Accepted Manuscript The Comparison of Pedicle Screw and Cortical Screw in Posterior Lumbar Inter-body Fusion: a Prospective Randomized Non-inferiority Trial Gun Woo Lee, MD, Jung-Hwan Son, MD, Myun-Whan Ahn, MD, Ho-Joong Kim, MD, Jin S. Yeom, MD PII: S-0()000- DOI: 0.0/j.spinee.0.0.0 Reference: SPINEE To appear in: The Spine Journal Received Date: June 0 Revised Date: January 0 Accepted Date: February 0 Please cite this article as: Lee GW, Son J-H, Ahn M-W, Kim H-J, Yeom JS, The Comparison of Pedicle Screw and Cortical Screw in Posterior Lumbar Inter-body Fusion: a Prospective Randomized Noninferiority Trial, The Spine Journal (0), doi: 0.0/j.spinee.0.0.0. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
The Comparison of Pedicle Screw and Cortical Screw in Posterior Lumbar Interbody Fusion: a Prospective Randomized Non-inferiority Trial Gun Woo Lee, MD a,*, Jung-Hwan Son, MD b, Myun-Whan Ahn, MD c, Ho-Joong Kim, MD d, Jin S. Yeom, MD d a Department of Orthopaedic Surgery, Armed Forces Yangju Hospital, Yangju, -, Republic of Korea b Department of Orthopaedic Surgery, Kosin University Gospel Hospital, Busan, Republic of Korea c Spine Centrer and Department of Orthopaedic Surgery, Yeungnam University Hospital, Daegu, Republic of Korea d Spine Centrer and Department of Orthopaedic Surgery, Seoul National University College of Medicine and Seoul National University Bundang Hospital, Sungnam, Korea * Corresponding author: Gun Woo Lee, MD Department of Orthopaedic Surgery, Armed Forces Yangju Hospital, Yongam-ri, -, Eunhyeon-myeon, Yangju-si Gyeonggi-do, -, Republic of Korea Tel: --- E-mail address: gwlee@gmail.com
Running Head: Acknowledgements: none
Abstract Background Context: Pedicle screws (PS) offer great benefits in posterior lumbar inter- 0 0 body fusion (PLIF), but several drawbacks of PS, including the risk of superior facet joint violation and muscle injury, have also pointed out. Recently, cortical screws (CS) were invented, which can be placed without the drawbacks associated with PS. However, whether or not CS in PLIF can provide similar or greater clinical and radiological outcomes compared to those of PS has not been fully evaluated in clinical research studies. Purpose: To evaluate whether the CS provides similar results to the PS in PLIF, in terms of fusion rate, clinical and surgical outcomes, and complications. Study Design: Prospective, randomized, non-inferiority trial Patient Sample: Seventy-nine eligible patients were randomly assigned to either group A ( patients), for which PS was utilized, or group B (0 patients), for which CS was utilized. Outcome Measure: The primary study endpoint was to measure fusion rate using dynamic radiographs and CT scans. Secondary endpoints included intensity of lower back pain and pain radiating to the leg using visual analogue scales, and also, functional status using the Oswestry disability index, surgical morbidity, and additional outcomes such as pedicle fracture and mechanical failure. Methods: We compared baseline data in both groups. To evaluate the efficacy of CS in PLIF compared to PS, we compared fusion rates, clinical outcomes, and complications after surgery in both groups. No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.
Results: At the six- and twelve-month follow-up points, similar fusion rates were observed in both groups (P = 0. and 0., respectively). According to the clinical 0 outcome, CS provided similar improvements in pain amelioration and functional status compared to PS, with no significant differences. Additionally, CS resulted in significantly less surgical morbidity, including shorter incision length, quicker operative time, and less blood loss, compared to PS. Conclusion: CS in PLIF provides similar clinical and radiological outcomes compared to PS in PLIF. Based on the current study, we suggest CS to be a reasonable alternative to PS in PLIF.
INTRODUCTION Posterior lumbar inter-body fusion (PLIF) surgery with pedicle screw (PS) has 0 0 recently been widely used as an effective surgical method for certain lumbar pathologies such as spondylolisthesis [-]. PS has been recognized as an irreplaceable instrument in fusion surgery of the lumbar spine due to its advantages [,-]. However, concerns regarding PS include the risk of superior facet joint violation during screw placement or dissection, the skin incision length, and the amount of lateral muscle dissection due to the entry point being lateral to the midline, near the lateral wall of facet joint. In spite of those drawbacks, there was little choice for spine surgeons but to utilize PS, resulting from the lack of alternatives. Recently, cortical screws (CS) using cortical screw trajectories in the lumbar spine were introduced for posterior stabilization [-]. Some experimental studies have demonstrated that CS provide similar strength as compared to PS [-]. Perez-Orribo et al. [] reported that the bilateral CS-rod fixation technique could provide similar stability in cadaveric experiments compared to PS-rod fixation, regardless of the presence of the inter-body cages. Because of their favorable entry point (near the pars articularis) and favorable passage (through the pedicle supero-laterally from the entry point), CS are expected to reduce the rate of facet joint violation, as well as to achieve better clinical and surgical outcomes. However, postoperative outcomes when using CS in PLIF have not been fully described.
To date, the therapeutic efficacy of CS in PLIF has yet to be fully described. Furthermore, to the best of our knowledge, outcomes using CS and PS for PLIF have no yet been compared in a prospective randomized study. Therefore, we analyzed and compared the clinical and radiological outcomes of CS and PS in PLIF, using a prospective, randomized design via a non-inferiority trial. We hypothesized that CS would result in comparable efficacy in terms of fusion rate, clinical, and surgical outcomes, in comparison with PS in PLIF.
METHODS Participants 0 0 This study was approved by the institutional review board. follows. Inclusion criteria were as First, patients were diagnosed with certain lumbar pathologies, including LSS with severe foraminal stenosis and isthmic spondylolisthesis, using lumbar spine radiographs, computed tomography (CT) scans, and magnetic resonance images (MRI) that corresponded to clinical manifestations and physical examinations. Second, patients were required to have shown no improvement in clinical symptoms despite several conservative treatments (including medication, physical therapy, and injection treatment) over a period of six months or more. Third, patients were required to have undergone PLIF at a single level using screws (PS or CS) and inter-body polyetheretherketone (PEEK) cages. Fourth, patients were between 0 and 0 years of age. Fifth, patients were volunteers for this study with their written consent. Finally, patients were required to complete a one year or longer follow-up period. Exclusion criteria were as follows: fractures, infection or tumors in the lumbar spine; osteoporosis diagnosed by a T-score less than -. on dual-energy X-ray absorptiometry (DEXA) bone densitometry measurements, multi-level fusion surgery, hemorrhagic disorders, such as hemophilia and thrombocythemia, patient inability to accurately complete preoperative and postoperative questionnaires, and lack of patient suitability for this study, as judged by the corresponding author. The inclusion and exclusion criteria were applied in order to avoid confounding effects on outcome variables.
Sample size estimation 0 0 This study was conducted to determine whether CS are a posterior stabilizer in PLIF surgery compared to PS based on the fusion rate and clinical outcomes. Thus, we used the non-inferiority criteria to calculate the appropriate sample size []. The primary endpoint was the fusion rate, and the expected fusion rate of the control group using PS (group A) was %, which is in agreement with several studies [-]. For noninferiority of CS versus PS in PLIF with a two-sided % significance level, a power of 0%, and a noninferiority margin of %, a sample size of patients for each group was necessary. Given an anticipated dropout rate of 0%, a total of patients were required. Randomization Patients were randomly assigned into group A, for which PS was utilized, or group B, for which CS was utilized. The group allocation (PS or CS screw type) was blinded to the patient, not to the surgeon and other health providers, meaning that this is single-blind study in regards to the patient. Randomization was conducted by a computer-generated allocation program (nqquery Advisor PPS.0, Saugus, MA, USA), which assigns numbers in strict chronological sequences and enters regular sequences for each study group. Randomization was stratified via three variables: () age (0s versus 0s), () smoking status (smoker versus non-smoker), and () operation level (L- versus L-S). Each study participant was allocated a unique randomization number upon screening completion.
Surgical procedures and postoperative protocols All surgeries were performed by a single orthopedic surgeon who used the same operative 0 0 technique for each surgery. In the surgeries, posterior decompression via partial laminectomy was performed following a posterior midline skin incision. When necessary, a partial or total facetectomy was also performed. In each patient, two PEEK cages (CAPSTONE, Medtronic, Memphis TN, USA) were routinely utilized for inter-body fusion with the auto-graft bone materials that were locally obtained during posterior decompression. To improve the fusion rate, mixtures of locally-harvested auto-graft bone and demineralized bone matrix (DBM, Korea Bone Bank, Seoul, Korea) were placed and packed around the cages. In group A, bilateral screw-rod systems with PS (CD Horizon Legacy system, Medtronic, Memphis TN, USA) were used under fluoroscopic guidance, and. x mm screws were utilized for each patient in group A. In group B, a bilateral screw-rod system with CS (MIDLF, Medtronic Sofamor Danek, Memphis TN, USA) was used under fluoroscopic guidance (Fig. ), and. x 0 mm screws in L and L and. x mm screws in S were utilized. Patients in both groups were admitted to the same wards following the operation and were then treated with the same postoperative protocols. All patients were permitted to ambulate the first day after surgery, and the majority of patients were discharged from the hospital on postoperative day fourteen. Patients were encouraged to avoid sitting for long periods of time during the first month following surgery. After three months post-surgery, patients were allowed to resume normal activities, including heavy lifting.
Outcome measures The primary post-surgery study endpoint was fusion rate. Fusion status was determined at 0 0 six and twelve months after surgery. Fusion was defined by the difference less than two degrees in Cobb angles in lateral radiographs taken in flexion and extension and by the presence of a continuous fusion mass either inside or outside the cage as seen on CT imaging. Non-union was declared if the difference in Cobb angle was greater than two degrees, or if the fusion mass on CT scans was discontinuous. An orthopedic spine surgeon, who was not involved in patient treatment, performed all dynamic radiography and CT measurements. Dynamic radiograph measurements were carried out using the picture archiving and communication system (PACS) program (Infinitt, Bracknell, Berkshire, UK). To mitigate measurement error, all dynamic radiograph measurements were performed according to several criteria. First, lateral flexion and extension radiographs were simultaneously viewed on dual monitors. Second, images were viewed at 00% magnification. Third, all radiographs were changed to the bone image setting for detailed evaluation of the bone. All CT scans were taken using.0-mm intervals (Mx000 IDT; Philips Medical System, Best, Netherlands). There were several secondary endpoints. Secondary endpoints included the intensity of lower back pain and pain radiating to the lower extremity (each measured separately using a visual analogue scale (VAS)), functional status (using the Oswestry disability index (ODI)), surgical morbidity (based on operating time, incision length, estimated blood loss, and hospital stay), and additional outcomes including infection rate or mechanical failure.
These data were collected prospectively by the corresponding author, both preoperatively and at each regular follow-up visit. Statistical analysis Independent Student s t-tests or analysis of variance (ANOVA) tests were used for continuous variables, and the Fisher s exact test was used for proportional variables. SPSS software version.0 (SPSS, Chicago, IL, USA) was used for all analyses. Twosided P-values < 0.0 were considered to be statistically significant.
RESULTS Patient characteristics 0 0 Seventy-nine eligible patients were randomly assigned to group A ( patients) and group B (0 patients). Of them, patients ( in group A and in group B) were qualified for the study, each of whom fully complied with the inclusion criteria (Fig. ). Patients were similar between groups with respect to demographic characteristics such as age, gender, smoking status, height, weight, BMI, and preoperative lumbar pathology (Table ). Primary outcome measure (fusion rate) According to the dynamic radiographs, fusion at six months post-surgery was achieved in / patients (.%) in group A, and in / patients (.%) in group B. The difference in fusion rate was not significant (P = 0.). At twelve months post-surgery, fusion was achieved in / patients (.%) in group A and in / patients (.%) in group B, which was not a significant difference (P = 0.) (Table ). On CT scan, fusion at six months post-surgery was achieved in / patients (.0%) in group A and in / patients (.%) in group B, which was not significantly different between groups (P = 0.). On one year after surgery, / patients (.%) in group A and / patients (.%) in group B achieved fusion, with no significant difference between groups (P = 0.) (Table ). Secondary outcome measures 0
Mean VAS scores for lower back pain indicated that one-year postoperative pain levels were significantly lower than preoperative levels for both groups, with mean scores 0 0 decreasing from. ±. preoperatively to.0 ±.0 at one postoperative year in group A, and from. ±. to. ±. in group B (P = 0.). These VAS scores were not significantly different between the two groups. However, the VAS scores for lower back pain at postoperative week one were significantly different between the groups at. ±. for group A and. ±. for group B (P = 0.0). VAS scores for radiating pain also improved significantly in both groups, with mean scores decreasing from. ±. preoperatively to. ± 0. at one postoperative year in group A, and from. ±. to. ± 0. in group B, but there were no significant differences between the groups (P = 0.) (Fig. and Table ). In addition, the mean ODI score also improved from. ± 0. preoperatively to.0 ±. one year after surgery in group A, and from. ±. preoperatively to 0. ±. one year after surgery in group B. These ODI scores were not significantly different between the two groups (P = 0.) (Fig. and Table ). Surgical morbidities, including blood loss, operation time, hospital stay, and incision length, are described in Table. Of which, group B was associated with better outcomes compared to group A, in terms of blood loss, operation time, and incision length (P = 0.0, 0.0, and 0.0, respectively). Facet joint violation as evalutaed on postoperative CT was occurred at / (%) in group A and 0/ (0%) in group B, which was significantly different between the groups (P < 0.0). Mechanical problems such as bony fracture at
the pars or pedicle due to screw placement, screw fracture, screw migration, and cage migration were not present in any patients of either group. On postoperative CT scan, malpositioned screws were seen in two in group A patients. No malpositioned screws were seen in group B. There were no complications such as fever, swelling, or deep infection for any patient. However, there was one instance of a local superficial infection at the surgical site in one of group A patient. The infection was resolved without complication after wound debridement.
DISCUSSION There were several principle findings of the current study. Similar fusion rates were 0 0 observed in both groups at six- and twelve-month follow-up, with no significant differences between the groups. Clinically, CS provided similar improvements in pain relief and functional status as compared to PS in PLIF. In addition, CS resulted in lower surgical morbidity measured by blood loss, operation time, and incision length, as compared to PS. Based on the current study, we suggest that using CS in PLIF could provide similar outcomes to PS at the one-year follow-up point, and thus, CS might be a reasonable alternative to PS in PLIF. Some experimental studies have demonstrated the ability of CS to provide sufficient strength to endure a similar level of stress compared to PS [-]. Perez-Orribo et al. [] also reported that the bilateral CS-rod fixation technique could provide similar stability in cadaveric experiments compared to PS-rod fixation, regardless of whether an inter-body device is present. However, whether CS could provide sufficient clinical outcomes and fusion rates without complications has not yet been fully evaluated in clinical research studies. Thus, we aimed to evaluate the fusion rate, clinical outcomes, and potential complications of CS in PLIF, and to compare these outcomes to PS in PLIF, using a prospective, randomized, non-inferiority design. In the current study, fusion rates were not significantly different between the two screw types. For example, the fusion rate at the first postoperative year was.% in group A versus.% in group B according to dynamic radiographs and.% in group A versus.% in group B according to CT scans
(P = 0. and 0., respectively). Radiologic complications such as loosened or pulled- out screw were not observed in any patients of both groups. Clinically, there was no 0 0 statistically significant difference between the two groups in improvement in pain intensity and ODI scores. However, in the immediate postoperative period, within one week of surgery, CS provided significantly better lower back pain scores compared to PS, which was caused by smaller skin incision and with less muscle dissection of CS, as described the surgical outcomes of the current study. PS has been recognized as an irreplaceable instrument in fusion surgery of the lumbar spine due to its advantages, such as its ability to produce sufficient stability to the destabilized lumbar segment and its ease of use and placement in the area [,-,0,], but some drawbacks to PS have been pointed out. One concern for PS is the risk of superior articulating facet violation during screw placement or dissection [,,,], and another is the need of long skin incision and significant muscle dissection due to the very lateral to midline entry point of PS, at the lateral wall of the pedicle. Previous studies revealed that superior facet joint violations were a common occurrence during PS placement, with an incidence of %-% in open surgery and %-00% in percutaneous surgery [,]. In the late 000s, CS using cortical screw trajectories was invented, such that screws could be placed without those drawbacks of PS [-,]. Due to the entry point of the CS being near the pars articularis, which is far from the superior facet joint, the risk of superior facet violation is much lower than in PS. The current study also showed that the facet joint violation occurred at % in group A and 0% in group B (P < 0.0). In addition, the CS entry point allows screw placement with a smaller skin incision and with less muscle
dissection and injury compared to PS, which were also demonstrated by outcomes of the current study. In addition, the risk of cortical bone violation of the pedicle or the pars 0 0 when using CS is less than when using PS because CS placement is made during the visualization of several landmarks. For example, the starting point is at the crosshairs of a line bisecting the pars interarticular, which is approximately 0 to mm below the superior facet joint capsule. Also, determination of the CS placement can be easily made under fluoroscopy. Moreover, there has been concern regarding the risk of bony fracture at the pars or pedicle due to CS placement because the angle of screw insertion is too steep and the CS screw length is shorter than PS, but no fracture was observed in the current study. The current study has some limitations. First, we did not conduct the current study with a sufficient sample size because this study was designed as a non-inferiority trial. There have not been reports of the outcomes of CS in PLIF, so we conducted this study as a preliminary clinical trial. Since the completion of this study, we have performed an additional comparative study between CS and PS in PLIF with a larger sample size and longer follow-up times. Second, this study had a short follow-up period of one year. To better establish the outcomes of CS in PLIF for LSS patients, further studies should be performed using a larger sample size, an extended follow-up period, and a prospective study design. Third, this study was conducted on patients without osteoporosis, as seen on DEXA scan, who underwent single-level PLIF surgery in the L- or L-S segments. In other words, the results of this study cannot be applied to subjects having multilevel fusion surgeries, surgeries on other lumbar segments, or those with osteoporotic bone. Fourth,
because this study was conducted in limited population, mainly males between the ages of 0-0 years, statistical analysis may be complicated due to the inherent non-normal 0 distribution, and our conclusions might not be acceptable for all patient populations. Thus, further studies should be performed with patients of a broader age range and with both sexes. Finally, this study was not blinded to the surgeons, assessors for evaluating the radiologic images, and other health care providers due to the nature of the study type, which might produce the performance bias. Despite these limitations, the current study has some unique strengths. Because our hospital is an armed force hospital, follow-up visits for each enrolled patient were possible. Also, this is the first clinical research study with a prospective-randomized design to evaluate CS outcomes in PLIF. Moreover, the data in the current study were obtained from a homogenous population with respect to physical activity, since the research was performed at an armed forces hospital. Such population homogeneity reduces the risk of confounding factors on outcome variables. Due to a paucity of articles regarding the efficacy of CS in PLIF, hopefully this study can serve as a baseline for further research on CS.
CONCLUSION The current study was conducted to evaluate the efficacy of CS compared to PS in PLIF 0 one year after surgery using a prospective, randomized, non-inferiority design. There was no significant difference in fusion rate between CS and PS, which was the primary endpoint. In addition, there was no statistically significant difference in clinical outcomes, based on pain intensity and ODI status, between CS and PS use. Moreover, CS in PLIF resulted in less facet joint violation and surgical morbidity than PS. Based on these results, we suggest that the CS would provide similar outcomes compared to PS in PLIF at one year after surgery, and thus, CS is a reasonable alternative to PS in PLIF. Additional studies should be performed with larger sample sizes, extended follow-up periods, and with prospective-randomized designs to better understand the clinical and radiological outcomes of these two screws.
Funding No funds were received in support of the present work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.
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Figure Legends 0 Figure. Cortical screw trajectory. On axial (A, L; B, S) and sagittal (C, L; D, S) CT images, the CS was inserted through the pedicle in a the supero-lateral direction from the entry point, which was located near the pars articularis. Figure. Flow diagram for enrolled patients. Figure. Mean VAS for back pain (A), mean VAS for radiating pain to the lower extremity (B), and mean ODI (C) scores by time point. The VAS and ODI were collected at each follow-up time. Error bars represent standard deviations. * Statistically significant difference between scores at baseline and at each follow-up time (P < 0.0) ** Statistically significant difference between groups at the follow-up times (P < 0.0)
Table. Demographic Data Group B Group C P Case - Age (year). ±.. ±. 0. Gender (male / female) / / 0. Height (cm). ± 0.. ±. 0. Weight (kg). ±.. ±. 0. BMI (kg/m ). ±.. ±. 0.0 BMD (T-score). ± 0.. ± 0. 0. Smoking status 0. smoker (%) (.) (.%) non-smoker (%) (.) (.%) Lumbar pathology (%) LSS with foraminal stenosis 0 (.) (.) Isthmic spondylolisthesis (.) (.) Degenerative spondylolisthesis (0.) (.) Fusion level 0. L- (%) (.) (.) L-S (%) 0 (.) 0 (.) Values in data cells represent mean ± SD (standard deviation). BMI, body mass index; BMD, bone mineral density; LSS, lumbar spinal stenosis
Table. Fusion rate at one year post-surgery Group B (n = ) Using dynamic radiographs at postoperative one year Group C (n = ) P Fusion Nonunion Union rate (%).. 0. Using CT scans at postoperative one year Fusion Nonunion Union rate (%).. 0.
Table. Clinical outcomes Clinical Parameters Group B (n = ) Group C (n = ) P VAS for lower back pain Pre-operative. ±.. ±. 0. week postoperative. ±.. ±. 0.0* weeks postoperative. ±.0.0 ± 0. 0. weeks postoperative.0 ± 0.. ±. 0. month postoperative. ± 0.. ± 0. 0. months postoperative. ± 0.. ±.0 0. months postoperative.0 ±.. ± 0. 0. year postoperative.0 ±.0. ±. 0. VAS for radiating pain Pre-operative. ±.. ±. 0. month postoperative. ± 0..0 ± 0. 0. months postoperative.0 ± 0. 0. ± 0. 0. months postoperative. ± 0.. ± 0. 0. year postoperative. ± 0.. ± 0. 0. ODI score Pre-operative. ± 0.. ±. 0. months postoperative. ±.. ±. 0.0 months postoperative 0. ±.. ± 0. 0.
year postoperative.0 ±. 0. ±. 0. Values in data cells represent mean ± SD (standard deviation). VAS, visual analogue scale; ODI, oswestry disability index *, meaning significant difference between groups (P < 0.0)
Table. Surgical outcomes Group B (n = ) Group C (n = ) P Blood loss (ml) 0 ± 0 ± 0 0.0* Operation time (hours). ± 0.. ± 0. 0.0* Hospital stay (day). ±.. ±. 0. Incision length (mm) 0. ±.. ±. 0.0* Values in data cells represent mean ± SD (standard deviation). *, meaning significant difference between groups (P < 0.0)
AC C EP TE D M AN U SC RI PT
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