Paradoxical motion in L5-S1 adult spondylolytic spondylolisthesis

Abstract

Introduction: In patients with spondylolisthesis, it is assumed that flexion accentuates anterior displacement, whereas extension causes some reduction. Paradoxical movement-where flexion causes reduction of spondylolisthesis and extension increases the anterior translation, is rarely described. In this study, we investigate the prevalence of paradoxical motion in patients with L5-S1 spondylolytic spondylolisthesis and why this abnormal motion occurs.

Materials and methods: Flexion and extension radiographs of 41 patients with grade I and II spondylolytic spondylolisthesis of the L5-S1 segment were analysed. Patients who had previous lumbar spine surgery, recent lumbar spine trauma, those more than 50 years of age and those with poor quality radiographs were excluded.

Results: There were 24 male and 17 female patients. The average age was 32.7 years. Of the 41 patients, 29 (70.7%) showed no significant instability. Six (15%) patients showed anterolisthesis, where flexion accentuated the forward displacement, while further six (15%) patients showed paradoxical motion. Statistical analyses found that patients with paradoxical motion had a significantly higher slip angle.

Conclusion: In this study, we have demonstrated that: (1) paradoxical motion in spondylolytic spondylolisthesis is more common than previously thought. (2) Patients without anterolisthesis during flexion in dynamic radiographs may still have (paradoxical) instability. (3) Paradoxical motion may be more common in patients with a low sacral slope and increased lumbosacral lordosis.

Fig. 1

Method of calculating sagittal translation. A baseline parallel to the S1 superior endplate is drawn. The posterior superior edge of S1 and posterior inferior edge of L5 are identified two perpendicular lines are extrapolated with reference to the S1 endplate. The difference measured is the sagittal translation = (b − a) mm

Fig. 2

Radiographs of a lady who had spondylolytic spondylolisthesis with paradoxical motion. Left indicates extension accentuates sagittal translation (10.18 mm) more than flexion (4.01 mm)

Fig. 3

Forty-five-year-old male also showed spondylolytic spondylolisthesis with paradoxical motion. Left indicates extension increases displacement (9.91 mm) while flexion causes some reduction (4.99 mm)

Fig. 4

An example of the radiographic parameters used for analysis in a lateral (neutral) radiograph

Fig. 5

Schematic diagram of the lumbar spine during extension (a) and flexion (b): during extension, there is a posterior compressive force with impingement, displacing the L5 vertebra forward, causing paradoxical motion. During flexion, this compression force becomes a distractive force, and the anterolisthesis is less pronounced

Fig. 6

Two possible aetiologies of spondylolysis: a horizontal orientation of L5-S1 junction with low sacral slope resulting in impingement effect. b Vertical orientation of L5-S1 with high sacral slope causing excessive traction on pars—adapted and modified from Roussouly [9]