Anterior knee pain or patellofemoral knee pain syndrome is one of the most commonest injuries seen in runners. Excessive foot pronation, either rightly or wrongly, has long been linked to it. The putative model of the mechanism is that if the foot excessively pronates, then the tibia rotates internally too much causing misalignment at the knee and patella maltracking resulting in the symptoms. Clinically, the use of that model is successful; there being two good randomized controlled trials showing that when you use foot orthotics to try and treat the excessive pronation, the knee problem gets better (Collins et al & Eng et al). There is no doubt about that, as that is what the evidence says. There is no evidence showing foot orthotics don’t work for this.
Where the model falls down is that all of the prospective risk factor studies and almost all of the cross-sectional risk factor studies have shown that there is no link between excessive foot pronation and anterior knee pain (despite the foot orthotic studies showing they work!). Some of those studies do suffer from the problem of which measure of overpronation is used (see my discussion on that here). I have already discussed this paradox and proposed an alternative model by which the foot orthotics could have worked independent of the “pronation” (ie lower the rearfoot inversion moment, so the proximal control elements can better do their job). Our understanding of overpronation continues to evolve and most of what is written online about it is nonsensical, yet unfortunately has huge influences on peoples understanding (or misunderstanding) of it.
Just when I start to think that we are making progress with a better understanding, this study appears:
Evaluating runners with and without anterior knee pain using the time to contact the ankle joint complexes’ range of motion boundary
Pedro Rodrigues, Trampas TenBroek, Richard Van Emmerik, Joseph Hamill
Gait & Posture; Article in Press
Little biomechanical evidence exists to support the association between excessive foot pronation and anterior knee pain (AKP). One issue could be the way excessive pronation has been defined. Recent evidence has suggested that evaluating pronation in the context of the joint’s available range of motion (ROM, anatomical threshold) provides greater insight on when pronation contributes to injury. Theoretically, quantifying the amount of time the joint has to respond before reaching end range (neuromuscular threshold) could provide additional insight. Therefore the purpose of this study was to use a neuromuscular threshold, the time to contact (TtC) the ankle joint complex’s ROM boundary, to evaluate runners with and without AKP.
Nineteen healthy and seventeen runners with AKP had their ROM and running biomechanics evaluated. The TtC was calculated using each individual’s angular distance from end range (eversion buffer) and eversion velocity. Data were recorded over ten stance phases and evaluated using a one way analysis of variance and 95% confidence intervals.
Runners with AKP had significantly shorter TtC the joint’s ROM boundary when compared to healthy runners (64.0ms vs. 35.6ms, p=0.01). While not statistically significant, this shorter TtC was in large part due to having a smaller eversion buffer, however velocity was found to have a substantial influence on the TtC of select individuals. These results provide evidence that a link between pronation and AKP exists when using anatomical and neuromuscular based thresholds.
What these researchers did was to evaluate a different measure of ‘pronation’ rather than one of the more traditional measures used in the studies that found no links. They evaluated the subject specific measure of how much eversion that they had left in the rearfoot during gait and how much time it took the foot to get there. They found that that those with anterior knee pain has less eversion left and they got to that end range quicker compared to the healthy group.
This study does muddy the water somewhat, swinging the pendulum back to parameters associated with overpronation being a factor in anterior knee pain. It also offers another alternative explanation as to how foot orthotics may work in anterior knee pain. Hypothetically, foot orthotics can slow the eversion, giving the body more of a chance to react to changes in alignment during gait. This is not inconsistent with the model I proposed, just adds another dimension to the mix.
The only issue I have is that this is a cross-sectional study which is lower down in the hierarchy of evidence, so it would be good to see this concept evaluated in a prospective study.
As always: I go where the evidence takes me until convinced otherwise.