Postoperative complications of S2AI versus iliac screw in spinopelvic fixation: a meta-analysis and recent trends review

BACKGROUND CONTEXTIliac screw constructs have been a major advancement in spinopelvic fixation demonstrating superior biomechanics as compared with earlier pelvic spanning constructs. However, drawbacks such as screw site prominence and wound complication have led to the development of a lower profile S2AI iliac screw.PURPOSEIn this study, we aimed to study the differences in complication rates between the traditional iliac and S2AI fixations via a pooled analysis of the available head-to-head comparisons between S2AI and iliac screws. We also aimed to study the iliac screw complications trend over the years particularly with reference to recent modifications in its screw insertion techniques.STUDY DESIGNA meta-analysis with attention to the comparison of patients who underwent iliac screws and S2AI screws was conducted.METHODSThe following databases were utilized: PubMed, Scopus, Web of Science, Embase, and Cochrane Central Register of Controlled Trials database. Using the search terms: iliac, iliac bolts, S2AI, sacral 2 alar iliac, sacral two alar iliac, reviewers independently selected eligible studies, analyzed data and evaluated the risk of bias. Data analysis was conducted using RevMan 5.3 software.RESULTA total of 215 articles were identified, with 6 clinical studies directly comparing outcomes of S2AI pelvic fixation versus iliac screw fixation. A total of 477 patients were included, of which 255 patients (53.5%) underwent S2AI screw and 222 (46.5%) underwent iliac screw fixation. Our pooled analysis favored S2AI screws with regards to postoperative complications of screw prominence (odds ratio [OR]=5.99, 95% confidence interval [CI]=2.168–16.523, p<.001), screw loosening (OR=3.36, 95% CI=1.415–7.998, p=.006), implant breakage (OR=2.30, 95% CI=1.189–4.443, p=.013), and revision surgery (OR=7.84, 95% CI=3.224–19.080, p<.001). Although there was a trend toward more wound complications in conventional iliac screw techniques when compared with S2AI, it was not statistically significant.CONCLUSIONSpinopelvic fixation is an evolving technique. The results from this study showed that S2AI screws with a lower profile have made a significant impact in reducing complications associated with conventional iliac screws. With recent entry point modification and further advancement in the conventional iliac screw technique, such as the “subcrestal iliac screw technique” which reduces the iliac screw complication rate but avoids S2AI-associated SIJ violation. Further studies may be needed to investigate whether these newer iliac screw techniques can narrow the difference in complication rates between iliac screws and S2AI screw techniques.     

Hounsfield unit of screw trajectory as a predictor of pedicle screw loosening after single level lumbar interbody fusion

Object

This study aims to clarify the clinical potential of Hounsfield unit (HU), measured on computed tomography (CT) images, as a predictor of pedicle screw (PS) loosening, compared to bone mineral density (BMD).

Technik der perkutanen SI-Verschraubung mit Unterstützung durch konventionellen C-Bogen

Background

During percutaneous iliosacral screw fixation, fluoroscopy with a conventional C-arm X-ray unit is still the standard procedure for intraoperative orientation. Lateral sacral images in combination with the inlet and outlet view are always necessary. Nevertheless, the complex pelvic anatomy makes it difficult to prevent malpositioning of screws.

Operative technique

Defining the correct entry into the bone is the decisive step for ideal screw placement. The better this is defined, the larger safety margins will be concerning cortical perforation by the screws. In the lateral view, an entry ventral to the sacral canal has to be avoided as well as an entry into the cranial half of the first sacral vertebra. To improve the surgeon’s three-dimensional orientation with the help of his personal experience and two-dimensional images, it is recommended to place the tip of the screws in the center of the sacrum (in AP view) whenever possible. Routinely performed postoperative CT imaging of 24 screws, consecutively implanted according to the standards described, revealed no case of malpositioning.

Conclusion

Standard X-ray views in combination with standardized aiming of screw entry position and final screw thread position enable the surgeon to find the “safe zone” for iliosacral screw insertion and to prevent iliosacral screw malpositioning with high accuracy.     

Sacropelvic fixation versus fusion to the sacrum for spondylodesis in multilevel degenerative spine disease

Study design

Retrospective study.

Objective

For successful multilevel correction and stabilization of degenerative spinal deformities, a rigid basal construct to the sacrum is indispensable. The primary objective of this study was to compare the results of two different sacropelvic fixation techniques to conventional stabilization to the sacrum in patients with multilevel degenerative spine disease.

Methods

A total of 69 patients with multisegmental fusion surgery (mean number of stabilized functional spinal units: 7.0 ± 3.3) with a minimum of 1-year follow-up were included. 32 patients received fixation to the sacrum (S1), 23 patients received S1 and iliac screw fixation (iliac) and 14 patients were treated with iliosacral plate fixation (plate). Primary outcome parameters were radiographic outcome concerning fusion in the segment L5–S1, rate of screw loosening, back and buttock pain reduction [numeric rating scale for pain evaluation: 0 indicating no pain, 10 indicating the worst pain], overall extent of disability after surgery (Oswestry Disability Index) and the number of complications.

Results

The three groups did not differ in body mass index, ASA score, the number of stabilized functional spinal units, duration of surgery, the number of previous spine surgeries, or postoperative complication rate. The incidence of L5–S1 pseudarthrosis after 1 year in the S1, iliac, and plate groups was 19, 0, and 29 %, respectively (p < 0.05 iliac vs. plate). The incidence of screw loosening after 1 year in the S1, iliac, and plate groups was 22, 4, and 43 %, respectively (p < 0.05 iliac vs. plate). Average Oswestry scores after 1 year in the S1, iliac, and plate groups were 40 ± 18, 42 ± 20, and 58 ± 18, respectively (p < 0.05 both S1 and iliac vs. plate).

Conclusion

The surgical treatment of multilevel degenerative spine disease carries a significant risk for pseudarthrosis and screw loosening, mandating a rigid sacropelvic fixation. The use of an iliosacral plate resulted in an inferior surgical and clinical outcome when compared to iliac screws.     

Investigation of bone quality of the first and second sacral segments amongst trauma patients: concerns about iliosacral screw fixation

Background

Iliosacral screw fixation has become a common method for surgical stabilization of acute disruptions of the pelvic ring. Placement of iliosacral screws into the first sacral (S1) body is the preferred method of fixation, but size limitations and sacral dysmorphism may preclude S1 fixation. In these clinical situations, fixation into the second sacral (S2) body has been recommended. The objective of this study was to evaluate the bone quality of the S1 compared to S2 in the described “safe zone” of iliosacral screw fixation in trauma patients.

Materials and methods

The pelvic computed tomography scans of 25 consecutive trauma patients, ages 18–49, at a level 1 trauma center were prospectively analyzed. Hounsfield units, a standardized computed tomography attenuation coefficient, was utilized to measure regional cancellous bone mineral density of the S1 and S2. No change in the clinical protocol or treatment occurred as a consequence of inclusion in this study.

Results

A statically significant difference in bone quality was found when comparing the first and second sacral segment (p = 0.0001). Age, gender, or smoking status did not independently affect bone quality.

Conclusion

In relatively young, otherwise healthy trauma patients there is a statistically significant difference in the bone density of the first sacral segment compared to the second sacral segment. This study highlights the need for future biomechanical studies to investigate whether this difference is clinically relevant. Due to the relative osteopenia in the second sacral segment, which may impact the quality of fixation, we feel this technique should be used with caution.

Level of evidence

III     

Cement Augmentation in Sacroiliac Screw Fixation Offers Modest Biomechanical Advantages in a Cadaver Model

Background

Sacroiliac screw fixation in elderly patients with pelvic fractures is prone to failure owing to impaired bone quality. Cement augmentation has been proposed as a possible solution, because in other anatomic areas this has been shown to reduce screw loosening. However, to our knowledge, this has not been evaluated for sacroiliac screws.

Questions/purposes

We investigated the potential biomechanical benefit of cement augmentation of sacroiliac screw fixation in a cadaver model of osteoporotic bone, specifically with respect to screw loosening, construct survival, and fracture-site motion.

Methods

Standardized complete sacral ala fractures with intact posterior ligaments in combination with ipsilateral upper and lower pubic rami fractures were created in osteoporotic cadaver pelves and stabilized by three fixation techniques: sacroiliac (n = 5) with sacroiliac screws in S1 and S2, cemented (n = 5) with addition of cement augmentation, and transsacral (n = 5) with a single transsacral screw in S1. A cyclic loading protocol was applied with torque (1.5 Nm) and increasing axial force (250–750 N). Screw loosening, construct survival, and sacral fracture-site motion were measured by optoelectric motion tracking. A sample-size calculation revealed five samples per group to be required to achieve a power of 0.80 to detect 50% reduction in screw loosening.

Results

Screw motion in relation to the sacrum during loading with 250 N/1.5 Nm was not different among the three groups (sacroiliac: 1.2 mm, range, 0.6–1.9; cemented: 0.7 mm, range, 0.5–1.3; transsacral: 1.1 mm, range, 0.6–2.3) (p = 0.940). Screw subsidence was less in the cemented group (3.0 mm, range, 1.2–3.7) compared with the sacroiliac (5.7 mm, range, 4.7–10.4) or transsacral group (5.6 mm, range, 3.8–10.5) (p = 0.031). There was no difference with the numbers available in the median number of cycles needed until failure; this was 2921 cycles (range, 2586–5450) in the cemented group, 2570 cycles (range, 2500–5107) for the sacroiliac specimens, and 2578 cycles (range, 2540–2623) in the transsacral group (p = 0.153). The cemented group absorbed more energy before failure (8.2 × 10⁵ N*cycles; range, 6.6 × 10⁵–22.6 × 10⁵) compared with the transsacral group (6.5 × 10⁵ N*cycles; range, 6.4 × 10⁵–6.7 × 10⁵) (p = 0.016). There was no difference with the numbers available in terms of fracture site motion (sacroiliac: 2.9 mm, range, 0.7–5.4; cemented: 1.2 mm, range, 0.6–1.9; transsacral: 2.1 mm, range, 1.2–4.8). Probability values for all between-group comparisons were greater than 0.05.

Conclusions

The addition of cement to standard sacroiliac screw fixation seemed to change the mode and dynamics of failure in this cadaveric mechanical model. Although no advantages to cement were observed in terms of screw motion or cycles to failure among the different constructs, a cemented, two-screw sacroiliac screw construct resulted in less screw subsidence and greater energy absorbed to failure than an uncemented single transsacral screw.

Clinical Relevance

In osteoporotic bone, the addition of cement to sacroiliac screw fixation might improve screw anchorage. However, larger mechanical studies using these findings as pilot data should be performed before applying these preliminary findings clinically.

     

A comparison of union rates and complications between single screw and double screw fixation of sliding calcaneal osteotomy

Background

The number of screws used for sliding calcaneal osteotomy fixation has not been examined in the literature. The purpose of this paper is to examine this topic.

Supplemental S1 fixation for type C pelvic ring injuries: biomechanical study of a long iliosacral versus a transsacral screw

Background

A single iliosacral screw placed into the S1 vertebral body has been shown to be clinically unreliable for certain type C pelvic ring injuries. Insertion of a second supplemental iliosacral screw into the S1 or S2 vertebral body has been widely used. However, clinical fixation failures have been reported using this technique, and a supplemental long iliosacral or transsacral screw has been used. The purpose of this study was to compare the biomechanical effect of a supplemental S1 long iliosacral screw versus a transsacral screw in an unstable type C vertically oriented sacral fracture model.

Materials and methods

A type C pelvic ring injury was created in ten osteopenic/osteoporotic cadaver pelves by performing vertical osteotomies through zone 2 of the sacrum and the ipsilateral pubic rami. The sacrum was reduced maintaining a 2-mm fracture gap to simulate a closed-reduction model. All specimens were fixed using one 7.0-mm iliosacral screw into the S1 body. A supplemental long iliosacral screw was placed into the S1 body in five specimens. A supplemental transsacral S1 screw was placed in the other five. Each pelvis underwent 100,000 cycles at 250 N, followed by loading to failure. Vertical displacements at 25,000, 50,000, 75,000, and 100,000 cycles and failure force were recorded.

Results

Vertical displacement increased significantly (p < 0.05) within each group with each increase in the number of cycles. However, there was no statistically significant difference between groups in displacement or load to failure.

Conclusions

Although intuitively a transsacral screw may seem to be better than a long iliosacral screw in conveying additional stability to an unstable sacral fracture fixation construct, we were not able to identify any biomechanical advantage of one method over the other.

Level of evidence

Does not apply—biomechanical study.     

Screw perforation features in 129 consecutive patients performed computer-guided cervical pedicle screw insertion

Study design

A cross-sectional study of the data retrospectively collected by chart review.

Objectives

This study aimed to clarify screw perforation features in 129 consecutive patients treated with computer-assisted cervical pedicle screw (CPS) insertion and to determine important considerations for computer-assisted CPS insertion.

Summary of background data

CPS fixation has been criticized for the potential risk of serious injury to neurovascular structures. To avoid such serious risks, computed tomography (CT)-based navigation has been used during CPS insertion, but screw perforation can occur even with the use of a navigation system.

Methods

The records of 129 consecutive patients who underwent cervical (C2–C7) pedicle screw insertion using a CT-based navigation system from September 1997 to August 2013 were reviewed. Postoperative CT images were used to evaluate the accuracy of screw placement. The screw insertion status was classified as grade 1 (no perforation), indicating that the screw was accurately inserted in pedicle; grade 2 (minor perforation), indicating perforation of less than 50 % of the screw diameter; and grade 3 (major perforation), indicating perforation of 50 % or more of the screw diameter. We analyzed the direction and rate of screw perforation according to the vertebral level.

Results

The rate of grade 3 pedicle screw perforations was 6.7 % (39/579), whereas the combined rate of grades 2 and 3 perforations was 20.0 % (116/579). No clinically significant complications, such as vertebral artery injury, spinal cord injury, or nerve root injury, were caused by the screw perforations. Of the screws showing grade 3 perforation, 30.8 % screws were medially perforated and 69.2 % screws were laterally perforated. Of the screws showing grades 2 and 3 perforation, 21.6 % screws were medially perforated and 78.4 % screws were laterally perforated. Furthermore, we evaluated screw perforation rates according to the vertebral level. Grade 3 pedicle screw perforation occurred in 6.1 % of C2 screws; 7.5 % of C3 screws; 13.0 % of C4 screws; 6.5 % of C5 screws; 3.2 % of C6 screws; and 4.0 % of C7 screws. Grades 2 and 3 pedicle screw perforations occurred in 12.1 % of C2 screws, 22.6 % of C3 screws, 31.5 % of C4 screws, 22.2 % of C5 screws, 14.4 % of C6 screws, and 12.1 % of C7 screws. C3–5 screw perforation rate was significantly higher than C6–7 (p = 0.0024).

Conclusions

Careful insertion of pedicle screws is necessary, especially at C3 to C5, even when using a CT-based navigation system. Pedicle screws tend to be laterally perforated.     

Trans-iliosacral plating for vertically unstable fractures of sacral spine associated with spinopelvic dissociation: A cadaveric study

Background:

The treatment algorithm for sacral fracture associated with vertical shear pelvic fracture has not emerged. Our aim was to study a new approach of fixation for comminuted and vertically unstable fracture pattern with spinopelvic dissociation to overcome inconsistent outcome and avoid complications associated with fixations. We propose fixation with well-contoured thick reconstruction plate spreading across sacrum from one iliac bone to another with fixation points in iliac wing, sacral ala and sacral pedicle on either side. Present biomechanical study tests the four fixation pattern to compare their stiffness to vertical compressive forces.

Materials and Methods:

Dissection was performed on human cadavers through posterior midline paraspinal approach elevating erector spinae from insertion with two flaps. Feasibility of surgical exposure and placement of contoured plate for fixation was evaluated. Ten age and sex matched computed tomography scans of pelvis with both hips were obtained. Reconstructions were performed with advantage windows 4.2 (GE Light Speed QX/I, General Electric, Milwaukee, WI, USA). Using the annotation tools, direct digital CT measurement (0.6 mm increments) of three linear parameters was carried out. Readings were recorded at S2 sacral level. Pelvic CT scans were extensively studied for entry point, trajectory and estimated length for screw placement in S2 pedicle, sacral ala and iliac wing. Readings were recorded for desired angulation of screw in iliac wing ala of sacrum and sacral pedicle with respect to midline. The readings were analyzed by the values of mean and standard deviation. Biomechanical efficacy of fixation methods was studied separately on synthetic bone. Four fixation patterns given below were tested to compare their stiffness to vertical compressive forces: 1) Single S1 iliosacral screw (7.5 mm cancellous screw), 2) Two S1 and S2 iliosacral screws, 3) Isolated trans-iliosacral plate, 4) Trans-iliosacral plate + single S1 iliosacral screw.

Statistical Analysis:

Mean of desired angulation for inserting screws and percentage of displacement on biomechanical testing was evaluated.

Results:

Mean angulations for inserting sacral pedicel were 12.3° (SD 2.7°) convergent to midline and divergent of 14° (SD 2.3°) for sacral ala screw and 23° (SD 4.9°) for iliac wing screw. All screws needed to be inserted at an angle of 90° to sacral dorsum to avoid violation of root canals. Cross headed displacement across fracture site was measured and plotted against the applied vertical shear load of 300 N in five cycles each for all the four configurations. Also, the force required for cross headed displacement of 2.5 mm and 5 mm was recorded for all configurations. Transmitted load across both ischial tuberosities was measured to resolve unequal distribution of forces. Taking one screw construct (configuration 1) as standard base reference, trans-iliosacral plate construct (configuration 3) showed equal rigidity to standard reference. Two screw construct (configuration 2) was 12% stronger and trans-iliosacral plate (configuration 4) with screw was 9% stronger at 2.5 mm displacing on 300 N force, while it showed 30% and 6%, respectively, at 5 mm cross-headed displacement.

Conclusions:

Trans-iliosacral plating is feasible anatomically, biomechanically and radiologically for sacral fractures associated with vertical shear pelvic fractures. Low profile of plate reduces the risk of hardware prominence and decreases the need for implant removal. Also, the fixation pattern of plate allows to spare mobile lumbosacral junction which is an important segment for spinal mobility. Biomechanical studies revealed that rigidity offered by plate for cross headed displacement across fracture site is equal to sacroiliac screws and further rigidity of construct can be increased with addition of one more screw. There is need for precountered thicker plate in future.     

Percutaneous iliosacral screwing in pelvic ring injury using three-dimensional fluoroscopy

Background

Iliosacral screw fixation is a popular technique for treatment of unstable pelvic injuries involving the posterior ring. However, screw malposition may result in dangerous complications involving injury to adjacent neurovascular structures. This study was conducted in order to evaluate the results and efficacy of using three-dimensional fluoroscopy in the performance of iliosacral screw fixation.

Methods

Twenty-nine patients (31 cases, two bilateral) who suffered injury to the pelvic ring requiring surgical treatment were included in this study. According to the Association for Osteosynthesis-Orthopaedic Trauma Association (AO-OTA) classification, there were 14 patients with type B, 13 patients with type C, and 2 patients with a bilateral sacral fracture. The mean age of patients was 39 years. Once the guide pin had been inserted, its safety was confirmed using three-dimensional fluoroscopy; screw fixation was then performed. Eighteen patients underwent percutaneous iliosacral screw fixation and anterior fixation, while 11 patents underwent screw fixation only. Postoperative computed tomography (CT) was performed for evaluation of the screw position, including any invasion into the sacral foramen or canal and neurovascular injury. The perforation of the screw was divided according to the location (sacral zones I, II, and III) and the degree (grade 0, no perforation; grade 1, perforation <2 mm; grade 2, perforation between 2 and 4 mm; grade 3, perforation >4 mm).

Results

The mean operation time was 35.6 min, and the mean radiation exposure time was 85.9 s. For accurate location of the guide pin, one patient underwent three-dimensional reconstruction twice. None of the patients required reoperation or suffered any neurovascular injury. Although seven cases involved perforation, all were less than 2 mm (grade 0: 24 cases, grade 1: 7 cases).

Conclusions

When performing percutaneous iliosacral screw fixation in a patient with an unstable pelvic ring injury, use of three-dimensional fluoroscopy may allow for accurate location of the screw and result in fewer complications.     

An anatomic study on the placement of the second sacral screw and its clinical applications

Background

The fixation of lumbosacral and sacral pelvis can be performed on the ilium and the Second Sacrum Vertebrae (S2). Although several studies on the anatomical and biomechanical features of S2 screw fixation have been published, little clinical application has been reported, especially combination of anatomical investigation and clinical study. This study was performed to design and optimize the method of pedicle screw placement for S2.

Materials and methods

Fifteen adult dry sacrum specimens were prepared and truncated from the S1–S2 and S2–S3 vertebral fusion remnants, and the morphology of the S2 vertebral body was observed from this section. The intersection of the horizontal line through the lowest point of the inferior edge of the first posterior sacral foramen and the lateral sacral crest was the entry point (Point X). The screws were inserted anterolaterally or anteromedially at Point X in 10 cadavers, with all of the screws penetrating the sacrum. Finally, the S2 sacral screw fixation technique was applied to a total of 13 patients with lumbosacral lesions, and the clinical outcome was evaluated at a minimum follow-up of 1 year.

Results

Two S2 sacral screw placement methods were developed, i.e., the anterolateral and anteromedial insertions. Seven patients had complete preoperative, postoperative, and follow-up data. In all cases, the bilateral S2 screws were placed in good position and the fixation was firm. There was no surgical wound infection or internal fixation loosening. All the patients achieved partial bone graft healing, which was verified by computed tomography.

Conclusions

The intersection of the horizontal line through the lowest point of the inferior edge of the first posterior sacral foramen and the lateral sacral crest can be used as the entry point for S2 sacral screw fixation. The S2 pedicle screw fixation shows good clinical effectiveness and safety for stable reconstruction of lumbosacral lesions.     

Vertically unstable pelvic fractures fixed with percutaneous iliosacral screws: does posterior injury pattern predict fixation failure?

OBJECTIVE: To measure the failure rate of percutaneous iliosacral screw fixation of vertically unstable pelvic fractures and particularly to test the hypothesis that fixations in which the posterior injury is a vertical fracture of the sacrum are more likely to fail than fixations with dislocations or fracture-dislocations of the sacroiliac joint. DESIGN: Retrospective review. SETTING: Level 1 trauma center. METHODS: All patients with pelvic fractures admitted between January 1, 1993, and December 31, 1998, were identified from the trauma registry. Hospital records were used to identify patients treated with iliosacral screws. Radiologic studies were examined to identify patients who had unequivocally vertically unstable pelvic fractures. Immediate postoperative and follow-up anteroposterior, inlet, and outlet radiographs from a minimum of 12 months postinjury were examined. Position, length, and numbers of iliosacral screws and any evidence of screw failure (eg, bending or breakage) were recorded. Residual postoperative displacement and late displacement of the posterior pelvis were measured. The main outcome measure was failure, defined as at least 1cm of combined vertical displacement of the posterior pelvis compared with immediate postoperative position. The main analysis was for association between fracture pattern and failure. Patient demographic data, iliosacral screw position, and anterior pelvic fixation method also were studied. RESULTS: The study group comprised 62 patients with unequivocally vertically unstable pelvic fractures in whom the posterior injury was treated with closed reduction and percutaneous iliosacral screw fixation. Of patients, 32 had dislocations or fracture-dislocations of the sacroiliac joint, and 30 had vertical fractures of the sacrum. Fixation failed in four patients, all with vertical sacral fractures and all within the first 3 weeks after surgery. These four patients required revision fixation. In two further cases with vertical sacral fractures, there was evidence that the fracture had only barely been held by the fixation, but these fractures healed, and follow-up radiographs did not meet the displacement criteria for failure. A vertical sacral fracture pattern was associated significantly with failure (Fisher exact test, P = 0.04); the excess risk of failure compared with sacroiliac joint injury was 13% (95% confidence interval 1% to 25%). There was no significant association between failure and anterior fixation method, iliosacral screw arrangement or length, or any demographic or injury variable. CONCLUSIONS: Percutaneous iliosacral screw fixation is a useful technique in the management of vertically unstable pelvic fractures, but a vertical sacral fracture should make the surgeon more wary of fixation failure and loss of reduction.     

Simple mathematical model of sacroiliac screws safe‐zone—Easy to implement by pelvic inlet and outlet views

Percutaneous sacral screw fixation is the mainstay of posterior pelvic ring fixation. This study quantifies the accuracy of fluoroscopic screw placement using post‐operative CT scans and redefines the fluoroscopic safe zone using a mathematical calculation obtained from Inlet and outlet images. The authors hypothesized that a mathematical calculation of screw placement within the ala will improve accuracy of screw placement. A retrospective review of consecutive patients admitted to a level 1 trauma center with pelvic fractures fixed with iliosacral screws from January 2011 to December 2014 was performed. Accuracy of screw placement was determined by comparing fluoroscopy to post‐operative CT scans. A mathematical calculation of screw position within the sacral ala was applied to determine assess screw position and compared to CT findings. Ninety‐four patients with 156 screws met inclusion criteria, of which 50 (32.0%) had a cortical breech on CT. The sensitivity and specificity of the inlet–outlet safe zone using mathematical calculation were 97.1% and 84.0%, respectively. The positive and negative predictive values were 92.7% and 93.3%, respectively. Overall accuracies of the radiographic inlet–outlet and lateral safe zones were 92.9% and 70.0%, respectively (p‐value = 0.004). Sacral dysmorphism was not found to be associated with sacral cortical breech. A Simple mathematical calculation (screw position relative to percentage of bone width) on the inlet–outlet provides an accurate way to predict the accuracy of sacroiliac screws. The method is easy to implement, part of the surgery work‐flow, and provides higher accuracy than relying on subjective interpretation of inlet, outlet, and lateral images. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1478–1484, 2017.

     

Analysis of the Risk Factors for Free Flap Necrosis in Soft Tissue Reconstruction of the Lower Limbs

Objective

Free flaps are widely used for the repair of soft tissue defects in the lower limbs, but there is still a specific rate of necrosis. Few clinical retrospective studies have analyzed the nontechnical risk factors for lower limb free flap necrosis. This study aimed to analyze the nontechnical causes of flap necrosis in lower limb soft tissue reconstruction in order to identify risk factors and improve the survival rate of free flaps.

Methods

Clinical data from 244 cases of soft tissue defects of the leg or foot that were repaired with a free flap from January 2011 to June 2020 were retrospectively analyzed. The flap results were divided into complete survival and necrosis groups. The patients' general information, smoking history, soft tissue defect site, Gustilo-Anderson classification, shock after injury, type and size of the flap, and time from injury to flap coverage were recorded. A logistic regression model was used to analyze the correlations between flap necrosis and possible risk factors.

Results

Of the 244 flaps, 32 suffered from partial or total necrosis, and 212 completely survived. Univariate analysis showed that age, smoking history, soft tissue defect site, and time from injury to flap coverage were significantly correlated with flap necrosis (p ≤ 0.2). Multivariate logistic regression analysis showed that moderate-to-severe smoking history (p < 0.001, odds ratio [OR] = 10.259, 95% confidence interval [CI] = 2.886–36.468), proximal leg defect (p = 0.006, OR = 7.095, 95% CI = 1.731–29.089), and time from injury to flap coverage >7 days (p = 0.003, OR = 12.351, 95% CI = 2.343–65.099) were statistically significant risk factors for flap necrosis (p < 0.05), and age was excluded (p = 0.666; p = 0.924).

Conclusion

The risk of flap necrosis was significantly increased when the soft tissue defect was located in the proximal leg, the time from injury to flap coverage was >7 days, and the patient had a moderate-to-severe smoking history. These three risk factors have an increased influence on flap necrosis and have guiding significance in predicting flap prognosis.     

Does iliosacral screw removal reduce postoperative pain in unstable pelvic fracture patients? A matched prospective cohort study

BackgroundTo compare pain and function in patients with unstable posterior pelvic fractures stabilized with posterior fixation who undergo iliosacral screw removal versus those who retain their iliosacral screws.MethodsA prospective observational cohort study identified 59 patients who reported pain at least 4 months after iliosacral screw fixation of an unstable posterior pelvic ring fracture from 2015–2019. The primary intervention was iliosacral screw removal versus a matched iliosacral screw retention control group. Patient-reported pain was measured with the 10-point Brief Pain Inventory, and patient-reported function was measured with the Majeed Pelvic Outcome Score. Both measured within 6 months of the intervention.ResultsBefore iliosacral screw removal, the mean pain was 4.7 (SD, 3.0) compared with 4.7 (SD, 3.0) in the matched control group. Following iliosacral screw removal, the average pain in the screw removal group was 3.7 (SD, 2.7) and 3.3 (SD, 2.5) in the matched control group. We found no evidence that iliosacral screw removal reduced pain in this population (mean difference, 0.2 points; 95% CI, -1.0 to 1.5; p = 0.71). In addition, the improvement in function after iliosacral screw removal was not statistically indistinguishable from zero (mean difference, 3.1 points; 95% CI, -4.6 to 10.9; p = 0.42).ConclusionsThe results suggest that iliosacral screw removal offers no significant pelvic pain or function benefit when compared with a matched control group. Surgeons should consider these data when managing patients with pelvic pain who are candidates for iliosacral screw removal.     

Comparison of the risk of breakage of two kinds of sacroiliac screws in the treatment of bilateral sacral fractures

Purpose

This study aimed at comparing the risk of breakage of lengthened sacroiliac screw and ordinary sacroiliac screw for the treatment of bilateral vertical sacral fractures to provide reference for clinical application.

Methods

A finite element model of type C pelvic ring injury (bilateral type Denis II fracture of sacrum) was produced. The bilateral sacral fractures were fixed with lengthened sacroiliac screw and ordinary sacroiliac screw in seven types of models, respectively. The maximal Von Mises stresses and stress distribution of the two kinds of screws in the case of standing on both feet were measured and compared.

Results

(1) Whether in lengthened sacroiliac screw or ordinary sacroiliac screw, the maximal Von Mises stress of screw fixation only in S1 segment is the largest, and the maximal Von Mises stress of screw fixation only in S2 segment is minor, and the maximal Von Mises stress of screw fixation in S1 and S2 segments, respectively, is the least. (2) When S1 and S2 were both fixed with ordinary screws, the maximal Von Mises stress of screw in S1 segment is larger than that of S2. When S1 and S2 were both fixed with lengthened screws, the maximal Von Mises stress of screw in S1 segment is similar to that of S2. (3) The maximal Von Mises stresses of bilateral symmetrical screws are similar. (4) When only S1 was fixed, the maximal Von Mises stress of lengthened screw is less than that of ordinary screw. When only S2 was fixed, the maximal Von Mises stress of lengthened screw is larger than that of ordinary screw. When S1 and S2 were both fixed, the maximal Von Mises stress of lengthened screw is slightly less than that of ordinary screw. (5) Whether in lengthened screw or ordinary screw, the stress concentrations all exhibited at the regions of screws corresponding to the sacral fracture regions and the part between sacral bilateral fracture lines. Compared with ordinary screw, the stress distribution in lengthened screw is more homogeneous. Whether in lengthened screw or ordinary screw, the stress distribution of only one sacral segment fixation is more concentrated than that of two sacral segments’ fixation. When S1 and S2 were both fixed, the stress distribution of upper screw is more concentrated and that of lower screw is more homogeneous.

Conclusion

In a finite elements simulated type C pelvic ring disruption (bilateral type Denis II sacral fracture), the breakage risk of screws fixed in double-segment bilaterally symmetrically is low, and the breakage risk of screws fixed in S2 segment is lower than that of S1 segment. The bilaterally symmetrical screw fixation in double-segment is strongly recommended to reduce the breakage risk of screws. In addition, the breakage risk of lengthened screws is lower than that of ordinary screws except when screws are fixed in only S2 segment, which merits attention.     

Prospective comparative study between straight and curved probe for pedicle screw insertion

Purpose

To evaluate difference in accuracy of pedicle screw insertion in thoracic and lumbosacral spine using a straight pedicle probe vis-à-vis a curved one.

Methods

Prospective, comparative, non-randomized, single-blind study. Straight and curved pedicle probes used on opposite sides of same vertebra in patients undergoing thoracolumbar pedicle screw fixation for various indications. Postoperative blinded evaluation for pedicle breaches done with a CT scan. Pedicle breaches graded as grade 0: no breach, grade 1: <2 mm, grade 2: 2–4 mm and grade 3: >4 mm breach.

Results

After appropriate statistical power analysis, 300 screws inserted in 59 patients from T4–L5 levels. No significant differences noted between the two probes in terms of screw length [two-tailed p = 0.16]; grade 0 screws [two-tailed p = 0.49] or screws with grade 2/3 breaches [two-tailed  p = 0.68]. With the right-hand-dominant operating-surgeon standing to left of patient during surgery, no difference noted between the two probes for either the right or left-side pedicle screw insertion [two-tailed p = 1]. Repeating these tests in the subset of thoracic pedicle screws too, revealed no significant difference.

Conclusions

No significant difference in outcome of pedicle screw insertion with either a straight or a curved pedicle probe.     

骶髂关节空心钉内固定导向器的研制及临床应用

目的 自行设计并研制一种骶骼关节空心钉内固定导向器,以期提高S1椎弓根空心钉置入的成功率及置入质量。方法 自行设计并研制的骶髂关节空心钉内固定导向器由带有测量长度的定位器、带有角度刻度表的水平面S1椎弓根空心钉置入角（TSA）、矢状面置入角(SSA)调节器及固定螺丝等组成。2006年6月至2009年10月共收治15例不稳定型骨盆骨折累及骶髂关节者,男6例,女9例;年龄19 ～ 60岁,平均45.6岁。不稳定型骨盆骨折经骶髂关节韧带3例,经骶骨Ⅰ区5例,累及骶骨Ⅱ区5例,累及骶骨Ⅲ区2例。15例患者均采用骶髂关节空心钉内固定导向器引导术中空心钉的操作,共置入18枚空心钉。结果 术后CT及X线片示18枚空心钉置入位置准确,与术前设计相比,具有相同或相近的TSA及SSA。结论 骶骼关节空心钉内固定导向器设计合理,使用方便,能提高S1椎弓根空心钉置入的准确性及置入质量,且可显著减少C型臂X线机的透视次数。     

Different Lengths of Percutaneous Transverse Iliosacral Screw in Geometric Osseous Fixation Pathway: A Finite-Element Analysis

ObjectiveTo evaluate the biomechanical performances of the sacroiliac screw fixation of the first sacral vertebra with different lengths of screws using the Finite-Element Method.MethodsFirst, pelvic CT images were generated from a healthy volunteer, and multislice sagittal views were produced to determine the axis for the first sacral vertebra geometric osseous fixation pathway (GOFP). Subsequently, according to the geometric size and mechanical parameters of the iliosacral screw, the screw models with the same diameter of 7.3 mm and different lengths of 80 mm, 90 mm, 100 mm, 110 mm, 120 mm, 130 mm and 140 mm were built. Then the seven screws were assembled with the pelvic model. The maximum von Mises stress and the shape variables were evaluated for the pelvis and the screws.ResultsResults are shown for the pelvic and GOFP screw, respectively. The simulation results show that the maximum von Mises stress in the cortex of the pelvic ring of the pelvis with the 130-mm length screw is the lowest among the pelvic models with different screws. Moreover, the peak displacement of the pelvis with the 130-mm length screw is the smallest. These results indicate that under the standing condition, a 130-mm length screw can decrease the stress concentration and result in a more effective transfer of stress within the reconstructed pelvis. In addition, the displacement of the screw with a 130-mm length is the smallest among all the considered screws. The peak von Mises stresses in the 130-mm length screw and the cortex are still within a low and elastic range below the yielding strengths of the materials.ConclusionThrough the finite element analysis, the GOFP can be used as a safe and effective way for iliosacral screw fixation. The optimal length of the screw may be 130 mm length.