Dynamic orthoses and force application
(Based on “Krotoski JB, Breger Stanton D. The Forces of Dynamic Orthotic Positioning: Ten Questions to Ask Before Applying a Dynamic Orthosis to the Hand. In Skirven, T. M., Osterman, A. L., Fedorczyk, J., & Amadio, P. C. (2011).Rehabilitation of the hand and upper extremity, 2-volume set: expert consult. Elsevier Health Sciences.)
Orthoses for mobilization are commonly used in hand therapy interventions to substitute for weak or absent muscles or to apply force to stiff tissue and joints to regain passive joint motion. Orthoses using too much force can cause injury to body structures resulting in pain and edema. Too little force will not achieve the desired goals of the intervention.
Dr. Paul Brand identified the following 10 basic questions for therapists to consider when applying a mobilization orthosis to a specific joint:
- How much force?
- Through what surface?
- For how long?
- To what structure?
- By what leverage?
- Against what reaction?
- For what purpose?
- Measured by what scale?
- Avoiding what harm?
- Warned by what signs?
Dr. Brand’s original chapter in the classic “Rehabilitation of the Hand: Surgery and Therapy” has been updated and revised in the 6th edition “Rehabilitation of the Hand and Upper Extremity” of this two volume set. A brief summary of this enlightening chapter’s contents with regard to each of the above questions follows here, but it is highly recommended to read the entire chapter for increased comprehension and understanding of the topic.
1. How much force?
According to the authors, it has been suggested to use between 100 and 250 grams of force on an individual finger. A quick and easy method to measure force is by using a Haldex gauge. Place the patient’s finger in its finger cuff with the orthosis in place and allow the rubber band or elastic thread to hold the intended tension on the finger segment. Measure the length of the elastic thread under this tension. Then remove the finger cuff from the patient, elongate the thread to the same length and measure the tension with the Haldex gauge. Make adjustments to the tension as needed.
2. Through what surface?
Most of the time therapists apply force in the hand orthosis using finger cuffs. If the pressure is too great, the skin inside the finger cuff will show signs of redness and the patient may complain of discomfort. Make sure the area of the finger cuff is wide enough to disperse this pressure, especially if the pressure is to be applied continuously. The size of the finger cuff should be 4-cm2 with 200 grams of force. If the cuff is to be worn intermittently, then the pressure will not cause harm to the tissue. Have the patient wear the cuff for a short time and check the skin for redness.
Make sure the cuff fits well under the finger – thermoplastic cuffs that are custom made for each specific finger will distribute the pressure more evenly then soft finger cuffs.
3. For how long?
The best way to lengthen tight tissues is to keep them in a state of mild tension for a long period of time. For best results in tissue remodeling, the ideal orthosis would be worn 24 hours a day. Tissue remodeling requires less force than we think, but for longer periods of time than most of us allow.
Develop a wearing schedule with your patient that maximizes the time in the orthosis.
4. To what structure?
The target tissue should be identified, whether it is tight skin, tight ligaments or adhered tissue. Consider if it is a tissue that can be affected by the pull of a mobilization orthosis. If there appears to be a bony block to movement or a joint has a very hard end feel, an orthosis may not be the most effective or useful intervention.
5. By what leverage?
It is useful to think in terms of lever arms and the joint axis as the fulcrum when constructing an orthosis. We want the lever arm to be as long as possible to apply the force to a tight structure.
The term “mechanical advantage” refers to the ratio between the length of the lever through which the force is applied and the length of the lever through which the force is delivered. Think of a sling placed under the proximal phalanx to extend the MCP joint of the index finger versus a sling placed under the distal phalanx to do the same task. The ratio should be between 2:1 and 5:1. The length of the finger is used to apply the force and half of the thickness of the finger is used to deliver the force.
6. Against what reaction?
When placing force on one part of the hand in an orthosis to pull up, we are also placing another force on the hand to push down. Remember to always stabilize the proximal joint with enough molding and conformability in the orthosis so that the proximal edge is stable and in total contact with the extremity.
7. For what purpose?
Remember to clearly define the goals of the mobilization orthosis in order to determine its effectiveness over time. 10 degrees of increased passive joint range of motion is an indication that the orthosis is doing its job.
8. Measured by what scale?
While for many therapists, active and passive range of motion are the most important measures for guiding orthotic intervention, one should add a functional scale to assess the client’s limitations in ADL’s and work/ leisure activities to determine the true benefits of this intervention over the course of treatment.
9. Avoiding what harm?
As with other therapeutic interventions, be careful with tissue assessment and evaluation. An orthosis fabricated to gain passive motion at a tight joint may actually cause harm by creating too much pressure and lead to unnecessary inflammation, pain and additional complications. Monitor each mobilization orthosis and patient carefully and regularly.
10. Warned by what signs?
Although perhaps not performed as routinely today as desired, Dr. Brand envisioned that therapists would monitor edema and skin temperature in the hand regularly to assess tissue reaction and cellular health. Hot areas indicate inflammation and lower temperatures with swelling indicate inactivity. Make sure to assess your patient’s skin for areas of redness, skin and tissue irritation, and swelling.
Orfit Industries offers therapists many options for the fabrication of low profile and effective mobilization orthoses.
Check out Orfit’s Dynasyst system of Orfitubes and Orfitube Adjustors.
Attach a Orfitube Adjustor to the orthosis using dry heat to both parts. Secure the Orfitube in place with the small Allen wrench. It is simple to adjust the angle and direction of the line of pull by rotating the Orfitube or pulling it out a bit from the Adjustor. Thread the finger cuff through the Orfitube and adjust the tension as outlined.
The Dynasyst – Kit Single Orfitube Adjuster has everything you need for 5 finger outriggers plus you will have a lot of extra Orfitube left over for your next orthosis. Orfit offers three different strength elastic threads.
Try orthotic fabrication for the weakened wrist using Orfit’s pre-coiled Wrist coils for dynamic wrist extension assist orthoses. We also offer pre-coiled wires in different variations and sizes for a variety of applications.
Orfit Industries allows you to create the most appropriate mobilization orthosis for your client, matching your clinical knowledge with our expertise in manufacture of low temperature thermoplastic materials, and many options of outrigger designs.