Apodosis to Job 31:13, Job 31:16, Job 31:17, Job 31:19, Job 31:20, Job 31:21. If I had done those crimes, I should have made a bad use of my influence (“my arm,” figuratively, Job 31:21): therefore, if I have done them let my arm (literally) suffer. Job alludes to Eliphaz’ charge (Job 22:9). The first “arm” is rather the shoulder. The second “arm” is the forearm.
from the bone - literally, “a reed”; hence the upper arm, above the elbow.