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This flexion deformity of the proximal interphalangeal joint is due to interruption of the central slip of the extensor tendon such that the lateral slips separate and the head of the proximal phalanx pops through the gap like a finger through a button hole (thus the name, from French boutonnière "button hole"). The distal joint is ...
Central slip is the tendon on the top of the finger attached to the middle bone of the finger, aiding the straightening of the middle PIP joint [1] The primary cause of boutonnière deformity is trauma, such as blunt force, lacerations, or dislocations.
The relative length of the digit varies during motion of the IP joints. The length of the palmar aspect decreases during flexion while the dorsal aspect increases by about 24 mm. The useful range of motion of the PIP joint is 30–70°, increasing from the index finger to the little finger.
The lateral and medial portions of the palmar aponeurosis are thin, fibrous layers, which cover, on the radial side, the muscles of the ball of the thumb, and, on the ulnar side, the muscles of the little finger; they are continuous with the central portion and with the fascia on the dorsum of the hand.
The classification of central polydactyly is based on the extent of duplication and involves the following three types: Type I is a central duplication, not attached to the adjacent finger by osseous or ligamentous attachments; it frequently does not include bones, joints, cartilage, or tendons.
As the tendons cross the interphalangeal joints, they furnish them with dorsal ligaments. The tendon to the index finger is accompanied by the tendon of extensor indicis, which lies on its ulnar side. On the back of the hand, the tendons to the middle, ring, and little fingers are connected by two obliquely placed bands, one from the third ...
A single median band passes down the middle of the finger along the back of the proximal phalanx, inserting into the base of the middle phalanx. A band known as the retinacular ligament runs obliquely along the middle phalanx, and connects the fibrous digital sheath on the anterior side of the phalanges to the extensor expansion.
To perform the test, a patient is asked to hold an object, usually a flat object such as a piece of paper, between the thumb and index finger (pinch grip). The examiner then attempts to pull the object out of the subject's hands. [2] A normal individual will be able to maintain a hold on the object without difficulty.