Video: Main bones of the lower limb

Our legs are pretty important. I mean, they help us walk, run, stand, and even dance. The Irish dancing star, Michael Flatley certainly viewed his legs as a prized possession as he's had his insured for a whopping 40 million dollars. If I were ever going to insure my legs, I would really want to know all about them first. I mean, we all know that the foot bone’s connected to the leg bone, the leg bone’s connected to the knee bone – but it's a bit more complex than that. Don't worry, though, because I'm going to guide you step-by-step throughout today's tutorial on the main bones and joints of the lower limb. You can decide at the end if you think your legs are worth insuring or not.

The bones and joints of the lower limb can be divided into three separate groups which include the bones of the pelvic girdle and thigh, the bones of the leg, and the bones of the foot. We'll begin today's tutorial at the most proximal region of the lower limb where we will discuss the bones and joints of the pelvic girdle and thigh. Then we will move distally to reach the bones and joints of the foot. To finish off, we'll take a quick look at some clinical applications to help consolidate our knowledge.

So let's begin with the bones and associated joints of the pelvic girdle and thigh.

Highlighted here in green is the bony pelvis. The pelvic girdle forms the anterolateral aspect of the bony pelvis. It's made up of two hip bones – a left hip bone and a right hip bone – which are also known as the innominate bones of the pelvis. Each hip bone is actually composed of three bones – the ilium, the ischium, and pubis – that fuse together towards the end of puberty. These three bones contribute to the formation of a socket-like structure known as the acetabulum, which we can see here from this lateral view of the left hip bone. Let's take a closer look at each of these three bones now.

The ilium is the large wing-like bone of the pelvis that extends superiorly. It is the largest of the three elements of the hip bone and it contributes to the superior formation of the acetabulum. Due to the orientation of the bony pelvis, the anterosuperior aspect of the ilium, highlighted here in green, can be easily identified and palpated. Just try to find it on yourself.

The ischium is the L-shaped bone that forms the posteroinferior part of the hip bone and thus contributes to the posteroinferior formation of the acetabulum as we can see here. The pubis is the smallest and most medially located element of the hip bone. It lies just anterior to the urinary bladder. The pubis contributes to the anteroinferior position of the acetabulum. The ischium and pubis together form the large obturator foramen.

Now let's take a look at this anterior view of the pelvis where we can see both hip bones. Forming the posterior wall of the bony pelvis is the pelvic spine or the pelvic portion of the vertebral column which is composed of two bones – the sacrum and the coccyx. The sacrum is located at the bottom of the vertebral column and is formed by the fusion of the five sacral vertebrae.

Articulating with the distal end of the sacrum is the coccyx. It marks the terminal end of the vertebral column and kind of looks like a little tail which is why it is known as the tailbone. The pelvic girdle and the pelvic spine together form the bony pelvis of the human body. Each hip bone articulates anteriorly with the pubic symphysis with its counterpart from the other side. The pubic symphysis is a cartilaginous connection between both pubis of the hip bones. Posteriorly, the ilium of both hip bones articulates with the sacrum at the sacroiliac joints forming a continuous ring of bone. We can see the two sacroiliac joints in this image here.

Another very important part of this region is the hip joint, a synovial ball-and-socket articulation between the hip bone and the femur. Let's take a closer look at the joint with this image which is a lateral perspective of the left hip joint with the bone separated so that we can have a better look at the articular surfaces.

As we have seen already, the acetabulum forms the socket component of the hip joint while the ball is formed by the head of the femur. The hip joint is a highly mobile joint allowing for three degrees of freedom. Ball-and-socket joints are the most mobile joints in the human body but consequently are also subject to instability.

Moving distally, we find the femur which is the longest and strongest bone of the body. The location of this bone can be determined by its name as femur is the Latin word for the thigh. This bone therefore sits between the hip and knee joint forming the bony framework of the thigh.

The distal aspect of the femur articulates with the patella and the tibia of the leg to form the knee joint. As we can see in this sagittal section, the knee joint consists of two articulations – the tibiofemoral and the patellofemoral articulation. The tibiofemoral joint is an articulation between the tibia and the femur while the patellofemoral joint is an articulation between the patella and the femur. These two joints work together to create movements at the knee.

The knee joint is classified as a modified hinge joint, allowing for flexion and extension as well as slight medial and lateral rotation. Slight medial rotation occurs during knee flexion and the last stage of extension of the knee whereas lateral rotation occurs when unlocking the knee. The patella sits just anterior to the knee joint which is why it is also known as the kneecap. The patella is considered to be a sesamoid bone because it is contained within a tendon. Actually, it is the largest sesamoid bone in the body and sits embedded in the tendon of the muscles of the anterior thigh. Let's take a look again at this image that shows a cross-sectional view of the knee joint, and as we've already seen, the patella articulates solely with the femur and does not articulate with the tibia at the patellofemoral joint.

Moving distally, we arrive at the bones of the leg. Many people identified the leg to be the whole lower limb; however, anatomically, the leg is defined as the region between the knee and the ankle joint. The two bones of the leg are the tibia and the fibula. The tibia is the second largest bone in the body after the femur. It is the main weightbearing bone of the leg and is therefore vitally important in standing, walking, and running. Lateral to the tibia, we find another bone of the leg – the fibula.

The fibula is a long thin bone on the lateral aspect of the leg. If you ever break a bone in your leg, it is much more likely that you will break your fibula rather than your tibia due to its slight frame and lateral positioning. The fibula sits tucked in under the proximal part of the tibia forming here the superior tibiofibular joint. This joint is a plane synovial joint allowing for slight gliding movements of the fibula against the tibia. The distal aspect of the tibia and fibula articulate together to form the inferior tibiofibular joint. This joint aids in holding the fibula securely against the tibia to prevent displacement. It is a fibrous joint as both bony surfaces of the joint are bound by a fibrous tissue.

The distal aspect of both tibia and fibula contributes to the formation of the ankle joint. In this joint, the distal parts of the tibia and fibula articulate with the body of the talus which is a bone of the foot. The bony prominences that you can feel on the medial and lateral aspects of the ankle are bony protrusions of the tibia and fibula known as the medial and lateral malleoli. The ankle is classified as a synovial hinge joint. This joint mainly allows dorsiflexion and plantarflexion of the foot which leads us to the next section of this tutorial which is the bones of the foot.

The foot contains a total of 26 bones which can be divided into three separate groups – the 7 tarsal bones, the 5 metatarsal bones, and the 14 phalanges. The tarsal bones include the calcaneus, the talus, the navicular, the cuboid, and the three cuneiform bones. The calcaneus and talus form the proximal row of tarsal bones while the navicular, cuboid, and cuneiform bones form the distal row of tarsal bones.

So starting with the proximal row, we've already talked about the talus. This bone can also be known as the ankle bone as it is the linking bone between the foot and the leg. Inferior to the talus and supporting it, we find the largest and most posterior bone of the foot which is the calcaneus. This is the protruding heel bone which plays an important role in weightbearing and stability.

Moving on to the distal row of tarsal bones, we meet the navicular bone which lies just distal to the talus. Navi in Latin means boat thus describing the rocker bottom boat-like appearance of the bone. The navicular bone lies on the medial aspect of the foot and articulates proximally with the talus and distally with the cuneiform bones. You can easily palpate the navicular bone on the medial aspect of your foot. Lateral to the navicular bone, you can find the cuboid bone. The cuboid is a cube-shaped bone, as its name suggests, which articulates with the calcaneus proximally, the navicular and cuneiforms medially, and the metatarsal bones distally. Medial to the cuboid and distal to the navicular bone are these wedge-shaped cuneiform bones which are named after their location to each other. All the cuneiform bones articulate with the navicular proximally and the metatarsal bones distally.

Let's change to an inferior perspective of the foot to have a better view of the cuneiform bones. The medial cuneiform lies on the medial aspect of the foot as its name suggests and is the most medially positioned cuneiform bone. The intermediate cuneiform sits sandwiched between the other two cuneiform bones which we can see here. The lateral cuneiform is the most lateral of the cuneiform bones. It lies at the central portion of the foot and articulates with the cuboid laterally and intermediate cuneiform medially.

The 7 tarsal bones articulate with each other at the intertarsal joints. The intertarsal joints connect the tarsal bones together allowing for movement between the joints. Some of the intertarsal joints have specific names such as the subtalar joint which is the articulation between the talus and calcaneus. While other tarsal joints have limited movement, the subtalar joint is quite mobile and works together with the ankle joint to create movements of the foot.

Distal to the tarsal bones, we meet the 5 metatarsal bones. These bones are located at the middle of the foot and form a bridge between the tarsal bones and the phalanges. The metatarsal bones are named after their positioning. The metatarsal bone of the great toe is known as the first metatarsal; this is the second, third, and fourth, and finally, the more lateral is the fifth metatarsal bone. The proximal ends of the five metatarsal bones articulate with the distal row of tarsal bones forming the tarsometatarsal joints. The first three metatarsals articulate with the cuneiform bones while the fourth and fifth metatarsals articulate with the cuboid.

The tarsometatarsal joints are also known as the Lisfranc joint complex named after the French surgeon Jacques Lisfranc de St. Martin who carried out many operations on the foot. Tarsometatarsal joints are plane joints that allow slight gliding movements.

The distal ends of the metatarsal bones articulate with the next group of bones in the foot – the phalanges. The phalanges are the bones which can be found in our toes. The phalanges are divided into proximal, middle, and distal phalanges. Much like the metatarsal bones, the phalanges are also numbered from one to five with the great toe containing the first phalanges and the little toe the fifth.

The proximal phalanges, as their name suggests, are the most proximally located phalanges. There are five proximal phalanges, one in each toe of the foot. The proximal ends of the proximal phalanges articulate with the distal ends of the metatarsals forming the metatarsophalangeal joints. These joints are also numbered according to each toe or digit. For example, these are the second, third, and fourth metatarsophalangeal joints. The metatarsophalangeal joints allow for two degrees of freedom and permit movements of the toes.

The middle phalanges lie sandwiched between the proximal and distal phalanges. There are only four middle phalanges in each foot as there is none in the great toe. The middle phalanges are numbered from two to five with this one being two and this one five.

The final bones of the foot are the distal phalanges. There are five distal phalanges, one in each toe. These tiny bones can be found at the tips of our toes. In the four lateral toes, there are proximal, middle, and distal phalanges but in the great toe which is also known as the hallux, there's only a proximal and distal phalanx. The proximal and distal phalanges are therefore larger in the great toe.

The articulations between these phalanges are known as the interphalangeal joints. Between the proximal and middle phalanges are the proximal interphalangeal joints and between the middle and distal phalanges we find the distal interphalangeal joints. Proximal and distal interphalangeal joints can only be found in digits two to five. As there are only two phalanges in the great toe, the articulation is just known as the interphalangeal joint. All interphalangeal joints are hinge joints thus only allowing movements of flexion and extension.

Before we complete this tutorial, let's just take a quick look at some clinical notes on the bones of the lower limb.

While most people have 26 bones in their feet, some people can actually have a few extra. An os trigonum is an extra or accessory bone of the talus present in some individuals. This small accessory bone usually develops as the posterior aspect of the talus and protrudes posteriorly. In the majority of cases, it causes no problems at all. Many people don't even know they have an os trigonum. When problematic, it is known as trigonum syndrome. This syndrome which is also known as the nutcracker injury can often occur in ballerinas, Irish dancers, and even soccer players. Continual plantarflexion of the foot when pointing the toes can cause the os trigonum to be crunched between the talus and the calcaneus much like a walnut in a nutcracker's mouth. This leads to friction between the os trigonum, the talus, and the calcaneus which can be painful and debilitating.

As it is a bony pathology, it can be diagnosed by x-ray and other imaging modalities. Treatment usually involves rest and ice and, in extreme cases, surgery.

Before we complete this tutorial, let's just quickly go over what we learnt today.

We begin this tutorial by looking at the bones of the pelvic girdle and thigh. The pelvic girdle is made up of the two hip bones and the pelvic spine is composed of the sacrum and the coccyx. Each hip bone is composed of three fused bones – the ilium, the ischium, and pubis. The bone of the thigh – the femur – articulates with the hip bone at the ball-and-socket hip joint.

Then we took a quick look at the knee joint where the distal aspect of the femur articulates with the tibia and patella. Moving distally, we describe the bones of the leg – the tibia and the fibula. The tibia is the main weightbearing bone of the leg. The fibula lies on the lateral aspect of the leg and articulates with the tibia at the superior and inferior tibiofibular joints. The distal aspect of the tibia and fibula articulates with the talus of the foot forming the ankle joint.

The bones of the foot can be divided into the tarsal bones, metatarsal bones, and phalanges. The tarsal bones include the calcaneus, talus, navicular, three cuneiforms, and cuboid bones. The tarsal bones articulate with each other at intertarsal joints. Distal to the tarsal bones are the metatarsal bones one to five. Proximally, the metatarsal bones articulate with the cuneiforms and cuboid bones at the tarsometatarsal joints. Distally, the five metatarsal bones articulate with the phalanges.

The phalanges are divided into proximal, middle, and distal phalanges. There are five proximal phalanges, one in each toe. The proximal phalanges articulate with the metatarsal bones at the metatarsophalangeal joints. We then met the middle phalanges. There are only four middle phalanges as there is none in the great toe. The middle phalanges articulate with the proximal phalanges at the proximal interphalangeal joints. The distal phalanges are at the tips of our toes. There are five distal phalanges, one in each toe. The distal phalanges articulate with the middle phalanges at the distal interphalangeal joints.

We finish the tutorial with a quick look at an accessory bone known as the os trigonum which can be found on the posterior aspect of the talus. When an os trigonum is problematic, it is known as trigonum syndrome. It is most commonly identified in ballerinas, Irish dancers, and soccer players due to regular plantarflexion movement at the ankle.

This brings our tutorial to a close. I hope you enjoyed learning about the bones of the lower limb, and happy studying!