| Objective:Ankylosing spondylitis(AS), a chronic inflammatory disease, involves mainly the axial spinal column. It will ultimately result in the bamboo-like spinal rigidity. The spinal column will be fixed to the bent-forward posture and the patient will develop the round-back deformity. This kind of disease can severely affect the patient's physical and mental health by leading to decrease of pulmonary ventilation, shifting forward of the body center of gravity, and influencing the daily life and appearance. Since Smith-Peterson adopted spinal osteotomy for the spinal hyperkyphosis of AS in 1945, the aorta injury has been among the most severe complications of the surgery although it has been improved on.In this experiment, the aortae from the fresh body of normal deceased were adopted to assess the breakdown load and ratio of stretching under different stretching velocity. Also discussed was its use in the correction for spinal hyperkyphosis caused by AS. Meanthwhile 68 cases of trans-articular process V-like laminar osteotomy for the hyperkyphosis caused by AS from our department were reviewed. The amount of stretching of anterior column and the ratio of stretching was determined to seek the safe range of stretching of the abodominal aorta in the osteotomy for AS. Materials and Methods:1) Eight cadavers of those died accidentally without history of cardiovascular diseases (male 6, female 2, and the range of age 25-40). One hour after death, the abdominal aortae were taken out and the branches were ligated. The specimens were then cooled gradually to -40 X. and preserved in nitrogen canister.2) Before the experiment, the arteries were rewarmed in normal saline. Two specimens of 2.5 cm were gotten from each artery with 16 specimens totally. Then the 16 specimens were randomized into 2 groups 8 in each. The experimental apparatus used was Instron Tester. The load was transmitted via the load transmitter with the maximum load being 200N. The stretching experiment was carried out on the specimens under different stretching velocity to measure the breakdown load, amount of stretching at breakage and rate of stretching of the abdominal aorta.3) The arterial specimens were studied with light microscope to exclude abdominal aorta disease.4) Sixty-eight cases of trans-articular process V-like laminar osteotomy for thehyperkyphosis caused by AS from our department were reviewed. The amount of postoperation stretching of anterior column and the ratio of stretching was measured. After operation, the arterial pulse in both the lower extremities and the basic life signs were carefully observed for the sign of aorta injury.Result:1) The biomechanical experiment showed the breakdown load and stretching ratio under different stretching velocity (see table below).Table 1 Biomechanical Properties of Abdominal Aorta under Different StretchingVelocity2) In our series of 68 cases of V-like laminar osteotomy for the hyperkyphosis caused by AS, the rate of anterior column of lumbar spine is about 11%, much lower than the rate of abdominal aorta breakage (23.5%). There was no life-threatening large vessel injury.Conclusion:1) The breakdown load and stretching rate of breakage differs with the stretching velocity. The greater is the stretching velocity, the greater is the breakdown load and the smaller is the rate of breakage and vice versa.2) The stretching rate of breakage of the abdominal aorta is 23.5% under the velocity of 60mm/s of stretching. In the correction of hyperkyphosis of AS, if stretching rate of the anterior column is less than the stretching rate of breakage of normal abdominal aorta, then the risk of abdominal aorta injury is very low. Of course, in the clinical application, what should be taken into consideration should also include the age of the patient, the influence of body type, and the difference between ex vivo blood vessel and in vivo blood vessel, which was not covered in this experiment.3) The greater is the stretching velocity, the smaller is the stretching rate of breakage. |
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