Author: Kevin B. Rosenbloom, C.Ped, Sports Biomechanist

Flexion at the hip joint, a starting point of ambulation. This summary will briefly discuss hip flexion, explore the muscle bodies that contribute to this movement and give some insight into the intriguing research about the muscles.

Flexion Essentials

Hip flexion is the frontal, superior raise of the thigh and leg at the hip joint. The range of motion has been estimated within 0-125° (Quinn 2019) but with increased flexibility, it has been seen that 150° is possible in healthy male adults (Roaas & Andersson 1982). The psoas major, psoas minor, iliacus, sartorius, rectus femoris and pectineus are all the most significant contributors to hip flexion (Visible Body 2019). It is important to note that other sources have suggested some contribution is applied within the medial compartment (adductor group) and the tensor fascia lata (lateral compartment) but it remains open for further research (Platzer 2004).

Inner Pelvis: The Iliopsoas Group

The psoas major are long fusiform muscles that attach to the sides of the lower vertebral column and lesser pelvis. As the muscles proceeds downward into the pelvis, their bodies’ thickness narrows as they pass over the iliopubic eminences and the anterior walls of the pelvis. Both the left and right p. major ends at tendons in front capsules at both hip joints. The tendons proceed to be inserted at their sides’ lesser femoral trochanters. The psoas minor are anteriorly placed muscles in front of the left and right P. major. These long and slender muscles originate from either side of the thoracic vertebra and with long and flat tendons that insert onto their respective pectineal lines and iliopectineal eminences. The iliacus muscles are flat, triangular constructions that fill in the inner lining of the large sections of the pelvis known as the iliac fossa. Both sides originate from the upper 60% of their sides iliac fossa and join the lateral psoas major. Both iliacus bodies decrease in width as they cover the anterior pelvis and connect to their respective tendons and lesser femoral trochanters.

Psoas major, psoas minor and the iliacus are placed into the iliopsoas muscle group. This is due to some individuals lacking a psoas minor altogether (Gray 1918). Reports have stated that 50% of human subjects observed an accompaniment of p. major and minor working together in motion and because p. major’s shared borders and insertions with iliacus, that their motions are also conjoined as well (Platzer 2004, Visible Body 2019). With Platzer’s notes it has been observed that when a patient is in a seated position and possesses weak iliopsoas muscles, hip flexion across the horizontal plane would be significantly hindered or not possible (246).

Anterior Pelvis: A More Distal Femoral Attachment

The longest muscles in the body, the sartorius, are narrow, thin muscles that originate from the anterior superior iliac spine on both sides of the pelvis. They run across the anterior part of the thighs and both insert on the medial sides of the knees at the medial femoral condyle. The rectus femoris muscles are fusiform-shaped muscles that originate from two tendons on either side of the pelvis, at the anterior inferior iliac spine and the superior groove just above the acetabulum. The main bodies of the muscles expand in width while they run distally down the center of the thighs. At the distal half-way mark of the thigh their widths narrow, mirroring their growth, as they connect and insert into tendons that encases the patella at each knee. Although the pectineus are considered part of the medial compartments, it does have its insertions on both sides of the pelvis at the anteriorly-located, superior pubic rami. The flat and quadrangular shape of the pectineus expands distally, laterally, and posteriorly as they insert into their side’s linea aspera of the lesser femoral trochanter.

The tendons from the sartorius, gracilis and semitendinosus muscles all make up the pes anserinus. Because all three have insertions into the knees at the tibia, severe overuse can lead to pain, swelling and tenderness known as pes anserine bursitis (Glencross 2018). The sartorius also have multiple functions other than contributing to hip flexion, but is considered only a synergist muscle and relatively not very strong. The rectus femoris are the most anterior part of the quadricep group, and are among the most powerful hip flexors. Because of their anterior position, pelvic origin and attachment to the patella, injuries caused by athletic forceful movements are most attributed to these muscles. The pectineus have been an interesting topic in medical physiology. Interpretation of which compartment it belongs to as settled down, but interesting information about its nerve innervation has been at the forefront. Along with the femoral nerve, which innervates 90%, it has also been noted that 8.7% of the time the accessory obturator nerve innervates because of the pectineus’ border with the pelvic obturator foramen (Woodburne).

Muscle Overview - Hip Flexors

Figure 1. Sketch of hip flexors (right), anterior view.

Psoas major [1]

Psoas minor [2]

Iliacus [3]

Sartorius [4]

Rectus femoris [5]

Pectineus [6]

References & Works Cited

Barclay, T. 2018. “Anatomy Explorer,” innerbody.com. Accessed 19 Mar 2019. https://www.innerbody.com/anatomy/muscular/leg-foot.

Glencross, P. M. 2018. “Pes Anserine Bursitis,” Medscape. Accessed 20 Mar 2019. https://emedicine.medscape.com/article/308694-overview.

Gray, H. 1918. “The Muscles and Fasciæ of the Lower Extremity,” Anatomy of the Human Body, 20th Ed. Lead & Febiger. Philadelphia & New York, USA. 466-472.

Platzer, W. 2004. Color Atlas of Human Anatomy, Vol. 1: Locomotor System 5th Ed. Thieme. New York, USA.

Quinn, E. 2019. “Generally Accepted Values for Normal Range of Motion (ROM) in Joints,” verywellhealth.com. Accessed 19 Mar 2019. https://www.verywellhealth.com/what-is-normal-range-of-motion-in-a-joint-3120361.

Roaas, A., Andersson, G. B. J., 1982. “Normal Range of Motion of the Hip, Knee and Ankle Joints in Male Subjects, 30-40 Years of Age,” Acta Orthopaedica Scandinavica, 53:2, 205-208. https://www.tandfonline.com/doi/abs/10.3109/17453678208992202.

Visible Body. 2019. “Muscle Premium,” VisibleBody.com. Purchasable Application. Accessed 21 Feb 2019.

Woodburne, R. “The Accessory Obturator Nerve and the Innervation of the Pectineus Muscle,” Michigan Library Med School: 367-369. Accessed 20 Mar 2019. https://deepblue.lib.umich.edu/bitstream/handle/2027.42/49789/1091360303_ftp.pdf?sequence=1.

Kevin B. Rosenbloom, C.Ped, Sports Biomechanist

Kevin B. Rosenbloom, founder and president of KevinRoot Medical, is a renowned certified pedorthist and sports biomechanist practicing in Santa Monica, CA. With his continuing research on the historical development of foot and ankle pathologies, comparative evolution of lower extremities and the modern environmental impacts on ambulation, he provides advanced biomechanical solutions for his patients and clients.