The introduction of the spine pedicle screws by Roy-Camille in 1970  and the subsequent development in the posterior segmental instrumentation systems have dramatically improved the outcomes of spinal fusion and guided the way to the current practices in the spine stabilization and fusion techniques. The need for accessing the anatomical entry points of the pedicle screws helped in the introduction of the relevant surgical exposure techniques. However, that required the stripping and vigorous retraction of the overlying paraspinal muscles from their anchoring points for the essential exposure with their subsequent mechanical, neural, and vascular damage. It was years later when the spine and paraspinal muscle biomechanic studies were well established, emphasizing the anchoring and stabilizing biomechanics of the paravertebral muscles and the subsequent sequels of their iatrogenic injury during the surgical techniques. Therefore, minimally invasive application techniques of screws were developed to avoid the collateral damage of the paraspinal muscles and the spinal biomechanics resulting in paraspinal muscle preservation and more rapid recovery. However, minimally invasive procedures also are not without additional shortcomings including a steep learning curve with a higher complication rate and long operation time during the learning period, along with additional surgical devices and costs.
Our cohort involved the insertion of 100 percutaneous pedicle screws in 51 vertebrae. The mean number of screws used per case was 5 ± 1.17 screws.
Our series involved 20 cases with mean operative time of 139.35 ± 63 min: 9 cases of traumatic fractures with a mean operative time of 87.3 ± 24.3 and 11 cases of degenerative pathologies with a mean operative time of 181 ± 52 min as that included the time required for neural tissue decompression and/or interbody prothesis application, and by omitting the time of neural decompression and/or interbody fusion, the time of applying the screws was comparable to the time needed in the traumatic cases who was operated for percutaneous pedicle screw fixation only. That was relatively similar to the operative time reported by the traumatic cases series managed by percutaneous pedicle screws fixation: Wild et al.  (87 minutes), Ni et al.  (78 min), Hong et al.  (97 min), Lee et al.  (83.2 min), and Tinelli et al.  (65–81 min). That mean was relatively longer than the trauma case series reported by Schmidt et al.  (47 min), Taha et al.  (70 min), and Gong et al.  (59.46 min) and the degenerative cases series Kim et al.  (150 min), Park et al.  (151 min), and Versteeg et al.  (122 min), which can be attributed to the higher experience of the operating surgeons (these series have an average number of 70 patients) and the use of advanced intraoperative imaging techniques.
On the other hand, the mean operative time was relatively shorter than the series reported by Pelegri et al.  (108 min), Palmisani et al.  (120 min), Fuentes et al. (100 min), Grossbach et al.  (195 min), and Elenany et al.  (154.5 min), and the degenerative case series; Raley et al.  (238 min) and Mobbs et al.  (272 min). That can be attributed to the more complex nature of the fractures involved in these series, while our study was dealing mainly with wedge (A2) fractures (89%).
Our series average blood loss was 168 ± 141 ml: 95.5 ± 28.7 ml for the traumatic cases and 227.3 ± 168.8 ml for the degenerative cases. That was relatively similar to the results reported in the trauma cases series of Taha et al.  (100 ml) and Grossbach et al.  (93 min). However, it was less than the recorded blood loss that was reported in the trauma series reported by Wild et al.  (194 ml), Lee et al.  (262 ml), and Elenany et al.  (174 ml), and the degenerative pathologies series reported by Kim et al.  (402 ml) and Park et al.  (302 ml), which may be attributed to the complexity of the involved cases in these series. On the other hand, our recorded blood loss was more than that reported in the trauma series reported by Ni et al.  (75 ml), Hong et al. (83 ml) , and Gong et al.  (59.5 ml), and the degenerative pathologies series reported by Mobbs et al.  (180 ml) and Versteeg et al.  (100 ml) that can be attributed to the higher level of experience of the surgeon, the shorter duration of the operation and the general morbidities of the patient.
The mean hospital stay duration in our series was 3.3 ± 1.38 days, 3.7 ± 1.64 days in the trauma cases series, and 2.9 ± 1 days in the degenerative case series. That was less than the average reported in the trauma series by Ni et al.  (5 days), Fuentes et al.  (4.5 days), Hong  et al. (11.1 days), Grossbach et al.  (7.6 days), Versteeg et al.  (7 days), Gong et al.  (5.28 days), and more than the average stay reported by Elenany et al.  (1.2 days). That can be attributed to the severity of other system injuries and the general condition of the patient which is related to the duration of the hospital admission in the other series [1,2,3,4,5,6,7].
Our first day post-operative total creatine kinase mean value was 986 ± 345.4 U/L ranging from 208 to 1924 U/L. Our tenth case has the highest postoperative CK total value (1924 U/L) and the second longest operative time (236 min) and had been operated for two levels percutaneous pedicle screw fixation, midline single-level laminectomy, discectomy, and posterior lumbar interbody fusion. That shows the possible direct relation between the post-operative creatine kinase level, the duration, and the extent of the operation, especially when a muscle stripping decompression technique was added to the procedure. The creatine kinase MB values showed mild post-operative elevation that ranged from 9 to 55 U/L and did not form more than 5.5% of the total post-operative creatine kinase value, indicating that the creatine kinase MM variance is responsible mainly for the elevation of post-operative value.
Our mean creatine kinase value was less than mean value reported by Lenke et al.  (2490 ± 3196 U/L), Iglesias et al.  (1185.8 ± 1234.6 U/L), and Linzer et al.  (1350 U/L) in their conventional surgery series; these augment the muscle sparing aim of this minimally invasive technique and correlated with the less muscle injury associated with the percutaneous pedicle screws fixation technique. Nevertheless, our study’s results showed higher creatine values in comparison to other minimally invasive techniques series as Kim et al.  (299.4 ± 48 U/L), Fan et al.  (347.9 ± 94.6 U/L), Arts et al.  (255.7 ± 209.8 U/L), Park et al.  (299.4 ± 54 U/L), Uehara et al.  (176 ± 104 U/L), Ohba et al.  (866 ± 503 U/L), and Gong et al.  (201.3 ± 45.9 U/L). That can be attributed to the following:
The mixed population of our study, which not only included traumatic but also degenerative spine pathologies which necessitates multiple level instrumentation and additional procedures as TLIF application.
Longer operative time which is directly related to the creatine kinase elevation values that can be explained by the initial learning curve of our study in comparison to other studies with higher number of included cases and the use of uniplanar fluoroscopy which add to the time of the operation.
The ethnic variation may have a role as all the previous studies were done on European, American, or Asian population, while all the cases included in this study were Egyptian. This can be attributed to Griffith et al study in which 94 patients underwent variable conventional spine surgery procedures and the first post-operative day mean total creatine kinase was 1205 ± 1727 U/L, ranging from 196 to 8828 U/L in black population, which was more than the values found in the white population with a mean value of 702 ± 928 U/L and ranging between 196 and 6514 U/L, denoting the possible variation between different ethnicities.
Our study has a total malpositioned screw ratio of 7% (7 screws), which was less than the ratio reported by Kim et al.  (11%), Mobbs et al.  (9.7%), Seok et al.  (14.3%), and Mohi et al.  (21.6%). On the other hand, it was more than the ratio reported by Wiesner et al. (6.6%), Ni et al.  (4%), Taha et al.  (5.45%), Tinelli et al.  (2.4%), and Phan et al.  (3%). When calculating the mean malpositioning ratio of the mentioned studies, it was found to be 7.15%, which is almost similar to our study’s mean. Mild (G1) misplacement was found in 4 (4%) of the screws in our study which was less than the mild (G1) misplacement ratio reported by Wiesner et al.  (6.1%), Wild et al.  (4.8%), Kim et al.  (9.4%), Mobbs et al.  (5.7%), Seok et al.  (10.6%), and Mohi et al.  (19%). On the other hand, moderate (G2) misplacement in our series was 3%, which was more than the ratio reported by Ni et al.  (1.9%), Kim et al.  (1.4%), Taha et al.  (1.6%), Seok et al.  (2.6%), and Mohi et al.  (2.6%). There were no cases of severe (G3) misplacement and no cases were symptomatic or developed weakened construct stability, and no revision surgeries were required. Out of the 7 misplaced screws in our series, 4 (57%) screws were misplaced medially, and 3 (43%) screws were misplaced laterally which showed no significant difference to the mean medial misplacement ratio of the previous studies which was 49.4% for medial misplacement and 44.4% for the lateral misplacement of the screws. When compared to conventional pedicle screws surgical technique series, our study showed an accuracy rate of 93%, which was higher than the 84.7% accuracy rate of conventional pedicular screws reported by Verma et al.  in his systematic review involving 2437 screws, Oh et al.  comparative study which involved 483 conventional screws with an accuracy rate of 86.6%, and Gelalis et al.  systematic review with an accuracy rate of 69–94% in 2412 conventional screws applied by free hand technique and accuracy rate of 28–85% in 1902 conventional screws applied by the aid of fluoroscopy.
This study has the following limitations:
Our study’s sample size was relatively small (20 patients) when compared to some other studies in the literature.
Our follow-up duration was 6 months, which highlights the short and midterm outcome, but does not reveal the long-term outcome of the procedure.
Our study was prospective non-randomized non-blinded study, which may suffer from selection, classification, and confounding biases.