Orthopedic fixation device having a double-threaded screw

Claim 1

An orthopedic fixation device comprising: a fixation plate having at least one round through holes; a direction adjusting ring having an inner threaded hole, a plurality of arresting edges located at an upper side thereof, a stopping edge located at a lower side thereof, and a slit formed between any two arresting edges of said a plurality of arresting edges; and a double-threaded bone screw provided at a lower end thereof with a first threaded portion for fastening onto a bone or vertebra, said double-threaded bone screw further provided at an upper end thereof with a head for urging and spreading said a plurality of arresting edges so as to cause said direction adjusting ring to be retained securely in said round through hole of said fixation plate, said double-threaded bone screw still further provided with a second threaded portion located between said first threaded portion and said head and engageable with said inner threaded hole of said direction adjusting ring; wherein said inner threaded hole of said direction adjusting ring has an axis which forms with an axis of an outer ring body of said direction adjusting ring an angle ranging between 3 and 15 degrees.