An accessory bone or supernumerary bone is a bone that is not normally present in the body, but can be found as a variant in a significant number of people. It poses a risk of being misdiagnosed as bone fractures on radiography. [2]
An accessory bone or supernumerary bone is a bone that is not normally present in the body, but can be found as a variant in a significant number of people. It poses a risk of being misdiagnosed as bone fractures on radiography. [2]
| Accessory bone | Prevalence on the right (R) and left (L) [5] |
|---|---|
| Os ulnostyloideum | 1.5% R, 2.4% L |
| Os centrale | 1.3% R, 2.1% L |
| Os trapezium secundarium | 0.5% R, 2.1% L |
| Os styloideum | 1.2% R, 1.2% L |
| Os radiale externum | 1% R, 0.9% L |
| Os triangulare | 1% R, 0.9% L |
| Os paratrapezium | 0.3% R, 0.9% L |
| Os capitatum secundarium | 0.8% R, 0.3% L |
| Os Hypotriquetrum | 0.5% R |
| Os hypolunatum | 0.3% L |
| Os epilunatum | 0.3% R, 0.3% L |
| Os ulnare externum | 0.3% L |
| Os pisiforme secundarium | 0.3% R |
| Os epitrapezium | 0.3% L |
| Os vesalianum manus | 0.3% L |
The os ulnostyloideum is an ulnar styloid process that is not fused to the rest of the ulna bone. [6] On X-rays, an os ulnostyloideum is sometimes mistaken for an avulsion fracture of the styloid process. However, the distinction between these is extremely difficult. [6] [7] It is alleged that the os ulnostyloideum has a close relationship with or is synonymous with the os triquetrum secundarium. [8]
The os carpi centrale (also briefly os centrale) is, where present, located on the dorsal side of the wrist between the scaphoid, the trapezoid and capitate, radially to the deep fossa of the capitate. The bone is present in almost every human embryo of 17–49 mm length, but then usually fuses with the ulnar side of the scaphoid. Sometimes it fuses with the capitate or the trapezoid. The literature also refers to an os centrale at the palm of the carpus, but this existence is questioned. [6]
In most primates, including orangutans and gibbons, the os centrale is an independent bone that is attached to the scaphoid by strong ligaments. Conversely, in African apes and humans, the os centrale normally fuses to the scaphoid early in development. [9] In chimpanzees, the bone fuses with the scaphoid first after birth, while in gibbons and orangutans this occurs first at older age. [10] A good number of scholars have construed the scaphoid-centrale fusion as a functional adaptation to knuckle-walking, [11] since a fused morphology would better cope with the increased shear stress on this joint during this kind of quadrupedal locomotion. The results from a simulation study have shown that fused scaphoid-centrales show lower stress values as compared to non fused morphologies, thus supporting a biomechanical explanation for the scaphoid-centrale fusion as a functional adaptation for knuckle-walking. [12]
Accessory bones at the ankle mainly include:
Os trigonum (further described below) may also be seen on an ankle X-ray.
| Bone | Prevalence [17] |
|---|---|
| Sesamoid bones | |
| Sesamoids at the metatarsophalangeal (MTP) joint of the great toe | Always present |
| Sesamoid of the second metatarsal | 0.4% |
| Sesamoid of the third metatarsal | 0.2% |
| Sesamoid of the fourth metatarsal | 0.1% |
| Sesamoids of the fifth metatarsal | 4.3% |
| Sesamoid of the interphalangeal (IP) joint of the great toe | 2–13% |
| Ossicles | |
| Os trigonum (not visible in this dorsoplantar projection) | 7–25% |
| Os peroneum | Up to 26% |
| Accessory navicular | 2–21% |
| Os intermetatarseum | 1–13% |
| Os supranaviculare, also called the talonavicular bone | 1.0–3.5% |
| Os calcaneus secundarium | 0.6–7% |
| Os supratalare | 0.2–2.4% |
| Os vesalianum | 0.1–1% |
| Os talotibiale | 0.5% |
An accessory navicular bone, also called os tibiale externum, occasionally develops in front of the ankle towards the inside of the foot. This bone may be present in approximately 2–21% of the general population and is usually asymptomatic. [18] [19] [20] When it is symptomatic, surgery may be necessary.
The Geist classification divides the accessory navicular bones into three types. [20]
The os trigonum or accessory talus represents a failure of fusion of the lateral tubercle of the posterior process of the talus bone. Is estimated to be present in 7–25% of adults. [17] It can be mistaken for an avulsion fracture of lateral tubercle of talus (Shepherd fracture) or a fracture of the Stieda process. In most cases, Os Trigonum will go unnoticed, but with some ankle injuries it can get trapped between the heel and ankle bones which irritates the surrounding structures, leading to Os Trigonum Syndrome. [21]
The carpal bones are the eight small bones that make up the wrist (carpus) that connects the hand to the forearm. The term "carpus" and "carpal" is derived from the Latin carpus and the Greek καρπός (karpós), meaning "wrist". In human anatomy, the main role of the carpal bones is to articulate with the radial and ulnar heads to form a highly mobile condyloid joint, to provide attachments for thenar and hypothenar muscles, and to form part of the rigid carpal tunnel which allows the median nerve and tendons of the anterior forearm muscles to be transmitted to the hand and fingers.
In anatomy, a sesamoid bone is a bone embedded within a tendon or a muscle. Its name is derived from the Greek word for 'sesame seed', indicating the small size of most sesamoids. Often, these bones form in response to strain, or can be present as a normal variant. The patella is the largest sesamoid bone in the body. Sesamoids act like pulleys, providing a smooth surface for tendons to slide over, increasing the tendon's ability to transmit muscular forces.
In human anatomy, the acromion is a bony process on the scapula. Together with the coracoid process it extends laterally over the shoulder joint. The acromion is a continuation of the scapular spine, and hooks over anteriorly. It articulates with the clavicle to form the acromioclavicular joint.
In human anatomy, the wrist is variously defined as (1) the carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand; (2) the wrist joint or radiocarpal joint, the joint between the radius and the carpus and; (3) the anatomical region surrounding the carpus including the distal parts of the bones of the forearm and the proximal parts of the metacarpus or five metacarpal bones and the series of joints between these bones, thus referred to as wrist joints. This region also includes the carpal tunnel, the anatomical snuff box, bracelet lines, the flexor retinaculum, and the extensor retinaculum.
The tibia, also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates ; it connects the knee with the ankle. The tibia is found on the medial side of the leg next to the fibula and closer to the median plane. The tibia is connected to the fibula by the interosseous membrane of leg, forming a type of fibrous joint called a syndesmosis with very little movement. The tibia is named for the flute tibia. It is the second largest bone in the human body, after the femur. The leg bones are the strongest long bones as they support the rest of the body.
The patella, also known as the kneecap, is a flat, rounded triangular bone which articulates with the femur and covers and protects the anterior articular surface of the knee joint. The patella is found in many tetrapods, such as mice, cats, birds and dogs, but not in whales, or most reptiles.
The scaphoid bone is one of the carpal bones of the wrist. It is situated between the hand and forearm on the thumb side of the wrist. It forms the radial border of the carpal tunnel. The scaphoid bone is the largest bone of the proximal row of wrist bones, its long axis being from above downward, lateralward, and forward. It is approximately the size and shape of a medium cashew nut.
The capitate bone is a bone in the human wrist found in the center of the carpal bone region, located at the distal end of the radius and ulna bones. It articulates with the third metacarpal bone and forms the third carpometacarpal joint. The capitate bone is the largest of the carpal bones in the human hand. It presents, above, a rounded portion or head, which is received into the concavity formed by the scaphoid and lunate bones; a constricted portion or neck; and below this, the body. The bone is also found in many other mammals, and is homologous with the "third distal carpal" of reptiles and amphibians.
The lunate bone is a carpal bone in the human hand. It is distinguished by its deep concavity and crescentic outline. It is situated in the center of the proximal row carpal bones, which lie between the ulna and radius and the hand. The lunate carpal bone is situated between the lateral scaphoid bone and medial triquetral bone.
The navicular bone is a small bone found in the feet of most mammals.
Flat feet, also called pes planus or fallen arches, is a postural deformity in which the arches of the foot collapse, with the entire sole of the foot coming into complete or near-complete contact with the ground. Sometimes children are born with flat feet (congenital). There is a functional relationship between the structure of the arch of the foot and the biomechanics of the lower leg. The arch provides an elastic, springy connection between the forefoot and the hind foot so that a majority of the forces incurred during weight bearing on the foot can be dissipated before the force reaches the long bones of the leg and thigh.
The talus, talus bone, astragalus, or ankle bone is one of the group of foot bones known as the tarsus. The tarsus forms the lower part of the ankle joint. It transmits the entire weight of the body from the lower legs to the foot.
An ankle fracture is a break of one or more of the bones that make up the ankle joint. Symptoms may include pain, swelling, bruising, and an inability to walk on the injured leg. Complications may include an associated high ankle sprain, compartment syndrome, stiffness, malunion, and post-traumatic arthritis.
An accessory navicular bone is an accessory bone of the foot that occasionally develops abnormally in front of the ankle towards the inside of the foot. This bone may be present in approximately 2-21% of the general population and is usually asymptomatic. When it is symptomatic, surgery may be necessary.
The fifth metatarsal bone is a long bone in the foot, and is palpable along the distal outer edges of the feet. It is the second smallest of the five metatarsal bones. The fifth metatarsal is analogous to the fifth metacarpal bone in the hand.
The scapholunate ligament is a ligament of the wrist.
In the skeleton of humans and other animals, a tubercle, tuberosity or apophysis is a protrusion or eminence that serves as an attachment for skeletal muscles. The muscles attach by tendons, where the enthesis is the connective tissue between the tendon and bone. A tuberosity is generally a larger tubercle.
Episternal ossicles are small bones that are sometimes present at the upper end of the chest bone. The prevalence of these ossicles is around 1.5%.