27 de Mar de 2023

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  2.  A pulley is a simple mechanical machine and consists of a wheel that turns readily on an axle.  The wheel is usually grooved for a rope or a wire cable.
  3.  In the human body, in most cases the pulley is replaced by a bone, cartilage or ligament and the cord is replaced by a muscle tendon.  The tendon is lubricated in a manner so that it may easily slide over the pulley. anat.pulley
  4.  The fibers of a muscle or a muscle tendon wrap around a bone or are deflected by a bone prominence.  When the direction of pull is altered, the bone or bony prominence causing the deflection forms an anatomical pulley. anat. pulley
  5.  Redirect force to make task easier.  It makes task easier by deflecting the action line of a muscle away from the joint axis, thus inc the MA for a muscle force.
  6.  The skeletal structure of the hand and fingers is a set of rigid bones. Consequently, it takes great muscular control to perform the fine movements of the hand.  Without this highly specialized level of control, we would have serious challenges performing all kinds of activities from simply grasping an object to the detailed motor control required to play a musical instrument or writing.
  7.  A unique biomechanical pulley system provides the high level of control necessary to move the rigid finger bones with precision. The flexor tendons of the fingers run along the anterior surface of the fingers, and these tendons are tethered close to the bones by connective tissue "pulleys" at eight different locations from the metacarpophalangeal (MCP) joint to the distal phalanx. MCP DP MP PP
  8. Because the tendons are closely tethered to the bones, their pulling force is more efficient. Let's take a look at these pulleys, how they work and what happens when they don't.
  9.  There are mainly two types of pulleys in the hand:  Annular Pulleys( five in number).  Cruciate pulleys or connective tissue pulleys(three in number). PP DP MCP MP
  10.  There are five annular pulleys in the fingers, and they are named A1,A2,A3,A4 & A5.  The A1, A3, and A5 pulleys are smaller and considered minor pulleys (mostly due to size and lack of importance).
  11.  The A2 and A4 pulleys are larger and are sometimes called the major pulleys.  The A1, A3, and A5 pulleys are located at the MCP, PIP and DIP joints respectively.  The A2 and A4 pulleys are located in the middle of the proximal and middle phalanx respectively
  12.  A1 pulley: The first annular pulley arises from the palmar plate and proximal portion of the proximal phalanx. The A1 pulley overlies the membranous sheath at the level of the MCP joint and is approximately 8 mm in width.  A2 pulley: The second annular pulley consists of oblique fibers that overlie annular fibers. It originates from the proximal and lateral areas of the proximal phalanx and is approximately 17 mm in width. DP PP MP MCP
  13.  A3 pulley: The third annular pulley is located at the level of the PIP joint. This pulley attaches to the palmar plate and is approximately 3 mm in width.  A4 pulley: Like the A2 pulley, the fourth annular pulley, located in the middle phalanx, also consists of oblique fibers overlying annular fibers and is always preserved during surgery of the retinacular system. The A4 pulley is approximately 6.7 mm in width and has been shown to be the most important biomechanical pulley for maintaining independent interphalangeal joint function. DP MP PP MCP
  14.  A5 pulley :The fifth annular pulley is located proximal to the DIP joint, just proximal to the termination of the membranous sheath. The A5 pulley is the thinnest of the 5 annular pulleys and has a width of 4 mm. DP MP PP MCP
  15.  The annular pulleys may be damaged from an acute injury or from various degenerative conditions in the fingers.  An example of the detrimental effect of rupture of the annular pulleys is shown in Figure.
  16.  In this image, the A3 pulley has been completely ruptured and there is a partial rupture to the A2 pulley. As a result, the tendon is pulled away from the PIP joint, in what is referred to as a bowstringing effect.
  17.  With the tendon pulled away from the PIP joint, its power is reduced and it is no longer able to produce normal range of motion. As a result, the hand is significantly weaker in gripping activities.
  18.  A second set of connective-tissue pulleys, called cruciate pulleys, gives additional support and stability to the tendon sheaths.  The term cruciate means cross, and you can see by their structure where they get their name. MCP PP MP DP
  19.  Their role for improving the flexor tendon's angle of pull is not as great, so if they are damaged, finger movement is not impaired as much as with the annular  The cruciate pulleys are much smaller than the annular pulleys. There are three cruciate pulleys, designated as C1, C2, and C3 pulleys.
  20.  C1 Pulley: The first cruciform pulley lies just distal to the A2 pulley.  C2 Pulley: The second cruciform pulley is located in the space between the A3 and A4 pulleys.  C3 Pulley: The third cruciform pulley is located distal to the A4 pulley. A number of anatomic variations have been described for the retinacular system DP MP PP MCP