The dog sesamoid bones are present near free-moving joints of the limbs. These small sesame-like bones develop within the tendons of a dog’s limbs.
Here, I will show the location of sesamoid bones in the dog with their number from each leg. In this article, you will also find the detailed anatomy of the largest sesamoid bone in a dog.
Quick overview: 98 small sesamoid bones develop within the moving joints of the dog’s legs. These bones have no Haversian system and no periosteum. You will find only one articular surface in these sesamoid bones that glide on a flat or convex surface of the leg’s bones.
I will also discuss the number of sesamoid bones from other animals compared to the dogs. Thus, you will count and identify various types of sesamoids from different animals with their specific location.
What are the sesamoid bones, and where are they located in a dog?
The sesamoids of the dogs are the small seed or sesame-like bones usually formed in the tendon. They may also develop in the ligamentous tissue over which the tendon passes.
Location: The sesamoid bones of a dog are located on the flat or convex surface of the long bones. You will usually find them near freely moving joints of the extremities bones.
Here, the diagram shows the typical features of the sesamoid bones from the dog’s leg. Anatomically, these sesamoid bones possess only one articular surface.
You may easily differentiate these sesamoid bones from other various types of bones of the canine skeleton. The below-mentioned article might help you to get the full idea of various types of bones from animal skeletons –
The main function of these bones is to protect tendons where the greatest friction is developed. Thus, they work as pully to avoid friction in the freely moving joints of the dog’s limb.
Let’s see the typical features of the canine sesamoid bone –
- Small elongated and slightly curved bones (size and shape may vary),
- Occurs in the moving joints of the extremities bones,
- Possess only one caudal articular surface,
The patella is the typical sesamoid bone of the dog’s stifle joint. All the features mentioned above of a sesamoid bone are present in the dog’s patella.
Type of dog sesamoid bone
Typically, you will find 2 major types of sesamoid bones in the dog’s limbs –
- Proximal sesamoid bones – located at the posterior aspect of the metacarpal and metatarsal bones and
- Distal sesamoid bones – located at the caudal aspect between the second and third phalanges of fore and hind limbs,
So, you might have good knowledge of the bones of the forelimb and hind limbs of the dogs. Thus, you will easily identify the location of these sesamoid bones from the dogs’s front and back legs.
The below-mentioned article will provide the complete guide on various bones of dog’s legs –
Proximal sesamoids in dog leg
You will find 2 proximal sesamoid bones on the palmar surface of each metacarpophalangeal joint. They are elongated and slightly curved small bones located in the tendon of insertion of the interosseous muscles.
They articulate with the corresponding facets at the palmar aspect of the distal end of the large metacarpal. Again, they also articulate at the palmar aspect with the proximal end of each first phalanx.
The anterior surfaces of these sesamoids are concave. Again, the articular and posterior surfaces of the sesamoids are convex.
For digits II – V of the dog’s forelimb, you will find 2 proximal sesamoid bones in each. However, a single sesamoid bone is located on the posterior aspect of the metacarpophalangeal joint of the digit I.
Thus, you will find 9 sesamoid bones in between the metacarpals and phalanges. Again, you will also find a similar number of proximal sesamoids between the metatarsal and phalanges.
- Total proximal sesamoid bones in dog’s limbs (fore and hind limb) = 36 (thirty-six),
The diagram shows the proximal sesamoid bones from the dog’s fore and hind limbs.
Distal sesamoids in the dog legs
First, I like to show you the location of the distal sesamoids from the dog’s legs. The distal sesamoids are located at the dorsal part of the metacarpophalangeal joint and between the 2nd and 3rd phalanges.
These are the small bony nodules found only on the dorsal surface of four main digits. But the cow and horse do not possess these small bony nodules on the metacarpophalangeal joint like the dogs.
The typical distal sesamoid bones are found at both the dorsal and palmar aspects of the distal interphalangeal joints. These are the cartilaginous sesamoids in the dog’s legs.
Total distal sesamoid bones (cartilaginous structure) –
- Dorsal to metacarpophalangeal joint = 4,
- Dorsal and palmar aspects of distal interphalangeal joints = (5+5) = 10,
So, the distal sesamoids in both the fore and hind limbs of the dog = 56. The calculation for the total proximal and distal sesamoids of the dog will provided in the next section.
The cow’s legs show only one posterior distal sesamoid bone for each digit.
How many sesamoid bones are in a dog?
The dog has 98 sesamoid bones both in the fore and hind limbs. I have encountered all the typical proximal sesamoid and distal cartilaginous sesamoid bones here.
Let’s see how there are 94 sesamoid bones in the dog’s legs –
- Proximal sesamoid bones in the forelimbs and hindlimbs = 36,
- Distal sesamoid bones in the forelimbs and hindlimbs = 56,
- Patella at the cranial surface of the stifle joint (hindlimbs) = 2, and
- Fabella in the dog legs = 4,
So, the total sesamoid bones in the dog’s skeleton = 98 (ninety-four).
But if you don’t count the dorsal and posterior cartilaginous sesamoid, then the number will be less. In this case, you will find 54 sesamoid bones in the dogs.
Table 1 shows the counting of the sesamoid bones from the canine skeleton –
| Dog sesamoid bones | Each Limbs | Numbers |
| Proximal sesamoid | 9 = (2 x 4 + 1×1) | 36 |
| Distal sesamoid (MPJ) | 4 | 16 |
| Distal sesamoid (dorsal and palmar) | 10 ( dorsal = 5; posterior =5) | 40 |
| Largest sesamoids | 1 (at stifle joint) | 2 |
| Fabella | 2 (lateral and medial) | 4 |
| Total sesamoids | In 4 limbs | 98 |
How many proximal sesamoids does a dog have?
Now, let’s see how there are 9 proximal sesamoids in each limb of the dog –
- The first digit possesses only 1 sesamoid at the posterior aspect of the metacarpophalangeal joint,
- The second to fifth digits possess 2 sesamoids in each at the posterior aspect of the metacarpophalangeal joints,
Thus, each limb consists of 9 sesamoid bones ( 2 bones x 4 digits + 1 bone x 1 digit).
The dorsal aspect of each of the four main digits (at a metacarpophalangeal joint) possesses 1 small bony structure. These are the dorsal sesamoids in the dog legs (both fore and hind legs).
Again, each distal interphalangeal joint possesses 1 dorsal and 1 posterior sesamoid bone. As the dog has five developed digits in each limb, you will find 10 distal sesamoids in each limb.
But 1 extra larger sesamoid is present in the stifle joint of the dog’s hindlimb. Thus, the sesamoids in each limb of the dogs are as follows –
- The right and left forelimbs of a dog = possess 46 sesamoids, and
- The right and left hindlimbs of a dog = possess 48 sesamoids,
What is the largest sesamoid bone in a dog?
The rough triangle patella is the largest sesamoid bone in a dog, located in the stifle joint. It is ovate and curved in the dog.
In the normal position, the patella of the dog articulates with the trochlea of the femur bone. And you know, the trochlea is located at the cranial distal end of the dog femur bone.
You may also know the detailed features of the dog femur bone, including the trochlea, from the below-mentioned article –
Three important patellar ligaments attach to the various surfaces of the patella. The diagram shows these 3 straight patellar ligaments from the dog stifle joint.
Let’s find more labeled diagrams on the dog’s largest sesamoid bone here.
Dog sesamoid bones anatomy
The patella (largest sesamoid) of a dog is comparatively larger than that of cows. Anatomically, this patella of the dog possesses two surfaces, three borders, and three angles.
The anterior surface of the patella is more convex in a dog. Again, the posterior articular surface is concave along the length and convex across the width.
This posterior surface is slightly smooth than the anterior and articulates with the corresponding groove of the trochlea.
The dorsal border of the dog patella is convex. Again, the lateral and medial borders of this sesamoid bone are irregular.
The medial angle is larger, whereas the lateral angle is blunt in dog patella. You will see the pointed appearance in the ventral angle of the dog patella.
The convex wider border of the dog patella is known as the base. In contrast, the pointed ventral angle is known as the apex of the patella.
So, the base is blunt and faces proximally. It extends beyond the articular surface of the patella.
However, the distally located pointed apex of the dog patella does not extend beyond the articular surface. Here, the articular surface of the patella is smooth and convex in all directions.
You will find several foramina enter this sesamoid bone from its medial aspect. The tendons from the quadriceps femoris muscles attach to the patella bone.
These tendons extend from the patella to the various aspects of the tibial tuberosity. And these are known as the patellar ligaments. You will find 3 straight patellar ligaments (dorsal, lateral, and medial) that attach to the dog patella.
Let’s know the detailed features of the dog tibia bone from the below-mentioned article –
What does the patella (largest sesamoid) bone do in the dog leg?
This largest sesamoid bone (patella) alters the direction of pull of the dog’s tendon of the quadriceps muscle. It protects the tendon and provides a greater bearing surface for running on the trochlea.
The presence of a few cartilaginous processes significantly increases the articular surface of the trochlea. These are the parapatellar fibrocartilages located on each side of the patella.
These fibrocartilages are grooved cartilage that articulates with the ridge of the femoral trochlea. You may find two or three parapatellar fibrocartilages in the stifle joint of the dog.
Dog stifle sesamoid bones
The dog has three stifle sesamoid bones in each hindlimb. One is a popliteal sesamoid, and the other two are small bean-shaped bones.
These two little bean-shaped bones are known as the fabella of the dogs. They are located in the head of the gastrocnemius muscle caudal to the stifle joint.
The third small sesamoid of the dog’s stifle is intercalated in the tendon of origin of the popliteus muscle.
The sesamoid located on the lateral head of the gastrocnemius muscle is larger compared to other sesamoids. This sesamoid is globular in shape and faces distally.
They have flat articular surfaces for articulation with the articular surface on the caudo-lateral femoral condyle.
The sesamoid in the medial head of the origin of the gastrocnemius muscle is smaller than the lateral one. It is angular and has no distinct articular surface on the medial condyle.
Dog popliteal sesamoid
The third sesamoid of the stifle joint is located in the tendon of origin of the popliteus muscle. This is the smallest sesamoid in this region and is also referred to as popliteal sesamoid in dogs.
Thus, you will find only one popliteal sesamoid bone in the hindlimb of a dog. This popliteal sesamoid bone articulates with the lateral condyle of the tibia bone.
How many sesamoid bones in a cow and a horse?
The cow has 26 sesamoid bones in the moving joints of the limbs. In contrast, the horse has 14 sesamoid bones attached to their extremities.
Let’s see how the cow has 26 actual sesamoid bones in their fore and hindlimb –
The cow has two developed digits, each containing 2 proximal sesamoid bones. These 2 proximal sesamoid bones are located between the distal part of the metacarpal and the proximal part of the first phalanx.
Again, each digit of the cow has only one distal sesamoid bone on its palmar or planter aspects. Thus, you will find a total 3 sesamoid bones for each digit.
Now, let’s calculate the total number of sesamoids from the cow skeleton –
- Sesamoid bones in the right and left forelimbs of the cow = 12,
- Sesamoid bones in the right and left hindlimbs of the cow = 14 (including the patella),
Total sesamoid bones in the cow = 26 (twenty six),
Here, Table 2 shows the number and location of the sesamoid bones from the cow skeleton –
| Cow sesamoid bones | Location | Number |
| Sesamoid in each forelimb | 6 | |
| Proximal sesamoid | Metacarpophalangeal joint (palmar aspect) | 4 |
| Distal sesamoid | Distal interphalangeal joint (palmar aspect) | 2 |
| Sesamoid in each hindlimb | 7 | |
| Largest sesamoid | In stifle joint (cranially on trochlear groove) | 1 |
| Proximal sesamoid | Metacarpophalangeal joint (plantar aspect) | 4 |
| Distal sesamoid | Distal interphalangeal joint (plantar aspect) | 2 |
| Sesamoid in 4 limbs | 26 |
Sesamoids in horses compared to the dogs
The horse has only one developed digit in each limb. Thus, each digit of the horse leg contains two proximal and one distal seamoid bone.
Let’s count the total sesamoid bones from the horse limbs –
- Each forelimb of the horse contain = 3 sesamoid bone,
- Each hindlimb of the horse contain = 4 sesamoid bone (including the patella),
Thus, the total sesamoid in 4 limbs of the horse = 14 (fourteen).
Sometimes, a small piece of bone may be found in the carpal and tarsal joints of the horse. Here, Table 3 shows the counting of total sesamoids from the horse skeleton –
| Horse sesamoids | Limbs | Total | Subtotal |
| Proximal sesamoids | Forelimb | 2 | 4 |
| Hindlimb | 2 | 4 | |
| Distal sesamoids | Forelimb | 1 | 2 |
| Hindlimb | 1 | 2 | |
| Largest sesamoid | Hindlimb | 1 | 2 |
| Total sesamoid | In both limbs | 14 |
Conclusion
The dog sesamoid bones are located in the free-moving joints of the front and hind legs. Both the fore and hind limbs of the dog possess 98 sesamoids.
The proximal and distal sesamoids from the dog’s forelimb and hindlimb vary structurally. Here, the dog’s patella, the largest sesamoid, has distinct anatomical features compared to other sesamoids.
