Study of Unloading at Lower Limbs Orthotics: Experiment and Simulation

Abstract

The rate of healing and rehabilitation in fractures of the feet depends on the level and the program of loading the damaged segment. The paper studied the possibilities of efficiently controlling the unloading level of the affected area by varying the degree of orthosis tightening (lateral compression). Among others, a hypothesis was tested‚ according to which only in a slip the limb by increasing the lateral compression is pushed up and the coefficient of unloading (CU) grows. Two types of shin-orthosis system models were developed and studied numerically for different variants of parameters: conical models using the package, based on boundary integral equation method and BEM, and personalized real form models based on the technology «CT scan –> Specialized processing software (Mimics) –> FEA package». The unloading coefficient dependence on the circumferential tightness for two types of “slippery” stocking materials was measured. When using both synthetic and silk stockings‚ experimental results did not show valid growth of CU with an increase in tightening (lateral compression) neither while standing nor walking. As calculations showed, pushing the shin up due to lateral compression may be to a maximum of ~ 1.2 mm even in total slip. At the same time‚ the shift of the shin surface as a result of the piston effect can reach several mm. Thus, the additional sediment due to the so-called “piston effect” (skin stretching under a load, as well as its shift-slip over thin and soft layer of subcutaneous fat) is several times greater than the effect of ejection due to lateral compression and associated unloading, and thus completely reduces them to nothing. Further possibilities and approaches to the problem of load programming at limb orthotics are discussed.