Anatomical variation

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An anatomical variation, anatomical variant, or anatomical variability is a presentation of body structure with morphological features different from those that are typically described in the majority of individuals. Anatomical variations are categorized into three types including morphometric (size or shape), consistency (present or absent), and spatial (proximal/distal or right/left). [1]

Contents

Variations are seen as normal in the sense that they are found consistently among different individuals, are mostly without symptoms, and are termed anatomical variations rather than abnormalities. [2]

Anatomical variations are mainly caused by genetics and may vary considerably between different populations. The rate of variation considerably differs between single organs, particularly in muscles. [2] Knowledge of anatomical variations is important in order to distinguish them from pathological conditions.

A very early paper published in 1898, presented anatomic variations to have a wide range and significance, [3] and before the use of X-ray technology, anatomic variations were mostly only found on cadaver studies. The use of imaging techniques have defined many such variations. [4]

Some variations are found in different species such as polydactyly, having more than the usual number of digits.

Variants of structures

Muscles

Kopsch gave a detailed listing of muscle variations. These included the absence of muscles; muscles that were doubled; muscles that were divided into two or more parts; an increase or decrease in the origin or insertion of the muscle; and the joining to adjacent organs. [2]

The palmaris longus muscle in the forearm is sometimes absent, as is the plantaris muscle in the leg. [5]

The sternalis muscle is a variant that lies in front of the pectoralis major and may show up on a mammogram. [6]

Bones

Usually there are five lumbar vertebrae but sometimes there are six, and sometimes there are four. [5]

Joints

A discoid meniscus is a rare thickened lateral meniscus in the knee joint that can sometimes be swollen and painful. [7]

Organs

The lungs are subject to anatomical variations. [8]

Clinical significance

Accessory small bones called ossicles may be mistaken for avulsion fractures.[ citation needed ]

See also

Related Research Articles

Anatomy Study of the structure of organisms and their parts

Anatomy is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science which deals with the structural organization of living things. It is an old science, having its beginnings in prehistoric times. Anatomy is inherently tied to developmental biology, embryology, comparative anatomy, evolutionary biology, and phylogeny, as these are the processes by which anatomy is generated, both over immediate and long-term timescales. Anatomy and physiology, which study the structure and function of organisms and their parts respectively, make a natural pair of related disciplines, and are often studied together. Human anatomy is one of the essential basic sciences that are applied in medicine.

Lung Primary organ of the respiratory system

The lungs are the primary organs of the respiratory system in humans and most animals including a few fish, and some snails. In mammals and most other vertebrates, two lungs are located near the backbone on either side of the heart. Their function in the respiratory system is to extract oxygen from the air and transfer it into the bloodstream, and to release carbon dioxide from the bloodstream into the atmosphere, in a process of gas exchange. Respiration is driven by different muscular systems in different species. Mammals, reptiles and birds use their different muscles to support and foster breathing. In earlier tetrapods, air was driven into the lungs by the pharyngeal muscles via buccal pumping, a mechanism still seen in amphibians. In humans, the main muscle of respiration that drives breathing is the diaphragm. The lungs also provide airflow that makes vocal sounds including human speech possible.

Femur Thigh bone

The femur, or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with the tibia (shinbone) and patella (kneecap), forming the knee joint. By most measures the two femurs are the strongest bones of the body, and in humans, the largest and thickest.

Knee Region around the kneecap

In humans and other primates, the knee joins the thigh with the leg and consists of two joints: one between the femur and tibia, and one between the femur and patella. It is the largest joint in the human body. The knee is a modified hinge joint, which permits flexion and extension as well as slight internal and external rotation. The knee is vulnerable to injury and to the development of osteoarthritis.

Joint Location at which two or more bones make contact

A joint or articulation is the connection made between bones, ossicles, or other hard structures in the body which link the skeletal system into a functional whole. They are constructed to allow for different degrees and types of movement. Some joints, such as the knee, elbow, and shoulder, are self-lubricating, almost frictionless, and are able to withstand compression and maintain heavy loads while still executing smooth and precise movements. Other joints such as sutures between the bones of the skull permit very little movement in order to protect the brain and the sense organs. The connection between a tooth and the jawbone is also called a joint, and is described as a fibrous joint known as a gomphosis. Joints are classified both structurally and functionally.

Sesamoid bone Bone embedded within a tendon or muscle

In anatomy, a sesamoid bone is a bone embedded within a tendon or a muscle. Its name is derived from the Arabic word for, 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.

Bronchus Airway in the respiratory tract

A bronchus is a passage or airway in the lower respiratory tract that conducts air into the lungs. The first or primary bronchi pronounced (BRAN-KAI) to branch from the trachea at the carina are the right main bronchus and the left main bronchus. These are the widest bronchi, and enter the right lung, and the left lung at each hilum. The main bronchi branch into narrower secondary bronchi or lobar bronchi, and these branch into narrower tertiary bronchi or segmental bronchi. Further divisions of the segmental bronchi are known as 4th order, 5th order, and 6th order segmental bronchi, or grouped together as subsegmental bronchi. The bronchi when too narrow to be supported by cartilage are known as bronchioles. No gas exchange takes place in the bronchi.

Psoas major muscle Long fusiform muscle located in the lumbar region

The psoas major is a long fusiform muscle located in the lateral lumbar region between the vertebral column and the brim of the lesser pelvis. It joins the iliacus muscle to form the iliopsoas. In animals, this muscle is equivalent to the tenderloin.

Meniscus (anatomy) Fibrocartilaginous part of a bone joint

A meniscus is a crescent-shaped fibrocartilaginous anatomical structure that, in contrast to an articular disc, only partly divides a joint cavity. In humans they are present in the knee, wrist, acromioclavicular, sternoclavicular, and temporomandibular joints; in other animals they may be present in other joints.

Vastus medialis Extensor muscle located medially in the thigh that extends the knee.

The vastus medialis is an extensor muscle located medially in the thigh that extends the knee. The vastus medialis is part of the quadriceps muscle group.

Popliteus muscle Muscle responsible for unlocking the knees during walking

The popliteus muscle in the leg is used for unlocking the knees when walking, by laterally rotating the femur on the tibia during the closed chain portion of the gait cycle. In open chain movements, the popliteus muscle medially rotates the tibia on the femur. It is also used when sitting down and standing up. It is the only muscle in the posterior (back) compartment of the lower leg that acts just on the knee and not on the ankle. The gastrocnemius muscle acts on both joints.

Plantaris muscle One of the superficial muscles of the superficial posterior compartment of the leg,

The plantaris is one of the superficial muscles of the superficial posterior compartment of the leg, one of the fascial compartments of the leg.

Shoulder girdle Set of bones which connects the arm to the axial skeleton on each side

The shoulder girdle or pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side. In humans it consists of the clavicle and scapula; in those species with three bones in the shoulder, it consists of the clavicle, scapula, and coracoid. Some mammalian species have only the scapula.

Sternalis muscle

The sternalismuscle is an anatomical variation that lies in front of the sternal end of the pectoralis major parallel to the margin of the sternum. The sternalis muscle may be a variation of the pectoralis major or of the rectus abdominis.

Human vestigiality Human traits which lost their original function through evolution

In the context of human evolution, human vestigiality involves those traits occurring in humans that have lost all or most of their original function through evolution. Although structures called vestigial often appear functionless, a vestigial structure may retain lesser functions or develop minor new ones. In some cases, structures once identified as vestigial simply had an unrecognized function. Vestigial organs are sometimes called rudimentary organs.

Meniscus tear Rupturing of the fibrocartilage strips in the knee called menisci

A tear of a meniscus is a rupturing of one or more of the fibrocartilage strips in the knee called menisci. When doctors and patients refer to "torn cartilage" in the knee, they actually may be referring to an injury to a meniscus at the top of one of the tibiae. Menisci can be torn during innocuous activities such as walking or squatting. They can also be torn by traumatic force encountered in sports or other forms of physical exertion. The traumatic action is most often a twisting movement at the knee while the leg is bent. In older adults, the meniscus can be damaged following prolonged 'wear and tear'. Especially acute injuries can lead to displaced tears which can cause mechanical symptoms such as clicking, catching, or locking during motion of the joint. The joint will be in pain when in use, but when there is no load, the pain goes away.

Discoid meniscus

Discoid meniscus is a rare human anatomic variant that usually affects the lateral meniscus of the knee. Usually a person with this anomaly has no complaints; however, it may present as pain, swelling, or a snapping sound heard from the affected knee. Strong suggestive findings on magnetic resonance imaging includes a thickened meniscal body seen on more than two contiguous sagittal slices.

Anatomical terminology Scientific terminology used by anatomists, zoologists, and health professionals

Anatomical terminology is a form of scientific terminology used by anatomists, zoologists, and health professionals such as doctors.

Axillary arch Muscular slip associated with latissimus dorsi muslce.

The axillary arch is a variant of the latissimus dorsi muscle in humans. It is found as a slip of muscle or fascia extending between the latissimus dorsi muscle and the pectoralis major. There is considerable variation in the exact position of its origin and insertions as well as its blood and nerve supply. The arch may occur on one or both sides of the body. A meta-analysis revealed that the axillary arch had an overall prevalence of 5.3% of limbs.

References

  1. Yammine, Kaissar (2014). "Evidence-Based Anatomy". Clinical Anatomy. 27 (6): 847–852. doi:10.1002/ca.22397. ISSN   0897-3806. PMC   4282349 . PMID   24797314.
  2. 1 2 3 "Anatomic variants".
  3. Cunningham, DJ (October 1898). "The Significance of Anatomical Variations". Journal of Anatomy and Physiology. 33 (Pt 1): 1–9. PMC   1327970 . PMID   17232348.
  4. Bell, Daniel J. "Anatomical variants | Radiology Reference Article | Radiopaedia.org". Radiopaedia.
  5. 1 2 Saladin, K (2012). Anatomy and Physiology (6th ed.). pp. 14–15. ISBN   9780073378251.
  6. Garg, T. "Sternalis muscle". radiopaedia.org. Retrieved 19 September 2019.
  7. Kim, JG; Han, SW; Lee, DH (2016-12-01). "Diagnosis and Treatment of Discoid Meniscus". Knee Surgery & Related Research. 28 (4): 255–262. doi: 10.5792/ksrr.16.050 . PMC   5134787 . PMID   27894171.
  8. Moore, K (2018). Clinically oriented anatomy (Eighth ed.). p. 342. ISBN   9781496347213.