[Stability effect of the suprajacent vertebrae after fixation in spondylolisthesis. Comparative study of two systems].

Background: This study was undertaken to evaluate vertebral stability after two different types of fusion fixation (rigid and semirigid) in spondylolisthesis.

Material And Methods: Ambispective study of a dynamic cohort constituted by 42 patients that underwent surgery between 1990 and 2000 for a spondilolistesis treatment. According to the fixing type, they were divided into two follow-up groups: to group 1, plate INO (semirigid system) was placed + posterolateral fusion (PLF), 20 cases; to group 2, plate INO was installed + intersomatic screw + PLF, 22 cases.

Results: Both groups achieved better listhesis, reduced pain according to Oswestry and SF36 Index (p <0.05), and less intervertebral height was lost. Group 1 lost the least amount (-0.61 mm) of invertebral height if grades of presurgical listhesis were 1-2, and higher (-2.0 mm) if grades of presurgical listhesis were 3-4. Inversely, group 2 lost the least (0.50 mm) if grade of listhesis was 3 or 4, and higher (-1.25 mm) if grades of listhesis were 1-2. From 4 to 7 years, in group 2 there was altered bending of 5.8 degrees to 8.3 degrees (p = 0.05), a significant difference from group 1. Group 2 showed higher flexion grades (p = 0.01) at 4-7 years postoperatively and a significant reduction in EVA (p = 0.04) at more than 7 years. The remaining patients showed no significant differences between groups. But loss of intervertebral height was higher in group 2 (-1.18 mm) than group 1 (-0.75 mm). Plate INO + PLF favored flexibility and reduced loss of intervertebral height in grades 1-2 of presurgical listhesis, INO + screw + PLF showed reduced listhesis and decrease of height lost in grades 3-4 of presurgical listhesis.

Conclusions: We recommended the use of INO + PLF in grades 1-2 of presurgical listhesis and INO + screw + PLF in grades 3-4 of listhesis presurgically.