Thigh Anatomy and Function

The Thigh

Overview of Thigh Anatomy

  • Focus on:

    • Compartments and innervations

    • Anterior compartment

    • Medial compartment

    • Posterior compartment

    • Vasculature

    • Health-related topics: muscle tear, compartment syndrome, Trendelenburg test and sign

Lumbosacral Plexus

  • Focus on the three terminal branches:

    Lumbosacral Plexus

    • Focus on the three terminal branches:

      • Femoral nerve (L2-L4):

        • Originates from the lumbar plexus. This nerve is crucial for locomotion, extending the knee and flexing the hip.

        • Primarily innervates the muscles of the anterior compartment of the thigh, including the Quadriceps Femoris (Rectus femoris, Vastus lateralis, Vastus medialis, Vastus intermedius), Sartorius, Iliopsoas, and Pectineus (which also receives some obturator innervation).

        • It is responsible for the general actions of knee extension and hip flexion.

        • Provides sensory innervation to the anterior thigh and anteromedial aspect of the leg via its cutaneous branches, notably the saphenous nerve.

      • Obturator nerve (L2-L4):

        • Originates from the lumbar plexus. It passes through the obturator foramen to reach the medial compartment.

        • Primarily innervates the muscles of the medial compartment of the thigh, collectively known as the adductor group. These include Adductor Longus, Adductor Brevis, Gracilis, Obturator Externus, and the adductor part of Adductor Magnus.

        • Responsible for the general action of adduction of the thigh and contributes to hip rotation.

        • Provides sensory innervation to a small area on the medial thigh.

      • Sciatic nerve (L4-S3):

        • Originates from the sacral plexus and is the largest nerve in the body.

        • Primarily innervates the muscles of the posterior compartment of the thigh, including Biceps Femoris (long head and short head), Semitendinosus, Semimembranosus, and the hamstring part of Adductor Magnus.

        • Responsible for the general actions of knee flexion and hip extension.

        • Typically divides into two main branches, the tibial nerve and the common fibular nerve (peroneal nerve), usually in the popliteal fossa, which further innervate the leg and foot. The tibial part innervates most of the posterior compartment muscles, while the common fibular part innervates the short head of biceps femoris.

        • Provides extensive sensory innervation to most of the posterior thigh, the entire leg, and the foot, playing a critical role in sensation and proprioception.

    • The three terminal branches correspond roughly to the three compartments of the thigh, providing their primary motor and sensory innervation, ensuring coordinated movement and sensation.

    • Obturator nerve (L2-L4)

    • Sciatic nerve (L4-S3)

  • The three terminal branches correspond roughly to the three compartments of the thigh.

Compartments of the Thigh

General Overview

  • There are three major compartments in the thigh:

    1. Anterior Compartment:

    • General Action: Extension of the knee

    • Innervation: Femoral Nerve

    1. Medial Compartment:

    • General Action: Adduction of the thigh

    • Innervation: Obturator Nerve

    1. Posterior Compartment:

    • General Action: Flexion of the knee

    • Innervation: Sciatic Nerve

    • Note: Some exceptions exist in the innervation patterns.

Muscles of the Anterior Compartment

  • Major muscles include:

    • Iliopsoas: Combination of iliacus and psoas muscles. Function: Flex hip.

    • Sartorius:

    • Attachments: ASIS and pes anserinus (common tendon to tibia).

    • Function: Flex hip, flex knee, laterally rotate femur.

    • Innervation: Femoral nerve.

    • Quadriceps Femoris:

    • Composed of four bellies: Rectus femoris, Vastus lateralis, Vastus medialis, Vastus intermedius.

    • Function: Extend knee, flex hip.

    • Innervation: Femoral nerve.

Quadriceps Femoris Details

  • Rectus Femoris:

    • Attachments: Proximal attachment to the Anterior Inferior Iliac Spine (AIIS).

    • Functions: Flexes knee and hip.

  • Vastus Muscles:

    • All vastus muscles attach proximally to the femur. Function: All four flex the hip and extend the knee. Innervation: All innervated by the femoral nerve.

Patellar Ligament and Dislocation

  • The patella is a sesamoid bone formed within a tendon, connecting the quadriceps femoris to the tibial tuberosity. The patellar ligament attaches to the tibial tuberosity.

  • Greater knowledge of patellar dislocation:

    • Lateral dislocation is more common, attributed to the dominance of the vastus lateralis in training.

Muscles of the Medial Compartment

  • Adductor Group:

    • Common function: Adductors of the leg (collectively referred to as “groin”).

    • Proximally attached: To ischiopubic ramus (the area between ischium and pubis).

    • Innervation: Mostly by the obturator nerve.

  • Major muscles:

    • Pectineus:

    • Attachments: Pectineal line of pubis, lesser trochanter and linea aspera of femur.

    • Function: Adduct and flex hip; Innervation: femoral nerve.

    • Adductor Longus:

    • Attachments: Pubis (external part), linea aspera of femur.

    • Function: Adduct hip, medially rotate hip; Innervation: Obturator nerve.

    • Adductor Brevis:

    • Attachments: Pubis (external part), pectineal line, linea aspera of femur.

    • Function: Adduct hip; Innervation: Obturator nerve.

    • Gracilis:

    • Attachments: Inferior pubic ramus of pubis to tibia (via pes anserinus).

    • Function: Adduct hip, flex knee; Innervation: Obturator nerve.

    • Obturator Externus:

    • Attachments: External surface of obturator membrane to trochanteric fossa of femur.

    • Function: Lateral rotation of hip; Innervation: Obturator nerve.

    • Adductor Magnus:

    • Has two parts:

      • Adductor part:

      • Attachments: ischiopubic ramus to linea aspera of femur. Innervated by obturator nerve.

      • Hamstring part:

      • Attachments: ischial tuberosity to adductor tubercle of femur. Innervated by sciatic nerve.

Neurovasculature of the Thigh

  • Include:

    • ✔ Femoral nerve (L2-4)

    • ✔ Obturator nerve (L2-4)

  • The Femoral Triangle:

    • Borders:

    • Superior: Inguinal ligament.

    • Inferior/Lateral: Sartorius.

    • Medial: Adductor Longus.

    • Contents:

    • Femoral Nerve

    • Femoral Artery

    • Femoral Vein

    • Lymphatics

    • Enclosed in: Femoral sheath.

Posterior Compartment of the Thigh

  • Functions: Knee flexion, hip extension.

  • Innervation: By the Sciatic Nerve (including both tibial and fibular portions).

  • All muscles innervated by the tibial portion except for the short head of biceps femoris which is innervated by the common fibular nerve.

  • Major muscles:

    • Biceps Femoris (long and short head).

    • Semitendinosus.

    • Semimembranosus.

    • Adductor Magnus (hamstring part).

Posterior Compartment Muscle Details

  • Semitendinosus:

    • Attachments: ischial tuberosity to tibia (via pes anserinus).

    • Innervation: Sciatic nerve (tibial part).

    • Function: Hip extension, knee flexion, rotation of knee and tibia.

  • Semimembranosus:

    • Attachments: ischial tuberosity to tibia.

    • Innervation: Sciatic nerve (tibial part).

    • Function: Hip extension, knee flexion, rotation of knee and tibia.

  • Biceps Femoris:

    • Long Head:

    • Attachments: ischial tuberosity to fibular head.

    • Innervation: Sciatic nerve (tibial part).

    • Short Head:

    • Attachments: linea aspera to fibular head.

    • Innervation: Sciatic nerve (common fibular part).

    • Function: Knee flexion, hip extension, lateral rotation of lower leg.

Transition of Major Vasculature

  • Transition from femoral artery to popliteal artery at the popliteal fossa (located behind the knee).

  • Femoral vein transitions to popliteal vein as well as the sciatic nerve dividing into the tibial nerve and common fibular nerve at this point.

Venous and Lymphatic Drainage of the Thigh

Superficial Venous and Lymph Drainage

  • Superficial Inginal Lymph Nodes:

    • Located in superior and inferior groups; found external to the fascia lata.

    • Includes popliteal lymph nodes.

    • Associated with great saphenous vein and its tributaries.

  • Great Saphenous Vein:

    • Runs along the medial border of the patella and the medial malleolus before draining into the femoral vein.

Deep Venous Drainage

  • Deep venous drainage largely mirrors the arterial supply:

    • Deep veins include:

    • External iliac vein

    • Deep circumflex iliac vein

    • Inferior epigastric vein

    • Medial and lateral circumflex femoral veins

    • Obturator vein

    • Profunda femoris vein.

Health-related Topics in the Thigh

Common Muscle Tears

  • Posterior and medial compartments are more prone to tears due to sudden lengthening (overstretch).

    • Common injuries:

    • “Pulled hamstring” (associated with posterior compartment).

    • “Pulled groin” (associated with medial compartment).

    • Note: Common attachment on ischial tuberosity is susceptible to avulsion fractures. It is important to always stretch before exercise to prevent injury.

Compartment Syndrome

  • Thigh muscles are compartmentalized by intermuscular septa, creating compartments.

  • Conditions such as infections or bruises can lead to swelling of muscles within a compartment, compressing neurovasculature and causing:

    • Severe pain

    • Loss of sensation or function of distal structures.

  • Treatment:

    • Surgical intervention, often referred to as fasciotomy, may be necessary to release the pressure.

Additional Assessments

  • Trendelenburg Test:

    • This clinical test is utilized to assess gluteal muscle function and hip stability.

    • Assesses the adequacy of gluteus medius and minimus during unilateral stance, specifically looking for pelvic tilt and hip joint dynamics.

Conclusion

  • Understanding the anatomy, innervation, and functions of the thigh is crucial for diagnosing and treating musculoskeletal conditions, as well as implementing effective rehabilitation strategies.