This is part 14 of a series that should be read in order.
Key Points:
- Based on typical material used, what are the 3 types of shock absorbing orthoses described?
- What are some of the biomechanics of poor shock absorption?
- When EVA is used for the frame, what are 3 common variations from most supportive to least supportive?
- Describe the 2 basic types of Hannaford orthoses.
- BC device is explored in depth, including Rx writing
The Shock Absorption Orthosis
I use 2 very wonderful, and special, orthoses all the time in my practice. They were inspired by Drs. Howard Dananberg and David Hannaford. Of course, patient selection is very important as they both produce very powerful mechanical changes. Again, I recommend having a range of offerings for your patients by adding these two types. These are the C (Shock Absorbing) and H (sagittal plane help with Hallux push off) orthoses. They are unique as they do not completely follow any measurement, although Dr. Dananberg can pick up the need for his H device on computerized gait evaluation. For me, it is more a feel for when a patient may need one of the shock absorbing or sagittal plane devices. They have to make sense according to the patient’s biomechanics and symptomatology. There will be more on this later. These next 2 posts are on shock absorption first, and then I will have an additional one for sagittal plane.
Let’s start by describing from our original list of corrective orthoses the summary of our Shock Absorbing Orthoses. This is our C for cushion orthoses, with the gold standard in my practice being the Hannaford version.
Shock Absorption ( C): BC, C1/C2, C3/C4/C5, C6, and C7
BC: Balanced Device with additional cushioning material
C1: Material that you used to make B device is changed to softer and more flexible, like lowering thickness of the polypropylene or changing polypropylene to sub-ortholen (™)
C2: Not only is the plastic softer, with more flexibility, less rigidity in the rearfoot post is used, by either softer density or intentional increased motion applied
C3: Basic material change to standard EVA on same mold with full frame fill
C4: EVA product with half EVA frame fill
C5: Basic EVA product with softer material and 1/2 EVA frame fill
C6: Hannaford full length 2 layer Plastazote design with firm white Plastazote (pressed against non-corrected mold)
C7: Hannaford full length 2 layer Plastazote design with soft white Plastazote (pressed against non-corrected mold)
Like any of our categories, the base can be your B (Balanced) orthosis and we can simply vary the location and amount of the cushioning applied. This is our BC device. The next differential is C1/C2 which are more shock absorbing, very similar, but still using a plastic frame. Then, C3/C4/C5 increase the shock attenuation properties of this device, going to the various EVA devices which can vary the amount of support and cushion. We finish our discussion with C6 and C7. These are the Hannaford devices made with Plastazote (memory foam) material. And, even though most laboratories do not make this product, it is 25% of all the orthotic devices I prescribe. You can find the description here: Biomechanical guidelines
There is a fine line between cushioning, and losing support. However, even though our goal should be to always make a patient more stable, many patients need shock absorption just as much. I even call poor shock absorption “vertical plane instability”. It can be their lack of shock absorption at their feet that is causing their joint arthralgia (knee, hip and back), or stress fractures, or severe muscle aches. The poorer your shock absorption ability, the harder muscles have to work to protect your skeletal structures. Especially as we age, adding more shock absorption in some way to any orthotic device can be so helpful, and us seniors will thank you for it.
What are some of the biomechanics of poor shock absorption? This could be rephrased: “When should we order a C Type orthosis”? As we age, and our bones get weaker, the use of a shock absorbing device can dramatically help the leg discomfort the patient feels. Typically, the muscles which protect the skeletal structure have to work harder with each step and start complaining in various ways. A patient with a poor fat pad, which can also thin with age, just loves these devices, with the Hannafords my personal favorite. Overall mechanical rigidity, where we lack the shock absorbing motion of pronation, is a big cause and typically treated with these devices. However, adding motion into any orthotic device (B, P, S or M) can improve shock absorption in the majority of patients. Patients who have limited subtalar joints, function in their MPP (maximally pronated position), or supinate, not pronate, during the contact phase technically have less pronation then they should at heel contact, and are thus poor at absorbing the body’s shock of GRF (ground reactive force). These patients can be helped with standard orthotic designs of P and S to either get them out of their MPP or stop their contact phase supination. And, for those of us that make a lot of custom orthotic devices for patients, occasionally we run into a patient with plastic hyper-sensitivity who needs the support only a plastic device will give them, but can not tolerate the “hardness”. This may come out in your historical review before you even make them a pair of orthotic devices, due to their past experiences.
Today I will cover BC, and next week the rest of these devices. BC is your Balanced orthotic device with extra cushioning in one location, like the heel or forefoot, or both. This will be typically a closed cell material like Poron (™). Poron rips when used against the skin, so has to be under the top cover. The top cover can be an open cell product like Spenco (™) or Neolon which is my preferable shock absorbing top cover material. Here you have a stable device with some added shock attenuation. Remember that the solid plastic part of the device should be at the base of the shoe for best stability. All cushion material should be above the plastic, not under. When under the device, it can destabilize the device leading to more instability. The shoes you put the orthoses into can make a big difference. If you are going for shock absorption in the orthotic device, you probably want a shoe that is not top of the line stability. Shoes like the Brooks Beast or Ariel and New Balance 1540 are very stable, but hard. These are called Motion Control shoes in general. Find a stable shoe that has good shock absorption.
Prescription for BC Device:
- Balanced cast to Heel Vertical (only in B1)
- Lab discretion balancing B2 (but typically to center the heel at vertical)
- Can also use same principles in any P, S, or ML device)
- 5/32 polypropylene (unless weight demands 3/16 or 1/8 )
- 18 mm Heel Cup Heights
- Standard Width and Arch Height
- Zero degree Extrinsic Rearfoot Post
- 1/8 inch Spenco (™) full length
- Add soft material (Poron or Spenco (™) as forefoot extension
- Common to use soft Poron as heel cushion (between top cover and plastic)
Next week I will discuss the Rx writing for the other types of devices.
Review of all the Orthotic Types Being Presented
Corrective Orthotic Devices
↓
- Balancing (B): (B1 and B2)
- Pronators (P): BP, P1, P2, P3, P4, P5, and P6
- Supinators (S): BS, S1, S2, S3
- M/L Instability (ML): BML, ML1, ML2, ML3, ML4, ML5, and ML6
- Shock Absorption (C): BC, C1/C2, C3/C4/C5, C6, and C7
- Sagittal Plane (H): BH, H1, H2, and H3
