Influence of bone mineral density on the fixation of thoracolumbar implants. A comparative study of transpedicular screws, laminar hooks, and spinous process wires

Posteriorly directed load to failure testing of four different types of spinal implants was performed in individual T5 to S1 vertebra harvested from seven fresh-frozen human cadaveric spines. The implants tested were: 1) Drummond spinous process wires, 2) Harrington laminar hooks, 3) Cotrel-Dubousset transpedicular screws, and 4) Steffee VSP transpedicular screws. The ultimate failure of each implant was compared with the bone mineral density of each vertebra to determine which implants, if any, were particularly advantageous in osteoporotic vertebrae. Before biomechanical testing, the spines were analyzed in vitro by dual photon absorptiometry to determine the bone mineral densities (gm/cm2) of each vertebra. The mean tensile loads to failure for each of the implants tested were as follows: Cotrel-Dubousset transpedicular screws: 345 Newtons; spinous process wire/button: 382 Newtons; Steffee transpedicular screws: 430 Newtons; and laminar hooks: 646 Newtons. The difference between the loads to failure for laminar hooks and the other implants was significant (P less than 0.05) using one-way analysis of variance. The overall correlation coefficient for bone mineral density with ultimate load to failure was 0.30 (P less than 0.001). The correlation coefficients were 0.47 (P less than 0.001) for spinous process wires alone; 0.096 (not significant) for laminar hooks alone; 0.37 (P less than 0.001) for Cotrel-Dubousset pedicle screws; and 0.48 (P less than 0.001) for Steffee pedicle screws. Of the four different implants tested, laminar hooks were most resistant to failure from posteriorly directed forces.(ABSTRACT TRUNCATED AT 250 WORDS)     

Torsional rigidity of scoliosis constructs

STUDY DESIGN: A biomechanical study of the rigidity of various scoliosis constructs instrumented with and without caudal pedicle screw anchors and with none, one, or two cross-link devices. OBJECTIVES: To determine whether the increased torsional rigidity provided by distal pedicle screw fixation might make cross-linking unnecessary. SUMMARY OF BACKGROUND DATA: Pedicle screws and cross-linking devices have been shown to increase the structural rigidity of spinal constructs. Their relative contributions to scoliosis construct rigidity has not been determined. METHODS: "Short" (T2-T11) and "long" (T2-L3) scoliosis constructs were mounted on an industrially fabricated spine model and tested in a hydraulic testing machine. Four different short and four different long constructs were tested: hooks only, hooks with concave side thoracic sublaminar wires, hooks with distal pedicle screw anchors, and hooks, distal pedicle screw anchors, and concave thoracic sublaminar wires. There were four iterations for each construct tested: no cross-links, one superior cross-link at T4-T5, one inferior cross-link at T9-T10, and two cross-links. Torsional rigidity was tested by applying a rotational torque at T2. Vertebral body motion was recorded with a three-dimensional video analysis system. RESULTS: Constructs with distal pedicle screws were statistically more rigid in torsion than those with hooks as distal anchors. The additional torsional rigidity from one or more cross-links was negligible compared with that provided by pedicle screws. CONCLUSIONS: With pedicle screws as distal anchors in scoliosis constructs, cross-linking with one or two devices adds very little additional rotational stiffness and may be unnecessary in many cases.     

Pullout strength of pedicle screws versus pedicle and laminar hooks in the thoracic spine

While the biomechanical properties of pedicle screws have proven to be superior in the lumbar spine, little is known concerning pullout strength of pedicle screws in comparison to hooks in the thoracic spine. In vitro biomechanical pullout testing was performed to evaluate the axial pullout strength of pedicle screws versus pedicle and laminar hooks in the thoracic spine with regard to surgical correction techniques in scoliosis. Nine human cadaveric thoracic spines were harvested and disarticulated. To simulate a typical posterior segmental scoliosis instrumentation, standard pedicle hooks were used between T4 and T8 and supralaminar hooks between T9 and T12 and tested against pedicle screws. The pedicle screws were loaded strictly longitudinal to their axis; the hooks were loaded perpendicular to the intended rod direction. In total, 90 pullout tests were performed. Average pullout strength of the pedicle screws was significantly higher than in the hook group (T4-T8: 531 N versus 321 N, T9-T12: 807 N versus 600 N, p < 0.05). Both screw diameter and the bone mineral density (BMD) had significant influence on the pullout strength in the screw group. For scoliosis correction, pedicle screws might be beneficial, especially for rigid thoracic curves, since they are significantly more resistant to axial pullout than both pedicle and laminar hooks.     

Biomechanical comparison of two-level cervical locking posterior screw/rod and hook/rod techniques.

BACKGROUND CONTEXT: Locking posterior instrumentation in the cervical spine can be attached using 1) pedicle screws, 2) lateral mass screws, or 3) laminar hooks. This order of options is in order of decreasing technical difficulty and decreasing depth of fixation, and is thought to be in order of decreasing stability. PURPOSE: We sought to determine whether substantially different biomechanical stability can be achieved in a two-level construct using pedicle screws, lateral mass screws, or laminar hooks. Secondarily, we sought to quantify the differential and additional stability provided by an anterior plate. STUDY DESIGN: In vitro biomechanical flexibility experiment comparing three different posterior constructs for stabilizing the cervical spine after three-column injury. METHODS: Twenty-one human cadaveric cervical spines were divided into three groups. Group 1 received lateral mass screws at C5 and C6 and pedicle screws at C7; Group 2 received lateral mass screws at C5 and C6 and laminar hooks at C7; Group 3 received pedicle screws at C5, C6, and C7. Specimens were nondestructively tested intact, after a three-column two-level injury, after posterior C5-C7 rod fixation, after two-level discectomy and anterior plating, and after removing posterior fixation. Angular motion was recorded during flexion, extension, lateral bending, and axial rotation. Posterior hardware was subsequently failed by dorsal loading. RESULTS: Laminar hooks performed well in resisting flexion and extension but were less effective in resisting lateral bending and axial rotation, allowing greater range of motion (ROM) than screw constructs and allowing a significantly greater percentage of the two-level ROM to occur across the hook level than the screw level (p<.03). Adding an anterior plate significantly improved stability in all three groups. With combined hardware, Group 3 resisted axial rotation significantly worse than the other groups. Posterior instrumentation resisted lateral bending significantly better than anterior plating in all groups (p<.04) and resisted flexion and axial rotation significantly better than anterior plating in most cases. Standard deviation of the ROM was greater with anterior than with posterior fixation. There was no significant difference among groups in resistance to failure (p=.74). CONCLUSIONS: Individual pedicle screws are known to outperform lateral mass screws in terms of pullout resistance, but they offered no apparent advantage in terms of construct stability or failure of whole constructs. Larger standard deviations in anterior fixation imply more variability in the quality of fixation. In most loading modes, laminar hooks provided similar stability to lateral mass screws or pedicle screws; caudal laminar hooks are therefore an acceptable alternative posteriorly. Posterior two-level fixation is less variable and slightly more stable than anterior fixation. Combined instrumentation is significantly more stable than either anterior or posterior alone.     

Biomechanical evaluation of a new fixation device for the thoracic spine

The technology used in surgery for spinal deformity has progressed rapidly in recent years. Commonly used fixation techniques may include monofilament wires, sublaminar wires and cables, and pedicle screws. Unfortunately, neurological complications can occur with all of these, compromising the patients’ health and quality of life. Recently, an alternative fixation technique using a metal clamp and polyester belt was developed to replace hooks and sublaminar wiring in scoliosis surgery. The goal of this study was to compare the pull-out strength of this new construct with sublaminar wiring, laminar hooks and pedicle screws. Forty thoracic vertebrae from five fresh frozen human thoracic spines (T5–12) were divided into five groups (8 per group), such that BMD values, pedicle diameter, and vertebral levels were equally distributed. They were then potted in polymethylmethacrylate and anchored with metal screws and polyethylene bands. One of five fixation methods was applied to the right side of the vertebra in each group: Pedicle screw, sublaminar belt with clamp, figure-8 belt with clamp, sublaminar wire, or laminar hook. Pull-out strength was then assessed using a custom jig in a servohydraulic tester. The mean failure load of the pedicle screw group was significantly larger than that of the figure-8 clamp (P = 0.001), sublaminar belt (0.0172), and sublaminar wire groups (P = 0.04) with no significant difference in pull-out strength between the latter three constructs. The most common mode of failure was the fracture of the pedicle. BMD was significantly correlated with failure load only in the figure-8 clamp and pedicle screw constructs. Only the pedicle screw had a statistically significant higher failure load than the sublaminar clamp. The sublaminar method of applying the belt and clamp device was superior to the figure-8 method. The sublaminar belt and clamp construct compared favorably to the traditional methods of sublaminar wires and laminar hooks, and should be considered as an alternative fixation device in the thoracic spine.     

Biomechanical evaluation of pedicle screws versus pedicle and laminar hooks in the thoracic spine.

BACKGROUND CONTEXT: Pedicle screws have been shown to be superior to hooks in the lumbar spine, but few studies have addressed their use in the thoracic spine. PURPOSE: The objective of this study was to biomechanically evaluate the pullout strength of pedicle screws in the thoracic spine and compare them to laminar hooks. STUDY DESING/SETTING: Twelve vertebrae (T1-T12) were harvested from each of five embalmed human cadavers (n=60). The age of the donors averaged 83+8.5 years. After bone mineral density had been measured in the vertebrae (mean=0.47 g/cm(3)), spines were disarticulated. Some pedicles were damaged during disarticulation or preparation for testing, so that 100 out of a possible 120 pullout tests were performed. METHODS: Each vertebra was secured using a custom-made jig, and a posteriorly directed force was applied to either the screw or the claw. Constructs were ramped to failure at 3 mm/min using a Mini Bionix II materials testing machine (MTS, Eden Prairie, MN). RESULTS: Pedicle claws had an average pullout strength of 577 N, whereas the pullout strength of pedicle screws averaged 309 N. Hooks installed using the claw method in the thoracic spine had an overwhelming advantage in pullout strength versus pedicle screws. Even in extremely osteoporotic bone, the claw withstood 88% greater pullout load. CONCLUSION: The results of this study indicate that hooks should be considered when supplemental instrumentation is required in thoracic vertebrae, especially in osteoporotic bone.     

2- to 4-year outcome of dorsal double rod instrumentation spondylodesis in idiopathic scoliosis]

INTRODUCTION: In order to evaluate the results of posterior correction and fusion using the Münster Posterior Doublerod-System (MPDS) 48 patients with idiopathic scoliosis were studied prospectively. METHODS: All patients underwent clinical examination and radiological analysis of the frontal and sagittal plane preoperatively, postoperatively and at follow-up (2-4 years). Pedicle screws were used at the lumbar and thoracolumbar spine exclusively. RESULTS: The preoperative average Cobb angle was 61.4 degrees with an average flexibility of 36.8% to 38.8 degrees. The average postoperative Cobb angle was 24.8 degrees (59.6%) with an average loss of correction of 2.6 degrees Cobb angle (3.6%). Due to the use of thoracolumbar and lumbar pedicle screws instrumented fusion could be stopped at the lower endvertebra in 71%. Patients in whom only pedicle screws had been used improved correction of frontal plane could be shown compared to combined instrumentations with hooks and screws. CONCLUSION: The posterior instrumentation guarantees primary stability with good results of correction and allows brace free treatment postoperatively. The postoperative correction compared to the results at follow-up proves the stability of the instrumentation largely. The results of mainly pedicle screw based instrumentations verify that an improved correction can be achieved. In most cases fusion levels end at the lower end vertebra and therefore are shorter compared to instrumentation's based on hooks only.     

采用旋转加原位弯棒原理重建脊柱骨折矢状面形态

目的 探讨使用钉钩加原位弯棒技术治疗胸腰椎骨折,在恢复椎体高度的同时对脊柱矢状面形态满意重建的原理和疗效。方法 自１９９７年７月起使用ＣＤ和ＴＳＲＨ治疗胸腰段骨折脱位４８例,其中男４１例,女７例,年龄１７～５４岁。手术方法（以Ｌ１为例）：在Ｔ１２和Ｌ２置入椎弓根螺钉,Ｔ１１和Ｌ２安置偏心椎板钩,对棒按照固定区正常矢状面形态预弯,置入双侧椎弓根螺钉孔内,此时棒的预弯平面位于冠状面上。先用撑开力恢复伤     

寰椎后弓椎板钩联合枢椎椎弓根螺钉固定治疗游离齿状突并可复性寰枢椎脱位

背景：游离齿状突并可复性寰枢椎脱位常需要手术治疗,但目前缺乏操作简单且安全有效的寰枢椎内固定方式。 目的：评估寰椎后弓椎板钩联合枢椎椎弓根螺钉固定植骨融合治疗游离齿状突并可复性寰枢椎脱位的疗效。 方法：回顾性分析2005年7月至2012年6月采用寰椎后弓椎板钩联合枢椎椎弓根螺钉固定自体髂骨植骨融合术治疗游离齿状突并可复性寰枢椎脱位患者l1例。对脱位复位情况、内固定植骨融合率、JOA功能评分、影像学评估及术后并发症等进行分析。 结果：11例术中均未发生椎动脉和脊髓损伤。术后均获得随访,随访时间为12~37个月,平均25个月,均未发生内固定物松动、断裂,术后疼痛和神经症状均得到缓解,术后JOA评分较术前明显改善（P＜0.01）,寰枢椎均融合。 结论：寰椎后弓椎板钩联合枢椎椎弓根螺钉固定植骨融合术治疗游离齿状突并可复性寰枢椎脱位是一种安全有效的方法。     

Comparative analysis of pedicle screw and hook instrumentation in posterior correction and fusion of idiopathic thoracic scoliosis

Posterior correction and fusion with segmental hook instrumentation represent the gold standard in the surgical treatment of progressive idiopathic thoracic scoliosis. However, there is a debate over whether pedicle screws are safe in scoliosis surgery and whether their usage might enable a better curve correction and a shorter fusion length. The details of curve correction, fusion length and complication rate of 99 patients with idiopathic thoracic scoliosis treated with either hook or pedicle screw instrumentation were analyzed. Forty-nine patients had been operated with the Cotrel-Dubousset system using hooks exclusively ("hook group"). Fifty patients had been operated with either a combination of pedicle screws in the lumbar and lower thoracic and hooks in the upper thoracic spine or exclusive pedicle screw instrumentation using the Münster Posterior Double Rod System ("screw group"). The preoperative Cobb angle averaged 61.3 degrees (range 40 degrees-84 degrees ) in the hook group and 62.5 degrees (range 43 degrees-94 degrees ) in the screw group. Average primary curve correction was 51.7% in the hook group and 55.8% in the screw group ( P>0.05). However, at follow-up (2-12 years later) primary curve correction was significantly greater ( P=0.001) in the screw group (at 50.1%) compared to the hook group (at 41.1%). Secondary lumbar curve correction was significantly greater ( P=0.04) in the screw group (54.9%) compared to the hook group (46.9%). Correction of the apical vertebral rotation according to Perdriolle was minimal in both groups. Apical vertebral translation was corrected by 42.0% in the hook group and 55.6% in the screw group ( P=0.008). Correction of the tilt of the lowest instrumented vertebra averaged 48.1% in the hook group and 66.2% in the screw group ( P=0.0004). There were no differences concerning correction of the sagittal plane deformity between the two groups. Fusion length was, on average, 0.6 segments shorter in the screw group compared to the hook group ( P=0.03). With pedicle screws, the lowest instrumented vertebra was usually one below the lower end vertebra, whereas in the hook group it was between one and two vertebrae below the lower end vertebra. Both operative time and intraoperative blood loss were significantly higher in the hook group ( P<0.0001). One pedicle screw at T5 was exchanged due to the direct proximity to the aorta. There were no neurologic complications related to pedicle screw instrumentation. Pedicle screw instrumentation alone or in combination with proximal hook instrumentation offers a significantly better primary and secondary curve correction in idiopathic thoracic scoliosis and enables a significantly shorter fusion length.     

Posterior fixation of thoracolumbar burst fracture: short-segment pedicle fixation versus long-segment instrumentation

OBJECTIVE: The treatment of thoracolumbar burst fracture is a controversial issue. Short-segment (SS) pedicle fixation has become a popular treatment option. However, there are several studies regarding the high rate of failure. The aim of this prospective study was to compare SS versus long-segment (LS) instrumentation. METHODS: For this purpose, 18 consecutive patients were assigned to two groups. Group 1 included nine patients treated by SS pedicle fixation, whereas group 2 included nine patients treated by LS instrumentation. SS instrumentation was pedicle fixation one level above and below the fractured vertebra. LS instrumentation was hook fixation (claw hooks attached to second upper vertebra and infralaminar hooks attached to first upper vertebra) above and pedicle fixation (pedicle screws attached to first and second lower vertebrae) below the fractured vertebra. RESULTS: As a result, measurements of local kyphosis, sagittal index, and anterior vertebral height compression showed that the LS group had a better outcome at final follow-up (P < 0.05). Also, the SS group had a 55% failure rate, whereas the LS group had prolonged operative time and increased blood loss. However, there was no difference between the two groups according to Low Back Outcome Score. CONCLUSIONS: In conclusion, radiographic parameters demonstrated that LS instrumentation is a more effective management of thoracolumbar burst fractures. Nevertheless, clinical outcome was the same between the two groups. However, our conclusions were based on posterior-only surgery. Anterior column support would negate the need for LS fixation. Also, SS would have been more successful if two above and two below pedicle screws were used.     

寰椎后弓椎板钩联合枢椎椎弓根螺钉固定治疗Ⅱ型齿突骨折

目的评估寰椎后弓椎板钩联合枢椎椎弓根螺钉固定植骨融合治疗Ⅱ型齿突骨折的疗效。方法2004年3月-2007年3月对13例Ⅱ型齿突骨折患者以寰椎后弓椎板钩联合枢椎椎弓根螺钉固定自体髂骨植骨融合术进行治疗，其中6例伴脊髓受损症状。结果术中未发生椎动脉和脊髓损伤；平均随访时间为18个月（6—32个月）；未发生内固定物松动、断裂。所有患者寰枢椎均融合。6例脊髓受损患者术前JOA评分为10．1分（9．2～11．8分），术后2周JOA评分为15．6分（15．2～16．8分）。结论寰椎后弓椎板钩联合枢椎椎弓根螺钉固定植骨融合术治疗Ⅱ型齿突骨折是一种安全有效的方法。     

Biomechanical analysis of a novel hook-screw technique for C1-2 stabilization

The Food and Drug Administration has not cleared the following medical devices for the use described in this study. The following medical devices are being discussed for an off-label use: cervical lateral mass screws. Object As an alternative for cases in which the anatomy and spatial relationship between C-2 and a vertebral artery precludes insertion of C-2 pedicle/pars or C1-2 transarticular screws, a technique that includes opposing laminar hooks (claw) at C-2 combined with C-1 lateral mass screws may be used. The biomechanical stability of this alternate technique was compared with that of a standard screw-rod technique in vitro. Methods Flexibility tests were performed in 7 specimens (occiput to C-3) in the following 6 different conditions: 1) intact; 2) after creating instability and attaching a posterior cable/graft at C1-2; 3) after removing the graft and attaching a construct comprising C-1 lateral mass screws and C-2 laminar claws; 4) after reattaching the posterior cable-graft at C1-2 (posterior hardware still in place); 5) after removing the posterior cable-graft and laminar hooks and placing C-2 pedicle screws interconnected to C-1 lateral mass screws via rod; and 6) after reattaching the posterior cable-graft at C1-2 (screw-rod construct still in place). Results All types of stabilization significantly reduced the range of motion, lax zone, and stiff zone compared with the intact condition. There was no significant biomechanical difference in terms of range of motion or lax zone between the screw-rod construct and the screw-claw-rod construct in any direction of loading. Conclusions The screw-claw-rod technique restricts motion much like the standard Harms technique, making it an acceptable alternative technique when aberrant arterial anatomy precludes the placement of C-2 pars/pedicle screws or C1-2 transarticular screws.     

胸椎经关节突关节椎弓根螺钉固定的可行性研究

 目的明确胸椎后路经关节突关节椎弓根螺钉固定的解剖学可行性和技术参数.为临床应用提供参考。方法取 20具胸椎标本.仔细解剖胸椎的后侧和前侧方.以清楚地暴露胸椎椎板和椎弓根。以椎板下缘向上、外缘向内各 7 mm为进钉点.在 T_1.2、T_5.6、T_9.10直视下置入经关节突关节椎弓根螺钉.通过直接的置钉和 CT重建.观察胸椎后路经关节突关节椎弓根螺钉实际置钉的可行性.测量经关节突关节椎弓根螺钉内固定进钉角度和钉道长度。结果所有胸椎后路经关节突关节椎弓根螺钉均由上位胸椎下关节突经关节突关节.进入下位胸椎的椎弓根.成功置入下位胸椎的椎体内。重建 CT测量发现螺钉在横断面的外倾角度为 2.1°±0.7°.在矢状面的尾倾角度为 41.4°±3.2°.在各节段间略有不同.但差异无统计学意义。平均的螺钉钉道长度为(40.6±4.9) mm.钉道长度由上胸椎向中、下胸椎呈逐渐增加趋势.差异有统计学意义(F=74.09, P<0.01)。结论胸椎后路经关节突关节椎弓根螺钉具有解剖学可行性.可以作为胸椎椎弓根螺钉固定的一种补充内固定方法.但置钉时要求较高的准确性。     

Comparative analysis of pedicle screw versus hybrid instrumentation in adolescent idiopathic scoliosis surgery

The expectations of both the patient and surgeon have been greatly revised in the last 10 years with the introduction of pedicle screws (PS) in spinal surgery. In this study, we have retrospectively evaluated and compared the results of PS instrumentation and the Hybrid System (HS), the latter consists of pedicle screws, sublaminar wire and hooks. The mean follow-up period was 60.1 months (range: 49-94 months) for the patients of the HS group and 29.3 months (range: 24-35 months) for those of the PS group. In the HS group, pedicle screws were used at the thoracolumbar junction and lumbar vertebra, the bilateral pediculotransverse claw hook configuration was used at the cranial end of the instrumentation, sublaminar wire was used on the concave side of the apical region and the compressive hook was used on the convex side. In the PS group, PS were used on the concave sides at all levels and on the convex side of the cranial and caudal end of instrumentation, in the transition zone and at the apex. The two groups were comparable for variables such as mean age, preoperative Cobb angle, thoracic kyphosis angle, lordosis angle, coronal balance, flexibility of the curve, apical vertebra rotation (AVR), apical vertebra rotation (AVT) and the number of vertebrae included in the fusion (p > 0.05). The parameters of values of correction, ratio of correction loss, AV derotation, AVT correction ratio, amount of blood loss, operation time, postoperative global coronal and sagittal balance, thoracic kyphosis angle and lumbar lordosis angle were measured at the last follow-up and used for comparing the HS and PS groups. There was no statistically significant difference between the groups for correction ratio, postoperative coronal balance, postoperative thoracic kyphosis and lumbar lordosis angle, operation time, amount of blood loss and number of fixation points (p > 0.05) The difference for the ratio of correction loss, AV derotation angle and the AVT correction ratio at the last follow-up visit and for the total follow-up period between the groups was found to be statistically significant (p < 0.05). Although it is possible to obtain a similar amount of correction by either instrumentation system, the loss of correction seems to be lower with the more rigid PS construction. The PS system also has a stronger effect on vertebral bodies, thereby providing better AV de-rotation. There was no significant difference (p > 0.05) between the groups in terms of correction rate, postoperative coronal and sagittal balance, operation time, blood loss and number of fixation points. This may indicate that anchor points are more important than the use - or not - of screws. Correction durability and AV de-rotation was better with PS instrumentation, while AVT was better corrected by HS instrumentation (p < 0.05). We propose that the reason for the better correction of AVT with HS instrumentation is the forceful translation offered by the sublaminar wire at the apical region, while the reason for the better correction durability of the PS instrumentation may be due to the fact that multiple pedicle screws which afford three-column control are better at maintaining the correction and preventing late deterioration.     

A biomechanical analysis of the self-retaining pedicle hook device in posterior spinal fixation

Regular hooks lack initial fixation to the spine during spinal deformity surgery. This runs the risk of posterior hook dislodgement during manipulation and correction of the spinal deformity, that may lead to loss of correction, hook migration, and post-operative junctional kyphosis. To prevent hook dislodgement during surgery, a self-retaining pedicle hook device (SPHD) is available that is made up of two counter-positioned hooks forming a monoblock posterior claw device. The initial segmental posterior fixation strength of a SPHD, however, is unknown. A biomechanical pull-out study of posterior segmental spinal fixation in a cadaver vertebral model was designed to investigate the axial pull-out strength for a SPHD, and compared to the pull-out strength of a pedicle screw. Ten porcine lumbar vertebral bodies were instrumented in pairs with two different instrumentation constructs after measuring the bone mineral density of each individual vertebra. The instrumentation constructs were extracted employing a material testing system using axial forces. The maximum pull-out forces were recorded at the time of the construct failure. Failure of the SPHD appeared in rotation and lateral displacement, without fracturing of the posterior structures. The average pull-out strength of the SPHD was 236 N versus 1,047 N in the pedicle screws (P < 0.001). The pull-out strength of the pedicle screws showed greater correlation with the BMC compared to the SPHD (P < 0.005). The SPHD showed to provide a significant inferior segmental fixation to the posterior spine in comparison to pedicle screw fixation. Despite the beneficial characteristics of the monoblock claw construct in a SPHD, that decreases the risk of posterior hook dislodgement during surgery compared to regular hooks, the SPHD does not improve the pull-out strength in such a way that it may provide a biomechanically solid alternative to pedicle screw fixation in the posterior spine.     

寰椎椎板钩联合枢椎椎弓根螺钉内固定的力学稳定性评价

目的 评价寰椎椎板钩联合枢椎椎弓根螺钉内固定的生物力学稳定性.方法 取6具新鲜尸体颈椎标本置于1.5 N·m载荷下,测量C_(1-2)节段的三维运动范围(ROM).标本按随机顺序,依次行完整状态(完整状态组)、不稳状态(齿状突周围韧带切除,为不稳状态组)、经寰枢关节间隙螺钉联合Gallic内固定(固定A组)、寰椎椎板钩联合枢椎椎弓根螺钉内固定(固定B组)、寰枢椎椎弓根螺钉内固定(固定C组)5种状态下的三维ROM值测量.比较各组标本的屈伸、侧屈、旋转ROM值.结果 完整状态组、不稳状态组、固定A、B、C组的平均屈伸ROM值分别为17.78°、30.69°、2.25°、2.93°、2.73°,组间比较差异有统计学意义(F=216.69,P=0.000);平均侧屈ROM值分别为9.56°、17.18°、1.91°、2.30°、2.05°,组间比较差异有统计学意义(F=122.75,P=0.000);平均旋转ROM值分别为44.19°、57.30°、1.22°、2.88°、2.07°,组间比较差异有统计学意义(F=154.54,P=0.000).固定A、B、C组较完整状态组和不稳状态组各个方向的ROM值均明显减少,差异均有统计学意义(P<0.05),但固定A、B、C组之间符个方向的ROM值比较差异均无统计学意义(P>0.05).结论 寰椎椎板钩联合枢椎椎弓根螺钉内固定可提供与经寰枢关节间隙螺钉联合Gallic内固定和寰枢椎椎弓根螺钉内固定相当的力学稳定性.在以上两种方法无法实施时,可作为一种安全的替代.     

椎弓根螺钉置入对幼犬胸椎形态发育的影响

目的:通过动物实验观察椎弓根螺钉置入对胸椎形态发育的影响。方法:将16只2月龄幼犬随机分为3组,A组(3只)为空白对照组,自T7～T13后路切开,显露椎板;B组(5只)为对照组,以螺钉穿过神经弓中心软骨联合对目标椎椎弓根仅做隧道破坏,螺钉不置留;C组(8只)为实验组,螺钉穿过神经弓中心软骨联合并留置于椎弓根内。实验的目标椎设计为T8、T10、T12,目标椎的上下两个脊椎的各相应测量指标取平均值做为其自身对照。应用CT测量并观察脊椎的形态学指标变化。结果:术后3个月,C组目标椎椎管面积、椎管横径、椎管纵径、椎弓根长度与相邻脊椎平均值比较显著减少(P<0.05),而A组、B组间未发现明显差异;各组椎体横径、椎体纵径、椎体高度测量结果显示目标椎与相邻脊椎平均值无显著性差异(P>0.05)。结论:椎弓根螺钉内固定术对于幼犬胸椎椎管、椎弓的发育有显著影响,有可能导致医源性椎管狭窄;对于椎体发育无明确影响。     

寰椎椎板钩联合枢椎椎弓根螺钉治疗寰枢椎失稳的临床疗效

目的探讨后路寰椎椎板钩联合枢椎椎弓根螺钉技术治疗寰枢椎失稳的临床疗效。方法 2009年12月-2012年12月,行后路寰椎椎板钩联合枢椎椎弓根螺钉固定技术的寰枢椎失稳患者,有效随访资料36例,其中男26例,女10例;年龄21-66岁,平均42.3岁;有脊髓损伤症状者28例,日本骨科学会（Japanese Orthopaedic Association,JOA）评分9.3±1.8;有颈枕区疼痛症状者30例,颈枕区视觉模拟量表（visual analog scale,VAS）评分3.9±1.1;36例患者颈椎障碍功能指数（neck disability index,NDI）术前27.6±8.3;有发作性眩晕症状者6例;寰枢椎脱位26例,术前均行颅骨牵引术并达到复位。结果所有患者均顺利完成手术。术中出血量为80-600 mL,平均295 mL;手术时间95-210 min,平均157 min。术后随访个6-42个月,平均21个月,35例术后6月获得融合,影像学检查可见连续骨小梁,植骨融合率97.2%。末次随访JOA评分改善至13.7±2.0,平均改善率58%;术后VAS评分1.8±0.9;NDI降低至12.9±6.4。JOA评分、VAS评分和NDI评分术前与术后对比差异均具有统计学意义（P〈0.05）。术中未出现椎动脉、脊髓神经损伤或脑脊液漏等并发症。随访期间未发现椎板钩脱位、松动,6例有发作性眩晕患者眩晕症状消失。结论寰椎椎板钩联合枢椎椎弓根螺钉技术手术操作简单、风险低,手术时间短,有良好临床的效果,可作为治疗寰枢椎失稳的一种选择。     

峡部植骨固定术治疗腰椎峡部裂

目的探讨峡部植骨固定术治疗腰椎峡部裂的临床疗效。方法自1998年12月~2005年8月应用峡部植骨固定术治疗腰椎峡部裂患者26例,经椎板AO空心拉力螺钉固定峡部裂7例,椎弓根螺钉合并椎板钩固定19例,峡部裂处均取髂骨植骨。术后3~6个月复查。术前及复查时采用VAS评分进行临床功能评价,摄腰椎双斜位和动力位X线片观察峡部愈合情况和椎间活动度变化。结果术前和随访时VAS评分分别为6.25±1.24、2.14±1.13,差异有显著统计学意义(P<0.01);椎间活动度分别为8.3°±2.4°、8.1°±2.1°,差异无统计学意义(P>0.05)。所有患者斜位X线片示峡部已经无透亮线。结论峡部植骨固定术是治疗腰椎峡部裂所致腰痛的一种合理、简单、安全的术式。