Early clinical outcome of midline lumbar fusion in the treatment of senile lumbar degeneration and precautions for screw placements

English Keywords:Cortical bone trajectory  Midline lumbar fusion  Lumbar spine  Fusion

English Abstract:

  【Abstract】 Objectives: To explore the potential advantages of midline lumbar fusion(MIDLF) in the patients with lumbar disc herniation and discuss the safety and precautions of cortical bone trajectory(CBT) screw fixation technique. Methods: A retrospective analysis was made of 16 patients with senile lumbar degeneration treated with MIDLF from April to September 2018, including 8 males and 8 females. The age ranged from 58 to 81 years, with an average of 68.7±7.7 years. All patients were operated L4/5. CBT screw fixation technique was used in all operations. The selection of the insertion point refers to the intersection of about 5mm (a value) below the lowest tip of the inferior articular process of the upper vertebra and about 4mm (b value) inward from the narrowest point of the isthmus. The operation time, intraoperative blood loss and complications were recorded. Visual analog scale(VAS) was used to evaluate the low back pain and leg pain. JOA was used to assess the functional outcome of patients before and after operation. All patients were scanned using CT before and 12 months after discharge. The accuracy of screw placement was evaluated by Rao classification criteria. Excellent rate of screw placement = number of excellent screws/total number of screws × 100%. The lateral angle, caudal angle, a value and b value of the screws were measured by CT before discharge. The four parameters mentioned above were compared between the no perforation group and the perforation group. Results: The average operation time was 174.3±27.9min (133-232min), the average intraoperative blood loss was 69.3±36.7ml(30-150ml), the average postoperative total drainage volume was 147.5±95.2ml (20-315ml), and the average postoperative hospital days were 2.5±0.8 days(2-4 days). The average follow-up time was 15.1±2.0months(12-20 months). One patient developed foot drop and hematoma, and 5 CBTs were fixed with pedicle screws. No complications occurred in other patients. The VAS score of low back pain before surgery was 4.5±1.7 and at the final follow-up was 1.1±0.5, with significant lystatistical difference(t=7.013, P<0.001); the VAS scoreof leg pain before surgery was 5.6±1.0 and at the final follow-up was 1.1±0.9, the difference was statistically significant(t=13.006, P<0.001). The JOA score was 15.7±2.4 preoperative and 23.9±2.1 at the final follow-up, the difference was statistically significant (t=-16.364, P=0.000). According to the postoperative CT before discharge, the Rao classification was performed: 46 screws in grade 0, 4 screws in grade 1, 3 screws in grade 2, 6 screws in grade 3. The excellent rate of screw placement was 84.7%(50/59). Thirteen screws(13/59, 22%) perforatedthe cortical bone, including 3 cases perforated the inner wall of pedicle and 10 cases perforated the vertebrate. There were significant differences in lateral angle(11.0°±3.7° vs 14.9°±3.8°, P=0.002) between the no perforation group and the perforation group, and no significant differences were found in caudal angle (15.0°±8.4° vs 16.9°±9.2°, P=0.502), a value(5.6°±1.2° vs 5.7°±1.4°, P=0.687) and b value (4.1°±1.0° vs 4.4°±1.6°, P=0.459). Conclusions: MIDLF is an effective technique for lumbar spine surgery. The selection of the insertion point should refer to the intersection point of 5.6-5.7mm (a value) below the most tip of the inferior articular process of the upper segment and 4.1-4.4mm (b value) moving inward from the narrowest point of the isthmus. CBT screw insertion has low error tolerance and therefore it′s highly technical demanding. During screws placement, the inclination of the screws should not be too largeandthe lateral angle of 11° is suggested.