keepeth [shamar] all his bones [`etsem]: not
one ['echad] of them [hennah] is broken [shabar]. KJV-Interlinear
20 He keeps
all his bones; not one of them is broken. ESV
The deliverance of the Christian, follows the pattern of the deliverance and protection of the Savior.
When Christ went to the cross, the typical policy of the executioners was to break the bones of the one hanging on the cross, in order to hurry their death.
However, Jesus was already dead physically and therefore His legs were not broken, thus the fulfillment of this prophecy.
But in this psalm, the non-broken bones of the righteous, or of the individual believer is stated in a way that portrays the protection of the person, by God.
This has nothing to do with a person falling or breaking a bone from time to time. Obviously that happens in life.
But the principle here is to symbolize the entire framework of the body, which is in reference to the person. God protects the whole, not just a part or portion here or there, but the whole life of the individual believer.
God protected Jesus, in the helplessness of His humanity while hanging on the cross, and foresaw the protection hundreds of years prior to the time of the cross, and so too, God protects the individual believer, having foreseen the need for protection clear back in eternity past.