Muscles Of The Lower Limb Review Sheet 13

Muscles of the lower limb play a crucial role in movement, stability, and overall functionality of the human body. From enabling us to walk, run, jump, to maintaining posture and balance, these muscles are constantly at work. Understanding their individual functions, origins, insertions, and innervations is essential for healthcare professionals, athletes, and anyone interested in human anatomy and biomechanics. This comprehensive review delves into the intricate details of the lower limb muscles, providing a structured overview suitable for study and reference.

Muscles of the Lower Limb: A Detailed Review

The lower limb muscles can be broadly categorized into three main groups: muscles of the hip and thigh, muscles of the leg, and muscles of the foot. Each group is further divided into anterior, posterior, medial, and lateral compartments, each with specific functions. We will explore these compartments and their constituent muscles in detail.

I. Muscles of the Hip and Thigh

These muscles are responsible for movements at the hip and knee joints. They provide power for locomotion and stability for the pelvis.

A. Anterior Compartment of the Thigh

This compartment primarily contains the knee extensors.

• 1. Sartorius: The longest muscle in the human body, the sartorius, originates from the anterior superior iliac spine (ASIS) and inserts on the medial surface of the proximal tibia. Its primary actions include:

  • Flexion, abduction, and external rotation of the hip.
  • Flexion of the knee.
  • Assists in medial rotation of the tibia when the knee is flexed.

  Innervation: Femoral nerve (L2-L3).

• 2. Quadriceps Femoris: This is a powerful group of four muscles that act as the primary knee extensors. It includes:

  • a. Rectus Femoris: Originates from the anterior inferior iliac spine (AIIS) and the acetabulum, inserting via the patellar tendon into the tibial tuberosity. It's unique among the quadriceps as it crosses both the hip and knee joints, allowing it to also flex the hip.

    • Action: Knee extension and hip flexion.

    • Innervation: Femoral nerve (L2-L4).

  • b. Vastus Lateralis: The largest of the quadriceps, originating from the greater trochanter, intertrochanteric line, and linea aspera of the femur, inserting via the patellar tendon into the tibial tuberosity.

    • Action: Knee extension.

    • Innervation: Femoral nerve (L2-L4).

  • c. Vastus Medialis: Originates from the intertrochanteric line and linea aspera of the femur, inserting via the patellar tendon into the tibial tuberosity. It plays a crucial role in stabilizing the patella.

    • Action: Knee extension and patellar tracking.

    • Innervation: Femoral nerve (L2-L4).

  • d. Vastus Intermedius: Located deep to the rectus femoris, originating from the anterior and lateral surfaces of the femur, inserting via the patellar tendon into the tibial tuberosity.

    • Action: Knee extension.

    • Innervation: Femoral nerve (L2-L4).

B. Medial Compartment of the Thigh (Adductor Group)

This compartment contains the muscles responsible for adducting the thigh at the hip joint.

• 1. Adductor Longus: Originates from the pubic body and inserts on the linea aspera of the femur.

  • Action: Adduction, flexion, and external rotation of the hip.

  • Innervation: Obturator nerve (L2-L4).

• 2. Adductor Brevis: Lies deep to the adductor longus, originating from the inferior pubic ramus and inserting on the linea aspera of the femur.

  • Action: Adduction, flexion, and external rotation of the hip.

  • Innervation: Obturator nerve (L2-L4).

• 3. Adductor Magnus: The largest of the adductor muscles, with a dual origin: the inferior pubic ramus, ischial ramus, and ischial tuberosity. It has a dual insertion: the linea aspera and adductor tubercle of the femur. Its unique structure allows it to act as both an adductor and a hamstring muscle.

  • Action: Adduction, flexion (anterior fibers), and extension (posterior fibers) of the hip.

  • Innervation: Obturator nerve (L2-L4) (adductor portion) and Sciatic nerve (tibial division) (hamstring portion).

• 4. Gracilis: The most medial muscle of the adductor group, originating from the inferior pubic ramus and inserting on the medial surface of the proximal tibia (pes anserinus). It is the only adductor that crosses the knee joint.

  • Action: Adduction of the hip, flexion of the knee, and assists in medial rotation of the tibia when the knee is flexed.

  • Innervation: Obturator nerve (L2-L3).

• 5. Pectineus: Located in the superior part of the medial compartment, originating from the superior pubic ramus and inserting on the pectineal line of the femur.

  • Action: Adduction, flexion, and external rotation of the hip.

  • Innervation: Femoral nerve (L2-L3) and sometimes a branch from the obturator nerve.

C. Posterior Compartment of the Thigh (Hamstring Group)

These muscles are responsible for knee flexion and hip extension.

• 1. Biceps Femoris: Has two heads: a long head and a short head. The long head originates from the ischial tuberosity, while the short head originates from the linea aspera of the femur. Both heads converge to insert on the fibular head.

  • Action: Knee flexion, hip extension (long head only), and external rotation of the hip when the knee is flexed.

  • Innervation: Long head - Sciatic nerve (tibial division) (L5-S2); Short head - Sciatic nerve (common fibular division) (L5-S2).

• 2. Semitendinosus: Originates from the ischial tuberosity and inserts on the medial surface of the proximal tibia (pes anserinus). Its long tendon gives it its name.

  • Action: Knee flexion, hip extension, and assists in medial rotation of the tibia when the knee is flexed.

  • Innervation: Sciatic nerve (tibial division) (L5-S2).

• 3. Semimembranosus: Originates from the ischial tuberosity and inserts on the posterior aspect of the medial tibial condyle.

  • Action: Knee flexion, hip extension, and assists in medial rotation of the tibia when the knee is flexed.

  • Innervation: Sciatic nerve (tibial division) (L5-S2).

D. Gluteal Region

This region contains muscles responsible for movements at the hip joint, particularly abduction, extension, and rotation.

• 1. Gluteus Maximus: The largest muscle in the body, originating from the posterior iliac crest, sacrum, coccyx, and thoracolumbar fascia, inserting on the gluteal tuberosity of the femur and the iliotibial tract (IT band).

  • Action: Hip extension, external rotation, and abduction of the hip; also helps to stabilize the hip and thigh. It's particularly important during forceful movements like running and climbing stairs.

  • Innervation: Inferior gluteal nerve (L5-S2).

• 2. Gluteus Medius: Originates from the outer surface of the ilium between the anterior and posterior gluteal lines, inserting on the greater trochanter of the femur.

  • Action: Hip abduction and medial rotation of the hip; also crucial for stabilizing the pelvis during walking and preventing the contralateral hip from dropping.

  • Innervation: Superior gluteal nerve (L4-S1).

• 3. Gluteus Minimus: Located deep to the gluteus medius, originating from the outer surface of the ilium between the anterior and inferior gluteal lines, inserting on the greater trochanter of the femur.

  • Action: Hip abduction and medial rotation of the hip; works synergistically with the gluteus medius for pelvic stabilization.

  • Innervation: Superior gluteal nerve (L4-S1).

• 4. Tensor Fasciae Latae (TFL): Originates from the anterior superior iliac spine (ASIS) and inserts into the iliotibial tract (IT band).

  • Action: Hip flexion, abduction, and medial rotation of the hip; also helps to stabilize the knee through its connection to the IT band.

  • Innervation: Superior gluteal nerve (L4-S1).

• 5. Deep External Rotators of the Hip: A group of six small muscles located deep to the gluteus maximus, responsible for external rotation of the hip. These include:

  • a. Piriformis: Originates from the anterior surface of the sacrum and inserts on the greater trochanter of the femur. The sciatic nerve often passes underneath or even through the piriformis muscle, making it clinically significant.

    • Action: External rotation of the hip when the hip is extended; abduction of the hip when the hip is flexed.

    • Innervation: Nerve to piriformis (S1-S2).

  • b. Obturator Internus: Originates from the internal surface of the obturator membrane and surrounding bone, inserting on the greater trochanter of the femur.

    • Action: External rotation of the hip when the hip is extended; abduction of the hip when the hip is flexed.

    • Innervation: Nerve to obturator internus (L5-S1).

  • c. Obturator Externus: Originates from the external surface of the obturator membrane and surrounding bone, inserting on the trochanteric fossa of the femur.

    • Action: External rotation of the hip.

    • Innervation: Obturator nerve (L3-L4).

  • d. Superior Gemellus: Originates from the ischial spine and inserts on the greater trochanter of the femur (along with the obturator internus).

    • Action: External rotation of the hip when the hip is extended; abduction of the hip when the hip is flexed.

    • Innervation: Nerve to obturator internus (L5-S1).

  • e. Inferior Gemellus: Originates from the ischial tuberosity and inserts on the greater trochanter of the femur (along with the obturator internus).

    • Action: External rotation of the hip when the hip is extended; abduction of the hip when the hip is flexed.

    • Innervation: Nerve to quadratus femoris (L4-S1).

  • f. Quadratus Femoris: Originates from the ischial tuberosity and inserts on the quadrate tubercle of the femur.

    • Action: External rotation of the hip.

    • Innervation: Nerve to quadratus femoris (L4-S1).

II. Muscles of the Leg

These muscles are responsible for movements at the ankle and foot. They are crucial for walking, running, and maintaining balance.

A. Anterior Compartment of the Leg

This compartment contains the dorsiflexors of the ankle and extensors of the toes.

• 1. Tibialis Anterior: Originates from the lateral surface of the tibia and interosseous membrane, inserting on the medial cuneiform and first metatarsal.

  • Action: Dorsiflexion and inversion of the ankle.

  • Innervation: Deep fibular (peroneal) nerve (L4-S1).

• 2. Extensor Hallucis Longus: Originates from the fibula and interosseous membrane, inserting on the distal phalanx of the great toe.

  • Action: Dorsiflexion of the ankle and extension of the great toe.

  • Innervation: Deep fibular (peroneal) nerve (L4-S1).

• 3. Extensor Digitorum Longus: Originates from the tibia, fibula, and interosseous membrane, dividing into four tendons that insert on the dorsal surfaces of the middle and distal phalanges of the lateral four toes.

  • Action: Dorsiflexion of the ankle and extension of the lateral four toes.

  • Innervation: Deep fibular (peroneal) nerve (L4-S1).

• 4. Fibularis (Peroneus) Tertius: Often considered a part of the extensor digitorum longus, originating from the fibula and interosseous membrane, inserting on the base of the fifth metatarsal.

  • Action: Dorsiflexion and eversion of the ankle.

  • Innervation: Deep fibular (peroneal) nerve (L4-S1).

B. Lateral Compartment of the Leg

This compartment contains the evertors of the ankle.

• 1. Fibularis (Peroneus) Longus: Originates from the fibula and inserts on the plantar surface of the medial cuneiform and first metatarsal. Its tendon runs along the sole of the foot.

  • Action: Eversion and plantarflexion of the ankle; also supports the transverse arch of the foot.

  • Innervation: Superficial fibular (peroneal) nerve (L5-S2).

• 2. Fibularis (Peroneus) Brevis: Originates from the fibula and inserts on the base of the fifth metatarsal.

  • Action: Eversion and plantarflexion of the ankle.

  • Innervation: Superficial fibular (peroneal) nerve (L5-S2).

C. Superficial Posterior Compartment of the Leg

This compartment contains the plantarflexors of the ankle.

• 1. Gastrocnemius: Has two heads: a medial head originating from the medial femoral condyle and a lateral head originating from the lateral femoral condyle. Both heads converge to form the Achilles tendon, which inserts on the calcaneus.

  • Action: Plantarflexion of the ankle and flexion of the knee.

  • Innervation: Tibial nerve (S1-S2).

• 2. Soleus: Lies deep to the gastrocnemius, originating from the tibia and fibula, also inserting via the Achilles tendon on the calcaneus.

  • Action: Plantarflexion of the ankle. Crucial for maintaining posture and balance during standing.

  • Innervation: Tibial nerve (S1-S2).

• 3. Plantaris: A small muscle with a long tendon, originating from the lateral femoral epicondyle and inserting on the calcaneus (or sometimes the Achilles tendon). Its function is minimal and sometimes absent.

  • Action: Weak plantarflexion of the ankle and flexion of the knee.

  • Innervation: Tibial nerve (S1-S2).

D. Deep Posterior Compartment of the Leg

This compartment contains muscles responsible for plantarflexion, inversion, and toe flexion.

• 1. Popliteus: Originates from the lateral femoral condyle and inserts on the posterior surface of the tibia.

  • Action: Flexion and medial rotation of the tibia on the femur (or lateral rotation of the femur on the tibia), unlocking the knee joint for flexion.

  • Innervation: Tibial nerve (L4-S1).

• 2. Flexor Hallucis Longus: Originates from the fibula and interosseous membrane, inserting on the distal phalanx of the great toe.

  • Action: Plantarflexion of the ankle and flexion of the great toe.

  • Innervation: Tibial nerve (S2-S3).

• 3. Flexor Digitorum Longus: Originates from the tibia and inserts on the plantar surfaces of the distal phalanges of the lateral four toes.

  • Action: Plantarflexion of the ankle and flexion of the lateral four toes.

  • Innervation: Tibial nerve (S2-S3).

• 4. Tibialis Posterior: Originates from the tibia, fibula, and interosseous membrane, inserting on multiple tarsal bones (navicular, cuneiforms, cuboid) and the bases of metatarsals 2-4.

  • Action: Plantarflexion and inversion of the ankle; also supports the medial longitudinal arch of the foot.

  • Innervation: Tibial nerve (L4-L5).

III. Muscles of the Foot

The muscles of the foot are intrinsic, meaning their origins and insertions are both within the foot. They contribute to fine motor control, arch support, and stability during gait. They are divided into dorsal and plantar groups.

A. Dorsal Muscles of the Foot

• 1. Extensor Hallucis Brevis: Originates from the calcaneus and inserts on the proximal phalanx of the great toe.

  • Action: Extension of the great toe.

  • Innervation: Deep fibular (peroneal) nerve (S1-S2).

• 2. Extensor Digitorum Brevis: Originates from the calcaneus and divides into tendons that insert on the proximal phalanges of toes 2-4.

  • Action: Extension of toes 2-4.

  • Innervation: Deep fibular (peroneal) nerve (S1-S2).

B. Plantar Muscles of the Foot

These muscles are organized into four layers.

• First Layer (Superficial):

  • 1. Abductor Hallucis: Originates from the calcaneus and inserts on the proximal phalanx of the great toe.

    • Action: Abduction and flexion of the great toe.

    • Innervation: Medial plantar nerve (S2-S3).

  • 2. Flexor Digitorum Brevis: Originates from the calcaneus and divides into tendons that insert on the middle phalanges of toes 2-5.

    • Action: Flexion of toes 2-5 at the proximal interphalangeal joints.

    • Innervation: Medial plantar nerve (S2-S3).

  • 3. Abductor Digiti Minimi: Originates from the calcaneus and inserts on the proximal phalanx of the fifth toe.

    • Action: Abduction and flexion of the fifth toe.

    • Innervation: Lateral plantar nerve (S2-S3).

• Second Layer:

  • 1. Quadratus Plantae: Originates from the calcaneus and inserts on the tendon of the flexor digitorum longus.

    • Action: Assists in flexing toes 2-5 by correcting the oblique pull of the flexor digitorum longus tendon.

    • Innervation: Lateral plantar nerve (S1-S2).

  • 2. Lumbricals (four muscles): Originate from the tendons of the flexor digitorum longus and insert on the dorsal expansions of toes 2-5.

    • Action: Flexion of the metatarsophalangeal joints and extension of the interphalangeal joints of toes 2-5.

    • Innervation: Medial plantar nerve (lumbrical 1) and Lateral plantar nerve (lumbricals 2-4).

• Third Layer:

  • 1. Flexor Hallucis Brevis: Originates from the cuboid and lateral cuneiform and inserts on the proximal phalanx of the great toe.

    • Action: Flexion of the great toe at the metatarsophalangeal joint.

    • Innervation: Medial plantar nerve (S2-S3).

  • 2. Adductor Hallucis: Has two heads: an oblique head and a transverse head. Both heads converge to insert on the proximal phalanx of the great toe.

    • Action: Adduction and flexion of the great toe.

    • Innervation: Lateral plantar nerve (S2-S3).

  • 3. Flexor Digiti Minimi Brevis: Originates from the base of the fifth metatarsal and inserts on the proximal phalanx of the fifth toe.

    • Action: Flexion of the fifth toe at the metatarsophalangeal joint.

    • Innervation: Lateral plantar nerve (S2-S3).

• Fourth Layer (Deepest):

  • 1. Plantar Interossei (three muscles): Originate from the medial sides of metatarsals 3-5 and insert on the medial sides of the proximal phalanges of the same toes.

    • Action: Adduction of toes 3-5 towards the second toe, flexion of the metatarsophalangeal joints, and extension of the interphalangeal joints.

    • Innervation: Lateral plantar nerve (S2-S3).

  • 2. Dorsal Interossei (four muscles): Originate from the adjacent sides of metatarsals and insert on the proximal phalanges of toes 2-4.

    • Action: Abduction of toes 2-4 away from the second toe, flexion of the metatarsophalangeal joints, and extension of the interphalangeal joints.

    • Innervation: Lateral plantar nerve (S2-S3).

Clinical Significance

Understanding the anatomy and function of lower limb muscles is crucial for diagnosing and treating various musculoskeletal conditions. Some common clinical conditions related to these muscles include:

• Muscle strains and tears: Common in athletes, particularly involving the hamstrings, quadriceps, and calf muscles.
• Tendinitis: Inflammation of tendons, such as Achilles tendinitis or patellar tendinitis.
• Compartment syndrome: Increased pressure within a muscle compartment, leading to ischemia and nerve damage.
• Piriformis syndrome: Compression of the sciatic nerve by the piriformis muscle, causing buttock and leg pain.
• Plantar fasciitis: Inflammation of the plantar fascia, causing heel pain.
• Shin splints: Pain along the tibia, often due to overuse and inflammation of the muscles and tendons.

Conclusion

The muscles of the lower limb are a complex and interconnected system that allows for a wide range of movements and functions. By understanding the individual muscles, their origins, insertions, actions, and innervations, healthcare professionals and individuals alike can gain a deeper appreciation for the biomechanics of the human body and better address related clinical conditions. This comprehensive review serves as a valuable resource for anyone seeking to enhance their knowledge of this essential aspect of human anatomy.