Sesamoid bones are what medicine refers to as flat-round bones that are embedded in tendons. These bones enhance the biomechanical effects of tendons and keep tendon attachments at a distance from bones to prevent pressure damage. Fatigue fractures are the most common symptoms of disease in sesamoid bones.
What are sesamoid bones?
Sesamoid bones are tendon bones. Together with long bones, flat bones, short bones and irregular bones, sesamoid bones make up the total of five different types of bones. In humans, they are found particularly in the wrist and ankle joints. Each sesamoid bone is grown or embedded in a tendon. The ossicle holds the tendons and surrounding bones apart at a specific distance. Most often, the small ossicles occur in tendons at a joint. The largest and best known sesamoid bone is the patella, also known as the kneecap. The patella is embedded in the tendon apparatus known as the quadriceps femoris muscle and is involved in the articular surfaces of the knee joint. Like all sesamoid bones, the patella creates a greater distance between the surrounding bones and tendons. How many sesamoid bones a person has is relatively individual. For example, not everyone has the fabella of the knee joint. Women are slightly more likely to have this spacer bone than men. Animals also have sesamoid bones. In horses, for example, the samesamoid bones between the pastern and the long bone fall into this group.
Anatomy and structure
In general, sesamoid bones are flat and round. In terms of their size and shape, human sesamoid bones are dependent on their location but are relatively variable. For example, the patella of the knee joint runs triangularly in the tendon of the quadriceps femoris muscle and passes into the knee joint. The fabella at the lateral head of the gastrocnemius, on the other hand, is bean-shaped in the tendon of the gastrocnemius muscle, but is not found in every person. The so-called ossa sesamoidea of the hand are also sesamoid bones. These include the os pisiforme, which is one of the carpal bones and is embedded in the tendon of the flexor carpi ulnaris muscle. The best known sesamoid bone of the hand is the pea bone. The metacarpal, in turn, consists of the ossa metacarpalia. Sesamoid bones can also occur in this area. Usually, about two to three of the bones sit distally here. In the foot, sesamoid bones are also found in the area of the ossa sesamoidea. They are located in the flexor tendons of the great toe.
Function and tasks
All sesamoid bones have the function of a spacer. They keep the tendon away from the surrounding bones and especially the adjacent joints, thereby facilitating movement, among other things. In fact, the way the sesamoid bones are constructed helps the muscle on a tendon to have a greater pulling effect. The bones are therefore often referred to as switch points. Thanks to the patella, the lower leg can be stretched, for example, even if the thigh muscle involved is not particularly strong. The stretching is associated with a perceived low effort for the person, because the tendon associated with sesamoid bones achieves a better biomechanical leverage effect thanks to the knuckles. In this context, the sesamoid bones also perform the function of a pulley, thus granting the tendon additional protection. Some tendons run along a joint. As they pass through a joint, tendons with sesamoid bones are protected from damage that could occur as a result of the compressive action. The sesamoid bone redirects the tendons for this purpose, preventing pressure damage. Without sesamoid bones, when a tendon runs along a joint, it can also be damaged by bruising, for example. In this context, the sesamoid bones prevent the tendon from slipping into the joint space and becoming painfully pinched.
Diseases
Sesamoid bones are often affected by fatigue fractures. Such fractures usually manifest as a sharp pain that occurs only with exertion. For example, a sesamoid fracture in the foot might manifest itself during jogging, causing shooting pain that completely resolves during a period of rest. Fatigue fractures are usually a result of repetitive stress, such as those associated with certain sports. As a rule, a fatigue fracture of the sesamoid bones is initially treated by immobilization.Under certain circumstances, however, chipped bone material is also removed during surgery. In addition to fractures, inflammations of the sesamoid bone can also occur. In most cases, these inflammations are characterized by overheating and radiate to the metatarsophalangeal joint near the sesamoid bone. Inflammatory processes also sometimes present themselves as a concomitant of sesamoid fractures or bone fractures in the immediate vicinity of the sesamoid bone, since malpositions and incorrect loads can thus occur. If the sesamoid bones of the foot are affected by inflammation, orthopedic insoles are usually advised as a therapeutic measure. Sometimes an aseptic necrosis of the bone occurs in the course of a fracture and inflammation of the sesamoid bone. In order to avoid this late consequence, relief is urgently advised. Orthopedic insoles, for example, can support this relief in the case of complaints in the foot. The sesamoid bones of the hand can likewise be affected by fractures, inflammation, or necrosis as a result of overloading in the context of chronic incorrect loading.
