Historically, it has been commonly accepted that heel spur formation is an abnormal finding and very closely correlated with the symptoms of heel pain. It was reported that excessive traction (pulling) of the plantar fascia on its attachment at the heel resulted in chronic inflammation, which in turn resulted in a reactive ossification and subsequent extra bone forming in the shape of a ‘spur’. This is perhaps why heel spurs and ‘plantar fasciitis’ are still to this day thought by many to be one entity. Causation has been a point of confusion; does the traction and inflammation cause a heel spur, or does a heel spur cause tissue inflammation?
It is not uncommon to see statements that ‘plantar fasciitis’ is caused by heel spurs , but is this factually correct?
The plantar calcaneal spur has been classically described as a bone outgrowth localised just anterior to the medial tuberosity of the calcaneus. This can not often be palpated clinically, but only seen radiologically as shown in the x-ray
Another long term belief has been that individuals with heel pain are more likely to have pronated (flat) feet. As research has shown that lowering of the medial longitudinal arch of the foot increases plantar fascial tension it is easy to see how the connection between foot pronation, heel pain and heel spurs has been made. However the concern is that any individual who presents to a specialist with heel pain and ‘flat feet’ could be hastily assigned a diagnosis of “plantar fasciitis caused by a heel spur”. This is clearly unacceptable, and a specialist should have a much more thorough understanding of the research behind the pathological process. So, how common are heel spurs? Are they always problematic? Are they actually caused by traction? And what is their relationship with the plantar fascia?
How common are heel spurs? Studies have shown that heel spurs are more common in pain free individuals than first thought, and it has been reported that anywhere between 11 and 27% of the population have radiographic evidence of a spur.
Clearly this suggests they are not always associated with symptoms, and are not necessarily considered as ‘abnormal’ as once thought. Interestingly, even a study performed over 45 years ago on 323 patients concluded that the plantar calcaneal spur was never the cause of pain and probably a normal manifestation of the aging process.
However, the research does suggest that calcaneal spurs do seem to be over-represented in certain groups, such as females, individuals with osteoarthritis and older people. Calcaneal spurs have also found to be more common in those who are overweight.
Where are heel spurs?
It has long been thought that heel spurs and plantar fascia problems were undeniably linked. Go However, it is interesting to hear how the anatomic studies report the actual location of the bony protrusion. Far from agreeing it resides solely within the plantar fascia as once thought, many studies found it can also be found above the plantar fascia. Some found it was much more commonly located in the other intrinsic musculature, (namely Flexor Digitorum Brevis and Abductor Digiti Minimi) and one study was as bold to firmly conclude that spurs do not develop within the plantar fascia.
What is clear is that there is huge variability in the location of heel spur formation, and if we cannot unequivocally state that the spur is within the fascia (which we cannot) then the validity of its link with ‘plantar fasciitis’ is questionable.
MRI of heel spur (arrow). PF=plantar fascia. M=1st layer of foot muscles
What causes heel spurs?
The traditional theory for formation of plantar calcaneal spurs is what Menz and colleagues refer to as the longitudinal traction hypothesis, i.e. the plantar fascia pulling on the heel bone and causing the formation of a spur. Despite the anatomical studies showed that the spur is far from consistently found in the fascia, it has been suggested that there could be an element of tensile force exerted on the calcaneus from a variety of the other structures which attach to it.
An alternative theory, termed the vertical compression hypothesis and was proposed by Kumai and Benjamin in 2002. This theory suggests that calcaneal spurs are outgrowths which form in response to repetitive vertical stress in an attempt to protect against microfractures. This idea is supported by histological studies which show that the bony trabeculae are NOT aligned in the direction of soft tissue traction. Li and Muehleman found that the direction of the trabeculae suggested that the force causing the pathological response was consistent with the external ground reaction force vector.
Conclusions
So what does all this mean ? It means that we used to think a spur was caused by the plantar fascia pulling on the bone. This is highly unlikely as the spur is seldom found in the plantar fascia. If traction is the cause it is more likely to be caused by other musculature such as Flexor Digitorum Brevis or Abductor Digiti Minimi. However these bony protrusions could instead be caused by the repetitive vertical loading (the heel continuously hitting the floor, and the floor of course hitting it back) with the spur forming as a protective mechanism. Of course we cannot overlook the fact that there may be a combination of both traction and compression present in the aetiology of spur development. We also know that anywhere up to a quarter of the population may have a heel spur, but this will not always be problematic.
So, in summary:
The pathophysiology of plantar calcaneal heel spurs is poorly understood.
The presence of a plantar calcaneal spur does not always lead to the development of heel pain.
Plantar calcaneal spurs do appear to be associated with obesity, osteoarthritis and the aging process.
It is unclear whether spur formation is due to longitudinal traction of the plantar tissues or an adaptive response to vertical loading/compression (or both).
It is erroneous to assume there is a causal relationship between plantar calcaneal spurs and ‘plantar fasciitis’.
References
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