RESEARCH ARTICLE |
https://doi.org/10.5005/jp-journals-11003-0147 |
Morphological and Morphometric Study of Psoas Minor Muscle and Its Clinical Importance: A Cadaveric Study
1,4–7Department of Anatomy, Armed Forces Medical College, Pune, Maharashtra, India
2Department of Anatomy, Shija Academy of Health Sciences, Imphal, Manipur, India
3Department of Anatomy, All India Institute of Medical Sciences, Kalyani, West Bengal, India
Corresponding Author: Subhash Bhukya, Department of Anatomy, All India Institute of Medical Sciences, Kalyani, West Bengal, India, Phone: +91 9703189506, e-mail: subhashbhukya@gmail.com
Received: 09 August 2024; Accepted: 27 September 2024; Published on: 31 December 2024
ABSTRACT
Psoas minor, which is present anterior to the psoas major in a variable proportion of the population. The study aimed to examine the psoas minor, a vestigial muscle in the posterior abdominal wall, in terms of its presence, morphology, variations, and measurements within a western Maharashtra population using 41 formalin-fixed cadavers. Results showed that the psoas minor was present in 48.78% of the cadavers, with equal occurrence between male and female subjects. No variations in the muscle’s proximal and distal attachments were identified, except for a unique “double-headed” psoas minor found in one specimen. The mean length and maximum width of the muscle belly were 7.29 ± 0.129 cm and 1.45 ± 0.60 cm, respectively, on the right side, and 7.08 ± 0.147 cm and 1.33 ± 0.148 cm on the left side. For the tendon, the mean length and maximum width were 16.87 ± 0.302 cm and 0.92 ± 0.08 cm on the right, and 17.10 ± 0.35 cm and 0.80 ± 0.087 cm on the left. The findings suggest that the presence or absence of the psoas minor is important for various medical professionals, including anatomists, clinicians, radiologists, sports medicine specialists, and physiotherapists. The prevalence of this muscle varies by race, but not by gender. Additionally, no connection was found between the absence of the psoas minor and the absence of other vestigial muscles. This study provides valuable insights into the characteristics of the psoas minor in a specific population.
Keywords: Cadaver, Psoas minor, Vestigial muscle
How to cite this article: Acharya AP, Angom MD, Bhukya S, et al. Morphological and Morphometric Study of Psoas Minor Muscle and Its Clinical Importance: A Cadaveric Study. J Med Acad 2024;7(2):47–50.
Source of support: Nil
Conflict of interest: None
INTRODUCTION
The posterior abdominal wall is a complex anatomical structure composed of several muscles that contribute to its formation, including the psoas major, quadratus lumborum, and iliacus muscles. Notably, there exists an inconstant muscle, the psoas minor, which is present anterior to the psoas major in a variable proportion of the population. The psoas minor, when present, is characterized by a small fusiform muscle belly and a long, flat tendon, originating from the lateral aspects of the T12 and L1 vertebrae and the intervertebral disc between them. It inserts onto the iliopubic eminence, pecten pubis, and fascia iliaca, with its blood supply predominantly from the lumbar arteries and innervation from the ventral ramus of the L1 spinal nerve.1
Functionally, the psoas minor acts as a weak flexor of the lumbar spine during bilateral contraction, and as a lateral spine bender during unilateral contraction. It also has a role in stabilizing the hip joint and tensing the fascia iliaca, although it cannot be tested clinically.2 Evolutionarily, the psoas minor is more developed in quadrupeds, particularly those that engage in fast running, leaping, or brachiating, while it has regressed in bipedal humans, with variations in its presence attributed to ethnicity and racial traits.3
Clinically, psoas minor is of significance due to its association with psoas minor syndrome, which can manifest as pain in the lower abdominal quadrants, mimicking various abdominal emergencies.2 This study aims to estimate the prevalence of the psoas minor muscle in the western Maharashtra population and to investigate its morphological and morphometric characteristics, as well as to elucidate its clinical significance.
Given the background and the potential clinical implications of the psoas minor muscle, this research seeks to provide a comprehensive analysis of its occurrence and anatomical details within the western Maharashtra population. By doing so, we aim to contribute to the broader understanding of the muscle’s variations, which can enhance the clinical diagnosis and treatment of conditions associated with the psoas minor, such as the psoas minor syndrome. Furthermore, exploring the evolutionary perspective might shed light on the functional adaptations of the human musculoskeletal system. This study’s findings could be valuable for clinicians, anatomists, and researchers interested in the morphological diversity of the human body and its clinical impacts. Hence, the aim of the study was to describe the occurrence of psoas minor muscle and to study its morphology and morphometry in western Maharashtra population.
METHODOLOGY
The study was conducted in accordance with ethical standards and guidelines for research involving human cadavers. The use of cadavers for this study was approved by the Institutional Ethics Committee of the Armed Forces Medical College, Pune, India.
Study Design and Setting
This was a descriptive cross-sectional study conducted at the Department of Anatomy, Armed Forces Medical College, Pune, India. The study used 41 embalmed adult cadavers donated for educational and research purposes. Consent for the use of these bodies was obtained from the body donors or their next of kin prior to their inclusion in the study.
Inclusion Criteria
Aged between 65–98 years. Comprising both genders, with 19 males and 22 females.
Exclusion Criteria
Cadavers with visible scars, marks of injury, and a history of surgery on the anterior abdominal wall or back of the trunk were excluded from the study.
Procedures
The cadavers were dissected by medical students as a part of their routine anatomy education. For the purpose of this study, the posterior abdominal wall was carefully exposed following the removal of abdominal viscera and peritoneum. Detailed examination was conducted to identify the presence or absence of the psoas minor muscle.
Data Collection
In cases where the psoas minor was present, the following parameters were meticulously recorded:
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Attachments of the muscle.
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Morphology of the muscle, including any variations.
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Length of the muscle belly.
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Maximum width of the muscle belly.
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Length of the tendon.
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Maximum width of the tendon.
All measurements were taken with a measuring tape and recorded in centimeters (Fig. 1). The length of the muscle belly was determined from its proximal attachment to the distal point of attachment to the tendon. The tendon length was measured from the proximal attachment on the muscle belly to the point of insertion on the iliopectineal eminence.
Fig. 1 Measurements of belly of psoas minor muscle and its tendon
Statistical Analysis
Data were summarized as ranges and mean values. An unpaired t-test was utilized to compare means between two independent groups when the variance was equal, while an F-test was used to compare variances within the groups. Statistical significance was set at a p-value <0.05.
RESULTS
In our study, psoas minor was present in 20 cadavers out of 41, the occurrence being 48.78%. Out of these 20 cadavers with psoas minor, 10 were males and 10 were females. Psoas minor was present bilaterally in all of these 20 cadavers (Fig. 2).
Fig. 2 Presence of psoas minor bilaterally
Proximally, psoas minor was attached to twelfth thoracic vertebra, first lumbar vertebra, and the intervening intervertebral disc in all 20 cadavers. Distally, psoas minor tendon fanned out near the iliopectineal eminence and was attached to the iliopubic eminence and pecten pubis after merging with fascia iliaca laterally and obturator fascia medially in all 20 cadavers (Fig. 3). Therefore, we did not observe any variation in the proximal as well as distal attachment of psoas minor muscle.
Fig. 3 Attachment of psoas minor tendon
A two-headed psoas minor consisting of a lateral head and a medial head was noted in one male cadaver on the right side (Figs 4 and 5). This variation in the morphology of the muscle has been described to be the rarest of all known morphological variations.2 The genitofemoral nerve was seen to be exiting between the two heads. The tendons of both the heads were also split proximally which joined to form one thick tendon distally. The left psoas minor was normal in morphology with a slender tendon. No other variation in morphology was observed in the remaining 19 cadavers.
Fig. 4 Double headed psoas minor with genitofemoral nerve exiting between the two heads
Fig. 5 IPMTPB dividing the pelvic brim into three zones13
On the right side, the mean length of the muscle belly was 7.29 ± 0.129 cm, range being 5.8–8.3 cm and the mean of maximum width of the muscle belly was 1.45 ± 0.6 cm, range being 0.8–3.5 cm. On the left side, the mean length of the muscle belly was 7.08 ± 0.147 cm, range being 5.6–8.1 cm and the mean of maximum width of the muscle belly was 1.33 ± 0.148 cm, range being 0.7–3.8 cm.
On the right side, the mean length of the tendon was 16.87 ± 0.302 cm, range being 15.3–20.0 cm and the mean maximum width of the tendon was 0.92 ± 0.08 cm, range being 0.6–2.0 cm. On the left side, the mean length of the tendon was 17.10 ± 0.35 cm, range being 15.3–20.6 cm and the mean maximum width of the tendon was 0.80 ± 0.087 cm, range being 0.5–2.2 cm. The above morphometric measurements have been tabulated in Tables 1 and 2.
| Sl no. | Psoas minor | Male | Female | Total |
|---|---|---|---|---|
| 1 | Present bilaterally | 10 (24.39%) | 10 (24.39%) | 20 (48.78%) |
| 2 | Present unilaterally | Nil | Nil | Nil |
| 3 | Absent | 9 (21.95%) | 12 (29.26%) | 21 (51.21%) |
| Sl no. | Variables | Right side (cm) | Left side (cm) |
|---|---|---|---|
| 1 | Mean muscle belly length | 7.29 ± 0.129 | 7.08 ± 0.147 |
| 2 | Mean of maximum muscle belly width | 1.45 ± 0.6 | 1.33 ± 0.148 |
| 3 | Mean tendon length | 16.87 ± 0.302 | 17.10 ± 0.35 |
| 4 | Mean of maximum tendon width | 0.92 ± 0.08 | 0.80 ± 0.087 |
The above data was analyzed using unpaired t-test and F-test which showed no statistically significant difference between the morphometric measurements of the psoas major muscle belly and tendon of the right and left sides. The analysis has been presented in Table 3.
| Sl no. | Data analyzed | Unpaired t-test | F-test | Significantly different (p < 0.05) |
|---|---|---|---|---|
| 1 | Right muscle belly length vs left muscle belly length |
p-value = 0.2916 | p-value = 0.5765 | No |
| 2 | Right maximum muscle belly width vs left maximum muscle belly width | p-value = 0.6906 | p-value = 0.6226 | No |
| 3 | Right tendon length vs left tendon length | p-value = 0.6228 | p-value = 0.5114 | No |
| 4 | Right maximum tendon width vs left maximum tendon width | p-value = 0.3212 | p-value = 0.9548 | No |
DISCUSSION
The psoas minor muscle exhibits significant variability in its prevalence and morphology, as evidenced by the disparities reported in various studies. Our findings indicate a prevalence of 48.78% in the studied population, which is consistent with the range of prevalences observed in different racial and geographic groups. Historical data from Seib suggested racial differences, with a 50% prevalence in orientals, 43% in whites, and 33% in blacks.4 These findings are supported by more recent studies such as those by Joshi et al. with a 30% prevalence,5 Farias et al. reporting 26.66% in Brazil,6 and Guerra et al.7 with 59.09% in human fetuses.
The morphological variations in the origin and insertion of the psoas minor muscle are also notable. While some researchers have reported the muscle originating from the first and second lumbar vertebrae,8,9 our study observed origins from the twelfth thoracic and first lumbar vertebrae. As for the insertion, we found that the psoas minor tendon tends to fan out near the iliopectineal eminence and merges with the fascia iliaca and obturator fascia, which has not been commonly noted in the literature.
A genetic or embryological basis for the agenesis of psoas minor may be hypothesized, particularly when considering the inconsistent presence of other vestigial muscles such as palmaris longus and peroneus tertius. Developmentally, these muscles originate from the dermomyotome, part of the somite, and differentiate into skeletal muscles by the 8th week of embryonic development.10 This development is likely influenced by local signaling factors, suggesting that the agenesis of vestigial muscles may be due to disruptions in these localized cues rather than a synchronized muscle development process.11
Clinically, the presence and variations of the psoas minor muscle can have implications for diagnosis and treatment in various medical fields. Psoas minor strain may lead to symptoms that mimic other abdominal conditions such as appendicitis or diverticulitis. Meanwhile, Neumann and Garceau proposed a novel function for the psoas minor, suggesting it enhances the biomechanical stability of the iliopsoas, warranting further anatomical-biomechanical studies to test this hypothesis.12 Zhang et al. in their study explored the relationship between the insertion of psoas minor tendon on the pelvic brim (IPMTPB) and placement of screws to fix acetabular fracture through Stoppa approach.13 They concluded that insertion of tendon of psoas minor on pelvic brim can be considered as an anatomic landmark for extra-articular screw placement in Stoppa surgery. The posterior and anterior edges of the tendon divide the area from the sacroiliac joint to the pubic symphysis into three zones (d1, d2, and d3). Screws that are inserted cranially in zone d1 and vertical to the bone surface or more caudally in zone d3 will not penetrate the hip joint. For cases with absent psoas minor, the measurements obtained from this study may help to locate the safe zones. Therefore, the insertion of the psoas minor tendon on the pelvic brim, as a landmark, provides an alternative method for insertion of screws outside the hip joint.
CONCLUSION
The psoas minor is a vestigial muscle with variable prevalence across races, but no gender disparity has been observed. Its presence is clinically relevant, as psoas minor syndrome can mimic acute abdominal conditions. Awareness of this muscle is important for anatomists, clinicians, radiologists, and physiotherapists. Despite studies, no link has been found between the absence of the psoas minor and other inconstant muscles, suggesting unique developmental pathways. Accurate knowledge of its presence or agenesis is crucial for diagnosis and treatment in related medical fields, emphasizing the importance of individual anatomical variation in clinical practice.
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