Use your old mannequin skin to make a open fracture you can use over and over again. Cut 2 layers of skin. Make a lacerartion in the upper layer and use a piece of artificial bone. Glue the layer with the laceration on top on the second layer. Use superglue to secure the peace of bone on the lower layer. Use some blood to make it look real and attach this wound on arm or leg with some bandage.
If you want you can also attach a electrocath catheter connected with a 50ml syringe to make it bleed.