Patient characteristics
Table 1 shows the characteristics of the 65 patients whose data was included in the present study. The ratio of males to females was 1.097. Herniations at L4-5 and L5-S were more frequent than at L3-4 in this series. There were no cases of L1-2 or L2-3 herniation included in this study. Disc degeneration by Pfirrmann grading showed that grade 2 was most frequent and there were no cases of grade 1. Fourteen patients showed endplate changes as determined by Modic type. There were no cases of surgical site infection in this series, nor were there other critical complications such as thromboembolic events or nerve root injuries.
Clinical outcomes (VAS and ODI)
The time course changes of detailed LBP VAS scores are shown in Table 2. Before surgery, LBP while the patient was in motion was significantly higher than LBP while they were sitting (paired t test, t(64) = 1.997, p = 0.025). The increased LBP found while they were in motion as well as the LBP while they were standing and sitting was significantly improved following discectomy (repeated majors ANOVA, F(3, 2) = 315.5, p < 0.01). By contrast, at 1 year after surgery, the residual LBP while they were sitting was significantly higher than the LBP while they were in motion or standing (paired t test, t(64) = 2.200, p = 0.015). The time course changes of bilateral LBP, LEP, and LEN VAS scores were shown in Table 3. LBP on the affected side was significantly higher than that on the opposite side (paired t test, t(64) = 6.848, p < 0.01). The LBP on the affected side was improved significantly following surgery, and LBP relief was maintained on both sides until the 1 year follow-up. LEP and LEN on the affected side were also significantly greater than before surgery (paired t-test, LEP: t(64) = 14.32, LEN: t(64) = 10.28, p < 0.01). Significant improvements of LEP and LEN on the affected side were shown and the relief was maintained on both sides until the 1 year follow-up (repeated measures ANOVA, LEP: F(3, 1) = 174.5, LEN: F(3, 1) = 107.2, p < 0.01), although mild LEP and LEN remained on the affected side. ODI also showed significant improvements following discectomy (Table 4).
Taking the results of the detailed LBP VAS scores into account, we investigated the temporal changes in LBP VAS scores while the patient was in motion and while they were sitting. The time course of changes of the detailed LBP VAS and surgical level are shown in Figure 2. There was no significant difference in LBP before surgery at the various surgical levels. However, the residual LBP VAS score while the patient was in motion and while they were sitting was significantly increased at the L3-4 level at 1 year after surgery (one factor ANOVA, motion: F = 11.87, sitting: F = 6.735, p < 0.01).
Time course changes in detailed LBP VAS scores and surgical procedures (C, T, and B groups) were shown in Figure 3. LBP while the patients were in motion was significantly higher before surgery in those of group T (one factor ANOVA, F = 3.246, p = 0.046), and therefore the residual LBP at 3 months after surgery was also higher in those in group T (one factor ANOVA, F = 7.519, p < 0.01). However, at 1 year after discectomy, the residual LBP became almost equal for all 3 surgical procedures (one factor ANOVA, F = 0.263, p = 0.770).
Correlation between MRI findings and VAS
The time course of changes in Pfirrmann grade and Modic type are shown in Table 5. Overall, significant changes in both Pfirrmann grade and Modic type were observed (Chi-squared test, Pfirrmann: X2 (6, N = 62) = 55.46, Modic: X2 (9, N = 62) = 50.61, p < 0.01). Seventeen patients had changes in Pfirrmann grade following discectomy. We divided them into 2 groups: Pfirrmann grade changing (PC group) and not changing (PN group). After discectomy, Modic type changed in 12 patients, and we also divided them into 2 groups: Modic type changing (MC group) and not changing (MN group).
Considering that residual LBP while the patient was sitting was increased at 1 year after discectomy, we investigated the relationship between the Pfirrmann grade, Modic type, and LBP VAS score while the patients were sitting at 1 year after discectomy. LBP VAS scores while they were sitting at 1 year after discectomy were 31.5 (21.1) for those in the PC group and 12.9 (20.7) for those in the PN group; notably, they were significantly higher in those in the PC group (t(60) = 3.138, p < 0.01, Fig 4A). In addition, LBP VAS scores while they were sitting at 1 year after discectomy were 30.8 (25.7) for those in the MC group and 14.9 (20.5) for those in the MN group, showing the scores were significantly higher in those in the MC group (t(60) = 2.304, p = 0.025, Fig 4B).