Leg Length Discrepancy and Plantar Fasciitis

The development of plantar fasciitis is believed to be due to excessive mechanical stress placed on the plantar fascia that is greater than it can withstand. The plantar fascia is a strong and tough connective tissue that is designed to withstand high levels of mechanical stress. There are many reasons why the plantar fascia might be subject to increased levels of stress including muscular tightness of the calves and hamstrings, excess foot pronation etc. In this article, I would like to give a brief mention to leg length discrepancy as a potential causative factor for increased mechanical stress on the plantar fascia which may lead to plantar fasciitis, which is often overlooked by health professionals treating this condition.

Leg length discrepancy is a fairly common phenomenon and there is a lack of consensus on how much of a difference is too much. It is suggested that a difference greater than 1cm is clinically significant and may lead to a patients symptoms, however the evidence to prove this is lacking. Differences greater than 2cm is reported to affect 1 in 1000 people (Mahmood et al 2010). When a person does have a large leg length discrepancy (whatever large is), It is generally accepted that compensations by the body occur to lengthen the short leg and shorten the long leg in an attempt to provide a 'balance', however the nature of these compensations varies from person to person.

Leg length discrepancy can be described as two types:

1 - structural, this means there is a true difference where the bone in one side of the body is longer/shorter than the bone of the opposite side of the body

2 - functional, this means the skeleton is equal in length on left and right sides, however, a discrepancy occurs due to altered mechanics of the lower legs

For efficient movement to occur, proper symmetry and alignment of the body are necessary. If asymmetry exists, in particular by leg length discrepancy, then gait and posture are disrupted and symptoms can occur ( Mahmood et al 2010).

There is a lack of clinical research looking at leg length discrepancy is an isolated cause of heel pain, however, Mahmood and colleagues (2010) investigated 26 patients diagnosed with plantar fasciitis. They used a combination of methods to measure leg lengths in order to improve the accuracy of measurement. They found that 87.5% of patients with left heel pain measured the left leg being the longer side and that 93.3% of patients with right heel pain measured the right leg being the longer side. These findings indicate a strong correlation between a longer leg and plantar fasciitis pain.

On the other hand, it should be made clear that the quality of this study is not the most robust, due to a small number of people included in the study and the methods used for measuring leg length difference have been shown to be unreliable. This study demonstrates a strong correlation but it does not necessarily demonstrate causation. This is an important difference to note. Correlation and causation are not the same thing. Causation indicates that one event is the result of the occurrence of the other event, whereas correlation may be coincidental. In order for us to be more sure whether leg length difference is actually a cause of plantar fasciitis, more research studies are required.

My opinion

Personally I routinely assess for leg length differences with my patients. If I can see a difference and I feel this is contributing to increased mechanical stress on the plantar fascia which is injured, then I am inclined to prescribe an insert for the patient to wear in their shoe. I would recommend that clinicians assess for a leg length discrepancy routinely when performing a physical examination of patients with heel pain and consider the clinical relevance of this on an individual basis. Future research into leg length discrepancy as a causative factor needs to be conducted so that patients and clinicians can be better guided on the relevance of a leg length discrepancy.

Thanks for reading. Comments welcome.

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