A finite element study: the quantitative correlation between the displacement of osteotomy end and metatarsalgia during forefoot loading pattern in percutaneous minimal invasion surgery of hallux valgus

Abstract Objective To investigate the quantitative correlation between the osteotomy end displacement and the occurrence of transfer metatarsalgia in percutaneous minimal invasion surgery of bunion in the forefoot loading pattern.Methods The simulation of the operation of minimally invasive treatment of hallux valgus using the established finite element model with the period of forefoot load mode facilitated the correction of the distal end of the first metatarsal head after osteotomy by steps of 0–6 mm from inside to outside and from top to bottom; each displacement distance was 2 mm. The stress data were collected and analyzed at the osteotomy end and under each metatarsal head in the gait cycle, the quantitative correlation between the vertical and horizontal displacement and between the stress changes under the first and second metatarsal heads was clarified. Then, the correlation between the pressure changes of the first and second metatarsal heads in the gait cycle and the occurrence of postoperative transfer metatarsalgia was analyzed, and accurate quantitative indicators of displacement during the operation were identified.Results The forefoot loading pattern of the gait cycle assessed in the finite element model before and after percutaneous minimal invasion surgery of hallux valgus showed that when the horizontal displacement is 4 mm, the correlation between the pressure x at the distal end of the osteotomy (under the first metatarsal) and the corresponding pressure y under the second metatarsal is negative, the R value is -0.894, and the quantitative correlation is y=-0.6504x + 0.5232 with increasing vertical displacement. When the vertical displacement is 4 mm, the stress under the first metatarsal increases with the increase in horizontal displacement. Conversely, the pressure under the second metatarsal decreases. Both have a high correlation with horizontal displacement, with R values of 0.981 and − 0.890. Also, in this interval, the pressure x at the distal end of the osteotomy (under the first metatarsal) has the highest correlation with the corresponding pressure y under the second metatarsal head, the R value is -0.830, and the quantitative correlation equation is y=-0.4528x + 0.4159.Conclusion When the distal end of the first metatarsal osteotomy is shifted outwards by 4 mm, and the metatarsal side is shifted by 4 mm through bone setting manipulation during operation, percutaneous minimal invasion surgery of hallux valgus can reduce or cure hallux valgus. This might elevate the metatarsal pain during forefoot loading and avoid transfer metatarsalgia after hallux valgus operation.