This is part 13 of a series that should be read in order.
Key Points:
- Review the basics of Med/Lat Orthosis Design
- Review the Corrections of P and ML orthoses
- Review all the common modifications to an orthosis for better lateral support
The Medial Lateral Instability Orthosis
A few weeks ago I began to explore medial lateral instability orthosis. Remember the two key points:
- You first design an orthosis in your mind based on the overall pronation for each foot.
- You then reduce the pronation correction some due to the lateral instability of the patient and add some lateral protections/modifications.
Let’s look at P4 and ML4 for example. Here is the review of corrections expected from P (Pronation orthoses). These are average corrections and patients can be different, so you need to measure the RCSP and OCSP at orthotic dispense followed by watching them walk. You then will get both static change and make sure dynamically you are seeing that the same direction of stability is being obtained.
P1 3-4 degrees of heel inversion
P2 4-5 degrees of heel inversion
P3 5-6 degrees of heel inversion
P4 7-8 degrees of heel inversion
P5 9-10 degrees of heel inversion
P6 12-13 degrees of heel inversion
Here are the corrections than expected for the equivalent ML orthoses.
ML1 1-3 degrees of heel inversion
ML2 2-4 degrees of heel inversion
ML3 3-5 degrees of heel inversion
ML4 5-7 degrees of heel inversion
ML5 7-9 degrees of heel inversion
ML6 10-12 degrees of heel inversion
Will you get these exact corrections? No, and this is because they are estimates of the corrections I have seen over the years. But, these devices do make the progressive change you are seeking, with more pronation correction in a P4 than P2, and ML5 than ML3 as examples.
P4 should then give us 7-8 degrees of pronatory correction, and ML4 about 1-2 degrees less or 5-7 degrees of pronatory control. You then figure out what will give you that pronatory support, but you then add lateral protection. This reasoning has helped me avoid the mistake of not correcting the pronation enough. Therefore, if the patient by pronation standards requires a P4 device, we are going to give a P3 device and add supinatory modifications. So, it is not as simple as just lowering the medial support, you must prescribe some anti-supination support which I will review. I recently had a student in my class requiring a 20 degrees of inverted correction due to her 4 degrees of heel valgus standing (P2), but had severe supination on gait due to an ankle injury. I made a 10 inverted device (P1 device) and added Denton modification, valgus wedge, high lateral heel cup and a lateral flange. It perfectly controlled both her pronatory and supinatory problems. This is how the ML orthotic devices are designed.
How do you decide on the supination support modifications? We have just discussed all of the S (Supination) Orthoses, and how the modifications escalate based on the severity of the lateral instability. This can be something easily observed, or more subtle (like a history of torn lateral ankle ligaments without a sign of this lateral instability). In the subtle cases, you want to control pronation well, but are a little or a lot concerned about protecting the lateral column. These modifications, summarized here, can be in your skill set to apply to a present orthotic device, when you order a new orthotic device, or want to remove it when there is too much. There are so many Basic Changes to an orthotic device you can make for less pronatory support, and therefore, more supinatory support. Therefore, in my list below, I have summarized the modifications with both its Complexity and your ability to add or subtract easily in the office (Adjustability). You can see how this process is easier if you can adjust orthoses in your lab.
Anti-Supination Modalities (Improved Lateral Support)
- Zero Motion Rearfoot Post (this is a Basic Change) Post Motion can be ground into or removed easily
- Denton Modification (this is also called a Lateral Frame Fill which is a basic change) Easily Added or Removed
- Richie Wedgie introduced by Dr. Doug Richie (Basic Change) Easily Added or Removed
- Support sub 4/5 metatarsal heads (Basic Change) Easily Added or Removed
- 1/8 inch Valgus Wedge to Sulcus (Moderate Change) Easily Added or Removed
- 3/16 to 1/4 inch Valgus Wedge to Sulcus (Significant Change) Easily Added or Removed
- Lateral Flange (Basic Change) Lab must do however (there is a temporary version done with top covers if you are really skilled
- Raising Lateral Heel Cup (Basic Change) Lab Needed, You can Adjust lower in office
- Lowering Medial Heel Cup (Basic Change with Deep Heel Cups) Easily Done but Lab needed to Reverse
- Full Support Any Forefoot Valgus (Basic Change in B1 orthoses) Lab only
- Temporary Lateral Kirby Skive (Moderate Change) Easily Added or Removed
- Thinning Heel Contact Point (Basic Change) Easily Done, but Lab needed to Add Back
- Remove 1/2 to Complete Medial Half Rearfoot Post (Basic Change) Easily Removed but Lab Required to Add Back (there you are leaving the lateral 1/2 of the post intact)
- Extrinsic Cuboid Pad (Basic Change) Easily Added and Removed
- Intrinsic Cuboid Pad (AKA Feehery Modification) Significant Change Requiring Lab to do
- Thinning Medial Arch with Medial Arch Frame Fill (Basic Change) Easily Done and Reversed by adding Medial Arch Frame Fill
- Removing Part or All of the Medial Frame Fill (Basic Change) Easily Done and Reversed
- First Ray Cut Out (Moderate Change) Easily Done, but non-Reversible
- Ordering More Medial Arch Fill Than Standard Amount (Moderate Change) Easy to Order, but Lab would have to Change if too low arch created other than added soft material into the arch dorsally or adding a firm medial arch frame fill plantarly to the plastic
- Setting Cast 2-3 degrees Everted (Significant Change) All Done at the Lab
- Lateral Kirby Skive 3-4 mm Standard (Significant Change) All Done at the Lab
- Outsole or Midsole Valgus Wedging (Significant Change) World of Shoe Repair Cobblers for Outsole
In the office, it is so easy for me to add a Denton modification, lower the medial heel cup some, decrease the width of the medial ½ of the rearfoot post, narrow the frame width medially, and even add a temporary Kirby. So often, you think you are just dealing with a pronator when you are actually treating one of these Medial Lateral Instability patients. I had 2 of these patients in my Podiatry class last week. Maybe this is why they went to Podiatry School in the first place.
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 (M): 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
