Position of the aorta relative to the spine in patients with thoracolumbar/lumbar kyphosis secondary to ankylosing spondylitis

Radiologic and clinical outcomes of combining pedicle subtraction osteotomy and Smith-Peterson osteotomy in correcting severe ankylosing spondylitis kyphosis

The aim of this study was to explore the validity and safety of the combination of one-level pedicle subtraction osteotomy (PSO) and one-level Smith-Petersen osteotomy (SPO) in correcting severe ankylosing spondylitis kyphosis. Twenty-five AS patients undergoing one-level PSO and one-level SPO with a minimum of 2-year follow-up were included. Radiographical analyses included T5-T12 kyphosis (TK), L1-S1 lordosis (LL), global kyphosis (GK), osteotomized vertebral angle (OVA), sagittal vertical axis (SVA) and pelvic parameters. The computed tomographic (CT) scans of the spine were used to measure the aortic diameter and length. Clinical outcomes were evaluated by Oswestry Disability Index (ODI) questionnaire. The mean correction of OVA at PSO level and SPO level was 33.6° ± 9.2° and 26.0° ± 13.2° respectively. An average correction of 69.3° ± 23.2° in GK was achieved. The mean operation time was 372.6 ± 60.1 min and the estimated blood loss averaged 1790.4 ± 953.3 ml. The mean increase of aortic length after surgery was 3.6 cm. An average decrease of 0.25 cm in aortic diameter at the PSO level was observed after surgery. There was no significant difference in aortic diameter at the SPO level between pre- and post-operation. ODI was improved from 30.2 ± 19.3 before surgery to 15.5 ± 13.9 at the last visit. The combination of one-level SPO and one-level PSO could achieve satisfactory correction outcomes in AS patients with severe kyphosis (GK ≥ 80°) needing a correction of > 60°.

Effects of pedicle subtraction osteotomy on aortic morphology and hemodynamics in ankylosing spondylitis with kyphosis: a finite element analysis study

Osteotomy can correct kyphosis, restore the spinal sequence, and restore the healthy appearance of a patient. However, the aorta is stretched during pedicle subtraction osteotomy (PSO), and some surgeons are concerned about aortic injury. We used finite element analysis to construct an aortic model to simulate hemodynamic changes during osteotomy. 16 patients with ankylosing spondylitis kyphosis who had undergone a two-level osteotomy at the L1 and L3 levels was included in this study. Aortic computed tomography angiography (CTA) was performed, and a 3D image model was constructed. The length, transverse diameter, and curvature of the aorta were used to evaluate morphological changes. Finite element analysis was used to analyze the changes in aortic fluid dynamics. Blood pressure, wall shear stress, and blood flow velocity were compared pre- and postoperatively. The overall length of the aorta before surgery was 424.3 ± 42.9 mm, and the overall length of the aorta after surgery was 436.2 ± 54.8 mm. The aortic curvature decreased from 0.27 ± 0.13 to 0.17 ± 0.09. The mean transverse diameter of the aorta did not change (19.3 ± 6.6 vs. 19.2 ± 7.4 mm, P > 0.05). The blood flow velocity (2.8 ± 1.1 vs. 1.5 ± 0.8 m/s, P < 0.05), blood pressure (6.6 ± 1.7 vs. 4.3 ± 1.2 Kpa, P < 0.05), and wall shear stress (47.6 ± 17.3 vs. 22.3 ± 8.6, P < 0.05) at the T10-L4 level decreased postoperatively. Changes in LL were significantly correlated with changes in ld, dc, blood flow velocity, blood pressure and wall shear stress (ld : r = 0.713, P < 0.001; dc: r = 0.626,P = 0.010; blood flow velocity: r= - 0.541, P = 0.041; blood pressure: r = - 0.601, P = 0.016; wall shear stress: r= - 0.594, P = 0.027). The aorta was stretched, and its curvature decreased. The mean transverse diameter of the aorta did not change. Blood flow velocity, blood pressure, and wall shear stress decreased after surgery. Our study provides hemodynamic support for the possible cardiovascular benefits of osteotomes.

Advancing Prone-Transpsoas Spine Surgery: A Narrative Review and Evolution of Indications with Representative Cases

The Prone Transpsoas (PTP) approach to lumbar spine surgery, emerging as an evolution of lateral lumbar interbody fusion (LLIF), offers significant advantages over traditional methods. PTP has demonstrated increased lumbar lordosis gains compared to LLIF, owing to the natural increase in lordosis afforded by prone positioning. Additionally, the prone position offers anatomical advantages, with shifts in the psoas muscle and lumbar plexus, reducing the likelihood of postoperative femoral plexopathy and moving critical peritoneal contents away from the approach. Furthermore, operative efficiency is a notable benefit of PTP. By eliminating the need for intraoperative position changes, PTP reduces surgical time, which in turn decreases the risk of complications and operative costs. Finally, its versatility extends to various lumbar pathologies, including degeneration, adjacent segment disease, and deformities. The growing body of evidence indicates that PTP is at least as safe as traditional approaches, with a potentially better complication profile. In this narrative review, we review the historical evolution of lateral interbody fusion, culminating in the prone transpsoas approach. We also describe several adjuncts of PTP, including robotics and radiation-reduction methods. Finally, we illustrate the versatility of PTP and its uses, ranging from 'simple' degenerative cases to complex deformity surgeries.

A new mathematical model for evaluating surface changes in the mid-abdominal sagittal plane after two-level pedicle reduction osteotomy in patients with ankylosing spondylitis

BACKGROUND

The purpose of this study was to create a mathematical model to precalculate the acreage change in the abdominal median sagittal plane (ac-AMSP) of patients with ankylosing spondylitis (AS) for whom two-level pedicle subtraction osteotomy (PSO) was planned.

METHODS

A single-centre retrospective review of prospectively collected data was conducted among 11 adults with AS. Acreage of the abdominal median sagittal plane (a-AMSP) was performed. The distances and angles between the osteotomy apexes, anterosuperior edge of T12, xiphoid process, superior edge of the pubis, and anterosuperior corner of the sacrum were measured on preoperative thoracolumbar computed tomography. A mathematical model was created using basic trigonometric functions in accordance with the abdominal parameters. Planned osteotomized vertebra angles (POVAs) were substituted into the mathematical model, and the predictive ac-AMSP (P-AC) was obtained. A paired sample t test was performed to determine the differences between the P-AC and actual ac-AMSP (A-AC) and between the predictive acreage change rate (P-CR) and actual acreage change rate (A-CR).

RESULTS

The mean age and GK were 44.4 ± 8.99 years and 102.9° ± 19.17°, respectively. No significant difference exists between A-CR and P-CR via mathematical modeling (p > 0.05). No statistically significant difference existed between POVA and actual osteotomized vertebra angles (AOVA) (p > 0.05). A statistically significant difference was observed between preoperative and postoperative measurements of LL, SVA, and GK variables (p < 0.001).

CONCLUSIONS

The novel mathematical model was reliable in predicting the ac-AMSP in AS patients undergoing two-level PSO.

Not All Osteophytes Are Located on the Right Side of the Vertebrae in Diffuse Idiopathic Skeletal Hyperostosis: A Quantitative Analysis in Relation to the Position of Aorta

OBJECTIVE

Diffuse idiopathic skeletal hyperostosis (DISH) is characterized by osteophytes in the anterior vertebrae, and the presence of aorta may have an impact on their formation. However, the anatomical positional relationship between the aorta and osteophytes in patients with DISH remains controversial. This study aimed to evaluate the position of osteophytes in relation to aorta in DISH, and the influence of aortic pulsation on the formation of osteophytes from the perspective of morphology.

METHODS

We conducted a retrospective review of 101 patients diagnosed with DISH and symptomatic lumbar spinal stenosis between June 2018 and December 2021. A total of 637 segments with heterotopic ossification in DISH were used for quantitative measurements on CT scans. The Cartesian coordinate system was built up on the axial CT scans to reflect the relative position between aorta and osteophytes. Osteophytes were divided into adjacent aorta group (AD group) and non-adjacent aorta group (N-AD group). In terms of the morphology, osteophytes in the AD group were further divided into convex, flat, and concave types. The relative position between aorta and osteophytes, and the aorta-osteophyte distance and morphology of osteophytes were compared. Univariate analysis of variance was performed for multiple groups, and two independent-samples t-tests were used for two groups.

RESULTS

From T5 to L4, aorta gradually descended from left side to middle of vertebrae, and osteophytes gradually shifted from right side of vertebrae (T5-T10) to bilateral sides (T11-L4). Of 637 osteophytes in DISH, 60.1% (383/637) were in AD group, including convex type 0.6% (4/637), flat type 34.7% (221/637), and concave type 24.8% (158/637). The N-AD group accounted for 39.9% (254/637). Flat osteophytes were concentrated in T5-T12, while concave osteophytes in T11-L4. Overall, the aorta-osteophyte distance of concave type was significantly smaller than that of flat type.

CONCLUSION

Osteophytes are not always located on the right side of vertebrae, but move with the position of the descending aorta. Furthermore, the morphology of osteophytes varies by vertebral segment in DISH, which is related to aorta descending anteriorly in the spine.

Pedicle Morphology of Lower Thoracic and Lumbar Spine in Ankylosing Spondylitis Patients with Thoracolumbar Kyphosis: A Comparison with Fracture Patients

Objective

The pedicle morphology of ankylosing spondylitis (AS)‐related thoracolumbar kyphosis patients may be different from that of individuals with normal spine due to the ectopic ossification and kyphotic deformity. However, there was no literature analyzing the pedicle morphology of AS patients with thoracolumbar kyphosis. Therefore, the present study aimed to investigate the pedicle morphology of lower thoracic and lumbar spine (T9‐L5) in ankylosing spondylitis (AS)‐related thoracolumbar kyphosis patients.

Methods

A retrospective review of AS patients with thoracolumbar kyphosis (AS group) and the patients with spinal or rib fracture (fracture group) who underwent CT scans of the lower thoracic and lumbar spine between February 2017 and September 2018 was performed. Patients with spinal tumor, spinal tuberculosis, severe degenerative spinal diseases including degenerative scoliosis, degenerative spondylolisthesis, degenerative spinal stenosis or history of previous spine surgery, or AS patients with pseudarthrosis which influenced the measurement of pedicle parameters were excluded. The measured parameters on CT images included transverse pedicle angle (TPA), transverse pedicle width (TPW), chord length (CL), pedicle length (PL), and sagittal pedicle angle (SPA). The intraclass correlation coefficient (ICC) was used to evaluate the agreement of radiographic parameters between observers. The independent sample t test was applied for the comparison of pedicle parameters between the two groups. The gender distribution between the two groups were compared using the Fisher's exact test.

Results

A total of 1444 pedicles of 53 AS‐related thoracolumbar kyphosis patients and 30 patients with fracture were analyzed. TPA was significantly smaller in AS group (p < 0.05). Significantly larger TPW was found in AS group in the lumbar spine (p < 0.05). TPW ≥ 7.5 mm was observed in 95.3%–98.1% of the pedicles at the levels of L3‐L5 in AS group. The CL and PL were significantly larger in AS group at the levels of T9‐L5 (p < 0.05). The CL ≥ 50 mm was found in 84.0%–96.2% of the pedicles in mid‐to‐lower lumbar spine in AS group. Significantly smaller SPA was found in AS group at the levels from L3 to L5 (p < 0.05).

Conclusions

Pedicle screws with relatively large diameter of 7.5 mm and length of 50 mm could be used in mid‐to‐lower lumbar spine in the majority of AS‐related thoracolumbar kyphosis patients. Also, the insertion angle of pedicle screws in both the transverse and sagittal plane should be appropriately reduced in these patients. This study may help surgeons select the pedicle screws of appropriate size in AS patients.

Different angular kyphosis locations have different relative positions of aorta to spine in patients with Pott's deformity

Background

The position of the aorta relative to the spine in kyphosis secondary to Pott's deformity is little understood. The purpose of this study was to investigate the anatomic relationship between the aorta and the spine in patients with Pott’s deformity and to compare it with the normal people.

Methods

Seventy-six patients with Pott’s deformity (Group TB) and seventy-two age- and sex-matched patients with a normal spine (group NC) were enrolled in this study. The relative position of aorta to the spine was evaluated from T4 to L4 on the computed tomographic angiography scans for controls and at the apex level for TB patient, and was classified into 4 kinds of degrees.

Results

The left pedicle-aorta angle in group TB was significantly larger than that in group NC at the T6-L3 levels. Group TB exhibited significantly smaller left pedicle-aorta distance, pedicular line-aorta distance and vertebra/rib-aorta distance than those in group NC at the T5-T10 levels, but bigger at the L1-3 levels. Patients with grade 3 and 4 aorta had more segments involved compared with those with grade 1 aorta. Patients with grade 2, 3, and 4 aorta showed larger kyphotic angles than those with grade 1.

Conclusions

Patients whose morbid segments involved only thoracic vertebrae presented with an “Ω” shaped aorta in sagittal plane, and 4 different kinds of degrees of aorta relative to the vertebra/rib in axial plane. Patients whose morbid segments covered lumbar vertebrae presented with an “M” shaped aorta in sagittal plane, and the aorta shifted further from apex vertebra but was located in close proximity to the vertebral body at levels above and below the osteotomy levels in axial plane.

The position of the aorta relative to the spine in patients with adult degenerative scoliosis

Study design

A retrospective analysis was conducted to analyze the position of the aorta by MRI in patients with adult degenerative scoliosis.

Objective

This study aimed to investigate the relative anatomic positions of the aorta and spine in patients with adult degenerative scoliosis (ADS).

Summary of background data

Aorta injury is a rare complication of spinal surgeries. However, there would be a disastrous consequence once it happened. Therefore, knowing about the position of aorta is of great importance.

Methods

A retrospective analysis was performed in 90 patients with ADS and 132 participants without spine deformity. ADS patients were divided into several groups such as left scoliosis, left scoliosis with thoracolumbar kyphosis, right scoliosis, and right scoliosis with thoracolumbar kyphosis. The aorta-vertebrae angle (α) and aorta-vertebrae distance (d) in each level of T12–L4 were measured by using a Cartesian coordinate system. t test of independent samples was performed, α and d were compared, and Pearson correlation analysis was employed for α, d, and X-ray radiographic measurements.

Result

The changes of α were not statistically significant (P > 0.05) in LS and LKS groups but d (P < 0.05) was longer in LKS group compared with the control group. In the right malformed group, there was no significant change in the angle (P > 0.05) in the abdominal aorta but longer d (P < 0.05) than the normal group. There was longer d in the RKS group compared with the RS group (P < 0.05). Pearson correlation analysis showed that there was a positive correlation between d and TLK (r = 0.439, P < 0.05).

Conclusion

In patients with ADS, a relative normal position is maintained between the aorta and vertebrae. While the aorta is slightly away from the left pedicle in RS patients and farther away in patients with kyphosis, the angle of kyphosis would become bigger and d becomes longer. Therefore, the surgeons should be aware of the changes of the aorta position to avoid the disastrous vessel injuries.

Systemic changes associated with quality of life after surgical treatment of kyphotic deformity in patients with ankylosing spondylitis: a systematic review

PURPOSE

In addition to changes in the skeletal system after spinal osteotomy for treatment of kyphotic deformity in advanced-stage AS patients, many other systemic changes associated with the patients' quality of life were reported. The purpose of this study was to conduct a systemic review of the literature to determine systemic changes associated with patients' quality of life following correction of kyphotic deformity secondary to ankylosing spondylitis.

METHODS

We searched the databases PubMed, EMBASE, Clinicalkey and Cochrane Library without time restriction. Selected papers were assessed by published guidelines. We investigated systemic changes associated with patients' quality of life after surgical treatment of advanced ankylosing spondylitis.

RESULTS

The initial search yielded 888 citations. Twelve of these studies met the inclusion and exclusion criteria. Two were level II evidence study, and ten were level III evidence studies. Changes were reported including aorta length, abdominal morphology, digestive function, cardiopulmonary function, psychological status, and sexual activity.

CONCLUSIONS

In addition to skeletal changes after spinal osteotomy for treatment of kyphotic deformity in advanced-stage AS patients, many other changes were reported. Spine surgeons should pay more attention to these life quality-related changes and be aware of potential risks when performing surgery for advanced-stage AS patients. These slides can be retrieved under Electronic Supplementary Material.

Great Vessel Excursion: Prone Versus Supine Position

Background

It is theorized that pedicle screws could be placed into the anterior vertebral cortex to increase biomechanical strength by 20% to 25%. Although stereotactic navigational tools allow for accurate docking of spinal implants, no data exist regarding operative positioning as it relates to great vessel alignment. Our hypothesis is that the great vessels fall anteriorly, with prone positioning providing a safer margin for implantation of screws from a posterior approach.

Methods

Volunteers underwent magnetic resonance imaging of the spine. Twenty healthy volunteers, affiliated with the academic medical center performing the study, underwent magnetic resonance imaging in both the supine and prone positions. Measurements were taken of the distance (mm) from the projected tip of a pedicle screw to the neighboring great vessels.Measurements were made at every other vertebral level from T3 to L5 by bisecting the pedicle in the transverse and sagittal planes and projecting the trajectory of a screw to the anterior cortex. We then evaluated great vessel position in relationship to the tip of the projected pedicle screw at the anterior cortex in the supine and prone orientations.

Results

The vessels were found to lie in a range of 2 to 10 mm from the anterior cortex. The comparison between the supine and prone positions showed that the great vessels in the lumbar region are held securely by the surrounding soft tissue. However, in the thoracic spine, anterior excursion does occur, just not as we expected. The aorta moves anteriorly while prone by 1.4 to 5 mm; however, its movement causes it to slide forward along the vertebra, shortening the distance to the anterior cortex. As a result, the screw trajectory is in a riskier geographic location. In the thoracolumbar area, the inferior vena cava translates 1.7 to 2.9 mm.

Conclusions

These data suggest that the risks of vascular injury from anterior cortical fixation of the vertebra using pedicle screws placed posteriorly in the prone position are apparent. In the lumbar region, the upper thoracic region around the aortic arch, and the thoracolumbar junction the great vessels remain close to the vertebra. While in the mid-thoracic region, the aorta moves closer to the area of screw penetration anteriorly when the subject is prone.

Clinical Relevance

Spine surgeons commonly attempt pedicle screw placement into the anterior cortex of the vertebral body. Our study helps elucidate the inherent risks of this technique due to vessel positioning when prone.

Position of the Aorta Relative to Vertebrae in Patients with Degenerative Thoracolumbar or Lumbar Scoliosis: A Case-Control Study

OBJECTIVE

To investigate the position of the aorta relative to the spine in patients with de novo lumbar scoliosis (DLS).

METHODS

This study enrolled 142 patients with DLS, including 80 cases of left thoracolumbar/lumbar scoliosis (left group) and 62 cases of right scoliosis (right group). In addition, 132 cases free of deformity were allocated to the control group. Parameters of the Cobb angle and apical vertebrae were measured by radiograph, whereas the left pedicle-vertebrae angle (α), rotation angle (γ), and left pedicle-vertebrae distance (d) of T12-L4 were obtained by magnetic resonance imaging. Independent sample t test was performed to compare α, γ, and d between the DLS and control groups, followed by a Pearson correlation analysis to study the correlation between Cobb angle and α, γ, and d.

RESULTS

No difference was found between the right group and control group (P = 0.554). The value of mean d (4.62 ± 0.57 cm) gradually increased from T12 to L4 in the left group and showed significant difference with the corresponding value in the control group (4.44 ± 0.43 cm; P < 0.001). There was no significant difference between the right group and control group (P = 0.762). The value of mean d (4.54 ± 1.84 cm) showed no significant difference between the right group and control group (P = 0.530). The correlation analysis showed a significant correlation between rotation angle γ and Cobb angle (P < 0.001), but not in α and d with Cobb angle.

CONCLUSIONS

Although the position of the aorta relative to the spine showed no significant difference between patients with DLS and normal subjects, great attention should still be paid to prevent DLS-induced aorta injury.

Accuracy of Freehand Pedicle Screw Placement in Surgical Correction of Thoracolumbar Kyphosis Secondary to Ankylosing Spondylitis: A Computed Tomography Investigation of 2314 Consecutive Screws

OBJECTIVE

To evaluate the accuracy and safety of freehand pedicle screw placement in surgical correction for thoracolumbar kyphosis caused by ankylosing spondylitis (AS).

METHODS

We retrospectively reviewed 266 consecutive patients with AS who underwent osteotomy for kyphosis correction with freehand screw insertion from January 1998 to April 2015 at our institution. A total of 2314 pedicle screws in 158 patients with AS with postoperative computed tomography scans were included in the study. Postoperative computed tomography was performed to classify accuracy of screws, using the established Gertbein classification (grade 0: no perforation, grade 1: perforation <2 mm, grade 2: perforation between 2 and 4 mm, and grade 3: perforation >4 mm). Patients were divided into 2 groups according to coronal Cobb angle: group A (n = 21, Cobb angle ≥10°), group B (n = 137, Cobb angle <10°).

RESULTS

Among the 2314 pedicle screws, 2168 pedicle screw placements were categorized as grade 0, 71 were grade 1, 51 were grade 2, and 24 were grade 3. Breaches occurred more frequently in L1-S1 than the thoracic spine (7.1% and 5.4%, respectively). T5 (25.0%) and S1 (17.7%) experienced the greatest breach rate, whereas T8, L1, and L3 had the lowest breach rate. The breach rate of group A was greater than that of group B (7.9% vs. 6.1%). None of the breaches resulted in either neurologic deficits or vascular complications.

CONCLUSIONS

Freehand pedicle screw placement can be performed safely with acceptable breach rate in patients with AS and thoracolumbar kyphosis.

The position of the aorta relative to the spine in patients with Pott's thoracolumbar angular kyphosis

STUDY DESIGN

Analyze the position of the aorta in patients with Pott's thoracolumbar angular kyphosis by computed tomography.

OBJECTIVE

To investigate the anatomic position of the aorta relative to spine in patients with Pott's thoracolumbar angular kyphosis.

SUMMARY OF BACKGROUND DATA

The complication of aorta injury is rare in the procedure of spinal osteotomy for the correction of Pott's thoracolumbar angular kyphotic deformity. However, there would be a disastrous consequence once it happened. Therefore, knowing about the position of aorta relative to the spine is of great importance. From the authors' knowledge, there are no reports about the research on the position of the aorta relative to the spine in patients with Pott's thoracolumbar angular kyphosis.

METHODS

Thirty patients with Pott's thoracolumbar angular kyphosis and thirty patients without spine deformity were recruited and divided into two groups. The CT images of both groups from T10 to L1 were obtained to evaluate the left pedicle-aorta angle and distance. In the patients with Pott's thoracolumbar angular kyphosis, the affected vertebral bodies were fused, so we measured the left pedicle-aorta angle and distance of the fused vertebral bodies. For the normal group, we measured the left pedicle-aorta angle and distance from T10 to L1 and got the average data, then compared with the Pott's group with independent sample t test. The Pearson correlation analysis was used to evaluate the association between the change of the aortic position and Konstam's angle and LL.

RESULTS

The left pedicle-aorta angles (-8.95 + 2.89°) in Pott's group are smaller and the distances (6.36 + 0.77 cm) are larger than those in normal group (P < 0.05). In patients with Pott's thoracolumbar angular kyphosis, with increased Konstam's angle, the left pedicle-aorta angles becomes smaller (r = -0.495, P < 0.05) and the left pedicle-aorta distances becomes larger (r = 0.486, P < 0.05). However, there is no remarkable correlation between lumbar lordosis and the left pedicle-aorta angles or distances.

CONCLUSION

In patients with Pott's thoracolumbar angular kyphosis, the aorta of the fused vertebrate shifts anteromedially to the vertebral body, and the aorta is relatively farther away from the vertebral body compared with the normal subjects. Therefore, the surgeon should be aware of the change of the position of the aorta to avoid the disastrous complication vessel injury.

Does the Position of the Aorta Change With the Altered Body Position in Ankylosing Spondylitis Patients With Thoracolumbar Kyphosis?: A Magnetic Resonance Imaging Investigation

STUDY DESIGN

A prospective magnetic resonance imaging study.

OBJECTIVE

To quantitatively explore the differences in the anatomic position of the aorta relative to the spine between supine and prone positions in ankylosing spondylitis (AS) patients with thoracolumbar kyphosis.

SUMMARY OF BACKGROUND DATA

Aortic complications may occur during the lumbar spine osteotomy in correcting thoracolumbar kyphosis secondary to AS, and a clear understanding of the spatial relationship between the aorta and the vertebrae is essential to prevent these iatrogenic complications. However, previous anatomic study was performed with AS patients in the supine position, which was different from the prone position adopted in surgery. To date, no report has been published to investigate the mobility of the aorta relative to the vertebrae between supine and prone positions in AS patients with thoracolumbar kyphosis.

MATERIALS AND METHODS

From March 2013 to September 2014, 22 AS patients (21 males, 1 female) with thoracolumbar kyphosis with a mean age of 30.7 years (range, 19-46 y) were recruited. Magnetic resonance imaging examinations from T9 to L3 in both the supine and prone positions were performed, and the left pedicle-aorta (LtP-Ao) angle and LtP-Ao distance were measured at each level. The differences of these parameters between the 2 positions were compared by the paired sample t test, and the relationships between the shifting of the aorta and the change of global kyphosis and lumbar lordosis were evaluated by the Pearson correlation coefficient. The level of significance (α) was set at 0.05.

RESULTS

At T9-L3 levels, no significant difference was noted in LtP-Ao distances (43.78 vs. 44.42 mm; P=0.077) and LtP-Ao angles (0.82 vs. 0.22 degrees; P=0.053) between supine and prone positions. The correlation analysis also revealed no remarkable correlation between the change of LtP-Ao angle and increase of global kyphosis and lumbar lordosis in the prone position.

CONCLUSIONS

There is no significant change of the relative positions between the aorta and the vertebrae at T9-L3 levels after the patient turned to a prone position, which implied that the mobility and range of motion of the aorta is limited in advanced stage of AS.

Does the position of conus medullaris change with increased thoracolumbar kyphosis in ankylosing spondylitis patients?

To date, only a few reports described the potential factors influencing the position of conus medullaris. One previous study revealed no significant change of conus locations in patients with idiopathic scoliosis; however, the effect of ankylosing spondylitis (AS)-related thoracolumbar kyphosis on conus position remains unexplored. Therefore, we aimed to investigate the variation of conus medullaris terminations in patients with thoracolumbar kyphosis secondary to AS when compared with normal subjects, and evaluated the relationship between conus positions and the magnitude of kyphosis. In this study, MR images of 96 AS patients with thoracolumbar kyphosis, including 86 males and 10 females with an average of 34.6 years (range, 17-65 years), and 100 age-matched normal controls were reviewed to determine the conus terminations in relation to spinal levels. Sagittal parameters of the AS group measured on radiograph included: global kyphosis (GK), thoracic kyphosis (TK), lumbar lordosis (LL), and thoracolumbar junction (TLJ). Finally, conus tips located at the mean level of the lower 3rd of L1 in both groups, there was no significant difference of the conus distributions between AS and control group (P = 0.49). In addition, conus medullaris displayed similar positions in AS patients among various apical region groups (P = 0.88), and no significant difference was found when AS population was stratified into GK ranges of 30° (P = 0.173). Also, no remarkable correlation of the conus positions with GK (r = -0.15, P = 0.15), TK (r = -0.10, P = 0.34), LL (r = -0.10, P = 0.32), and TLJ (r = -0.06, P = 0.54) was identified. This study showed the conus terminations displayed a wide range of distributions in AS patients with thoracolumbar kyphosis, which was similar to normal subjects. Moreover, the conus located at a relatively fixed position and would not be affected by the change of kyphosis magnitude, which is an important knowledge that surgeons should acquire in surgical correction of the deformity in these patients.

Does the Traversing Length of the Aorta Change After Closing Wedge Osteotomy for Ankylosing Spondylitis Patients With Thoracolumbar Kyphosis?: A Magnetic Resonance Imaging Investigation

STUDY DESIGN

A prospective magnetic resonance imaging (MRI) study.

OBJECTIVE

To investigate the change in aortic traversing length in patients with thoracolumbar kyphosis secondary to ankylosing spondylitis (AS) after closing wedge osteotomy (CWO).

SUMMARY OF BACKGROUND DATA

The CWO has been widely adopted for the correction of thoracolumbar kyphosis caused by AS. During this procedure, the aorta may be elongated in the instrumented area, which implies a potential risk of the aortic injury. To date, no reports have been specifically published using MRI to investigate the alteration in aortic traversing length in patients with AS undergoing CWO.

METHODS

From June 2013 to July 2015, 24 patients with AS with thoracolumbar kyphosis with a mean age of 38.1 years were recruited in the present study. All patients underwent single-level CWO. MRI examinations were performed before and 2 weeks after surgery. For each subject, the aortic diameter and length were measured on the MRI. Radiographic measurements included the global kyphosis, thoracic kyphosis, lumbar lordosis, local kyhosis, angle of fusion levels, and anterior height of the osteotomized vertebra. The height of these patients was also recorded.

RESULTS

The aortic traversing length significantly increased by an average of 2.0 cm after surgery. Significant changes in height, global kyphosis, lumbar lordosis, local kyphosis, and angle of fusion levels were observed (P < 0.01), whereas the anterior height of the osteotomized vertebra was comparable before and after surgery (P > 0.05). In addition, the correlation analysis revealed a significant correlation between the aortic traversing length and changes in global kyphosis, lumbar lordosis, local kyphosis, angle of fusion levels, and height (P < 0.01).

CONCLUSION

The stretch of the aorta after CWO for the correction of thoracolumbar kyphosis was quantitatively verified by MRI investigation in the present study. Spine surgeons should be aware of the potential vulnerability of aortic injury in patients with AS undergoing CWO.

LEVEL OF EVIDENCE

4.