Prospective studies add to our knowledge of risk factors for overuse injury. The problem with these types of studies is the choice of variables or parameters to measure. The more variables that are chosen to see if they are or are not predictive, the more participants you need in the study which raises logistical problems. If you limit the number of variables, then there will always be at least a few people who won’t like the results as their “pet” clinical test or predictor was not included in the study. I am regularly guilty of being one of them! For that reason, it was good to see this study appear that measured a totally different set of variables, those related to plantar pressures:
Can RSScan footscan® D3D™ software predict injury in a military population following plantar pressure assessment? A prospective cohort study
Andrew Franklyn-Miller, James Bilzon, Cassie Wilson, Paul McCrory
The Foot; Available online 11 November 2013
Injury in initial military training is common with incidences from 25-65% of recruits sustaining musculoskeletal injury. Risk factors for injury include extrinsic factors such as rapid onset of high volume training, but intrinsic factors such as lower limb biomechanics and foot type. Prediction of injury would allow more effective training delivery, reduce manpower wastage and improve duty of care to individuals by addressing potential interventions. Plantar pressure interpretation of footfall has been shown to reflect biomechanical intrinsic abnormality although no quantifiable method of risk stratification exists.
To identify if pressure plate assessment of walking gait is predictive of injury in a military population.
200 male subjects commencing Naval Officer training were assessed by plantar pressure plate recording, of foot contact pressures. A software interpretation, D3D™, stratified the interpretation to measure 4 specific areas of potential correction. Participants were graded as to High, Medium and low risk of injury and subsequently followed up for injury through their basic training.
Seventy two percent of all injuries were attributed to subjects in the High and Medium risk of injury as defined by the risk categorization. 47% of all injuries were sustained in the high-risk group. Participants categorized in the high-risk group for injury were significantly more likely to sustain injury than in medium or low groups (p < 0.001, OR 5.28 with 95% CI 2.88, 9.70).
Plantar pressure assessment of risk for overuse lower limb injury can be predictive of sustaining an overuse injury in a controlled training environment.
This was not necessarily a study on runners, but on a military population that do a lot of running. Most of the injuries that they sustained were the typical overuse injuries that runners get. The participants had their plantar pressure pattern determined by walking over a pressure plate (RSScan). The propriety D3D™ software was then used to categorize them into high, medium or low risk groups. About 50% of the injuries occurred in the high risk group with about 25% in both the low and medium risk groups, so yes the plantar pressure pattern could be used to predict those who were at more risk.
The only issue I have is that we do not know what the pressure pattern that was used to classify feet into the thee different categories was. The propriety D3D™ software from RSScan is what is used to assist with foot orthotics prescription and it makes suggestions based on the pressure pattern. (The study did not use foot orthotics, it just used the output from the software to classify the feet).
According to the RSScan website, the software does this:
Advanced calculations use the dynamic data to assess the distribution of forces at key times during the stance phase. This allows the correct orthotic to be prescribed to balance discrepancies in foot mechanics that occur during the gait cycle.
In the methods of the above paper, this was described as
Based upon the ratios of loading for 4 regions of the foot: Heel, Mid foot (medial and lateral) and Forefoot a correction is automatically recommended in this area of foot contact, if the range of ratio is exceeded within the software programme. This would result in a correction being applied to a custom orthoses.
I not actually sure what all of that actually means as my experience with plantar pressure measuring software is with brands other than RSScan so a lot more information would have been helpful.
An algorithm obviously makes one or more of these recommendations, so the above study classified the feet according to the number of modifications that the software made for foot orthotic variables. Those with more recommendations were classified as high risk as they had more variables that were detected as being outside normal values for that variable. I just not comfortable with not knowing exactly what those pressure patterns were and how they were translated to a foot orthotic prescription recommendation. Obviously this is propriety to RSScan. I just know from my own experience with plantar pressure measurements that there can be different kinematic and kinetic variables leading to similar pressure patterns and also that different clinicians will interpret different pressure patterns differently. There are many different plantar pressure platforms available, so the information is not translatable to those and the information is not translatable to a simple clinical test that could have predicted the same thing. It would be good to see if a clinical test could predict the pressure pattern that was predictive of injury, as it would certainly simplify things down to a more practical application as a screening tool.
Despite this ‘discomfort’ I have, classifying the the feet this way was still predictive of injury.
As always, I go where the evidence takes me until convinced otherwise.