The palmar aponeurosis, along with the skin, is responsible for the strength of the palm. It is an important component of the gripping apparatus.
What is the palmar aponeurosis?
The term palmar aponeurosis is composed of the terms palma manus for the palm of the hand and aponeurosis, which is used to describe a tendon plate. Based on the usual functional designation for a tendon as the originating and attaching part of a muscle, there may be definitional problems with the term here. Although the palmar aponeurosis can be considered a fan-shaped continuation of the tendon of the palmaris longus muscle, unfortunately this muscle does not occur in 20% of people. In that case, the palmaris brevis muscle alone provides the muscular connection to the tendon plate. Histologically, however, the palmar aponeurosis belongs to the tendon tissue, which is very similar to the surrounding fascial structures. Therefore, some authors refer to the total complex of connected tendons and fascia of the palm as palmar fascia or palmar fascial complex. The palmar aponeurosis in a narrow sense represents the triangular tendon plate, the tip of which is located in the wrist region, while the broader part extends to the rays of fingers II-V.
Anatomy and structure
Starting from the wrist, the 4 longitudinal fibrous tracts fan out and extend to the fingers, where they radiate into the tendon sheaths of the finger flexors. They are reinforced by transverse fiber bundles, which are functionally similar to webbed fingers. In the wrist region, the tendon of the palmaris longus muscle arrives and begins to widen. This area is connected to the retinaculum flexorum, a tight ligamentous connection that holds the long flexor tendons in the so-called carpal tunnel. The fibers of this system reinforce the thin portion of the palmar aponeurosis. Other transverse reinforcements are located in the region of the metacarpals, known as the ligamentum metacarpale transversum, and as the fasciculi transversale in the region of the metacarpophalangeal joints. Laterally, the palmar aponeurosis merges with the fasciculi of the muscles of the ball of the big and little fingers. The palmaris brevis muscle radiates into the tendon tissue coming from the little finger side. It is a cutaneous muscle, which means that its origin has no bone contact. The palmar aponeurosis is fused to the skin with a dense network of connective fibers, into which the intervening layer of fat is firmly bound.
Function and tasks
The skin, in conjunction with the palmar aponeurosis and the intervening fat layer, forms a firm yet soft cushioning layer that provides protection from external influences. In particular, pressure loads when supporting or holding objects forcefully can be effectively buffered in this way. At the same time, the skin is strengthened by this cross-linking and its displaceability is limited. This ensures controlled contact during grasping and holding and reduces sensitivity. This function is significantly supported by the two muscles that radiate into the palmar aponeurosis. In the case of a hollow hand, the palm is brought closer together as a whole and purely passive tension can be lost. The musculi palmares longus et brevis counteract this by contracting and tightening the entire connective tissue structure. Subjectively, the firmness and tension of the palm is noticeable when shaking hands, including individual differences. The structures that run below the palmar aponeurosis are protected by it from damage that can act on them from the outside. These structures include the tendons of the long and short finger flexors, as well as the vessels and nerves that partially pierce the tendon plate and travel to their supply areas. Like the tendons of the finger flexors, the taut-elastic tissue of the palmar aponeurosis is stretched during extension. This preload creates potential energy that can be exploited for force development at the onset of finger flexion. Athletes take advantage of this mechanical advantage when they lunge to hit, as in volleyball.
Diseases
The nature of the palmar aponeurosis, like that of all connective tissue, depends on the constitutional conditions of the individual. In people with connective tissue weakness, the strength is less, and the whole structure feels softer.On the other hand, years of hard physical work not only changes the skin on the surface, but also the tightness of the underlying layers. Injuries to the palm or the tendons that tighten it can have very painful effects and temporarily change the properties of the palmar aponeurosis. Frequently, cuts occur in this area, which people inflict on themselves consciously or unconsciously. In the palm of the hand, broken glass can leave such cuts, which not infrequently heal poorly. Severing of the tendons that run along the forearm near the wrist occurs in unsuccessful suicide attempts when the cut runs across the longitudinal axis. This can also affect the palmaris longus muscle and thus the tension of the palmar aponeurosis. A specific disease that specifically affects the palmar aponeurosis is Dupuytren’s contracture. The slow progression begins with nodular and strand-like indurations of the tendon plate that are palpable but do not initially cause discomfort or functional limitations. As it worsens, the junctions with the tendon sheaths of the finger flexors are also affected. Most often, this process causes the little finger and ring finger to be pulled toward the palm and become immobile; the other fingers may or may not follow. The cause of this disease is still unknown. However, it is certain that the incidence is higher with increased tobacco and alcohol abuse, as well as with diabetes. One treatment option is surgical removal of the indurations in order to restore finger mobility. However, the risk of recurrence is very high.
