Pedicle morphometry in the upper thoracic spine: limits to safe screw placement in older patients

Percutaneous Kyphoplasty via Transverse Process-Rib-Pedicle Approach for Upper and Middle Thoracic Osteoporosis Fracture with Pedicle Stenosis

OBJECTIVE

To explore the clinical effect of percutaneous kyphoplasty (PKP) via process-rib-pedicle approach for upper and middle thoracic osteoporosis fractures with pedicle stenosis.

METHODS

This study is a retrospective observational study. In this study, we retrospectively analyzed the data of 62 patients with upper thoracic vertebral bone loss compression fracture treated via the process-rib-pedicle pathway PKP at the First Affiliated Hospital of Soochow University from January 2020 to December 2022. The patients were divided into group A (unilateral PKP, 38 cases) and group B (bilateral PKP, 24 cases). The aspects of surgical safety, clinical efficacy, and radiological outcome were investigated.

RESULTS

All 62 patients successfully completed the surgery without any spinal cord, nerve, or vascular injury, and there were no complications such as infection and vascular embolism. The differences in visual analog scale scores（P < 0.05）, Oswestry disability index functional index（P < 0.05）, and Cobb angle（P < 0.05） were significant when comparing preoperative and postoperative periods, and the differences were not significant when comparing the postoperative periods (P > 0.05). There were no statistically significant differences in days of hospital stay (P = 0.653) and the rate of bone cement leakage (P = 0.537) between the 2 groups.

CONCLUSIONS

For upper middle osteoporotic thoracic vertebral fractures with pedicle stenosis, puncture via the process-rib-pedicle path is a safe and reliable puncture route, and more than 2.5 ml of cement can achieve good clinical outcomes, regardless of bilateral or unilateral PKP.

O-Arm Assisted Cervicothoracic Spine Pedicle Screw Placement Accuracy Is Higher Than C-Arm Fluoroscopy

OBJECTIVE

We compared the accuracy of C-arm fluoroscopy versus O-arm-assisted pedicle screw (PS) placement in the cervicothoracic spinal junction (CTSJ).

METHODS

Patients who underwent PS placement in the CTSJ (C7-T4) at our hospital were included in this study. Of 37 patients who underwent PS placement in the CTSJ, 20 underwent intraoperative C-arm fluoroscopy-assisted surgery (C Group) and 17 underwent intraoperative O-arm-assisted surgery (O Group). In total, 159 PSs were placed-73 in the C Group and 86 in the O Group. The accuracy of PS placement was compared between the C Group and O Group using the classification proposed by Gertzbein and Robbins to analyze pedicle violation.

RESULTS

PS accuracy was higher in the O Group than C Group; PS placement evaluated as grade A, representing no perforation, was 95.3% (82/86) for the O Group, whereas it was 78.1% (57/73) for the C Group. There was a clear statistically significant difference in accuracy of PS placement between the groups (P = 0.0013).

CONCLUSIONS

O-arm-assisted surgery improved the accuracy of PS placement in the CTSJ.

Morphometric analysis of the proximal thoracic pedicles in Lenke II and IV adolescent idiopathic scoliosis: an evaluation of the feasibility for pedicle screw insertion

PURPOSE

Pedicles on the concave side of the proximal thoracic (PT) curve in adolescent idiopathic scoliosis (AIS) patients with Lenke II and IV deformities tend to be narrow and dysplastic, making pedicle screw (PS) insertion challenging. The aim of this study was to evaluate the feasibility for PS placement in these patients using pedicle chord length, diameter, and channel morphology.

METHODS

In this retrospective study, 56 consecutive AIS patients with Lenke II or IV curves who underwent instrumented posterior spinal fusion (PSF) were studied. The mean age at surgery was 14.8 years and the mean PT curve measured 45°. Two independent investigators evaluated all visible pedicles from T₁ to T₆ vertebral levels using axial images from intraoperative computed tomography-guided navigation recording the pedicle: (1) maximum transverse diameter 'd' at the isthmus, (2) maximum chord length 'l', and (3) qualitative assessment of the channel morphology (types A-D).

RESULTS

Two hundred and sixty-eight concave and 264 convex pedicles were measured. The mean 'd' of the concave pedicles at T₃ and T₄ was < 3.0 mm, compared to > 5.0 mm for the convex counterparts (p < 0.001). Of all concave pedicle channels, 48% had morphology characteristics that were riskier for PS cannulation (type C or D) compared to 2% of all convex pedicle channels (type A or B) (p < 0.001).

CONCLUSION

Almost half of all concave pedicles have morphologic characteristics that make them too small to accommodate a PS. Though PSs could be inserted using an in-out-in technique in these patients, alternative fixation anchors may improve strength and safety.

Computed tomography-guided microwave ablation combined with percutaneous vertebroplasty for treatment of painful high thoracic vertebral metastases

PURPOSE

To retrospectively evaluate the efficacy and safety of computed tomography (CT)-guided microwave ablation (MWA) combined with percutaneous vertebroplasty (PVP) as a treatment for painful high thoracic vertebral metastases (T1-T4).

MATERIALS AND METHODS

In this retrospective study, 23 adult patients (33 high thoracic vertebral metastases) with moderate to severe pain were treated with CT-guided MWA and PVP. The procedural effectiveness was evaluated using a Visual Analog Scale (VAS), daily morphine consumption, and the Oswestry Disability Index (ODI) before and immediately after the procedure and during follow-up.

RESULTS

Technical success was achieved in all patients. The mean pre-procedure VAS score and morphine doses were 6.7 ± 1.7 (5-10) and 105.2 ± 32.7 (30-150) mg, respectively. The mean VAS scores and daily morphine doses at 24 h and 1, 4, 12, and 24 weeks post-operatively were 3.2 ± 1.4 and 41.3 ± 9.6 mg; 1.8 ± 1.0 and 31.5 ± 12.2 mg; 1.4 ± 1.3 and 19.6 ± 12.4 mg; 1.1 ± 0.8 and 14.5 ± 9.6 mg; and 1.0 ± 0.7 and 13.9 ± 9.3 mg, respectively (all p < 0.001). ODI scores significantly decreased (p < 0.05). Minor cement leakage occurred in 10 patients (30.30%) with no symptoms. Follow-up imaging showed no local tumor progression.

CONCLUSIONS

Preliminary results suggest MWA combined with PVP is an effective and safe treatment for painful high thoracic vertebral metastases (T1-T4) and can significantly relieve pain and improve the quality of life of patients. However, its efficacy should be confirmed by mid- and long-term studies.

Preoperative Assessment of the Feasibility of Pedicle Screw Insertion at the Proximal Thoracic Curve in Lenke Type 2 Idiopathic Scoliosis

STUDY DESIGN

Retrospective cohort study.

OBJECTIVES

To investigate the feasibility of inserting pedicle screws in the proximal thoracic (PT) curve in Lenke type 2 idiopathic scoliosis, using post-myelography computed tomography (CT).

METHODS

Post-myelography CT images of 46 Japanese patients, 10 to 30 years old, who underwent surgery for Lenke type 2 idiopathic scoliosis were analyzed. A new parameter "SAPS" (space available for pedicle screw) was introduced, which defines the minimal distance between the lateral cortex of the pedicle and the spinal cord, with a SAPS <4.5 mm being "unacceptable." All 460 pedicles (T2 through T6) were analyzed. Pedicle diameter was classified according to the Akazawa grading system.

RESULTS

Most pedicles on the right side at T3 (84.8%) and T4 (97.8%) were unacceptable. The unacceptable rate was 58.7% and 15.2% on the right side at T5 and T6, respectively. A larger Cobb angle of the PT curve was associated with a greater incidence of unacceptable SAPS at these levels. For a Cobb angle of the PT curve >40°, most right T5 pedicles were unacceptable. On the left side, most pedicles from T2 to T5 were acceptable. When T5 was the caudal end vertebra of the PT curve, the left T6 pedicles had an unacceptable SAPS in some cases. When the width of the pedicle channel was ≥2 mm (Akazawa grade 1 or 2), all pedicles from T2 to T6, on both sides, were acceptable.

CONCLUSIONS

Post-myelography CT enabled us to clearly demonstrate the feasibility of inserting pedicle screws in the PT region.

The Clinical Effect of Kyphoplasty Using the Extrapedicular Approach in the Treatment of Thoracic Osteoporotic Vertebral Compression Fracture

BACKGROUND

To evaluate the clinical effect of kyphoplasty with the extrapedicular approach in the treatment of thoracic osteoporotic compression fractures, including upper, middle, and lower thoracic.

METHODS

From April 2014 to December 2016, 50 cases (55 vertebrae) of thoracic osteoporotic fractures were treated with balloon kyphoplasty using the extrapedicular approach. Symptomatic levels ranged from T3 to T12 and were confirmed based on medical history, physical examination, and medical imaging. Pain relief, restoration of vertebral anterior and median height, and kyphosis correction were retrospectively compared before and after operation by using the visual analogue scale and radiography, respectively. In addition, bone cement leakage location and complications were recorded.

RESULTS

Operations were successfully performed in all the cases, with an average surgery time of 77 minutes and follow-up period of 15 months (range, 6-36 months). The visual analogue scale scores at 3 days after operation and final follow-up were significantly reduced (P < 0.05). The vertebral anterior margin and median height on radiography after surgery were significantly improved (P < 0.05), and the kyphosis was significantly corrected. Four cases had cement leakage but no other adverse events. No blood vessel or spinal cord puncture injury during surgery or blood vessel embolism, pulmonary embolism, or fat embolism after surgery was found.

CONCLUSIONS

Extrapedicular kyphoplasty is safe and effective in treating thoracic osteoporotic vertebral compression fractures. It can rapidly relieve backache, restore the body height of the fractured thoracic vertebra, and correct kyphosis. In addition, it can improve patient quality of life.

Surgery for traumatic fractures of the upper thoracic spine (T1-T6)

Background:

The management of traumatic upper thoracic spine fractures (T1–T6) is complex due to the unique biomechanical/physiological characteristics of these levels and the nature of the injuries. They are commonly associated with multiple other traumatic injuries and severe spinal cord injuries. We describe the safety and efficacy of surgery for achieving stability and maintaining reduction of upper thoracic T1–T6 spine fractures.

Methods:

We retrospectively analyzed a series of traumatic unstable upper thoracic (T1–T6) spine fractures treated at one institution between 1993 and 2016. All patients were assessed neurologically and underwent complete preoperative radiographic analysis of their T1–T6 spine fractures including assessment of instability. Neurological and radiographic outcomes including fusion rates, kyphotic deformity, and successful reduction of the fracture were evaluated along with hospital length of stay (LOS), intensive care unit LOS, and overall complication rates.

Results:

There were 43 patients (29 males, 14 females) with an average age of 37.7 years. Between 1993 and 1999, 8 patients were treated with hook/rod constructs, whereas between 1995 and 2016, 35 patients received pedicle screw fixation utilizing intraoperative fluoroscopy or computed tomography (CT) navigation. Forty-three patients had a total of 178 levels fused. In this series, there were no intraoperative vascular or neurological complications. Instrumentation was removed in five patients due to pain, wound infection, or hardware failure. The mean hospital LOS was 21.1 days (range 4–59 days), and there was a 95% fusion rate based on follow-up imaging (X-rays or CT scan).

Conclusions:

Surgical treatment of upper thoracic spine fractures (T1–T6), although complex, is safe and effective. Reduction and fixation of these fractures decreases the risk of further neurological complications, allows for earlier mobilization, and correlates with shorter hospital LOS and improved outcomes.

Cortical Bone Trajectory Screw Fixation in the Upper and Middle Thoracic Spine (T1-T8): An Anatomic and Radiographic Assessment

OBJECTIVE

To assess an alternative method of cortical bone trajectory (CBT) screw placement in the thoracic spine from T1 to T8 and to investigate the proper entry point, screw insertion angle, screw length, and diameter.

METHODS

Computed tomography images of 80 patients were used to measure all related parameters. Ten cadaveric spines were studied and 4.5-mm screws were inserted into both sides of the vertebrae. Computed tomography of all vertebrae previously inserted with CBT screws was performed and lateral or medial pedicle wall violation was checked.

RESULTS

Of the inserted 160 CBT screws, 41.25% (66/160) penetrated the lateral pedicle wall, and the proportion of medial pedicle wall violation accounted for 0.625% (1/160). Maximal screw length tended to gradually increase from T1 to T8 (from 24.54 mm at T1 to 29.53 mm at T8). Compared with T4 and T5, maximal screw diameters of other thoracic levels were wider, ranging from 4.63 mm at T4 to 5.53 mm at T8. The greatest lateral angle was 8.66° in men and 8.39° in women at T8, whereas the smallest lateral angle was 4.97° in men and 4.67° in women at T1. The cephalad angle ranged from 17.23° at T7 to 31.50° at T1 and it was significantly larger in men at T7 (P < 0.05), T6 and T8 (P < 0.01).

CONCLUSIONS

Based on the results of this study, we suggest that patients could be placed with 4.5 × 25.0-30.0 mm CBT screws from T1 to T8 through the pedicle or pedicle rib unit.

The use of fluoroscopic guided percutaneous pedicle screws in the upper thoracic spine (T1-T6): Is it safe?

PURPOSE

This study analysed the accuracy and safety of the fluoroscopic guided percutaneous screws in the upper thoracic vertebrae (T1-T6).

METHODS

Computed tomography scans from 74 patients were retrospectively evaluated between January 2008 and December 2012. Pedicle perforations were classified by two types of grading systems. For medial, lateral, superior and inferior perforations: grade 0 - no violation; grade 1 - <2 mm; grade 2 - 2-4 mm and grade 3 - >4 mm. For anterior perforations: grade 0 - no violation; grade 1 - <4 mm; grade 2 - 4-6 mm and grade 3 - >6 mm.

RESULTS

There were 35 (47.3%) male and 39 (52.7%) female patients with a total 260 thoracic pedicle screws (T1-T6) analysed. There were 32 screw perforations which account to a perforation rate of 12.3% (11.2% grade 1, 0.7% grade 2 and 0.4% grade 3). None led to pedicle screw-related complications. The perforation rate was highest at T1 (33.3%, all grade 1 perforations), followed by T6 (14.5%) and T4 (14.0%).

CONCLUSION

Fluoroscopic guided percutaneous pedicle screws of the upper thoracic spine (T1-T6) are technically more demanding and carry potential risks of serious complications. Extra precautions need to be taken when fluoroscopic guided percutaneous pedicle screws are placed at T1 and T2 levels, due to high medial pedicular angulation and obstruction of lateral fluoroscopic images by the shoulder girdle and at T4-T6 levels, due to smaller pedicular width.

Safe corridor for the implantation of thoracolumbar pedicle screws in growing pigs: A morphometric study

The pig spine is widely used as a large animal model for preclinical research in human medicine to test new spinal implants and surgical procedures. Among them, pedicle screw is one of the most common method of fixation of those implants. However, the pedicle of the porcine vertebra is not as well defined and not as large as the pedicle of the human vertebra. Therefore, the position of the screw should be adapted to the pig and not merely transposed based on the literature on humans. The purpose of this study is to determine the characteristics of the optimum implantation corridors for pedicle screws in the thoracolumbar spine of piglets of different ages using computed tomography (CT) and to determine the size and length of these corridors in pigs of different ages. CT scans from five groups of age: 6, 10, 14, 18, and 26 weeks were reviewed. For each thoracolumbar vertebrae, the pedicle width, pedicle axis length, and the pedicle angle was measured for the left and right pedicle. A total of 326 thoracic vertebrae and 126 lumbar vertebrae were included in the study. Pedicles are statistically larger but not longer for the lumbar vertebrae. An important variation of the pedicle angle is observed along the spine. In all pigs, an abrupt modification of the pedicle angle between T10 and T11 was observed, which corresponds to the level of the anticlinal vertebra which is the vertebra for which the spinous process is nearly perpendicular to the vertebral body. In conclusion, this study provides a quantitative database of pedicle screw implantation corridors in pigs of different ages. When using pedicle screws in experimental studies in pigs, these results should be considered for selecting the most suitable implants for the study but also to ensure a correct and safer screw position. Improving study procedures may limit postoperative complications and pain, thereby limiting the use of live animals.

T-1 pedicle subtraction osteotomy for the treatment of rigid cervical kyphotic deformity: report of 4 cases

Cervical kyphotic deformity represents a difficult to treat pathology often arising from multiple factors including, but not limited to, traumatic injuries, degenerative changes, and ankylosing spondylitis. Furthermore, treatment of these deformities becomes increasingly difficult with any preexisting instrumentation. Currently, several options exist to treat these severe deformities, with the Smith-Petersen osteotomy and C-7 pedicle subtraction osteotomy being the most frequently used approaches. However, these techniques come with significant risk to the patient including nerve root injury as well as compression of the vertebral arteries. The authors here report on a series of 4 patients with rigid cervical deformity who underwent T-1 pedicle subtraction osteotomy. The authors review the relevant literature and provide a novel, less risky, and potentially more corrective approach for treating cervical deformities.

3D printing-assisted preoperative plan of pedicle screw placement for middle-upper thoracic trauma: a cohort study

BACKGROUND

This study aimed to evaluate the application of 3D printing in assisting preoperative plan of pedicle screw placement for treating middle-upper thoracic trauma.

METHODS

A preoperative plan was implemented in seven patients suffering from middle-upper thoracic (T3-T7) trauma between March 2013 and February 2016. In the 3D printing models, entry points of 56 pedicle screws (Magerl method) and 4 important parameters of the pedicle screws were measured, including optimal diameter (ϕ, mm), length (L, mm), inclined angle (α), head-tilting angle (+β), and tail-tilting angle (-β). In the surgery, bare-hands fixation of pedicle screws was performed using 3D printing models and the measured parameters as guidance.

RESULTS

A total of seven patients were enrolled, including five men and two women, with the age of 21-62 years (mean age of 37.7 years). The position of the pedicle screw was evaluated postoperatively using a computerized tomography scan. Totally, 56 pedicle screws were placed, including 33 pieces of level 0, 18 pieces of level 1, 4 pieces of level 2 (pierced lateral wall), and 1 piece of level 3 (pierced lateral wall, no adverse consequences), with a fine rate of 91.0%.

CONCLUSIONS

3D printing technique is an intuitive and effective assistive technology to pedicle screw fixation for treating middle-upper thoracic vertebrae, which improve the accuracy of bare-hands screw placement and reduce empirical errors.

TRIAL REGISTRATION

The trial was approved by the Ethics Committee of the Fujian Provincial Hospital. It was registered on March 1st, 2013, and the registration number was K2013-03-001.

The Effect of Transpedicular Screw Design on Its Performance in Vertebral Bone Under Tensile Loads: A Parametric Study

STUDY DESIGN

A biomechanical study using bovine thoracolumbar spines.

OBJECTIVE

To study investigated whether thread design parameters aimed at altering the state of stress at the screw-bone interface increase the screw's holding power.

SUMMARY AND BACKGROUND DATA

Internal spinal fixators utilizing transpedicular screw fixation are used to achieve early stabilization of the injured spine in a range of clinical conditions. Despite advances in the design of internal spinal fixation systems, implant loosening, and catastrophic failures at the screw-bone interface remains a serious complication in adult spine surgery. Although the performance of the screws in the vertebral bone critically depends on ability of screw thread design to provide and maintain adequate bone purchase, the effect of individual thread design parameters on screw performance and the failure process of the screw-bone interface, remains unclear.

METHODS

On the basis of the AO Schanz thread, this parametric study used 96 lumbar bovine vertebrae instrumented with 19 screw designs to investigate the effects of pitch, ratio of major to minor diameter, screw insertion depth, and major diameter, on screw performance under pure tensile loading. The effect of vertebral morphometry on screw performance and the extent of damage within the failed screw-bone interface were evaluated.

RESULTS

The increase in screw insertion depth, screw pitch, and the ratio of major to minor diameter, significantly affected screw performance under tensile loads. Complex interactions existed between the major diameter and each of the design variables. Vertebral morphometry had little effect on screw performance while the damage within the failed bone-screw interface confined to the immediate region of the screw threads.

CONCLUSIONS

Design variables, able to reduce shear stresses or modify the complex stress profile at the bone-screw interface, are more effective in preventing early failure of the interface.

Minimally invasive cortical bone trajectory screws placement via pedicle or pedicle rib unit in the lower thoracic spine: a cadaveric and radiographic study

PURPOSE

To evaluate the feasibility of cortical bone trajectory (CBT) screws fixation via pedicle or pedicle rib unit in the cadaveric thoracic spine (T9-T12).

METHODS

Computed tomography (CT) images of 100 patients are analyzed by multiplanar reconstruction. Ten cadaveric thoracic spines are used to insert 4.5 × 35.0 mm CBT screws at all levels from T9 to T12.

RESULTS

Maximal screw length obtained by CT has a tendency to gradually increase from T9 (29.64 mm) to T12 (32.84 mm), and the difference reaches significant level at all levels except T9 versus T10 (P < 0.01). Maximal screw diameter increases from T9 (4.92 mm) to T12 (7.47 mm) and the difference reaches significant level among all levels (P < 0.01). Lateral angle increases from T9 (7.37°) to T12 (10.47°), and the difference reaches significant level among all levels except T11 versus T12. Cephalad angle from T9 to T12 are 19.03°, 22.10°, 25.62° and 27.50° (P < 0.01), respectively. The percentage of the inner and outer pedicle breakage are 2.5 and 22.5 %, respectively. The violation of lateral pedicle wall occurs at T9 and T10, especially for women at T9.

CONCLUSIONS

Both radiographic and cadaveric studies establish the feasibility of CBT screws placement via pedicle or pedicle rib unit in the lower thoracic spine (T9-T12). Furthermore, our measurements are also useful for application of this technique.

Minimally invasive screw fixation of fractures in the thoracic spine: CT-controlled pre-surgical guidewire implantation in routine clinical practice

AIM

To evaluate the feasibility and accuracy of minimally invasive, transpedicular screw placement in cervicothoracic fractures with the help of computed tomography (CT)-controlled guidewires.

MATERIALS AND METHODS

Two hundred and ninety-three guidewires were inserted in 35 patients (42.9±21.2 years) under CT fluoroscopy (286 thoracic, seven cervical). There were 28 traumatic cases, three pathological fractures, three fractures due to infectious infiltrations, and one osteoporotic fracture. In 151 pedicles, screw placement was performed in the CT room. CT images were reviewed regarding accuracy and cortical violations using the popular 2 mm increment deviation classification of Gertzbein and Robbins.

RESULTS

Guidewire implantation resulted in only 28 cortical contacts. Minor encroachments of the pedicle wall by inserted screws occurred in 39.1% (59 of 151) and in 23.8% if taking unavoidable encroachments into account (30 of 59). Pedicular isthmus width correlated to cortical guidewire contacts (r=-0.449; p=0.077) and pedicle violations (all graded "A") by the inserted screws (r=-0.581; p=0.049). Total procedural duration was 138.6±44.2 minutes, representing 14.5±11.6 minutes for each pedicle, while showing a significant correlation against higher vertebral levels (r=-0.849; p=0.0002) and the occurrence of pedicle violations (r=-0.641; p=0.027).

CONCLUSIONS

The treatment of vertebral fractures with a guidewire-based pedicle screw insertion technique under CT imaging results in very high accuracy and a low complication rate.

Computed tomographic-based morphometric study of thoracic spine and its relevance to anaesthetic and spinal surgical procedures

BACKGROUND

To collect a baseline computer software aided normative morphometric data of thoracic spine in the Indian population and analyze it to give pre-procedural guidelines to clinicians for safe surgical and anaesthetic procedures in the thoracic spine.

METHODS

CT scans of thoracic spine of patients free from spinal disorders were reviewed in a total of 600 vertebrae in 50 patients. Parameters recorded with the help of computer software were pedicle width, length and height, transverse pedicle angles, chord length, canal dimensions, body width and height, spinous process angle and transverse process length.

RESULTS

Pedicle width decreased from T1 (9.27 ± 1.01) to T4 (4.5 ± 0.93) and increased to T12 (8.31 ± 1.83). At T4 76% and at T5 62% of the pedicles were smaller than 5 mm and would not accept 4 mm screw with 1.0-mm clearance. However, at T1 2%, at T11 7% and at T12 8% would not accept a 4 mm screw. Chord length gradually increased in upper thoracic vertebrae and was relatively constant in middle and decreased in lower thoracic vertebrae. Shortest estimated chord length was at T1 (30.30 ± 2.11). On an average, from T1 to T6 and at T11 and T12, a screw length of 25-30 mm could be accommodated and from T7 to T10, 30-35 mm screw length could be accommodated. Transverse pedicle angle decreased from T1 (35.4 ± 2.21) to T12 (-9.8 ± 2.39). Canal dimensions were narrowest at T4/T5 (20.02 ± 1.23) in anteroposterior and 21.12 ± 1.23 in interpedicular diameters. Spinous process angle increased from T1 (30.11 ± 6.74) to T6 (57.89 ± 9.31) and decreased to 16.21 ± 7.38 at T12. Transverse process length increased from T1 to T7 (23.54 + 2.12 to 31.21 + 1.91) and then decreased to 12.11 + 2.3 at T12. Vertebral body dimensions showed increasing trends from T1 to T12.

CONCLUSIONS

A thorough knowledge of anatomical and radiological characteristics of the spine and their variations is essential for the clinicians. Data collected in the present study provides baseline normative values in Indian population and will help in guiding safe and effective completion of both surgical and anaesthetic procedures in the thoracic spine. Computer software aided morphometric data can help in selecting appropriate size and optimal placement of the implant with minimal procedural difficulties and complications during spine surgery.

Accuracy and safety of fluoroscopic guided percutaneous pedicle screws in thoracic and lumbosacral spine: a review of 2000 screws

STUDY DESIGN

Retrospective study.

OBJECTIVE

To investigate the accuracy and safety of percutaneous pedicle screws placed using fluoroscopic guidance in the thoracic and lumbosacral spine.

SUMMARY OF BACKGROUND DATA

Several studies had examined the accuracy and safety of percutaneous pedicle screws but provided large variations in their results with small number of patients or few number of pedicle screws evaluated.

METHODS

Computerized tomography of patients who had surgery with fluoroscopic guided percutaneous pedicle screws were chosen from 2 centers: (1) European patients from University Medical Center Hamburg-Eppendorf, Germany and (2) Asian patients from University Malaya Medical Centre, Malaysia. Screw perforations were classified into Grade 0, Grade 1 (<2 mm), Grade 2 (2-4 mm), and Grade 3 (>4 mm).

RESULTS

In total, 2000 percutaneous pedicle screws from 273 patients were analyzed: 1290 screws from 183 European patients and 710 screws from 90 Asian patients. The mean age was 59.1 ± 15.6. There were 140 male patients and 133 female patients. The total perforation rate was 9.4% with 151 (7.5%) Grade 1, 31 (1.6%) Grade 2, and 5 (0.3%) Grade 3 perforations. The total perforation rates among Europeans were 9.4% and among Asians were 9.3%. There was no difference between the 2 groups (P > 0.05). There were 3 distinct peaks in perforation rates (trimodal distribution) at T1, midthoracic region (T4-T7), and lumbosacral junction (L5 and S1). The highest perforation rates were at T1 (33.3%), S1 (19.4%), and T4 (18.6%).

CONCLUSION

Implantation of percutaneous pedicle screws insertion using fluoroscopic guidance is safe and has the accuracy comparable to open techniques of pedicle screws insertion.

LEVEL OF EVIDENCE

4.

A comparison of feasibility and safety of percutaneous fluoroscopic guided thoracic pedicle screws between Europeans and Asians: is there any difference?

PURPOSE

To directly compare the safety of fluoroscopic guided percutaneous thoracic pedicle screw placement between Caucasians and Asians.

METHODS

This was a retrospective computerized tomography (CT) evaluation study of 880 fluoroscopic guided percutaneous pedicle screws. 440 screws were inserted in 73 European patients and 440 screws were inserted in 75 Asian patients. Screw perforations were classified into Grade 0: no violation; Grade 1: <2 mm perforation; Grade 2: 2-4 mm perforation; and Grade 3: >4 mm perforation. For anterior perforations, the pedicle perforations were classified into Grade 0: no violation, Grade 1: <4 mm perforation; Grade 2: 4-6 mm perforation; and Grade 3: >6 mm perforation.

RESULTS

The inter-rater reliability was adequate with a kappa value of 0.83. The mean age of the study group was 58.3 ± 15.6 years. The indications for surgery were tumor (70.3 %), infection (18.2 %), trauma (6.8 %), osteoporotic fracture (2.7 %) and degenerative diseases (2.0 %). The overall screw perforation rate was 9.7 %, in Europeans 9.1 % and in Asians 10.2 % (p > 0.05). Grade 1 perforation rate was 8.4 %, Grade 2 was 1.2 % and Grade 3 was 0.1 % with no difference in the grade of perforations between Europeans and Asians (p > 0.05). The perforation rate was the highest in T1 (33.3 %), followed by T6 (14.5 %) and T4 (14.0 %). Majority of perforations occurred medially (43.5 %), followed by laterally (25.9 %), and anteriorly (23.5 %). There was no statistical significant difference (p > 0.05) in the perforation rates between right-sided pedicle screws and left-sided pedicle screws (R: 10.0 %, L: 9.3 %).

CONCLUSIONS

There were no statistical significant differences in the overall perforation rates, grades of perforations, direction of perforations for implantation of percutaneous thoracic pedicle screws insertion using fluoroscopic guidance between Europeans and Asians. The safety profile for this technique was comparable to the current reported perforation rates for conventional open pedicle screw technique.

Pedicle morphometry of upper thoracic vertebrae: an anatomic study of 503 cadaveric specimens

STUDY DESIGN

An anatomic study of pedicle dimensions was performed for upper thoracic vertebrae from American human subjects.

OBJECTIVE

To quantify the dimensions of the upper thoracic pedicles and to better define the demographic factors that could ultimately govern the caliber selection of pedicle screws.

SUMMARY OF BACKGROUND DATA

Transpedicular screw fixation allows for segmental instrumentation into multiple vertebrae across multilevel fusion area, offering considerable biomechanical advantage over the conventional hook and lateral mass fixation. Large variations in morphology from previous studies may be related to differences in demographics, sample size, and methodology.

METHODS

For this study, T1-T6 vertebrae from 503 American human cadavers were directly measured with a digital caliper. Examiner measured each vertebra to determine medial-lateral pedicle width and cranial-caudal pedicle height. Demographic information regarding age, sex, and race, as well as body height and weight, was available for all 503 subjects.

RESULTS

Pedicle height generally increased in size caudally down the upper thoracic spine, but the highest pedicle height was at the T3 level with a mean of 12.25 mm. Pedicle width displayed a narrowing pattern moving down. The widest pedicle width was at the T1 level with a mean of 8.66 mm. The 2 older age groups had larger pedicles than the 2 younger age groups. Males have larger pedicles than females for all upper thoracic levels. The tallest and heaviest groups had larger pedicles than the shorter and lighter groups, respectively. Race was not a significant factor in affecting pedicle dimension.

CONCLUSION

Our large-scale study of American specimens characterized the relationship between pedicle dimensions and a variety of demographic factors such as age, sex, body height, and weight. With substantial statistical power, this study showed that male, older, taller, and heavier individuals had larger pedicles.

LEVEL OF EVIDENCE

N/A.

The ventral lamina and superior facet rule: a morphometric analysis for an ideal thoracic pedicle screw starting point

BACKGROUND CONTEXT

With the increasing popularity of thoracic pedicle screws, the freehand technique has been espoused to be safe and effective. However, there is currently no objective, definable landmark to assist with freehand insertion of pedicle screws in the thoracic spine. With our own increasing surgical experience, we have noted a reproducible and unique anatomic structure known as the ventral lamina.

PURPOSE

We set out to define the morphologic relationship of the ventral lamina to the superior articular facet (SAF) and pedicle, and describe an optimal medial-lateral pedicle screw starting point in the thoracic spine.

STUDY DESIGN

We conducted an in vitro fresh-frozen human cadaveric study.

METHODS

One hundred fifteen thoracic spine vertebral levels were evaluated. After the vertebral body was removed, Kirschner wires were inserted retrograde along the four boundaries of the pedicle. Using digital calipers, we measured width of the SAF and pedicle at the isthmus, and from the borders of the SAF to the boundaries of the pedicle. We calculated the morphologic relationship of the ventral lamina and the center of the pedicle (COP) to the SAF.

RESULTS

Two hundred twenty-nine pedicles were measured, with one pedicle excluded because of fracture of the SAF during disarticulation. The ventral lamina was clearly identifiable at all levels, forming the roof of the spinal canal and confluent with the medial pedicle wall (MPW). The mean distance from the SAF midline to the MPW was 1.36±1.23 mm medial. The MPW was lateral to SAF midline in 34 pedicles (14.85%) and, on average, was a distance of 0.52±0.51 mm lateral. The mean distance from the SAF midline to the COP was 2.17±1.38 mm lateral. The COP was medial to SAF midline in only 11 pedicles (4.80%).

CONCLUSIONS

The ventral lamina is an anatomically reproducible structure located consistently medial to the SAF midline (85%). We also found the COP consistently lateral to the SAF midline (95%). Based on these morphologic findings, the medial-lateral starting point for thoracic pedicle screws should be 2 to 3 mm lateral to the SAF midline (superior facet rule), allowing screw placement in the COP and avoiding penetration into the spinal canal.

Evaluation of thoracic pedicle morphometry in a Chinese population using 3D reformatted CT

The aim of this study was to investigate the detailed three-dimensional morphology of the pedicles from T1 to T12 in 120 Chinese patients using a light-speed Vct CT (General Electric). After reformatting the original images, the following parameters were studied: outer pedicle width (OPW), outer pedicle height (OPH), pedicle chord length (PCL), pedicle cortical thickness (PCT) of the isthmus, and transverse pedicle angle (TPA). The mean outer pedicle width, outer pedicle height, and pedicle chord length were significantly smaller in females than in males at all levels (P < 0.01). The percentage of outer pedicle width ≤ 5.0 mm and ≤ 4.5 mm was high at mid-thoracic pedicles. No significant differences were found in transverse pedicle angle and pedicle cortical thickness in males and females. Pedicle cortical thickness was significantly thinner in patients over 50 years old compared with patients below 50 years old at most levels. The results showed that a screw of larger than 4.5 mm would be too large for mid-thoracic segments in Chinese population, especially for female patients. Considering the amount of variation between individuals and the complicated structure of the thoracic pedicles, the use of the transpedicular screw fixation must be individualized for each patient and based on detailed preoperative assessment. Reformatted CT assessment is essential before this procedure is performed.

Accuracy of image-guided pedicle screw placement using intraoperative computed tomography-based navigation with automated referencing. Part II: thoracolumbar spine

BACKGROUND

Image-guided spinal instrumentation may reduce complications in spinal instrumentation.

OBJECTIVE

To assess accuracy, time efficiency, and staff radiation exposure during thoracolumbar screw instrumentation guided by intraoperative computed tomography (iCT)-based neuronavigation (iCT-N).

METHODS

In 55 patients treated for idiopathic and degenerative deformities, 826 screws were inserted in the thoracic (T2-T12; n = 243) and lumbosacral (L1-S1; n = 545) spine, as well as ilium (n = 38) guided by iCT-N. Up to 17 segments were instrumented following a single automated registration sequence with the dynamic reference arc (DRA) uniformly attached to L5. Accuracy of iCT-N was assessed by calculating angular deviations between individual navigated tool trajectories and final implant positions. Final screw positions were also graded according to established classification systems. Clinical and radiological outcome was assessed at 12 to 14 months.

RESULTS

Additional intraoperative fluoroscopy was unnecessary, eliminating staff radiation exposure. Unisegmental K-wire insertion required 4.6 ± 2.9 minutes. Of the thoracic pedicle screws 98.4% were assigned grades I to III according to the Heary classification, with 1.6% grade IV placement. In the lumbar spine, 94.4% of screws were completely contained (Gertzbein classification grade 0), 4.6% displayed minor pedicle breaches <2 mm (grade 1), and 1% of lumbar screws deviated by >2 to <4 mm (grade 2). The accuracy of iCT-N progressively deteriorates with increasing distance from the DRA, but allows safe instrumentation of up to 12 segments.

CONCLUSION

iCT-N using automated referencing allows for safe, highly accurate multilevel instrumentation of the entire thoracolumbosacral spine and ilium, rendering additional intraoperative imaging dispensable. In addition, automated registration is time-efficient and significantly reduces the need for re-registration in multilevel surgery.

Safety of fluoroscopy guided percutaneous access to the thoracic spine

BACKGROUND

Fluoroscopy-guided percutaneous access to thoracic vertebrae is technically demanding due to the complex radiological anatomy and close proximity of the spinal cord, major vessels and pleural cavity. There is a trend towards computed tomography (CT) guidance due to a perceived reduction in the risk of spinal canal intrusion by instrumentation causing neurological injury. Due to limited access to CT guidance, there is a need for safe fluoroscopy-guided percutaneous access to the thoracic spine.

PURPOSE

To evaluate the safety of a strict radio-anatomical protocol in avoiding access-related neurological complications due to tool misplacement in fluoroscopy-guided percutaneous procedures on the thoracic spine.

METHOD

A combined two-surgeon prospective case series of 444 procedures (biopsy, vertebroplasty or kyphoplasty) covering all thoracic vertebral levels T1-T12. Clinical examination and routine observations were used to identify access-related complications including neurological, vascular and visceral injury using physiological parameters.

RESULTS

No patient in our series was identified to have sustained a neurological deficit or deterioration of preoperative neurological status.

CONCLUSION

Percutaneous access to the thoracic spine using fluoroscopic guidance is safe. The crucial step of the protocol is not to advance the tool beyond the medial pedicle wall on the anterior-posterior projection until the tip of the instrument has reached the posterior vertebral cortex on the lateral projection.

Thoracic pedicle morphometry in different body height population: a three-dimensional study using reformatted computed tomography

STUDY DESIGN

A three-dimensional study of the thoracic pedicle (T1-T12) morphometry in Chinese patients with different body height, using reformatted computed tomography (CT).

OBJECTIVE

To quantify the dimensions of the thoracic pedicles and to analyze the relationship between body height and thoracic pedicle parameters.

SUMMARY OF BACKGROUND DATA

The thoracic pedicle morphometry has been studied extensively in different populations using various techniques. Previous studies have shown a significantly smaller size of the thoracic pedicles in women than in men and in Asians than in Caucasians. Some authors postulated that it is the body height that contributes to the variation in the pedicle size. To our knowledge, however, no study has specifically analyzed the relationship between body height and thoracic pedicle parameters in detail.

METHODS

In this study, T1 to T12 vertebrae were imaged in 126 Chinese patients by a Lightspeed Vct CT (General Electric, Bridgeport, Connecticut, USA). After reformatting the original images, the following parameters were calculated: outer pedicle width, outer pedicle height and pedicle cortical thickness of the pedicle isthmus, pedicle length, and transverse pedicle angle. All measured data were statistically analyzed by the independent t test and Pearson correlation test using SPSS software (SPSS Inc, Chicago, IL).

RESULTS

The thoracic pedicle parameters were significantly smaller in women than in men except for the transverse pedicle angles and the pedicle cortical thickness. The percentage of outer pedicle widths less than 4.5 mm was extremely high at T3 to T9 in females and T4 to T7 in males. There was a much higher percentage of pedicle width of 4.5 mm or lesser, 4.0 mm or lesser, and 3.5 mm or lesser when body height was less than 160 cm. Body height is probably one of the main factors that contribute to the variation in pedicle size since a significant positive correlation was observed between pedicle size and body height.

CONCLUSION

Body height is probably one of the main factors that contribute to the variation in pedicle size among different ethnic and sex groups. Transpedicular procedures using a 4.5-mm screw may not be applicable to much of the Chinese population at the upper and middle thoracic segments, especially for patients less than 160 cm in height. A reformatted CT evaluation is routinely recommended not only for choosing the proper screw but also for determining the feasibility of a true transpedicular procedure.

Accuracy of Image-Guided Pedicle Screw Placement Using Intraoperative Computed Tomography-Based Navigation With Automated Referencing, Part I: Cervicothoracic Spine

BACKGROUND:

Image-guided spinal instrumentation reduces the incidence of implant misplacement.

OBJECTIVE:

To assess the accuracy of intraoperative computed tomography (iCT)-based neuronavigation (iCT-N).

METHODS:

In 35 patients (age range, 18-87 years), a total of 248 pedicle screws were placed in the cervical (C1-C7) and upper and midthoracic (T1-T8) spine. An automated iCT registration sequence was used for multisegmental instrumentation, with the reference frame fixed to either a Mayfield head clamp and/or the most distal spinous process within the instrumentation. Pediculation was performed with navigated drill guides or Jamshidi cannulas. The angular deviation between navigated tool trajectory and final implant positions (evaluated on postinstrumentation iCT or postoperative CT scans) was calculated to assess the accuracy of iCT-N. Final screw positions were also graded according to established classification systems. Mean follow-up was 16.7 months.

RESULTS:

Clinically significant screw misplacement or iCT-N failure mandating conversion to conventional technique did not occur. A total of 71.4% of patients self-rated their outcome as excellent or good at 12 months; 99.3% of cervical screws were compliant with Neo classification grades 0 and 1 (grade 2, 0.7%), and neurovascular injury did not occur. In addition, 97.8% of thoracic pedicle screws were assigned grades I to III of the Heary classification, with 2.2% grade IV placement. Accuracy of iCT-N progressively deteriorated with increasing distance from the spinal reference clamp but allowed safe instrumentation of up to 10 segments.

CONCLUSION:

Image-guided spinal instrumentation using iCT-N with automated referencing allows safe, highly accurate multilevel instrumentation of the cervical and upper and midthoracic spine. In addition, iCT-N significantly reduces the need for reregistration in multilevel surgery.

Morphometric measurements of cadaveric thoracic spine in Indian population and its clinical applications

STUDY DESIGN

Analysis of morphometric data obtained from direct measurements of 100 cadaveric thoracic spines in Indian population.

PURPOSE

To collect a base line morphometric data and analyze it in reference to the musculoskeletal anatomy and biomechanics of the spine; implants and instrumentations; and to suggest the requisite modification in spinal surgery instrumentations.

OVERVIEW OF LITERATURE

Most of the previous studies in the world literature have focused primarily on the parameters of the pedicle and to the authors' knowledge; no study has been published from the Indian subcontinent reporting a detailed morphometry of the thoracic spine.

METHODS

One thousand and two hundred thoracic vertebrae were studied by direct measurements for linear and angular dimensions of the vertebral body, spinal canal, pedicle, and spinous and transverse processes in 100 human cadavers.

RESULTS

Thirty-five point five percent of all the pedicles; 71% of T5 pedicles; 54.6% of all the female pedicles; and 94.4% of the T5 pedicles in females were smaller than 5 mm in mid-pedicle width dimension. Transverse pedicle angle was more at all levels and pedicles were sagittaly angulated in cephalad direction in comparison to other studies. Minimum value of interpedicular distance was at T5 (15.48 ± 1.24). Vertebral body width showed slight decrease from T1 to T4. The transverse process length was relatively constant between T2 to T10. The spinous process angle showed increasing trend from T1 to T6 and then gradually decreased to T12.

CONCLUSIONS

Most of the trends in changes of the parameters from T1 to T12 can be explained on the basis of local musculoskeletal anatomy and biomechanical stresses. The smallest diameter screw and shortest available screw for adults may not be safe in majority of the Indian population in mid-thoracic region. The results of the present study can help in designing implants and instrumentations; understanding spine pathologies; and management of spinal disorders in this part of the world.

A computed tomography-based morphometric study of thoracic pedicle anatomy in a random United States trauma population

OBJECT

The objective of this study was to establish normative data for thoracic pedicle anatomy in the US adult population. To this end, CT scans chosen at random from an adult database were evaluated to determine the ideal pedicle screw (PS) length, diameter, trajectory, and starting point in the thoracic spine. The role of patient sex and side of screw placement were also assessed. The authors postulated that this information would be of value in guiding safe implant size and placement for surgeons in training.

METHODS

One hundred patients (50 males and 50 females) were selected via retrospective review of a hospital trauma registry database over a 6-month period. Patients included in the study were older than 18 years of age, had axial bone-window CT images of the thoracic spine, and had no evidence of spinal trauma. For each pedicle, the pedicle width, pedicle-rib width, estimated screw length, trajectory, and ideal entry point were measured using eFilm Lite software. Statistical analysis was performed using the Student t-test.

RESULTS

The shortest mean estimated PS length was at T-1 (33.9 ± 3.3 mm), and the longest was at T-9 (44.9 ± 4.4 mm). Pedicle screw length was significantly affected by patient sex; men could accommodate a PS from T1-12 a mean of 4.0 ± 1.0 mm longer than in women (p < 0.001). Pedicle width showed marked variation by spinal level, with T-4 (4.4 ± 1.1 mm) having the narrowest width and T-12 (8.3 ± 1.7 mm) having the widest. Pedicle width had an obvious affect on potential screw diameter; 65% of patients had a least 1 pedicle at T-4 that was < 5 mm in diameter and therefore would not accept a 4.0-mm screw with 1.0 mm of clearance, as compared with only 2% of patients with a similar status at T-12. Sex variation was also apparent, as thoracic pedicles from T-1 to T-12 were a mean of 1.4 ± 0.2 mm wider in men than in women (p < 0.001). The PS trajectory in the axial plane was measured, showing a marked decrease from T-1 to T-4, stabilization from T-5 to T-10, followed by a decrease at T11-12. When screw trajectory was stratified by side of placement, a mean of 1.7° ± 0.5° of increased medialization was required for ideal pedicle cannulation from T-3 to T-12 on the left as compared with the right side, presumably because of developmental changes in the vertebral body caused by the aorta (p < 0.05 for T3-12, except for T-5, where p = 0.051). The junction of the superior articular process, lamina, and the superior ridge of the transverse process was shown to be a conserved surface landmark for PS placement.

CONCLUSIONS

Preoperative CT evaluation is important in choosing PS length, diameter, trajectory, and entry point due to variation based on spinal level, patient sex, and side of placement. These data are valuable for resident and fellow training to guide the safe use of thoracic PSs.

Comparison of radiographic and computed tomographic measurement of pedicle and vertebral body dimensions in Koreans: the ratio of pedicle transverse diameter to vertebral body transverse diameter

This study was designed to investigate the characteristics of pedicle transverse diameters (PD), vertebral body transverse diameters (VBD), especially the ratios of PD/VBD (CT ratio), which has never been discussed, in Koreans using computed tomography (CT) scans and to evaluate the possibility of obtaining more accurate estimations of PD from plain radiographs using the CT ratios in each spine level. The T1-L5 vertebrae of 50 participants were analyzed prospectively with CT scans (CT-VBD and CT-PD), and the T9-L5 vertebrae of the same participants were investigated with plain radiographs (X-VBD and X-PD). The CT ratio had a higher correlation with the CT-PD (r2 = 0.630) from T1 to L5, especially in the lower thoracic and lumbar spine (T9-L5, r2 = 0.737). The correlation of VBDs between the two radiologic tools (r2 = 0.896) was higher than that of the PDs (r2 = 0.665). Based on the data, equations for the estimation of a more accurate PD from plain radiographs were developed as follows: estimated PD = estimated VBD × [1.014 × (X-VBD) + 0.152] × the mean CT ratio at each spinal level. The correlation between the estimated PD and the CT-PD (r2 = 0.852) was improved compared with that (r2 = 0.665) between the X-PD and the CT-PD. In conclusion, the CT ratio showed a very similar changing trends to CT-PD from T1 to L5 regardless of sex and body mass, and the measurement error of PD from only plain radiographs could be minimized using estimated VBD and the mean CT ratio at each spinal level.

Biomechanical comparison of translaminar versus pedicle screws at T1 and T2 in long subaxial cervical constructs

OBJECTIVE

The first in vitro biomechanical investigation comparing the immediate and postcyclical rigidities of thoracic translaminar versus pedicle screws in posterior constructs crossing the cervicothoracic junction (CTJ).

METHODS

Ten human cadaveric spines underwent C4-C6 lateral mass screw and T1-T2 translaminar (n = 5) versus pedicle (n = 5) screw fixation. Spines were then potted in polymethylmethacrylate bone cement and placed on a materials testing machine. Rotation about the axis of bending was measured using passive retroreflective markers and infrared motion capture cameras. The motion of C6 relative to T2 in flexion-extension and lateral bending was assessed uninstrumented, immediately after instrumentation, and after 40,000 cycles of 4 N.m flexion-extension and lateral bending moments at 1 Hz. The effect of instrumentation and cyclical loading on rotational motion across the CTJ was analyzed for significance.

RESULTS

Compared with preinstrumented spines, pedicle and translaminar screw constructs significantly (P < 0.001) decreased motion during flexion-extension and lateral bending. After cyclical loading, rotational motion at the CTJ was significantly increased (P < 0.05) during flexion-extension and lateral bending in both groups. With flexion-extension, the mean rotational motion across the CTJ was similar in the translaminar and pedicle constructs immediately after fixation, but slightly greater (P = 0.03) after cyclical loading in the translaminar versus the pedicle screw constructs (0.39 degrees versus 0.26 degrees). Nevertheless, after cyclical loading, the mean angular motion across the CTJ remained less than one half of a degree in both groups. With lateral bending, the mean rotational motion was similar in both translaminar and pedicle screw constructs.

CONCLUSION

Both upper thoracic translaminar and pedicle screws allow for rigid fixation at the CTJ. Although translaminar screw constructs demonstrated one eighth of a degree more motion at the CTJ after cycling, this minimal difference is likely less than would influence the biological fusion process. Upper thoracic translaminar screws are a biomechanically effective option to rigidly stabilize the CTJ.

Free-hand thoracic pedicle screws placed by neurosurgery residents: a CT analysis

Free-hand thoracic pedicle screw placement is becoming more prevalent within neurosurgery residency training programs. This technique implements anatomic landmarks and tactile palpation without fluoroscopy or navigation to place thoracic pedicle screws. Because this technique is performed by surgeons in training, we wished to analyze the rate at which these screws were properly placed by residents by retrospectively reviewing the accuracy of resident-placed free-hand thoracic pedicle screws using computed tomography imaging. A total of 268 resident-placed thoracic pedicle screws was analyzed using axial computed tomography by an independent attending neuroradiologist. Eighty-five percent of the screws were completely within the pedicle and that 15% of the screws violated the pedicle cortex. The majority of the breaches were lateral breaches between 2 and 4 mm (46%). There was no clinical evidence of neurovascular injury or injury to the esophagus. There were no re-operations for screw replacement. We concluded that under appropriate supervision, neurosurgery residents can safely place free-hand thoracic pedicle screws with an acceptable breach rate.

Pedicle morphometry for thoracic screw fixation in ethnic koreans : radiological assessment using computed tomographic myelography

OBJECTIVE

In the thoracic spine, insertion of a pedicle screw is annoying due to small pedicle size and wide morphological variation between different levels of the spine and between individuals. The aim of our study was to analyze radiologic parameters of the pedicle morphometry from T1 to T8 using computed tomographic myelography (CTM) in Korean population.

METHODS

For evaluation of the thoracic pedicle morphometry, the authors prospectively analyzed a consecutive series of 26 patients with stable thoracic spines. With the consent of patients, thoracic CTM were performed, from T1 to T8. We calculated the transverse outer diameters and the transverse angles of the pedicle, distance from the cord to the inner cortical wall of the pedicle, and distance from the cord to the dura.

RESULTS

Transverse outer pedicle diameter was widest at T1 (7.66 +/- 2.14 mm) and narrowest at T4 (4.38 +/- 1.55 mm). Transverse pedicle angle was widest at T1 (30.2 +/- 12.0 degrees ) and it became less than 9.0 degrees below T6 level. Theoretical safety zone of the medial perforation of the pedicle screw, namely, distance from the cord to inner cortical wall of the pedicle was more than 4.5 mm.

CONCLUSION

Based on this study, we suggest that the current pedicle screw system is not always suitable for Korean patients. Computed tomography is required before performing a transpedicular screw fixation at the thoracic levels.

Clinical and radiographic outcomes of pedicle screw fixation for upper thoracic spine (T1–5) fractures: a retrospective cohort study of 27 cases

Object

The use of pedicle screws (PSs) for stabilization of unstable thoracolumbar fractures has become the standard of care, but PS efficacy has not been reported in the upper thoracic spine. The primary outcome of this study was to determine the efficacy of PS fixation to achieve and maintain reduction of unstable upper thoracic spine fractures (T1–5). Secondary outcomes included scores on a 1-year postoperative generic health-related quality of life (QOL) questionnaire and postoperative complications.

Methods

This study was a retrospective analysis and cross-sectional outcome assessment of cases prospectively entered into a spine database from 1997 to 2004. All patients with a traumatic, unstable upper thoracic spine (T1–5) fracture who underwent PS fixation were included. Preoperative CT scans with sagittal plane reformatted images were used to determine kyphotic deformity and compared with immediate postoperative and latest follow-up radiographs or CT scans. Patient charts, operative notes, and the results of postoperative follow-up examinations were reviewed. Patients were mailed the Short Form-36v2 (SF-36 version 2) by an independent study coordinator.

Results

Cases involving 27 patients (23 male, 4 female) were evaluated. The patients' mean age was 39.9 years (range 16–73 years). In all, 251 PSs were passed between T-1 and T-8. The mean true kyphotic deformity was 18.2° preoperatively, 8.7° (p < 0.0005) initially postoperatively, and 10.1° at final follow-up (mean 2.3 years postoperatively). The mean SF-36 physical component summary score was 35.89 while the mental component summary score was 56.43 at a minimum of 1-year postoperatively (mean 3.2 years). There were no intraoperative vascular or neural complications.

Conclusions

In the hands of fellowship-trained spinal surgeons, PS fixation for reduction and stabilization of upper thoracic spine fractures is a safe and efficacious technique. Health-related QOL outcome data are deficient for spine trauma patients and should be an essential component of quantifying treatment outcomes.

DECISION MAKING IN ADULT DEFORMITY

SPINAL DEFORMITY AFFECTS adults and adolescents in different ways. Adult deformity patients are skeletally mature and tend to have relatively fixed curves, whereas adolescent patients are skeletally immature with flexible curves. As a result, adult patients typically present with back pain and neurological concerns, whereas adolescents present with cosmetic complaints. The goals of surgery on the adult deformity patient are to treat pain and relieve neurological problems while maintaining or achieving three-dimensional balance. The absolute degree of coronal curve correction in an adult deformity patient is less important than maintaining good sagittal balance. Issues that must be addressed in the preoperative decision-making process include the approach to the surgery, the timing of the surgery, and the location of the end of the construct. Twenty years ago, anteroposterior surgery was the most common procedure used for adults with fixed curves; however, recent advances in technology and techniques have led to more frequent use of purely posterior approaches. The posterior approach allows for greater curve correction owing to two major advances in the surgical method: osteotomy techniques, which release fixed deformities, and pedicle screw instrumentation in the thoracolumbar spine, which achieves greater curve correction with fewer levels of fixation. The optimal timing of surgery and the levels to be treated remain open to debate. Each adult patient's treatment must be individualized to achieve the best coronal correction possible while maintaining sagittal balance to preserve the three-dimensional balance of the spine.

Cortex of the pedicle of the vertebral arch. Part I: Deformation characteristics during screw insertion

OBJECT

Elastic deformation has been proposed as a mechanism by which vertebral pedicles can maintain pullout strength when conical screws are backed out from full insertion. The response to the insertion technique may influence both the extent of deformation and the risk of acute fracture during screw placement. The aim of this study was to determine the deformation characteristics of the lumbar pedicle cortex during screw placement.

METHODS

Lumbar pedicles with linear strain gauges attached at the lateral and medial cortices were instrumented using 7.5-mm pedicle screws with or without preconditioning by insertion and removal of 6.5-mm screws. The strains and elastic recoveries of the medial and lateral cortices were determined.

RESULTS

Mean medial wall strains tended to be lower than mean lateral wall strains when the 6.5-mm and 7.5-mm screw data were pooled (p = 0.07). After the screws had been removed, 71 to 79% of the deformation at the lateral cortex and 70 to 96% of the deformation at the medial cortex recovered. When inserted first, the 7.5-mm screw caused more plastic deformation at the cortex than it did when inserted after the 6.5-mm screw. Occasional idiosyncratic strain patterns were observed. No gross fracture was observed during screw placement.

CONCLUSIONS

Screw insertion generated plastic deformation at the pedicle cortex even though the screw did not directly contact the cortex. The lateral and medial cortices responded differently to screw insertion. The technique of screw insertion affected the deformation behavior of the lumbar pedicles. With myriad options for screw selection and placement available, further study is needed before optimal placement parameters can be verified.

Cortex of the pedicle of the vertebral arch. Part II: microstructure

Object

Although the gross anatomy of the pedicle in the human spine has been investigated in great detail, knowledge of the microanatomy of trabecular and cortical structures of the pedicle is limited. An understanding of the mechanical properties and structure of the pedicle bone is essential for improving the quality of pedicle screw placement. To enhance this understanding, the authors examined human cadaveric lumbar vertebrae.

Methods

In this study, the authors obtained seven human cadaveric lumbar vertebrae. The lateral and medial cortices of these pedicle specimens were sectioned and embedded in polymethylmethacrylate. Cross-sectional slices of cortex were obtained from each specimen and imaged with the aid of a high-resolution light microscope. Assessments of osteonal orientation, determinations of relative dimensions, and histomorphometric studies were performed.

Results

The cortex of the pedicle in each human lumbar vertebra had an osteonal structure with haversian canals laid down mainly in the anteroposterior (longitudinal) direction. The organization of osteons across the transverse cross-section was not homogeneous. The layer of lamellar bone that typically envelops cortical bone structures (such as in long bones) was not observed, and the lateral cortex was significantly thinner than the medial cortex (p< 0.05).

Conclusions

The cortical bone surrounding the pedicle differed from bone in other anatomical regions such as the anterior vertebral body and femur. The osteonal orientation and lack of a lamellar sheath may account for the unique deformation characteristics of the pedicle cortex seen during pedicle screw placement.

Thoracic pedicle screw placement: analysis using anatomical landmarks without image guidance

STUDY DESIGN

Prospective laboratory study analyzing the technique of pedicle screw placement in a cadaveric model.

OBJECTIVES

To determine whether a freehand technique without image guidance can be used to safely place pedicle screws in the thoracic spine.

SUMMARY OF BACKGROUND DATA

The use of thoracic pedicle screws for the treatment of spinal deformity has been gaining increased acceptance among surgeons. Although these implants improve deformity correction, there is still concern regarding the risks to neurological and vascular structures and regarding the experience level needed to use this implant. This study was designed to determine whether these implants could be placed safely without imaging modalities.

METHODS

Six fresh cadaveric specimens were instrumented from vertebral segments T4-T11. Ninety-six screws were placed along the anatomical axis of the pedicle. Pedicles were dissected to determine the wall violations, the position of neural structures, and the lateral coverage of the pedicle by the rib head.

RESULTS

Ninety-seven percent of screws had less than 1 mm of wall violation, with 84 screws (87.5%) fully contained within the pedicle. Four screws (4.16%) violated the medial cortex. No violations occurred superiorly, inferiorly, or anteriorly. Nerve roots were in contact with the inferior pedicle wall at all levels. The average distance from nerve to the superior pedicle ranged from 3.85 to 5.04 mm.

CONCLUSIONS

Placing pedicle screws along the anatomical axis without image guidance produced a low level of pedicle wall disruption. This technique uses a reproducible start point at each level, and the results are equal to or better than those of other cadaveric studies that have used guidance systems.

Pedicle screw placement accuracy: a meta-analysis

STUDY DESIGN

A meta-analysis of the published literature was conducted specifically looking at accuracy and the postoperative methods used for the assessment of pedicle screw placement in the human spine.

OBJECTIVES

This study specifically aimed to identify postoperative methods used for pedicle screw placement assessment, including the most common method, and to report cumulative pedicle screw placement study statistics from synthesis of the published literature.

SUMMARY OF BACKGROUND DATA

Safety concerns have driven specific interests in the accuracy and precision of pedicle screw placement. A large variation in reported accuracy may exist partly due to the lack of a standardized evaluation method and/or the lack of consensus to what, or in which range, is pedicle screw placement accuracy considered satisfactory.

METHODS

A MEDLINE search was executed covering the span from 1966 until 2006, and references from identified papers were reviewed. An extensive database was constructed for synthesis of the identified studies. Subgroups and descriptive statistics were determined based on the type of population, in vivo or cadaveric, and separated based on whether the assistance of navigation was employed.

RESULTS

In total, we report on 130 studies resulting in 37,337 total pedicle screws implanted, of which 34,107 (91.3%) were identified as accurately placed for the combined in vivo and cadaveric populations. The most common assessment method identified pedicle screw violations simply as either present or absent. Overall, the median placement accuracy for the in vivo assisted navigation subgroup (95.2%) was higher than that of the subgroup without the use of navigation (90.3%).

CONCLUSIONS

Navigation does indeed provide a higher accuracy in the placement of pedicle screws for most of the subgroups presented. However, an exception is found at the thoracic levels for both the in vivo and cadaveric populations, where no advantage in the use of navigation was found.

Basic Science Research Related to Chiropractic Spinal Adjusting: The State of the Art and Recommendations Revisited

OBJECTIVE

The objectives of this white paper are to review and summarize the basic science literature relevant to spinal fixation (subluxation) and spinal adjusting procedures and to make specific recommendations for future research.

METHODS

PubMed, CINAHL, ICL, OSTMED, and MANTIS databases were searched by a multidisciplinary team for reports of basic science research (since 1995) related to spinal fixation (subluxation) and spinal adjusting (spinal manipulation). In addition, hand searches of the reference sections of studies judged to be important by the authors were also obtained. Each author used key words they determined to be most important to their field in designing their individual search strategy. Both animal and human studies were included in the literature searches, summaries, and recommendations for future research produced in this project.

DISCUSSION

The following topic areas were identified: anatomy, biomechanics, somatic nervous system, animal models, immune system, and human studies related to the autonomic nervous system. A relevant summary of each topic area and specific recommendations for future research in each area were the primary objectives of this project.

CONCLUSIONS

The summaries of the literature for the 6 topic sections (anatomy, biomechanics, somatic nervous system, animal models, immune system, and human studies related to the autonomic nervous system) indicated that a significant body of basic science research evaluating chiropractic spinal adjusting has been completed and published since the 1997 basic science white paper. Much more basic science research in these fields needs to be accomplished, and the recommendations at the end of each topic section should help researchers, funding agencies, and other decision makers develop specific research priorities.

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.

Clinical and radiological results after parapedicular screw fixation of the thoracic spine

OBJECT

The proximity of thoracic pedicles to the spinal cord and neurovascular structures has prompted numerous efforts to obtain proper screw placement. The aim of this study was to evaluate the feasibility and efficacy of thoracic parapedicular (intercostovertebral) screw fixation by following anatomical landmarks and using fluoroscopy.

METHODS

Thoracic parapedicular screw fixation was performed in 41 patients (328 screws). Postoperative computerized tomography scans were obtained in all cases to analyze the position of each screw with respect to the pedicle rib unit, the spinal canal, and the vertebral body (VB) according to a proposed novel grading system. Additionally, screw convergence angles were calculated for each instrumented level. There was no additional morbidity associated with parapedicular screw insertion. In a single case a screw suspected of entering the spinal canal was revised without causing neurological damage. The remaining screws were placed entirely within the pedicle rib unit and VB without breaching the neural foramina, pleura, or vascular structures.

CONCLUSIONS

Thoracic and thoracolumbar instability can be treated adequately and safely by using parapedicular screw fixation guided by anatomical landmarks and fluoroscopic imaging. The use of computer-aided navigation may be beneficial but does not appear to be mandatory.

Trabecular architecture of lumbar vertebral pedicle

STUDY DESIGN

Investigation on architecture of lumbar pedicle.

OBJECTIVE

To determine morphological properties of pedicular cancellous bone.

SUMMARY OF BACKGROUND DATA

Many researchers have been stimulated to study trabecular architecture by improvements in stereological technology. Although the structure of vertebral cancellous bone has been well studied in the literature, no information is available about the architecture of pedicular cancellous bone.

METHODS

Eight cadaveric L3 lumbar vertebrae were harvested. After collecting the bone mineral density (BMD) data on the vertebrae, pedicle isthmuses were removed from the vertebral bodies using a reciprocal hand saw. The BMD measurements were done on the dissected pedicle isthmus specimens. All the specimens were then analyzed using a micro-computed tomography unit. Morphologic parameters of trabecular bone were calculated.

RESULTS

Bone volume was found as 0.209 +/- 0.046, whereas Tb.Th, Tb.Sp, and Tb.N were found to be 0.201 +/- 0.035 mm, 0.930 +/- 0.123 mm, and 1.098 +/- 0.136 mm(-1), respectively. Connectivity density and structure model index were observed to be 3.135 +/- 0.918 mm(-3), 0.37, whereas degree of anisotropy value was 1.241 +/- 0.093. Vertebral BMD could explain 63% of variance in bone density of a pedicle isthmus.

CONCLUSIONS

The structure of the pedicular cancellous bone is somewhat different from that of vertebral body. The trabecular architecture within the pedicle isthmus is isotropic and plate-like. The thickness and number of the trabeculae were greater than those of vertebral trabeculae. Decrease in the bone volume with age is mainly by thinning of the trabeculae and increasing in trabecular spacing, but not by loss of mass.

Transcostovertebral kyphoplasty of the mid and high thoracic spine

While Kyphoplasty is increasingly becoming a recognised minimally invasive treatment option for osteoporotic vertebral fractures and neoplastic vertebral collapse, the experience in the treatment of vertebrae of the mid (T5-8)- and high (T1-4) thoracic levels is limited. The slender pedicle morphology restricts the transpedicular approach at these levels, necessitating extrapedicular placement techniques. Fifty five vertebrae of 32 consecutive patients were treated with kyphoplasty at levels ranging from T2-T8 for vertebral fractures (27 patients) or osteolytic collapse (5 patients). All procedures were performed through the transcostovertebral approach under fluoroscopic guidance. The radioanatomical landmarks of this minimally invasive approach were consistently identified and strictly adhered to. One fracture required open instrumentation due to posterior column injury in addition to kyphoplasty. Identification of specific radioanatomical landmarks allowed precise tool introduction in all cases without intraspinal or paravertebral malplacement. Average operating time for patients with osteoporotic fractures was 30 min per level (range 13-60 min) and 52 min per level (range 35-95 min) in neoplastic cases. Biopsy yield in patients with known or suspected malignancies was 100%. Epidural cement leakage was detected in one patient with pedicular osteolysis. Perforation of the lateral vertebral cortex during balloon inflation occurred in another patient. Both intraoperative complications were without clinical significance. Kyphoplasty in mid- to -high thoracic levels is possible via the transcostovertebral route under fluoroscopic guidance. Strict adherence to a stepwise protocol of tool introduction following defined radioanatomical landmarks is mandatory for the safe completion of this minimally invasive technique.

Evaluation and treatment of adult spinal deformity

✓ Spinal deformity is a complex and dynamic process that occurs in both the sagittal and coronal planes of the thoracolumbar spine. Successful treatment is aimed at achieving satisfactory balance in both of these planes. The spinal curvatures in the adult differ greatly from those in adolescents. As a general rule the adult curves tend to be stiffer, whereas adolescent curves are more flexible. In addition to cosmetic concerns, adult patients frequently present with pain and neurological symptoms in contrast to adolescents who usually do not experience this degree of pain or neurological symptoms. The treatment of adult spinal deformity differs substantially from that of adolescent deformity. Surgeries in the former tend to be more complex procedures associated with higher rates of intra- and perioperative complications. The goals of surgery in the adult are to obtain a solid fusion with a balanced spine, to relieve pain, and to prevent further deformity. A secondary goal is to correct the curve, and, in so doing, to improve the cosmetic appearance. In this review the author addresses the basic principles of spinal corrective surgery in the adult and provides insight into the varied treatment options available.

Morphometric study of the thoracic vertebral pedicle in an Indian population

STUDY DESIGN

Morphometric study of the thoracic vertebral pedicular parameters and comparison with the previous studies in the literature.

OBJECTIVES

To define pedicular dimensions and screw placement in the Indian population.

SUMMARY OF THE BACKGROUND DATA

Pedicular morphometric characteristics vary in different population groups. Thoracic pedicular screw fixation is being used more frequently with the advent of better imaging methods. Because of the small size and close proximity to the neurovascular structures, thoracic pedicle fixation has little margin of safety.

METHODS

T1-T12 vertebral pedicles were studied in 18 cadavers by direct, roentgenographic, and computerized tomographic scan methods. The following parameters were studied: transverse diameter, transverse angle, sagittal diameter, sagittal angle, chord length, interpedicular distance, pedicle entrance point, and pedicle cortical thickness (medial and lateral). RESULTS.: Transverse diameter was more than 6 mm at both ends of the thoracic spine (T1, T2, T11, and T12). Between T3-T9 levels, it was less than 5 mm at some levels. The transverse angle was widest at T1 (30 degrees) and was less than 5 degrees from T5 to T12. Pedicles were directed cephalad in the sagittal plane at all thoracic levels. Sagittal angle was less than 12 degrees at all thoracic levels. Chord length was largest at T11 (37.3 mm) and smallest at T1 and T2 (29.9 mm). Interpedicular distance was 29 mm at T12 and 21.3 mm at T1. Medial pedicular cortex was thicker than lateral cortex at all levels.

CONCLUSIONS

These results suggest that even a 4-mm screw should be used carefully at the midthoracic level; 5-mm screw seems to be safe at upper and lower thoracic spine. Because of very small sagittal and transverse angle at mid and lower thoracic levels, the pedicular screw should be inserted along almost perpendicular line in these planes; 25-mm and 30-mm screw length appears to be safe at upper thoracic and lower thoracic levels, respectively. Pedicle entrance point lies along the midtrans-verse line at upper thoracic levels and along the upper border of transverse process at lower thoracic levels.