Pedicle Dimensions Research Articles

Pedicular Anatomy of the First Sacral Segment in Transitional Variations of the Lumbo-Sacral Junction

The study aims to investigate the dimensions and angular orientations of the pedicles of the first sacral segment at the L5-S1 junctions affected by transitional variations. Measurement of parameters of the S1 pedicle and its orientation in sacra with (1) Accessory L5-S1 articulations, (2) Sacralisation of the L5, and (3) Lumbarisation of the first sacral segment, and comparing data with that observed in normal sacra. Lumbosacral fusion with instrumentation and screw fixation is commonly practiced to treat unstable L5-S1 junctions caused by a host of reasons. Though morphometric data pertaining to normal S1 pedicle structure is available in literature, it is hard to find such information regarding pedicles of first sacral segments associated with transitional variations. Transitional states at the lumbosacral junctions are often linked to development of L5-S1 instability. It thus becomes imperative to investigate S1 pedicular anatomy in context of these variations to prevent inadvertent surgical injuries and optimizing effects of screw placement in such sacral variations. S1 pedicle dimensions were measured in normal and L5-S1 transition affected sacra. Slope of the pedicle was measured with respect to the sagittal and the horizontal planes. Linear parameters were similar in the normal sacra and those with L5-S1 accessory articulations. Sacralisation reduced all dimensions including pedicle height, sagittal and transverse dimensions. Lumbarisation was associated with small length between the facet and the sacral promontory. Sacralisation reduced the sagittal angulation of the pedicles but substantially increased its downward slope. Lumbarised pedicles were more obtuse with the sagittal plane and less steep in front. S1 pedicle morphology and angulation in the first sacral segment are different from the normal in L5-S1 transitional situations and hence should be mapped accordingly in screw placements at the region in context of such common variations.

Inter- and intraobserver reliability assessment of computed tomographic 3D measurement of pedicles in scoliosis and size matching with pedicle screws

In patients with scoliosis, the morphology of the pedicles differs from those in normal spines. Preoperative three-dimensional information of these complex anatomic situations means a great advantage for the surgeon in order to assess which pedicles can be instrumented safely avoiding screw misplacement and for the decisions in choosing the appropriate screw size. The objective of this study was to measure pedicle dimensions in scoliotic spines on three-dimensional computed tomographic (CT) scans and to determine the intra- and interobserver reliability of the method. Additionally, the pedicles that cannot be instrumented safely by available screws were identified. All pedicles from T1 to L5 in 30 patients with scoliosis were measured by two independent observers. The pedicle width, height and length were assessed for two times with a 3-week interval. Intraclass correlation coefficients were used to determine the intra- and interobserver reliabilities. The diameters of the pedicles were matched with the dimensions of the smallest available pedicle screws of scoliosis implant systems. The intrarater reliability was strong in 60% of the parameters and moderate in 40%. The interrater reliability was strong in all parameters but in pedicle length. The concave-sided pedicles in the curve revealed to be smaller compared to the convex-sided ones. The highest percentage of size mismatch was found in levels T7 (31%) and T8 (33%). Measurement of pedicle dimensions on three-dimensional CT scans is a reliable but time-consuming procedure to assess pedicle dimensions. CT measuring should be reserved for special cases, where the anatomic situation remains unclear despite X-ray. In scoliotic spines, one-third of the mid-thoracic pedicles cannot be instrumented safely with pedicle screws.

Factors affecting the accurate placement of percutaneous pedicle screws during minimally invasive transforaminal lumbar interbody fusion

We retrospectively evaluated 488 percutaneous pedicle screws in 110 consecutive patients that had undergone minimally invasive transforaminal lumbar interbody fusion (MITLIF) to determine the incidence of pedicle screw misplacement and its relevant risk factors. Screw placements were classified based on postoperative computed tomographic findings as "correct", "cortical encroachment" or as "frank penetration". Age, gender, body mass index, bone mineral density, diagnosis, operation time, estimated blood loss (EBL), level of fusion, surgeon's position, spinal alignment, quality/quantity of multifidus muscle, and depth to screw entry point were considered to be demographic and anatomical variables capable of affecting pedicle screw placement. Pedicle dimensions, facet joint arthritis, screw location (ipsilateral or contralateral), screw length, screw diameter, and screw trajectory angle were regarded as screw-related variables. Logistic regression analysis was conducted to examine relations between these variables and the correctness of screw placement. The incidence of cortical encroachment was 12.5% (61 screws), and frank penetration was found for 54 (11.1%) screws. Two patients (0.4%) with medial penetration underwent revision for unbearable radicular pain and foot drop, respectively. The odds ratios of significant risk factors for pedicle screw misplacement were 3.373 (95% CI 1.095-10.391) for obesity, 1.141 (95% CI 1.024-1.271) for pedicle convergent angle, 1.013 (95% CI 1.006-1.065) for EBL >400 cc, and 1.003 (95% CI 1.000-1.006) for cross-sectional area of multifidus muscle. Although percutaneous insertion of pedicle screws was performed safely during MITLIF, several risk factors should be considered to improve placement accuracy.

Anatomical Feasibility of Pediatric Cervical Pedicle Screw Insertion by Computed Tomographic Morphometric Evaluation of 376 Pediatric Cervical Pedicles

Prospective analysis of computed tomographic images of 376 normal pediatric cervical pedicles. To study the normal cervical pedicle morphometrics, the changes in pedicle morphology with skeletal growth, and the possibility of pedicle screw insertion. Although the usage of cervical pedicle screws in adults has become established, the feasibility of its application in children has not been studied. There are no in vivo studies that define the normal pediatric cervical pedicle morphometrics and its changes with growth and development of the child. A total of 376 normal pediatric cervical spine pedicles of 30 children (mean age = 6.7 ± 3.9 years) were analyzed for pedicle width (PW), pedicle height (PH), pedicle length (PL), pedicle axis length (PAL), transverse pedicle angle (TPA), and sagittal pedicle angle (SPA). The study population was categorized into three age groups (A: <5 years, B: 5-10 years, and C >10 years). The mean values of these parameters in the different age groups and the possibility of application cervical pedicle screws were studied. RESULTS.: The mean PW was lowest in the C3 vertebra and increased distally to be widest at C7. Sixty percent of C3 pedicles had a width less than 4 mm making screw passage risky and unsafe. With growth, the PW increased at all levels but this increase was significant only up to the age of 10 years. More than 75% of adult pedicle dimensions were achieved by 5 years of age. The mean PL at all levels remained the same with no significant increase with growth. However, the PAL showed continuous increase with growth similar to PW. The PAL also showed an increase from C3 to C7. The PH was always more than the PW at any level. Mild insignificant asymmetry was present between the right and left side pedicles in all values. With growth, there was a gradual increase in PW, PH, and PAL but was mainly before the age of 10 years. Majority of C3 pedicles were thin making screw fixation unsafe. However, at all other levels, the pedicle morphometrics per se were adequate and do not restrict safe application of 3-mm cervical pedicle screw.

Systematic Review of Cervical Pedicle Dimensions and Projections

A systematic review of the published literature was conducted specifically looking at studies reporting linear dimension and angular projection data on the anatomy of the cervical pedicle (C1-C7) via radiography or direct measurement. This study aimed to report a more accurate set of dimension data and identify differences based on race and gender, increasing the sample size by aggregating similar data of prior studies measuring the cervical pedicle in Asian, European/American, male, and female populations. A wide variation in the reports of the dimensions and projections of the cervical pedicle exist partly due to the uniqueness of this structure as well as the effects of small sample sizes and variable races and genders of sample populations of previous studies. An extensive literature search was executed, and identified articles were reviewed. A comprehensive database was constructed for synthesis of the identified studies. Subgroups were determined based on the type of population (race, gender, location of study) and radiographic or direct cadaveric measurement. Descriptive statistics were used to analyze and compare these subgroups including: means, standard deviations, and Student t test with the Bonferroni adjustment. In total, the current study reports on 33 studies with the measurements of 1311 partial and complete cervical spines. At a 95% confidence interval statistically significant differences between races were found only at C3 and C4 levels in the pedicle axis length. Male-to-female significant differences existed only at the pedicle axis length of C5 in the Asian population, while sex differences existed in the outer pedicle width and height of C3, C4, C5, C6, and C7 in the European/American population. The current study has found that there is no statistical difference in measuring the cervical pedicle via radiography (CT) or directly. There are more significant differences comparing the cervical pedicles of males and females in the European/American population than exists in the Asian population (specifically in pedicle width and height). There are also significant differences at C3 and C4 cervical pedicle between the Asian and European/American population (specifically in the pedicle axis length and transverse angle).

Thoracic pedicle screw insertion in Asian cadaveric specimen: does radiological pedicle profile affect outcome?

Pedicle screw instrumentation has superior biomechanical as well as clinical outcome. Thoracic pedicles show great variation in different population groups, particularly in Asians who have been shown to have smaller pedicle dimensions. Although plain radiographs are widely performed prior to spine surgery, no studies have been done so far to investigate whether the thoracic pedicle profile on plain radiographs affect thoracic pedicle screw insertion. Therefore, this is a cadaveric study aimed to determine the relationship between plain radiographic thoracic pedicle profile in Asians and the outcome of pedicle screw insertion in the thoracic spine. A pre-insertion radiograph with an enlargement reference scale was performed and surgeons were blinded to the plain radiographic morphometry of the thoracic pedicles. From the pre-insertion radiograph, the normalized pedicle width and height (which controls for any magnification error) as well as the pedicle width:body width (PWBW) and pedicle width:pedicle height (PWPH) ratio was derived. 240 pedicle screws were inserted in ten Asian cadavers from T1 to T12 using the funnel technique. 5.0 mm screws were used from T1 to T6 while 6.0 mm screws were used from T7 to T12. Perforations were detected by direct visualization via wide laminectomies after pedicle screw insertion. The outcome of thoracic pedicle screw insertion was correlated with the radiological profile using independent t-test. Pearson correlation coefficient was used to investigate the correlation between the ratios and the normalised pedicle width and height. The narrowest pedicle width is from T3 to T6 determined from normalized measurement of the pedicle width. T5 pedicle width is the smallest measuring 4.1 ± 1.3 mm. The overall perforation rate is 10.4% (25 perforations). There is only one significant perforation. There were twice as many lateral and inferior perforations compared to the medial perforations. 48% of the perforations occurred at T1, T2 and T3. Pedicles <4.0 mm in width and upper thoracic pedicles are risk factors for pedicle perforation. The normalised pedicle width has a high degree of linear correlation with PWBW and a normalised pedicle width of 4.0 mm correlated with a PWBW ratio of 0.3. Plain radiographic thoracic pedicle morphometry has an influence on the outcome of thoracic pedicle screw insertion in Asian cadavers. Pedicle width <4.0 mm is associated with higher risk of pedicle perforation. This critical value corresponds to a PWBW ratio of 0.3. Identification of such pedicle profile warrants full evaluation of the morphometry of the thoracic pedicles and possibly extra-pedicular techniques should be employed to avert the risk of critical pedicle perforation.

Computed Tomographic Evaluation of Pedicle Dimension and Lumbar Spinal Canal

Aim Pedicular screws have known, well-recognized complications; however, the surgeon should be aware of the morphometry of the pedicles, as well as the anatomy of the surrounding neural structures to minimize these risks. This study examined the physical characteristics of lumbar pedicles and this study is unique for this purpose. Materials and Methods Twenty-five vertebrae were selected in either sex, 18 years or older, and E-film computer software was used to measure the different diameters of pedicle. Results The L5 pedicle was the widest (16.8 mm), whereas L1 was the narrowest (8.25 mm). This figure was 8.82, 10.48, and 12.86 for L2, L3, and L4, respectively. The longitudinal depth of the pedicle was 47.98, 48.68, 50.42, 48.32, and 47.8 for L1, L2, L3, L4, and L5, respectively. Statistically significant differences were found between some dimensions detected in our study and similar studies. Conclusions The shape and diameter of the pedicles are different in different races. Some differences were found in our study with regard to pedicle dimensions.

Morphometric Comparisons Between the Pedicle and the Pedicle Rib Unit in the Immature Chinese Thoracic Spine

Morphology comparisons between the pedicle and pedicle rib unit in the immature spine were conducted through computed tomographic scans. To establish reference data concerning the dimensions of the pedicle rib unit for normal children. Until recently, studies on extrapedicular fixation were mostly based on adults. No published study has assessed the morphology of the pedicle rib unit in the normal immature population. Establishment of the basic morphometric characteristics may be beneficial in treating immature patients with spinal disorders. Measurements were carried out on the chest computed tomography scans of the immature Chinese patients without any spinal disorder findings. The width, chord length, and transverse angle of the pedicle rib unit were obtained and compared with the corresponding pedicle index. Difference between sex groups was measured, and significant statistical correlations were carefully studied to determine potentially important clinical relationships. The mean values and the standard deviations obtained for each thoracic segment were determined. The width, chord length, and transverse angle of the pedicle rib unit were significantly larger than corresponding pedicle measurements at all levels. Significant difference for measurements between sexes was found at some segments. Compared with the sex, age seemed to have a more significant effect on the measurements. Linear pedicle and pedicle rib unit dimensions had good correlations with age, whereas the transverse angle seemed to change little with age. Compared with the dimensions of the immature pedicle, the significantly larger size of the corresponding pedicle rib unit provides a more ample space, which accommodates screws with larger diameters. Extrapedicular vertebral body fixation was anatomically feasible for the immature spine. The new procedure should be cautiously applied to avoid potential implant failures or a new deformity because of the growth of the immature spine.

Anatomical Considerations for Subaxial (C2) Pedicle Screw Placement

Radiographic study. More detailed anatomical knowledge of the C2 pedicle is required to optimize and minimize the risk of screw placement. The aim of this study was to evaluate the linear and angular dimensions of the true C2 pedicle using axial computed tomography. Although earlier studies have analyzed the anatomy of the C2 pars interarticularis, little attention has been focused on the dimensions of the C2 pedicle. Ninety-three patients (47 males, 46 females; mean age 48.4 y) who had previous cervical spinal computed tomography imaging were evaluated for this study. Axial images of the C2 pedicle were selected and the following pedicle parameters were determined: pedicle width (the mediolateral diameter of the pedicle isthmus, perpendicular to the pedicle axis) and pedicle transverse angle (PTA, ie, the angle between the pedicle axis and the midline of the vertebral body). The overall mean pedicle width was 5.8+/-1.2 mm. The mean pedicle width in male patients (6.0+/-1.3 mm) was greater than that in the female patients (5.6+/-1.1 mm). This difference was not found to be statistically significant (P=0.679). The overall mean PTA was 43.9+/-3.9 degrees. The mean PTA in male patients was 43.2+/-3.8 degrees, whereas that in female patients was 44.7+/-3.7 degrees. Given the significant variability in pedicle widths and the need for precise trajectory planning in pedicle cannulation, preoperative planning is absolutely mandatory. A significant percentage of patients have pedicle widths that may not accommodate screw fixation. In addition, the angle of entry into the C2 pedicle must be carefully measured for safe instrumentation at this level.

Anatomic considerations for C2 pedicle screw placement: the use of computerized tomography measurements

OBJECTIVE: more detailed anatomical knowledge of the C2 pedicle is required to optimize and minimize the risk of screw placement. The aim of this study was to evaluate the linear and angular dimensions of the true C2 pedicle using axial CT. METHODS: ninety three patients (47 males, 46 females mean age 48 years) who had cervical spinal CT imaging performed were evaluated for this study. Axial images of the C2 pedicle were selected and the following pedicle parameters were determined: pedicle width (PW, the mediolateral diameter of the pedicle isthmus, perpendicular to the pedicle axis) and pedicle transverse angle (PTA, that is, the angle between the pedicle axis and the midline of the vertebral body). RESULTS: the overall mean pedicle width was 5.8 1.2mm. The mean pedicle width in males (6.01.3mm) was greater than that in the female subjects (5.6 1.1mm). This difference was not found to be statistically significant (p=.6790). The overall mean pedicle transverse angle was 43.93.9 degrees. The mean PTA in males was 43.23.8 degrees, while that in females was 44.73.7 degrees. CONCLUSION: preoperative planning is absolutely mandatory, particularly in determining not only screw trajectory, but in analyzing individual patient anatomy and reception to a C2 pedicle screw.

CT evaluation of cervical pedicle in a Chinese population for surgical application of transpedicular screw placement

The lower cervical pedicle size differs between the Chinese and the non-Chinese population. Knowledge of pedicle dimensions and surface landmarks is crucial for the safe placement of screws, but few quantitative data concerning the lower cervical pedicle using CT scan and multiplanar reformations (MPR) in a Chinese population exist. The aim of this study was to evaluate lower cervical pedicle (C3-C7) dimensions in a Chinese population by computed axial tomography for surgical application. The dimensions of the pedicles (C3-C7) were determined in 60 patients from CT images of cervical spinal lesions. Measurements of pedicle height, width, pedicle axis length, effective length, and two angles of the pedicles, the distances from the projection point of the pedicle axis to the lateral edge of the lateral mass and to the inferior edge of the superior facet were measured. The smallest outer pedicle width was found at C3 among the female and C4 among the male. This measurement was significantly different between male and female patients in the outer pedicle width (P < 0.05; independent samples t test) at C3 and C4. The mean values of the outer pedicle width ranged from 5.4 to 6.7 mm in males, and 4.4 to 6.3 mm in females. The projection point of the pedicle axis in the lateral-superior area of the cervical lateral mass was the most important. There were significant correlations (P < 0.01; Kendall's W test) between the vertebral level and both pedicle angles (PTA and PSA). The smallest pedicle transverse angle was at C7 in males and females. The cervical spinal cord or vertebral artery may be at risk of injury if the angulation of the screw insert is over-medial or over-lateral in the transverse plane. Therefore, preoperative CT evaluation of pedicle transverse angle is very important. Considering the amount of variation among individuals, our data on CT measurements of pedicle in a Chinese population in conjunction with evaluation of the results of preoperative CT may enhance the safety of transpedicular screw fixation in the lower cervical spine.

Venous Bypass Drainage of the Small Saphenous Vein in the Neurovascular Pedicle of the Sural Flap: Anatomical Study and Clinical Implications

Little is known about the necessary dimensions of the neurovascular pedicle of the sural flap for inclusion of the concomitant bypass veins of the small saphenous vein to secure sufficient retrograde venous flow. Therefore, the authors evaluated the anatomical basis for venous outflow of the sural flap and were able to give recommendations as to the necessary pedicle width for the flap to be transferred safely. The collateral bypass pathway of the small saphenous vein was studied in five formalin-preserved cadaver legs. The authors evaluated the usefulness of duplex sonography to visualize the venous collateral system of the small saphenous vein in five legs of healthy volunteers. The pedicle width necessary to bypass the small saphenous vein ranged from 1.4 to 3.1 cm in the human cadavers and 0.09 to 1.5 cm in the duplex group. In both groups, only one side, medial or lateral to the small saphenous vein, was responsible for a total proximal-to-distal bypass. The opposite side partly bypassed the vein. Ultrasonography alone without Doppler was sufficient to visualize this variable suprafascial venous network. Preoperative evaluation of the venous system through duplex sonography is essential to localize on which side the bypass veins are present, making it possible to decrease the width of the pedicle without interfering with the reliability of the sural flap.

Anatomical considerations for cervical pedicle screw insertion: the use of multiplanar computerized tomography reconstruction measurements

The purpose of this study was to evaluate the linear and angular parameters of the vertebral body (VB) required for cervical pedicle screw (CPS) insertion by using multiplanar computerized tomography (CT) reconstructions. Three hundred fifteen vertebrae from C-3 to C-7 in 63 patients were studied. Pedicle dimensions such as pedicle transverse angle (PTA), pedicle sagittal angle (PSA), and pedicle outer width (POW) were measured on axial CT reconstructions, as were linear parameters including the lateral mass thickness (LMT), the anteroposterior (AP) and mediolateral distances between spinal canal and transverse foramen, and spinal canal longitudinal and transverse diameter. In addition, the correlations between PTA and other parameters were calculated using univariate linear regression analysis. The overall mean LMT ranged from 10.7 to 12.6 mm. The smallest mean AP spinal canal-transverse foramen distance was found at C-7 (1.1 mm),whereas the largest mean distance was at C-4 (3.1 mm). The smallest mean mediolateral spinal canal-transverse foramen distance was found at C-4 (1.2 mm), whereas the largest mean distance was at C-7 (4.7 mm). There were significant intergroup differences between male and female patients except for PTA and spinal canal longitudinal diameter. The PTA had a direct linear correlation with AP and mediolateral spinal canal-transverse foramen distances. The largest Pearson coefficient was 0.71 between the PTA and AP spinal canal-transverse foramen distance and the inverse one was -0.73 between the PTA and mediolateral spinal canal-transverse foramen distance. Analysis of the data obtained in this study suggests that not only pedicle dimensions but also linear and angular parameters of the VB can be useful data when inserting a CPS.

Pedicle dimensions of the thoracic and lumbar vertebrae in the Greek population

The aim of this study is to understand the magnitude of the pedicle's diameters for the use of pedicle screw fixation in spinal instrumentation. Pedicle dimensions from T1 to L5 were measured in 16 whole human cadaver spines (eight women and eight men). The mean age at the time of death was 67.2 (range: 59-84 years). The external transverse, the external sagittal, and the internal transverse diameter pedicle widths were measured with electronic calipers both on the right and left pedicles. The widest external transverse diameter was at the L5 level with a mean of 13.61 mm (range: 10.29-16.20 mm). The narrowest external transverse pedicle diameter was at the T5 level with a mean of 5.09 mm (range: 4.10-6.88 mm). The widest external sagittal pedicle diameter was at the T11 level with a mean of 17.02 mm (range: 14.84-19.57 mm), while the narrowest one was at T1 level with a mean of 8.90 mm (range: 7.18-11.37 mm). The maximum internal transverse pedicle diameter was at the L5 level with a mean 8.95 mm (range: 7.10-11.21 mm), while the minimum was at the T5 level with a mean 3.90 mm (range: 3.10-4.82 mm). Statistical significant greater pedicle dimensions were found in males at multiple levels. Pedicle dimensions at the levels from T3 to T8 need preoperative evaluation with computed tomography before the insertion of pedicle screws with diameter more than 5 mm. Pedicles at T12 to L5 levels may accommodate screws of 7 mm diameter.

Transpedicular Screw Placement Evaluated by Axial Computed Tomography of the Cervical Pedicle

We evaluated the trajectory of transpedicular screws in the cervical spine using axial computed tomography (CT). To provide a safe transpedicular screw trajectory by measuring the dimensions of the cervical pedicle and evaluating the entrance points and the insertion angles of transpedicular screws. The morphology of the cervical pedicle has been studied, but few in vivo CT-based studies of pedicle dimensions and transpedicular screw placement in the cervical spine have been reported. The dimensions of the pedicles (C3-C7) were determined in 30 patients with cervical spinal lesions from CT images. The space available for transpedicular screws (SAS) was defined as the distance between two parallel lines tangential to the spinal canal and the transverse foramen, respectively. SAS was evaluated at 25 degrees and 50 degrees insertion angles. SAS at a 25 degrees insertion angle (SAS-25) ranged from 4.7 to 5.4 mm. SAS at 50 degrees (SAS-50) ranged from 6.1 to 6.6 mm. SAS-25 and SAS-50 were significantly different. Four-millimeter-diameter screws would fit in all 120 C3-C6 vertebrae studied at 50 degrees, but 20 (17%) would not fit at 25 degrees. Axial CT measurements should facilitate transpedicular screw fixation in the cervical spine. We believe that the screw insertion angle should be close to 50 degrees, which is the mean pedicle transverse angle from C3-C6. The entry point of the pedicle screw should be located as laterally as possible in the posterior surface of the lateral mass.

Accurate Determination of Isthmus of Lumbar Pedicle: A Morphometric Study using Reformatted Computed Tomographic Images

Lumbar pedicle isthmus, the narrowest section of pedicle, was investigated. To determine the lumbar pedicle isthmus accurately and measure related parameters. Accurate anatomic knowledge of pedicle parameters is critical for a successful transpedicular procedure. Many studies on lumbar pedicle dimensions have been conducted, yet less is known about how to obtain these data and their veracity. In fact, the narrowest section is present in the pedicle, i.e., the isthmus of the pedicle. This is the bottleneck of the pedicle; to determine and measure it could illustrate the true morphologic characteristics of the lumbar pedicle. Ultra high-speed spiral CT scan of lumbar spine was performed in 41 patients of Chinese origin. After reformation of the original images, isthmus and transverse plane of pedicle axis were determined. Eleven dimensions of isthmus plane and three dimensions of transverse plane were calculated using software. Pedicle endosteal width and height in female patients who were over the age of 50 were greater than those of female patients younger than 50 years old. The isthmus endosteal width from L1 to L5 was 5.2, 6.0, 7.5, 7.5, and 8.7 mm and 4.0, 4.1, 5.4, 5.7, and 7.1 mm, respectively, in men and women. Isthmus inclination inclined to midline with less than 10 degrees above L3 but increased in L4 and 30 degrees in L5. An objective narrowest section, the pedicle isthmus, exists in lumbar pedicle axis. The parameters of isthmus, especially isthmus endosteal width, show the morphologic characteristics of the lumbar pedicle and are the most important data provided for transpedicular procedures. The small pedicles of female patients over the age of 50 also show certain primary osteoporosis. Isthmus inclination puts the pedicle in a more complicated space position. A better understanding of the complicated structure of the pedicle isthmus guarantees success in transpedicular procedures.

Open versus endoscopic lumbar pedicle screw fixation and posterolateral fusion in a sheep model: a feasibility study

Background context Conventional open procedures for lumbar pedicle screw instrumentation are often associated with significant morbidity resulting in longer postoperative recovery and hence have led to the advent of less invasive techniques of spinal instrumentation and fusion. Purpose This study compares lumbar pedicle screw fixation and posterolateral fusion using endoscopic and open techniques in a sheep model. Study design Endoscopic and open techniques of lumbar pedicle screw instrumentation and posterolateral fusion are compared in a sheep model (12 sheep in each group). The safety and fusion outcome are assessed by postoperative computed tomography (CT) scans performed at 6 months. Methods Twelve sheep underwent bilateral L4–L5 pedicle screw fixation and posterolateral fusion by means of endoscopic instrumentation and another 12 sheep by means of conventional open technique. For posterolateral fusions, an autologous iliac crest bone or bone graft substitute (Healos/MP52; Orquest, Mountain View, CA) was used on either the animal's left or right side. The animals were euthanized 6 months after surgery and the lumbar spines were harvested. Pedicle dimensions and screw insertion angles were measured and the two techniques were compared using CT and image analysis software. Pedicle screw misplacement was detected by means of direct inspection and CT scan, and fusions were evaluated by CT scans. Results The endoscopic group's screw insertion angle was more convergent, corresponded more closely to the human pedicle angle and was less variable than in the open technique. Three of the endoscopic group's 48 screws were misplaced medially, whereas in the open technique, 5 screws were misplaced laterally. Posterolateral bone fusion masses were palpable 6 months after surgery for both the autologous bone grafts and graft substitutes. There were no complications. The ratio of screw to pedicle diameter was approximately 0.6, greater than in human studies. Conclusions Despite differences between pedicle dimensions and screw angles, most screws could be inserted into the sheep pedicle using endoscopic or open techniques. Bone fusion was successful in both groups. Thus, minimally invasive, endoscopic transpedicular screw–plate fixation and posterolateral fusion is feasible, and as effective as the conventional open technique.

Morphometric Evaluation of Subaxial Cervical Vertebrae for Surgical Application of Transpedicular Screw Fixation

A morphometric evaluation of pedicle projections in 29 cervical spinal columns (C3-C7) for three-dimensional surgical anatomy for safe surgery was proposed. In this study, pedicles and intimate structures of the subaxial vertebrae from C3 to C7 were evaluated to provide some morphometric data for cervical transpedicular screw fixation. Detailed knowledge of surgical anatomy and variation of the subaxial vertebrae is a must for safe and effective surgery of the region. Although there are several clinical studies of transpedicular fixation, few studies have been performed on cervical pedicle measurements and their projection. In 29 dried bone cervical spinal columns (C3-C7), pedicle dimensions (pedicle height, width, length), measurements of lateral mass and pedicle length distance and pedicle axis length, investigation of distances of superior facet-midpedicle axis and inferior facet-midpedicle axis, and transverse and sagittal angles of the pedicles were performed in linear and angular measurements. The obtained data from the series revealed that the mean values were approximately ranging from 6.7 to 7.2 mm for pedicle height, 4.4 to 4.9 mm for pedicle width, 5.3 to 6.2 mm for pedicle length, 15.3 to 16.0 mm for lateral mass and pedicle length, 22.2 to 27.7 mm for pedicle axis length, 3.8 to 5.3 mm for superior facet-midpedicle axis distance, 9.9 to 12.0 mm for inferior facet-midpedicle axis distance, 42.3 degrees to 51.5 degrees for transverse angle, and 5.2 degrees to 14.1 degrees for sagittal angle. Linear measurements of pedicle dimensions and also axial angles from horizontal and vertical planes may provide some anatomic limitations for subaxial cervical transpedicular screw fixation, and also contribute to the safety of the surgical procedure. One should also rely on tomographic data and computer-assisted guidance systems.

P8. Thoracic pedicle expansion after pedicle screw insertion in a pediatric cadaveric spine: a biomechanical analysis

BACKGROUND CONTEXT: Prior studies suggested significant pedicle expansion in immature spines during pedicle screw insertion, but no biomechanical studies have confirmed the viscoelasticity of the pediatric pedicle. Studies of adult cadavers demonstrate a mild increase in pedicle dimensions prior to fracture, but to a much lesser degree than radiographic assessments of the pediatric pedicle have suggested.

Transpedicular screwing of the seventh cervical vertebra: anatomical considerations and surgical technique.

The purpose of this study was first to assess the feasibility of C7 transpedicular screwing with a morphological study and secondly to evaluate the safety of such a surgical technique when guided only by posterior landmarks. Eighteen C7 vertebrae, harvested from fresh human cadavers, were included in this study. First the morphometry of C7 pedicle was performed on computed tomography with multiplanar reconstructions. Results of this quantitative anatomy were compared with the literature data. Secondly 30 pedicle screws, whose placement was guided only by anatomical features on the posterior face of the dorsal arch, were inserted in 15 C7 vertebrae. A second computed tomographic examination was done after the surgical procedure to check the screw placement in both planes. The average pedicular width was 6+/-1.2 mm and the average height was 5.8+/-1.1 mm. The pedicle angulation in the transverse plane was 33.3 degrees +/-6.6 degrees, the pedicle angulation in the sagittal plane was 4.3 degrees +/-4.5 degrees downward with reference to the lower endplate of C7. The average distance from the entry point of transpedicular screwing to the anterior cortex of the vertebral body was 29+/-3 mm. Concerning the safety of transpedicular screwing, 63% of screws were found entirely inside the pedicle without any violation of the pedicle cortex. Most of pedicle violations were observed in the transverse plane. No grade II violation of the pedicle was observed. Dimensions of the C7 pedicle are amply compatible with transpedicular fixation using 3.5 mm screws. Such a surgical technique seems to be an interesting option when posterior fixation of C7 is required. Nevertheless morphological guidelines appeared not to be sufficient to ensure safe transpedicular screwing. Laminoforaminotomy is strongly recommended, although it has not been evaluated in this study.