Fabrication of the CROW Boot

By Steve Hill, BOCO, CO

It goes by many names. CROW boot, walking boot, healing boot and anterior/posterior AFO, among others. No matter what you call it, the CROW boot is more popular now than ever. Well, more popular with therapists, doctors and patients anyway. Most technicians still consider it to be a pain in the Barcalounger. One of the most labor intensive orthosis, the CROW boot is the last ditch effort to keep amputation at bay.

The CROW boot, by definition, is an anterior/posterior, full contact and full circumference AFO with a walking sole. Its intended purpose is to protect the affected ankle/foot from further damage by replacing the shoe with an orthotic device suitable for ambulating in. For this reason it must be total contact, otherwise the decubitus ulcers and diabetic skin will continue to break down.

CROW stands for Charcot Restraint Orthotic Walker. I tell you this because I once had a practitioner order a custom CROW boot and was surprised when it came back to him without black plastic (which he didn’t order). He complained saying “It’s supposed to be black! What do you think CROW stands for?” When I told him what I thought it stood for, he just got kinda quiet and then said “Yeah, that’s right. I was just checking to see if you knew.”

Okay, I can live with that…

And black plastic is usually the best choice, generally speaking. It blends in better, especially if you wear black shoes. We usually use co-poly due to the nature of pigmented polypropylene. Black polypro doesn’t have the normal rigid characteristic once it’s heated. It just becomes more difficult to work with so you might as well just go with co-poly which acts the way it’s supposed to.

Modifications

To begin with, the cast must be perfect. If it isn’t, you might as well toss it in the garbage and recast. Due to the nature of Charcot ankle and Diabetes, any rubbing and pressure will irritate the limb and cause further damage, which totally negates the whole point.

Once the cast has been filled and stripped, carefully clean the soap/powder off of the mold with a sureform. Don’t flatten the plantar surface, there may be an ulcer, but the Charcot ankle almost always runs on the bottom. You don’t want to create pressure there. Skive off about a quarter inch or so from the dorsal aspect, from ankle crease to about mid-foot. This is to allow for the foot to drop into the ½”+ foam UCB and maintain total contact.

Once the cast is prepared for plaster, mark the areas of build-up and apply plaster. Build-ups will be minimal, but you’ll have to give a little clearance at the ankle, metatarsal, navicular and possibly the cuboid. Extend the toe box by about a half inch. This is to allow room for the toes and prevents them from hitting and tearing off toenails (yikes!). A flair at the top is optional, but suggested. Smooth up cast as usual.

Vacuum Forming

The first thing we want to do is to form the removable UCB insert. Determine its shape, UCB style or SMO style, and draw it onto the cast. Add one layer of stocking and form insert with your choice of materials. Typically, this insert will be ½” thick when completed and can be formed from almost any single or combination of soft materials, such as Pelite, cork, Tri-Lam, PPT, Volara… almost anything that achieves your end goals. Sand insert to shape, tapering edges slightly for a more cosmetic appearance.

Adding a little contact cement to the edges of the insert, glue on it to the cast making sure it sticks well to the first layer of stocking. Add another layer of stocking of top of UCB and cast. Vacuum form some ¼” foam on to the cast, add another stocking and pull plastic (3/16” – ¼”) over top, forming the posterior section. Cut off cast and finish out once plastic has cooled sufficiently. Keep the trim lines just anterior of midline for easy donning and doffing.

Reapply posterior section (with UCB insert) to the cast. Due to shrinkage, you might have to remove some plaster from the cast at the distal/plantar toe box to get it back on again. Now this next step is important. Run a castsaw barrier down the length of the posterior aspect, from above the proximal flair to the end of the toes. Forgetting this step will virtually necessitate doing the entire process, up to this point, all over again.

Pull another layer of stocking over the cast and vacuum form the anterior layer of foam. The advantage of vacuum forming the foam is that it gives you and easy way to cut-away the excess foam where it overlaps at the anterior/posterior. No sense in padding the overlap, is there? What we do is to just remove the foam once it’s formed, cut along the groove in the foam made by the posterior section and reapply the foam to the cast, stapling it in place.

Add yet another layer of stocking and pull the anterior section. Be sure that the knot at the end of stocking doesn’t interfere with the overlap at the end of the toe box. Once the plastic has cooled, cut the anterior section off of the mold and sand to shape. There shouldn’t be more than ¾” of overlap at the anterior/posterior juncture. Now comes the hard part.

Rocker Sole

A walking boot isn’t a walking boot without a layer of crepe or similar material on the plantar surface. And, more often than not, you’ll want to add a rocker bottom too. This is where it gets a little tricky, but practice will make it much easier over time. There are several ways to do it, but this is our method.

First, trace the shape of the foot onto the crepe (or whatever material you’re using for the rocker shape) and cut it out. Rough up the plastic on the plantar surface where you want the crepe attached so that the glue will have something to stick to. Apply liberal amounts of glue. We use Barge but feel free to use whatever you like best. Heat the crepe up in the oven and form it over the bottom of the foot. It helps to wrap it with elastic bandage to ensure a good fit. Carefully sand off the excess crepe from the sides and form a rocker shape.

Continue to add layers of crepe until the proper shape and height are achieved. I like to leave off the final, thin, textured layer of material until fitting time so that you can fine-tune the rocker shape as needed, but that’s up to you. If you find that you’ve made some minor scratches to the plastic while sanding the crepe, you can buff them out and flame polish the surface for a more attractive appearance.

Strap It!

Now all that’s left is to apply the straps. This can be done to suit the needs of the patient, just be sure to put enough straps on it to supply good circumferential pressure. Some folks like to put the strap on the distal/plantar surface before adding the crepe rocker bottom, making it difficult to fix the strap if it tears or wears. I like to attach the strap where I can drill it out and fix it if need be, but that’s just me.

That’s pretty much it. There are some things to be aware of though. The fit should be snug, but not tight. While making the removable UCB insert, you might want to make more than one. They have a tendency to get compacted down (and nasty), especially if the patient has decubitus ulcers. And because these patients are typically also insensate diabetics, frequent follow up visits, particularly within the first few days, are highly recommended.