[Comparative study between 3D guide plate assisted and free-hand insertion of anterior cervical transpedicular screw].

OBJECTIVE: To compare accuracy of anterior cervical pedicle screws between assist of rapid prototyping 3D guide plate and free-hand insertion, and evaluate the safety of two methods. METHODS: Eight adult cervical cadaver specimens after formaldehyde immersion, including 4 males and 4 females, aged 32 to 65(40.3±5.6) years old. After X-ray examination to exclude bone damage and deformity, 4 of them (3D guide plate group) randomly selected were for CT scan to obtain DICOM format data, and the data was imported into Mimics software for model, designed the ideal entry point and nail path for anterior cervicaltranspedicular screw (ATPS). After obtaining the personalized guide plate of the nail channel, it was exported as STL data, and the individual guide plate was printed by rapid prototyping and 3D printing technology. In turn, with the assistance of 3D guide plates, one-to-one personalized ATPS screws were placed on the four lower cervical cadaver specimens. Another 4 (free-hand group) lower cervical cadaver specimens were implanted with ATPS screws using free-hand technique. All specimens were performed CT thin-layer scanning and three-dimensional reconstruction after operation. The Tomasino method was used to evaluate the safety of the screws on the CT cross-sectional and sagittal images, to determine whether there was a cortical puncture of the lower and inner edges of the pedicle. According to the CT rating results, gradeⅠandⅡwere safe, and grade Ⅲ- Ⅴ were dangerous.And the accuracy of screws was recorded and analyzed between two groups. RESULTS: Two screws were inserted in each segment from C3 to C7 in 8 adult cadavers. A total of 80 screws were inserted, 40 in the 3D guide plate group, and 40 in the free-hand group. The Tomasino screw rating method was used to evaluate the safety of screw, 21 screws were gradeⅠ, 14 screws were gradeⅡ, 3 screws were grade Ⅲ, 1 screw was grade Ⅳ, 2 screws were grade Ⅴ in 3D guide plate group, while 14 screws were gradeⅠ, 8 screws were gradeⅡ, 8 screws were grade Ⅲ, 6 screws were grade Ⅳ, 2 screws were grade Ⅴ in free-hand group. The safety rate of 3D guide plate group was 87.5%, and 55.0% of the free hand group (χ2=8.7, P=0.003). CONCLUSION: The 3D printing rapid prototyping guide plate assisted insertion of the anterior cervical pedicle screw can significantly improve the accuracy and safety, and provide a theoretical basis for further clinical application.

The clinical relevance of the presence of bridging syndesmophytes on kyphosis correction and maintenance following pedicle subtraction osteotomy for thoracolumbar kyphotic deformity in ankylosing spondylitis: a comparative cohort study.

BACKGROUND: The presence of bridging syndesmophytes (BS) in spinal osteotomy region serves traditionally as one critical determinant for selection of osteotomy techniques. While nowadays the proportion of kyphotic ankylosing spondylitis (AS) patients receiving pedicle subtraction osteotomy (PSO) with yet mobile neighboring disc has seen a substantial increase. Literatures investigating the clinical relevance of the presence of BS on kyphosis correction and maintenance following PSO are scarce. METHODS: A total of 71 thoracolumbar kyphotic AS patients treated with single-level PSO at our hospital between September 2010 and August 2014 were retrospectively reviewed, 32 of whom were stratified into the BS group (BG). The operative corrections of multiple spino-pelvic sagittal parameters were assessed. Comparison of the contribution of adjacent disc wedging to total correction per PSO segment was made between the BS and non-BS groups (NBG). The correction loss were also evaluated and compared with a minimum 2-year follow-up. RESULTS: A significantly younger age (30.97 ± 8.28 vs. 40.31 ± 8.44 yrs., p < 0.001), smaller pelvic incidence (PI) (43.03 ± 10.60 vs. 49.36 ± 9.75°, p = 0.011), greater wedging index of osteotomized vertebra (1.17 ± 0.16 vs. 1.09 ± 0.08, p = 0.011) and larger local kyphosis (19.59 ± 10.84 vs. 13.56 ± 8.50°, p = 0.013) was observed in NBG preoperatively. Patients in BG and NBG accomplished comparable amount of kyphosis correction per PSO segment (40.22 ± 7.09 vs. 43.85 ± 8.71°, p = 0.062). However, the contribution of adjacent disc wedging to total correction per PSO was significantly larger in NBG [8.10 ± 6.19 (18.5%) vs. 1.09 ± 2.88° (2.7%), p < 0.001]. By ultimate follow-up, the global kyphosis (18.26 ± 10.97 vs. 21.51 ± 10.89°, p < 0.05) and thoracic kyphosis (37.95 ± 11.87 vs. 42.87 ± 11.56°, p < 0.05) deteriorated significantly in the NBG but not BG, so was further pelvic retroversion as represented by increased pelvic tilt (19.46 ± 8.13 vs. 23.44 ± 8.19°, p < 0.05) and decreased sacral slope (23.02 ± 9.12 vs. 18.62 ± 10.10°, p < 0.05). Loss of corrections concerning contribution of adjacent disc wedging was also larger in NBG (1.41 ± 3.27 vs. 0.22 ± 1.49°, p < 0.05). CONCLUSIONS: Our study might suggest that the evaluation and treatment methods of kyphotic AS patients needed to be fine-tuned with appropriate subgrouping by the presence of syndesmophytes with bamboo sign as they were potentially distinct groups with different PI, contributor of lordosing capability and prognosis that might require separate analysis.

Radiological morphology variances of osteotomized vertebra-disc complex following pedicle subtraction osteotomy for ankylosing spondylitis with thoracolumbar kyphosis: the incidence, mechanisms, and prognosis.

BACKGROUND CONTEXT: Inaccurate osteotomy cut along with incomplete or even subluxated bone-on-bone closure of osteotomy gap following pedicle subtraction osteotomy (PSO) may be disastrous, hampering the lordosing effect and increasing the likelihood of complications. The inelastic yet osteoporotic spine in ankylosing spondylitis (AS) is specially predisposed to such suboptimal osteotomy, while the relevant data concerning this issue are scarce. PURPOSE: This study aimed to analyze the incidence of radiological morphology variances (RMV) of osteotomized vertebra-disc complex (OVDC) following PSO in patients with kyphotic AS, conceptualize the mechanisms of the deviated morphology, and investigate the prognosis. STUDY DESIGN: This is a retrospective radiological data analysis. PATIENT SAMPLE: The sample being screened comprises 71 patients with thoracolumbar kyphotic AS who underwent single-level PSO at our hospital between March 2006 and February 2014. They were stratified by the presence of bridging syndesmophytes (BS) locating within the OVDC. OUTCOME MEASURES: Any irregular radiological configuration of OVDC other than the wedge morphology would be considered as RMV and were studied with care to fully describe and classify the spectrum of deviated morphologic features. Multiple spinopelvic sagittal parameters were measured to assess both the regional lordosing effect and the global realignment of sagittal spinal profile. METHODS: For each selected patient with confirmed RMV, the radiological morphology was assessed, defined, and categorized. The prognosis involving surgical corrections and maintenance of spinopelvic sagittal parameters, as well as the remodeling in disordered osteotomized vertebral shape over time, were also investigated. RESULTS: The incidence of RMV was 21.9% in positive BS group (PG) and 30.8% in negative BS group (NG). Inappropriate angle and range of osteotomy accounted for the largest share (1 pts for PG and 10 pts for NG, 57.9%) of mechanisms responsible for RMV, followed by vertebral subluxation (VS) (5 pts for PG and 2 pts for NG, 36.8%) and failed osteotomy gap closure (1 pts for PG, 5.3%). For these patients, the mean bony lordosing effect per PSO segment was 36.0°±8.9° postoperatively, and decreased to 34.7°±8.7° by a mean follow-up of 3 years (p=.076). The magnitude of neighboring disc opening was significantly higher in NG (10.2°±6.5° vs. 2.4°±3.2°, p=.009). The global kyphosis and sagittal vertical axis were significantly corrected (77.0°±21.2° vs. 24.4°±18.8°; 160.6°±72.4° vs. 48.2°±38.6 mm, all p<.001) and remained stable by the ultimate follow-up (p>.05). No devastating neurologic deficits were noticed. Patients with VS and failed osteotomy gap closure exclusively showed solid bone healing and adaptive remodeling without rod breakage at final follow-up. CONCLUSIONS: Radiological morphology variances of OVDC were a high occurrence following PSO in AS, being mainly attributed to inaccurate osteotomy cut and VS. Neighboring disc opening and rotational or translational subluxation were major available remedial mechanisms strengthening the lordosing effect when that of vertebral wedging was impaired and insufficient. The bone fusion and remodeling concerning the subluxated or dislocated osteotomized vertebra was utterly favorable, maintaining the kyphosis correction and preventing instrumentation failure.

[Anatomical feature of lumbar and S1 pedicle in patients with thoracolumbar kyphosis secondary to ankylosing spondylitis].

OBJECTIVE: To measure the correlative parameters of vertebral pedicles from L1 to S1 by CT scan in the patients with thoracolumbar kyphosis secondary to ankylosing spondylitis(AS) and disc degenerative disease(DDD), and analyze their anatomical difference in order to provide the selection and placement of pedicle screw during operation. METHODS: The clinical data of 30 male AS patients (AS group) with the mean age of(35.7±9.5) years (ranged, 23 to 51) and 30 male DDD patients (DDD group) with the mean age of(52.4±8.9) years(ranged, 39 to 64) underwent surgery in our institution from March 2012 to November 2014 were analyzed. The CT scans of lumbar and sacrum were performed before surgery. The parameters of vertebral pedicle from L1 to S1 were measured and compared, including pedicle width (PW), pedicle screw path length (PL), pedicle height (PH), pedicle transverse angle (EA), and pedicle inclined angle (FA). Paired sample t-test was used to detect the divergence in the above-mentioned data between left and right sides. In addition, results between two groups were compared using independent sample t-test. RESULTS: The study showed that a gradual increase in the average pedicle width both AS group and DDD group from L1 to S1. The average PW of AS group was bigger than DDD group in L5 and S1(P<0.05), it was(16.47±2.66) mm and (21.76±2.97)mm vs. (14.51±2.11)mm and (18.87±2.14) mm respectively;the average PL of DDD group was smaller than AS group from L1 to S1(P<0.05); the both maximum of PL were in L3 segment; the average EA of AS group was smaller than DDD group from L1 to S1; the average FA of AS group was significantly smaller than DDD group from L3 to S1, (P<0.05), was(-2.88±10.24)°, (-7.88±10.22)°, (-7.70±10.40)°, (-5.15±10.25)° vs. (4.05±2.21)°, (7.79±4.38)°, (7.07±3.21)°, (12.62±3.21)°, respectively. CONCLUSIONS: Increasing the strength of internal fixation is feasible to insert the larger and bigger pedicle screws in low lumbar and S1 among AS patients, while the EA should be decreased properly and the direction on the sagittal plane should be adjusted.