The Human Hand

 

One of the most amazing and complex structures in the human body is the hand.  Many of us fail to realize the intricate mechanics involved in the structure and working of the human hand.

 

One of the largest challenges faced by robotic and prosthetic engineers is to design a working hand that can gently grasp and hold objects without crushing them.  I’ve seen some prosthetic hands on science specials that are coming close to some of the abilities of the human hand.  These involve a series of servo motors, wires, computer programming and sensors that have taken thousands of hours and dollars to develop.

 

Today, we are going to take a brief look at the anatomy of the hand to show how complex and intricately designed it is.  Along with the hand, we will take a look at the wrist, to which the hand is attached, and allows for a significant part of the movement and function of the hand.  Even though this is only a brief overview of the hand and wrist, it will be the most comprehensive article in the series on the human body as there is so much involved with the structure and workings of the human hand.

 

Generally I use a number of references for each of the different sections in this series.  However, today’s article on the wrist and hand will be based largely on the classic work Gray’s Anatomy by Dr. Henry Gray, a Fellow of the Royal College of Surgeons in merry ole England at the turn of the twentieth century.  Even though Gray’s Anatomy is over one hundred years old, it is considered by many professionals as the definitive work on human anatomy in general. It is still used by many universities and medical schools today.

 

I.          Bones of Hand and Wrist – There are 27 bones that make up the wrist and hand.

 

A.        Carpals – There are 8 carpal bones that make up the wrist.  They are uniquely shaped and fit together like a three dimensional puzzle.  However, their unique shapes and the way the fit together are perfectly designed to allow the flexible movements of the wrist.  The carpal bones are divided into two groups:

 

1.         Upper Row – The upper row of carpals are those closest to the arm.

 

a.         Scaphoid – The largest bone of the upper row.  It articulates (connects) to the radius of the forearm along with 4 other bones of the wrist; the trapezium, and trapezoid below, os magnum and semilunar internally.

 

b.         Semilunar – This bone is easily identifiable due to its deep concave shape.  It articulates with the radius of the forearm and 4 other bones of the wrist; the os magnum and unciform below, scaphoid and cuneiform on either side.

 

c.         Cuneiform – This is a wedge shape bone that articulates with the interarticular fibro-cartilage which connects to the lower end of the ulna of the forearm, and 3 bones of the wrist: the semilunar externally, the pisiform in front and the unciform below.

 

d.         Pisiform – So named for its pea shape (pisum = pea).  The pisiform articulate with only 1 bone; the cuneiform.

 

2.         Lower Row – The lower row of wrist bones are the 4 bones that articulate to the metacarpals of the palm of the hand.

 

a.         Trapezium – The most irregularly shaped bones of the wrist.  It articulates with the scaphoid above, the trapezoid and second metacarpal internally and first metacarpal below.

 

b.         Trapezoid – The smallest bone of the second row.  It articulates with the scaphoid above, second metacarpal below, trapezium externally and os magnum internally.

 

c.         Os Magnum – The largest of all the bones in the wrist and articulates more bones than any other of the bones in the wrist.  It connects to the scaphoid and semilunar above, the second, third and fourth metacarpal below, the trapezoid on the radial side and the unciform on the ulnar side.

 

d.         Unciform – The unciform is characterized by a flat projection on the palmer surface.  It articulates with the semilunar above, the fourth and fifth metacarpal below, the cuneiform internally and the os magnum externally.

 

B.        Metacarpals – There are 5 metacarpal bones that make up the palm of the hand.

 

C.        Phalanges – There are 14 phalanges or finger bones.

 

1.         Proximal Phalanges – There are 5 proximal phalanges that make up the first joint of the fingers and thumb that extend out from the palm.

 

2.         Intermediate Phalanges – There are only 4 intermediate phalanges that make up the middle section of the 4 fingers.  There is no intermediate phalanx (singular for phalanges) in the thumb.

 

3.         Distal Phalanges – There are 5 distal phalanges that comprise the outermost section of the fingers and thumb.

 

II.         Articulations of the Hand and Wrist – Articulations refer to the joints between bones and the ligaments that help connect them to each other.

 

A.        Dorsal Ligaments – Extends across the dorsal surface of the wrist connecting the scaphoid to the semilunar, the semilunar to the cuneiform, the trapezium to the trapezoid, the trapezoid to the os magnum, and the os magnum to the unciform.  The dorsal ligaments are the strongest and most obvious ligaments on the upper surface of the wrist and hand.  It connects the metacarpal bones of the palm of the hand to the carpals of the wrist.  In the palm of the hand, the dorsal ligaments run laterally connecting the metacarpals to each other.

 

B.        Palmar Ligaments – Consists of 2 strong bands that connect the scaphoid to the semilunar, the semilunar to the cuneiform and the pisiform to the unciform, and base of the fifth metacarpal.  They are not as strong at the dorsal ligament and are located deep below the anterior ligament.  The palmar ligaments on the under or palm side of the wrist and hand are much like the dorsal ligaments as they connect the under surfaces of the carpal bones to the metacarpal bones and the metacarpals laterally connecting to each other.  Additionally, there are three palmar ligaments that attach to the third metacarpal (middle finger).  One is an external ligament that runs from the runs above the tendon sheath from the trapezium to the third metacarpal.  The second runs through the sheath from the os magnum, and the third is internal and runs below the sheath from the unciform and connect to the third metacarpal.

 

C.        Interosseous Ligaments – The interosseous ligaments consist of two slender bundles of fibrous tissue that connect the semilunar on one side to the scaphoid and to the cuneiform on the other side.  There are also three thicker interosseous ligaments that are involved with the lower row of carpals and extend from the os magnum and unciform to the third and fourth metacarpals.

 

D.        Capsular Ligament – This is a very thin ligament that connects the pisiform with the cuneiform.

 

E.        Lateral Ligaments – There are two short lateral ligaments.  The larger and strongest runs on the radial side and connects the scaphoid to the trapezium.  The second is smaller and not as strong and runs on the ulnar side connecting the cuneiform to the unciform.  There are also two lateral ligaments that attach from the end of each metacarpal to opposite sides of each proximal phalanx.  Then two more, one on each side that attach from the proximal to the intermediate phalanges except in the thumb where it attaches directly to the distal phalanx, and then two more on the four fingers attaching the intermediate phalanges to the distal phalanges.

 

F.         Transverse Metacarpal Ligaments – These consist of a band of narrow fibrous ligaments that run along the upper surface of the hand toward the outer ends of the metacarpals.  They only connect the first four metacarpals and not the fifth which goes to the thumb.

 

G.        Anterior Ligaments – These are dense and thick ligaments on the palmar side of the hand.  They attach somewhat loosely to the outer end of each metacarpal and attach very firmly to the first phalanges of each finger.  They are associated with the transverse metacarpal ligaments.  There is a distinct groove in each anterior ligament in which a flexor tendon passes through.  There are also short and very strong anterior ligaments that attach to the underside of each proximal phalanges and connects it to the underside of the intermediate phalanges, except in the thumb where it connects directly to the distal phalanx, and the another anterior ligament in the four fingers attaching the intermediate phalanges to the distal phalanges.

 

H.        Anterior Angular Ligament – This is a very strong ligament that arches above and forms a canal along the deep groove on the front of the carpus.  The anterior angular ligament attaches pisiform and unciform and connects to the scaphoid and trapezium.  The flexor tendons of the fingers pass through the canal formed by this ligament.

 

III.        Muscles and Tendons of the Wrist and Hand – The muscles of the hand are generally divided into different groups.  The grouping depends upon the sources one uses.  Gray’s Anatomy breaks down the muscles of the hand into three groups: radial, ulnar and mid palmar.  Some more current sources break the muscle groups into two groups: intrinsic and extrinsic, but since I have been using Dr. Gray’s work throughout this article, I will use his grouping for the muscles and tendons of the hand.  But before getting into those muscle groupings, we need to look at some of the fascia of the wrist and hands.

 

With muscles, there are abductors and adductors.  Abductors draw body parts, such as arms and fingers away from the mid-line of the body.  Adductors draw the same body parts toward the body’s mid-line.

 

A.        Fascia of the Hand and Wrist – The fascia of the hands and wrist consist of membranes and tendons.

 

1.         Synovial Membrane – The synovial membrane is an extensive soft tissue that lines much of the non-cartilaginous surfaces of the bones in the wrist and extending to the metacarpal bones of the palm of the hand.  It plays a very important role in the connection of the carpal bones to each other and to the metacarpals.  There are two synovial membranes that serve to encase the tendons that run under the ligaments through the wrist to the hand.  One of the two membranes extends from the end of the forearm and extends out to the distal end of the thumb.  The other similarly starts in the forearm and extends to the palm of the hand and ends at the distal end of the little finger.  There are also three additional small synovial membranes that extend from the out edges of the three middle metacarpals out to the distal end of the three middle fingers.

 

2.         Deep Palmar Fascia – The deep palmar fascia is a sheath that surrounds the muscles of the hand.  It starts as one central sheath and then divides into three sheaths.

 

a.         Central – This is the largest of the three sections of the deep palmar sheath.  It is very thick, strong and triangular in shape and covers the bulk of the palm of the hand.  As it reaches the fingers, it further divides into four slips, one for each finger.

 

b.         Lateral – There are two lateral portions of the deep palmar fascia.  They are thinner than the central section.  One of the lateral portions surrounds the muscles of the ball of the thumb on the radial side of the hand and the other surrounds the muscles of the little finger on the ulnar side of the hand.

 

3.         Tendons – There are numerous flexor tendons involved with the wrist and hand.  They act like steel cables connecting muscles to the various bones in the hand, especially to the fingers.

 

B.        Radial Group – Consists of the muscles and tendons associated with the thumb.

 

1.         Abductor Pollicis

 

2.         Opponens Pollicis

 

3.         Flexor Brevis Pollicis

 

4.         Adductor Obliquus Pollicis

 

5.         Adductor Transversus Pollicis

 

6.         Nerves of the Radial Group

 

a.         Sixth Cervical Nerve – The first three muscles of the radial group are innervated by the sixth cervical nerve via the median nerve.

 

b.         Eighth Cervical Nerve – The last three muscles of this group are innervated by the eighth cervical nerve via the ulnar nerve.

 

C.        Ulnar Group – Consists of the muscles and tendons associated with the little finger.

 

1.         Palmaris Brevis

 

2.         Abductor Minimi Digiti

 

3.         Flexor Brevis Minimi Digiti

 

4.         Opponens Minimi Digiti

 

5.         Nerve of the Ulnar Group – The muscles of the ulnar group are innervated by the eighth cervical nerve via the ulnar nerve.

 

D.        Mid Palmar Group – Consists of the muscles and tendons associate with the middle three fingers.

 

1.         Lumbricales

 

2.         Interossei –

 

a.         Dorsal Interossei

 

b.         Palmar Interossei

 

3.         Nerves –

 

a.         Sixth Cervical Nerve – The two outer lumbricales are innervated by the sixth cervical nerve via the third and fourth digital branches of the median nerve.

 

b.         Eighth Cervical Nerve – The two inner lumbricales and both interossei are innervated by the eighth cervical nerve via the deep palmar branch of the ulnar nerve.

 

Keep in mind that this was a brief overview of the wrists and hands.  Rather than go into a very detailed description of each muscle and how the attached and functions, I chose to just list them.  If you have access to a copy of Gray’s Anatomy, I would highly suggest you check out the various sections involving the various sections of the wrist and hand.  The diagrams in the book will further reveal the extremely intricate design of the wrists and hands.  The design and function so complex that it should be obvious to virtually everyone that it would be impossible to explain the origin of them from an evolutionary view of origins.  Only an infinitely wise Creator can account for the miracle of the human hand.

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When master logician/scientist Jonathan Sarfati takes on another front of the creation/evolution battle, his fans know theyre going to experience an intellectual feast of cut-and- thrust philosophical swordsmanship with the opponents of Genesis creation/ID. But readers are in for an additional treat, toohis passion (not revealed in his previous books) for digging into the details of lifes breathtaking designs.

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