Efectividad de la fijación con tornillos transdiscales para la espondilolistesis ístmica de alto grado

Resumen

ABSTRACT Background: High-grade spondylolisthesis is a disease that can be highly disabling, although its prevalene is relatively low. Several surgical techniques have been described to stabilize and prevent the progression of the L5-S1 sliding, but none has demonstrated superiority so this topic remains controversial. Posterolateral pedicle fusion has gained popularity in the last two decades, but its mechanical construction seems to be unsatisfactory because of a relatively high rate of complications and secondary sliding progression. Transdiscal L5-S1 fixation theoretically provides a more efficient mechanical construction, but although clinical results have been promising the evidences available to date are scarce including small non-comparative series. Purpose: To compare outcomes between transdiscal and conventional pedicle fixation for high-grade L5-S1 spondylolisthesis. Design: This was a retrospective case–control study with patients prospectively followed. A prospective comparative study was not performed due to the relative low prevalence. The study population consisted on patients surgically treated at the Spine Unit of La Fe Hospital (Valencia, Spain) between 2007 and 2012. Although retrospective, patients had been prospectively evaluated pre- and postoperatively. Methods: Twenty-five consecutive patients with mean age of 36.7 years underwent transdiscal fixation and 31 other with mean age of 42.0 years to pedicle fixation were clinically and radiographically compared. Baseline data were not significantly different between groups. Postoperative follow-up was similar in both groups, with a mean time of 2.7 years (range, 2 to 5.3). The main outcome was clinical assessment using Oswestry Disability Index (ODI). The patients were also assessment by the Core Outcomes Measures Index (COMI), Short-Form 12 (SF-12), and pain visual analog scale (VAS). Radiographic spinopelvic parameters were also evaluated. In addition, a pilot biomechanical functional assessment study was conducted using the software NedLumbar which synchronized an analysis of movements (kinematic study) and another of efforts and charges (kinetic study). Among the previously described patients, 10 were randomly selected (5 of each sex) from each of the two treatment groups. The kinematic variables were the speed and angular acceleration of the lumbar segments involved when performing movements. The kinetic variables were the force exerted by the lower limbs when performing movements with or without weight lifting. Results: Surgery time, blood loss, and hospital stay were similar between groups. At last follow-up, clinical and radiographic outcomes were significantly improved in both groups. Comparing the groups, both lumbar and leg pain VAS were similar between groups, but ODI (20.2 vs. 31.6, p = 0.010), COMI (1.6 vs. 2.8, p = 0.012), and SF-12 physical (84.3 vs. 61.5, p = 0.004) and mental (81.5 vs. 69.4, p = 0.021) scores were significantly better in the transdiscal group. The neurologic complication rate was similar in both groups. There were 4 pseudoarthroses in the pedicle group, and none in the transdiscal group. Both kinetic and kinematic biomechanical outcomes were significantly better in the transpedicular group. Statistical power: A posteriori Cohen’s statistical power analysis was performed in relation to the main outcome (postoperative ODI score). Considering a clinically relevant difference between groups of 10, with standard deviation of 14, and a minimum sample size of 25 in each group, for an alpha error of 0.05 the study power was 81 %, which is considered valid for biomedical studies. Conclusion: L5-S1 transdiscal screw fixation provided better functional and radiographic outcomes at medium-term than conventional pedicle fixation for high-grade spondylolisthesis, although transdiscal sacral screws are difficult to place in correct position. Keywords: Spondylolisthesis; Sacrolumbar; Transdiscal screw; Transvertebral screw; Transacral screw; Pedicle screw; Functional outcome; Biomechanical outcome.