Brian Woods, Manchester.
I suspect that this numbness relates to damage done during your operation.
Your description fits with a diagnosis of ulnar neuropathy, the second most common form of tingling fingers (after carpal tunnel syndrome). It occurs when the ulnar nerve — which runs the length of the arm and, among other things, conveys sensation to the little finger, part of the ring finger and the palm — becomes pinched.
Typically, the nerve becomes compressed in a groove close to the elbow causing tingling and numbness of the little finger and half of the adjacent ring finger.
This is in contrast to carpal tunnel syndrome, which is also caused by a pinched nerve but in this case it is the median nerve — the other main nerve supplying the hand. It becomes trapped close to the wrist joint, causing symptoms in the thumb and index finger.
The ulnar nerve can be damaged at the elbow by acute trauma, such as a fracture, or it can be irritated by compression from leaning on the elbow — or, most commonly, by keeping the elbow flexed for a prolonged period of time.
I suspect this is the cause in your case.
During your recent abdominal operation, it is likely that once you were anaesthetised and on the operating table your arms were flexed at the elbow and laid on your chest, away from the area of the surgery.