Study For Applied Anatomy And Biomechanics Of The First Metatarsophalangeal Joint

Objective:To study the changes of the anatomical structure and the range of motion of the first metatarsophalangeal joint in of hallux valgus.The another aim of this study was to compare the immediate effect of Yshaped and inverted L capsulorrhaphy methods on the ROM in the first MTPJ.Methods :Sixteen fresh human cadaveric feet were included,and then were divided into 2 groups,valgus foot group and normal anatomical group,according to their hallux valgus angle.The data of some anatomical structures were measured,compared and analysed.The specimens were mounted in a custom-made biomechanical loading device,allowing surgical preparation and simulating stress loading for measuring ROM in6 directions.Next,ten fresh human cadaveric feet were included and divided into 2 groups,and then were performed with Y-shaped and inverted L capsulorrhaphy respectively.Passive dorsiflexion(DF)and plantarflexion(PF)of the 1st MTPJ were then compared and analyzed preand postoperatively.Results:The thickness of the 1st MTPJ medial capsule,the length of the oblique head of the adductor tendon and the thickness of the abductor tendon in the hallux valgus group were 2.2±0.8,13.9±3.9 and 3.1±0.9mm respectively,which were significantly lower than those in the control group(P<0.05).The length and width of the superficial transverse metatarsal ligament were 14.5±4.2 and 13.2±5.8mm respectively,the length and width of the deep transverse metatarsal ligament were 2.3±0.8mm and1.6±0.5mm respectively,and the length,width and thickness of the oblique head of the adductor tendon were 13.9±3.9,7.8±2.1 and 3.5±1.3respectively,which were significantly larger than those in the control group(P<0.05).In addition,the ROM of the 1st MTPJ in the six directions including dorsiflexion,plantar flexion,adduction,abduction,internal rotation and external rotation were 65.8±13.3°,15.1±4.2°,5.2±1.2°,20.6±5.5°,25.2±7.4° and 12.5±4.8° respectively in hallux valgus group,which were significantly lower than those in the control group(P<0.05).After the “Y”-shaped medial tightening capsulorrhaphy on the normal anatomical foot,the dorsiflexion,plantarflexion and total ROM of 1st MTPJ decreased by 10.5±6.1 °(P=0.054),1.1±4.9°(P=0.809)and10.4±4.8°(P=0.081)respectively,but these differences were not statistically significant.The dorsiflexion and total ROM decreased by25.8±10.6°(P<0.05)and 25.1±8.2°(P<0.05)respectively after the inverted “L” capsulorrhaphy.The dorsiflexion and total ROM were reduced to varying degrees in these two kinds of capsulorrhaphies.Compared with the inverted “L” capsulorrhaphy,the loss of dorsiflexion ROM(P<0.05)and total ROM(P<0.05)of “Y”-shaped capsulorrhaphy was significantly less.Conclusion: The anatomy of articular capsule and related ligaments and tendons of the 1st MTPJ were changed significantly in hallux valgus.In addition,the ROM in 6 directions of the 1st MTPJ of hallux valgus was significantly reduced.The inverted “L” capsulorrhaphy may lead to a ROM loss of the 1st MTPJ immediately after surgery,while “Y”-shaped capsulorrhaphy is less likely to result in a ROM loss in the 1st MTPJ.