Bones of the Lower Limbs

The femur is the long bone located in the thigh that is the longest and strongest bone of the body. The femur articulates with the coxal (hip) bone and functions as an attachment site for muscles in the lower limb and buttocks. The proximal end of the femur is the head. The head of the femur projects medially, is round in shape, and forms a ball-and-socket joint at the acetabulum (deep cavity) of the coxal bone. The neck of the femur is a narrower region below the head. Around the neck are two trochanters (rounded bony protrusions) that serve as muscle insertion points. The greater trochanter is lateral and superior to the neck, and the lesser trochanter is found medial and inferior to the neck. Below the neck is the shaft (body) of the femur. It is angled so the distal end is more medial than the proximal end. This allows for better balance. The proximal region of the shaft has the gluteal tuberosity (bony projection) on the posterior side. This is the attachment site of gluteal muscles.

The distal region of the femur articulates with the tibia (shin bone) at medial and lateral condyles (round bony protrusions at the end of a bone). Each side of the condyles contains an epicondyle. The medial and lateral epicondyles are attachment points for knee stabilizing ligaments. The anterior distal end of the femur has a smooth patellar surface that articulates with the patella (kneecap) found within the major tendon of the quadriceps muscle of the leg. The patella is a short, triangular bone that protects the knee joint and prevents the muscle tendon in the quadriceps from rubbing against the distal end of the femur. The lower leg is found between the knee and ankle and is made up of two bones, the tibia and fibula. The tibia, also known as the shinbone, articulates with the femur. The tibia is the second longest bone in the body. The proximal end of the tibia consists of flat medial and lateral condyles that articulate with the round condyles of the femur to form the knee joint. The anterior surface of the tibia, near the proximal end, has a tibial tuberosity. The tibial tuberosity is the site of anterior thigh muscle attachment. The medial malleolus is a large bony bump that is found beyond the shaft at the distal end of the tibia. The medial malleolus can be palpated (felt) medially near the ankle. It forms a partial socket used to articulate with the talus bone of the ankle. The fibula is a thin long bone lateral to the tibia that acts to stabilize the ankle. The fibula is much thinner than the tibia. Found on the lateral side of the leg, it does not bear weight like the tibia. Its main function is to provide a site for muscle attachment in the leg. In fact, a lot of muscles surround this bone. Articulation with the tibia occurs at the head of the fibula, which is a small round structure found at the proximal end of the fibula. At this articulation between the fibula and tibia, a superior tibiofibular joint is formed. At the distal end, the fibula and tibia articulate at the inferior tibiofibular joint. A palpable lateral malleolus is at the distal end of the fibula, opposite the medial malleolus of the tibia.

The ankle and foot form a complex structure, which includes an arch in the center. The 33 joints found in this region provide flexibility and allow for balance and shock absorption during locomotion. The ankle and foot are made up of short bones called tarsals, long bones called metatarsals, and the phalanges. Each tarsal bone makes up a set of seven short bones that form the ankle and the posterior portion of the foot. They include the talus, calcaneus, cuboid, navicular, medial cuneiform, intermediate cuneiform, and lateral cuneiform. The talus bone articulates with the tibia and fibula of the lower leg to create the ankle joint. The tibia bears weight on the talus, while the fibula stabilizes the ankle joint. The calcaneus tarsal is the heel of the foot and the largest of the tarsals. In order to be weight bearing, the remaining five bones are tightly held together with the help of ligaments below the talus. The navicular bone is distal to the talus bone and proximal to the three cuneiform bones, which articulate with the navicular bone. The cuboid bone runs laterally to the navicular and lateral cuneiform bones. Collectively, these five bones bond together to form a wedge-shaped structure. This shape is important, as it contributes to the formation of the natural curve or arch in the foot.

The front region of the foot is made of metatarsals and phalanges (toes). Each metatarsal bone makes up a set of five bones that helps form the arch in the foot, articulate with the distal tarsals. Like the metacarpals in the hand, metatarsals are numbered from I to V beginning with the medial side of the foot, and each metatarsal contains a proximal base, a shaft, and a distal head. The arch of the foot is supported by ligaments and tendons. Its structure gives it elastic properties that help distribute the weight of the body with minimal stress on the bones and joints during locomotion. The presence of the arch also provides recoil to decrease the amount of energy expended during walking and running. Distally, the metatarsals articulate with the proximal phalanges of the toes, forming a metatarsophalangeal joint.

Both fingers and toes are called phalanges, and these bones have many similarities. Starting with the medial (big) toe called the hallux, these are numbered from I to V. The hallux has a proximal and distal phalange, and phalanges II to V have a proximal, middle, and distal. When the phalange bones articulate with one another, an interphalangeal joint is formed. All metatarsals and phalange bones have a proximal base, a shaft, and a distal head. The phalanges of the foot are shorter than the phalanges of the hand and are not nearly as dexterous. While the fingers specialize in grasping and manipulating objects, the toes function to provide balance, stability, and a platform to push off during walking and running and also help push the body forward during these movements.