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You Lost My Alignment!
By Craig MacKenzie, CP, RTP(c)  How many times have you heard those words? I know I've heard them quite a few times over the last 18 years. The problem is there are quite a few ways to lose an alignment when using a vertical alignment jig.
There are a few ways to manage
your jobs and jigs in order to minimize the possibility of losing your alignment.
Three factors contribute to a lost alignment:
- technician error,
- prosthetist error, and
- jig set-up issues.
The most common technical errors are in the setup of the job in the jig and the use of the alignment collars. When setting a job in a jig, it's important to remember that not all pyramids are created equal; some are smaller than others. So when you undo the medial and anterior screws to remove the foot, note the general angle of the tube beforehand. If the angle in the jig doesn't look the same, then the two pyramids are different. This may not be a problem if you don't change anything, but most technicians will "zero out" the mounting plate before bonding the newly laminated socket. Zeroing out the set screws will change the socket/pylon relationship and change the way the ground reaction forces travel through the socket.
Another common technical error is marking the collar before removing it for lamination. The marks never really line up, and you could potentially change the height or toe in/out of the prosthesis. To eliminate this problem, remove the regular set screw from the top front of the collar and replace it with a point set screw, then drill a 5/32-in. hole in the top of the mandrel. The point of the set screw, when tightened, will always locate the collar in exactly the same position (Figure 1).
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Figure 1 |
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Prosthetists can also contribute to alignment error. The best thing about alignment jigs is the ability to change the alignment; the worst thing is the ability to change the alignment. How many times have you heard the words "the alignment is perfect; just move it a half inch laterally and a half inch posteriorly"? The issue is that the alignment wasn't perfect. By changing the alignment in the jig, the prosthetist has changed how the ground reaction forces are transmitted through the prosthesis. The only way to be sure of the alignment is changing it in the check socket stage and realigning the patient. Especially with all the dynamic feet on the market today, any change can make a big difference. There are many different plates and alignment devices out there to make this process less time consuming, and in the end it will eliminate any costly remakes.
Finally, the jigs themselves can be a source of error. Plaster on any part of the jig could prevent the jig from indexing correctly. A Scotch Brite pad and a little WD-40 every two or three months can keep your jigs moving freely. Making sure that all the knobs and set screws are tight before filling the socket can save a few headaches in the long run. Over time, some jigs can develop a little play. This can cause problems if you can't remember whether you pushed the pipe to the right or to the left when you filled the socket. Depending on which jig we use at Velocity Labs, that play can move the cast 1/8 in. to 3/8 in. medial or lateral, so we have an unwritten rule that all pipes are pushed to the right, then tightened before filling.
I know I haven't covered all the issues with alignment jigs, but I hope that you will find some of this information useful. If you have a unique solution to a problem, please share it with
The O&P EDGE
(
press@opedge.com
).
Craig MacKenzie, CP, RTP(c), is the owner of Velocity Labs Inc., Orlando, Florida, and president of Evolution Liners Inc., Orlando. He may be contacted by phone at 407.841.6335 or via e-mail:craigm@velocity-labs.com 
Table Of Contents - February 2007
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