Introduction:
In the human body, the arm is part of the upper limb that extends through the hand and fingers between the shoulder and the elbow. The arm can be divided into the upper arm and the forearm. The upper arm extends from the shoulder to the elbow joint, and the forearm extends from the elbow joint to the hand. The arm consists of a few long bones and many muscles that work together to bring about movements. The arm is responsible for performing many important functions and tasks in the body through the hand.
What Is the Humerus Bone?
The humerus is the longest and largest bone of the upper arm. The term humerus is a Latin word meaning upper arm. It is the only bone of the upper arm that articulates with the shoulder and elbow joints. The main function of the humerus bone is to support the shoulders. In addition, the humerus bone provides a skeletal framework for the attachment of muscles that help to move the upper limb and its parts. Many powerful muscles are present around the humerus bone, which is attributed as the representation of strength.
What Is the Structure of the Humerus Bone?
The structure of the humerus bone is mainly divided into three parts: the upper extremity, the shaft, and the lower extremity.
Upper Extremity:
The upper extremity is large, round-shaped, that converges downward to continue as the shaft. The portions of the upper extremity are:
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Head:
The head of the upper extremity in the humerus bone is hemispherical in shape, and they are larger in males compared to females.
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Neck:
The neck is the narrow area below the head that connects with the shaft.
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Greater Tubercle:
The greater tubercle is a large bulge at the backside of the head portion placed away from the midline.
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Lesser Tubercle:
The lesser tubercle is a small bulge at the backside of the head portion but is comparatively visible from the front, and it is more prominent than the greater tubercle.
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Bicipital Groove:
Bicipital groove is a long, narrow, deep depression present between the greater and the lesser tubercle. As it moves through the shaft, the bicipital groove becomes shallow and disappears.
Shaft:
The shaft is the body of the humerus bone that is triangular or cylindrical in shape. Anatomically the two major portions of the shaft are:
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Deltoid Tuberosity:
The deltoid tuberosity is a small rough bulge on the lateral surface (the surface which faces away from the midline of the human body) of the shaft, almost near to the middle region. It is the site of attachment to one of the shoulder muscles.
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Spiral Groove:
The spiral groove is a shallow depression that is present on the backside of the shaft. It runs in an oblique direction and looks like a spiral curve. The spiral groove accommodates the radial nerve (one of the nerves of the upper limb), and hence they are also known as the radial sulcus.
Lower Extremity:
The lower extremity of the humerus bone is flat and broad. When the forearm and the palm are facing forward, the parts of the lower extremity can be visualized from the front and the back.
The portions present in the front side of the lower extremity are:
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Coronoid Fossa and Radial Fossa:
These are the hollow cavities present at the end of the shaft.
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Capitellum and Trochlea:
These are the large bony prominence below the coronoid and radial fossa and are called the condyle of the humerus. The capitellum is ball-shaped, and the trochlea is spool-shaped.
The portions present in the backside of the lower extremity are:
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Olecranon Fossa:
It is a large deep triangular cavity.
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Trochlea:
This is the extension of the trochlear prominence on the backside.
Apart from this, there are two epicondyles in the lower extremity. Epicondyle means a small bony prominence above the condyle. They are named according to their positions:
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Lateral Epicondyle:
It is a smaller eminence near the capitellum.
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Medial Epicondyle:
It is comparatively larger and more prominent than the lateral epicondyle and is present near the trochlea.
Where Is the Humerus Bone Located?
The humerus bone is present in the upper arm between the shoulder and the elbow. The head of the humerus articulates with a shallow cavity in the shoulder bone, forming one of the shoulder joints.
In the lower extremity, the capitulum and the radial fossa articulate with the radius, and the trochlea, coronoid, and olecranon fossa articulate with the ulna. The radius and the ulna are the two long bones of the forearm. These articulations form the elbow joints. The shoulder joints and the elbow joints are surrounded and supported by various muscles, ligaments, and tendons.
What Type of Bone Is the Humerus?
The humerus bone is classified as a long bone because it is longer than it is wide. The long bones support weight and help in movements. The outer cover of the humerus is made of strong, compact bone (densely packed) that surrounds the inner hollow medullary cavity in the shaft. The upper and the lower extremities are reinforced with spongy bones (less dense with pores). Bone marrows are present in the long bones to produce new blood cells and to store fats. The entire bone is covered by a thin layer called the periosteum. The end of the humerus is shielded by a special smooth tissue called the articular cartilage that gives friction-free movements at the joints.
What Is the Function of the Humerus Bone?
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The upper extremity of the humerus bone forms the shoulder joint, which is a ball and socket type of joint that brings about rotation, up, down, and side movements of the arm.
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The lower extremity of the humerus bone forms the elbow joint, which is a hinge type of joint that brings about extending and bending of the forearm.
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The humerus bone acts as a pillar of insertion for many important muscles of the arm.
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Many arteries, veins, and nerves travel along the humerus bone.
What Are the Diseases and Disorders Associated With Humerus Bone?
1. Fractures:
This is a common condition caused by injury or trauma. The shaft of the humerus has a higher incidence of fracture, especially in active young adults. But in the elderly, the most frequent site of the humerus bone fracture is the neck in the upper extremity.
2. Shoulder Joint Diseases:
The inflammation of the structures present in and around the shoulder joints causes pain and swelling. In some cases, there is a chronic inflammation of the capsule in the shoulder joint, which is known as frozen shoulder syndrome. There is stiffness and dysfunction of the arm.
3. Common Bone Diseases:
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Bone Tumor: This can be cancerous or non-cancerous lesions pertaining to the bone.
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Osteoporosis: A condition in which the bones become less dense, weak, and brittle.
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Osteopetrosis: A condition in which the bone becomes abnormally dense and tends to fracture frequently.
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Rickets and Osteomalacia: The bones become soft and deform due to severe deficiency of Vitamin D.
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Osteogenesis Imperfecta: It is a genetic disorder that causes imperfect bone formation.
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Paget's Disease: Disruption in the bone remodeling causes Paget's disease.
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Fibrous Dysplasia: A condition in which the soft fibrous tissue develops in place of the normal bone.
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Osteomyelitis: It is a bacterial infection of the bone.
4. Metastatic Bone Disease: Cancer that originates in one area of the body and spreads to the bone is called metastatic bone disease. The humerus bone is the common site of spread, and it causes significant destruction to the bone.
Conclusion:
The humerus is the single long bone of the upper arm that aids in supporting the skeletal muscles to perform a wide range of movements. The movements of the humerus are very important for all the activities associated with the arm. The basic knowledge of the structure of the humerus bone helps to understand the general functions of the musculoskeletal system in the body.
