Patient baseline characteristics
Follow-ups were performed at 12–36 months; the K-Rod group had an average of 29.5 months, and the rigid group had 28.3 months. Age, bleeding volume during operation, follow-up date, total drainage volume, total hospitalization time and operation time did not significantly differ between the groups. The total cost of hospitalization in K-Rod group was ¥11.7 ± 1.29 ten thousand, and that in Rigid group was 10.6 ± 1.64 ten thousand. The costs of the K-Rod group exceeded those of the rigid fixation group (P < 0.05) (Table 1).
Table 1
General data | K-Rod(N = 25) | Rigid(N = 15) | P |
Age(years) | 66 ± 6.79 | 61 ± 7.17 | 0.674 |
SEX | | | |
Female | 12(48%) | 8(53.33%) | 0.752 |
Male | 13(52%) | 7(46.66%) |
Follow-up(months) | 29.48 ± 4. 97 | 28.26 ± 5. 88 | 0.483 |
Operation Time(mins) | 289 ± 34.40 | 307 ± 49.06 | 0.162 |
Intraoperative blood loss(mL) | 480 ± 270.03 | 462 ± 294.14 | 0.845 |
Postoperative drainage(mL) | 340 ± 120.34 | 332 ± 55.32 | 0.810 |
Hospital stay(days) | 15 ± 3.50 | 16 ± 3.35 | 0.748 |
Expenses(ten thousands) | 11.7 ± 1.29 | 10.6 ± 1.64 | 0.018 |
Note: Data are presented as mean ± standard deviation. P values are based on the t test; P > 0.05 compared with K-Rod and Rigid. |
Clinical Efficacy
The scores of JOA, ODI and VAS were compared between K-Rod group and rigid group. The P values of JOA, ODI and VAS in K-Rod group were less than 0.05 before and after the operation. Improvements in JOA, ODI and VAS were comparable between the groups (Table 2).
Table 2
Scores of JOA, ODI and VAS
Index | K-Rod(N = 25) Rigid(N = 15) JOA ODI VAS JOA ODI VAS |
Pre-operative | 14.6 ± 1.26 | 37.92 ± 2.58 | 6.48 ± 0.96 | 14.6 ± 0.828 | 38.00 ± 2.20 | 6.53 ± 0.92 |
Post-operative | 22.68 ± 0.85 | 15.24 ± 2.71 | 2.24 ± 0.723 | 22.40 ± 0.986 | 15.20 ± 1.01 | 15.20 ± 1.01 |
P | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 | 0.000 |
P’ | JOA (0.461) | | ODI (0.247) | | VAS (0.391) | |
Note: Data are the mean ± SD. Data were compared through t-tests, P means Post- vs. pre-operative, P < 0.05; P’ means K-Rod group compare with rigid group, P > 0.05. P < 0.05 mean statistically significant differences. |
The clinical efficacy of modified Macnab in K-Rod group was 84.00%. K-Rod caused no improvement over the rigid group (P > 0.05) (Table 3).
Table 3
Clinical assessment of modified Macnab
Group | N | Excellent | Good | Fair | Poor | The Excellent/Good rate | P |
K-Rod | 25 | 6 | 15 | 3 | 1 | 84.00% | 1.0 |
Rigid | 15 | 4 | 8 | 2 | 1 | 80.00% | |
Note: Data were compared using a chi-square test, P < 0.05 significant difference. |
Radiologic Outcomes Of Fusion Rate
At the last follow-up, there were 17 fusion segments in the K-Rod group; 16 were judged as strong fusion, and 1 was judged as possible fusion, with a fusion rate of 94.11%. There were 37 fusion segments in the rigid fixation group, 36 were judged as strong fusion, and 1 was judged as possible fusion. The fusion rate was 97.30%, which was comparable across the groups (P > 0.05).
Table 4
Fusion rates of the two groups
Grading | K-Rod (N = 17) | Rigid (N = 37) | P |
Fusion | 16 | 36 | |
Possible fusion | 1 | 1 | |
Non-fusion | 0 | 0 | |
Fusion rate (%) | 94.11% | 97.30% | 0.535 |
Note: P values are based on the chi-square test, P < 0.05 mean statistically significant differences. |
Rom And Lumbar Lordosis Angle Assessments
Preoperative and postoperative radiologic parameters including lumbar lordosis angle and ROM in the K-Rod and rigid groups are shown in Fig. 1. The lumbar lordosis angle between the two groups was similar in both pre-operation and post-operation (P > 0.05). However, the lumbar lordosis angle was lower in the K-Rod group at the last follow-up (P < 0.05), but not post-operation (P > 0.05). The decrease of the K-Rod group was slower than that of the rigid group, suggesting that the K-Rod group had a positive effect on lumbar lordosis angle maintenance (Fig. 1a). Furthermore, the total lumbar ROM of both groups at the final follow-up was lower than prior to the operation (P < 0.05) (Fig. 1b); the lower and upper adjacent showed an improved and significantly increased ROM (P < 0.05), while the ROM of the adjacent segments in the rigid group (13.82 ± 6.65)° increased vs. the K-Rod group (24.94 ± 9.61)° at the last follow-up (P < 0.05). Thus, the K-Rod group led to a higher ROM of the lumbar spine (P < 0.05). The upper and lower adjacent segments did not differ between groups (P > 0.05) (Fig. 1c, d). At the last follow-up, the number of fixed segment ROMs were lower in the K-Rod group compared with those prior to the operation (P < 0.05), suggesting that fixed segment ROMs in the K-Rod group were limited and that the K-Rod dynamic stabilization system can effectively stabilize non-fusion intervertebral activity (Fig. 1e).
Radiologic Outcomes Of Isr Value
ISR values in the K-Rod and rigid groups are shown in Fig. 2. The ISR value of upper adjacent segment between the two groups was similar including pre-operation and post-operation (P > 0.05). However, the ISR values of the upper adjacent segments were higher in the K-Rod group at the last follow-up (P < 0.05), suggesting that K-Rod prevented the degeneration of adjacent segments (Fig. 2a). The results of lower adjacent segments were quite similar to upper adjacent segments, which confirms the results again (Fig. 2b). The ISR values of the non-fusion and fixed segments in the K-Rod group increased after operation (P < 0.05), but declined significantly until the last follow up (P < 0.05). The ISR value of the last follow-up in the K-Rod group exceeded that observed prior to the operation (P < 0.05) (Fig. 2c).
Radiologic Outcomes Of Degeneration In Adjacent Segments
According to the modified Pfirrmann grading system, the incidence of degeneration of adjacent segments was 2.5% in the K-Rod group and 26.3% in the rigid group. The incidence of adjacent segment degeneration in the K-Rod group was significantly lower than the rigid group (P < 0.05) (Table 5).
Table 5
The modified Prirrmann grade rate of proximal adjacent in two groups.
| Proximal adjacent segment | P | |
K-Rod | 2.5% | 0.012 | |
Rigid | 26.3% | |
Note: Data were compared using a chi-square test, P < 0.05 mean statistically significant differences. |
According to the UCLA system, the incidence of adjacent segment degeneration was 5.0% in the K-Rod group and 31.6% in the rigid group. Adjacent segment degeneration of the K-Rod group was significantly lower than the rigid group (P < 0.05) (Table 6).
Table 6
UCLA system evaluation of intervertebral space.
| Proximal adjacent segment | P |
K-Rod | 5.0% | 0.018 |
Rigid | 31.6% |
Note: Data were compared using a chi-square test, P < 0.05 mean statistical significant differences. |
Radiologic Outcomes Of Typical Case
Typical case (Fig. 3): Fig. 3a-d (K-rod group): Male, 63 years old, with DLSS (L2/3, L3/4, and L4/5), K-Rod dynamic internal fixation and fusion, postoperative symptoms significantly improved. According to the improved Pfirrmann classification, adjacent segment L1/2 were all grade 3, adjacent segment L5/S1 were all grade 6, no significant degeneration. Figure 3e-h (Rigid group): A 61-year-old female patient with DLSS (L3/4, L4/5) underwent L3/4, L4/5 decompression and rigid fixation. Postoperative symptoms improved significantly. According to the modified Pfirrmann classification, L2/3 of the upper adjacent segment degenerated from preoperative grade 4 to postoperative grade 5, and L5/S1 of the lower adjacent segment degenerated from preoperative grade 3 to postoperative grade 4.