What is the Difference Between Femur and Humerus

The main difference between femur and humerus is that femur is the long bone of the upper leg whereas humerus is the long bone of the upper arm. Furthermore, the length and the average diameter of the femur are higher than that of the humerus. Besides, the femur is the largest bone of the human body while humerus is the second largest bone. 

In brief, femur and humerus are two of the largest long bones of the human body. They occur singly in the upper part of the limbs. 

Key Areas Covered 

1. What is Femur
     – Definition, Anatomy, Function
2. What is Humerus
     – Definition, Anatomy, Function
3. What are the Similarities Between Femur and Humerus
     – Outline of Common Features
4. What is the Difference Between Femur and Humerus
     – Comparison of Key Differences  

Key Terms 

Diaphysis, Epiphysis, Femur, Humerus, Long Bones, Upper Limbs

What is Femur 

The femur or the thigh bone is the proximal bone of the hindlimb in tetrapod vertebrates. It is the longest and strongest bone of the human body. The femur can resist forces of 1,800 to 2,500 pounds. It also does not fracture easily. In general, the femur takes part in weight-bearing, transforming the bodyweight mainly towards the tibia.

Femur – Anatomy

As a long bone, the femur comprises a diaphysis (shaft or body) and two epiphyses (extremities), which articulate with adjacent bones in the hip and knee. 

Figure 1: Anatomical features of Femur

Furthermore, the upper extremity of the femur is longer and has a shape of two-thirds of a sphere. Also, its shaft is almost cylindrical. Moreover, it is convex in front and concaves behind. In addition to these, the lower extremity of the femur is larger and has a cuboidal shape. It also consists of two oblong eminences known as the condyles. 

What is Humerus 

The humerus is the long bone of the upper arm. Generally, it runs from the shoulder to the elbow. It is the second-longest and the strongest bone of the human body although it does not involve weight-bearing in the upright position.

Humerus – Anatomy

Similar to the femur, the humerus contains a diaphysis and two epiphyses. 

Figure 2: General Anatomy of a Long Bone Based on the Humerus

Moreover, the upper extremity of the humerus articulates with the scapula and the clavicle bone in order to form the pectoral girdle. Generally, the head of the humerus is a hemisphere. Also, it contains the greater and the lesser tubercles separated by the bicipital sulcus, which is a deep groove, extending longitudinally. In contrast, the shaft of the humerus is triangular to cylindrical, with three surfaces: anterolateral, anteromedial, and posterior. The characteristic anatomical features of the shaft include the Deltoid tuberosity, which acts as the site of insertion of deltoideus muscle, radial sulcus, a shallow oblique groove through which the radial nerve passes along with deep vessels, and the nutrient foramen in the anteromedial surface through which the nutrient arteries enter the humerus. 

Figure 3: Humerus – Anatomical Features

Furthermore, the lower extremity of the humerus forms the elbow and the anterior surface of the lower extremity the bone contains three fossae. They are the olecranon fossa, which accommodates the olecranon process of the ulna during extension of the elbow, the coronoid fossa, which receives the coronoid process of the ulna during maximum flexion of the elbow, and radial fossa, which receives the head of the radius during maximum flexion of the elbow. In addition to these, the anatomical features of the posterior surface are the Capitulum, which articulates with the head of the radius and the trochlea, which articulates with the ulna. 

Similarities Between Femur and Humerus  

• Femur and humerus are corresponding long bones of the upper limbs of the human body.  
• They are the longest and the strongest bones that occur alone in the upper arms.  
• Their two main anatomical features are the epiphysis and diaphysis.  
• The epiphysis is the wider section at each end of the bone filled with spongy bones with red bone marrow inside. Also, each epiphysis meets the diaphysis at the metaphysis, which is the narrow area, containing the epiphyseal line.    
• The diaphysis is the tubular shaft, which runs between the proximal and distal ends of the bone. Basically, the medullary cavity is the hollow region filled with yellow bone marrow.  In addition, the walls are composed of compact bone, which is hard and dense.  
• Meanwhile,  endosteum is the delicate, membranous lining of the medullary cavity. Bone growth, repair, and remodelling occur at the endosteum.    
• The periosteum is the fibrous membrane of the outer membrane of the medullary cavity, containing blood vessels, nerves, and lymphatic vessels, which nourish compact bone.  Also, both tendons and ligaments attach to the periosteum. However,  periosteum does not occur where the epiphyses meet other bones to form joints.  
• Articular cartilage covers the epiphyses at joints, reducing friction and acting as a shock absorber.   

Difference Between Femur and Humerus 

Definition 

Femur refers to the bone of the thigh or the upper hindlimb, articulating at the hip and the knee, while humerus refers to the bone of the upper arm or forelimb, forming joints at the shoulder and the elbow. 

Occurrence 

The femur is the long bone of the upper leg while the humerus is the long bone of the upper arm. 

Length and Average Diameter 

Moreover, the femur has the highest length and an average diameter while humerus has a comparatively low length and average diameter. 

Size and the Strength 

In fact, the femur is the largest and the strongest bone of the human body while humerus is the second-largest and strongest bone. 

Upper Extremity  

The upper extremity of the femur contains the head, neck, the two trochanters, and adjacent structures while the upper extremity of the humerus contains a rounded head, a narrow neck, and two short processes called tubercles. 

Length of the Head and the Neck 

Furthermore, the neck of the femur is longer, making the head very distinct, while the head and the neck of the humerus is comparatively shorter. 

The shape of the Head 

The head of the femur is about two-thirds of a sphere while the head of the humerus is almost hemispherical. 

Articulation of the Upper Extremity 

Furthermore, the head of the femur articulates with the acetabulum in the pelvic bone, forming the hip joint, while the head of the humerus articulates to the scapula and to the clavicle to form the pectoral girdle. 

Anatomy of the Diaphysis 

While the diaphysis of the femur is long, slender and almost cylindrical in form, the diaphysis of the humerus is triangular to cylindrical with three surfaces: anterolateral, anteromedial, ad posterior. 

Lower Extremity 

The lower extremity of the femur contains two condyles separated by an epicondyle while the lower extremity of the humerus contains 2 epicondyles, 2 processes (trochlea & capitulum), and 3 fossae (radial fossa, coronoid fossa, and olecranon fossa).  

Condyles 

The condyles of the femur are much bigger while the condyles of the humerus are comparatively smaller. 

Articulation of the Lower Extremity 

The lower extremity of the femur articulates with the tibia and kneecap, forming the knee joint, while the lower extremity of the humerus articulates to the two bones of the lower arm, the radius and ulna.  

Wight Bearing 

Moreover, the femur takes part in weight-bearing of the body in the upright position while humerus does not take part in weight-bearing in the upright position. 

Conclusion 

The femur is the long bone of the upper leg, being the longest and strongest. Basically, it has a long neck. Also, the upper extremity of the femur articulates to form the pelvic bone while its lower extremity articulates to form the knee joint. In contrast, the humerus is the second longest and strongest bone of the human body, occurring in the upper arm. Generally, its upper extremity articulates to form the pectoral girdle while the lower extremity articulates to form the elbow joint. Therefore, the main difference between femur and humerus is their size, strength, and the form of articulation. 

References:

1. Jones, Oliver. “The Femur.” TeachMe Anatomy, 8 Apr. 2019. Available Here.
2. Jones, Oliver. “The Humerus.” TeachMeAnatomy, 16 June 2019, Available Here.

Image Courtesy:

1. “Fumur Anterior annoted” By Frank Gaillard – Own work (CC BY-SA 3.0) via Commons Wikimedia   
2. “603 Anatomy of Long Bone” By OpenStax College – Anatomy & Physiology, Connexions Web site. (CC BY 3.0) via Commons Wikimedia   
3. “HumerusBack” By BDB (CC BY-SA 3.0) via Commons Wikimedia