Drilling, not a benign procedure: laboratory simulation of true drilling depth

IntroductionDrilling is an integral part of almost all boney operations. Various anatomical structures coursing close to the bone are at risk if the drill bit projects beyond the far cortex. Aim of this study was to evaluate and quantify the depth to which surgeons over drill beyond the far cortex.Materials and methodsDuring an AO course 153 (41 females, 112 males) surgeons and physicians were invited to participate in this study. Each participant performed 3 bicortical drillings on generic artificial bone. Polystyrene plates were mounted on the far cortex of the bone to allow for exact measurement of the over penetration of the drill bit.ResultsA total of 462 bicortical drilling manoeuvres were analysed. The average projection of the drill bit beyond the far cortex was 6.31 mm. No significant statistical correlation was noted between the specialty or the experience of the participant and depth of over drilling.ConclusionsIt is remarkable that the mean and the range of far cortex over-penetration was quite similar amongst surgeons of differing grades and experience. The results of this study should return to mind to pay attention when drilling particularly in anatomical sites where nerve and vessels coursing close to the far cortex.     

The treatment of primary vertebral tumors by radical resection and prosthetic vertebral replacement

The basic principles for the treatment of primary vertebral tumors include radical resection of the tumor, insertion of a prosthetic vertebral body, and bone grafting within and around the prosthetic vertebral body. Since 1970, the authors have treated 12 cases with this procedure. In order to improve the vertebral prosthesis, 94 dried adult vertebral column specimens were studied. The anterior cortex of each vertebral body was thicker than the posterior cortex. The thickness of the anterior cortex of the dorsolumbar vertebral bodies progressively increases from the proximal to caudal vertebra. The lower lumbar vertebrae are therefore almost twice as thick as the upper dorsal vertebrae. The cortices of the vertebral bodies, especially the anterior cortex, serve as a strut against the pressure of the prosthesis. Four types of prostheses were used. The Type 1 prosthesis failed to take into account the anatomic features of the dorsolumbar vertebral bodies in cross section. Types 2, 3, and 4 are modified versions with specific indications for their use.     

颈椎前路减压异体骨笼植入术

目的:评价颈椎前路环钻法减压、异体骨笼植入融合术的临床疗效.方法:采用椎间盘切除、异体骨笼植入治疗颈椎椎间盘病变患者60例,男25例,女35例;年龄37～72岁,平均47岁.并对其治疗结果进行分析.结果:60例患者平均随访23.2个月,不但临床症状得到改善,而且取得了骨愈合,并能维持颈椎解剖关系,无局部及全身异常反应.结论:颈椎前路环钻法减压、异体骨笼植入是具有应用前景的新方法.     

Depth of insertion of transpedicular vertebral screws into human vertebrae: effect upon screw-vertebra interface strength

Improvement in the strength of the transpedicular screw-vertebra interface by increasing the depth of screw insertion may provide improved performance of spinal implants using such screws. Within human cadaveric vertebrae, we measured the failure strength of Vermont Spinal Fixator (VSF) screws under flexion or torsion loads and of Schanz screws under pull-out loads (along the screw axis). Comparisons between opposite pedicles of vertebral specimens were made at 50 vs. 80% and 80 vs. 100% of maximum available insertion depth. Mean failure strength of VSF screws at 50% depth was 75-77% (depending upon load type) of that at 80% depth; strength for screws at 100% ("to-cortex") depth was 124-154% of that at 80%. Reanalysis of the data from Lavaste shows, contrary to his conclusion, a 26% increase in strength from a 5-mm increase in screw depth of insertion. All these differences were significant (p less than 0.05) by the matched-pairs t test. Benefit from the increased strength of deeper screw placement must be balanced against possible increased operative risk. A "near-approach" x-ray view is suggested here to decrease that presumed operative risk.     

Repair and regeneration of vertebral body after antero-lateral partial vertebrectomy using beta-tricalcium phosphate

Antero-lateral partial vertebrectomy (ALPV) was used for decompression in 91 patients with multilevel cervical disorders. The high-speed drill was used to excise about 1/3 of the vertebral body for relief of anterior compression of the cord and nerve roots under the operating microscope. The key point was opening of the medial wall of the foramen of transverse process at the beginning of the ALPV, allowing the determination of the lateral borders of the ALPVs. To repair and regenerate the vertebral body, a beta-tricalcium phosphate (beta-TCP) block was trimmed into a cuneiform shape and implanted into the sites of the ALPV excluding the upper and lowermost vertebral bodies. Postoperative computed tomography confirmed that beta-TCP was gradually replaced by newly formed bone from the surface towards the center of the block, and that the affected vertebral body was remodeled by 6 to 12 months after the implantation of beta-TCP. The cortical bone borders on the bone marrow at the site of the regeneration. The pedicles on the side of the ALPVs were rebuilt during regeneration of the affected vertebrae. Thus, the vertebral foramen of the cervical spine was widened in the anterior direction at the levels of the ALPVs, resulting in restoration of the physiological size of the cervical cord. The cervical curvature remained unchanged and a certain degree of cervical mobility (mean 86%) was preserved in this series.     

Decompression of the vertebral artery for bow-hunter's stroke. Case report

A case of cerebellar infarction induced by repeated neck rotation ("bow-hunter's stroke") is reported. The most likely mechanism is that repeated rotational neck movement brings about thickening of the atlanto-occipital membrane, fixing the vertebral artery in the vascular groove of the atlas. The vertebral artery is thus pinched at the time of neck rotation, leading to thrombus formation. Embolization results in cerebellar infarction. Surgical decompression of the vertebral artery at the level of the atlas in this case relieved the symptoms, and postoperative angiography demonstrated good flow within the vertebral artery even when the neck was rotated. It was not necessary to restrict the patient's neck movement postoperatively.     

Biomechanical compression tests with a new implant for thoracolumbar vertebral body replacement

The authors present an investigation into the biomechanical functioning of a new titanium implant for vertebral body replacement (Synex). Possible indications are fractures and/or dislocations with damage of the anterior column, posttraumatic kyphosis and tumors of the thoracolumbar spine. The construction must be supplemented by a stabilizing posterior or anterior implant. For best fit and contact with adjacent end-plates, Synex is distractable in situ. We performed comparative compression tests with Synex and MOSS ("Harms mesh cage") on human cadaveric specimens of intact vertebrae (L1). The aim of the study was to measure the compressive strength of the vertebral body end-plate in uniaxial loading via both implants to exclude collapse of Synex in vivo. Twelve human cadaveric specimens of intact vertebrae (L1) were divided into two identical groups (matched pairs) according to bone mineral density (BMD), determined using dual-energy quantitative computed tomography (DE-QCT). The specimens were loaded with an axial compression force at a constant speed of 5 mm/min to failure, and the displacement was recorded with a continuous load-displacement curve. The mean ultimate compression force (Fmax) showed a tendency towards a higher reading for Synex: 3396 N versus 2719 N (non-significant). The displacement until Fmax was 2.9 mm in the Synex group, which was half as far as in the MOSS group (5.8 mm). The difference was significant (P < 0.001). The compression force was twice as high, and significantly (P < 0.05) higher with Synex at displacements of 1 mm, 1.5 mm and 2 mm. A significant (P < 0.001) correlation (R = 0.89) between Fmax and BMD was found. Synex was found to be at least comparable to MOSS concerning the compressive performance at the vertebral end-plate. A possible consequence of the significantly higher mean compression forces between 1 and 2 mm displacement might be decreased collapse of the implant into the vertebral body in vivo.     

数字化虚拟手术系统在胸腰椎骨折治疗中的应用价值

目的探讨数字化虚拟手术系统(digital virtual surgery system,DVSS)在治疗胸腰段骨折中的应用价值并验证其准确性。方法 2008年3月—2011年6月,对113例胸腰段单椎体爆裂型Denis B型骨折患者采用传统后路短节段经伤椎置钉行复位固定(A组)。2012年3月—2014年9月,对128例胸腰段单椎体爆裂型Denis B型骨折患者术前应用DVSS模拟骨折复位,制定最佳手术方案后行后路短节段经伤椎置钉(B组),手术方式与A组相同。比较2组病例手术时间、术中透视时间、术中出血量、椎弓根侧壁及椎体前方骨皮质穿破情况。结果 2组均无感染、血肿发生。B组在手术时间、术中透视时间、椎弓根钉穿破椎弓根侧壁与椎体前方骨皮质方面均优于A组,差异有统计学意义(P0.05)。2组出血量相比,差异无统计学意义(P0.05)。2组病例均未发生其他不良后果。结论应用DVSS辅助脊柱外科手术具有操作简便、安全性高、精确度可信的临床效果,而且便于推广。     

The risk of injury to the axillary nerve, artery, and vein from proximal locking screws of humeral intramedullary nails.

An elderly female cadaver fore-quarter amputation was dissected, and a custom straight intramedullary nail with a 55 degrees oblique downward lateral to medial proximal screw was inserted with a trocar protruding beyond the medial cortex of the humeral surgical neck. The main trunk of the axillary nerve was found to be at risk with any penetration from anterior to posterior and any screw penetration beyond the medial cortex with internal rotation. The axillary artery and vein were at risk with penetration of over 3 cm by a drill point or screw tip whether a transverse or oblique downward screw was used. Transverse screws inserted through the humeral neck from lateral to medial have the potential for damaging a small branch of the axillary nerve laterally, and care must be taken of the lateral humerus while inserting these screws. Screws inserted in a downward direction near the greater tuberosity, if originating above the equator of the humeral head, may cause impingement.     

Creation of transosseous patellar tunnels during extensor mechanism repair: technical note

Transosseous patellar tunnels commonly are used in the repair of acute or chronic patellar tendon or quadriceps tendon ruptures. Commonly, a small diameter (2.0-3.5 mm) drill bit is used to create these drill tunnels. However, drill bits are relatively brittle and susceptible to breakage. The use of a larger diameter smooth Steinmann pin (3/32") is recommended to create transosseous patellar tunnels to eliminate this potential complication.     

弹性弧形骨钻用于椎体成形术的实验研究

目的观察自制弹性弧形骨钻在体外骨质疏松椎体成形术中的手术效果,从而探讨其在椎体成形术中的应用价值。方法采用乙二胺四乙酸二钠盐(EDTA-Na2)浸泡法制备小牛体外骨质疏松椎体,将40个骨质疏松椎体随机分为A、B两组,每组各20个椎体行椎体成形术,A组行常规直钻穿刺,B组采用自制弹性弧形骨钻穿刺,弧形方向朝向穿刺对侧,深度达到椎体中前1/3终止,对两组穿刺骨钻及骨水泥是否达到或越过椎体矢状中线进行统计分析。结果 EDTA-Na2浸泡法脱钙9 d时成功制备出体外骨质疏松椎体,直钻穿刺组钻头达到或越过椎体矢状中线有7个椎体,骨水泥分布达到或越过椎体矢状中线11个;弹性弧形骨钻组穿刺钻头达到或越过椎体矢状中线有18个椎体,骨水泥分布达到或越过椎体矢状中线19个,两组骨钻穿刺效果及骨水泥分布上的差异有统计学意义(P0.05)。A组9个椎体发生骨水泥椎管内渗漏,B组4个椎体发生骨水泥椎管内渗漏,两组间在骨水泥渗漏上差异无统计学意义(P0.05)。结论自制弹性弧形骨钻通过一侧椎弓根穿刺,可以建立一个达到或越过椎体矢状中线的骨性通道,引导骨水泥向穿刺对侧分布,避免了双侧椎弓根穿刺的弊端,其实验效果优于直骨钻。     

Development and Application of an Inside-to-Out Drill Bit for Anterior Cruciate Ligament Reconstruction

We report a novel drilling device for anterior cruciate ligament (ACL) reconstruction that has been developed. We invented a special inside-to-out drill bit that can make a bone socket in an inside-to-out fashion. A blade at the tip of a 4.5-mm diameter drill bit closes when the drill bit is in orthograde rotation, but the blade opens when the drill bit is in reverse rotation. The special drill bit is introduced into the joint through a 4.5-mm diameter bone tunnel rotating the bit in the orthograde direction. Then the drill bit is switched to reverse rotation and is pulled backward so that it bores the bone from the inside out. We have used this special drill bit in treating 31 ACL-injured knees and have experienced no problems or complications with the procedure.     

定向弧形骨钻用于椎体成形术的实验研究

目的：观察自制定向弧形骨钻在体外骨质疏松椎体成形术中的手术效果。方法采用乙二胺四乙酸二钠盐（ EDTA-Na2）浸泡法制备小牛体外骨质疏松椎体,将40个成功制备的骨质疏松椎体随机分为A、B 2组,每组20个椎体行椎体成形术,A组常规直钻穿刺,B组采用自制定向弧形骨钻穿刺,弧形方向朝向穿刺对侧,深度达到椎体中前1/3终止,对2组穿刺骨钻钻头距椎体对侧外缘距离、骨水泥是否达到或越过椎体矢状中线进行比较。结果 EDTA-Na2浸泡法脱钙9 d成功制备出体外骨质疏松椎体。 A组钻头距对侧椎体外缘（2．50±0．32）cm,与B组（0．90±0．26）cm有显著性差异（t＝17．354, P＝0．000）;A组骨水泥分布达到或越过椎体矢状中线椎体数为11个,B组19个,2组比较有统计学差异（Fisher’s检验,P＝0．004）;A组9个椎体发生骨水泥椎管内渗漏,B组4个椎体,2组骨水泥渗漏无显著性差异（Fisher’s检验,P＝0．176）。结论自制定向弧形骨钻通过一侧椎弓根穿刺,可以建立一个达到或越过椎体矢状中线的骨性通道,引导骨水泥向穿刺对侧分布,避免了双侧椎弓根穿刺的弊端,实验效果优于直骨钻,但在骨水泥渗漏的预防方面并未表现出优势。     

Structural features and thickness of the vertebral cortex in the thoracolumbar spine

STUDY DESIGN: The thickness and structure of the vertebral body cortex were examined from sections of human cadaveric vertebrae. OBJECTIVES: The objectives were to identify the principal structural features of the cortex, to directly measure the minimum and maximum thicknesses of the cortex in the thoracolumbar spine, and to compare regional variations in the structure of the cortex. SUMMARY OF BACKGROUND DATA: The thickness of the vertebral cortical shell contributes to the compressive strength of the vertebral body. There is little consensus concerning the thickness and morphology of vertebral shell and endplate along the spine in existing data. METHODS: Human T1, T5, T9, L1, and L5 vertebral bodies (mean age 70.4 years) from 20 cadaveric spines were sectioned and photographed. The minimum and maximum cortical thickness of the shells and endplates in the midsagittal plane were measured from magnified images. RESULTS: The anterior shell thickness was significantly greater than the posterior shell and both endplates. Endplate thickness was greatest in the lower lumbar vertebrae. There was a significant decrease in cortex thickness over the central portion of endplates and shells, with a mean minimum thickness of 0.40 mm and a mean maximum thickness of 0.86 mm, with an overall mean of 0.64 +/- 0.41 mm. Increased porosity was also observed along the central regions of the cortical shells. In the lower thoracic and lumbar spine, a double-layered endplate structure was observed. CONCLUSIONS: Invasive techniques provide the only means to directly resolve the thickness and distribution of bone in the vertebral cortex. The cortex thickness and structure varies along the endplates and the anterior and posterior surfaces of the vertebral body. The implications of the so called double-layered endplate structure are unknown, but indicate the need for further study.     

Surgical stabilization of the cervical spine after trauma.

Surgical stabilization should be individualized for each patient. The procedure used should provide both immediate and prolonged stability at the site of instability. The choice of procedure depends on knowledge of the structures providing stability and of the mechanism of injury. Pure flexon injuries without comminution or disruption of ligaments are stable and do not require surgical treatment. Flexion-rotation dislocations, with either unilateral or bilateral facet dislocation, should be treated by posterior open reduction and fusion if they cannot be reduced by a closed method or if there is demonstratable motion on three-month flexion-extension roentgenograms. A comminuted burst ("teardrop") fracture produced by axial loading of the vertebral bodies should be stabilized by an anterior cortical strut graft for early mobilization and realignment of the spinal column to prevent progressive deformity.     

Roentgenographic measurement of pedicle screw penetration

Potential complications due to pedicle screw penetration of the anterior cortex include injury to vascular, visceral, ureteral, sympathetic, and neural structures. This study examined the accuracy of lateral roentgenographic techniques in determining actual screw penetration in vertebral levels T12 through S1 of ten unilateral sets of pedicles in five anatomic specimens. A true lateral roentgenogram alone was inaccurate for determining the penetration of the anterior cortex by a pedicle screw. The greatest discrepancy between roentgenographically apparent and actual screw penetration was found at the L4 and L5 levels. Deviation from a true lateral roentgenographic axis resulted in the most pronounced change in roentgenographically apparent screw penetration at L4 and L5. The roentgenographic axes resulting in the closest approximation of actual screw penetrations were 5 degrees and 10 degrees above the true lateral axis for the T12-L3 and the L4-S1 levels, respectively. At 50% apparent penetration, the screw may be safely assumed to not be penetrating the anterior cortex using a true lateral roentgenogram. At 80% apparent penetration, 30% and 10% probabilities of actual screw penetration of the anterior cortex exist at L4 and L5, respectively. At 100% apparent penetration, there is an almost 100% probability that the screw is actually protruding through the anterior cortex.     

椎体内部强化术后术椎塌陷的危险因素分析

目的 :探讨椎体内部强化术,包括经皮椎体成形术(PVP)、椎体后凸成形术(PKP),术后术椎塌陷的发生率、独立危险因素以及预防措施。方法:回顾性分析2012年1月至2013年6月经椎体内部强化术治疗并获得随访的154例单节段骨质疏松性椎体压缩骨折(OVCF)患者的临床资料,其中男65例,女89例,年龄57~90岁,平均(76.20±9.35)岁。随访时间6~30个月,平均(15.43±6.81)个月,术后随访患者均接受X线检查,部分患者接受MRI检查。分析与术椎塌陷相关的可能危险因素,包括性别、年龄、手术方式(PVP或PKP)、骨质疏松程度T评分、术椎节段水平、是否合并椎体骨坏死、术椎骨水泥填充模式、术椎前缘高度恢复率。并将可能的危险因素作为研究对象,采用多因素Logistic逐步回归分析法筛选影响术椎塌陷的独立危险因素。结果:随访周期内共发现29例发生术椎塌陷,术椎塌陷的发生率为18.83%。多因素Logistic逐步回归分析显示手术方式(OR=0.171,P=0.010),骨质疏松程度T评分(OR=0.242,P=0.024),是否合并椎体骨坏死(OR=12.225,P=0.003),术椎骨水泥填充模式(OR=10.461,P=0.000)以及术椎前缘高度恢复率(OR=0.316,P=0.019)是影响术椎塌陷的独立危险因素。结论:椎体内部强化术后术椎塌陷的发生率较高,其发生率与多种因素相关,其中手术方式、骨质疏松程度T评分、是否合并椎体骨坏死、术椎骨水泥填充模式、术椎前缘高度恢复率是影响术椎塌陷的独立危险因素。术前严格筛选患者,术中注重骨水泥的对称性均匀分布,术后积极抗骨质疏松治疗,可降低术后术椎塌陷的发生率。     

Real-time tracking of vertebral body movement with implantable reference microsensors.

OBJECTIVE: In the spine, navigation techniques serve mainly to control and accurately target insertion of implants. The main source of error is that the spine is not a rigid organ, but rather a chain of semiflexible movement segments. Any intraoperative manipulation of the patient alters the geometry and volumetry as compared to the 3D volume model created from the image data. Thus, the objective of the study was to implement the theoretical principle of microsensor referencing in a model experiment and to clarify which anatomical structures are suitable for intermittent implantation of positional sensors, as illustrated with cervical vertebral bodies. MATERIALS AND METHODS: Laboratory tests were conducted using 70 models of human cervical vertebral bodies. The first experiment investigated whether arbitrary movements of vertebral bodies can be tracked with the positional information from the implanted microsensors. The accuracy of this movement monitoring was determined quantitatively on the basis of positional error measurement. In the second experiment, different ventral and dorsal surgical operations were simulated on five models of the cervical spine. Quantifiable measurement values such as the spatial extension of the intervertebral space and the relative positions of the planes of the upper plates were determined. RESULTS: With respect to the differing anatomy of the individual vertebral bodies of the cervical spine, the sensors could be placed securely with a 5x2 mm drill. The registration error (RE) was determined as a root mean square error. The mean value was 0.9425 mm (range: 0.57-1.2 mm; median: 0.9400 mm; SD: 0.1903 mm). The precision of the movement monitoring of the vertebral body was investigated along its three main axes. The error tolerance between post-interventional 3D reconstruction and direct measurement on the model did not exceed 1.3 mm in the distance measurements or 2.5 degrees in the angular measurements. The tomograms on the system monitor could be updated in close to real time on the basis of the positional information from the reference sensor. CONCLUSIONS: Motion sensors implanted into the vertebral bodies communicated any change in position to the navigation system in close to real time, thus enabling the preoperative image data set to be updated. The experiments described could ultimately show that continuous real-time visualization of individual vertebral body movements along the movement axes (flexion-extension, tilting and rotation) is possible with high accuracy using implantable microsensors. A future application of such microsensors might be the integration of robot systems into spinal microsurgery.     

Heat generation and heat protection in methylmethacrylate cementation of vertebral bodies

Summary For metastatic disease of the spine, anterior operations on the vertebral bodies often include methylmethacrylate cementation. The cement curing process may produce high temperatures in the surroundings, as demonstrated in joint replacement surgery, and there is a risk of thermal injury to the spinal nerves. In cadavers, we studied the heat arising during curing of cement on the dural sac, and the temperature of the cement surface was measured when the vertebral body was reconstructed using acrylic cement in the same way as in tumor surgery. The temperature increase on the surface of the dural sac during polymerization was between 4° and 12°C, depending on the amount of protection. Only a moderate temperature elevation was measured on the surface of the dural sac, provided that the posterior cortex of the vertebra was retained together with 0.5 cm of the spongious bone or a silicone membrane.     

Characteristics of a prevalent vertebral deformity predict subsequent vertebral fracture: results from the European Prospective Osteoporosis Study (EPOS)

The presence of a prevalent vertebral deformity increases the risk of a future vertebral fracture. The aim of this study was to determine whether certain characteristics of the prevalent deformity, including its shape and location in the spine, influenced this effect. The 3100 men and 3500 women who took part in this analysis were recruited from population registers for participation in the European Prospective Osteoporosis Study (EPOS). Subjects had lateral thoracic and lumbar spine x-rays at baseline, and again after a mean interval of 3.8 years. Prevalent morphometric vertebral deformities on the baseline film were identified by the McCloskey-Kanis method. Incident fractures were defined as vertebrae that also satisfied the McCloskey-Kanis criterion for prevalent deformities on the follow-up film, and in addition had at least one height (anterior, mid, or posterior) which had reduced by at least 20% between films. Poisson regression was used to assess the association between various characteristics of the prevalent deformity and the risk of an incident vertebral fracture, with generalised estimating equations used to allow for the fact that each subject contributed several vertebrae to the analysis. The risk of an incident fracture increased with the number of prevalent deformities: relative risk (RR) for one prevalent deformity 3.2 (95% confidence interval (CI); 2.1, 4.8); 9.8 (95% CI;6.1, 15.8) for 2; and 23.3 (95% CI;15.3, 35.4) for 3 or more. Relative risks differed significantly according to the shape of the prevalent deformity, ranging from 5.9 (95% CI; 4.1, 8.6) if the anterior and mid heights were reduced to 1.6 (95% CI;0.8, 3.2) if the posterior and mid heights were reduced. Risks varied also according to the severity of the deformity. There were fivefold differences in relative risk of incident fracture depending on the location of the prevalent deformity within the spine. Compared to vertebrae in subjects with no deformities at baseline, the relative risk of an incident fracture within three vertebrae of a prevalent deformity was greater (7.7 (95% CI;5.6, 10.5)) than the risk in more distant vertebrae (4.0 (95% CI;2.6, 6.0)). In summary, the risk of a subsequent vertebral fracture in individuals with preexisting deformities is importantly influenced by the characteristics of these deformities.