Unilateral Agenesis of Iliopsoas Muscle

Abstract

Agenesis of the psoas minor muscle is very common as it can be absent in approximately 56% of the population. Moreover, previous three case reports described hypoplasia of the psoas muscle. However, our case had complete agenesis of the three iliopsoas muscle components on the right side. A 26-year-old woman presented with right-side weak hip flexion that had persisted for 2 years. Magnetic resonance imaging revealed complete agenesis of the right iliopsoas muscle, and no spine pathology was detected. Radiologists should put agenesis of the iliopsoas muscle into consideration in patients presented with weak hip flexion especially when no spine pathology is detected. Follow-up is advised to study the long-term effects of iliopsoas muscle agenesis. To the best of our knowledge, we believe that this is the first report in the general literature.

Keywords

agenesis - iliopsoas muscle - MRI - the iliacus muscle - the major psoas - the minor psoas

Introduction

The iliopsoas muscle is composed of three muscles: (1) major psoas, (2) minor psoas, and (3) iliacus muscle. The origin of the iliopsoas muscle is the transverse processes of vertebrae L2–L4 (or L1–L3) and it inserts into the lesser trochanteric tubercle. The short collateral branches of the lumbar plexus (L1–L3) innervate the psoas major and minor muscles, whereas the iliacus muscle is innervated by the femoral nerve or terminal nerve of the lumbar plexus (L1–L4). Its prime function is flexion and external rotation of the hip joint.[1] [2]

Agenesis of the psoas minor is very common; according to reports, it has a 56% chance of being congenitally absent. Moreover, there have been few reports about unilateral hypoplasia of the psoas muscle.[3] [4]

However, no reports were to be found describing a complete agenesis of the iliopsoas muscle. To the best of our knowledge, we believe that this is the first report in the general literature.

The purpose of this case report is to discuss the case of a 26-year-old woman who presented with right-side weak hip flexion caused by unilateral complete agenesis of the iliopsoas muscle.

Case Presentation

A 26-year-old woman presented to the outpatient clinic complaining of difficulty in elevating her right leg during walking for 2 years. Her past medical history was unremarkable. Her physical examination revealed left hip flexion weakness. Neurological examination was normal. Laboratory data were within normal range. Since peripheral neuropathy was suspected, a nerve conduction study was performed; however, it was normal.

Next the patient underwent a whole spine magnetic resonance imaging (MRI) scan to identify any possible spine pathology that could explain her compliant, which showed a normal lumbosacral vertebral body height and alignment. There was no central canal or foraminal compromise, and no disk bulge or herniation was noted ([Fig. 1]).

Fig. 1 Spinal sagittal T2-weighted magnetic resonance imaging. (A) Sagittal whole spine. (B) Sagittal lumbosacral spine. There was normal lumbosacral vertebral body height and alignment, and there was no central canal or foraminal compromise, no disk bulge, or herniation.

However, a complete agenesis of the right iliopsoas muscle was incidentally detected ([Fig. 2]).

Fig. 2 Lumbar level coronal T2-weighted magnetic resonance imaging. Left psoas and iliacus muscles are present (white arrows). Complete absence of psoas and iliacus muscle on the right side (complete agenesis).

Along with agenesis of the right iliopsoas muscle, there was disuse atrophy and fat infiltration of the ipsilateral paraspinal ([Fig. 3]).

Fig. 3 Lumbar level axial T2-weighted magnetic resonance imaging. Atrophy and fat infiltration of the right paraspinal muscles. The white arrow indicates the iliacus muscle. ES, erector spinae; MF, multifidus; PM, psoas major.

No other disease that could have caused this anomaly in our patient was present; no history of trauma or muscle abscess was observed.

Discussion

The iliopsoas muscle consists of three muscles, the psoas major and minor, and the iliacus muscle arising from the transverse processes of the L2–L4 (or L1–L3) vertebrae and it inserts directly into the lesser trochanteric tubercle processes. The short collateral branches of the lumbar plexus (L1–L3) innervate the psoas major and minor muscles, whereas the iliacus muscle is innervated by the femoral nerve or terminal nerve of the lumbar plexus (L1–L4). The primary function of the iliopsoas muscle is to flex and externally rotate the hip joint, playing a crucial role in maintaining the strength and integrity of the hip joint. It is necessary for proper standing or sitting lumbar posture as well as for proper walking and running.[2]

The psoas minor is a muscle arising from the vertebral bodies of T12 and L1. Agenesis of this muscle is very common as it can be absent in approximately 56% of the population.[3] Moreover, three case reports described unilateral hypoplasia of the psoas muscle, and the clinical picture ranged from patients being asymptomatic to those suffering from low back pain. Degenerative changes of the spine with scoliotic posture and hyperextension of the left hip joint were also described, and the case reports concluded that these changes were attributed to unilateral muscle hypoplasia considering the function of the muscle in stabilizing the spine and in flexing the hip joint.[4] However, our case had complete agenesis of the three iliopsoas muscle components on the right side. There was no apparent pathological etiology explaining this finding. Our patient had complaints of weakness in the elevation of the right lower limb while walking. Examination revealed weak flexion of the right hip. MRI revealed complete agenesis of the right iliopsoas muscle; there were no degenerative changes in the spine. However, a thorough musculoskeletal screening may be helpful in detecting the long-term consequences of iliopsoas agenesis. No spine pathology could explain the right hip's weak flexion. No other disease that could have caused agenesis of the iliopsoas muscle in our patient was present. Further studies are needed to extrapolate the real prevalence of iliopsoas muscle agenesis and its consequences on the quality of life. The understanding of the actual prevalence of the condition and its impact on daily functioning could be useful insights for the management of the patients with this condition and in the development of particular therapeutic strategies.

Conclusion

In this study, we presented the case of a patient with a complaint of weak elevation of the right leg who was diagnosed incidentally with agenesis of the right iliopsoas muscle while undergoing MRI for spinal abnormalities. This condition was not caused by any disease and did not lead to degenerative changes in the spine. No spine pathology explaining her symptoms was detected. Radiologists should consider agenesis of the iliopsoas muscle in patients with weak hip flexion, especially when no spine pathology is detected. Follow-up is advised to study the long-term effects of iliopsoas muscle agenesis. Further studies are necessary to extrapolate the real prevalence of iliopsoas muscle agenesis and its consequences on the quality of life.

Conflict of Interest

None declared.

• References

• 1 Smith HS, Dubin A. Physical examination of the patient with pain. In: Argoff CE, McCleane G. eds. Pain Management Secrets. 3rd ed.. Philadelphia, PA: Mosby; 2009: 32-41
• 2 Bordoni B, Varacallo M. Anatomy, Bony Pelvis and Lower Limb, Iliopsoas Muscle. Treasure Island, FL: StatPearls Publishing; 2023
• 3 Singh D, Agarwal S. Morphological study of psoas minor muscles with embryological basis and clinical insights. J Clin Diagn Res 2021; 15 (04) AC10-AC14
• 4 Akyol M, Çiçekçi M. Unilateral hypoplasia of distal part of the psoas muscle: an incidental rare anomaly. Turkiye Klinikleri Case Rep 2021; 29 (02) 101-104

Publication History

Received: 20 June 2024

Accepted: 15 October 2024

Article published online:
26 November 2024