| Transfer metatarsalgia is mainly localized pain below the lateral metatarsal heads caused by foot operation or trauma, and it common appeared after hallux valgus surgery in clinical. General sequence is that:firstly it appeared in second metatarsal head, and then appeared by the outer third to fifth ones. Jones found that the incidence rate of transfer lesion about the first metatarsal head and neck osteotomy (Austin, Reverdin, Improved Reverdin) after operation was6%. Shapiro and Heller reported Mitchell osteotomy,33%of patients had transfer metatarsalgia after operation.10feet of transfer metatarsalgia after operation was classified by Guo Lin,3feet by Keller operation; each2feet by Mitchell and Wilson operation; each1foot by Scarf, Loison and metatarsophalangeal joint fusion operation.According to the literature, there were more than200kinds of operations of treating hallux valgus,and8to9kinds of operations were used a lot in clinical. But no matter what kind of operation, the occurrence of transfer metatarsalgia was inevitable. Now it has been one of main reasons that the patients were not satisfied with the effect of operation. And it is puzzling many foot and ankle surgeons at home and abroad. Professor Wen Jianmin used a combination of traditional Chinese medicine and Western medicine of minimally invasive method for treating hallux valgus. Through the clinical observation and verification of more than20thousand cases of hallux valgus in the past20years, it was found that the excellent rate of operations is reach to98.5%. The operation was accepted by the majority of patients due to its small wound, less pain and complication, satisfied orthopedic, and patients can walk in the postoperative etc. But sometimes, it also occurred transfer metatarsalgia cases in clinic. So foot and ankle surgeons are facing a task is to find out the reasons and solve them.In recent years, finite element analysis is used to biomechanics, especially in mechanical research of human skeletal structure, finite element analysis method simulated the mechanics experiment becomes one effective method when the traditional mechanics experiment can hardly directly carry on. The biggest characteristic of finite element analysis method is no damage to the organism, and it simulates the biomechanical behavior of living within the organization, the simulation environment and biomechanical test with high accuracy, and the model using with repeatability. In addition, it has the advantages of time saving, fast, low cost, and wide application in research effectiveness.This paper adopts one patient with transfer metatarsalgia for minimally invasive operation after treatment of hallux valgus deformity of integrated traditional Chinese and Western medicine, and finite element modeling for the right foot. According to the operation characteristics, assumptions are selected for the short shrinking of the first metatarsal, the osteotomy distal displacement of the first metatarsal, and the angle variation of the first tarsometatarsal joint. Through the load and calculation analysis of model, the plantar stress variation characteristics were observed comprehensively, biomechanical mechanism of transfer metatarsalgia was explored.1. Objective1.1Build the finite element model of transfer metatarsalgia foot of hallux valgus postoperative.1.2Research and explore biomechanical occurring mechanism of transfer metatarsalgia of hallux valgus postoperative.2. Methods2.1Use one right foot of transfer metatarsalgia of hallux valgus postoperative, image the foot by CT, build finite element model of foot by VTK5.0, Geomagic Studio8.0and ANSYS12.0. After test and verify the availability and reliability, imitate loading human body gravity with static up-right, observe stress distribution of forefoot metatarsal heads. In addition, using Foot-scan test system test when a static upright, and then comparing the difference between before and after ones.2.2The actual short shrinking is5mm of the first metatarsal according to X ray measurement before and after operation. Carry out the first metatarsal extend operation using the finite element model for5times and each time is extend1mm until recovery to the length of pre-operation. Observe the stress changing of forefoot metatarsal head in stance phase.2.3Simulate the distal osteotomy of first metatarsal, move to dorsal direction (2mm,4mm) and plantar direction (2mm,4mm) separately. Observe the stress changing of forefoot metatarsal head in stance phase.2.4Simulate first tarsometatarsal joint angle at9°,12°,15°. Observe the stress changing of forefoot metatarsal head in stance phase. 3. Results3.1Establish three-dimension finite element models for transfer metatarsalgia foot of hallux valgus operation and simulated tissues of skeleton, cartilage, plantar fascia and soft tissue, total91,093hexahedron units, and128,302nodes. The finite element model is reliability and effective by test and verify. The plantar stress of finite element model and foot scan measurement were compared in stance phase, both stress distribution trends.3.2Simulate the first metatarsal lengthening operation, and extend the first metatarsal1mm each time for5times until the first metatarsal recover to preoperative length. In static state, the stress of fibular sesamoid is increasing (1.888Mpa-2.534Mpa), the stress of second metatarsal is descending (1.393Mpa-1.209Mpa), the stress of third metatarsal is descending (1.311Mpa～1.255Mpa), the stress of fourth metatarsal is descending (2.138Mpa～1.818Mpa), the stress changing of tibial sesamoid and fifth metatarsal is not obviously.3.3Simulate the distal osteotomy of first metatarsal, move to dorsal direction (2mm,4mm) and plantar direction (2mm,4mm) separately, when the distal osteotomy of first metatarsal move from plantar4mm to dorsal4mm, the stress of first metatarsal is gradually descending,(tibial sesamoid1.107～0.435Mpa, fibular sesamoid1.935-1.697Mpa), the stress of second metatarsal is gradually increasing (1.246～1.543Mpa), the stress of third metatarsal is increasing (1.209～1.705Mpa), the stress changing of fourth and fifth metatarsal is not obviously.3.4Simulate first tarsometatarsal joint angle changing, setting the angles at9°,12°,15°, when the angle of first tarsometatarsal joint is increasing, the stress of tibial sesamoid is decreasing gradually (0.876-0.291Mpa),the stress of second metatarsal is increasing (1.393～1.789Mpa), the stress of third metatarsal is increasing gradually (1.311～2.672Mpa), the stress of fifth metatarsal is increasing gradually (2.470～3.571Mpa), the stress changing of fibular sesamoid and fourth metatarsal is not obviously.4. Conclusion4.1In this study a three-dimensional finite element model is established, and it is accurate and reliable.4.2The first metatarsal length, the first metatarsal osteotomy distal position, and the first tarsometatarsal joint angle changing will impact on the forefoot plantar stress after hallux valgus operation. 4.3The first metatarsal shortening after hallux valgus operation will cause the loading increasing of lateral metatarsal head, and appear the risk of transfer metatarsalgia. In contrast, the the second metatarsal stress ratio of third metatarsal stress increased rapidly, it may be the reason of transfer metatarsalgia more violations of the second metatarsal. The operation should not interrupt and impact the first metatarsal length and to obtain normal plantar stress distribution relatively.4.4The first metatarsal head move to the dorsal after operation and lead to destruction of surrounding normal configuration of it, and the stress transfer to lateral. According to the first metatarsal shortening and its inclination angle to decide the metatarsal far end osteotomy and to recovery the normal stress distribution of foot and reduce the incidence of transfer metatarsalgia.4.5With the angle increasing of the first tarsometatarsal joint, the loading mode of plantar is changing, and the weight-bearing of lateral metatarsal is increasing. The stress of the third metatarsal head than the second one increase is more obvious, it may trigger a new round of transfer metatarsalgia. The first tarsometatarsal joint instability may be a potential factor in transfer metatarsalgia happened.The above factors may lead to the occurrence of transfer metatarsalgia, and it should be give rise to enough attention by clinician. |
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