Mackie Joints: Treating the Extreme
February 2018 Issue
I treated a patient with cerebral palsy during his physical therapy appointment. He had extreme wrist flexion contractures, elbow contractures, and hypertonia. The physical therapist had tried serial casting to no avail, and the casting had begun to cause skin breakdown. Initially, I fitted the patient with off-the-shelf elbow splints, but there wasn't an off-the-shelf solution for wrist contractures as severe as his (Figure 1). Instead, I casted him for custom splints that used Mackie joints with great results (Figure 2). Here is the process I used to fabricate the splints.
The patient's wrists were in 135 degrees of hyperflexion, so even with the therapist's help I had difficulty getting him in the proper position to make the cast. When taking casts of hands, remember to put an excess amount of Vaseline on the thumb to make sure the cast will come off and leave the thumb portion somewhat loose so the cast doesn't get caught at the interphalangeal (IP) joint of the thumb.
For ease of fabrication, you can cut the casts and correct them to 180 degrees or close to it (Figure 3). For small casts, I use thin aluminum bar stock that is small enough to go inside the standard mandrel pipe, as the mandrel. I use the water pipe, cut to about eight inches, with a few screws tapped into it close to one end for a pipe converter. After they are poured and stripped, reshape the hand section to have a good finger plate that is wide enough to accommodate finger separators, if required. The finger plate should be deep enough so the sides are wide enough to rivet the joint bars to. If you break the thumb off, reattach with Super Glue or a similar adhesive. If the thumb piece is a bit larger after that, make sure that the IP joint is the right diameter and build up the tip to a cylindrical shape (Figure 4).
After the plaster modifications are done, and the cast is smoothed up, it is time to bend the metal. Find the joint centers, figure out where the bars will lie, and ensure there will be at least two rivet sites on each bar. You will most likely have to do a three-point bend using a long pipe as a breaker bar to curve the bars so they follow the contours of the finger plate. It is not critical to get the joints at the dead center or to have the bends lie perfectly against the cast at this point, because after the plastic is pulled, some of the curves will change slightly. Just get it close so you can see how they are going to be situated (Figure 5). I put the Mackie joint on the lateral side and the flatter bar on the medial side since it has less bulk and is less likely to rub his skin.
After the bars are bent up, pull the foam lining (Also pictured in Figure 4). I used 1/8 in. AliPlast, but you can use whatever you like. Pull a piece of foam around the forearm and end the distal line at the wrist center. For the hand section, cut a hole in the padding for the thumb, pull it over the cast, and cut it at the wrist center as well. Pull a small piece of foam around the thumb and attach it to the hand pad. Smooth up the seams and transitions or it will look knobby when the plastic is pulled.
After the foam is finished, pull a nylon over the cast. You can let the nylon span a bit between the thumb and the finger plate. At this point, you can allow the foam to stick to the plastic or you can baby powder it depending on whether you want your rivets to be under or over the foam. If you want the foam over the rivets, powder the nylon.
When pulling the plastic and dealing with transfer patterns, I use WD-40 silicone spray to wet the transfer paper. Wipe off the excess silicone, and when the plastic reaches working temperature, smear the paper onto the plastic and make sure to rub out any bubbles; 30 seconds or so is enough to get a good transfer. Peel the paper off and pull the plastic quickly. The pattern will get blurry if you put the plastic back in the oven after the pattern is rubbed into it. In a controlled manner, pull the plastic to span between the thumb and finger plate (Figure 6). Once the plastic cools, put the bars on it so you can get your trim lines. If you want the padding to stick to the plastic, cut it off as is. If you want the padding to come out, cut your trim lines a bit bigger so that you have a bit of wiggle room for shrinkage. After the plastic pieces are cut off and smoothed up, trim your bars to the right length. Smooth up any dings, and you can even paint the bars to match the Mackie joint. Drill holes in the bars and the plastic parts to rivet the bars in place. Speedy rivets are sufficient for a pediatric application.
There are many ways to strap a device like this, but I used a 1 in. figure-eight-type strap to hold the wrist in position, a 1 in. strap to hold the fingers down, and a 1½ in. strap to hold the forearm in place. You can use the ars as holding points for the straps. After the straps and bars are attached, glue the pad in place, or if you riveted through the padding, you can cover the rivets with Teflon spots. You can quickly make finger separators out of AliPlast by heating and folding a 1 in. strip into a W shape. Attach the finger separators with a sticky hook and loop fastener such as Velcro so they can be moved later if needed (Figure 7).
It is a complicated device and somewhat labor intensive, but it will give a great outcome for patients with this type of contracture. I hope this is helpful for you. If you have any questions or would like to see more pictures of the process, send me an email.
Travis Petersen, BOCP, COA, works at A.O.P. Orthotics and Prosthetics, Fayetteville, North Carolina, as a practitioner and clinic manager. He has also worked as a practitioner and technician for companies in Missouri. He can be contacted at email@example.com.