Welcome to tendinopathy blog 31.
The blog (subscribe here) this week focuses on a systematic review of risk factors for plantar fasciopathy by van Leeuwen et al. Well done to the authors as this is a huge piece of work. It highlights that we don’t really know much, or know much less than what we think, about plantar fasciaopthy aetiology. But I think there are some excellent clinical messages and lessons in there for us to unravel.
Hope you enjoy…
Higher body mass index is associated with plantar fasciopathy/‘plantar fasciitis’: systematic review and meta-analysis of various clinical and imaging risk factors
What they did: The authors identified 51 studies, including 1 prospective study and the remaining case-control and cross sectional studies. They focused on BMI, biomechanical factors (e.g. flexibility, kinematics, etc) and imaging and activity related factors. Gender and age were not included because they argue that most studies match for these factors. They defined plantar fasciopathy as heel pain during rest or exercise or tenderness on palpation, that was there for >1 month and provoked by the first few steps in the morning or after a period of rest. For all studies that supplied adequate data, mean differences (MD) for continuous data and odds ratios for dichotomous data with 95% CI were calculated.
What they found: In the one prospective study, 166 runners were included and the incidence of plantar fasciopathy was 31.3%. Six variables were significantly associated with a higher risk of PF: varus knee alignment (OR 5.63 (95% CI 2.01 to 15.72)), use of spiked athletic shoes (OR 5.49 (95% CI 1.71 to 17.64)), cavus arch posture (OR 5.52 (95% CI 2.12 to 14.33)), greater number of days of practice per week (OR 2.59 (95% CI 1.68 to 3.99)), greater number of years of activity (MD 3.30 (1.01 to 5.59)), and running more kilometres per week (MD 20.00 (12.12 to 27.88)).
In the case control and cross sectional studies, higher body mass index was consistently associated with plantar fasciopathy. e.g. A significantly higher BMI was found in the PF group compared to the control group (pooled MD 2.3 kg/m2 (95% CI 1.3 to 3.2)).
Hamstring flexibility restriction: the authors report that two studies have found an association between hamstring restriction and plantar fasciopathy.
But unfortunately that is were the consistent relationships between associated factors and plantar fasciopathy end! The rest is a bit of a mess, let’s take a look…
Muscle strength: isokinetic dynamometry deficits in calf strength were identified in one study, but another study found greater calf raise test endurance in cases with plantar fasciopathy vs controls. Lower toe flexor muscle strength in cases vs controls was identified in another study.
Other flexibility: Ankle flexibility was interesting, some studies showed increased, others showed decreased range among group with plantar fasciopathy, and yet others showed no relationship. Similarly, reduced first metatarsophalangeal joint extension was linked with plantar fasciopathy, but some studies showed no relationship.
Static foot posture: 11 studies investigated foot posture and lower limb alignment. The one that most people talk about, a pronated foot type, was linked in some studies but the odds ratio was small 1.3 (95% CI 0.42 to 2.18). Important to note that many other studies showed no relationship. Again, inconsistent findings.
Kinematics: Surely foot dynamic pronation is consistently linked with plantar fasciopathy! Sorry to disappoint, but NO. One study found that greater maximum pronation and pronation velocity were linked with plantar fasciopathy, but in another study change in arch angle were was not associated. Yes the measures are different, and the literature is limited, but you can see we are struggling to get any consistency.
Imaging findings: Multiple studies have found thickening of the plantar fascia, heel spurs and increased vascularity on imaging, as well as a larger fat pad. The key point to make here is that obviously these findings are not absolute and as we know they may be present in people who do not have pain.
Activity level: One study found an association between increased occupational standing time on hard surfaces and another between people who spend most of their time standing and plantar fasciopathy. To spoil the party another study found not association between standing time or having a standing job. Furthermore, undertaking no regular exercise was associated with an increased prevalence (OR 3.64 (95% CI 1.62 to 8.19) while physical activity three times a week for more than 20 min was associated with decreased prevalence of PF (OR 0.33 (95% CI 0.14 to 0.74)), suggesting some activity is better than none.
Clinical interpretation: In the authors own words: ‘The strongest clinical association was for BMI and there was some consistency for reduced hamstring flexibility, but overall, the evidence supporting associations for ankle and first MTP ROM, muscle strength, kinematic and kinetic factors, foot posture and physical activity levels was either inconsistent or inconclusive.’ A word of caution re BMI, it was associated with plantar fasciopathy in lots of studies among older sedentary folk but only one study among sports active people, so more evidence is needed among the young folk.
So why so much inconsistency, especially with the biomechanical variables. Surely it should be more straightforward than this!!! There are many potential explanations. Firstly, studies often do things very differently, for example they look at different populations or measure factors such as flexibility or ‘strength’ differently. A good example is ankle dorsiflexion flexibility, which was measured in about as many different ways you can think of ie knee bent, knee straight, weightbearing, non weightbearing, whilst standing on your head, etc (ps one of those I made up).
We also need to consider the reliability of some of the associated factors. ‘Strength’ is a good example as we know motor performance is influenced by many factors such as time of day, motivation, etc, etc. So are we actually capturing an individual’s true ability? i.e. are these tests valid?
Finally, we have to appreciate that many of these biomechanical risk factors are probably a small piece of the multifactorial puzzle that likely leads to plantar heel pain. This is highlighted by the size of the odds ratios in the systematic review we are discussing (e.g 1.3 for pronated foot type). Because of this, there is probably a watering down effect within a large sample, because these factors may only be relevant or present for certain individuals.
So the key clinical question for us is how do we know whether a biomechanical factor, such as restricted dorsiflexion is relevant. The easiest way is if it is linked to pain. For example, if they have a painful hop and sticking a heel wedge in reduces pain, this increases your confidence that it may be relevant. Although as we know the mechanisms of reduced pain may be something completely remote to ankle DF, eg top down expectation mechanisms.
If pain cannot guide us we may then make the assumption that there is a biomechanical link between, for example restricted dorsiflexion and plantar fasciopathy. But then how do we know it is significant/big enough to worry about? Can we influence it? And if we can, for example a heel wedge, will this change the biomechanics favourably and more important the person plantar fasciopathy? Lots of assumptions we have to make if we go down this road. Of course clinically we often do, but it is important to pick your biomechanical battles, ie when it is worth intervening.
Sometimes the lack of clear association with plantar fasciopathy pain can work in our favour, as in explaining to patients that pathology is not that much of a big deal. “Hey, listen, you have a thickened plantar fascia but so do many people who don’t have pain”.
But I think the key question from this review has to be; what do we do about BMI? Do we change it and will it change prognosis? Probably! Seems more worthwhile than chasing biomechanics based on this evidence, but not an easy think to change.
See you next time
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