关键词: 骨, 有限元, 足踝, 足下垂, 足, 背屈, 肌腱转位, 生物力学, 畸形

Abstract: BACKGROUND: The transposition of the posterior tibial tendon is the gold standard for the treatment of foot drop caused by irreversible damage to the common peroneal nerve. There are many reports on its clinical efficacy, but there has been a lack of detailed finite element force analysis.
OBJECTIVE: To reconstruct the three-dimensional finite element model of foot drop caused by common peroneal nerve injury, analyze mechanical characteristics and verify with traditional experience
METHODS: (1) CT data of a male patient with left foot drop caused by left common peroneal nerve injury were collected and imported in the software to reconstruct foot and ankle bones with a series software, such as MIMICS, Cero, Abaqus, and ANSYS. (2) Ten young volunteers were enrolled. Their muscle strengths were measured by electrical trigger potentiometer and the root mean square amplitude of surface electromyogram–RMS were calculated. (3) The finite element model of the normal foot was established by limiting material parameters of every part. Based on this model, we simulated the foot drop state caused by total injury of the common peroneal nerve. (4) The posterior tibial tendon transposition, entocuneiform, mesocuneiform, and ectocuneiform were identified as the tendon anchored points. The foot was fixed at dorsiflexion position 10° through the transferent tendon, and the tibialis posterior muscle strength would drop one level after the transposition. (5) After analysis of finite element on the two droop states of three different anchoring positions, the ankle dorsiflexion angles, internal and external rotation angles, and the maximum stress of the transposition of the tendon were calculated under these nine conditions. The implementation of the research program meets the ethical requirements of 3201 Hospital Affiliated to Xi'an Jiaotong University. All patients were fully informed and agreed to the trial process.
RESULTS AND CONCLUSION: (1) Dorsiflexion and plantar flexion angles of the normal foot model were close to and less than the limit angle (Dorsiflexion 25.62° < 27°, plantar flexion 43.67° < 45°). The dorsiflexion angle of the pendulous foot model was -44.65°, which was close to the research subject's dorsiflexion angle of -47°. (2) Tendon transposition anchored on the mesocuneiform had maximum correction angle and minimum stress of the tendon; tendon transposition anchored on the ectocuneiform had the worst effect of correction of deformity, maximum stress of the tendon and effect of mildly valgus ankle joint; anchored on the entocuneiform had effect of varus ankle joint. (3) The stress concentration of the tendon after transposition was near the anchor point where the tendon touched the bone. (4) Results indicate that the ankle biomechanical model established by the finite element can preliminarily simulate normal foot and drop foot which was caused by common peroneal nerve injury. Making mesocuneiform as anchor point in the treatment of foot drop deformity means better orthopedic effect about drop foot. This conclusion is similar to traditional experience. Individualized treatment regimens should be emphasized. The results of individual stress analysis may not be applicable to all patients.

Key words: bone, finite element, ankle, foot drop, foot, dorsiflexion, tendon transposition, biomechanics, deformity