Sacroiliac Screw Fixation Research Articles

Projective invariant biplanar registration of a compact modular orthopaedic robot

This paper presents a compact orthopedic robot designed with modular concept. The layout of the modular configuration is adaptive to various conditions such as surgical workspace and targeting path. A biplanar algorithm is adopted for the mapping from the fluoroscopic image to the robot, while the former affine based method is satisfactory only when the projection rays are basically perpendicular to the reference coordinate planes. This paper introduces the area cross-ratio as a projective invariant to improve the registration accuracy for non-orthogonal orientations, so that the robotic system could be applied to more orthopedic procedures under various C-Arm orientation conditions. The system configurations for femoral neck screw and sacroiliac screw fixation are presented. The accuracy of the robotic system and its efficacy for the two typical applications are validated by experiments.

Sacroiliac screw fixation: A mini review of surgical technique.

The sacral percutaneous fixation has many advantages but can be associated with a significant exposure to X-ray radiation. Currently, sacroiliac screw fixation represents the only minimally invasive technique to stabilize the posterior pelvic ring. It is a technique that should be used by experienced surgeons. We present a practical review of important aspects of this technique.

Comparaison mécanique entre vis sacro-iliaques longues ou courtes pour l’ostéosynthèse de fractures du sacrum : analyse par éléments finis

Summary Objective To compare the stability of lengthened sacroiliac screw and standard sacroiliac screw for the treatment of unilateral vertical sacral fractures; to provide reference for clinical applications. Methods A finite element model of Tile type C pelvic ring injury (unilateral Denis type II fracture of the sacrum) was produced. The unilateral sacral fractures were fixed with lengthened sacroiliac screw and sacroiliac screw in six different types of models respectively. The translation and angle displacement of the superior surface of the sacrum (in standing position on both feet) were measured and compared. Results The stability of one lengthened sacroiliac screw fixation in S1 or S2 segment is superior to that of one sacroiliac screw fixation in the same sacral segment. The stability of one lengthened sacroiliac screw fixation in S1 and S2 segments respectively is superior to that of one sacroiliac screw fixation in S1 and S2 segments respectively. The stability of one lengthened sacroiliac screw fixation in S1 and S2 segments respectively is superior to that of one lengthened sacroiliac screw fixation in S1 or S2 segment. The stability of one sacroiliac screw fixation in S1 and S2 segments respectively is markedly superior to that of one sacroiliac screw fixation in S1 or S2 segment. The vertical and rotational stability of lengthened sacroiliac screw fixation and sacroiliac screw fixation in S2 is superior to that of S1. Conclusion In a finite element model of type C pelvic ring disruption, S1 and S2 lengthened sacroiliac screws should be utilized for the fixation as regularly as possible and the most stable fixation is the combination of the lengthened sacroiliac screws of S1 and S2 segments. Even if lengthened sacroiliac screws cannot be systematically used due to specific conditions, one sacroiliac screw fixation in S1 and S2 segments respectively is recommended. No matter which kind of sacroiliac screw is used, if only one screw can be implanted, the fixation in S2 segment is more recommended than that in S1. Level of evidence Experimental study Level III.

The influence of sacral morphology on the existence of secure S1 and S2 transverse bone corridors for iliosacroiliac screw fixation

Sacroiliac (SI) screw fixation for unstable pelvic fractures stands out as the only minimally invasive method among all other ORIF procedures. A strictly transverse screw trajectory is needed for central or bilateral fracture patterns up to a complete iliosacroiliac fixation. However, secure screw insertion is aggravated by a narrow sacroiliac bone stock. This study investigates the influence of a highly variable sacral morphology to the existence of S1 and S2 transverse corridors.The analysis contained in this study is based on 125 CT datasets of intact human pelvises. First, sacral dysplasia was identified using the “lateral sacral triangle” method in a lateral 3-D semi-transparent pelvic view. Second, 3-D corridors for a 7.3mm screw in the upper two sacral levels were visualised using a proprietary IT workflow of custom-made programme scripts based on the Amira®-software. Shape-describing measurement variables were calculated as output variables.The results show a significant linear correlation between ratioT and the screw-limiting S1 isthmus height (Pearson coefficient of 0.84). A boundary ratio of 1.5 represented a positive predictive value of 96% for the existence of a transverse S1-corridor for at least one 7.3mm screw. In 100 out of 125 pelvises (80%), a sufficient S1 corridor existed, whereas in 124 specimens (99%), an S2 corridor was found. Statistics revealed significantly larger S1 and S2 corridors in males compared to females (p<0.05). However, no gender-related differences were observed for clinically relevant numbers of up to 3 screws in S1 and 1 screw in S2.The expanse of the S1 corridor is highly influenced by the dimensions of the dysplastic elevated upper sacrum, whereas the S2 corridor is not affected. Hence, in dysplastic pelvises, sacroiliac screw insertion should be recommended into the 2nd sacral segment. Our IT workflow for the automatic computation of 3-D corridors may assist in surgical pre-operative planning. Furthermore, the workflow could be implemented in computer-assisted surgery applications involving pelvic trauma.

Mechanical comparison between lengthened and short sacroiliac screws in sacral fracture fixation: A finite element analysis

To compare the stability of lengthened sacroiliac screw and standard sacroiliac screw for the treatment of unilateral vertical sacral fractures; to provide reference for clinical applications. A finite element model of Tile type C pelvic ring injury (unilateral Denis type II fracture of the sacrum) was produced. The unilateral sacral fractures were fixed with lengthened sacroiliac screw and sacroiliac screw in six different types of models respectively. The translation and angle displacement of the superior surface of the sacrum (in standing position on both feet) were measured and compared. The stability of one lengthened sacroiliac screw fixation in S1 or S2 segment is superior to that of one sacroiliac screw fixation in the same sacral segment. The stability of one lengthened sacroiliac screw fixation in S1 and S2 segments respectively is superior to that of one sacroiliac screw fixation in S1 and S2 segments respectively. The stability of one lengthened sacroiliac screw fixation in S1 and S2 segments respectively is superior to that of one lengthened sacroiliac screw fixation in S1 or S2 segment. The stability of one sacroiliac screw fixation in S1 and S2 segments respectively is markedly superior to that of one sacroiliac screw fixation in S1 or S2 segment. The vertical and rotational stability of lengthened sacroiliac screw fixation and sacroiliac screw fixation in S2 is superior to that of S1. In a finite element model of type C pelvic ring disruption, S1 and S2 lengthened sacroiliac screws should be utilized for the fixation as regularly as possible and the most stable fixation is the combination of the lengthened sacroiliac screws of S1 and S2 segments. Even if lengthened sacroiliac screws cannot be systematically used due to specific conditions, one sacroiliac screw fixation in S1 and S2 segments respectively is recommended. No matter which kind of sacroiliac screw is used, if only one screw can be implanted, the fixation in S2 segment is more recommended than that in S1. Experimental study Level III.

CT-based 3-D visualisation of secure bone corridors and optimal trajectories for sacroiliac screws

Sacroiliac screw (SI) fixation represents the only minimally invasive method to stabilise unstable injuries of the posterior pelvic ring. However, it is technically demanding. The narrow sacral proportions and a high inter-individual shape variability places adjacent neurovascular structures at potential risk. In this study a CT-based virtual analysis of the iliosacral anatomy in the human pelvis was performed to visualise and analyse 3-D bone corridors for the safe placement of SI-screws in the first sacral segment.Computer-aided calculation of 3-D transverse and general SI-corridors as a sum of all inner-bony 7.3-mm screw positions was done with custom-made software algorithms based on CT-scans of intact human pelvises. Radiomorphometric analysis of 11 CT-DICOM datasets using the software Amira 4.2. Optimal screw tracks allowing the greatest safety distance to the cortex were computed. Corridor geometry and optimal tracks were visualised; measurement data were calculated.A transverse corridor existed in 10 pelvises. In one dysmorphic pelvis, the pedicular height at the level of the 1st neural foramina came below the critical distance of 7.3mm defined by the outer screw diameter. The mean corridor volume was 45.2cm3, with a length of 14.9cm. The oval cross-section measured 2.8cm2. The diameter of the optimal screw pathway with the greatest safety distance was 14.2mm. A double cone-shaped general corridor for screw penetration up to the centre of the S1-body was calculated bilaterally for every pelvis. The mean volume was 120.6cm3 for the left side and 115.8cm3 for the right side. The iliac entry area measured 49.1 versus 46.0cm2. Optimal screw tracks were calculated in terms of projected inlet and outlet angles. Multiple optimal screw positions existed for each pelvis.The described method allows an automated 3-D analysis with regard to secure SI-screw corridors even with a high number of CT-datasets. Corridor visualisation and calculation of optimal screw tracks trains the visual thinking of the surgeon and can improve pre-operative planning. Prospectively, the introduced method can be implemented in computer-assisted surgery applications involving pelvic trauma.

Biomechanical Study of 4-hole Pubic Symphyseal Plating: Locked Versus Unlocked Constructs

To the authors' knowledge, no published studies have examined the use of locking plates on injuries of the anterior pelvic ring. The purpose of this study was to determine whether locked plates provide enhanced stability in the treatment of pubic symphyseal disruptions. Completely unstable pelvic injuries were simulated in pelvic Sawbones (model 1301; Pacific Research Laboratories, Vashon, Washington) and 2 different fixation constructs used for anterior fixation (4-hole, 3.5-mm pubic symphysis plate with all locked or all unlocked screws). Adjunctive sacroiliac screw fixation with a single 7.3-mm screw placed into S1 was used in all specimens. Specimens were analyzed for motion at the pubic symphysis and sacroiliac joints using a Material Testing System (MTS Systems Corporation, Eden Prairie, Minnesota). Each specimen was subjected to compressive loading in a single-limb stance. Side loading was also examined. The main outcome measurement was motion at the pubic symphysis and sacroiliac joints and overall construct stiffness. No significant difference existed in overall construct stiffness between the 2 methods of pubic symphysis fixation. The motions at the pubic symphysis or injured sacroiliac joints were not significantly different. In addition, motion at the pubic symphysis joint with lateral load was not improved with a locking construct.No significant difference existed between 4-hole locked or unlocked constructs used for fixation of the pubic symphysis. No apparent advantage of locking screws exists for disruptions of the pubic symphysis, and recent reports have questioned the possibility of catastrophic failure.

Parameters of lengthened sacroiliac screw fixation: a radiological anatomy study

To provide the anatomical basis for the feasibility and clinical practice of lengthened sacroiliac screw fixation, by measuring various related indicators of the safe insertion regions of S1 and S2 lengthened sacroiliac screws. A total of 66 healthy pelvises of adults were scanned by 64-slice spiral CT and the length, width and height of the safe insertion regions for S1 and S2 lengthened sacroiliac screw were measured. The safe screw entrance point locations were described with a quantitative method. The indicators were recorded by descriptive statistics and the statistics of left and right sides, segments of S1 and S2, and different layers (including top, middle and bottom parts) of S1 and S2 were compared. The lengths of ilium within the safe insertion regions for lengthened screws are more than 16 mm. The width and height of the safe insertion region of S1 and S2 are almost all more than 7.3 mm. Generally, the width and height of S1 are larger than those of S2. The reference ranges of the best/safest entrance point locations of lengthened sacroiliac screws are as follows-S1: 42.21-63.69 mm in front of posterior superior iliac spine, 32.77-53.75 mm above the highest point of the greater sciatic notch; S2: 22.68-54.28 mm in front of posterior superior iliac spine, 14.06-33.70 mm above the highest point of the greater sciatic notch. (1) There is anatomical feasibility for the placements of S1 and S2 lengthened sacroiliac screws. (2) φ 7.3-mm partial thread cannulated screw (thread length 16 mm) and φ 6.5-mm partial thread cancellous screw(thread length 16 mm) can be used as lengthened sacroiliac lag screw. (3) The safe insertion space of S1 is larger than that of S2. (4) There is safe space for placement of at least one piece of lengthened sacroiliac screw in both S1 and S2. (5) The best/safest entrance points of S1 and S2 can be approximately located with anatomical landmarks.

Intraoperative fluoroscopy in percutaneous sacroiliac screw fixation based on anatomic measurement and digital reconstructed CT data

Objective To explore the intraoperative fluoroscopy in percutaneous sacroiliac screw fixation based on anatomic measurement and digital reconstructed CT data. Methods The CT data of the pelvis at prostration were collected for 3D reconstruction of the pelvic models from 30 patients with injury to the pelvis or acetabulum.Then the anatomical boundaries of the safe zone of sacroiliac screw insertion were marked on the 3D models,including the upper,front and back cortex boundaries of S1 vertebra,the front and bottom cortex boundaries of sacral foramen area,and the sacral alar slope. The angles between these anatomical boundaries and the pelvic baseline were measured on the sagittal plane.The digital reconstructed radiology (DRR) was applied to form the inlet,outlet and lateral images of fluoroscopy.The standard protocol to acquire accurate intraoperative images was analyzed by characterization of important anatomic landmarks.Results The angles between the upper,front and back cortex boundaries of S1 vertebra and the baseline (αl,α2,α3) were respectively 37.7°± 8.6°(from 23.2°to 50.8°),22.9° ± 6.7° (from 13.1° to 32.0°),41.9°± 6.8° (from 33.0°to 54.8°).The angles between the front and bottom cortex boundaries of sacral foramen area and the baseline (α4,α5) were 37.0°± 12.0° (from 19.9° to 63.1°) and 38.8°± 8.0° (from 25.7°to 54.6°).The angle between the alar slope and the baseline (α6) was 82.4°± 13.0°(from 70.3°to117.3°).The characteristic manifestations of important anatomic landmarks were observed in the simulated fluoroscopy images. Conclusions It is recommended that the projecting angles in the inlet and outlet views should be decided according to the specific data of each patient.Because the alar slope can not be clearly identified in the outlet view due to its large inclination,the position of screw insertion should be verified in the lateral view to prevent the screw from penetrating the slope to hurt the L5 nerve and iliac vessels. Key words: Bone nails; Pelvis; Tomography, X-ray computed; Image processing, computer-assisted; Sacroiliac joint

Implantatentfernung nach Beckenringfraktur

Pelvic ring fractures are considered as rare injuries. Minimally invasive sacroiliac screw fixation has been used increasingly in recent years as an operative strategy for the treatment of these injuries, if the dorsal pelvic ring needed to be addressed. Treatment options for the anterior pelvic ring comprise plates, screws or external fixation. Based on the limited number of publications on this subject and our own experience with 80 patients who suffered pelvic ring B- or C-type injuries during a period of 8 years we are able to show that the indication for hardware removal in the pelvic ring should be strictly defined. In some cases like external fixation, implant-associated infection, malpositioning, allergic implant reaction, critical soft tissue covering, palpable hardware and consolidated juvenile fractures implant removal is certainly indicated. In patients without symptoms and in patients with trauma-associated symptoms which are not definitely associated with the hardware, the removal should be only indicated after thorough consideration of the risks versus the benefits and additionally by taking the initial injury pattern into account. If despite all these objections the hardware removal has been indicated it should always be considered that hardware removal may be challenging with several possible severe complications.

Comparison of stability of two kinds of sacro-iliac screws in the fixation of bilateral sacral fractures in a finite element model

ObjectiveTo compare the stability of lengthened sacro-iliac screw and sacro-iliac screw for the treatment of bilateral vertical sacral fractures to provide reference for clinical application. MethodsA finite element model of Tile C pelvic ring injury (bilateral type Denis II fracture of sacrum) was produced. (Tile and Denis are surgeons, who put forward the classifications of pelvic ring injury and sacral fracture respectively.) The bilateral sacral fractures were fixed with a lengthened sacro-iliac screw and a sacro-iliac screw in seven types of models, respectively. The translation and angular displacement of the superior surface of the sacrum in the case of standing on both feet were measured and compared. ResultsThe stability of one lengthened sacro-iliac screw fixation in the S1 or S2 segment is superior to that of two bidirectional sacro-iliac screws in the same sacral segment; the stability of one lengthened sacro-iliac screw fixation in S1 and S2 segments, respectively, is superior to that of two bidirectional sacro-iliac screw fixation in S1 and S2 segments, respectively; the stability of one lengthened sacro-iliac screw fixation in S1 and S2 segments, respectively, is superior to that of one lengthened sacro-iliac screw fixation in the S1 or S2 segment; the stability of two bidirectional sacro-iliac screw fixation in S1 and S2 segments, respectively, is markedly superior to that of two bidirectional sacro-iliac screw fixation in the S1 or S2 segment and is also markedly superior to that of one sacro-iliac screw fixation in the S1 segment and one sacro-iliac screw fixation in the S2 segment; the vertical stability of the lengthened sacro-iliac screw or the sacro-iliac screw fixation in S2 is superior to that of S1. The rotational stability of the lengthened sacro-iliac screw or sacro-iliac screw fixation in S1 is superior to that of S2. ConclusionS1 and S2 lengthened sacro-iliac screws should be used for the fixation in bilateral sacral fractures of Tile C pelvic ring injury as far as possible and the most stable fixation is the combination of the lengthened sacro-iliac screws of S1 and S2 segments. Even if lengthened sacro-iliac screws cannot be used due to limited conditions, two bidirectional sacro-iliac screw fixation in S1 and S2 segments, respectively, is recommended. No matter which kind of sacro-iliac screw is applied, the fixation combination of S1 and S2 segments is strongly recommended to maximise the stability of the pelvic posterior ring.

Stabilization of fatigue fractures of the dorsal pelvis with a trans-sacral bar. Operative technique and outcome

IntroductionDue to ageing of our population the number of fatigue fractures of the pelvic ring is steadily growing. These fractures are often treated with bed rest but may result in a disabling immobility with severe pain. An operative treatment is an option in these cases. The aim of operative treatment is bony healing obtained by stable fixation giving back to the patient's previous mobility. Optimal surgical treatment is currently under debate. Sacroiliac screw fixation and sacroplasty are used for stabilization of the dorsal pelvis. Due to the technique and the low density of spongious sacral bone, no or only low compression in the fracture site is obtained, which may inhibit bony healing. The trans-sacral bar compression osteosynthesis is presented as an alternative procedure. We present the outcome of 11 patients, who were treated with this method. MethodsThe patient is placed in prone position on the operation table. Under image intensifier control, a 5mm threaded sacral bar is inserted through the body of S1 from the left to the right dorsal ilium. Nuts are placed over the bar achieving fracture compression. When anterior pelvic instability is present, an anterior osteosynthesis is also performed. Clinical and radiological outcome were evaluated one year after index surgery with different scoring systems. ResultsEleven patients (9 F and 2 M) were treated between 2005 and 2010. The mean age of the patients was 73 years at time of operation. There were no mechanical complications. Postoperatively there was a temporary nerve palsy of L5 in one case. The mean follow-up was 14 months. In all patients, a bony healing of the dorsal pelvic ring was achieved. Seven patients showed a major clinical improvement, in four patients a moderate. ConclusionsTrans-sacral bar osteosynthesis is a promising method for stabilization of fatigue fractures of the pelvic ring. Only with this method, a high interfragmentary compression is achieved, independent of the quality of the spongious bone of the sacral body.

Minimally invasive stabilisation of posterior pelvic-ring instabilities with a transiliac locked compression plate

Sacroiliac screw fixation is the method of choice for the definitive treatment of unstable posterior pelvic-ring injuries; however, this technique is demanding and associated with a high risk of iatrogenic neurovascular damage. This study evaluates whether minimally invasive transiliac locked compression plate stabilisation may be an alternative to sacroiliac screw fixation in unstable posterior pelvic-ring injuries. We performed a retrospective analysis of patients with unstable pelvic-ring injuries treated with a transiliac locked compression plate at a level I trauma centre. Outcome evaluation was assessed using the Pelvic Outcome Score and analysis of complications, intraoperative fluoroscopic time, and duration of the surgical procedure. Twenty-one patients were available for follow-up after an average of 30 months. The main findings were as follows: Overall outcome for the Pelvic Outcome Score was excellent in 47.6% (ten patients), good in 19% (four patients), fair in 28.6% (six patients), and poor in 4.8% (one patient). Average operation time was 101 min and intraoperative fluoroscopic time averaged 74.2 s. No iatrogenic neurovascular injuries were observed. Minimally invasive transiliac locked compression plate stabilisation may be a good alternative to sacral screw fixation because it is quick, safe and associated with a good functional outcome.

Prevalence of sacral dysmorphia in a prospective trauma population: Implications for a "safe" surgical corridor for sacro-iliac screw placement

BackgroundPercutaneous sacro-iliac (SI) screw fixation represents a widely used technique in the management of unstable posterior pelvic ring injuries and sacral fractures. The misplacement of SI-screws under fluoroscopic guidance represents a critical complication for these patients. This study was designed to determine the prevalence of sacral dysmorphia and the radiographic anatomy of surgical S1 and S2 corridors in a representative trauma population.MethodsProspective observational cohort study on a consecutive series of 344 skeletally mature trauma patients of both genders enrolled between January 1, 2007, to September 30, 2007, at a single academic level 1 trauma center. Inclusion criteria included a pelvic CT scan as part of the initial diagnostic trauma work-up. The prevalence of sacral dysmorphia was determined by plain radiographic pelvic films and CT scan analysis. The anatomy of sacral corridors was analyzed on 3 mm reconstruction sections derived from multislice CT scan, in the axial, coronal, and sagittal plane. "Safe" potential surgical corridors at S1 and S2 were calculated based on these measurements.ResultsRadiographic evidence of sacral dysmorphia was detected in 49 patients (14.5%). The prevalence of sacral dysmorphia was not significantly different between male and female patients (12.2% vs. 19.2%; P = 0.069). In contrast, significant gender-related differences were detected with regard to radiographic analysis of surgical corridors for SI-screw placement, with female trauma patients (n = 99) having significantly narrower corridors at S1 and S2 in all evaluated planes (axial, coronal, sagittal), compared to male counterparts (n = 245; P < 0.01). In addition, the mean S2 body height was higher in dysmorphic compared to normal sacra, albeit without statistical significance (P = 0.06), implying S2 as a safe surgical corridor of choice in patients with sacral dysmorphia.ConclusionsThese findings emphasize a high prevalence of sacral dysmorphia in a representative trauma population and imply a higher risk of SI-screw misplacement in female patients. Preoperative planning for percutaneous SI-screw fixation for unstable pelvic and sacral fractures must include a detailed CT scan analysis to determine the safety of surgical corridors.

Retrospective Review of Lumbosacral Dissociations in Blast Injuries

Retrospective review of medical records and radiographs. We assessed the clinical outcomes of lumbosacral dissociation (LSD) after traumatic, combat-related injuries, and to review our management of these distinct injuries and report our preliminary follow-up. LSD injuries are an anatomic separation of the pelvis from the spinal column, and are the result of high-energy trauma. A relative increase in these injuries has been seen in young healthy combat casualties subjected to high-energy blast trauma. We performed a retrospective review of inpatient/outpatient medical records and radiographs for all patients treated at our institution with combat-related lumbosacral dissociations. Twenty-three patients met inclusion criteria of combat-related lumbosacral dissociations with one-year follow-up. Patients were treated as follows: no fixation (9), sacroiliac screw fixation (8), posterior spinal fusion (5) and sacral plate (1). All patients with radiographic evidence of a zone III sacral fracture, in addition to associated lumbar fractures indicating loss of the iliolumbar ligamentous complex integrity were included. In 15 patients, the sacral fracture were an H or U type zone III fracture, whereas in the remaining nine, the sacral fracture was severely comminuted and unable to classify (six open fractures). There was no difference in visual analog scale (VAS) between treatment modalities. Two open injuries had residual infections. One patient treated with an L4-ilium posterior spinal fusion with instrumentation required instrumentation removal for infection. At a mean follow-up of 1.71 years (range, 1-4.5), 11 patients (48%) still reported residual pain and the mean VAS at latest follow-up was 1.7 (range, 0-7). Operative stabilization promoted healing and earlier mobilization, but carries a high-postoperative risk of infection. Nonoperative management should be considered in patients whose comorbidities prevent safe stabilization.

Minimally Invasive Sacroiliac Fixation in Oncologic Patients With Sacral Insufficiency Fractures Using a Fluoroscopy-based Navigation System

Surgical technique article with retrospective case series. Sacral insufficiency fractures are commonly encountered in oncologic patients and constitute a cause for persistent lower back and pelvic pain. The aim of this study is to describe the modified technique of navigated percutaneous sacroiliac (SI) fixation using multiple long screws per level that cross both SI joints and engage bilateral iliac bones; furthermore to evaluate its safety and efficacy in oncologic patients with sacral insufficiency fractures. Six oncologic patients (3 male, 3 female, mean age: 58.8 y) with sacral insufficiency fractures who had undergone additional radiation therapy were operated with navigated percutaneous fixation. Two patients had failed preoperative sacroplasty and 1 had failed SI pinning. Eighteen SI screws were placed (15 at S1 level and 3 at S2). In the majority of cases the screws were long enough to engage bilateral ilium and sacrum. Additionally, 1 patient underwent percutaneous iliolumbar instrumentation and in 4 patients we performed concomitant sacroplasty or polymethylmethacrylate screw augmentation. The patients were followed for 18.8 months in average (range: 12-30 mo). Outcome was assessed using the Karnofsky Performance Status score (KPS), pain scale (0-10) and detailed neurologic examination. In 1 case, a revision of a screw was required due to radiculopathy. There was no perioperative morbidity or mortality. No hardware failure was encountered. There was significant improvement in KPS (P=0.04) and pain levels (P=0.02). These preliminary data suggest that navigated percutaneous SI screw fixation is a safe and effective intervention in terms of pain control and performance status improvement in oncologic patients with sacral insufficiency fractures. For optimal fixation, multiple long screws that engage both iliac bones may be inserted through the S1 level in a safe manner. The technique may be combined with sacroplasty or closed posterior instrumentation to augment the screw fixation. Further investigation is needed to compare this technique with other treatment modalities.

An Anatomical Update on the Morphologic Variations of S1 and S2

Although percutaneous fixation with iliosacral screws has been shown to be a safe and reproducible method for sacroiliac dislocation and sacral fractures, it is a technically demanding technique, and one of its contraindications is sacral anatomical variations and dysmorphism. The incidence and pattern of S1 and S2 anatomical variations were evaluated in 61 patients (35 women and 26 men) using magnetic resonance imaging of the sacrum in an attempt to explore the possible existence of groups of individuals in whom percutaneous sacroiliac fixation is difficult due to local anatomy. S1 and S2 dimensions in both the transverse and coronal planes were recorded and evaluated. In each individual, S1 and S2 dimensions both in the coronal and transverse planes were proportional, with S2 dimensions being 80% of those of S1 on average. Patients were separated into 4 groups based on the S1 and S2 body size and the asymmetry of dimensions in the transverse and coronal planes. In 48 patients (78.6%), dimensions in both planes were symmetrical despite the varying size of the S1 and S2 body. In 2 patients (3.3%) there was a combination of large transverse plane and small coronal plane dimensions, with large S1 and S2 body size. In 9 patients (14.8%), coronal plane dimensions were disproportionately smaller compared to those of the transverse plane, with a varying size of S1 and S2 body making effective sacroiliac screw insertion a difficult task. Thus, a preoperative imaging study, preferably computed tomography scan, of S1 and S2 body size and coronal plane dimensions and an intraoperative fluoroscopic control of S1 and S2 dimensions on the coronal plane are suggested for safe sacroiliac screw fixation.

The lateral sacral triangle—A decision support for secure transverse sacroiliac screw insertion

Sacroiliac (SI) screw fixation represents an effective method to stabilise pelvic injuries. However, to date neither reliable radiological landmarks nor effective anatomical classifications of the sacrum exist. This study investigates the influence of variability in sacral shape on secure transverse SI-screw positioning. Furthermore, consistent correlations of these anatomical conditions are analysed with respect to standard planar pelvic views. For shape analysis, 80 human computed tomography data sets were segmented with the software Amira 4.2 to obtain 3D reconstructions. We identified anatomical conditions (ACs) according to the extent of the effect on the bony screw pathway. Subsequently, the pelvis was spatially aligned using representative bone protuberances in order to create standard Matta projections. In each view, the ACs were described in terms of distance from bone landmarks. Three-dimensional shape analysis revealed the height of the pedicular isthmus (PH) as the limiting variable for secure screw insertion. The lateral and outlet views allowed an orthogonal projection of PH. In the lateral view, the ratio of the lateral sacral triangle framed by the S1 body height and width showed a high correlation to PH ( p = 0.0001). A boundary ratio of 1.5 represented a reliable variable to determine whether or not a screw can be inserted (positive predictive value: 97%). In the outlet view, the distance between the S1 endplate and the SI joint top level (EJ) strongly correlated with PH ( p = 0.0001). With EJ ≤ 0 mm, screw insertion was possible in all cases (100%). SI-screw insertion requires a well-planned procedure. Orientation of the sacral pedicle is of extreme relevance. A narrow sacroiliac channel and high sacral shape variability limit secure screw placement. However, no determining parameters exist, allowing accurate prediction of secure screw insertion based on X-rays or fluoroscopy. The lateral sacral triangle in the lateral view represents a simple and accurate preoperative method of support for the surgeon's decision to undertake this procedure. No additional technical effort is necessary. A boundary ratio of 1.5 predicts a sufficient bone stock for at least one 7.3 mm screw. Furthermore, the evaluation of the outlet projection can be used to assess the safety of the operation. Basically, a preoperative lateral pelvic image should be mandatory.

Minimal-invasive Stabilisierung einer bilateralen Sakrumfraktur mit lumbopelviner Dissoziation

This case report describes our technique of percutaneous sacroiliac screw fixation of a bilateral sacral fracture with spinopelvic dissociation. It is based on the description of an iliosacroiliac bony corridor delimited by the following landmarks: the sacral ala in a superior-anterior direction, the first sacral foramen on both sides in an inferior-posterior direction, and the sacral channel posteriorly. The described operating method, which uses a 6.5-mm parallel drill sleeve, allows the safe and strictly transversal positioning of a 7.3-mm screw on each side with the threads interlocking. It provides a separate and fracture-adapted compression of the screws. The interlocking SI screw threads increase the pull-out strength. Operating time and radiation dose can be reduced significantly by this method.

Die supraacetabuläre Beckenzwinge

The anatomic region on the lateral cortex of the ileum, where a palpable groove is formed by angulations of the lateral cortex of the iliac wing, is recommended as the insertion point for the pelvic emergency clamp by many authors. In our opinion this technique often leads to an incomplete closure of the anterior pelvic ring as well as to bacterial contamination of the access for the sacroiliac joint screw fixation and is accompanied by a risk for nerve and vessel injuries. To reduce these risks the pelvic clamp was placed at a supra-acetabular location. The goal of our study was to report on our experiences with the supra-acetabular position of the pelvic emergency clamp and to compare our results with the current literature. From September 1998 to February 2006 the pelvic emergency clamp was applied in 15 polytraumatized patients (9 male, 6 female), with a mean age of 46 years (19-93) and a mean injury severity score (ISS) of 40 points (25-66) with mechanically and hemodynamically unstable pelvic ring fractures. According to the AO classification the injury pattern was type B2 in four cases, type B3 in one case, type C1 in seven cases, type C2 in two cases and type C3 in one case. The pelvic clamp was percutaneously applied 2-3 cm cranial to the acetabular roof. The duration from hospital admission until the pelvic emergency clamp was applied amounted to an average of 54 min (15-150); the procedure itself was performed in all cases in less than 15 min. The mean Hb at arrival in the emergency department was 7.4 (2.4-13.8) mg/dl and the mean systolic blood pressure 69 (0-130) mmHg. In 14 patients a complete closure of the anterior and posterior pelvic ring could be achieved; in 1 patient an overcompression of the anterior pelvic ring was observed. Four patients died due to massive bleeding. Three patients with isolated pelvic ring fractures became hemodynamically stable within 20 min after treatment with the supra-acetabular pelvic clamp. Nine patients needed additional emergency surgery because of intracerebral, intrathoracic or intra-abdominal injuries. On average in the first 6 h, 36.7 (9-175) units of erythrocyte concentrates and 34.5 (4-200) units of fresh frozen plasma were transfused. The supra-acetabular pelvic clamp leads to a homogeneous force distribution to the pelvic ring and enables complete closure of the anterior and posterior pelvic ring in unstable pelvic fractures. Reduction of the intrapelvic volume and compression of the posterior pelvic ring can thus be achieved. Risks for intrapelvic perforation or injuries of vessels and nerves are low. No bacterial contamination of the access for the sacroiliac screw fixation occurs. To avoid overcompression of the unstable pelvic ring, manual or radiological control of the closure of the ventral pelvic ring is necessary.