Patient baseline characteristics
All patients were followed up for 15~37 months, of which Isobar TTL group had an average of 22.00 months and rigid group had 25.18 months. Operation time of patients in Isobar TTL group ranged from 125 to 199 minutes, and the average time were 163.64 minutes. In addition, rigid group operation time were 145~222 minutes, and the average time were185.67 minutes. Intraoperative blood loss of Isobar TTL group was 245 ml and blood loss in rigid group was from 300 to 1300 ml. In a word, there was no significant difference between the two groups in age, bleeding volume during operation, follow-up time, total hospitalization time and operation time (Table 1).
Clinical efficacy
Isobar TTL group of patients on admission ODI was 81.84±6.63 at pre-operation, at the time of the last follow-up it was 30.15±4.38. Compared with pre-operation, it improved significantly. Grading rigid group patients on admission ODI was 82.21±5.86 at preoperation and it was 28.06±5.39 at the last follow-up. Compared with pre-operation, it improved 65.87%. Isobar TTL group on VAS was 6.82±1.77 points at pre-operation, but at the time of the last follow-up it was 2.75±0.86 points. Rigid group on VAS was 6.70±1.51 points preoperatively, but at the time of the last follow-up it was 2.58 ±0.86 points. The scores of ODI and VAS at post-operation were not significantly different between Isobar TTL group and rigid group. But the P value of ODI and VAS in Isobar TTL group was less than 0.05 at before and after operation. However, there was no significant difference in the improvement rates of ODI and VAS between the two groups (Table 2).
Greenough judge standard clinical curative effect, postoperative dynamic group at the time of the last follow-up, excellent good rate was 85.0%, but excellent good rate in the rigid group was 71.4%. However, there was no significant difference between Isobar TTL group and rigid group (P > 0.05) (Table 3).
Radiologic outcomes of fusion rate
At the last follow-up, there were 20 fusion segments in the Isobar TTL group, 19 segments were judged as strong fusion, and 1 segment was judged as possible fusion, with a fusion rate of 95.00%. There were 42 fusion segments in rigid fixation group, 40 segments were judged as strong fusion, and 2 segments was judged as possible fusion. The fusion rate was 97.30%. There was no significant difference in fusion rate between the two groups (P > 0.05).
Radiologic outcomes of lumbar mobility and height of intervertebral space
The preoperative and postoperative height of intervertebral space in the Isobar TTL and rigid groups are shown in Figure 1. The pre-operative height of intervertebral space of L2/3 and L3/4 between the two groups was similar (P > 0.05). And, the surgery intervertebral space height of L3/4 in rigid group at the last follow-up was better than these in Isobar TTL group, which means intervertebral fusion cage is helpful to the recovery of intervertebral height. However, the height of intervertebral space of upper adjacent segments of L2/3 in the rigid group were lower than those in the Isobar TTL group at the last follow-up (P < 0.05), indicating that Isobar TTL could slow down the degeneration of adjacent segments to a certain extent (Fig. 1b).
The preoperative and postoperative radiologic parameters including total lumbar mobility, L2/3 and L3/4 ROM in two groups are shown in Figure 1. The total lumbar ROM of the two groups at the last follow-up was significantly lower than pre-operation (P < 0.05). There was no statistical difference in the total lumbar ROM between the two groups at last follow-up (P > 0.05) (Fig. 1c).
At the last follow-up, the number of fixed segment ROMs of L3/4 in Isobar TTL group was significantly lower than pre-operation (P < 0.05), suggesting that fixed segment ROMs in Isobar TTL group were limited, but it still retains some of the spinal motion. Nevertheless, the fixed segment ROMs of L3/4 in rigid group is immobile because of fusion in L3/4 (Fig. 1d).
The ROM of upper adjacent segments of L2/3 in the last follow-up of rigid group increased significantly (P < 0.05), while the ROM of L2/3 in Isobar TTL group haven’t changed between pre-operation and the last follow-up. In addition, the ROM of upper adjacent segments in the rigid group increased significantly compared with these in the Isobar TTL group at the last follow-up (P < 0.05). It indicated that the Isobar TTL group was better than the rigid group to retain a certain range of motion of the lumbar spine.
Radiologic outcomes of degeneration in adjacent segments
According to the modified Pfirrmann grading system of adjacent segment and dynamic fixed segment disc to evaluate the degree of degeneration. The incidence of degeneration of adjacent segments was 10.00% in Isobar TTL group, and 14.3% in rigid group. The incidence of adjacent segment degeneration of Isobar TTL group was significantly slow than the rigid group (P < 0.05) (Table 5).
According to the UCLA system, the incidence of adjacent segment degeneration was 5.0% in the Isobar TTL group and 19.0% in the rigid group. The incidence of adjacent segment degeneration of Isobar TTL group was significantly slow than the rigid group (P < 0.05) (Table 6).