3.4.2. Pain Intensity after Implant Removal

Of the 27 observational studies, nine [39,41,44,46,49,53,56,59,63] reported significant pain relief after implant removal; of these, four studies [39,41,44,59] reported the decision to remove the pedicle screw instrument due to implant-associated symptoms such as pain or discomfort, while in three studies [46,53,59] the patients were asymptomatic before implant removal. One retrospective cohort study [47] found that 10 of 27 patients had increasing back pain after implant removal, while in another retrospective cohort study [60], 12 of 21 patients reported reduced back pain or discomfort after surgery. In addition, one study [64] found no significant changes after implant removal.

#### *3.5. Secondary Outcomes*

### 3.5.1. Improvement of Segmental Motion Angle

Among the observational studies, six [38,44–47,58] reported improvement after implant removal, three [56,59,63] reported decreased Oswestry Disability Index (ODI) scores, and one [60] reported four of 21 patients had improved range of motion. In contrast, four studies [49,55,62,64] demonstrated no or slight improvement after implant removal but the segmental motion angle was considered to be motionless.

#### 3.5.2. Removal-Related Complications

One case report [30] reported inadvertent screw migration into the retroperitoneal space, while one case series [37] reported that pedicular screws fractured and the threaded parts of the screws were, therefore, left in 1 patient.

For the 27 observational studies, five [38,46,51–53] reported wound infection after implant removal, Two studies [39,44] reported vertebral height loss after implant removal, seven [43,45,47,49,50,54,60] reported disc degeneration and progressive loss of injured disc height, and one [40] reported revision surgery after implant removal.
