The nerve to quadratus femoris is a small motor nerve that arises from the sacral plexus, specifically from the ventral rami of the L4, L5, and S1 spinal nerves. It provides motor innervation to the quadratus femoris muscle and the inferior gemellus muscle.
Location
The nerve to quadratus femoris exits the pelvis via the greater sciatic foramen, below the piriformis muscle, and runs anterior to the sciatic nerve. It travels deep within the hip region, coursing between the ischium and the posterior hip joint, where it provides innervation to the quadratus femoris muscle. Unlike other nerves in the region, it stays deeper, near the posterior side of the hip joint, and does not extend into the lower limb.
Structure and Anatomy
The nerve to quadratus femoris is a motor nerve that innervates the quadratus femoris and inferior gemellus muscles, playing a critical role in hip movement. Below is a detailed description of its anatomy, including its origin, course, anatomical relationships, and branches.
Origin
The nerve to quadratus femoris arises from the sacral plexus, specifically from the ventral rami of L4, L5, and S1 spinal nerves. These spinal nerve roots converge to form the nerve as part of the complex network of the sacral plexus. The nerve is composed entirely of motor fibers, meaning it lacks sensory components.
Course
Pelvic Region
The nerve to quadratus femoris exits the pelvis through the greater sciatic foramen, located below the piriformis muscle. This pathway is similar to other nerves from the sacral plexus, including the sciatic and inferior gluteal nerves. However, the nerve to quadratus femoris takes a deeper and more anterior course compared to these nerves. It runs anterior to the sciatic nerve and remains closely associated with the hip joint.
Gluteal Region
After exiting the greater sciatic foramen, the nerve travels deep within the gluteal region, passing between the ischium (part of the pelvis) and the posterior aspect of the hip joint. It follows a more anterior course compared to other nerves in the region, such as the sciatic and inferior gluteal nerves, which are positioned more posteriorly.
The nerve runs deep to the gemellus inferior muscle and the quadratus femoris muscle, two muscles responsible for hip lateral rotation and stabilization. The nerve travels toward the ischial tuberosity, a bony prominence in the pelvis, and along the back of the hip joint.
Anatomical Relationships
Piriformis Muscle
The nerve to quadratus femoris exits the pelvis below the piriformis muscle, a key anatomical landmark. Unlike the sciatic nerve and other nerves that pass posterior to the hip joint, the nerve to quadratus femoris remains deep and anterior, closer to the hip joint capsule.
Sciatic Nerve
The nerve to quadratus femoris runs anterior to the sciatic nerve, maintaining a deep position relative to other structures in the gluteal region. The sciatic nerve, by contrast, passes more posteriorly and remains superficial to the nerve to quadratus femoris.
Quadratus Femoris and Inferior Gemellus Muscles
The nerve to quadratus femoris directly innervates the quadratus femoris muscle and the inferior gemellus muscle. The quadratus femoris is a flat, rectangular muscle located on the posterior aspect of the hip joint, while the inferior gemellus is a smaller muscle that assists in lateral rotation of the thigh. The nerve courses underneath these muscles, entering their deep surfaces to provide motor innervation.
Posterior Hip Joint Capsule
The nerve to quadratus femoris is closely related to the posterior aspect of the hip joint capsule. As it travels through the gluteal region, it runs just anterior to the sciatic nerve and posterior to the hip joint, contributing to its close relationship with the hip joint structures.
Ischium
The nerve runs near the ischial tuberosity, a prominent bony structure on the inferior aspect of the pelvis. This ischial tuberosity serves as an attachment point for various muscles in the gluteal region, including the hamstrings, and is a notable landmark along the course of the nerve.
Branches
The nerve to quadratus femoris gives off motor branches that innervate both the quadratus femoris and the inferior gemellus muscles. These branches emerge as the nerve reaches the deep surface of the muscles, ensuring that the entire muscle mass is innervated.
Branches to Quadratus Femoris
The primary branch of the nerve supplies the quadratus femoris muscle, a deep muscle of the hip responsible for lateral rotation and stabilization of the femoral head in the acetabulum. The nerve enters the muscle’s deep surface and provides motor innervation to the muscle fibers.
Branches to Inferior Gemellus
The nerve also provides a motor branch to the inferior gemellus muscle, which lies just superior to the quadratus femoris. The inferior gemellus assists the quadratus femoris in lateral rotation of the thigh.
Small Articular Branch
In some cases, the nerve to quadratus femoris gives off a small articular branch that provides proprioceptive input to the hip joint capsule. This branch helps convey sensory information related to the position and movement of the hip joint, although the nerve is primarily motor.
Anatomical Landmarks
- Greater Sciatic Foramen: The nerve exits the pelvis through this opening, below the piriformis muscle.
- Ischial Tuberosity: The nerve travels near this bony prominence of the pelvis as it courses toward the quadratus femoris muscle.
- Hip Joint Capsule: The nerve runs near the posterior aspect of the hip joint capsule, sometimes providing a small articular branch to it.
Variations in Anatomy
Anatomical variations in the course of the nerve to quadratus femoris are rare, though in some individuals, the nerve may have a slightly different path or give off additional small branches. The relationship between the nerve and the sciatic nerve may also vary slightly, though the nerve generally stays anterior and deep.
Termination
The nerve to quadratus femoris terminates by innervating the quadratus femoris muscle and inferior gemellus muscle. After giving off its final motor branches to these muscles, the nerve does not extend beyond the hip joint region.
Function
The nerve to quadratus femoris is a motor nerve that primarily innervates the quadratus femoris muscle and the inferior gemellus muscle. These muscles play important roles in controlling hip movement, specifically in lateral rotation and stabilization of the hip joint. Below is a detailed breakdown of its functions.
Motor Innervation of the Quadratus Femoris Muscle
The primary function of the nerve to quadratus femoris is to provide motor innervation to the quadratus femoris muscle, which is a deep muscle located in the posterior hip region. The quadratus femoris has two main functions related to the hip:
Hip Lateral (External) Rotation
The quadratus femoris muscle, under the control of the nerve to quadratus femoris, is responsible for lateral (external) rotation of the hip. This movement involves rotating the thigh outward, away from the midline of the body. Lateral rotation of the hip is crucial for various movements, including:
- Turning the foot outward.
- Pivoting or rotating the leg.
- Maintaining balance during walking or running. This action is especially important in activities requiring controlled movement of the lower limb, such as sports or directional changes.
Hip Joint Stabilization
The quadratus femoris muscle also contributes to the stabilization of the hip joint, which is crucial during weight-bearing activities. The muscle helps hold the femoral head securely within the acetabulum (hip socket), providing support and stability to the joint during standing, walking, and running. This stabilizing function is particularly important for preventing dislocation or excessive movement of the femoral head in the acetabulum.
Motor Innervation of the Inferior Gemellus Muscle
The nerve to quadratus femoris also provides motor innervation to the inferior gemellus muscle, a small muscle located above the quadratus femoris. The inferior gemellus works together with the quadratus femoris to perform similar functions:
Lateral Rotation of the Hip
Like the quadratus femoris, the inferior gemellus is involved in lateral (external) rotation of the hip. This muscle assists in turning the thigh outward, and its coordinated action with other muscles in the hip region helps control the lower limb during movements such as walking, pivoting, and changing direction.
Support for Deep Gluteal Muscles
The inferior gemellus assists the deep external rotators of the hip, including the obturator internus and superior gemellus, in stabilizing and controlling the hip joint. Although the inferior gemellus is smaller than the quadratus femoris, it plays a supportive role in external rotation and stability.
Role in Hip Joint Proprioception
In some cases, the nerve to quadratus femoris may send a small articular branch to the hip joint capsule. This branch contributes to proprioception, which is the body’s ability to sense the position and movement of the hip joint. Although the nerve is primarily motor, this articular branch helps relay information about the position and stability of the hip joint during movement, which is important for balance and coordination.
No Sensory Function
The nerve to quadratus femoris is primarily a motor nerve, meaning it does not have a significant sensory function. Any proprioceptive input it provides to the hip joint is minimal, and sensory innervation of the skin in the surrounding region is handled by other nerves, such as the posterior cutaneous nerve of the thigh and clunial nerves.
Clinical Significance
The nerve to quadratus femoris is crucial for hip joint function, specifically for controlling lateral rotation and stabilization of the hip. Damage or dysfunction of this nerve can lead to significant clinical implications.
Weakness in Hip Lateral Rotation
Injury to the nerve to quadratus femoris can result in weakness or paralysis of the quadratus femoris and inferior gemellus muscles, which are responsible for external rotation of the hip. This weakness may manifest as difficulty turning the leg outward or maintaining proper alignment during activities like walking or running.
Hip Joint Instability
Because the quadratus femoris plays a key role in stabilizing the hip joint, damage to this nerve can lead to instability of the hip. This may increase the risk of hip dislocation or difficulty maintaining hip joint stability during weight-bearing activities.
Groin or Hip Pain
In cases where the nerve to quadratus femoris is compressed or injured, patients may experience deep hip or groin pain. This is sometimes associated with conditions like piriformis syndrome or other causes of sciatic nerve compression, as the nerve runs close to the sciatic nerve.
