The goal: In this article you will learn five biomechanical principles and three splinting solutions that leads to the performance of fine hand movements in neurological impaired patients, such as picking up a pen in between the thumb and the index finger.
Moreover, you may use these concepts as starting point to develop your own personalized solutions, with your patients.
Warning: this is not a 5-minute course. Consider taking at least one-two hours to start metabolizing all these concepts.
If you are serious about solving neurorehab problems it’s well worth the time, I promise.
Part 1: Splint design based on 5 principles of hand biomechanics.
First things first, here are the five biomechanical principles you should consider:
1. Palmar concavity, as pre-requisite for effective finger orientation
2. Allow 90-degree flexion MCP (dorsal collateral ligament MCP joints)
3. Finger flexion towards scaphoid
4. The role of intrinsic hand muscles for fine pinch
5. Tenodesis effect
You may have already got familiar with these principles, but I strongly recommend viewing this tutorial to understand the direct link between hand biomechanics and proper splint design.
Part 2: Two examples of splinting for hand dexterity
Now that we learned the theoretical basics, let’s have a look at a couple of practical applications. Here is a first video I made a while ago, on how to make these two splints:
1. A dynamic splint to mimic the function of intrinsic muscles, by stabilizing the MCP joint (versus MCP hyperextension) while at the same time recreating palmar concavity and allowing full interphalangeal joint extension
2. A static splint to stabilize the thumb in opposition, which could be optionally be used as anchor point for dynamic elements (as it was done for the previous splint).
Recently I have preferred a more practical way to attach the elastics to the splint, by simply making a loop to block the elastic when passing through a hole (instead of using automatic buttons:
Of course, you may decide to attach these elastic to other splints, like for this wrist-hand splint where I needed to stabilize not only the hand and thumb, but also the wrist:
Finally, the splint to stabilize the thumb can be done with two stripes of thermoplastic material (as shown in the first video of this section) or even one long line making two loops, one at the base and one at the edge of the first metacarpal:
Here the important concept is that there are three points of stability to consider:
1. The base of the thumb
2. The edge of the thumb
3. The base of the index
Very shortly, the base of the thumb needs to be stabilized with a force towards the wrist, while we need to create enough distance between the edge of the thumb and the base of the index; and of course, place the edge of the thumb in opposition with the index and middle finger.
Part 3: A dynamic solution to enhance the tenodesis effect.
Patients with spinal cord injury may have the ability to flex/extend the wrist, but paresis at the level of intrinsic muscles and/or extrinsic muscles for finger flexion/extension. These patients typically use the tenodesis effect (finger extension induced by wrist flexion, finger flexion induced by wrist extension), though sometimes the force generated is not sufficient for an effective grip.
My guess is that this splint may help enhance the tenodesis effect. It consists of a bracelet with outriggers to pull the base of the fingers in different directions, depending on the effect we want to accomplish.
By leaving the wrist free to move, wrist flexion may increase the tensioning of elastics placed dorsally, hence enhancing finger extension; the other way around, wrist extension may increase the tensioning of elastic placed palmarly. The same concept applies to the thumb, where a combination of two elastics may generate thumb opposition secondary to wrist extension. The key point here is to locate the outrigger properly, because it will ultimately determine the efficacy of the pulley system.
Part 4: Decision-making algorithms
At this point you may wonder how to decide which solution works best for each patient. Here is a last video where I explained a decision-making algorithm to design a functional hand orthosis, based on specific patient’s needs.
To recap, we learned five principles of biomechanics, and three splints based on these principles and with the goal of recreate fine hand movements. The three splints are (1) a dynamic stabilization of the MCP joint with elastics, (2) a novel form of thumb splinting, and (3) a dynamic splint to enhance the tenodesis effect. And a decision making algorithm to guide you through the design of customized solutions.
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