Rakesh, 30-yrs has marked swelling on palmar aspect of the wrist. Persistent flexion of fingers and apparent shortening of middle finger is seen. There is paresthesia over palmar aspect of the thumb, index, middle, and a questionable portion of the ring finger, yet when wrist is gently flexed, intense pain spreads over this area. Sensation over palm is normal. Partial flexion of fingers in this case is best explained by which of the following?