Lateral Screw Research Articles

245. Comprehensive biomechanical profile of anterior column realignment for minimally invasive deformity correction

BACKGROUND CONTEXT To achieve clinical success in minimally invasive spinal approaches to deformity correction, the optimal construct should provide sound biomechanics without limiting lordotic correction. Anterior column realignment (ACR) is a powerful, but highly destabilizing minimally invasive technique for sagittal realignment with growing popularity; however, the biomechanics of this construct have never been previously investigated in a biomechanical study. In particular, it is unclear to what degree lateral plate fixation across the ACR construct constrains segmental lordosis and promotes improved biomechanics, nor whether supplemental rod fixation provides additional biomechanical benefit. PURPOSE The purpose of this study was to comprehensively evaluate the effect of ACR design on radiographic lordosis, range of motion (ROM) stability, and rod strain (RS) in a cadaveric model. We hypothesized that anterolateral fixation and four-rod (4R) supplementation would decrease rod strain (RS) and improve segmental stability (ROM) in a cadaveric ACR model. STUDY DESIGN/SETTING In vitro biomechanical study using human cadaveric specimens. PATIENT SAMPLE Seven fresh-frozen lumbar spine cadaveric specimens (T12–sacrum) were selected for this study (2F/5M, 52±13yrs, DEXA 1.02g/cm2). OUTCOME MEASURES Primary outcome measure of interest was maximum segmental lordosis measured using lateral radiograph. Secondary outcomes were range of motion (ROM) stability and posterior rod strain (RS) at L3/4. METHODS Standard nondestructive flexibility tests (7.5 Nm) were performed following 30° ACR at L3/4 and pedicle screw fixation from L1 to S1. First, maximum lordosis was measured after no osteotomies (G0), grade 1 (G1), and grade 2 (G2) osteotomies with either single screw lateral fixation (ACR+1XLP) or screws into both L3 and L4 (ACR+2XLP). Uni-axial strain gauges were placed midway between L3/L4 pedicle screws on the posterior surface of right rod. ROM and RS were recorded during applications of continuous dynamic loads in a 6DOF robot in flexion (FL), extension (EX), compression (C), lateral bending (LB), and axial rotation (AR). Conditions included: 1) intact, 2) intact+pedicle screws and 2 rods (PSR+2R), 3) ACR+1XLP+2R, 4) ACR+2XLP+2R, 5) ACR+1XLP+4 rods, 6) ACR+2XLP+4R. Data were analyzed using RM-ANOVA (p RESULTS Mean segmental lordosis increased from G0 (14.9°), to G1(18.7°), to G2(29.7°). There were no differences between 1XLP or 2XLP(p>.15). ACR+1XLP+2R was less stable than all other ACR conditions in FL, EX, and AR (p .48). Adding extra rods to ACR+1XLP and ACR+2XLP reduced primary rod strain in all directions of loading (p .16). There was no difference in strain between ACR+2XLP+2R and ACR+2XLP+4R (p>.48). CONCLUSIONS The ACR is a highly destabilizing procedure. For maximum stability, ACR constructs should contain either 2-screw fixation or 4 rods. Anterolateral fixation with two screws can be used without compromising the maximal achievable lordosis, but do not provide the same RS reduction as 4 rods. Combining these two techniques did not provide any additional benefit. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.

Surgicoanatomical aspect in vascular variations of the V3 segment of vertebral artery as a risk factor for C1 instrumentation

ObjectAwareness of vascular anomalies in V3 segment of vertebral artery (VA) is crucial to avoid iatrogenic injuries during surgical procedure. This study aimed to analyze the incidence of V3 segment vascular variations and demonstrate the importance of deciding the surgical strategy for C1 screw placement. MethodsPrevalence of vascular variations and morphometric measurements of the VA in the region of the craniocervical junction in 200 cases based on three-dimensional computed tomographic angiography (3D-CTA) scans were studied. ResultsThe VA has a variable course through C2 before it passes above its groove on the posterior arch of C1. Following the vascular variations of V3 segments of VA were persistent including first intersegmental artery (FIA), fenestration (FEN) of the VA, high-riding (HRVA and the posterior inferior cerebellar artery (PICA) branch originating from the C1/2 part of VA. HRVA was observed in 10.1% of patients, FIA in 1.8%, FEN in 1.3%, and PICA in 1.3%. One hundred and twenty-three (24.1%) patients were identified to have HRVA, 6% present on both sides. ConclusionThe VA with FIA and FEN were rare in this study as many as a 10% the VA present over the starting point for C1 lateral screw. With respect to the vascular anatomy of V3 and more frequent left-sided VA dominancy, standard screw insertion should be started from the right side. Routine preoperative 3D-CTA evaluation is mandatory to prevent the VA injury when C1-C2 instrumentation is planned.

Digital Anatomy to Improve Screw Insertion Techniques for Plate-Screw Fixation of the Pubic Body.

Objectives This study aims to investigate screw insertion sites on the pubic body and the safe screw insertion parameters of a plate-screw fixation system based on the premise of avoiding damage to the inguinal canal and disruption of the rectus abdominis at the pubic symphysis and pubic crest. Research Methods Excluding cases with poor image quality, tumors, malformations, and fractures, the data of 80 healthy adults (40 males and 40 females aged from 21 to 83 years old, with an average age of 51.65 years) undergoing a computed tomography (CT) scan of the pelvis between January and June of 2017 were collected from Shandong Provincial Hospital. The CT scans were imported to Mimics® software to reconstruct three-dimensional pelvic models. A 3.5 mm pelvic reconstruction plate was placed starting at the outer edge of the pubic tubercle and along the pelvic brim. The two innermost screw insertion sites were marked. The safe range for the screw insertion sites was then determined. The screw insertion plane was selected to measure the safe screw insertion parameters. The length of the screw, the direction of insertion, and intersex differences were then explored via statistical analyses. Results The medial inclination angles (MIAs) of the screw insertion plane for males and females were 30.42±7.95° and 32.88±10.65°, respectively, with no statistically significant differences. For the medial screw, the maximum anterior inclination angle (MAIA), the maximum screw length, and the maximum posterior inclination angle (MPIA) were 46.51±4.01°, 12.40±9.53 mm, and 11.78±10.22° on average, respectively, with no significant differences by gender (P>0.05). For the lateral screw, the MAIA was 10.35±9.46° and showed no gender differences (P>0.05), but the male group had a greater MPIA (male 11.80±11.00° vs. female 6.23±7.91°, P<0.05) and maximum screw length (male 55.71±6.36 mm vs. female 48.68±8.65, P<0.001). For the tangential screw, the maximum screw length, MIA, and anterior/posterior inclination angle (APIA) were 52.19±8.33 mm, 31.65±9.42°, and 7.53±10.18°, respectively, with no significant differences in the angles by gender (both P>0.05), although the screw length in the male group was significantly longer than that in the female group. Conclusions Insertion of two screws into the pubic body through a plate from the lateral side of the pubic tubercle is safe and can maintain the origin of the rectus abdominis and the integrity of the inguinal canal compared to traditional plate-screw fixation. Considering that the pubic body is thinner on the lateral side, we suggest a more medial inclination angle for the lateral screw.

Structures at Risk During Percutaneous Screw Fixation for Talonavicular Fusion.

Talonavicular (TN) fusion using screws dorsomedially and dorsolaterally can cause neurovascular injury. The purpose of our cadaveric study was to evaluate the safety of percutaneous screw insertion in relation to dorsal neurovascular structures. Ten fresh-frozen cadaver legs were used for this study. Percutaneous cannulated screws were inserted to perform isolated TN arthrodesis. The screws were inserted at 3 consistent sites: a "medial screw" at the dorsomedial navicular where it intersected at the medial plane of the first cuneiform, a "central screw" at the edge of the dorsal navicular between the medial and intermediate cuneiforms, and a "lateral screw" at the edge of the dorsal navicular between the intermediate and lateral cuneiforms. Superficial and deep dissections were carried out to identify any injured nerves, arteries, and/or tendons. The medial screw injured the anterior tibialis tendon in 2 cases (20%), the central screw injured the extensor hallucis longus tendon in 3 cases (30%), and the lateral screw injured the anterior branch of the superior peroneal nerve (SPN), the lateral branch of the SPN, and the medial branch of the distal peroneal nerve (DPN) once each in a total of 3 cases (30%). Despite no direct injury, the central screw indicated a potential risk of neurovascular injury: closest distance to the anterior SPN was 2 mm and to the medial DPN 2 mm. Although neurovascular injury risk exists for all of these screw placements, TN fusion with a central screw introduced a potentially decreased risk of neurovascular injury at the expense of increased risk of tendon injury compared to the lateral screw. Based on these results, we recommend a careful dissection be performed prior to percutaneous screw insertion.

Safe Zone for Percutaneous Screw Fixation - Talonavicular Fusion

Category: Hindfoot Introduction/Purpose: Talonavicular fusion has been established as a reliable intervention for degenerative, inflammatory, and traumatic joint lesions as well as hindfoot deformities. In order to achieve optimal fusion, various versions of the procedure have been introduced in literature and have remained a topic of contention, with the most common variation involving the insertion of 1 to 3 screws dorsomedially and dorsolaterally. Dorsolateral screw placements commonly cause neurovasculature injury. The purpose of our cadaveric study was first to establish the safety of the dorsolateral percutaneous screw insertion in relation to these dorsal neurovascular structures, and then subsequently to standardize the ideal placement of the dorsolateral screw by comparing two insertion sites based on consistent bony landmarks. Methods: Ten fresh-frozen cadaver legs amputated at the knee were used for this study. Percutaneous cannulated screws were inserted to perform isolated talonavicular arthrodesis. The screws were inserted at 3 consistent sites: “medial screw” at dorsomedial navicular where it intersected at the medial plane of the first cuneiform, “central screw” at the edge of dorsal navicular between medial and intermediate cuneiforms, and “lateral screw” at the edge of dorsal navicular between intermediate and lateral cuneiforms. Superficial and deep dissections were carried out to identify any injured nerves, arteries, and tendons. Results: The mean age at death in our sample of cadavers was 80.1 ± 7.5 years (range 68 to 92) and had the BMI of 21.8 ± 2.4 (range 18.1 to 25.1). There were 5 males (50.0%) and 5 females (50.0%). The medial screw injured the anterior tibialis tendon in 2 cases (20.0%), the central screw injured the extensor hallucis longus tendon in 3 cases (30.0%), and the lateral screw injured the anterior branch of SPN, lateral branch of SPN, and medial branch of DPN once each in a total of 3 cases (30.0%). Conclusion: TN fusion with central screw placement at the interspace between the medial and intermediate cuneiforms protects the neurovasculatures of the foot to a superior extent than lateral screws between the intermediate and lateral cuneiforms.

Torsional Growth Modulation of Long Bones by Oblique Plating in a Rabbit Model.

There is evidence that oblique tension band plating can affect torsional growth in long bones. This study sought to determine if the torsional growth could be modulated based on the angles of the tension band plating and whether or not oblique plating affected overall longitudinal growth. New Zealand White rabbits (10.5 wk old) had one screw placed on the metaphyseal side and one on the epiphyseal side of both medial and lateral sides of the right knee distal femoral physis. The sham group (n=5) included screw placement only. For the plate group (n=13), unlocked plates, angled from 0 to 76 degrees, connected the screws and spanned the physis. Radiographs were taken at biweekly intervals. After 6 weeks of growth, hindlimbs were harvested and microCT scans performed. Femoral length, distances between screw heads and angle between the plates were measured on radiographs. Femoral length differences were compared between groups. Femoral version was measured from 3D microCT. Plate angle changes were correlated to the difference in femoral version between limbs using Pearson correlation (significance was set to P<0.05 for all comparisons). Femur length difference between the contralateral and the operative side was significantly greater in the plate group compared with the sham group over time (P=0.049). Medial and lateral screw distances changed significantly more in the sham group than the plate group on both sides (P<0.001). A greater initial angle between plates resulted in a greater change in the angle between plates (P<0.001). Significant correlations were found between right-left side femoral version differences and initial plate angle (P=0.003) and plate angle change (P=0.014). The torsional effect of oblique plating seems to correlate with the amount of initial plate angle, with an additional, not negligible, longitudinal growth effect. Placing plates at given angles across open physes may result in predictable changes in bone torsion allowing for a safer and less invasive option when treating childhood torsional deformities, but the resulting shortening of the ipsilateral femur must be considered.

Cannulated screw versus Kirschner-wire fixation for Milch II lateral condyle fractures in a paediatric sawbone model: a biomechanical comparison.

PurposeLateral condyle fractures of the humerus are common in the paediatric population, accounting for up to 20% of elbow fractures. Traditional management involves internal fixation with Kirschner (K)-wires, however, this has been associated with complications and insufficiently rigid fixation. Recently, cannulated screws have been proposed as a more stable method of fixation. While cannulated screws have been thought to allow earlier range of movement and shorten time to union, data regarding the biomechanical performance and optimal screw placement is scarce. We hypothesize that cannulated screw fixation is superior to K-wire fixation and screw placement can enhance the stability of the construct.MethodsPaediatric humerus sawbones with Milch II fractures were fixed with one of three methods. Fractures were reduced with either a single cannulated screw either through the centre of the capitellum (oblique), or placed up the lateral column across the growth plate (lateral), or fixed with two K-wires. Fixed sawbone fractures were then mechanically tested in two directions simulating in vivo forces.ResultsThe lateral screw construct had a higher maximum force to failure, higher stiffness and absorbed higher energy as compared with the K-wire fixation and oblique screw under an anterior force. When loaded from the posterior direction, only the lateral column screw was better than K-wire fixation.ConclusionsScrew fixation is a biomechanically effective alternative to K-wire fixation, especially when placed up the lateral column of the distal humerus. Further clinical studies are required before transcapitellar screw fixation can be adopted.

Malpositioned Pedicle Screw Compressed Thoracic Aorta of a Patient With Adolescent Idiopathic Scoliosis: Case Report and Literature Review

Background: Aortic injuries because of pedicle screw placement are quite rare, consequently management strategies to avoid vascular complications are lacking. Intraoperative or postoperative images to reveal the accuracy of screw placement in scoliotic misalignment with freehanded placed pedicle screws is therefore essential. Case Report: A 13-year-old girl with adolescent idiopathic scoliosis (AIS) was presented at the outpatient clinic of the authors department. Operative correction of the scoliotic misalignment including dorsal pedicle screw and rod placement with fusion from T3 to L4 was performed. Computed tomography scan after surgery showed left T9 screw malposition, accompanied by lateral compression of thoracic aorta. No clinical manifestations of aortic stenosis were noted. To avoid severe vascular complications, the thoracic screw was removed with the help of a specialized team of vascular as well as thoracic surgeons through extrapleural thoracotomy. After the removal of the malpositioned screw, the correction maneuvres were applied without the left T9 screw. No posttraumatic aortic aneurysm and other wall injury were identified after the revision surgery. The patient was discharged after 20 days of inpatient stay without the use external immobilization. The girl was in a good clinical condition after the 1-year follow-up visit without vascular or neurological complications. Conclusions: Malpositioned pedicle screws after dorsal correction in patients with adolescent idiopathic scoliosis might be challenging. Aortic injuries because of malpositioned screws are rare; nevertheless, the presence might be a life-threatening condition despite a clinical asymptomatic patient. As a consequence, the authors recommend to perform routine postoperative computed tomography scans combined with angiography in the case of significant lateral screw positioning.

Influence of screw combination and nail materials in the stability of anterograde reamed intramedullary nail in distal femoral fractures

Intramedullary nailing (IM) is a technique universally accepted to treat femoral diaphyseal fractures. The treatment of fractures located in the distal third remains a controversial issue though. A finite element model of the femur has been developed, analyzing distal fractures with several gap sizes combined with different interlocking combinations of distal screws with one oblique screw proximally to stabilize the intramedullary nail. The mechanical strength of the nail against bending and compression efforts was also studied. Beside the FE simulations, a clinical follow-up of 15 patients, 6 males and 9 females, with mean age of 53.2 years was carried out. Localizations of fractures were 10 in the right femur and 5 in the left femur, respectively.A fairly good correspondence agreement between clinical results and the simulated fractures in terms of gap size was found. Non-comminuted fractures had a mean consolidation time of 20.5 weeks (4.8 months), a tendency corresponding well to the mobility obtained in the FE simulations; Comminuted fractures on the other hand exhibited a higher mean consolidation period of 22.2 weeks (5.2 months) secondary to the excessive mobility at fracture site obtained by means of FE simulations.The best stability at fracture site was found for the system with three distal screws and the system with two distal screws placed medial lateral. The highest leverage of distal screws was obtained maximizing the distance between them and choosing the coronal plane for their orientation. The results obtained with both nail materials (stainless steel and titanium alloy) show a higher mobility when using titanium nails. Steel nails provide stiffer osteosyntheses than the titanium nails.In conclusion, the best screw combination in terms of stability to produce fracture healing and the least difficulties during treatment is the one which had one oblique proximal screw with two distal lateral screw implanted in the coronal plane.

Lateral Lumbar Interbody Fusion and in Situ Screw Fixation for Rostral Adjacent Segment Stenosis of the Lumbar Spine.

ObjectiveThe purpose of this study is to describe the detailed surgical technique and short-term clinical and radiological outcomes of lateral lumbar interbody fusion (LLIF) and in situ lateral screw fixation using a conventional minimally invasive screw fixation system (MISF) for revision surgery to treat rostral lumbar adjacent segment disease.MethodsThe medical and radiological records were retrospectively reviewed. The surgery was indicated in 10 consecutive patients with rostral adjacent segment stenosis and instability. After the insertion of the interbody cage, lateral screws were inserted into the cranial and caudal vertebra using the MISF through the same LLIF trajectory. The radiological and clinical outcomes were assessed preoperatively and at 1, 3, 6, and 12 months postoperatively.ResultsThe median follow-up period was 13 months (range, 3–48 months). Transient sensory changes in the left anterior thigh occurred in 3 patients, and 1 patient experienced subjective weakness; however, these symptoms normalized within 1 week. Back and leg pain were significantly improved (p<0.05). In the radiological analysis, both the segmental angle at the operated segment and anterior disc height were significantly increased. At 6 months postoperatively, solid bony fusion was confirmed in 7 patients. Subsidence and mechanical failure did not occur in any patients.ConclusionThis study demonstrates that LLIF and in situ lateral screw fixation may be an alternative surgical option for rostral lumbar adjacent segment disease.

Re-correction osteotomy with osteophyte graft for correction loss with non-union after high tibial osteotomy

A 68-year-old man with right knee varus osteoarthritis was treated by lateral closed-wedge high tibial osteotomy. A correction loss with non-union occurred 6 months after surgery and a re-correction osteotomy...

Predisposing Factors of Fracture Nonunion After Posterior C1 Lateral Mass Screws Combined with C2 Pedicle/Laminar Screw Fixation for Type II Odontoid Fracture.

The aim of this study was to explore the predisposing factors for fracture nonunion after a lateral screw was combined with C2 pedicle/laminar screw for a type II odontoid fracture and hopefully provide references in decision making and surgical planning for spinal surgeons. This is a retrospective study. By retrieving the medical records from January 2010 to July 2015 in our hospital, 117 type II odontoid fracture patients were reviewed. According to the occurrence of fracture union at the final follow-up, patients were divided into 2 groups: union and nonunion. To investigate the predisposing factors for fracture nonunion, 3 categorized factors were analyzed statistically: patient characteristics-age, sex, body mass index, preoperative Japanese Orthopaedic Association (JOA) scores, duration, comorbidity, and complicated injuries; surgical variables-surgery time, blood loss, C2 fixation manner, vertebral artery injury, bone source for fusion between the posterior arch of C1 and the laminae and spinous process of C2; radiographic parameters-preoperative and immediate postoperative data of C0-2 curvature, C2-7 curvature, C2-7 sagittal vertical axis, C7 slope, fracture classification, congenital hypoplastic vertebral artery, and the separation and displacement of the odontoid fracture. Other variables including JOA and visual analog scale scores for neck pain, neck stiffness, and patient satisfaction at final follow-up were recorded and compared between the 2 groups. Postoperative fracture nonunion was detected in 76 of 117 patients (65%) at final follow-up. There was no statistically significant difference between the 2 groups in patient characteristics of sex, body mass index, JOA score, comorbidity, and complicated injuries. The mean age at operation was younger in the union group than in the nonunion group, and the mean duration was shorter in the union group than in the nonunion group. There was no difference in surgical variables of surgery time, blood loss, C2 fixation manner, vertebral artery injury, bone source for fusion between the posterior arch of C1 and the laminae and spinous process of C2. There was no difference in radiographic parameters of fracture classification, congenital hypoplastic vertebral artery, preoperative and immediate postoperative C0-2 curvature, C2-7 curvature, C2-7 SVA, and C7 slope. No difference was found in preoperative and immediate postoperative displacement of the odontoid fracture or immediate postoperative separation of the odontoid fracture, while the preoperative separation of the odontoid fracture was shorter in the union group than in the nonunion group. The logistic regression analysis revealed that advanced age (>45 years), long duration (>2 months), and preoperative separation of the odontoid fracture (>4 mm) were independently associated with the postoperative fracture nonunion. There were no differences between the 2 groups in JOA, neck pain, neck stiffness, and patient satisfaction at final follow-up. Advanced age, long duration, and preoperative separation of odontoid fracture >4 mm are predisposing factors for fracture nonunion after posterior C1 lateral screw combined with C2 pedicle/laminar screw fixation for type II odontoid fracture. Our findings did not demonstrate any evidence of lower functional outcome and patients satisfaction for those patients who had odontoid nonunion.

Development of Biocomposite Based Anchor Screw System for Osteoporosis

With the recent advancements in arthroscopic surgery, the use of suture anchor has increased in the surgical treatment of rotator cuff tears. In the present study, we developed a suture anchor system for ligament reconstruction that can be applied to patients with osteoporosis or with low bone density. The anchor screws are made of biocomposites containing poly-L-lactic-co-glycolic acid (PLGA) and beta-tricalcium phosphate (β-TCP) in a 70:30 ratio. The suture anchor system consisted of medial and lateral screw. The lateral screw was designed in a hemicylindrical structure to prevent bone damage. The performance of the developed anchor screw was found to be greater than 402.5 N in a pull-out test.

Effects of vertical loading on lateral screw pile performance

The offshore wind energy sector faces new challenges as it moves into deeper water deployment. To meet these challenges, new and efficient foundation solutions are required. One potential solution is to upscale onshore screw piles but they require verification of performance for new geometries and demanding loading regimes. This paper presents a three-dimensional finite-element analysis investigation of screw pile behaviour when subjected to combined vertical and lateral loading in sand. In the investigation, the screw pile length and helical plate diameter were varied on piles with a fixed core diameter while subjecting the piles to combined axial and lateral loading. The results were compared with results from straight shafted piles with the same core diameter. The results of the analysis revealed that vertical compression loads increased the lateral capacity of the screw piles whereas vertical uplift loads marginally reduced the lateral capacity. The downside of this enhanced lateral capacity is that the screw piles experience higher bending moments. This suggests that, when using screw piles for offshore foundation applications, structures should be designed to maintain axial compressive loads on the piles and induced bending moments need to be adequately assessed when deciding on appropriate structural sections.

Comparison of curative effect of unilateral and bilateral vertebral pedicle screw instrumentation for treatment of thoracolumbar burst fractures

Objective To compare the efficacy of unilateral and bilateral pedicle screw instrumentation for treatment of thoracolumbar burst fractures. Methods A retrospective case-control analysis was made on 50 patients with thoracolumbar burst fractures free from neurological deficit admitted between January 2008 and October 2013. There were 37 males and 13 females, aged from 24 to 51 years (mean, 36 years). Injuries were caused by high falls in 23 patients, traffic accidents in 18 and crashing accidents in 9. Distribution of the injured segment was T11 in 6 patients, T12 in 16, L1 in 20 and L2 in 8. Based on the surgical procedures, the patients were assigned to unilateral pedicle screw fixation group (n=35) and bilateral pedicle screw fixation group (n=15). Operation time, intraoperative blood loss and hospital length of stay were recorded. Visual analogue scale (VAS), Oswestry disability index (ODI), kyphotic angle and anterior vertebral height were evaluated before surgery, after surgery and at 1-year follow-up. Results No screw lessening, screw breakage or infection occurred at 1-year follow-up. Unilateral and lateral pedicle screw instrumentation groups revealed no significant differences in operation time [(81.4± 10.0)min vs. (83.3±13.6)min], intraoperative blood loss [(194.0±65.4)ml vs. (212.0±61.9)ml] and hospital length of stay [(10.3±1.3)d vs. (9.9±1.5)d] (P>0.05). After operation, VAS and ODI in unilateral pedicle screw instrumentation group (3 points, 73.9) showed no significance from these in lateral pedicle screw instrumentation group (2 points, 72.1) (P>0.05). VAS was within 1 point and ODI was within 20 at 1-year follow-up, showing no significant differences between the two groups (P>0.05). After operation, correction of kyphotic Cobb angle and restoration of anterior vertebral body height in unilateral pedicle screw instrumentation group (8°, 26.7%) showed no significance from these in lateral pedicle screw instrumentation group (11°, 32.1%) (P>0.05). Loss of local kyphotic Cobb angle and anterior vertebral body height in unilateral pedicle screw instrumentation group (2°, 3%) showed no significance from these in lateral pedicle screw instrumentation group (1°, 2%) at 1-year follow-up (P>0.05). Conclusion Both methods have comparable efficacy in restoring vertebral height and improving spinal kyphosis for treatment of thoracolumbar burst fractures. Key words: Spinal fractures; Fracture fixation, internal; Pedicle screws

Applied anatomic study of narrow pedicle in thoracolumbar spine of adults

Objective To explore the demographic factors and the risk of the pedicle screw insertion of the narrow pedicles. Methods Thoracolumbar spine thin-section CT image data of 312 adults from September 2014 to September 2015 were analyzed. The pedicle width, medial and lateral cortical thickness, spongy bone thickness, spongy bone thickness/cortical thickness, e angle and screw path length of each pedicle were measured. The incidence and the distribution characteristics of the narrow pedicle were analyzed. Anatomic parameters and age, gender and stature were compared between the narrow pedicle group and non-narrow pedicle. The risk of the pedicle screw insertion of the narrow pedicle was assessed. Results Among the 3 081 pedicles, 74 narrow pedicles were determined as their pedicles width were less than 5 mm, and the proportion of narrow pedicle was 2.40%. Among the 312 subjects, 26 subjects were found having narrow pedicles, and the proportion of individuals with narrow pedicles in the population was 8.33% (26/312). The incidences of narrow pedicle in thoracolumbar spine were T10 0.32%, T11 0.32%, T12 0.98%, L1 7.54%, L2 2.92%. The spongy bone thickness, spongy bone thickness/cortical thickness of narrow pedicle were lower than non-narrow pedicle. However, there were no significant differences of medial and lateral cortical thickness, e angle and screw path length between the narrow pedicle and non-narrow pedicle. Difference of the mean age between the two subjects groups had no statistical significance. The percentage of female in narrow pedicle subjects group was 84.6% (22/26), which was higher than that in non-narrow pedicle subjects group (49.7%, 142/286). The mean stature of the male and female of stenosis pedicle group subjects were 163.8±1.3 cm and 152.5±4.3 cm, which were shorter than those of non-narrow subjects pedicle group (169.5±5.6 cm, 160.1±6.6 cm). The percentage of the cortical bone breakthrough by the pedicle screws of narrow pedicle group was (84.6%, 27/32), which was higher than that of non-narrow pedicle group (14.7%, 33/224). Conclusion L1 is the most common segment of thoracolumbar spine that narrow pedicle exist, which is the result of reduction of the spongy bone thickness. Narrow pedicle mostly appears in short stature female. There is high risk of cortical bone breakthrough by insertion of the posterior pedicle screws in the narrow pedicle. Key words: Thoracic vertebrae; Lumbar vertebrae; Tomography, X-ray computed; Anatomy

Pedicle screw placement accuracy impact and comparison between grading systems.

Background:Pedicle screw instrumentation is widely used for spinal stabilization. However, the accuracy for free-hand screw placement ranges from 69% to 94%. This study assesses the value of the existing classification systems, and investigates their impact on the ability to assess the accuracy of free-hand screw placement.Methods:Data were collected retrospectively from the medical records of 34 patients who received 224 pedicle screws placed utilizing a free-hand technique. Screw placement was evaluated employing the 2-mm increment and Zdichavsky et al. classification systems. Kappa coefficient and Landis and Koch interpretations were employed for statistical analysis.Results:The 2-mm increment classification system resulted in a total of 18 (8.03%) misplaced screws. Lateral screw misplacement was observed in 13 (5.8%) instances, with medial pedicle wall penetration being noted in 5 (2.23%). Of the 18 misplaced screws, 4 (22.22%) were classified as minor (≤2 mm), 12 (66.67%) as moderate (2–4 mm), and 2 (11.11%) as severe (>4 mm) (K = 0.882). The Zdichavsky et al. grading system categorized 208 (92.84%) pedicle screws as Ia, 10 (4.46%) as Ib, 1 (0.45%) as IIa, 2 (0.90%) as IIb, 2 (0.90%) as IIIa, and 1 (0.45%) as IIIb grade; this resulted in a total of 16 (7.14%) misplaced screws (K = 0.980). One patient exhibited a new postoperative radiculopathy attributed to poor screw placement. There were no additional early or late postsurgical complications attributed to screw misplacement.Conclusion:The free-hand pedicle screw placement technique is both safe and effective. Postoperative computed tomography studies; however, are useful to confirm the accuracy of screw placement. Although, the available grading systems proved reliable, easy to use, and clearly reflected the individual surgeon's skills, they do not clearly document whether screws are safely placed.

Integrated Fixation Cage Loosening Under Fatigue Loading.

Screw loosening is a well-known adverse event in traditional spinal fusion instrumentation. This phenomenon may hinder segmental stability of the spine leading to bony non-union. In recent years numerous lumbar integrated fixation cages (IFC) have been introduced that offer a low profile alternative to a standard cage with an anterior plate (AP+C). The fixation approach for IFCs is different than a traditional anterior approach; therefore, it is unclear whether IFCs may loosen from the surrounding bone over time. The purpose of this study was to quantify screw loosening of IFC devices compared to AP+C implants under fatigue loading using micro-CT and image processing techniques. L2-3 and L4-5 functional spinal units (FSUs) were obtained from nine human lumbar spines. These FSUs were then reconstructed with either AP+C or IFC implants designed to attach to vertebral bodies using four screws (two top and two bottom for AP+C; two medial and two lateral for IFC). The reconstructed specimens were fatigued in flexion-extension load of ±3 Nm at 1Hz for first 5,000 cycles and it was increased to ±5 Nm until 20,000 cycles. After removing screws to prevent image artifact, micro-CT scans were performed on all FSUs post-fatigue. These images were post-processed to calculate three-dimensional volumes around screw holes created due to damage at the screw-implant interface. IFC screws had significantly greater (p=0.008) screw hole volumes compared to AP+C screws after fatigue testing. This increased screw hole volume for IFC devices was mainly due to loosening in medial screws. Medial screws had significantly greater (p<0.003) screw hole volumes compared to lateral IFC screws and all AP+C screws. There was no difference (p>0.888) between the screw hole volumes of lateral IFC, top AP+C, and bottom AP+C screws. This study elucidated screw-loosening mechanisms in integrated fixation cages under simulated physiological loading. In particular, spatial differences in fixation was observed for IFC screws across the vertebra where medial screws loosened at a greater frequency compared to lateral screws post-fatigue. This novel technique may also be used to quantitatively investigate screw fixation post-fatigue testing in a variety of spinal devices.

Alignment After Intramedullary Nailing of Distal Tibia Fractures Without Fibula Fixation.

To evaluate the efficacy of intramedullary nailing of distal tibia fractures using modern techniques, without fibula fixation, in obtaining and maintaining alignment. Retrospective case review. Level-I academic trauma center. One hundred thirty-two consecutive patients with distal tibia fractures. Intramedullary nail of distal tibia fracture, without fibula fixation, was performed in consecutive patients using modern reduction techniques. Malalignment and malunion were defined as >5 degrees of varus/valgus angulation or anterior/posterior angulation on the initial postoperative or final anteroposterior and lateral x-rays. There were 122 consecutive patients (86 men and 36 women) 16-93 years of age (average, 43 years) with 36 (30%) open and 85 (70%) closed fractures with complete follow-up. Mechanism of injury did not predict the presence or level of fibula fracture. Upon presentation, varus/valgus and procurvatum/recurvatum angulation was greatest when the fibula was fractured at the level of the tibia fracture (P = 0.001 and 0.028). The most common intraoperative reduction aids were nailing in relative extension, transfixion external fixation, and clamps at the fracture site. The OTA fracture type or level/presence of fibula fracture did not influence malalignment (P = 0.86 and 0.66), malunion (P = 0.81 and 0.79), or the change in alignment during union, which averaged 0.9 degrees. We found an overall low rate of both malalignment (2%) and malunion (3%) after intramedullary nailing of distal tibial shaft fracture without fibula fixation. We conclude that when modern nailing techniques are used, which allow for confirmation of reduction by visualization in fluoroscopy, from nail placement to distal interlocking, fibula fixation is not necessary to obtain or maintain alignment. Furthermore, standard 2 medial to lateral screws distally afford adequate stability to hold the reduction during union with a 0.9-degree difference in the initial postoperative and final united films. Therapeutic level IV. See Instructions for Authors for a complete description of levels of evidence.

Computed tomography-based three-dimensional visualisation of bone corridors and trajectories for screws in open reduction and internal fixation of symphysis diastasis: a retrospective radiological study.

Typical stabilisation of pelvic open book injuries consists of plate fixation of the symphysis. No previous literature has been published about the evaluation of screw placement and their trajectory with four oblique 4.5mm screws using a four-hole plate in symphysis diastasis. The aim of this study was to define insertion points and angles of trajectory for crossed screw placement regardless of any plate design based on an analysis of three-dimensional computed tomography data sets. One hundred human pelvic CT data sets were collected. Unilateral and bilateral placements of crossed 4.5mm screws were simulated. Primary outcome measure was successful simulated screw placement without cortical breach. Secondary outcome measures included the anatomical measurements of the screw positions. Simulated screw placement of two oblique screws on each side of the pubic symphysis without cortical breach was achieved in all (100%) cases. There were a total of 400 screw simulations. Medial screws were longer, lateral screws had higher coronal angles, and the distance between both screws was higher on the right side (p<0.001 each). The lengths of the right lateral, right medial, left lateral, and left medial screws were 44.9, 65.8, 45.4, and 67.4mm, respectively. The sagittal angles to the dorsal surface area of the pubic rami were 10.5°, 11.1°, 9.0°, and 11.0°. The coronal angles to the vertical axis of the symphysis measured 39.5°, 16.0°, 33.8°, and 16.8°. The distances between these screws and the medial edge of the pubic crest were 33.5, 8.6, 29.5, and 7.3mm. Furthermore, certain sex- and side-related differences were noted. This series provides results about the feasibility and a detailed anatomical description of crossed screw placement. This is of special interest in pelvic surgery for choosing the entry points, safe screw channel parameters, and trajectories.