Lumbar Lordosis Curve and Psoas Major Muscle Angle in Magnetic Resonance Imaging Analysis

doi:10.21203/rs.3.rs-2357512/v1

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Lumbar Lordosis Curve and Psoas Major Muscle Angle in Magnetic Resonance Imaging Analysis

https://doi.org/10.21203/rs.3.rs-2357512/v1

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Background

Using axial MRI image, the psoas major muscle is known to work as an anatomical femoral head stabilizer and increases lumbar lordosis keeping the iliopsoas muscle in place at the lumbosacral region. The purpose of this study is to investigate psoas major muscle correlation with lumbar lordosis by analyzing the psoas major angle, which represents the psoas major muscle’s effect on pelvic alignment using sagittal MRI imaging.

Methods

A total of 1064 patients were included in this study. On lateral standing radiography, three pelvic parameters (sacral slope, pelvic tilt, pelvic incidence) can be measured. In the sagittal MRI imaging, the point where the psoas major muscle direction changes (the top of superior pubic ramus) was marked and the angle between the line connecting the two points and the proximal part of the psoas major muscle (Psoas major angle: PMA) was measured.

Results

The average age was 63.88 ± 13.52 (20–89) years old in total; 62.52 ± 15.24 in 426 male patients and 66.12 ± 11.72 in 638 female patients. The average age was older in female patients (p < 0.05). Using the structural equation, the correlation coefficient between PMA and SS was 0.237 (p < 0.001), between PMA and PT was 0.339 (p < 0.001), and between PMA and PI was 0.749 (p < 0.001). PMA has a statistically significant correlation in relation to PI, PT, and SS (p < 0.001).

Conclusion

PMA has a higher correlation with PT, which is related to pelvic compensation, than SS which is closely related to lumbar lordosis. It means that the psoas major muscle’s role of influencing spinopelvic alignment in the supine position is to maintain spinopelvic alignment by adjusting the pelvic tilt rather than by lumbar lordosis using the upper and lower muscle attachments.

Psoas major muscle

lumbar lordosis

iliopsoas muscle

MRI

The psoas major muscle originates from the vertebral bodies, transverse processes, and T12–L5 intervertebral discs. As the muscle courses distally, it rotates to the anterior oblique at the superior pubic ramus, lying anterior to the hip joint and femoral head, and inserts posterior to the femoral lesser trochanter. The psoas major muscle and iliacus muscle combine to form the iliopsoas muscle. It functions as a hip flexor, femoral adductor, and external rotator. The bilateral iliopsoas muscle contraction acts to lift the body from the supine position. When the iliopsoas and hip flexor muscles act together, the thigh is lifted toward the body, then with the legs in a fixed position, the body is lifted up toward the leg.

The psoas muscle, through the iliac fascia, connects the upper and lower body, outer and inner body, axial and appendicular skeletons, and anterior and posterior body. Therefore, it functions to maintain a biomechanically stable posture in both the moving and static states.

In the erect position, the iliopsoas muscle acts on the pelvis and lumbar spine and fixates it on the femur. When erect, the iliopsoas muscle assists in flexion, lateral bending, and contralateral rotation of the spine. [1] During ambulation, the ipsilateral psoas major muscle activates at the onset of hip flexion and the latter part of the swing phase. [2]

The iliopsoas muscle works as a femoral head stabilizer in the acetabulum at 0°–15° hip flexion, maintaining its erector action until 15°–45°, and as an effective femoral flexor at 45°–60°. [3] However, the psoas major muscle does not function as a hip flexor at 0°–45°5of flexion and its actual function in this posture is not understood. Lower fascicles tend to extend the upper lumbar spine by flexing the lower lumbar spine and upper fascicles. Also, some authors argue that the psoas muscle exerts compression force and large shear forces on the lumbar segments, while exerting small moment forces that tend to flex and extend the lumbar spine, which gives the spine its lordotic configuration. [4, 5]

Using axial MRI image, the psoas major muscle is known to work as an anatomical femoral head stabilizer and increases lumbar lordosis keeping the iliopsoas muscle in place at the lumbosacral region.

The authors hypothesized that this action would be related to the psoas major muscle’s role as a pulley, considering the psoas major muscle’s direction changes in the suprapubic area. This study was initiated to investigate it correlation with lumbar lordosis by analyzing the psoas major angle, which represents the psoas major muscle’s effect on pelvic alignment using sagittal MRI imaging.

Study design and patient population

The Institutional Review Board (approval No. CR-22-061) approved this study and informed consent was waived as the study only used image data analysis. Patients who had MRI images (sagittal, axial, and coronal views) with whole spine standing AP view were included until December 31, 2021. Patients who had spine surgery (decompression, spine fusion, vertebroplasty etc.), spinal deformity (scoliosis or kyphosis), and extreme age (< 20 years or > 90 years) who had insufficient medical information were excluded. A total of 1064 patients were included in this study.

Radiological Parameter Measurements

Standing lateral radiographs were obtained with patients looking straight ahead, elbows bent, and knuckles in the supraclavicular fossa bilaterally (Fits-on-clavicle position), with their knees and hips extended, using a 36-inch long cassette. [6]

On lateral standing radiography, three pelvic parameters can be measured. The sacral slope is the angle between the horizontal line and the cranial sacral endplate tangent. The pelvic tilt is the angle between the vertical line and the line joining the middle of the sacral plate and the center of the bicoxofemoral axis. The pelvic incidence is the angle between the line perpendicular to the middle of the cranial sacral endplate to the center of the bicoxofemoral axis.

After marking the lesser femoral trochanter, which is the psoas major muscle insertion site, in the sagittal MRI imaging, the point where the psoas major muscle direction changes (the top of superior pubic ramus) was marked and the angle between the line connecting the two points and the proximal part of the psoas major muscle (Psoas major angle: PMA) was measured. (Fig. 2)

Statistical Analysis

Pearson's correlation analysis using IBM SPSS version 19 was used to analyze the 1:1 correlation between age, PMA, SS, and PT. Since this study has a large sample size, a structural equation can be used to know the relationship in which several factors, including one or more dependent variables, affect each other or the indirect relationship through latent variables. In particular, a structural equation was used using AMOS (ver 2.0) program to determine the relationship between PMA and SS and between PMA and PT. The p value of 0.05 was considered to be statistically significant.

Epidemiological Characteristics

The average age was 63.88 ± 13.52 (20–89) years old in total; 62.52 ± 15.24 in 426 male patients and 66.12 ± 11.72 in 638 female patients. The average age was older in female patients. (p < 0.05)

The average SS was 25.97 ± 5.22°; 26.41 ± 5.22° in males and 25.68 ± 5.21 males in females. It was statistically significantly higher in male patients (p = 0.02). The average PT was 25.26 ± 10.65; 23.36 ± 10.47° in males and 26.52 ± 10.59 in females. It was statistically significantly different in female patients (p < 0.05). The average PI was 51.23 ± 9.76; 49.77 ± 9.58 in males and 52.20 ± 9.77 in females. It was statistically significantly higher in female patients (p < 0.05). The average PMA was 112.95 ± 8.45 degrees; 111.45 ± 8.75° in males and 113.95 ± 8.11 in females. It was significantly higher in female patients (p < 0.05). PI, PT, and PMA were higher in females. SS was higher in male patients, which was statistically significant.

Relationship Between Radiological Parameters

Correlating with age, r² of SS was − 0.008 (p = 0.805), r² of PT was − 0.067 (p = 0.029), r² of PI was 0.069 (p = 0.025), r² of PMA was 0.031 (p = 0.313). The statistically significant imaging factors that correlate with age were PT and PI, but both had very weak correlation. Correlating with PMA, r² of SS was 0.14 (p < 0.05), r² of PT was 0.754 (p < 0.05), r² of PI was 0.898 (p < 0.05). PMA shows a statistically significant strong positive correlation with PI and PT, and a weak positive correlation with SS.

Using the structural equation, the correlation coefficient between PMA and SS was 0.237 (p < 0.001), between PMA and PT was 0.339 (p < 0.001), and between PMA and PI was 0.749 (p < 0.001). PMA has a statistically significant correlation in relation to PI, PT, and SS (p < 0.001) (Fig. 3).

Pelvic movement is not very noticeable and many muscles attached to the pelvis do not have enough moments to solely perform specific hip movements, thus not much researches have been done on all pelvic movements. Walking on two legs is possible by the morphological adaptation of the lower limbs, pelvis, and spine, and the pelvis not only transmits the weight of the trunk to the lower limbs, but also acts as a rotational axis that accepts the repulsive force transmitted to the femur.

In order to walk upright without problems, it has been emphasized that the sagittal balance of the spine, as well as the relationship between the spine and the pelvis is important. Since a close relationship between spinal and pelvic parameters was observed, the pelvic parameters are important, but the spinal parameters must also be considered [7]. PI, one of the pelvic parameters, mainly shows 55 ± 10°, but has values that varies from 30–80° [8, 9]. PI has a strong correlation with lumbar lordosis[8], although not predictive of clinical outcomes. In order to use energy efficiently, the gravity line (the vertical passing through the midpoint of the L5 inferior endplate) and a line representing the ground reaction force (the vertical passing through the center of the femoral head) should be closer. To do this, pelvic retroversion is reduced as the pelvic tilt is decreased. Therefore, sacral slope is closely related to lumbar lordosis, and when the sacral slope is increased, the lumbar lordosis increases.

The psoas major anatomically flexes the lumbar spine and also plays a role in lateral bending. It is a powerful femoral flexor and since it is attached to the lesser trochanter of the femur, it also has a role in femoral external rotation. In addition, it also has a role in lumbar and pelvic flexion when the femur is fixed, such as in a standing position.

There are various opinions about the psoas major muscle’s role in the spine. The fact that the psoas major muscle has a role in stabilizing the lumbar spine has been previously suggested. Panjabi et al. found that the psoas major muscle has a role in the lumbar spine’s lateral stabilization in a study using an anatomical approach in 1990. Janavic et al. showed that when the lumbar motion segment is loaded under large compressive loads, it becomes much more stable, increasing lumbar spine stiffness [11]. Likewise, it is widely known that the psoas major muscle passes in front of the lower lumbar spine and posteriorly through the back of the joint in the upper lumbar spine. It functions as lower lumbar spine extensor and an upper lumbar spine flexor [12, 13]. In addition, the psoas major muscle is triangular rather than fusiform and the muscle fibers are not parallel in shape, thus, the pulling direction is different. It is argued that the upper part of the psoas major muscle, which is superficial and long and generates a strong moment arm, changes to a form that covers the lower fiber deeply and shortly while ambulating [12, 13]. Gibbon et al. argued that the anterior attachment is to the anteromedial aspect of the vertebral bodies and lumbar discs, which has a role in flexion and the posterior attachment is on the anteromedial aspect of all the lumbar transverse processes, which has a role in extension. It is reported that the anterior and posterior fasciculi innervation is separate [14].

The psoas major works differently depending on the slight difference in angle, change in posture, and the degree of lower extremity flexion. The psoas major’s appropriate role is lumbar spine stabilization in the sitting position and hip flexion in the supine or erect position [1]. Hadjipavlou et al. argued that the psoas major principally supports the trunk on the pelvis [15]. The psoas major is uniquely positioned to prevent spinal buckling and to control lordosis. Because of its attachment to the lesser femoral trochanter, it controls pelvic tilt. As the PM gives small anterior shear at the lower lumbar motion segments, it cannot be used to balance gravitational forces. In the supine position, with the hip at 0–45° of flexion, PMA reflecting the psoas major’s moment arm has the highest PI correlation, thus PMA in the supine position has a great correlation with lumbar lordosis [8]. It can be inferred that when PMA is increased by the psoas major in the supine position, the lumbar lordosis and sacral slope increases.

There were several limitations in this study. First, a study about spinopelvic alignment requires images taken in the standing position. The simple radiographs were taken in the standing position, but the MRI images were taken in the supine position. Therefore, it is thought that there will be some contradiction when comparing the two images. The authors tried to supplement this by analyzing numerous images of 1,064 patients. Second, the PMA’s role on spinopelvic alignment was only the result of the author’s inference through image analysis, and it was not supported by accurate cadaveric studies. If additional cadaveric or biomechanical studies are supported, better results are likely to emerge.

It was hypothesized that the triangular-shaped psoas major muscle played an important role during quadrupedal walking in hip flexion function, as well as spinopelvic alignment by acting as a lever while forming an angle in the pubic superior ramus while bipedal walking. In spinopelvic alignment, PMA has a close correlation with PI. PMA has a higher correlation with PT, which is related to pelvic compensation, than SS which is closely related to lumbar lordosis. It means that the psoas major muscle’s role of influencing spinopelvic alignment in the supine position is to maintain spinopelvic alignment by adjusting the pelvic tilt rather than by lumbar lordosis using the upper and lower muscle attachments.

The Institutional Review Board (approval No. CR-22-061) approved this study and informed consent was waived as the study only used image data analysis. All methods were carried out in accordance with relevant guidelines and regulations. All experimental protocols were approved by a CR-22-061 institutional review board.

Consent for publication: Not applicable

Availability of data and materials: The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Competing interests: The authors declare that they have no competing interests.

Funding: This work was supported by a grant from the Research Institute of Medical Science, Catholic University of Daegu (2022).

Authors' contributions: Sangbong Ko(SBK) decided and conceptualized this article, wrote manuscripts, and revised the draft. Heechan Kim(HCK) collected and analyzed the data. SBK prepared the figures and tables and was the guarantors of the overall content. All authors approved the final version of the manuscript and agreed to be accountable for all specs of the work.

Acknowledgements: Sehun Choi (Medical student, Daegu Catholic University Medical School),

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No competing interests reported.

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Version 1

posted

You are reading this latest preprint version

Lumbar Lordosis Curve and Psoas Major Muscle Angle in Magnetic Resonance Imaging Analysis

Status:

Version 1

Abstract

Background

Methods

Results

Conclusion

Figures

Background

Methods

Study design and patient population

Radiological Parameter Measurements

Statistical Analysis

Results

Epidemiological Characteristics

Relationship Between Radiological Parameters

Discussions

Conclusion

Declarations

References

Additional Declarations

Status:

Version 1