Lower Leg Bones and Anterior Compartment Muscles

Bones of the Lower Leg

• The tibia, a large, weight-bearing bone, articulates with the femur at the knee.
• The fibula is a slender bone situated laterally to the tibia.
• The interosseous membrane connects the tibia and fibula, serving as a muscle attachment site.
• The medial malleolus is the bony prominence at the distal end of the tibia.
• The lateral malleolus is the bony prominence at the distal end of the fibula.
• Dorsiflexion involves lifting the foot upwards.
• Plantar flexion involves pointing the toes downwards.
• Inversion involves turning the sole of the foot inwards, placing more weight on the lateral side.
• Eversion involves turning the sole of the foot outwards.
• Inversion has a greater range of motion compared to eversion; most movements occur in the bones of the Tarsus, not as much the ankle.

Anterior Compartment Muscles

• The anterior compartment muscles are located on the front of the leg, lateral to the tibia (shin bone).
• The Tibialis Anterior is the first muscle encountered laterally from the tibia.
  • It originates from the lateral tibial condyle and interosseous membrane.
  • It inserts onto the medial cuneiform bone and the base of the first metatarsal.
  • Its primary action is dorsiflexion of the foot.
  • It assists with inversion of the foot.
• The Extensor Digitorum Longus is a superficial muscle in the anterior compartment.
  • It originates from the lateral condyle of the tibia and the interosseous membrane.
  • It divides into tendons that attach to the four lateral toes (not the great toe).
  • Its actions include dorsiflexion of the foot and extension of the toes.
• The Extensor Hallucis Longus is a deep muscle, located beneath the Extensor Digitorum Longus.
  • It originates from the fibula and the interosseous membrane.
  • Its tendon runs to the great toe (hallux).
  • Its action is dorsiflexion of the foot and extension of the great toe.
• The Fibularis (Peroneus) Tertius is not present in all models.
  • It originates from the fibula and interosseous membrane.
  • It inserts onto the base of the fifth metatarsal.
  • Its actions include dorsiflexion and eversion of the foot.
• Dorsiflexion is important for lifting the toes during the swing phase of gait.
• Dorsiflexion eccentrically contracts to lower the toes to the ground, ensuring a smooth gait cycle.
• Nerve: deep fibular nerve.
• Artery: anterior tibial artery, which enters the compartment through the interosseous membrane.

Lateral Compartment Muscles

• The lateral compartment is the smallest compartment, located on the lateral side of the leg.
• The Fibularis (Peroneus) Longus is superficial to Fibularis Brevis.
  • It originates from the head of the fibula.
  • Its tendon runs posterior to the lateral malleolus, hooks underneath the foot, and inserts onto the medial cuneiform and the base of the first metatarsal.
• The Fibularis (Peroneus) Brevis is located inferiorly to Fibularis Longus.
  • It originates from the inferior part of the fibula.
  • Its tendon runs posterior to the lateral malleolus and inserts onto the base of the fifth metatarsal.
• The tendons of both muscles run through a single synovial sheath for smooth movement.
• Actions of these muscles help with balance while standing.
• These muscles counter the inverting muscles.
• Nerve: superficial fibular nerve.
• Blood supply: perforating branches from nearby arteries.