The pedograph as a window to the gait cycle
Ivo Waerlop DC, DABCN, Shawn Allen DC, DABCO, Robert Lardner, PT
Have you ever studied footprints on the beach or looked at the print left by a wet foot when you get out of the water? These are some of the most primitive types of pedographs.
The pedograph, 1st described by Harris and Beath in 1947 (1) is a rubber mat surface with multiple protruding, small grid lines on one side, which, when covered with ink, imprints an underlying sheet of paper when weight (usually a foot) passes over it. Relative plantar pressures are indicated by the size and density of the inked area (1, 2, 3), creating a “footprint” reflecting passages of force through the foot at that instance in time. They have fallen into and out of usage over the years, often discarded for more expensive technology such as pedobarographs, individual pressure sensors, and pressure sensitive mats, which have computer interfaces and can provide many useful measurements and calculations to assist the clinician with rendering a diagnosis. These systems, though more precise in some ways (provided a controlled, reproducible testing procedure) are often thousands of dollars, require a computer and the necessary skills, and have a substantial learning curve.
The pedograph in contrast is simplistic, inexpensive, and reliable and only requires that the user have an intact visual pathway and cerebral cortex and knowledge of the events occurring in the gait cycle. With some practice and a good knowledge base, the subtle nuances detected by the sensitive pedograph (nuances that can often be undetected with high end computer driven plantar pressure devices) can offer information critical to a precise diagnosis and give solid clues to gait flaws and compensations. With minimal training using a pedograph, reproducible “prints” can be produced for analysis, in light of your findings clinically. They also make wonderful educational tools for your patients.
An essential part of a comprehensive patient evaluation should include examination of the entire kinetic chain both in a static and dynamic fashion. Often what you see statically is either directly translated to or compensated for in the dynamic evaluation. (It is important to note that many of the available foot scan units available from orthotic companies scan a patient in a static standing position and give little information on how the feet and lower limb dynamically engage the ground during movement.) The pedograph is a useful visual tool representing a 2 dimensional image of tri-dimensional motion, and you are seeing the end product and compensation (or lack thereof) of the individual’s mechanics at that point in time. Because the specificity of what you are seeing refers to a particular point in time, technique and reproducibility are of paramount importance. Prints should be performed several times to insure what you are looking at is in fact what you are looking at, and not movement artifact because of the way the patient stepped on to or off of the mat.
Here is a brief case study: 40 year old female marathoner with a history of chronic right sacroiliac pain, worse after runs
You will notice that there is a distinct difference here between right and left dynamic plantar pressures. This is a fairly consistent pattern in SI joint symptom patients. Ignoring the heavy right heel print for now (topic for another time) she as a heavy print over the right 2nd and 3rd metatarsal heads with very little under the 1st ray complex or hallux (ie. pressures are more lateral on the foot). The left foot shows that the pressures are very much medial with good pressures under the hallux but none under the 1st metatarsal head. This patient is shifting her weight from left to right. This is substantiated by the slight external rotation of the right foot (and thus entire limb, although not seen well here on prints) on the print to accommodate the right frontal plane challenge. Of clinical importance, turning the right limb externally may help use the quadriceps with the hip abductors to protect falling to the right. As she progresses over the right foot she runs out of adequate hip extension (as determined on our physical exam) and thus is unable to get over to the first ray complex and hallux. As this needed range is challenged, but not met, the patient’s strategy is to spin the rearfoot inwards (technically external rotation) forcing the forefoot into supination-inversion causing propulsion off of the 2nd and 3rd MET heads. Some call this an "adductor twist" gait, which is adequate for what you see, but it has nothing to do with the adductor hip muscle group.
In summary, her attempt to move forward in the sagittal plane in the presence of limited right hip extension forces her to externally rotate the limb, toe off more laterally and gain the desired hip extension in this case through the low back instead of the hip, thus giving her the chronic SI joint irritation / loading. This is not the only compensatory strategy available to deal with this problem, there are others that can be used, but these will be left for another case presentation. In similar case scenarios, it would be prudent to evaluate the neuro –integrity of the abdominal wall, glutes, hip extensors and internal hip rotators as optimal cooperation of these functional units can often collectively produce the desired hip extension and internal rotation necessary to begin reducing the gait compensation described above.
With a pedograph, seeing is believing. When you have objective data about how an individual moves through space and how their joints and motor system help them to accomplish that, you have a better appreciation for the type or form of therapy which may be most appropriate. In essence, joint function deemed appropriate on the table does not necessarily translate to appropriate joint function when the feet are engaged on the ground, as many factors come into play. In the hands of a skilled clinician, seeing abnormal plantar pressures tells you where the biomechanical faults may lie, and thus where manipulation may be appropriate, which muscles need strengthening and where neuromotor coordination is lacking and gait rehabilitation is needed.
Drs. Waerlop and Allen have written the only text on the pedograph and its use in the clinical setting (with help of case studies). With Robert Lardner, the 3 also lecture nationally on gait and neuro-orthopedic gait pathomechanics and are biomechanics consultants for Vibram, USA. You can contact them at drivo@netzero.com and doc@doctorallen.com and rlpt@sbcglobal.net.
Bibliography
1. Harris WC, Beath T. Canadian Army Foot Survey, National Research Council, 1947
2. Shipley DE: Clinical Evaluation and care of the insensitive foot. Phys Ther 59(1), 13-18, 1979
3. Waerlop I, Allen S: Pedographs and Gait Analysis: Clinical Pearls and Case Studies. Trafford, Victoria BC, 2006
