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Anatomical Angle Made by the Fingers of an Extended Palm

Anatomical Angle Made by the Fingers of an Extended Palm



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Does the angle made by the fingers (excluding the thumb) of an extended palm (as shown in the figure below) have a name (such as the Lovibond or Cobb angle, for instance) ?

I have already checked Modeling the Constraints of Human Hand Motion, published by the Beckman Institute for Advanced Science and Technology at the University of Illinois at Urbana-Champaign, but it failed to provide any answers. (Perhaps there aren't any ?) Any input would be deeply appreciated.


Evolution of the human hand: the role of throwing and clubbing

It has been proposed that the hominid lineage began when a group of chimpanzee-like apes began to throw rocks and swing clubs at adversaries, and that this behaviour yielded reproductive advantages for millions of years, driving natural selection for improved throwing and clubbing prowess. This assertion leads to the prediction that the human hand should be adapted for throwing and clubbing, a topic that is explored in the following report. It is shown that the two fundamental human handgrips, first identified by J. R. Napier, and named by him the ‘precision grip’ and ‘power grip’, represent a throwing grip and a clubbing grip, thereby providing an evolutionary explanation for the two unique grips, and the extensive anatomical remodelling of the hand that made them possible. These results are supported by palaeoanthropological evidence.


Flexion and Extension

Flexion and extension are movements that take place within the sagittal plane and involve anterior or posterior movements of the body or limbs. For the vertebral column, flexion (anterior flexion) is an anterior (forward) bending of the neck or body, while extension involves a posterior-directed motion, such as straightening from a flexed position or bending backward. Lateral flexion is the bending of the neck or body toward the right or left side. These movements of the vertebral column involve both the symphysis joint formed by each intervertebral disc, as well as the plane type of synovial joint formed between the inferior articular processes of one vertebra and the superior articular processes of the next lower vertebra.

In the limbs, flexion decreases the angle between the bones (bending of the joint), while extension increases the angle and straightens the joint. For the upper limb, all anterior motions are flexion and all posterior motions are extension. These include anterior-posterior movements of the arm at the shoulder, the forearm at the elbow, the hand at the wrist, and the fingers at the metacarpophalangeal and interphalangeal joints. For the thumb, extension moves the thumb away from the palm of the hand, within the same plane as the palm, while flexion brings the thumb back against the index finger or into the palm. These motions take place at the first carpometacarpal joint. In the lower limb, bringing the thigh forward and upward is flexion at the hip joint, while any posterior-going motion of the thigh is extension. Note that extension of the thigh beyond the anatomical (standing) position is greatly limited by the ligaments that support the hip joint. Knee flexion is the bending of the knee to bring the foot toward the posterior thigh, and extension is the straightening of the knee. Flexion and extension movements are seen at the hinge, condyloid, saddle, and ball-and-socket joints of the limbs (see Figure 9.5.1a-d).

Hyperextension is the abnormal or excessive extension of a joint beyond its normal range of motion, thus resulting in injury. Similarly, hyperflexion is excessive flexion at a joint. Hyperextension injuries are common at hinge joints such as the knee or elbow. In cases of “whiplash” in which the head is suddenly moved backward and then forward, a patient may experience both hyperextension and hyperflexion of the cervical region.


Abduction, Adduction, and Circumduction

Figure 2. Abduction, adduction, and circumduction.

Abduction and adduction are motions of the limbs, hand, fingers, or toes in the coronal (medial–lateral) plane of movement. Moving the limb or hand laterally away from the body, or spreading the fingers or toes, is abduction. Adduction brings the limb or hand toward or across the midline of the body, or brings the fingers or toes together. Circumduction is the movement of the limb, hand, or fingers in a circular pattern, using the sequential combination of flexion, adduction, extension, and abduction motions.

Adduction, abduction, and circumduction take place at the shoulder, hip, wrist, metacarpophalangeal, and metatarsophalangeal joints.

Abduction and Adduction

Abduction and adduction motions occur within the coronal plane and involve medial-lateral motions of the limbs, fingers, toes, or thumb. Abduction moves the limb laterally away from the midline of the body, while adduction is the opposing movement that brings the limb toward the body or across the midline. For example, abduction is raising the arm at the shoulder joint, moving it laterally away from the body, while adduction brings the arm down to the side of the body. Similarly, abduction and adduction at the wrist moves the hand away from or toward the midline of the body. Spreading the fingers or toes apart is also abduction, while bringing the fingers or toes together is adduction. For the thumb, abduction is the anterior movement that brings the thumb to a 90° perpendicular position, pointing straight out from the palm. Adduction moves the thumb back to the anatomical position, next to the index finger. Abduction and adduction movements are seen at condyloid, saddle, and ball-and-socket joints (see Figure 2).

Circumduction

Circumduction is the movement of a body region in a circular manner, in which one end of the body region being moved stays relatively stationary while the other end describes a circle. It involves the sequential combination of flexion, adduction, extension, and abduction at a joint. This type of motion is found at biaxial condyloid and saddle joints, and at multiaxial ball-and-sockets joints (see Figure 2).


Dupuytren Anatomy

The anatomy of the hand is complex. It’s also hard to see. Dupuytren disease affects some structures in the hand which are so small they don’t appear in CT, MRI, or even most anatomy books. Everything is connected, which means that even in surgery, you can’t see some of the structures until you have already cut through them.

Because of this, Dupuytren anatomy is usually shown in diagrams such as these.

View of the palm, normal anatomy affected by Dupuytren disease. Click for larger.

Oblique views of the finger, deep and shallow:and a palm-up cross-section through the finger near the middle (PIP) finger joint:These are locations of common Dupuytren cords.
View from the palm:Oblique view of the finger:It’s hard to get a three-dimensional mental image from these two-dimensional drawings. A workaround is to use scrolling cross-sections, the way doctors look at CT or MRI images.

Part of the Dupuytren story has to do with the anatomy of the skin of the palm and how it resembles a quilt. A quilt is made by layering a sheet of fabric, then a layer of soft padding, then another layer of fabric and sewing these together with stitches passing through all layers. Crease designs can be made with patterns of extra stitches. The skin of the palm is anchored to the hand with threads that attach it to deeper layers. These deeper layers are anchored to deeper and deeper layers going in different directions all the way down to the bones in the back of the hand and fingers. Creases in the palm are areas where extra anchoring threads exist. Here’s a cross-section of the hand at the level of the palm where creases go sideways across the palm. In palmistry these creases are the head line and the heart line. The different structures at this level are color-coded.

At this level, the skin is anchored down and the layers under the skin absorb the stress and strain of gripping. This animation shows the same layers as in the cross-section picture. Click it to see a larger version.

Below, a video scrolling through cross-sections of a palm-up cadaver hand, progressing from mid-palm to fingertip. The upper right shows about where the section is. This video has colorized overlays of these structures to show their relationships. Tweak settings to get the sharpest video: Start the video. Stop it. Click the gear icon at the bottom. Choose quality. Choose 1080p HD (not auto). Play full screen.

Still not perfect, but a step forward toward a real three-dimensional model which could be used to study why Dupuytren affects some parts of the hand but not others.

Where does Dupuytren affect the hands? These are heat maps from about 2300 previously untreated patients I examined in my practice over the course of years.
The red circles below show how often different jointswere contracted. The bigger the circle and the darker the red, the more common.

The blue areas below show how common were locations of Dupuytren nodules, the early stage of disease. The darker the blue, the more common.

The blue areas below show how common were locations of Dupuytren cords, the late stage of disease. The darker the red, the more common.

The green areas below show how common were locations of Dupuytren spiral cords, where Dupuytren cords pass underneath nerves and arteries, bringing them up to the surface into harm’s way when doing surgery. The darker the green, the more common.

Why do these patterns exist? It’s a combination of the anatomy of the hand, the forces the hand experiences during use, the effect of the resting posture of the hand on hand anatomy, and the biology of Dupuytren. It’s not just one thing, or these diagrams would all line up. But they don’t. We need to understand the mechanobiology of Dupuytren disease – the crossroads of physical and biological forces – to make progress toward better treatment.


Energy

To better understand the “Energy” in the 6 Ji (Energy) Hands, we must first understand that the energetic transfer mentioned so often in the art of Kyusho (as seen in seminars, classes, video and text). We must look to the actual deployment and action that affects the attacked surface in a particular way by adding penetration and torque into the ballistic or manipulative action being performed.

To clarify this a bit, we have 3 main actions (there are others), which are predominantly used in Kyusho:

  1. Pressure on the nerve, it is not a slow or steady pressure, it is a quick pulsing action that transmits a rapid and acute electro-chemical reaction in the nerve manipulated.
  2. Rubbing action (actually stretching or stressing of a particular anatomical sensory receptor) is a rapid and deeply cutting action to activate a reflex action.
  3. Striking action, which is a deeper stretching, compressing or vibrational kinetic force to shock the nerve.

These types of energetic transfer are accomplished with proper physical and coordinated body actions using these specific hand positions. The correct action and application of torque or manipulative actions for these hand positions (along with some specific targets), can take years of study and practice to fully understand, but can actually be trained quickly to gain successful use and with no physical conditioning that can cause physical damage to the hands such as arthritis or joint damage.

There are 6 variations of torque involved in the hands actions and why the name of energy hands is so fitting. Investigating them in greater detail will enable the reader to better understand the specific hands as well as their individual possibilities.

1. Iron Bone Hand – twisting transference.

This hand position utilizes the first knuckle of the thumb for the attacking surface. The proper way to use this is in a double twisting action where the wrist simultaneously performs two twisting actions. On impact with the target, the wrist will simultaneously twist outward and downward so that the fingers travel (loosely), upward and away from the target. This focuses the energy down and into the target more readily and sends an acute shock wave into the nerve structure.

Some viable targets are Under Eye Brow, ST-5 up, St-5 down, TW-17, ST-9, SI-18, M-HN-14, M-HN-18, LV-13, LV-14, H-2, ST-17, GB-26, BL-23, GB-20, SP-11, ST-34 and many others.

2. Iron Sand Palm – Extending (Exploding) Transference

Using the palm of the hand (not the fingers), this is an ideal weapon for harder surfaces where the nerve is superficial such as in the GB-Cluster of the forehead. The GB-Cluster is actually two braches of the Supraorbital nerve that surfaces from behind the bone of the eye to transverse up from the corner of the eye as well as the middle of the eyebrow, up the forehead and into the hair line, just under the skin and other tissue. The method to use this weapon is to quickly extend the palm itself (as the fingers withdraw), on impact. This will cause a shock wave into the struck mass that is expansive in nature… think of the ripples in the water when an object enters it. This is also well suited for other targets that are found just under the skin on the harder foundation of the skull. These other viable targets are (but not limited to), ST-5, BL-10, ST-1, ST-3, M-HN-18, as there are many others.

3. Sword Hand (Wind Hand) – Snapping Transference

Used extensively in the Top Ten DVD and book, this weapon generates a lot of penetrating force due to the increase velocity of the weapon. Using the area called the heal of the palm or wrist bone, as the hand or arm travels to the target with a set velocity, it is then increased by jerking the wrist bone into the target causing a sharper surface area as well as sharper focal point of energy transfer. Some specific targets that react well with this attack are in softer tissue such as the neck for GB-20, LI-18 & ST-9, or even on harder surfaces like the back of the jaw at TW-15.

4. One blade of Grass Hand – Double directional transference

The double direction can be thought of in classical as Yin and Yang, or a simultaneous Push and Pull deployment. As an example the bent fingers can act as a pulling or stretching action as the extended finger jabs into the stretched nerve. For example, by grabbing the collar bone to activate the ST-10 or 11, this in affect stretches the nerve in between the strands of the sternocleidodmastoid muscle at ST-10 or ST-9 for a sharp penetrating jab from the extended index finger. This is accomplished with a torque of the wrist to gain focused and penetrating force with small efficient action.

5. Blood Pool Hand – forward rotational transference

This is for more powerful and percussive attack for many targets. It is better suited than the other hands for deeper penetration into the body targets or cavity using the forward rotational motion of the first two knuckles. However we cannot (as in all of the hand positions) negate the possibilities for poking, pulling or compressing type actions of the fingertips, or folding action of the palm.

Some targets such as K-27 just under the collarbone warrant, a deeper rolling (to stretch and compress), action. Interestingly as the name depicts “Blood Pool Hand” it was a tool used in the attack of organs where the blood actually pools. This could adversely affect or damage the Spleen, Liver, Kidney or even the Heart. Or as in the first target K-27 crucial vascular tissue to and from the Heart such as the Aortic or Jugular Arches.

6. Iron Claw Hand – Pulling Transference

This weapon is not new to most in the arts as it is one of the more common weapons. However it is not typically employed as was intended, nor is it typically taught to target Kyusho or Dim Mak in these modern times. However this is a very versatile weapon that originally targeted these weaker anatomical structures, such as on the Wrist, Forearm, Upper arm, Neck, Face even Minimally on the leg.

The correct application is to push surrounding structures away to expose the true target as it then compresses and twists to set (the Claws) into the structure. This single weapon is so vast in scope that we will devote another article and video presentation to illustrate them in more detail.


Background & Summary

The hand is a complex functional limb including over 30 muscles and more than 20 joints that allow performing a wide range of activities with a high level of precision. Kinematics is essential for hand functioning. The human hand has a linear actuator structure and it has control requirements that differ from the most common designs used to replicate it 1,2 . The analysis of complex hand movements is useful for several applications, including robotics 3,4 (to improve grasping by manipulators), 3D modelling 5 (to develop more realistic models of the hand for movies or computer games), rehabilitation and physiotherapy 6,7,8 (to improve hand rehabilitation), bioengineering, medicine and neuroscience (to better understand human hand movements, also in relationship to muscular and kinematic synergies 9,10 ).

Although studies are improving the understanding of hand kinematics 11,12,13,14,15 , scientific research in this field is still often affected by several limitations. First, most of the studies involve a small number of subjects (up to 10 subjects to our knowledge 13 ), lacking the possibility to generalize the results. Second, the studies often involve a small number of grasps, (up to 25 grasps to the best of our knowledge 13 ), lacking result completeness. Third, usually only postural movements were considered, without taking into account the entire movement, while “reach to grasp” and release are important phases in grasps modelling. Finally, most studies are based on raw instrumented glove data, which do not provide the linear outputs required to obtain reliable joint angles and can invalidate kinematic models obtained without a specific and accurate calibration method 16,17 .

Hand movements can be measured with different methods, but most of them fail when capturing kinematics while performing ADL (Activities of Daily Living). Goniometers do not allow for the simultaneous measurement of all DoFs (Degrees of Freedom). Electromagnetic systems are susceptible to magnetic and electrical interference from metallic objects in the environment. Marker-based optical systems can be used only within the area covered by the cameras, require a substantial amount of time to setup the markers, and markers often become occluded during the recording of tasks. Recently, portable and relatively low-cost devices became available, such as the Leap Motion controller system. However, these systems lack of accuracy to obtain reliable kinematic data during the performance of ADL 18 . At this point, instrumented gloves seem to be the most effective method for collecting data without occlusion problems and are among the most frequently used methods to collect data from finger joints and hand movements. However, the use of data gloves is not always straightforward. First, the response of the sensors can change depending on the size of the hand of the user. Second, the sensors can have non-linear relationships with the joint anatomical angles 16 , due to their position or due to the influence of other joint movements. Therefore, calibration processes are fundamental to obtain reliable gains for the sensors that record each degree of freedom.

Subject-specific data glove calibration procedures are time consuming. Thus, it is not easy to include them in data acquisition protocols (that are often already long and tiring). This consideration is true for healthy controls and particularly for patients and persons affected by disabilities, for which data acquisitions can be even more stressful and physically demanding.

A recently presented calibration method assures the possibility to calibrate the kinematic data recorded with a data glove in post-processing 17 . The method was described having a reasonable maximum precision error (below 5 degrees), thus it can improve the accuracy with which hand kinematics and anatomical angles are quantified.

In this work we apply the post-processing calibration method to kinematic data from 77 intact subjects included in the Ninapro (Non Invasive Adaptive Prosthetics) database (Ninapro Repository (http://ninapro.hevs.ch) and Zenodo 19 (10.5281/zenodo.3354437)). The novelty of the paper is related to the high number of subjects and movements and to the fact that the data are for the first time calibrated. The 77 subjects performed 40 hand movements and grasps plus rest, leading to our knowledge to the biggest hand kinematics dataset currently available. To obtain the hand anatomical angles, an across-subject calibration procedure 17 was applied.

This dataset aims at allowing worldwide research groups to study hand kinematics. The calibrated data are expected to foster the progress in many scientific domains, such as medicine, neuroscience, rehabilitation, physiotherapy, robotics, prosthetics and computer aided model design, leading for instance to a better understanding of human hand movements, improved rehabilitation protocols, robotic grasps that better correspond to human’s and more realistic 3D graphical models.

In conclusion, the kinematic dataset Ninapro DB9 improves the scientific state of the art with the most comprehensive reference for kinematic data existing to the best of our knowledge. The technical validation section verifies that the data are similar to data acquired in real-life conditions by statistical analyses and the visual inspection of the 3D hand model representations.


Range of Motion

Detailed articulation implies movement, and the hands move constantly. Not just for functional uses (holding a mug, typing) but also expressively, accompanying our words or reacting to our emotions. It's therefore no surprise that drawing hands well requires understanding how the fingers move.

The Thumb and Fingers

Let's start with the thumb, which works alone. Its real base, and centre of movement, is very low on the hand, where it meets the wrist.

  1. The natural relaxed position leaves a space between the Th and the rest of the hand.
  2. The Th can fold in as far as touching the root of LF, but this requires much tension and quickly becomes painful.
  3. The Th can extend as far as the width of the palm, but this also implies tension and gets painful.

The other four fingers have little sideways movement and mainly bend forward, parallel to each other. They can do this with a certain degree of autonomy, but never without some effect on the nearest fingers try for instance to bend your MF alone, and see what happens to the rest. The Th alone is completely independent.

When the hand closes into a fist and the fingers all curl together, the whole of the hand maintains a cupped shape, as if it was placed against a large ball. It’s just that the ball (here in red) gets smaller and the curvature stronger:

When the hand is fully extended (on the right), the fingers are either straight or bend slightly backwards, depending on flexibility. Some people’s fingers can bend back 90º if pressure is applied against them.

The fully closed fist is worth a detailed look:

  1. The 1st and 3rd fold of the fully bent finger meet, creating a cross.
  2. The 2nd fold appears to be an extension of the line of the finger.
  3. Part of the finger is covered by the flap of skin and the thumb, a reminder that the whole thumb structure is outermost. You can make your FF slip outside and cover the flap of skin, it's anatomically possible, but it is not a natural way to form a fist.
  4. The MF's knuckle protrudes most and the other knuckles fall away from it, so that from the angle shown here, the parallel fingers are visible from the outer side, not from the inner side.
  5. The 1st and 3rd fold meet and create a cross again.
  6. The thumb bends so that its last section is foreshortened.
  7. The skin fold here sticks out.
  8. When the hand makes a fist, the knuckles protrude and the "parenthesis" are visible.

The Hand as a Whole

When the hand is relaxed, the fingers curl slightly – more so when the hand is pointing up and gravity forces them bent. In both cases, the FF remains straightest and the rest fall away gradually, with the LF being the most bent. From the side, The gradation in the fingers makes the outer 2 or 3 peek out between FF and Th.

LF frequently “runs away” and stands isolated from the other fingers – another way of making hands look more natural. On the other hand, the FF and MF, or MF and RF, will often pair up, “sticking” together while the other 2 remain loose. This makes the hand look more lively. RF-LF pairings also occur, when the fingers are loosely bent.

Since the fingers are not the same length, they always present a gradation. When grasping something, like the cup below, the MF (1) wraps the most visibly around the object while the LF (2) barely shows.

When holding a pen or the like, MF, RF and LF curl back towards the palm if the object is held only between Th and FF (pick up a pencil lightly and observe this). If more pressure is applied, MF participates and straightens up as it presses against the object. Full pressure results in all the fingers pointing away as shown here.

As we have seen, the hand and wrist are remarkably articulated, each finger almost having a life of its own, which is why hands tend to stump the beginning illustrator. Yet when the hand starts to make sense, we tend to fall into the opposite trap, which is to draw hands too rationally – fingers carefully taking their places, parallel lines, careful alignments. The result is stiff and simply too tame for a part of the body that can speak as expressively as the eyes. It can work for certain types of characters (such as those whose personality shows stiffness or insensitivity) but more often than not, you’ll want to draw lively, expressive hands. For this you can go one of two ways: add attitude (i.e. add drama to the gesture, resulting in a dynamic hand position that would probably never be used in real life) or add natural-ness (observe the hands of people who aren’t thinking about them to see the casualness I’m referring to). I can’t possibly show every hand position there is, but I give below examples of constrained vs. natural/dynamic hand:

*Note in this particular case – trained fighters will always hold their fingers parallel while punching (as in the forced position), otherwise they may break their knuckles.


Bones and Joints

The foot is comprised of 28 bones (Figure 1). Where two bones meet a joint is formed –often supported by strong ligaments. It is helpful to think of the joints of the foot based on their mobility (Table 1). A few of the joints are quite mobile and are required for the foot to function normally from a biomechanical point of view. These are often referred to as essential joints. There are some joints that move a moderate amount, and there are other joints that are held tightly together with strong ligaments. These non-mobile joints are sometimes referred to as non-essential joints. (This may be a poor term in that it incorrectly implies that the joints are not important they are important. Rather the correct sense is only that movement from these joints is less critical.)

Table 1: Joint Function in the Foot

Mobile Joints of the Foot and Ankle (Essential Joints):

Ankle joint (tibiotalar joint)

Talonavicular joint (TN joint)

Metatarsophalangeal (MTP) joints

Joints that Move a Moderate Amount:

Cuboid-metatarsal joint for the fourth and fifth metatarsal.

Proximal interphalangeal joint (PIP)

Distal interphalageal joint (DIP)

Joints with Minimal Movement (Non-Essential Joints):

Tarsometatarsal (TMT) joint “Lisfranc” Joint (a.k.a. midfoot joint)

Bones of the lower leg and hindfoot: Tibia, Fibula, Talus, Calcaneus.
Joints of the hindfoot: Ankle (Tibiotalar), Subtalar.

Tibia and Fibula (long bones)

The foot is connected to the body where the talus articulates with the tibia and fibula. In a typical foot the tibia is responsible for supporting about 85% of body weight. The fibula accepts the remaining 15% its main role is to serve as the lateral wall of the ankle mortise (Figure 4). The tibia and fibula are held together by the tibiofibular syndesmosis, a collection of 5 ligaments. The prominence on the medial side of the distal tibia is known as the medial malleolus the distal aspect of the fibula is known as the lateral malleolus.

Talus

The talus is the top (most proximal) bone of the foot. Because it articulates with so many other bones, 70% of the talus is covered with hyaline cartilage (joint cartilage). The talus connects to the calcaneus on the underside through the subtalar joint, and distally it connects to the navicular through the talonavicular joint. These articulations allow the foot to rotate smoothly around the talus. Owing primarily to the fact that no tendons attach to it and that most of its surface is cartilage, the talus has a relatively poor blood supply. The lack of a robust blood supply means that injuries to this bone take greater time to heal than might be the case with other bones—and some injuries will not heal at all.

The talus is generally thought of as having three parts: the body, the head, and the neck (Figure 5). The talar body, which is roughly square in shape and is topped by the dome, connects the talus to the lower leg at the ankle joint. The talar head is adjacent to the navicular bone to form the talonavicular joint. The talar neck is located between the body and head of the talus. The talar neck is one of the few areas of the talus not covered with cartilage, and is thus the point of entry for the blood vessels supplying the talus.

Calcaneus

The calcaneus is commonly known as the heel bone. The calcaneus is the largest bone in the foot, and along with the talus, it makes up the area of the foot known as the hind-foot. There are three protrusions (anterior, middle, and posterior facet) on the superior surface of the calcaneus that allow the talus to sit on top of the calcaneus, forming the subtalar joint (Figure 6). The calcaneus also connects to the cuboid bone to form the calcaneal-cuboid joint.

Subtalar Joint

The talus rests above the calcaneus to form the subtalar joint (Figure 6) slightly offset laterally, towards the 5th metatarsal/small toe. This lateral positioning allows greater flexibility in inversion/eversion (tilting). The subtalar joint moves in concert with the talonavicular joint and the calcaneocuboid joint, two joints located near the front of the talus.

Bones of the midfoot: Cuboid, Navicular, Cuneiform (3).
Joints of the midfoot: talonavicular, calcaneocuboid, intercunneiform, tarsometatarsal (TMT).

Cuboid

The cuboid bone is a square-shaped bone on the lateral aspect of the foot. The main joint formed with the cuboid is the calcaneocuboid joint, where the distal aspect of the calcaneus articulates with the cuboid.

Navicular

The navicular is distal to the talus and connects with it through the talonavicular joint. The distal aspect connects to each of the three cuneiform bones. Like the talus, the navicular has a poor blood supply. On its medial side (closest to the middle of the foot) the navicular tuberosity is the main attachment of the posterior tibial tendon.

Transverse Tarsal Joint

The transverse tarsal joint is not a true joint, but the combination of the calcaneocuboid and talonavicular joints. When these two joints are aligned in parallel, the foot is flexible yet when their axes are divergent, the foot becomes stiff. The shift from a flexible state to a stiff one allows the foot to serve as a shock absorber and as a rigid level in different phases of gait.

Cuneiforms

There are three cuneiform bones in the foot: the medial, medial (intermediate), and lateral cuneiforms (Figure 7). These bones, along with the strong plantar and dorsal ligaments that connect to them, provide a good deal of stability for the foot.

Bones of the forefoot: Metatarsals (5), Phalanges (14), Sesamoid Bones (2)

Metatarsals

Each foot contains five metatarsals, numbered 1-5 medial (great toe) to lateral. The first three metatarsals medially are more rigidly held in place than the lateral two. The metatarsals articulate with the mid-foot at their base, a joint called the tarsal-metatarsal (TMT) joint, or Lisfranc joint. The TMT joint is made stable not only by strong ligaments connecting these bones, but also because the second metatarsal is recessed into the middle cuneiform in comparison to the others (Figure 7). The metatarsal heads are the main weight bearing surface and the site where the phalanges attached at the metatarsal-phalangeal (MTP) joint.

Phalanges

The first toe, also known as the great toe or hallux, is the only one to have two phalanges the other lesser toes have three. These are known as the proximal phalanx (closest to the ankle) and the distal phalanx (farthest from the ankle). The phalanges form interphalangeal joints between themselves: a proximal interphalaneal joint (PIP) and the distal interphalangeal joint (DIP) (Figure 8).

Sesamoid Bones

In the foot, there are two sesamoid bones located directly underneath the first metatarsal head, embedded in the medial (tibial) side and lateral (fibular) aspect of the flexor hallucis brevis tendon.

Common Ossicles of the Foot

Some feet contain accessory ossicles or accessory bones (Figure 9). These extra bones are developmental variants. Over 40 different ossicles of the foot have been reported. The most common accessory bones include:

Os Trigonum: Found at the posterior aspect of the talar body, this ossicle is connected to the talus via a fibrous union that failed to unite (ossify) between the lateral tubercle of the posterior process. An os trigonum is present in about 10% of the population.

Os Naviculare (Os Tibiale Externum or Accessory Navicular): This bone represents a failure to unite the ossification center the navicular tuberosity (where the tibialis posterior tendon inserts) to the main center of the bone. It is present in about 15% of the population.

Os Peroneum: This extra bone is found within the peroneus longus tendon sheath at the point where it wraps around the cuboid. It has been reported in about 20% of patients.

Bipartite Sesamoid: This condition occurs when one of the sesamoids associates with the great toe fails to ossify resulting in two bone segments connected by a fibrous union. It can be mistaken for a sesamoid fracture. Bipartite sesamoids are seen in about 20% of the population with more than 90% of them occurring in the tibial sesamoid.

Os Subfibulare: This extra bone is seen at the type of the fibula. It can be mistaken for an avulsion fracture. It is seen in 1-2% of the population.


Blood Supply

Hand has a rich vascular network contributed by radial and ulnar arteries.

Radial Artery in the Hand

Radial artery leaves the forearm by winding backwards around the wrist. It obliquely crosses the anatomical snuff box where it lies deep to the tendons that form it [Abductor pollicis longus, the extensor pollicis brevis and the extensor pollicis longus.]

It reaches the proximal end of the first interosseous space and passes between the two heads of the first dorsal interosseus muscle to reach the palm.

In the palm, the radial artery runs medially. At first it deep to the oblique head of the adductor pollicis, and then passes between the two heads of this muscle and known as the deep palmar arch.

On the dorsum of the hand, the radial artery gives off a branch to the lateral side of the dorsum of the thumb and first dorsal metacarpal artery. First dorsal metacarpal artery arises just before the radial artery passes into the interval between the two heads of the first dorsal interosseous muscle. It at once divides into two branches for the adjacent sides of the thumb and the index finger.

In the palm, the radial artery gives off princeps pollicis artery and radialis indicis artery.

Princeps pollicis artery divides at the base of the proximal phalanx into two branches for the palmar surface of the thumb.

The radialis indicis artery descends between the first dorsal interosseous muscle and the transverse head of the adductor pollicis and supplies the lateral side of the index finger.

It anastomoses with the princeps pollicis artery and gives a communicating branch to the superficial palmar arch.

Sometimes, The radialis indicis artery may arise from the princeps pollicis. Sometimes the princeps pollicis and the radialis indicis arteries arise by a common trunk called the first palmar metacarpal artery.

Ulnar Artery in the Hand

The ulnar artery runs distally in the forearm under the flexor carpi ulnaris muscle. At the wrist, it travels into the hand through the Guyon canal superficial to the flexor retinaculum. It divides into the superficial palmar branch and the deep palmar branch. These branches take part in the formation of the superficial and deep palmar arches respectively.

Arches of the hand are formed by anastomoses of the branches of the terminal parts of the ulna and radial arteries.

Superficial Palmar Arch

The superficial palmar arch is formed as the direct continuation of the ulnar artery beyond the flexor retinaculum.

The superficial palmar arch lies directly deep to the palmar fascia, palmaris brevis, and the palmar aponeurosis. It crosses the palm over the flexor digiti minimi, the flexor tendons of the fingers, the lumbricals, and the digital branches of the median nerve.

On the lateral side, superficial palmar branch of the radial artery, radialis indicis, and the princeps pollicis.

Superficial palmar arch gives rise to the volar common digital arteries and multiple branches to intrinsic muscles and skin. Distal in the palm, the common digital arteries bifurcate into the proper digital arteries.

It is interesting to note that in the palm, the arteries lie volar to the corresponding nerves but the relation is reversed in the digits.

Deep Palmar Arch

The deep palmar arch is formed mainly by the terminal part of the radial artery and is completed medially by the deep ulnar branch of the ulnar artery.

Deep to long tendons, the arch lies on the proximal parts of the shafts the metacarpals, and on the interossei. It lies under cover of the oblique head of the adductor pollicis, the flexor tendons of the fingers, and the lumbricals. The deep branch of the ulnar nerve lies within the concavity of the arch.

Three metacarpal arteries, which run distally in the second, third and fourth spaces supply the medial four metacarpals, and terminate at the finger clefts by joining the common digital branches of the superficial palmar.

Dorsally, the arch gives off three perforating arteries which pass through the medial three interosseous spaces to anastomose with the dorsal metacarpal arteries.

The distal perforating arteries connect the palmar digital branches of the superficial palmar arch with dorsal metacarpal arteries.

Recurrent branches pass proximally to supply the carpal bones and joints and end in the palmar carpal arch.

Veins generally follow the deep arterial system as venae comitantes. A superficial venous system also exists at the dorsum of the hand.

Synovial Sheaths and Bursae

Many of the tendons entering the hand are surrounded by synovial sheaths.

The synovial sheaths of the index finger, middle finger and ring finger are independent and terminate proximally at the levels of the heads of the metacarpals.

Synovial sheath of the little finger is continuous with the ulnar bursa and that of thumb with radial bursa. [Infections of the little finger and thumb can spread into the palm and even up radial and ulnar the wrist]. Half of the times, the radial and ulnar bursa communicate with each other behind the flexor retinaculum.