Posted on 22 Oct 2012 00:01
A close-packed position in a synovial joint is the position in which the joint surfaces become fully congruent and their area of contact is at a maximum. This position has been described as a "screwed in" or "screwed home" position, where the joint is tightly compressed and the ligaments and joint capsule are tense, allowing no more movement. This type of position results in the bones being "locked together" is essence, as if not joint existed between them, allowing them to transmit static forces most efficiently because the joint is extremely stable.
An example of this is the wrist being extended, or in maximum dorsiflexion, which is the typical position in which we push on objects with our hands, do pushups, etc. In this way, with the wrist being locked back in a tight position, force is transmitted from the hands through the wrist joint most efficiently. If the wrist were straight, it would be less stable.
Other examples are full extension of the knee (when the knee is straight), extension of the interphalangeal joints (when the fingers are straight), and maximum dorsiflexion of the foot (when the foot is flexed back toward the leg fully). All other joint positions are loose-packed positions.
While a close-packed position is the most efficient for handling a great amount of static force, it is more dangerous for dynamic forces. To understand this, think of jumping from a height and landing on your fully extended knees. The knees are in a close packed position, which does not allow them to help absorb the sudden high force applied to the body, resulting in more potential for injury, both to the joint and the rest of the body, such as the spine, which must absorb the force, as well. On the other hand, this position would be the best to support a heavy load on the shoulders.
For more information of this kind see Management of Common Musculoskeletal Disorders: Physical Therapy Principles and Methods by Management of Common Musculoskeletal Disorders: Physical Therapy Principles and Methods
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This page created 22 Oct 2012 00:01
Last updated 30 Apr 2016 04:09