Angular Slipping in Spondylolisthesis

Discussion

• as slip progresses, area of contact between L5 & S1 decreases & body of L5 tilts forward on sacrum;
  • this is referred to as sagittal rotation, angle of slipping, roll, L5/S1 kyphosis, or gibbus;
• slippage is not present in pts who have mild (grade-I or II) spondylolisthesis, but is more common in pts who have a 50 % slip & is always present in pts w/ 75 % slip;

risk factors for slippage

• preop slip angle > 35-40 deg;
• slip of more than 50%;
• kyphotic slip angle
• female;
• dysplastic spondylolisthesis
• back pain;
• abnormal gait;

measurement

• angle that is formed by extending a line along anterior border of body of L5 until it intersects line that has been drawn along the posterior border of the body of first sacral vertebra;
• slip angle is measured by drawing a line perpendicular to line drawn along posterior aspect of first sacral vertebral body and measuring angle between that and a line parallel to inferior end plate of L5