Biomechanics of increased exposure to lumbar injury caused by cyclic loading: Part 1. Loss of reflexive muscular stabilization

STUDY DESIGN: The recording of electromyographic responses from the in vivo lumbar multifidus of the cat, obtained while cyclic loading was applied as in occupational bending/lifting motion over time. OBJECTIVES: To determine whether the effectiveness of stabilizing reflexive muscular activity diminishes during prolonged cyclic activity; the recovery of lost muscle activity by a 10-minute rest; and whether such diminished muscular activity is caused by fatigue, neurologic habituation, or desensitization of mechanoreceptors in spinal viscoelastic tissues resulting from its laxity. SUMMARY OF BACKGROUND DATA: The literature repeatedly confirms observation that cyclic occupational functions expose workers to a 10-fold increase in episodes of low back injury and pain. The biomechanical evidence indicates that creep in the viscoelastic tissues of the spine causes increased laxity in the intervertebral joints. The impact of cyclic activity on the function of the muscles, which are the major stabilizing structures of the spine, is not known. METHODS: Electromyography was performed from the L1 to L7 in vivo multifidus muscles of the cat, while cyclic passive loading of 0.25 Hz was applied to L4-L5. Cyclic loading was applied for 50 minutes, followed by 10 minutes rest and a second 50-minute cyclic loading session. A third 50-minute cyclic loading period also was applied after the preload was reset to 0.5 N to offset the effect of laxity. RESULTS: Reflexive muscular activity was recorded from the multifidus muscles of all lumbar levels at the initiation of the first 50 minutes of cyclic loading. Activity recorded on electromyography quickly diminished with each cycle during the first 8 minutes of loading to 15% of its initial value. A slower decrease in muscular activity was evident throughout the remaining period, settling at 5% to 10% of its initial level by the end of 50 minutes. A 10-minute rest provided a 20% to 25% recovery of the electromyographic activity, but that was lost within the first minute of cycling. Offsetting the laxity in the spine resulted in full restoration of the electromyographic activity at all lumbar levels. CONCLUSIONS: The creep induced in the viscoelastic tissues of the spine as a result of cyclic loading desensitizes the mechanoreceptors within, which is manifest in dramatically diminished muscular activity, allowing full exposure to instability and injury, even before fatigue of the musculature sets in.     

Spontaneous regression of periodontoid pannus mass in psoriatic atlantoaxial subluxation. Case report

STUDY DESIGN: A case report of a 41-year-old man with psoriasis who had cervical myelopathy caused by atlantoaxial subluxation and periodontoid pannus mass. OBJECTIVE: To describe the possible mechanism underlying the periodontoid pannus formation and the optimal treatment for such cases. SUMMARY OF BACKGROUND DATA: Atlantoaxial subluxation causing spinal cord compression at the craniocervical junction may develop in patients with rheumatoid or psoriatic arthritis. Periodontoid pannus formation plays an important role in compromising the anteroposterior diameter of the spinal canal and in causing neurologic deficits. Transoral transpharyngeal excision of the pannus is sometimes thought necessary for anterior decompression of the spinal cord. Spontaneous resolution of the periodontoid pannus after posterior atlantoaxial fusion and fixation has been documented in rheumatoid arthritis, but not in psoriatic arthritis. METHODS: The patient underwent posterior atlantoaxial fusion and Halifax fixation. RESULTS: The patient experienced clinical improvement. Regression of the periodontoid pannus mass was observed on magnetic resonance imaging. CONCLUSIONS: Posterior fusion and instrumentation resulted in spontaneous regression of the pannus mass and symptomatic relief. This report provides evidence that atlantoaxial instability may be the sine qua non for the formation of periodontoid pannus, and that amelioration of such instability leads to spontaneous resolution of the pannus mass.     

烫伤后脂多糖受体CD14和肿瘤坏死因子-α基因表达的变化规律

目的 观察烫伤后机体主要脏器脂多糖受体ＣＤ１４（ＣＤ１４）和肿瘤坏死因子－α（ＴＮＦ－α）ｍＲＮＡ的表达的变化规律及二者的相互关系。方法 采用大鼠３５％Ⅲ度烫伤模型,分别于伤前,伤后１２,２４,４８,７２小时活杀动物,留取组织标本或分离腹腔巨噬细胞,检测组织或巨噬细胞ＣＤ１４,ＴＮＦ－αｍＲＮＡ表达。结果 烫伤后肝,肺,肾,肠等组织ＣＤ１４ｍＲＮＡ水平均有不同程度增高,分别于伤后１２小时和４８小时     

精氨酸对烧伤创面愈合的影响

目的 探讨精氨酸对烧伤创面愈合的影响和量效关系。方法 通过大鼠深Ⅱ度烫伤模型,伤后肠道站充不同剂量精氨酸,观察烧伤创面愈合时间,测定烧伤创面愈合面积百分比,创面Ｉ型／Ⅲ型胶原比例,羟脯氨酸（ＯＨＰ）含量和真皮细胞增殖周期,结果 每天补充１００－４００ｍｇ／ｋｇ精氨酸可缩短烧伤创面愈合时间,增加烧伤创面中ＯＨＰ含量,降低烧伤创面Ｉ／Ⅲ型胶原比例,加速真皮细胞ＤＮＡ复制。比较喂不同剂量精氨酸各组,发现     

游离骨膜与复合rhBMP2的异种骨联合移植修复骨缺损的实验研究

目的 探讨复合基因重组人ＢＭＰ２（ｒｈＢＭＰ２）的异种骨与游离骨膜（ＦＰ）联合移植修复节段性骨缺损的效果。方法 将ｒｈＢＭＰ２与去抗原牛松质骨载体（ＢＣＢ）复合,制成ｒｈＢＭＰ２／ＢＣＢ;选用新西兰大耳白兔２８只,制成烧骨干１５ｍｍ缺损动物模型,分别行ＦＰ和ｒｈＢＭＰ２／ＢＣＢ复合移植（ｎ＝６）、ｒｈＢＭ２／ＢＣＢ移植（ｎ＝６）和单纯ＢＣＢ移植（ｎ＝２）;术后４、８、１２、１６周取材,通过Ｘ线、生     

Hepatitis A vaccine in healthy adults: a comparison of immunogenicity and reactogenicity between two- and three-dose regimens

Inactivated hepatitis A virus (HAV) vaccine was administered to 55 healthy seronegative adult volunteers to evaluate the immunogenicity and adverse reactions of two doses of HAV vaccination (25 units) in comparison with a three-dose regimen. The volunteers were randomly assigned to receive one of the two regimens: 26 were vaccinated with two doses at 0 and 24 weeks (Group 1), and 29 were vaccinated with three doses at 0, 2, and 24 weeks (Group 2). The vaccine was well tolerated and there was no serious adverse reaction. In both groups, the seroconversion rate was 100% at week 28. At week 52, all remained positive for anti-HAV regardless of a two- or three-dose regimen. No statistically significant difference in seroconversion rates and geometric mean titers could be demonstrated between the two groups. Thus, the two-dose regimen may be favorable to save cost and time for active immunization against hepatitis A.