ARM: a modular hinged joint for the AO tubular external fixator.

Certain complex traumatic elbow lesions challenge the orthopaedic and trauma surgeon. If they are not treated correctly, they cause a high rate of disability, arising from elbow instablility and stiffness, either by fibrosis or joint incongruity. Injuries such as complex fractures of the proximal third of the ulna, coronoid fractures associated with radial head fractures (the "terrible triad"), are even worse if they are accompanied by soft tissue lesions. Hinged external fixators, complemented by other surgical procedures, are, for many, a recommended alternative when dealing with irreparable lesions. The AO tubular external fixator, by virtue of its versatility, is a very important tool in orthopaedics and trauma, but there is not the possibility of using it as a hinged fixator. The authors describe a prototype of a hinged joint that can be applied easily to the AO tubular external fixator, converting it into a hinged one. This hinged joint, in conjunction with the AO tubular external fixator, has been applied in 5 patients; 2 "terrible triads", one posterior elbow fracture-dislocation with radial head fracture, one Monteggia fracture-dislocation and an anterior elbow dislocation that developed a forearm compartment syndrome. The patients' age range was between 20 and 72 years (median 45,6); 4 were male and 1 female. In 3 patients, either a type III coronoid fracture or a radial head fracture, could not be repaired. One radial head was totally removed and another one partially removed. The remaining indications were because of severe soft tissue lesions. Results were evaluated using the Mayo Elbow Score Scale and the Broberg and Morrey radiographic evaluation scale. The median follow up was 18 months(range 6 to 48 months). All 5 patients got a maximum score of 100 points in the Mayo's Elbow Score Scale, indicating excellent results. No patient suffered elbow pain, or any type of elbow instability. The median range of motion in flexion was of 127.5 degrees (max. 140 degrees and min. 120 degrees ) and the median extension loss was 20 degrees (max. 25 degrees and min. 15 degrees ). One patient had pronation limited to 70 degrees and one had supination limited to 70 degrees . Every patient was able to resume a normal daily life activity and returned to normal work. In 3 patients the radiographic evaluation was Grade 0 and in the other 2, Grade I. Two complications occurred, one was a distal ulnar Schanz screw loosening with osteolysis and the other was a superficial infection of one Schanz screw. It can be concluded that good results can be obtained in injuries with severe elbow instability and soft tissue lesions, using this hinged external fixator. With this new clamp, the AO tubular external fixator is transformed into a hinged one and a new use is added to this already very versatile system. This clamp is very easy to apply.