Skeletal System – Hands and Feet

By Dr. Johannes Sobotta [Public domain], via Wikimedia Commons, modified.

The Hand

The human hand is a unique and incredibly dexterous tool make possible largely by the location and utilization of the skeletal features of the hand and forearm.

Above is a depiction of the bones of the hand. Nearest the wrist are the Carpus or Carpal bones. The broad flat part of the upper hand and palm are made possible by the Metacarpus or Metacarpal bones. When you strike someone with your knuckles you are actually making contact with the ends of the metacarpal bones.

The Phalanges

The fingers each consist of three bones, with the exception of the thumb which has two. These bones, referred to as phalanx bones, or by the plural term phalanges, are named according to their position.

The phalanges nearest the wrist (sometimes called the first phalanges) are referred to as proximal phalanges because they are proximal or closest to the wrist (or body). The distal phalanges (third phalanges) are the bones at the tips of the fingers and are so named because they are furthest from the body. The intermediate phalanges are obviously the bones in the middle, between the proximal and distal phalanges.

At the tip of each distal phalanx can be found the ungula tuberosity. This provides a broad support region for the pad of each finger.

There are fourteen phalanx bones in each hand. There are also five metacarpal bones and eight carpal bones in each hand, yielding a total of twenty-seven bones in each hand.

Each finger has a scientific name as well as a common name. The scientific name is seldom used except when one wishes to be specific about what is being referenced. We will not use the scientific names because they are beyond the scope and intent of our conversation. However, for completeness here are the scientific names for each digit of the hand.

Common Name(s) Scientific Name
Little finger, Pinky Digitus Minimus Manus
Ring finger Digitus Annularis
Middle finger Digitus Medius or Digitus Tertius
Index finger Digitus Secundus Manus
Thumb Pollex

Each joint on the finger also has a name. The finger joint nearest the tip of each finger is referred to as the Distal-Interphalangeal (or DIP) joint. The middle knuckle Proximal-Interphalangeal (or PIP) joint.

The Metacarpals

Your knuckles are located where the phalanges meet the metacarpal bones. This joint is called the Metacarpal Phalangeal (MCP) joint. The metacarpal bones are positioned between the phalanges and the carpals (discussed later) and can readily be felt at the back of the hand. There are five metacarpal bones in each hand, one for each finger and the thumb. They are numbered one through five, beginning with the thumb.

Metacarpal lengths vary greatly from one individual to another. Relatively speaking however, the first metacarpal bone is the shortest and the most stout while the second metacarpal is the longest. It also has the largest base. The diagram above suggests the third metacarpal is the longest, but in reality the second metacarpal is slightly longer than the third.

The two metacarpal bones that are most commonly broken are number one and number five. Number five is usually broken by striking a hard object with a fist (which can happen if rotational delivery is not used or if the elbow is allowed to flair outward while striking with a Ken Tsuki). The first metacarpal is most likely to break at its base (proximal end). This usually occurs if the thumb is pulled outward and away from the hand beyond its normal range of motion (hyperabduction). This can occur if the thumb is caught in clothing or against a body part as a strike is being delivered. Both conditions can occur as the result of an ill-formed hand strike.

The Carpals (Carpus)

The carpal bones at the base of the wrist serve as anchor points for the many tendons and ligaments that enable wrist movement. These bones function as a series of joints that enable the wrist to move with great flexibility and agility.

These bones are organized so that together they have a convex shape proximally (where they meet the radius and ulna bones) and a concave shape distally (where they meet the metacarpals). The carpals are organized as two rows and three columns of individual bones.

The first (proximal) row consists of the scaphoid, lunate, triquetrum, and pisiform. The distal row consists of the trapezium, trapezoid, capitate, and hamate bones. In both cases the bones are listed in order from the lateral to the medial side of the hand.

The pisiform is a sesamoid bone that forms in a tendon and is not present at birth. It develops through ossification of tendon tissues and usually does not fully develop until an individual is about twelve years of age. Its general location is shown in the diagram above, though it is not well depicted.

When thought of as three columns then these columns are (in order from the lateral to medial side of the hand):

  • The radial scaphoid column comprised of the scaphoid, trapezium, and trapezoid bones.
  • The lunate column comprised of the lunate and capitate bones.
  • The ulnar triquetral column comprised of the triquetrum and hamate bones.

The pisiform is not considered part of these columnar definitions.

Additional sesamoid bone formations occur in some individuals but are not consistently developed by everyone. These bones develop to provide additional leverage for tendons and develop after repeated stress and usage. A carpenter is likely to have a different set of additional sesamoid bones (if any) than a typist. These bones are not normally considered part of the carpals because they do not consistently appear in the general population and their presence can vary greatly from one individual to another.

The Foot

Blausen.com staff (2014). “Medical gallery of Blausen Medical 2014”. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. (Own work) [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons

The foot is similar to the hand but has substantial differences. The segments of the foot have similar but distinct names from the hand.

In the hand the bones in the wrist are called the carpal bones. Analogous bones in the foot are called the tarsal bones. In the back of the hand we have the metacarpal bones, where similar bones in the foot are called the metatarsal bones. Only the phalanges have the same name for both appendages.

The phalanges of the foot are much shorter and robust than the fingers of the hand. The metatarsal bones are generally analogous to the metacarpals of the hand. They are somewhat longer and more robust than the similar bones in the hand.

The arrangement of the tarsal bones is quite different than the carpal bones of the hand. This is largely due to the weigh bearing and mobility functions of the foot. The bones, especially the heel bone (calcaneus) are quite large in comparison with the wrist. They serve to absorb shock, provide structural and load-bearing support for the entire body, and afford the range of motion and flexibility required for balance and mobility.

Because of the smaller number of tarsal bones and their different purpose the ankle has a far smaller range of motion than the much more flexible wrist. The area between the tarsals and the metatarsals rises, particularly toward the inside of the foot to form an arch. This provides increased structural support for the body and acts as a resilient mechanism to absorb shock. When running much of this absorbed energy is returned as part of the spring in the next step. The arches provided by the tarsal and metatarsal bones of the foot are shown in the following diagram. This arch provides a very stable method for supporting additional weight not dissimilar from arches used in the construction of roman aqueducts and modern bridges.

 

There are a total of twenty-six bones in each foot. This is one less bone than found in each hand. The difference is in the ankle and wrist area where the wrist has eight carpal bones compared to seven tarsal bones in the foot.

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