Primary stability of shoulder arthrodesis using cannulated cancellous screws

There are no biomechanical studies available concerned with the primary stability of shoulder arthrodesis. The aim of our biomechanical investigations was to ascertain a minimal material combination with high primary stability for shoulder arthrodesis. For that purpose, the primary stability of 6 different forms of screw arthrodesis was investigated under the stress of abduction, adduction, anteversion, and retroversion. The mean values of the screw arthrodeses were compared with those of a 16-hole plate arthrodesis. All tests were carried out on 24 human specimens without destruction by use of a materials testing machine. The most stable form of screw arthrodesis for the load directions of abduction, adduction, anteversion, and retroversion results from a specific configuration of screws comprising 3 horizontal humeroglenoid screws and 3 vertical acromiohumeral screws (318.5 +/- 99.0 N). For three forms of arthrodesis, each with 3 humerus-glenoid screws (299.9 +/- 95.4 N), no significant difference (P = .530) was found compared with a 16-hole plate arthrodesis (293.4 +/- 89.3 N). The plate arthrodeses only achieved higher power values on abduction and adduction stress in comparison with screw arthrodesis with 3 humerus-glenoid screws. The difference was insignificant. Because arthrodesis with 3 humerus-glenoid screws was significantly more stable on stress of anteversion and retroversion, this particular screw arthrodesis is considered superior to plate arthrodeses. The use of the most stable form of screw arthrodesis may reduce nonunion.