When opening the Manual Data Entry form in Tracker™ Version 4, the software generates an error message which reads: "Ankylosis indication is not valid if data exists for opposite motion." Data cannot be entered after receiving this error. 

This error is caused by negative numbers in either the "Sacral Hip Flexion" or "Sacral Hip Extension" results.  The Manual Data Entry module evaluates these motions for ankylosis, and disallows a motion to be ankylosed, but still retains a record for the opposite motion.