Anatomy and Physiology 2e · The Appendicular Skeleton
Bones of the Lower Limb
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In 30 seconds
Each lower limb contains 30 bones, mirroring the upper limb's count but built for the opposite job. Where the upper limb maximizes mobility and fine control, the lower limb maximizes weight bearing, stability, and propulsion: the Femur The thigh bone — longest, heaviest, strongest bone in the body Full entry → (thigh), the Patella The kneecap — largest sesamoid bone, in the quadriceps tendon (kneecap), the Tibia The thick, medial, weight-bearing bone of the leg ("shin") Full entry → and Fibula The slender, lateral, non-weight-bearing bone of the leg Full entry → (leg), and the 26 bones of the foot — 7 tarsals, 5 metatarsals, and 14 phalanges.
The lower limb is organized for strength at every level. The femur is the longest, heaviest, and strongest bone in the body, built to carry the body's full weight on a single leg while walking. The tibia is the thick, medial weight-bearing bone of the leg, while the slender fibula is a lateral splint that mostly anchors muscles. The foot is a springy arch of small bones that absorbs impact and pushes off the ground. The same proximal-to-distal learning order works: femur → patella → tibia/fibula → tarsals → metatarsals → phalanges, with each joint (hip, knee, ankle) as the checkpoint between segments.
A useful habit is to compare the two limbs bone by bone: femur ↔ humerus, tibia/fibula ↔ radius/ulna (with reversed roles — the weight-bearing bone is medial in the leg but lateral in the forearm), tarsals ↔ carpals, metatarsals ↔ metacarpals, phalanges ↔ phalanges. The parallels make both lists easier to remember.
Why this matters
The lower limb is where the body meets the ground, so its bones carry the consequences of aging, injury, and daily wear:
- Hip fractures — most often through the neck of the femur in older adults with osteoporosis — are a leading cause of hospitalization and loss of independence in that population. The Femoral neck The angled region between the femoral head and shaft Full entry →'s anatomy (long, angled, with blood supply running along it) explains both why it breaks and why the head may lose its blood supply.
- Ankle injuries are among the most common musculoskeletal problems in clinics; the ankle's bony landmarks — the medial malleolus (tibia) and lateral malleolus (fibula) — frame the joint and tell you which bone is involved when the ankle twists.
- Knee problems center on the patella and the femoral condyles; the patella is the largest sesamoid bone in the body and a familiar source of anterior knee pain.
- Foot structure — the arches and their supporting bones and ligaments — explains flat feet, heel pain, and why the foot can absorb the force of running.
For clinicians, the lower limb's palpable landmarks (greater trochanter, Tibial tuberosity The bump on the front of the proximal tibia Full entry →, Malleoli The ankle bumps — medial (tibia) and lateral (fibula) Full entry →) are used constantly for assessment and describing pain — and for students, the femur, tibia, fibula, and foot bones are exam staples.
The college version
Core Concepts
The femur: the body's strongest bone
The femur has a rounded head that fits the acetabulum, with a small pit (the fovea capitis) for a ligament attachment. The neck angles the head out to the side; just below sit the greater trochanter (lateral, palpable at the hip) and lesser trochanter (posteromedial), connected by the intertrochanteric line and crest. The shaft is marked posteriorly by the linea aspera, a ridge where many thigh muscles attach. Distally the femur widens into the medial and lateral condyles, which rest on the tibia, and the medial and lateral epicondyles above them; between the condyles in front lies the smooth patellar surface where the kneecap glides, and behind them the intercondylar fossa houses the cruciate ligaments.
The neck of the femur deserves special attention: in older adults, especially those with osteoporosis, a fall can fracture it. Because the blood supply to the femoral head travels along the neck, some of these fractures interrupt it, putting the head at risk of avascular necrosis. That is why hip fractures in older adults are often treated surgically — a decision made by the care team, but one you can now explain anatomically.
The patella: the body's largest sesamoid bone
The patella is a triangular bone embedded within the tendon of the quadriceps femoris — a sesamoid bone, meaning it forms inside a tendon. It protects the front of the knee, increases the quadriceps' leverage, and glides on the patellar surface of the femur. Notably, it articulates only with the femur, not the tibia; its distal point anchors the patellar ligament to the tibial tuberosity.
The tibia and fibula: the leg pair
The tibia is the thick, medial bone of the leg and the only one that bears weight. Its proximal end has medial and lateral condyles (the "plateaus") that receive the femoral condyles, separated by the intercondylar eminence; the tibial tuberosity on the front is where the patellar ligament attaches — the bump below the kneecap. The sharp anterior border is the "shin." Distally, the tibia forms the medial malleolus (the inner ankle bump) and articulates with the Talus The tarsal that receives the tibia and fibula Full entry → of the foot.
The fibula is the slender, lateral bone of the leg. It does not bear body weight and does not articulate with the femur; it attaches to the tibia, anchors many muscles, and its distal end forms the lateral malleolus (the outer ankle bump), part of the ankle joint. The common fibular (peroneal) nerve wraps around the fibular neck, so fractures or pressure there can produce foot drop — a classic teaching point. The tibia and fibula are connected by the interosseous membrane, like the radius and ulna.
The foot: tarsals, metatarsals, phalanges
The foot's 7 tarsals include the talus (which receives the tibia and fibula and forms the ankle joint), the Calcaneus The heel bone, the largest tarsal Full entry → (the heel bone — the largest tarsal, taking the body's weight on the ground), the navicular, the cuboid, and the three cuneiforms (medial, intermediate, lateral). The 5 metatarsals form the instep and the ball of the foot, and the 14 phalanges form the toes: the great toe has 2, the other toes have 3 each.
The foot is not flat — it is arched. The medial longitudinal arch (high, springy), the lateral longitudinal arch (low), and the transverse arch are maintained by the shapes of the bones, strong ligaments (including the plantar fascia), and tendons that act like guy-wires. When these supports weaken, the arches can flatten (Pes planus Collapsed ("flat") foot arches Full entry →, "flat feet") — usually harmless, though it can contribute to foot pain in some people.
Common Confusions
| Do not confuse | With | Difference |
|---|---|---|
| Tibia | Fibula | Tibia is medial and weight-bearing (shin, medial malleolus); fibula is lateral, slender, non-weight-bearing (lateral malleolus) |
| Talus | Calcaneus | Talus is the ankle bone that meets the tibia/fibula; calcaneus is the heel bone on the ground |
| Medial malleolus | Lateral malleolus | Medial = tibia (inner ankle); lateral = fibula (outer ankle) |
| Patella articulating with the tibia | The knee being two bones | The patella articulates only with the femur's patellar surface; the femur–tibia contact is the main knee articulation |
| Greater trochanter | Lesser trochanter | Greater is lateral and palpable at the hip; lesser is posteromedial, below the neck |
| Tarsals | Metatarsals | Tarsals = 7 bones of the ankle/heel area; metatarsals = 5 bones of the instep/ball of the foot |
| Femoral head fracture | Femoral neck fracture | Both are "hip fractures," but the neck is the classic fracture site in older adults, with the blood-supply risk |
| Scaphoid (wrist) | Navicular (foot) | Scaphoid is a carpal; navicular is a tarsal — similar names, different limbs |
| Upper-limb parallel: radius/ulna | Tibia/fibula | In the forearm the weight-leading bone (radius) is lateral; in the leg the weight-bearing bone (tibia) is medial — the roles flip |
Eli explains
The same idea, in plain words
Explain it like I’m 10
Your leg bones are like the strong parts of a bridge, because they hold up your whole body. The femur is the longest, toughest bone in your body — the main steel beam. Below the knee, the thick shin bone (tibia) carries the weight; the skinny bone beside it (fibula) is more like a handrail for muscles. Your foot is a springy arch of small bones — like a curved bridge deck — that squashes a little when you land and springs back when you push off to walk or run.
Worked example
An 82-year-old woman with osteoporosis slips on a rug and falls, landing on her right side. She feels pain in the right hip and cannot stand, and her right leg appears shortened and slightly rotated outward. Walking through the anatomy: the force of the fall traveled through the greater trochanter into the femoral neck. With bone weakened by osteoporosis, the long, angled neck gave way. Because the vessels to the femoral head run along the neck, the fracture can deprive the head of blood — why it is treated seriously and usually surgically. The same fall in a young person with strong bone might produce no fracture. The educational point: knowing the femur's anatomy — neck, trochanters, blood supply — explains the classic "shortened, externally rotated leg" sign and why hip fractures in older adults are treated as urgent. The bedside clinician's role is assessment, comfort, and reporting; diagnosis and treatment decisions belong to the care team.
Key takeaways
- Lower limb = 30 bones: 1 femur + 1 patella + tibia and fibula + 7 tarsals + 5 metatarsals + 14 phalanges.
- Femur = longest, heaviest, strongest bone; head → neck (fracture site in older adults) → greater/lesser trochanters → linea aspera → medial/lateral condyles → patellar surface.
- Patella = largest sesamoid bone, embedded in the quadriceps tendon; articulates only with the femur, not the tibia.
- Tibia = medial, weight-bearing (shin, medial malleolus, tibial tuberosity); fibula = lateral, non-weight-bearing (lateral malleolus; common fibular nerve wraps its neck).
- Femoral neck fractures can interrupt the blood supply to the femoral head → avascular necrosis risk.
- Foot: talus (ankle joint) + calcaneus (heel) + navicular, cuboid, 3 cuneiforms + 5 metatarsals + 14 phalanges (great toe has 2).
- Foot arches (medial/lateral longitudinal, transverse) supported by bones, ligaments (plantar fascia), and tendons; collapse → pes planus (flat feet).
- Ankle landmarks: medial malleolus (tibia) and lateral malleolus (fibula) frame the joint; the ankle's most common sprains involve the lateral ligaments.
- Upper↔lower parallels: humerus↔femur, radius/ulna↔tibia/fibula (weight-bearing role reversed), carpals↔tarsals, metacarpals↔metatarsals.
Check yourself
6 review questions from the chapter. Try each one, then open the answer.
What are the 30 bones of one lower limb, broken down by region?
Show answer
1 femur, 1 patella, 2 leg bones (tibia, fibula), 7 tarsals, 5 metatarsals, and 14 phalanges.
Which bone of the leg bears body weight, and which one does not? Where is each malleolus?
Show answer
The tibia (medial) bears weight; the fibula (lateral) does not. The medial malleolus is part of the tibia; the lateral malleolus is part of the fibula.
Why is the femoral neck a classic fracture site in older adults, and what is the blood-supply concern?
Show answer
The neck is long and angled, and osteoporosis thins bone with age; the blood supply to the femoral head runs along the neck, so the fracture can interrupt it, risking avascular necrosis of the head.
Which bones form the ankle joint, and what is the role of the talus?
Show answer
The talus articulates with the tibia and fibula — it is the bone that forms the ankle joint proper; the calcaneus is the heel bone below it.
The patella articulates with which bone(s)?
Show answer
Only the femur (its patellar surface). The patella does not articulate with the tibia.
Name the three arches of the foot and what supports them.
Show answer
Medial and lateral longitudinal arches and the transverse arch, supported by bone shape, ligaments (including the plantar fascia), and tendons acting like guy-wires.
Study tools & related lessonsKey vocabulary · Related
Key vocabulary
- Femur
- The thigh bone — longest, heaviest, strongest bone in the body
- Femoral neck
- The angled region between the femoral head and shaft
- Greater / lesser trochanters
- Two large projections just below the femoral neck
- Patella
- The kneecap — largest sesamoid bone, in the quadriceps tendon
- Tibia
- The thick, medial, weight-bearing bone of the leg ("shin")
- Fibula
- The slender, lateral, non-weight-bearing bone of the leg
- Tibial tuberosity
- The bump on the front of the proximal tibia
- Malleoli
- The ankle bumps — medial (tibia) and lateral (fibula)
- Talus
- The tarsal that receives the tibia and fibula
- Calcaneus
- The heel bone, the largest tarsal
- Tarsals / metatarsals / phalanges
- 7 ankle/foot bones / 5 instep bones / 14 toe bones
- Pes planus
- Collapsed ("flat") foot arches
Sources & references
This lesson was adapted from the open educational references above; their licenses and attributions are preserved. See Copyright & Licensing.
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