, a 3-D distal radius fracture forearm model is established. By introducing the soft tissues and the splint, a complete 3-D forearm model is finally reconstructed. The model includes ulna, radius, humerus, muscle, ligament, joint, wrist, skin and splint. The correctness of the model is verified by comparing the results of numerical simulation with the results of previous literature and clinical experiments.
Results
When the elbow flexion angle increases from 0 to 120 degrees, the stress increases from 0.21 Mpa to 0.83 Mpa. When the elbow flexion angle increases from 0 to 120 degrees, the strain increases from 2–23%, and the maximum strain at the fracture end is about 22.5%. Also an analytical formula of the relationship fracture end strain and different elbow flexion angles is obtained by nonlinear fitting based on the simulation results, which is convenient for clinicians to predict fracture end strain.
Conclusions
During elbow flexion rehabilitation exercise, the stress of biceps brachii is large, and with the increase of elbow flexion angle, the stress shows an increasing trend. The stress in the area of distal radius fracture is also concentrated. Moderate stress concentration is helpful to the process of bone remodeling, so as to shorten the time of fracture healing. There was no obvious stress concentration in metacarpal bone and has little effect on the activity of metacarpophalangeal joint. The fretting strain at the fracture site can improve the speed of fracture healing, because the generation of early callus can absorb a lot of energy generated by fretting strain, which has an impact on the mechanical properties and plastic deformation ability of callus, and plays an important role in the stimulation of late osteogenesis.
Improvements in radiographic and clinical assessment of distal radius fracture healing by FE-estimated bone stiffness
