I’m working on an upcoming article on limb length discrepancy (LLD). While looking over some of the literature that is out there on the subject, I ran across a study that looked at the use of pressure mapping in evaluating simulated LLD.1 In that study, the authors found that with a LLD, the pressures in the forefoot are present for a prolonged amount of time, the propulsive phase of gait increases or lengthens, and the contact period of gait decreases or is shortened.1
All of this makes perfect sense with what I have seen in almost 20 years of experience using pressure mapping with my patients. With pressure mapping, one will usually see an early heel off on the shorter limb in comparison to the longer limb. This means that with the heel lifting early, the contact period of gait shortens as the heel needs to be in contact with the ground for this measure to be consistent. Finally, under the same circumstance of early heel lift, one will see a lengthened propulsive phase of gait as the foot balances primarily on the forefoot for a longer period.
Identifying a LLD with the use of pressure mapping sounds pretty simple, right? Well, it’s not quite as cut and dried unless one has also had the opportunity to perform a physical exam and confirm that the patient does indeed have signs of LLD. Otherwise, there can be many different reasons for why the heel will lift early on one limb versus the other.
The issue is, when looking at pressure mapping imaging, there are lots of things going on in the entire body that can look just like a LLD.
For instance, patients can have asymmetry in ankle joint range of motion (ROM). I have discussed this in previous blog posts. The reason that these two issues, LLD and decreased ROM of the ankle, can look the same is because they can both cause an early heel lift if the ankle ROM issue is asymmetrical. However, without measuring the ankle ROM via a physical exam and assessing for a LLD, you won’t know for sure which issue is causing the early heel lift.
Another example is when patients have an arthritic knee unilaterally. If you have examined patients like this, you will note that they often have a chronically flexed knee on the arthritic side. Due to this chronic knee flexion, the heel will lift early as the patient has to literally plantarflex his or her foot to maintain any type of symmetry at the hips when he or she walks.
As you can see, pressure mapping is an interesting tool for use in podiatric practice. However, just like every other tool, there are pros and cons regarding the information that the tool provides. Practical experience and insight can sharpen the use of tools like pressure mapping systems. Hopefully, over time, as more and more pressure mapping data becomes available for examination via artificial intelligence (AI) and/or machine learning (ML), those details will become more and more evident, and clinicians will be able to use this information for further clarification in their examinations.
Dr. Williams is a Past President and Fellow of the American Academy of Podiatric Sports Medicine. He is the Director of Breakthrough Sports Performance, LLC in Chicago. Dr. Williams has disclosed that is the Medical Director for Go 4-D and a consultant for HP FitStation.
- O’Toole GC, Makwana NK, Lunn J, Harty J, Stephens MM. The effect of leg length discrepancy on foot loading patterns and contact times. Foot Ankle Int. 2003;24(3):256-259.