As depicted in the photo. The panel that failed had to support not only its own weight, but the weight of the adjacent panel that was hinged to it.
First you will need a work area large enough to lay the panel down on. A couple of saw horses and a sheet of plywood will suffice.
Measure the distance between the bottom of the top Rail and the top of the bottom Rail of your shutter panel. Place the Pony clamps with stands on your work surface parallel to each other the same distance as the measurement you just took between upper and lower Rails.
Next, place three pieces of wood on top and perpendicular to the clamps. The outside pieces of wood should be at least as long as the Stiles of your damaged panel and no wider than their width. The center piece of wood will be used to support the upper and lower Rails as well as the Louvers and Tilt Rod.
Ensure that all louvers contain nylon louver pins. If all louver are not attached to the Tilt Rod, do not worry, this situation will be addressed later after the panel is fixed (replace missing tilt rod staple, replace missing louver staple).
Ensure Pony clamps are in the full open position. Position yourself adjacent to panel on working surface. Then position damaged shutter panel so the near stile is resting against Pony clamps.
Move all shutter louvers into louver pin holes of near Stile.
While doing so, monitor the shutter panel for square during this and upcoming procedures.
Next, slowly turn the Pony clamps and draw in the far Stile. You should close clamps to a point where the far Stile is just short of touching the far Louver Pins. At this point you should be able to insert far Louver Pins into far Stile without having near Louver Pins fall out of near Stile.
In situations where one Rail has not failed, it will be necessary to do the above procedure in the direction of the failed Rail. As depicted in figure 1, the bottom Rail has not yet completely failed. In this case you would slowly clamp and work your way up from top to bottom using the procedure as outlined in previous paragraph.
After the shutter panel is fully clamped, and all louvers are where they are supposed to be, our next step will be to mechanically fasten each corner of the shutter panel where Stiles and Rails meet.
Pre-drill two holes in each stile at each corner of shutter the panel. The holes should be counter-sunk through the Stiles and into the Rails. When drilling holes take note to ensure that your drill bit is square and level to shutter the frame. This will prevent screw from blowing through face of Rail.
Install screws in each hole. Drill bit and screw sized should be appropriate to panel. Some shutter panels may have smaller or larger dimensioned Stiles and Rails.
Take your time, and keep an eye on the all the Louvers. More often than not, Louver Pins will fall out of near and far Stile holes and will need to be re-positioned during this procedure.