Suss R A, Bundy K J
AJNR Am J Neuroradiol. 1984 Nov-Dec;5(6):783-6.
Unilateral posterior arch fractures of the atlas are discussed with two clinical examples and an experimental study of their mechanism. Laboratory fracturing of posterior arches of atlas specimens with a specially adapted universal testing machine produced nonsimultaneous fractures of the two sides in four of six specimens. In three of these specimens, a complete fracture on one side was temporarily displaced because the orientation of the leverage acting on the other side changed from sagittal to oblique. The consequent increase in the effective length of the lever arm reduced the angular deformation and strain on the second side. The second fracture occurred only after additional deflection of the posterior tubercle by up to 3 mm reproduced on the second side about the same angle of deformation that had caused the first fracture. A posterior arch fracture occurring by this mechanism will remain unilateral if the deflection is arrested before failure of the second side.
本文通过两个临床实例以及对寰椎单侧后弓骨折机制的实验研究进行讨论。使用经过特殊改装的万能试验机对寰椎标本的后弓进行实验室骨折测试，六个标本中有四个出现两侧非同时性骨折。在其中三个标本中，一侧的完全骨折出现暂时移位，原因是作用于另一侧的杠杆方向从矢状位变为斜位。杠杆臂有效长度的增加减少了另一侧的角变形和应变。只有在对后结节进行额外3毫米的偏转后，第二侧才出现骨折，此时第二侧再现了导致第一侧骨折的大致相同的变形角度。如果在第二侧骨折之前停止偏转，通过这种机制发生的后弓骨折将保持单侧性。
