A biomechanical investigation of different screw head designs for vertebral derotation in scoliosis surgery

Background Context

The posterior pedicle screw-rod system, which is widely used to correct spinal deformities, achieves a good correction rate in the frontal and coronal planes but not in the axial plane. Direct vertebral derotation (DVD) was developed to correct axial plane deformities. However, the design of screw head and body connection, in terms of monoaxial, polyaxial, and uniplanar screw, may influence the efficiency of DVD.

Position of polyaxial versus monoaxial screws in locked plating for proximal humeral fractures: analysis of a prospective randomized study

Background

Aim of the study was to compare the chosen position of polyaxial locking screws with the position of monoaxial screws in the humeral head of proximal humeral fractures treated by locked plating.

Methods

In a prospective randomized observational study, 124 consecutive patients (mean age 70.9 ± 14.8 years) sustaining a displaced proximal humeral fracture were treated with either monoaxial or polyaxial screw-inserted locking plate fixation. The chosen positions of locking screws were identified from standardized postoperative radiographs in anteroposterior and outlet-view, with regard to a regional mapping of the humeral head.

Results

In monoaxial locking technique, a mean of 6 screws purchased the humeral head (95 % CI 5.1–6.2), and in polyaxial locking technique, a mean of 4 screws (95 % CI 3.3–4.5), respectively. Screws were placed in the regions superolateral: monoaxial 24.8 %, polyaxial 20.7 % (p = 0.49); superomedial: monoaxial 21.9 %, polyaxial 20.0 % (p = 0.433); inferolateral: monoaxial 32.5 %, polyaxial 35.0 % (p = 0.354); inferomedial: monoaxial 20.8 %, polyaxial 24.2 % (p = 0.07), superoposterior: monoaxial 45.5 %, polyaxial 30.8 % (p = 0.57); superoanterior: monoaxial 4.4 %, polyaxial 8.3 % (p = 0.33); inferoposterior: monoaxial 22.5 %, polyaxial 29.8 % (p = 0.49) and inferoanterior: monoaxial 27.5 %, polyaxial: 31.2 % (p = 0.09).

Conclusion

The chosen screws’ position in monoaxial and polyaxial locking plate fixation of displaced proximal humeral fractures do not differ significantly. However, loss of fixation is observed more frequently if the fixation did not include at least one screw within the superoposterior region of the humeral head, suggesting that a screw purchasing the superoposterior region is beneficial in locked plating of proximal humeral fractures.

Level of evidence

Treatment Study, Level II.     

How Does a Novel Monoplanar Pedicle Screw Perform Biomechanically Relative to Monoaxial and Polyaxial Designs?

Background

Minimally invasive spinal fusions frequently require placement of pedicle screws through small incisions with limited visualization. Polyaxial pedicle screws are favored due to the difficulty of rod insertion with fixed monoaxial screws. Recently, a novel monoplanar screw became available that is mobile in the coronal plane to ease rod insertion but fixed in the sagittal plane to eliminate head slippage during flexion loads; however, the strength of this screw has not been established relative to other available screw designs.

Questions/purposes

We compared the static and dynamic load to failure in polyaxial, monoaxial, and monoplanar pedicle screws.

Methods

Six different manufacturers’ screws (42 total) were tested in three categories (polyaxial, n = 4; monoaxial, n = 1; monopolar, n = 1) utilizing titanium rods. An additional test was performed using cobalt-chromium rods with the monopolar screws only. Screws were embedded into polyethylene blocks and rods were attached using the manufacturers’ specifications. Static and dynamic testing was performed. Dynamic testing began at 80% of static yield strength at 1 Hz for 50,000 cycles.

Results

In static testing, monoaxial and monoplanar screws sustained higher loads than all polyaxial screw designs (range, 37%–425% higher; p < 0.001). The polyaxial screws failed at the head-screw interface, while the monoaxial and monoplanar screws failed by rod breakage in the static test. The dynamic loads to failure were greater with the monoplanar and monoaxial screws than with the polyaxial screws (range, 35%–560% higher; p < 0.001). With dynamic testing, polyaxial screws failed via screw-head slippage between 40% and 95% of static yield strength, while failures in monoaxial and monoplanar screws resulted from either screw shaft or rod breakage.

Conclusions

All polyaxial screws failed at the screw-head interface in static and dynamic testing and at lower values than monoaxial/monoplanar screw designs. Monoplanar and monoaxial screws failed at forces well above expected in vivo values; this was not the case for most polyaxial screws.

Clinical Relevance

Polyaxial screw heads slip on the screw shank at lower values than monoaxial or monoplanar screws, and this results in angular change between the rod and pedicle screw, which could cause loss of segmental lordosis. The novel monoplanar screw used in this study may combine ease of rod placement with sagittal plane strength.     

Design and biomechanical study of a modified pedicle screw

Objective： In pedicle screw fixation, the heads of monoaxial screws need to be directed in the same straight line to accommodate the rod placement by backing out during operation, which decreases the insertional torque and internal fixation strength. While polyaxial screws facilitate the assembly of the connecting rod, but its ball-in-cup locking mechanism reduces the static compressive bending yield strength as compared with monoaxial screws. Our study aimed to assess the mechanical performance of a modified pedicle screw.
Methods： In this study, the tail of the screw body of the modified pedicle screw was designed to be a cylindershaped structure that well matched the inner wall of the screw head and the screw head only rotated around the cyclinder. Monoaxial screws, modified screws and polyaxial screws were respectively assembled into 3 groups ofvertebrectomy models simulated by ultra high molecular weight polyethylene （UHMWPE） blocks. This model was developed according to a standard for destructive mechanical testing published by the American Society for Testing Materials （ASTM F1717-04）. Each screw design had 6 subgroups, including 3 for static tension, load compression and torsion tests, and the rest for dynamic compression tests. In dynamic tests, the cyclic loads were 25%, 50%, and 75% of the compressive bending ultimate loads respectively. Yield load, yield ultimate load, yield stiffness, torsional stiffness, cycles to failure and modes of failure for the 3 types of screws were recorded. The results of modified screws were compared with those ofmonoaxial and polyaxial screws.
Results： In static tests, results of bending stiffness, yield load, yield torque and torsional stiffness indicated no significant differences between the modified and monoaxial screws （P〉0.05）, but both differed significantly from those ofpolyaxial screws （P〈0.05）. In dynamic compression tests, both modified and monoaxial screws showed failures that occurred at the insertion point of screw body into the UHMWPE block, while the polyaxial screw group showed screw body swung up and down the screw head because of loosening of the ball-in-cup mechanism.
Conclusions： The modified screw is well-designed and biomechanically improved. And it can provide sufficient stability for segment fixation as monoaxial screws.     

复位前与复位后伤椎置钉固定胸腰椎骨折比较

[目的]比较复位棒辅助复位后伤椎置钉与常规复位前伤椎置钉短节段固定治疗Magerl A3型胸腰椎骨折的临床疗效.[方法] 2018年12月-2020年6月收住本院的59例Magerl A3型胸腰椎骨折患者随机分为两组.所有患者均接受短节段椎弓根钉固定,其中,32例采用自制复位棒复位后,再行伤椎置钉(复位置钉组);27例...     

经皮单平面椎弓根螺钉与开放椎弓根螺钉治疗胸腰椎骨折疗效比较

目的比较经皮单平面椎弓根螺钉与开放椎弓根螺钉内固定治疗单节段胸腰椎骨折的中期临床疗效。方法将76例胸腰椎骨折患者按治疗方法分为两组:42例采用经皮单平面椎弓根螺钉联合伤椎置万向钉治疗(经皮单平面组),34例采用传统后路开放式椎弓根螺钉固定术治疗(传统开放组)。比较两组围手术期相关指标、中期随访时影像学指标及腰背部疼痛改善情况。结果患者均获得随访,时间20~44个月。术中出血量、切口长度经皮单平面组均优于传统开放组,差异均有统计学意义(P0.05)。后凸Cobb角、矢状面指数、伤椎椎体前缘高度两组术后及末次随访与术前比较差异均有统计学意义(P0.05),两组间比较差异均无统计学意义(P0.05)。疼痛缓解术后3 d经皮单平面组较传统开放组更明显(P0.05),末次随访时两组差异无统计学意义(P0.05)。结论经皮单平面椎弓根螺钉固定治疗胸腰椎骨折疗效与传统开放手术相当,且创伤小。     

Solid and hollow pedicle screws affect the electrical resistance: A potential source of error with stimulus-evoked electromyography

Background:

Although stimulus evoked electromyography (EMG) is commonly used to confirm the accuracy of pedicle screw placement. There are no studies to differentiate between solid screws and hollow screws to the electrical resistance of pedicle screws. We speculate that the electrical resistance of the solid and hollow pedicle screws may be different and then a potential source of error with stimulus-evoked EMG may happen.

Materials and Methods:

Resistance measurements were obtained from 12 pedicle screw varieties (6 screws of each manufacturer) across the screw shank based on known constant current and measured voltage. The voltage was measured 5 times at each site.

Results:

Resistance of all solid screws ranged from 0.084 Ω to 0.151 Ω (mean =0.118 ± 0.024 Ω) and hollow screws ranged from 0.148 Ω to 0.402 Ω (mean = 0.285 ± 0.081 Ω). There was a significant difference of resistance between the solid screws and hollow screws (P < 0.05). The screw with the largest diameter no matter solid screws or hollow screws had lower resistance than screws with other diameters. No matter in solid screws group or hollow screws group, there were significant differences (P < 0.05) between the 5.0 mm screws and 6.0 mm screws, 6.0 mm screws and 7.0 mm screws, 5.0 mm screws and 7.0 mm screws, 4.5 mm screws and 5.5 mm screws, 5.5 mm screws and 6.5 mm screws, 4.5 mm screws and 6.5 mm screws. The resistance of hollow screws was much larger than the solid screws in the same diameter group (P < 0.05).

Conclusions:

Hollow pedicle screws have the potential for high electrical resistance compared to the solid pedicle screws and therefore may affect the EMG response during stimulus-evoked EMG testing in pedicle screw fixation especially in minimally invasive percutaneous pedical screw fixation surgery.     

经皮椎弓根螺钉内固定治疗胸腰椎骨折的生物力学及临床研究

 目的 通过生物力学测试及临床应用对经皮跨伤椎四钉内固定(万向钉固定)与开放手术四钉内固定(单向钉固定)进行比较。方法 取 12具新鲜冰冻小牛腰椎标本 L1~L5节段,随机分为单向钉固定组与万向钉固定组。制备腰椎前中柱损伤模型,比较两组在模型上的运动范围。分别应用 Sextant经皮跨伤椎四钉内固定与开放跨伤椎四钉内固定治疗无神经功能损伤的胸腰椎骨折 25例和 35例,观察其中随访超过 12个月的 11例和 18例的即时复位效果、矫正度丢失情况。结果 (1)生物力学试验院万向钉固定组在各个方向的运动范围均大于单向钉固定组,其中在前屈、后伸方向的差异有统计学意义; 单向钉固定组在前屈、后伸、侧屈方向上的稳定性较完整标本大,差异有统计学意义; 万向钉固定组在前屈、后伸方向上的稳定性与完整标本比较差异无统计学意义。(2)临床应用院两组术前、术后伤椎前缘高度、矢状位 Cobb角的组间差异均无统计学意义; 两组术后伤椎前缘高度、矢状面 Cobb角与术前比较差异均有统计学意义; 末次随访时经皮跨伤椎四钉内固定组伤椎前缘高度丢失(9.9%±5.1%)大于开放跨伤椎四钉内固定组(5.3%±6.8%)。结论 应用 Sextant系统经皮椎弓根螺钉内固定治疗无须神经减压的胸腰椎骨折较开放手术创伤小,但随访中伤椎前缘高度丢失明显。生物力学试验显示其在前屈、后伸运动方向上的强度较弱。     

A biomechanical study comparing polyaxial locking screw mechanisms

Objective

Locking plates have become ubiquitous in modern fracture surgery. Recently, manufacturers have developed locking plates with polyaxial screw capabilities in order to optimise screw placement. It has already been demonstrated that inserting uniaxial locking screws off axis results in weaker loads to failure. Our hypothesis was that even implants specifically designed for polyaxial insertion would experience a drop-off in resistance when using non-perpendicular screws.

Methods

Four different types (one monoaxial and three polyaxial locking plates) of readily available small fragment plates were tested. A biomechanical model was developed to test the screws until failure (defined as breakage and rapid loss of >50% force). Screws were inserted at 0, 10 and 15°.

Results

The standard monoaxial locking mechanism sustained saw a 60% reduction in force (332 N vs. 134 N) when screws were inserted cross-threaded at 10°. Two polyaxial systems saw similar significant reductions in force of 45% and 34%, respectively at 15°. A third system utilizing an end cap locking mechanism showed highly variable results with large standard deviations. Polyaxial screws showed on average only limited reduction at 10 degrees of insertion angle.

Conclusion

Newer designs of locking plates have attractive properties to allow more surgical options during fixation. However this freedom comes at the price of reduced force. Our results show that the safe zone for inserting these screws is closer to 20°, rather than the 30° indicated by the manufacturers. Also, the various polyaxial locking mechanisms seem to influence the overall resistance of the screws.     

Bone impregnated hip screw in femoral neck fracture: Clinicoradiological results

Background:

Femoral neck fractures are treated either by internal fixation or arthroplasty. Usually, cannulated cancellous screws are used for osteosynthesis of fracture neck of femur. The bone impregnated hip screw (BIHS) is an alternative implant, where osteosyntehsis is required in femoral neck fracture.

Materials and Methods:

The BIHS is a hollow screw with thread diameter 8.3 mm, shank diameter 6.5 mm and wall thickness 2.2 mm and holes in the shaft of the screw with diameter 2 mm, placed in a staggered fashion. Biomechanical and animal experimental studies were done. Clinical study was done in two phases: Phase 1 in a group of volunteers, only with BIHS was used in a pilot study and phase 2 comparative study was done in a group with AO cannulated screws and the other group treated with BIHS.

Results:

In the phase 1 study, out of 15 patients, only one patient had delayed union. In phase 2, there were 78 patients, 44 patients in BIHS showed early union, compared to the rest 34 cases of AO cannulated screws Out of 44 patients with BIHS, 41 patients had an excellent outcome, 2 had nonunions and one implant breakage was noted.

Conclusions:

Bone impregnated hip screw has shown to provide early solid union since it incorporates the biomechanical principles and also increases the osteogenic potential and hence, found superior to conventional cannulated cancellous screw.     

枢椎棘突螺钉单侧应用联合对侧椎弓根螺钉固定的有限元分析

目的分析枢椎棘突螺钉单侧应用联合对侧椎弓根螺钉固定在寰枢和枕颈固定中的生物力学稳定性。方法构建正常枢椎解剖、椎板薄和椎动脉变异椎弓根细小3种不同解剖状态下的完整上部颈椎有限元模型作为完整模型组,然后分别模拟齿状突骨折进行寰枢固定和寰椎骨折进行枕颈固定。在寰枢固定中,比较单侧枢椎棘突螺钉+对侧椎弓根螺钉+双侧寰椎侧块螺钉固定组(棘突螺钉组)和枢椎双侧椎弓根螺钉+双侧寰椎侧块螺钉固定组(椎弓根螺钉组);在枕颈固定中,比较单侧枢椎棘突螺钉+对侧椎弓根螺钉+枕骨螺钉固定组(棘突螺钉组)和枢椎双侧椎弓根螺钉+枕骨螺钉固定组(椎弓根螺钉组)。枢椎棘突螺钉分别测试水平、斜向、垂直置钉3种不同的固定技术。模拟颈椎运动,测量枕颈的屈伸、侧屈、旋转的关节活动范围(ROM)。结果在寰枢和枕颈固定中,棘突螺钉组和椎弓根螺钉组的C1~C2屈伸、侧屈、旋转ROM均较完整模型组均明显下降。在寰枢固定中棘突螺钉组C0~C2屈伸、侧屈、旋转的ROM大于椎弓根螺钉组;在枕颈固定中,棘突螺钉组C1~C2侧屈的ROM大于椎弓根螺钉组,棘突螺钉组的C0~C2旋转的ROM大于椎弓根螺钉组。枢椎棘突螺钉分别测试水平、斜向、垂直固定间有差异,但不明显。结论在寰枢和枕颈固定中,枢椎双侧椎弓根螺钉固定和枢椎单侧棘突螺钉联合对侧椎弓根螺钉组合式固定方法均具有良好的稳定性。在寰枢固定中,相对于枢椎棘突螺钉组合式固定,枢椎双侧椎弓根螺钉固定具有更好的寰枢稳定性。在枕颈固定中,枢椎双侧椎弓根螺钉固定在侧屈和旋转活动上较枢椎棘突螺钉组合式固定稳定性更好。枢椎三种棘突螺钉置钉技术间的稳定性差异并不明显。     

Biomechanical effects of polyaxial pedicle screw fixation on the lumbosacral segments with an anterior interbody cage support

Background  

Lumbosacral fusion is a relatively common procedure that is used in the management of an unstable spine. The anterior interbody cage has been involved to enhance the stability of a pedicle screw construct used at the lumbosacral junction. Biomechanical differences between polyaxial and monoaxial pedicle screws linked with various rod contours were investigated to analyze the respective effects on overall construct stiffness, cage strain, rod strain, and contact ratios at the vertebra-cage junction.     

Role of intraoperative Iso-C based navigation in challenging spine trauma

Background:

Pedicle screw fixation is the most preferred method of stabilizing unstable spinal fractures. Pedicle screw placement may be difficult in presence of fractured posterior elements, deformed spine, gross instability and spinal pathology. Challenging spine-fracture fixation is defined as the presence of one or more of the following: 1) obscured topographical landmarks as in ankylosing spondylitis, 2) fractures in occipitocervical or cervicothoracic regions and 3) preexisting altered spinal alignment. We report a series of pedicle screw insertion with guidance of navigation in difficult fixation problems..

Materials and Methods:

Fourteen patients [hangman''s fracture (n=3), odontoid fracture (n=4), C1C2 fracture (n=1) and spinal fracture with coexistent ankylosing spondylitis (n=6)] underwent posterior stabilization. Intraoperatively after surgical exposure, images were acquired by Iso-C 3D C-arm and transferred to navigation system. Instrumentation was performed with navigational assistance. Postoperatively, placements of pedicle screws were evaluated with radiographs and CT scan.

Results:

Sixty-seven pedicle screws (cervical, n=33; thoracic, n=6; lumbar, n=26; sacral n=2) and 15 lateral mass screws were inserted with navigation guidance. The average time of image data acquisition by Iso-C 3D C-arm and its transfer to workstation was 4 minutes (range, 2-6 minutes). Postoperative CT scan revealed ideal placement of screws in 63 pedicles (94%), grade 1 cortical breaches (<2 mm) in 3 pedicles (4.5%) and grade 2 cortical breach (2-4 mm) in one pedicle (1.5%). There were no neurovascular complications. Deep infection was encountered in one case, which settled with debridement.

Conclusions:

Intraoperative Iso-C 3D C-arm based navigation is a useful adjunct while stabilizing challenging spinal trauma, rendering feasibility, accuracy and safety of pedicle screw placement even in difficult situations.     

Type 4 capitellum fractures: Diagnosis and treatment strategies

Background:

Fractures of the capitellum are rare injuries of the elbow usually seen in the adolescents. This fracture is often missed in the emergency room if a proper radiograph is not available. Recent reports have described many modalities of treatment favoring headless screw for fixation. The facility for headless screw fixation, however, is not available in most centers. This paper presents the diagnosis and management of type 4 capituller fractures (Mckee) with gadgets available in a district hospital.

Materials and Methods:

Between 2004 and 2007 three patients with right sided type IV capetullar fracture were treated in a district hospital. There were two boys aged 15 and 17 and one 33 years old lady. In one case, the fracture was missed in the emergency room. A double arc sign in the lateral views of the X-rays of the elbow was seen in all the cases. In each case a preoperative CT scan was done and a diagnosis of Mckee type IV fracture of the capitellum was made. Under tourniquet, using extended lateral approach, open reduction and internal fixation was done using 4mm partially threaded AO cancellous screws (n=2) and 2.7 mm AO screws (n=1), under vision from posterior to anterior direction from the posterior aspect of lateral condyle of humerus avoiding articular penetration.

Results:

All the fractures united uneventfully. At the end of one year follow-up, two cases had excellent elbow function; implants were removed and there were no signs of AVN or arthritis. The third case had good elbow ROM at 11 months without AVN.

Conclusion:

Double arc sign on lateral X-rays of the elbow along with pre-operative CT scan evaluation is important to avoid a missed diagnosis and analysis of type IV capitellur fracture. Fixation with non-cannulated ordinary AO screws using extended Kocher''s lateral approach has given good results.     

Pullout strength of misplaced pedicle screws in the thoracic and lumbar vertebrae - A cadaveric study

Background:

The objective of this cadaveric study was to analyze the effects of iatrogenic pedicle perforations from screw misplacement on the mean pullout strength of lower thoracic and lumbar pedicle screws. We also investigated the effect of bone mineral density (BMD), diameter of pedicle screws, and the region of spine on the pullout strength of pedicle screws.

Materials and Methods:

Sixty fresh human cadaveric vertebrae (D10–L2) were harvested. Dual-energy X-ray absorptiometry (DEXA) scan of vertebrae was done for BMD. Titanium pedicle screws of different diameters (5.2 and 6.2 mm) were inserted in the thoracic and lumbar segments after dividing the specimens into three groups: a) standard pedicle screw (no cortical perforation); b) screw with medial cortical perforation; and c) screw with lateral cortical perforation. Finally, pullout load of pedicle screws was recorded using INSTRON Universal Testing Machine.

Results:

Compared with standard placement, medially misplaced screws had 9.4% greater mean pullout strength and laterally misplaced screws had 47.3% lesser mean pullout strength. The pullout strength of the 6.2 mm pedicle screws was 33% greater than that of the 5.2 mm pedicle screws. The pullout load of pedicle screws in lumbar vertebra was 13.9% greater than that in the thoracic vertebra (P = 0.105), but it was not statistically significant. There was no significant difference between pullout loads of vertebra with different BMD (P = 0.901).

Conclusion:

The mean pullout strength was less with lateral misplaced pedicle screws while medial misplaced pedicle screw had more pullout strength. The pullout load of 6.2 mm screws was greater than that of 5.2 mm pedicle screws. No significant correlation was found between bone mineral densities and the pullout strength of vertebra. Similarly, the pullout load of screw placed in thoracic and lumbar vertebrae was not significantly different.     

Transarticular screw fixation using neuronavigation: Technique

Background:

Transarticular screw placement needs highly accurate imaging. We assess the efficacy and accuracy of C1-C2 transarticular screw fixation using neuronavigation and also cast a technical note on the procedure.

Materials and Methods:

This study included a total of nine patients who underwent transarticular screw fixation using the neuronavigation system. A total of 15 screws were placed. All patients underwent postoperative CT scan with 3-Dimensional (3-D) reconstruction to check for the accuracy of implantation.

Results:

One patient had encroachment of the transverse foramen but there was no vertebral artery injury. There were no clinical complications or adverse sequelae.

Conclusion:

Neuronavigation is extremely helpful in C1-C2 transarticular screw fixation and gives excellent accuracy.     

The best location for proximal locking screw for femur interlocking nailing: A biomechanical study

Background:

Proximal locking screw deformation and screw fracture is a frequently seen problem for femur interlocking nailing that affects fracture healing. We realized that there is lack of literature for the right level for the proximal locking screw. We investigated the difference of locking screw bending resistance between the application of screws on different proximal femoral levels.

Materials and Methods:

We used a total of 80 proximal locking screws for eight groups, 10 screws for each group. Three-point bending tests were performed on four types of screws in two different trochanteric levels (the lesser trochanter and 20 mm proximal). We determined the yield points at three-point bending tests that a permanent deformation started in the locking screws using an axial compression testing machine.

Results:

The mean yield point value of 5 mm threaded locking screws applied 20 mm proximal of lesser trochanter was 1022 ± 49 (range 986–1057) (mean ± standard deviation, 95% confidence interval). On the other hand, the mean yield point value of the same type of locking screws applied on the lesser trochanteric level was 2089 ± 249 (range 1911–2268). Which means 103% increase of screw resistance between two levels (P = 0.000). In all screw groups, on the lesser trochanter line we determined 98–174% higher than the yield point values of the same type of locking screws in comparison with 20 mm proximal to the lesser trochanter (P = 0.000).

Conclusion:

According to our findings, there is twice as much difference in locking screw bending resistance between these two application levels. To avoid proximal locking screw deformation, locking screws should be placed in the level of the lesser trochanter in nailing of 1/3 middle and distal femur fractures.     

胸腰段钉棒系统内固定术后断钉原因分析

目的分析椎弓根螺钉术后断钉的原因。方法分析45例胸腰段骨折患者术后10例发生断钉的骨折类型、术中操作、产品设计、螺钉负荷、椎弓根螺钉置入情况、术后活动情况以及术后预防措施。结果 10例术后断钉患者中,术后1个月复查时发现断钉2例,术后4~6个月复查时发现断钉7例,术后30个月复查时发现断钉1例。T11断钉1例,T12断钉4例,L1断钉3例,L2断钉2例。未减压24例(其中含Chance骨折3例)中断钉4例,减压未植骨5例中断钉3例;减压植骨16例(其中含骨折脱位型4例)中断钉3例。45例中椎弓根螺钉预留骨界面过长4例中断钉3例。结论骨折类型与植骨、术中操作、撑开后螺钉负荷过大、术后活动不当、内固定取出过迟为螺钉断裂的主要原因。     

Accuracy and safety of free-hand pedicle screw fixation in age less than 10 years

Background:

Pedicle screws are being used commonly in the treatment of various spinal disorders. However, use of pedicle screws in the pediatric population is not routinely recommended because of the risk of complications. The present study was to evaluate the safety of pedicle screws placed in children aged less than 10 years with spinal deformities and to determine the accuracy and complication (early and late) of pedicle screw placement using the postoperative computed tomography (CT) scans.

Materials and Methods:

Thirty one patients (11 males and 20 females) who underwent 261 pedicle screw fixations (177 in thoracic vertebrae and 84 in lumbar vertebrae) for a variety of pediatric spinal deformities at a single institution were included in the study. The average age of patients was 7 years and 10 months. These patients underwent postoperative CT scan which was assessed by two independent observers (spine surgeons) not involved in the treatment.

Results:

Breach rate was 5.4% (14/261 screws) for all pedicles. Of the 177 screws placed in the thoracic spine, 13 (7.3%) had breached the pedicle, that is 92.7% of the screws were accurately placed within pedicles. Seven screws (4%) had breached the medial pedicle wall, 4 screws (2.3%) had breached the lateral pedicle wall and 2 screws (1.1%) had breached the superior or inferior pedicle wall respectively. Of the 84 screws placed in the lumbar spine, 83 (98.8%) screws were accurately placed within the pedicle. Only 1 screw (1.2%) was found to be laterally displaced. In addition, the breach rate was found to be 4.2% (11/261 screws) with respect to the vertebral bodies. No neurological, vascular or visceral complications were encountered.

Conclusions:

The accuracy of pedicle screw placement in pedicles and vertebral bodies were 94.6% and 95.8% respectively and there was no complication related to screw placement noted until the last followup. These results suggest that free-hand pedicle screw fixation can be safely used in patients younger than 10 years to treat a variety of spinal disorders.     

Augmented osteosynthesis with tensor fascia latae muscle pedicle bone grafting in neglected femoral neck fracture

Background:

Neglected intracapsular femoral neck fracture in young patients may fail to unite because of the excessive shearing strain at the fracture site and it is a surgical challenge to any orthopedic surgeon. The problem is compounded by resorption of the femoral neck and avascular necrosis (AVN) of femoral head. There is no satisfactory solution available in the management of femoral neck fracture as far as the union of the fracture and AVN of femoral head are concerned. Muscle pedicle bone grafting has been advocated to provide additional blood supply to the femoral head. We report a retrospective analysis of 48 cases of neglected femoral neck fracture treated by internal fixation and tensor fascia latae based muscle pedicle bone grafting.

Materials and Methods:

48 patients with femoral neck fractures with age varied from 20 to 53 years (average age 32.9 years) with male to female ratio of 2:1 were enrolled. All fractures were more than 3 weeks old with mean delay being 86 days (22–150 days). Open reduction and internal fixation along with tensor fascia latae muscle pedicle bone grafting was done in all cases. It was supplemented by multiple drilling and cortico-cancellous bone grafting. Fracture fixation was done with three parallel 6.5-mm AO cannulated cancellous lag screws and the graft fixed with a 4-mm cancellous screw to provide a secure fixation. During the followup period of 2-6.8 years (average 4.4 years) the results were assessed clinically by modified Harris hip scoring system and radiologically by the evidence of signs of fracture union.

Results:

Union was achieved in 41/48 (85.41%) cases which were followed for an average period of 4.4 years (2–6.8 years) with good functional results and ability to squat and sit cross-legged. Results were assessed according to modified Harris Hip Scoring system and found to be excellent in 19, good in 22, fair in 5, and poor in 2 patients. Complications were nonunion, (n=3) avascular necrosis (n=2), and coxa vara deformity (n=2).

Conclusion:

Internal fixation with muscle pedicle bone grafting is a suitable option to secure union in neglected femoral neck fractures in physiologically active patients with late presentation.