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Objective To compare the stress distributions on the anterior horn,body part and posterior horn of menisci between the normal and the injured knees with anterior cruciate ligament (ACL) deficiency using the three-dimensional finite element analysis.Methods A three-dimensional finite element model of tibiofemoral joint was created to simulate the motion states of the normal and ACL-deficiency knees at extension,as well as 15° and 30° flexions.Meanwhile,700N axial load and 134N posterior load were applied to the femur.Then,the stress on the anterior horn,body part and posterior horn of medial and lateral menisci were compared between the normal and ACL-deficient knees.Results With ACL deficiency,when stretching the knees straightly,the stress on the anterior horn of medial meniscus increased to 100.7％ of the normal knees,bigger than that of the affected lateral meniscus (30.7％).At 15° and 30° flexions,the stress on the posterior horn of the medial meniscus in ACL-deficiency knees increased by 36.4％ and 59.7％ respectively when compared to normal knees,while the stress on that of the lateral meniscus did not increase significantly.Apart from the stress on the body part of the lateral meniscus increasing by 39.5％ at extension in ACL-deficiency knees,no obvious changes were observed in the stress on the body part of the medial and lateral menisci.Conclusion ACL deficiency has different effect on the stress of different parts of the meniscus.It mainly increases the stress on the anterior horn of the medial meniscus at extension and that of the posterior horn of the medial meniscus at flexion.
RESUMO
Objective To detect the clinical effect of posterior reduction combined with H-shaped bone grafting and spinous process replantation for reconstruction of spinal structures in treatment of thoracolumbar fracture.Methods Forty-three patients with thoracolumbar burst fracture treated surgically from February 2008 to June 2012 were reviewed retrospectively.There were 30 male and 13 female patients aged 23 to 55 years (mean,38 years).Fracture resulted from high falls in 21 patients,traffic accidents in 16 patients,and a crush by heavy objects in 6 patients.Denis system was used for classification of fracture and Frankel rating for assessing the degree of nerve damage and recovery.After posterior reduction combined with H-shaped bone grafting and spinous process replantation for all patients,visual analogue scale (VAS) was utilized to assess symptom improvement and Cobb' s angle and sagittal spinal canal diameter were measured to help assess the treatment outcome.Results Pain was apparently eased at a 24-month follow-up (range,12-46 months).Cobb' s angle improved from preoperative 43.56° to postoperative 8.23° (t =1.33,P ＜ 0.01).CT findings showed mean spinal canal stenosis rate was 56.3％ before surgery and that mean sagittal canal diameter of the injured spine was larger than that of adjacent segments at follow-up,with the mean ratio of 116.3％ (range,111.3％-120.3％).Rate of spinal canal stenosis was negative for all patients and posterior canal with bone grafts healed.Spinal cord injury improved at least one Frankel grade.Conclusion Posterior reduction combined with H-shaped bone grafting and spinous process replantation is worthy of clinical application,for the procedure can restore the fractured thoracolumbar spine and posterior canal structure,but also effectively avoid the iatrogenic spinal stenosis.