-ksen
You are, my friend, a victim of a faulty translation of the Hebrew. The word ka-'ari does not mean 'pierce'. If 'pierce' were the intended meaning, the psalmist would have used a different word, probably nakar, which is used in 2 Kings 18:21:
Behold, you are relying now on Egypt, that broken reed of a staff, which will pierce the hand of any man who leans on it.
The faulty translation is based upon the assumption that the root of the word used is krh, which means 'to dig'. The problem is, karah refers to digging in the soil, and is made up of the letters kaph, resh and he. The actual word used (ka-'ari) is made up of kaph, 'aleph, resh, and yod.
The literal meaning of ka-'ari (and one which doesn't ignore the 'aleph) is "like a lion". A correct translation of the verse is "Like a lion they are gnawing at my hands and my feet." This ties in with the imagery of the rest of the psalm:
[13] they open wide their mouths at me,
like a ravening and roaring lion.
[16] Yea, dogs are round about me;
a company of evildoers encircle me;
Like a lion they are gnawing at my hands and my feet.
[21] Save me from the mouth of the lion...