HAND PHALANGES

The phalanges are digital bones in the hands and feet of most vertebrates. In primates, the thumbs and big toes have two phalanges while the other digits have three phalanges. The phalanges are classed as long bones.

Each proximal phalanx consists of three parts:

• The base, which represents the expanded proximal part. It has a concave, oval-shaped articular facet that articulates with the metacarpal head to form the metacarpophalangeal (MCP) joint. The base also contains nonarticular tubercles for the attachment of various soft tissue structures.
• The body, which continues distally from the base. It tapers distally and has two surfaces: dorsal and palmar. The dorsal surface is round and smooth, appearing convex in the transverse plane. The palmar surface is flat and rough, especially on the sides where the flexor fibrous sheaths of digits attach. The surface appears flat in the transverse plane but concave in the sagittal plane.
• The head, which represents the expanded and rounded distal part. It has a pulley-shaped articular surface that articulates with the base of the middle phalanx to form the proximal interphalangeal (PIP) joint. The heads consist of smooth grooves, especially on the palmar aspects. These grooves represent the attachment points of the collateral interphalangeal ligaments of hand.

Various ligaments attach to the proximal phalanges. The most complex one is the digital fascial complex which attaches the surrounding subcutaneous tissue and neurovasculature to the bony phalanges. The collateral and palmar metacarpophalangeal ligaments attach to the bases of the proximal phalanges. They provide strength to the metacarpophalangeal joints. The collateral interphalangeal ligaments of hand attach to the heads, supporting the PIP joints. The proximal phalanges are also covered by the extensor expansion of hand on the dorsal aspect.

The proximal phalanges are very mobile at the MCP joints. They are mainly capable of flexion, extension, adduction and abduction. Circumduction and rotation are also possible, especially at the MCP joint of the thumb. These movements are enabled by the action of several muscles:

• Posterior (extensor) forearm muscles, such as extensor digitorum, extensor pollicis brevis, extensor digiti minimi and extensor indicis.
• Metacarpal muscles, such as the lumbricals, palmar interossei and dorsal interossei.
• Thenar muscles, for example flexor pollicis brevis and adductor pollicis.
• Hypothenar muscles like abductor digiti minimi and flexor digiti minimi.

These muscles carry out their functions via their direct attachments to the bases of the proximal phalanges. In addition, many extensors carry out the movements via the extensor expansion of hand which covers the phalanges

Middle phalanges

There are four middle (intermediate) phalanges in each hand because the thumb is missing one. They have a similar structure to the proximal ones, consisting of a base, body and head. The base of each middle phalanx has two concave-shaped articular facets and matches the head of the corresponding proximal phalanx. Their apposition forms the PIP joint. The heads of the middle phalanges have a pulley-like appearance. They articulate with the bases of the distal phalanges to form the distal interphalangeal (DIP) joints of hand.

The middle phalanges are reinforced by the same ligaments supporting the proximal ones, digital fascial complex, collateral interphalangeal ligaments and extensor expansion of hand. The collateral interphalangeal ligaments attach to the base and heads of the middle phalanges to reinforce the PIP and DIP joints.

The middle phalanges are less mobile compared to the proximal phalanges. They are only capable of flexion and extension at the PIP joints. Only the flexor digitorum superficialis muscle attaches directly to the sides of the middle phalanges, flexing them at the PIP joints. The remaining contributions are provided by the action of the previously mentioned muscles; the forearm extensors, metacarpal, thenar and hypothenar muscle groups. Flexion and extension are transferred to the middle phalanges from the direct action of these muscles on the proximal phalanges or via the extensor expansion of hand.

Distal phalanges

Each hand has five distal phalanges, which look shorter and slightly thicker compared to the previous two sets. Each distal phalanx has a base, body and head. The base has a double articular facet which matches the shape of the head of the middle phalanx. The distal phalanges have a smooth and round dorsal surface. In contrast, their palmar surface is wrinkled and irregular. The nonarticular heads contain an irregular, curved shaped distal tuberosity. It serves as an anchor point for the pulps of the digits.

The distal phalanges are stabilized by the digital fascial complex, collateral interphalangeal ligaments and extensor expansion of hand. The collateral interphalangeal ligaments attach to the base of the distal phalanges to reinforce the DIP joints.

The distal phalanges are capable of flexion and extension at the DIP joints. Two forearm extensors and one flexor muscle insert directly into the bases of the distal phalanges, permitting these actions. These include flexor digitorum profundus, flexor pollicis longus and extensor pollicis longus. The previously mentioned muscle groups acting on the proximal and middle phalanges also act indirectly on the distal ones via the extensor expansion of hand.

BLOOD SUPPLY

The hand phalanges are richly supplied with blood, lymphatics, and nerves, and their development involves a precise pattern of ossification. The blood supply to the phalanges comes primarily from the digital arteries, which are branches of the superficial and deep palmar arches derived from the radial and ulnar arteries. These arteries run alongside the phalanges, especially near the lateral aspects, where they give off perforating branches that penetrate the bone through nutrient foramina. Venous drainage mirrors the arterial supply, with the digital veins draining into the superficial and deep venous systems of the hand. The lymphatic drainage follows the venous pathways, with lymphatic vessels accompanying the digital veins. These vessels drain into the epitrochlear and axillary lymph nodes, playing a crucial role in immune surveillance and fluid balance in the hand.

NERVOUS SUPPLY

The nervous supply of the phalanges is derived from the median, ulnar, and radial nerves, which innervate the hand based on their anatomical distribution. The median nerve supplies the palmar side of the first three and a half fingers and their corresponding phalanges, while the ulnar nerve supplies the remaining fingers. The radial nerve provides sensation to the dorsal aspect of the phalanges, primarily for the proximal portions of the first three fingers. These nerves are responsible for transmitting sensory information, including pain, touch, and temperature, and they also play a critical role in motor function by innervating the muscles controlling finger movement.

OSSIFICATION

Ossification of the hand phalanges follows a well-defined sequence. Each phalanx typically ossifies from one primary ossification center, which appears during fetal development, generally between the 8th and 12th weeks of gestation. A secondary ossification center forms at the base of the phalanx during early childhood, usually between 2 and 4 years of age, depending on the specific phalanx and its position in the hand. The fusion of the primary and secondary ossification centers, marking skeletal maturity, occurs by 15–18 years of age. The ossification sequence begins with the proximal phalanges, followed by the middle and distal phalanges. This progression is vital for assessing growth and development in pediatric radiology and clinical evaluations.

CARPAL BONES

 The Latin word "carpus" is derived from Greek καρπὁς meaning "wrist". The root "carp-" translates to "pluck", an action performed by the wrist.  In human anatomy, the main role of the wrist is to facilitate effective positioning of the hand and powerful use of the extensors and flexors of the forearm, and the mobility of individual carpal bones increase the freedom of movements at the wrist. 

There are 8 carpal bones, organized into two longitudinal rows, the proximal row contains Scaphoid, 

Lunate, Triquetrum and Pisiform and the distal row has Trapezium, Trapezoid, Capitate and 

Hamate.

SCAPHOID

It is a boat shaped bone and has a tubercle which is laterally, forwards and downwards.

The tubercle of the scaphoid gives attachment to flexor retinaculum and a few fibres of 

abductor pollicis brevis.

Scaphoid articulates with Radius, Lunate, Capitate, Trapezium and Trapezoid.

LUNATE

It is half-moon shaped or crescentic bone.

As it has a semi lunar surface, it articulates with the scaphoid on its lateral side. A quadrilateral 

surface for the triquetral on its medial side.

TRIQUETRAL 

It is a pyramid shaped bone.

The oval facet for the pisiform lies on the distal part of the palmar surface.

The medial and dorsal surfaces are continuous and nonarticular.

It articulates with pisiform, lunate, hamate and articular disc of the inferior radioulnar joint.

PISIFORM

It is a pea shaped bone.

The oval facet for the triquetral lies on the proximal part of the dorsal surface.

The lateral surface is grooved by the ulnar nerve.

It only articulates with Triquetral.

TRAPEZIUM

It is quadrangular in shape, has a crest and a groove anteriorly.

The palmar surface has a vertical groove for the tendon of the flexor carpi radialis.

The groove is limited literally by the crest of the trapezium.

The distal surface bears convexo-concave articular surface for the base of the 1st metacarpal bone.

It articulates with scaphoid, trapezium, capitate and 1st and 2nd metacarpal.

TRAPEZOID

It looks like a shoe of a baby.

The distal articular surface is bigger than the proximal.

The palmar nonarticular surface is prolonged laterally.

It articulates with scaphoid, trapezium, 2nd metacarpal and capitate.

CAPITATE

It is the largest bone in the carpal bones which has a rounded head.

The dorsomedial angle is the distal most projection from the body of the bone which bears a small facet for the 4th metacarpal bone.

It articulates with scaphoid, lunate, hamate, trapezoid and 2nd, 3rd & 4th metacarpals.

HAMATE

It is a wedge shaped with a hook near its base.

The hook projects from the distal parts of the palmar surface and is directed laterally.

MUSCLES AND LIGAMENTS

The intricate movements of the hand are facilitated by a delicate balance of muscular forces and a robust ligamentous network within the wrist. Two primary muscle groups contribute: extrinsic muscles, originating in the forearm, stabilize the wrist by maintaining hand position on the radius during coordinated muscle contractions. Intrinsic muscles, originating within the hand, fine-tune movements by balancing flexor and extensor forces.

The flexor carpi ulnaris, an extrinsic muscle, significantly influences wrist movement by inserting onto the hamate, pisiform, and the base of the fifth metacarpal. Intrinsic muscles demonstrate diverse origins: thenar muscles arise from the scaphoid and trapezium, the adductor pollicis originates from the capitate and second/third metacarpals, and hypothenar muscles originate from the pisiform and hamate.

A complex system of ligaments provides stability. Radiocarpal ligaments connect the radius to various carpal bones (scaphoid, lunate), while ulnocarpal ligaments connect the ulna to the lunate and capitate. Intercarpal ligaments bind the carpal bones together (e.g., lunotriquetral, scapholunate), forming a strong, interconnected structure. These ligaments, along with carpometacarpal and intermetacarpal ligaments, ensure stability during a wide range of hand movements.

BLOOD SUPPLY, LYMPHATICS AND NERVOUS SUPPLY

The radial artery, ulnar artery, and their anastomoses provide the blood supply of the wrist. The radial artery predominantly supplies the thumb and the lateral side of the index finger while the ulnar artery supplies the rest of the digits and the medial side of the index finger. In particular, vascular supply takes place via the anastomotic network consisting of three dorsal and three palmar arches, which arise from both the radial and ulnar arteries, that overlie the carpal bones. The scaphoid, capitate, and a minority of lunates (20%) all have one intraosseous vessel supply. Of note, the scaphoid has a single blood supply from the radial artery that enters from the distal portion of the bone to supply the proximal portion, thus making its proximal pole most vulnerable to avascular necrosis. The trapezoid and hamate both have two areas of blood supply without intraosseous anastomoses. The trapezium, triquetrum, pisiform, and most lunates (80%) have two areas of blood supply and consistent intraosseous anastomoses. Therefore, the rest of the carpal bones, excluding the scaphoid, capitate, and the minority of lunates, have a lower risk of developing avascular necrosis following a fracture.

Innervation of the wrist joint comes from the:

• anterior interosseous branch of the median nerve
• posterior interosseous branch of the radial nerve
• the dorsal and the deep branches of the ulnar nerve

The lateral antebrachial cutaneous nerve, the posterior interosseous nerve, the dorsal branch and the perforating branches of the ulnar nerve, and the superficial branch of the radial nerve innervate the wrist joint from the dorsum. The palmar cutaneous branch of the median nerve, the anterior interosseous nerve, and the main trunk and deep branch of the ulnar nerve innervate the wrist joint from the palmar side.

EMBRYOLOGY

Upper limb development initiates with the activation of a group of mesenchymal cells in the lateral mesoderm towards the end of the fourth week, with the limb buds becoming visible around day 26 or day 27. Each limb bud comprises a mass of mesenchyme covered by ectoderm. This mesenchyme remains undifferentiated until it is ready to develop into bone, cartilage, and blood vessels later in development. Meanwhile, at the apex of each limb bud, the ectoderm thickens to form the apical ectodermal ridge, which stimulates the growth and development of the upper limb bud in the proximal-distal axis. Other signaling centers and primary morphogens such as the zone of polarizing activity, derived from an aggregate of mesenchymal cells in the limb bud, and the Want pathway, expressed from the dorsal epidermis of the limb bud, also contribute to the development of the upper limb buds by regulating growth along the anteroposterior axis and the dorsoventral axis, respectively.

At the end of the sixth week of development, digital rays form in the hand plate. By the seventh week, the carpal chondrification process begins. The capitate and the hamate carpal bones are the first chondrogenic centers to appear as immature cartilage early in the eighth week while the pisiform is the last to appear later in the eighth week. The hamulus, otherwise known as the “hook of the hamate,” also appears as an immature cartilaginous tissue towards the end of the eighth week and does not complete its development until the thirteenth week. Last, in the fourteenth week, a vascular bud penetrates the lunate cartilage mold, an early sign of the osteogenic process that will complete during the first year of life.

Complied & Written by Dr. Palak Shah

Human Skeleton

As described in the previous blog, how our ancestors discovered Human Body, the first and foremost thing to study was the Human Skeleton.

Skeleton includes bones and cartilages which forms the main supporting framework of the bodyand which is primarily designed for a more effective production of movements by the attached muscles.

The number of bones when a child is born are 270 which fuses when he/she becomes an adult to 206 bones. 

There are mainly two divisions of human skeleton:

1. Axial skeleton which mainly consists of vertebral column, ribcage and skull. It mainly consists of 80 bones. It mainly forms the framework and protection of a human being. 

2. Appendicular Skeleton which is mainly consisting of shoulder girdle, upper limb, pelvic girdle and lower limb. It consists of total 126 bones in total. Its main role is to provide fine and gross motor movements. 

The below picture shows clear demarcation of axial and appendicular skeleton. 

There are 5 main functions of the Skeleton:

1. Support - It provides framework to which the whole body supports and it also maintains the shape.

2. Movement - There is movement between 2 bones qhich allows the movement. It is powered by the skeletal muscles which are attached to the bones.

3. Protection - It protects our vital organs like brain, spinal cord, lungs, heart, viscera, etc.

4. Blood Cells Production - The long bones in an adult human is a site of haematopoiesis i. e. development of blood cells in the bone marrow.

5. Endocrine Regulation - The bone cells release a hormone named as Osteocalcin which mainly helps in regulating blood sugar and fat metabolism.

THE TOTAL 206 BONES OF AN ADULT SKELETON

Human Body (206)
Axial Skeleton (80)		Appendicular Skeleton (126)
Skull (28)	Torso (52)	Upper Extremity (32 x 2 = 64)	Lower Extremity (31 x 2 = 62)
Paired Bones (11 x 2 = 22) Nasal Lacrimal Inferior Nasal Concha Maxiallary Zygomatic Temporal Palatine Parietal Malleus Incus Stapes	Paired Bones (12 x 2 = 24) Rib 1 Rib 2 Rib 3 Rib 4 Rib 5 Rib 6 Rib 7 Rib 8 (False) Rib 9 (False) Rib 10 (False) Rib 11 (Floating) Rib 12 (Floating)	Scapula Clavicle Humerus Radius Ulna Scaphoid Lunate Triquetrum Pisiform Hamate Capitate Trapezoid Trapezium Metacarpal 1 Proximal Phalange 1 Distal Phalange 1 Metacarpal 2 Proximal Phalange 2 Middle Phalange 2 Distal Phalange 2 Metacarpal 3 Proximal Phalange 3 Middle Phalange 3 Distal Phalange 3 Metacarpal 4 Proximal Phalange 4 Middle Phalange 4 Distal Phalange 4 Metacarpal 5 Proximal Phalange 5 Middle Phalange 5 Distal Phalange 5	Hip (Ilium, Ischium, Pubis) Femur Patella Tibia Fibula Talus Calcaneus Navicular Medial Cuneiform Middle Cuneiform Lateral Cuneiform Cuboid Metatarsal 1 Proximal Phalange 1 Distal Phalange 1 Metatarsal 2 Proximal Phalange 2 Middle Phalange 2 Distal Phalange 2 Metatarsal 3 Proximal Phalange 3 Middle Phalange 3 Distal Phalange 3 Metatarsal 4 Proximal Phalange 4 Middle Phalange 4 Distal Phalange 4 Metatarsal 5 Proximal Phalange 5 Middle Phalange 5 Distal Phalange 5
Frontal Ethmoid Vomer Sphenoid Mandible Occipital	Hyoid Sternum Cervical Vertebrae 1 (atlas) C2 (axis) C3 C4 C5 C6 C7 Thoracic Vertebrae 1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12 Lumbar Vertebrae 1 L2 L3 L4 L5 Sacrum Coccyx

Written and complied by: Dr. Palak Shah