To evaluate the post-operative functional reduction of the shoulder joint and the impacting factors to post-operative shoulder joint function in interlocking IM nailing treatment of humeral shaft fracture.

From April 1999 to August 2004, 35 patients (35 cases) whom admitted to hospital for humeral shaft fracture and treated using interlocking intramedullary nail were followed up for more than 1 year. 1 year post-operative shoulder joint function were evaluated using American Shoulder Elbow Surgery Scale (ASES). Pre-operative shoulder joint pain, radiologically degenerative change and extent of nail protrusion were evaluated, and each factor was correlated with function of the shoulder joint.

33 cases out of 35 cases showed union and average union period was 12 weeks. Complications consisted of 2 cases of nonunion, 1 case of infection, 1 case of loosening of distal fixing screw, 1 case of radial nerve palsy and 1 case of axillary nerve palsy. Shoulder joint function 3 months after operation : mean ASES score 78.2, 12 months after operation : mean ASES score 89.6. Pre-operative shoulder joint pain and nail protrusion showed to be statistically related to shoulder joint function.

If the operation leaves no protrusion of intramedullary nail, it can be concluded to be relatively safe and effective.