The connections of muscles to bone are usually thought of as long and collagenous tendons. Muscles, however, can also be attached by flat and sheetlike tendons called aponeuroses. In essence, the aponeurosis is the membranous expansion of a muscle or a muscle group. Under a microscope, it appears similar to a tendon, but it has fewer nerves and blood vessels.
There are several aponeuroses in the body, but the most well-known aponeuroses are found in the abdomen, palms and soles. In the abdomen, the external oblique, which is the largest and most superficial flat abdominal muscle, has its own aponeurosis. As the fibers of the external oblique run toward the midline, they become aponeurotic. The thinnest part of the external aponeurosis called linea alba can be found in the midline by tracing a vertical line along the umbilicus. With pregnancy or abdominal surgery, the external oblique aponeurosis can weaken, which is the reason why abdominal exercises are advisable after these events.
Palmar aponeurosis can be found in the hand. It overlies the soft tissues and the tendons of the flexor muscles. When there is a progressive increase in the fibrous tissue of this structure, a condition called Dupuytren’s contracture, or palmar fibromatosis, occurs. The fibrous bands that connect it to the bases of the fingers become shorter and thicker. This leads to marked flexion or bending of the digits, such that the digits cannot be straightened.
People who get Dupuytren’s contracture are often 40 years old or older. The most commonly affected fingers are the ring finger and the little finger, whereas the thumb and the index finger are usually spared. The progression is usually slow and painless. If it causes significant impairment or disability, Dupuytren’s contracture could be addressed through surgery. The procedure, however, is not curative and is fraught with complications, such as nerve and artery injuries and infection.
Plantar aponeurosis is found in the sole of the foot. The central part is very thick, but it thins out laterally and anteriorly. It is also called plantar fascia, because fasciae are connective tissues that are dense and regularly distributed. The main function of this structure is to support the arches of the foot and hold the foot structures together. As it goes to the digits, it splits into five bands that cover the digital tendons.
Inflammation of the aponeurosis plantar characterized by pain is called plantar fasciitis. It frequently occurs in athletes because of repetitive trauma to the soles. Foot deformities, obesity and age-related atrophy of the fat pad of the foot can also be predisposing factors.
Nonsurgical treatments of plantar fasciitis include rest, cold therapy, physical therapy, stretching and motion-control running shoes. Pharmacotherapy includes giving anti-inflammatory medications such as corticosteroids, aspirin, ibuprofen and other nonsteroidal anti-inflammatory drugs (NSAIDs). Orthotics or foot supports also can be tried. Surgery is a last resort because of the risk of nerve or artery injury and infection.