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The mystery of the fingers: Why are the proximal interphalangeal joints more flexible than the distal interphalangeal joints?
When discussing finger dexterity, the functional differences between the proximal interphalangeal joints (PIP) and distal interphalangeal joints (DIP) have attracted much attention. While these two joints share many structural similarities, why does the PIP joint have greater mobility?
The proximal interphalangeal joints allow the fingers to bend flexibly and contact the palm when bent, while the flexion ability of the distal interphalangeal joints is usually more limited.
Joint structure
Understanding the structural characteristics of these two joints is essential to understanding their mobility. The PIP joint is highly stable, with its transverse diameter being larger than its anterior-posterior diameter, which allows the joint to maintain good stability in a variety of positions. Relatively speaking, the distal interphalangeal joint has low stability, resulting in a limited range of motion.
Dorsal structure
On the dorsal side of the PIP joint, the structures of the joint capsule, extensor tendons, and skin are relatively weak and lax, allowing the bones to bend further than 100° during flexion. The extensor mechanism is divided into three bands at the PIP joint, with the central band attaching to the tubercle on the dorsal side of the middle phalanx, which increases the extension capacity of the joint.
Volverine Structures
Unlike the dorsal structures, the thick ligaments on the palmar side effectively prevent hyperextension. The palmar ligament of the PIP joint, called the palmar plate, is 2 to 3 mm thick and plays an important supporting role. It can better resist the forces close to the proximal phalanx, thus protecting the normal function of the joint.
The support of the palmar ligament and the cooperation of the lateral ligament make the fingers more stable when performing various movements, especially when fast and flexible movements are required.
Action Range
The only movements of the interphalangeal joints are flexion and extension, with the proximal interphalangeal joints able to flex about 100° and the distal interphalangeal joints to about 80°. This difference is mainly due to the structure of the ligaments around the joint and where they attach.
Clinical significanceThe shape and flexibility of the fingers change as the interphalangeal joints move, allowing the fingers to better coordinate during flexible operations.
For clinical medicine, the impact of the PIP and DIP joints cannot be underestimated. Rheumatoid arthritis often spares the DIP joints, whereas inflammation of the DIP joints often suggests the presence of other diseases such as osteoarthritis or psoriatic arthritis.
ConclusionWhether in daily life or in the professional field, finger dexterity is closely related to the precision of various operations. Understanding the differences between the proximal and distal interphalangeal joints undoubtedly provides us with a deeper understanding and allows us to think about how to better protect these precious joints and functions in life. Does this change What does this tell us about hand health?
