The Radiological Measurement, Distribution Of Forefoot Plantar Pressure And The Three-dimensional Finite Element Analysis Of Distal Osteotomy Of The First Metatarsal Via Mini-incision

ObjectiveTo investigate the radiological change and the distribution of plantar pressure after distal osteotomy of the first metatarsal via mini-incision, and to analyse the pre- and postoperaTive biomechanics of the feet by means of three-dimensional finite element.Laboratory proof was provided for the structural and functional changes of Hallux Valgus before and after the operation.Method1.56 cases of Hallux Valgus undergone distal osteotomy of the first metatarsal via mini-incision were examined by X-ray on weightbearing before operation and 3 months after operation.9 persons were choosen at random as the control group.Several parameters,including HVA,IMA,IMA(M1/5) and TSP,were measured and AOFAS score was carried out.The structural characters before and after operation were compared.2.17 cases of Hallux Valgus with 34 involved feet were examined by X-ray on weightbearing preoperatively and 3 months postoperatively.17 persons with normal feet were choosen as control group.Forefoot plantar pressure were measured during walking by Footscan system.The forefoot was divided into five regions according to the five metatarsals.The parameters,Peak Pressure(PP) and Pressure Time Integral(PTI) of the five regions,were compared pre- and postoperatively to evaluate the plantar pressure changes while walking.3.A Hallux Valgus patient without other foot deformities was selected in clinical.Computed Tomography scan was undertaken preoperatively.The data was imported into Abaqus,a kind of software for finite element analysis. A preoperative finite element model of Hallux Valgus was established and osteotomies based on the preoperative model at two different positions were simulated.Static stress analysis were carried on preoperative and postoperative finite element models. Result1.Compared with the preoperative weightbearing X-ray measurement,HVA was reduced to 5.97°from 34.39°,IMA was 5.36°from 11.44°,IMA(M1/5) was 21.25°from 31.17°and TSP reached 2.43 while 4.29 preoperatively.The parameters are of statistical significance.The postoperative result was close to the normal value.When the therapeutic effect of the 111 feet were evaluated,97 were excellent(87.4%),10 good(9.0%) and 4 poor(3.6%).AOFAS score was 89.0 while 67.1 preoperatively.2.Forefoot plantar pressure distribution of Hallux Valgus is quite different from that of normal feet.Among five regions PP and PTI under the third metatarsal are maximum,while the maximum of normal feet was under the second metatarsal.3.The stress distribution of the preoperative finite element model showed that pressure under the 3～5 metatarsal are maximum while that of the first metatarsal is minimum.According to the postoperative model, pressure under first metatarsal increased.However,pressure under the 3～5 metatarsal decreased obviously after relatively proximal osteotomy and that after relatively distal osteotomy changed scarcely.ConclusionThere are structural and biomechanical differences between Hallux Valgus and normal feet which can be embodied by the X-ray parameters and the distribution of plantar pressure.After distal osteotomy of the first metatarsal via mini-incision,all the weightbearing X-ray values are less than preoperative ones and the center of plantar pressure shifts medially. The three-dimensional finite element analysis showed that the way of relatively proximal osteotomy changed the plantar pressure distribution obviously and made the center of pressure shift medially as normal.