Pelvis & lower limb · Knee
Patella
The patella is the flat, triangular bone at the front of the knee. It lies within the quadriceps tendon, articulates with the patellar surface of the femur, and is continued below by the patellar ligament to the tibial tuberosity.
- Latin (TA)
- Patella
- Type
- Sesamoid bone: it develops inside a tendon
- Side
- Paired — right and left
- Model size
- 4.3 cm longest
Showing a right bone. Rotate it to inspect every surface; switch sides to practise siding.
3D model: Z-Anatomy (CC BY-SA 4.0), derived from BodyParts3D © DBCLS (CC BY-SA 2.1 JP). Adapted by PharmaWallah. Credits & licence
Landmarks
0 of 11 marked on the modelTap a landmark to find it on the bone and read what it is.
The thick upper border of the patella.
Where: Superiorly.
Why it matters: The quadriceps femoris tendon is attached to it.
Related: Quadriceps femoris tendon (rectus femoris and the vasti).
The pointed lower end of the patella.
Where: Inferiorly.
Why it matters: Gives attachment to the patellar ligament; pointing it downwards is the first step in orienting the bone.
Related: Patellar ligament.
Viva: What is attached to the apex of the patella?
The convex front surface, rough and pitted.
Where: Facing forwards, under the skin.
Why it matters: Covered by fibres of the quadriceps tendon; the prepatellar bursa lies between it and the skin.
The smooth, oval, cartilage-covered posterior surface.
Where: On the back of the patella, occupying most of it except the lower part near the apex.
Why it matters: Articulates with the patellar surface of the femur at the patellofemoral part of the knee joint.
Related: Patellar surface of the femur.
A smooth vertical ridge running down the articular surface.
Where: On the posterior surface, nearer the medial border.
Why it matters: Divides the articular surface into the lateral and medial facets; it fits the groove of the femoral patellar surface.
The larger articular facet, lateral to the vertical ridge.
Where: On the lateral part of the posterior surface.
Why it matters: Articulates with the lateral part of the femoral patellar surface; because it is larger, it is used to side the bone.
Viva: Which articular facet of the patella is larger?
The smaller articular facet, medial to the vertical ridge.
Where: On the medial part of the posterior surface.
Why it matters: Articulates with the medial part of the femoral patellar surface.
The thin medial edge of the patella.
Where: On the medial side, between the base and the apex.
Why it matters: Vastus medialis and the medial patellar retinaculum attach here; their pull helps prevent lateral displacement of the patella.
The lateral edge of the patella.
Where: On the lateral side, between the base and the apex.
Why it matters: Vastus lateralis and the lateral patellar retinaculum attach here.
Classification & region
Sesamoid bone: it develops inside a tendon (the quadriceps femoris tendon) where the tendon passes over a joint. It is the largest sesamoid bone in the body.
- Base
- The broad upper border, to which the quadriceps femoris tendon is attached.
- Apex
- The pointed lower end, to which the patellar ligament is attached.
- Anterior surface
- The rough, convex front surface, lying under the skin and crossed by tendon fibres.
- Articular (posterior) surface
- The smooth back surface covered by cartilage, divided by a vertical ridge into a larger lateral facet and a smaller medial facet; it glides on the patellar surface of the femur.
Hold it in the anatomical position
- Put the pointed apex downwards and the broad base upwards.
- Turn the smooth articular surface backwards (towards the femur) and the rough surface forwards.
Right or left? Side determination
- Place the apex downwards.
- Turn the smooth articular surface backwards, as if the bone were on your own knee (rough surface facing away from you).
- Find the vertical ridge on the articular surface and compare the two facets on either side of it.
- The larger, broader facet is the lateral facet: it lies on the side the bone belongs to. If the larger facet is on your right, it is a right patella.
Check yourself: switch the 3D model to “Left bone” and apply the same steps.
Articulations
- With the femur (patellar surface) at the Knee joint (patellofemoral part) — Articular (posterior) surface with its lateral and medial facets.
Muscle and ligament attachments
| Structure | Type | Where on the bone |
|---|---|---|
| Quadriceps femoris tendon (rectus femoris, vastus intermedius) | insertion | Base and anterior surface |
| Vastus medialis | insertion | Base and medial border |
| Vastus lateralis | insertion | Base and lateral border |
| Patellar ligament | ligament | Apex and the adjoining non-articular part of the posterior surface (runs to the tibial tuberosity) |
| Medial and lateral patellar retinacula | ligament | Medial and lateral borders |
Functions
- Increases the leverage of quadriceps femoris by holding its tendon further in front of the knee, making extension more efficient.
- Protects the front of the knee joint.
- Reduces friction between the quadriceps tendon and the femur as the knee bends and straightens.
Clinical & practical relevance
- Lateral dislocation of the patella occurs because the pull of quadriceps is directed slightly laterally; the vastus medialis, the medial retinaculum and the prominent lateral lip of the femoral patellar surface resist it.
- A direct blow or a violent quadriceps contraction can fracture the patella; if the fragments separate, the extensor mechanism of the knee is disrupted.
- Prepatellar bursitis ('housemaid's knee') is inflammation of the bursa in front of the patella, from repeated kneeling.
- The patellar ligament is tapped to test the knee-jerk (patellar) reflex, segments L3 and L4.
- A bipartite patella (an unfused separate piece, usually at the upper lateral corner) can be mistaken for a fracture on an X-ray.
Identification tips
- Apex down, articular surface back, larger facet tells the side.
- The patella touches only the femur: the patellar ligament, not the bone, reaches the tibia.
- 'Patellar ligament' and 'patellar tendon' are the same structure: it is the continuation of the quadriceps tendon.
Common student mistakes
- Saying the patella articulates with the tibia: it articulates only with the femur.
- Siding by the medial facet: the larger facet is lateral.
- Calling the patella a short bone: it is a sesamoid bone.
- Holding it with the apex upwards; the base is the broad upper border.
Common exam questions
Why is the patella called a sesamoid bone?Show answer
It develops within the tendon of quadriceps femoris where the tendon passes over the knee joint.
How do you determine the side of a patella?Show answer
Apex down, articular surface backwards; the larger lateral facet lies on the side the bone belongs to.
Name the attachments of the patella.Show answer
Quadriceps tendon to the base; vastus medialis and lateralis to the borders; patellar ligament to the apex; the retinacula to the medial and lateral borders.
Give the functions of the patella.Show answer
It increases the leverage of quadriceps, protects the knee, and reduces friction of the quadriceps tendon over the femur.
Why does the patella tend to dislocate laterally, and what prevents it?Show answer
Quadriceps pulls slightly laterally; vastus medialis, the medial retinaculum and the higher lateral lip of the femoral patellar surface resist it.
With which bone and surface does the patella articulate?Show answer
With the patellar surface of the femur only, at the patellofemoral part of the knee joint; it does not articulate with the tibia.
Revision summary
- Largest sesamoid bone, in the quadriceps tendon.
- Base above (quadriceps tendon); apex below (patellar ligament).
- Posterior articular surface: larger lateral facet, smaller medial facet, separated by a vertical ridge.
- Articulates only with the patellar surface of the femur.
- Improves the leverage of quadriceps and protects the knee.
- Lateral dislocation is resisted by vastus medialis and the lateral lip of the femoral patellar surface.
Test yourself on the patella
Spotting questions on bones, sides and landmarks — untimed, with explanations.
Joints of the patella
References
- Drake RL, Vogl AW, Mitchell AWM. Gray's Anatomy for Students. 5th ed. Philadelphia: Elsevier; 2023.
- Moore KL, Dalley AF, Agur AMR. Moore's Clinically Oriented Anatomy. 9th ed. Philadelphia: Wolters Kluwer; 2023.
- Federative International Programme for Anatomical Terminology (FIPAT). Terminologia Anatomica. 2nd ed. FIPAT.library.dal.ca; 2019. fipat.library.dal.ca/TA2
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