Video: Main bones of the upper extremity
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Please put your hands together for tonight's host, Mr. Kenhub! Thank you, thank you. I wanted to tell you a joke about bones but I thought you might not find it very ‘humerus.’ Okay, okay, wait. Wh... Read more
Please put your hands together for tonight's host, Mr. Kenhub! Thank you, thank you. I wanted to tell you a joke about bones but I thought you might not find it very ‘humerus.’ Okay, okay, wait. What about this one? I broke my finger today, but on the other hand, I was totally fine!
Okay, okay, let's get him off the stage. That was pretty bad. He must not have a ‘funny bone’ in his body. But seriously, enough of the jokes. Today, we're going to explore the main bones of the upper limb and there's more to it than just the humerus. We'll divide the bones of the upper limb into three groups – the bones of the pectoral girdle and arm, the bones of the forearm, and the bones of the hand. We will also explore the joints which are formed by articulations of the bones within each group and then finish off by taking a look at some clinical notes on the bones and joints of the upper limb.
Before we dive into the meat of this tutorial, I just want to quickly go over some of the terminology that we will meet today. We're going to explore the bones of the upper limb from the proximal to distal or from closest to the trunk to furthest away. As our bodies move, the position of structures relative to the rest of the body can change making it difficult to identify where structures lie in relation to one another. Therefore, when we study the human body, we always consider it in the anatomical position.
Here, the upper limbs are located on either side of the body parallel to the trunk, the elbow is fully extended, and the palms of the hand face forward. With the upper limb in an anatomical position, we can then describe structures or parts as being medial and lateral. Medial means that a structure is closer to the midline while lateral is further away from the midline.
As we move down to the forearm, we will meet two bones known as the ulnar and radial bones which are located medially and laterally, respectively. So when it comes to the upper limb, we often use the term ulnar instead of medial and radial as an alternative to lateral.
Okay, now that we've had a look at some of the terminology, let's begin exploring the main bones and joints of the pectoral girdle and arm.
The pectoral girdle, also known as the shoulder girdle, attaches the free part of the upper limb to the trunk. It comprises both claviculae and scapulae while the single bone of the arm is the humerus. Let's take a closer look at the bones that make up the pectoral girdle.
The clavicle or the collar bone is the bone that connects the bones of the upper limb to the trunk and is one of the most commonly fractured bones in the body. Its proximal sternal end articulates with the manubrium of the sternum while its distal end is known as the acromial end which will make more sense in just a moment. The scapula is commonly known as the shoulder blade because of its flat blade-like structure. That being said, it does have three bony processes as well as a bony spine on its posterior surface which creates a rather irregular-looking, odd-shaped bone.
The acromion, one of the processes of the scapula, is an extension of the spine that arises from the posterolateral aspect of the scapula. This process articulates with the acromial end of the clavicle to form one of the main joints of the pectoral girdle – the acromioclavicular joint.
Moving distally, we meet the bone of the arm, the humerus. The largest proximal part of the humerus, known as the humeral head, articulates with the pectoral girdle at the glenoid fossa of the scapula forming the shoulder or the glenohumeral joint which we know is highly mobile. The distal end features the condyle of the humerus which is formed by two irregular landmarks known as the trochlea and capitulum. It articulates with the bones of the forearm creating the elbow joint.
Moving distally, we meet the bones of the forearm which include the radius and the ulna. With the upper limb in the anatomical position, the radius sits on the lateral aspect while the ulna is situated medially. The ulna has a large proximal end and consists of a large hook-like process which is known as the olecranon process. You know that knobbly bony thing you feel on the back of your elbow? That is your olecranon.
On the anterior surface of the proximal ulna is the trochlear notch. This C-shaped notch articulates with the trochlea of the humerus at the elbow joint. The distal end of the ulna is much smaller than its proximal counterpart. Unlike the ulna, the radius has a small proximal end with a large distal end. The radius articulates with the ulna at the proximal and distal radioulnar joints. The radial head rotates around the ulna resulting in pronation and supination of the forearm.
At the distal end of the forearm, we meet the wrist joint. The definition of this joint can vary somewhat; however, anatomically, we consider it as being composed of the distal end of the radius, an articular disc which lies over the distal end of the ulnar bone, and the three carpal bones of the hand – the scaphoid, the lunate, and triquetrum bones which we will meet in just a second. It's important to note that the ulna does not participate in the wrist joint which is why it is correctly known as the radiocarpal joint.
Moving down to the last group – the bones of the hand. Although the hand seems like a small region, there are more bones in the hand than there are in the pectoral girdle, arm, and forearm combined. Altogether, there are 27 bones in total. It seems like an awful lot, but don't worry. I have a few tricks that you can use to remember them. First of all, the bones of the hand can be separated into the carpal bones, the metacarpal bones, and the phalanges.
Let's begin with the carpal bones. There are eight carpal bones altogether which are arranged into two groups of four. The first group of four is known as the proximal group or row. Three of the four bones here contribute to the formation of the wrist joint. The second group of four bones is known as the distal group or row. Each of these eight bones have separate names which we'll take a look at now.
So looking at the proximal row from lateral to medial of the anterior image of the hand, we meet the scaphoid, lunate, triquetrum or triquetral, and pisiform bones. The pisiform can be a little tricky to see sometimes as it sits stacked on top of the triquetrum bone hidden within the tendon of a muscle known as the flexor carpi ulnaris. The distal row from lateral to medial is made up of the trapezium, trapezoid, capitate, and hamate bones.
An easy way to remember these eight bones is to use this mnemonic – Sally (scaphoid), Left (lunate), The (triquetrum), Party (pisiform), To (trapezium), Take (trapezoid), Cathy (capitate), Home (hamate). Let's take a quick look at each of these bones individually.
The largest bone of the proximal carpal bones is the scaphoid bone. This bone sits on the lateral aspect of the hand and gets its name from the Greek word skaphos which means boat. This is because of its rocker-bottom, boat-like shape. It sits quite superficially and therefore can be easily palpated. Due to its large size and position, the scaphoid bone is the most commonly fractured carpal bone.
Just medial to the scaphoid bone is the lunate bone. The name of this bone is derived from its shape as the Latin word luna means crescent shape. This bone sits right in the middle of the proximal row of carpal bones and participates in the formation of the wrist joint. On the medial aspect of the proximal row of carpal bones, we meet the triquetrum and pisiform bones. The triquetrum bone receives its name from the Latin word triquetrus which translates to mean three-cornered describing its pyramidal appearance.
The pisiform bone is the smallest of the carpal bones and is named after the Latin word pisum which means pea. This little pea bone sits on top of the triquetrum bone on the medial aspect of the proximal row of carpal bones. It is a sesamoid bone which provides mechanical advantage for the flexor carpi ulnaris tendon.
Moving on to the distal row of carpal bones, we meet the trapezium bone on the lateral aspect of the hand. This is an angular-shaped bone which articulates with the first and second metacarpal bones. Just medial to the trapezium bone, we meet the smaller trapezoid bone. This bone is a wedge-shaped bone that articulates with the proximal aspect of the second metacarpal bone. Both the trapezium and trapezoid bones are named after the Greek word trapezion which translates to mean little table. This describes their angular four-cornered shape. To remember which is which, try memorizing the phrase ‘The trapezium is beside the thumb.’
Sitting at the center of the distal row is the capitate bone. This is the largest of the carpal bones and is derived from the Latin word caput which means head, describing its rounded shape superiorly. The capitate bone articulates with the third metacarpal bone of the hand. The final bone of the distal row of carpal bones is the hamate bone. This wedge-shaped bone gets its name from the Latin word hamulus which translates to mean little hook. On the anterior surface of the hamate bone is a small hook-like projection of bone known as the hook of the hamate. The hamate bone articulates with the fourth and fifth metacarpals.
Between the carpal bones and proximal and distal row of the carpal bones are the carpal joints. These are articulations which join the eight different carpal bones together. Distal to the carpal bones, we meet the metacarpal bones. There are five metacarpal bones which are numbered from one to five with the first metacarpal bone located laterally at the thumb and the fifth metacarpal bone situated medially at the little finger. Each metacarpal has a proximal base, a long body or shaft, and a distal rounded head. The bases of the five metacarpal bones articulate with the distal row of the five carpal bones at the five carpometacarpal joints.
Distally, or at the metacarpal heads, are the five metacarpophalangeal joints which are formed with our next group of bones of the hand, the phalanges. The phalanges form the bony framework of the fingers. While there are only five metacarpal bones in each hand, there are 14 phalanges which can be broken down into proximal, middle, and distal phalanges.
The proximal phalanges lie at the base of our fingers and are the largest bones of our fingers. The middle phalanges sit between the proximal and distal phalanges of the second to fifth fingers. Therefore, take note that the thumb does not have a middle phalanx. The proximal phalanges of the second to fifth fingers articulate with their middle counterparts to form proximal interphalangeal joints. The distal phalanges are the smallest phalanges of the hand and sit right at the fingertips. In the second to fifth fingers, the proximal end of each distal phalanx articulates with the distal end or the head of the adjacent middle phalanx forming a distal interphalangeal joint. As the thumb only contains a proximal and distal phalanx, there is just one interphalangeal joint in this digit.
Now that we've met some of the main bones of the upper limb, let's look at some clinical notes on this subject.
FOOSH injuries – short for falling onto an outstretched hand – are one of the most common types of injuries which occur in the upper limb when trying to break a fall. Depending on the way you fall or the impact that occurs on falling, this injury can cause ligament tears, fractures, and bruising. As we mentioned earlier, the scaphoid bone is one of the most commonly fractured carpal bones and usually occurs in response to FOOSH injuries.
As with all fractures, scaphoid fractures are painful especially on palpation of the affected area. Swelling around the base of the thumb and wrist will usually present. Scaphoid fractures are usually diagnosed through an x-ray of the wrist. They can be classified according to the level of displacement that occurs. In a non-displaced fracture, the bone fragments will line up correctly. In a displaced fracture which is more severe, the fragments will have moved from their usual position and gaps may present.
Following the injury, a cast or splint is applied in order to decrease movement at the joint. In more severe cases such as displaced fractures, surgical intervention may be necessary. It may take up to six months for a scaphoid fracture to heal completely.
That brings us to the end of this tutorial. Before you go, let's take a look at a quick summary of what we learnt today.
We began with the bones and joints of the pectoral girdle and arm identifying the clavicle, scapula, and humerus. The two main joints of this region are the acromioclavicular joint between the clavicle and the scapula and the glenohumeral joint between the scapula and the humerus. Moving distally, we identified the bones of the forearm – the radius and ulna. These bones articulate with the distal end of the humerus at the elbow joint.
At the distal end of the radius and ulna, we meet the wrist joint or the radiocarpal joint as it is correctly termed. This is the articulation between the radius and articular disc with the three carpal bones – the scaphoid, lunate, and triquetrum.
Onto the bones of the hand, we came to the carpal bones. There are eight carpal bones which are divided into two rows of four – a proximal and a distal row. The proximal row included the scaphoid, lunate, triquetrum, and pisiform bone while the distal row is made up of the trapezium, the trapezoid, the capitate, and hamate bones. The articulation between the carpal bones is known as the carpal joints or intercarpal joints. The distal row of carpal bones articulates with the five metacarpal bones at the carpometacarpal joints.
The metacarpal bones can be numbered fr