Leg length and leg length difference

Leg length difference is often seen as the cause of back problems, neck complaints, headaches and others. This is often also heard by various care providers such as physiotherapists, podotherapists, manipulators, and others. It is certainly true that a leg length difference, for example, can cause wear and tear on the knee. But more often there are no complaints. How does this work and, for example, does the prescription of a heel raise benefit?

Presence of leg length difference

Leg length differences are common. According to a somewhat older study in people without back problems, the following was found:

In another study, a leg length difference was seen in 70% of the people. Leg length differences are therefore common and seem to be a normal phenomenon.

Causes leg length difference

Medically speaking, there are several reasons for leg length differences:

• Congenital if, for example, the skeleton has a deviation in the predisposition (eg hip dysplasia)
• If there has been a disorder in the leg in childhood (for example inflammation, bone fracture or tumor). In the area concerned, the blood flow will have temporarily increased for recovery processes, as a result of which the growth plates can grow faster. There may also be an inhibition of growth, for example due to anti-cancer medication.
• A leg fracture or hip or knee replacement surgery later in life can also cause differences.
• An apparent leg length difference may occur due to left-right difference in an X-position of the knees or ankles, for example in the case of a sagged foot.
• An apparent difference can also occur because the posture is adjusted to avoid pain, such as with one-sided back or hip pain.

When is there a difference in leg length?

That is a difficult question to answer. There is no good definition of it. Do we already speak of difference in leg length at 1 mm, or 5 mm, or more? There are some problems attached to this.

• Opinions differ greatly. Some find a few millimeters sufficient to prescribe a heel raise. In the medical sector it is indicated from 1½-3 centimeters that it can cause problems.
• Another problem is that there are also different types of leg length differences. That can be confusing. For example, there is a: structural bone length difference: there is a difference in length of bones (femur, tibia). And there is b: functional leg length difference (the same as indicated above with apparent difference): left and right is used differently by, for example, sagging foot, hip osteoarthritis, pain avoiding behavior, and so on.
• Not unimportant when determining leg length: which measuring method is used? When handling a measuring tape, different bony marks can be used (inside ankle, outer ankle, side or front pelvis). This measurement method does not appear to be very reliable. When the measurements are repeated, differences of up to 2 cm can be found. When measuring with a spirit level in position, the pelvic girdle is often measured on the left-right side. The problem here is that not only the leg length is measured, but also the position and construction of the pelvis. The most reliable measurement is done with X-ray examination or CT/MRI scan, where the patient stands and the entire leg including pelvis is visible. The so-called plank method is the most suitable for daily practice. The test subject divides his weight between both legs. Shelves of 0.5 cm are placed under the short leg until the pelvis is straight. This is also a measurement of leg length and pelvis position at the same time.

Consequences and complaints due to leg length difference

There is always debate about that. We now know that leg length differences are common. We also know that back problems are common. The chance to find someone with a leg length difference and back pain simultaneously is therefore quite large. This does not mean that it causes the other: does the leg length difference give back complaints, or do the back complaints give the (functional) leg length difference. Or is there no connection? And if there is a link, to what extent does it cause the other or are there more factors involved? There are always more factors involved: someone who has very mobile joints will be able to absorb a leg length difference more easily without complaints than, for example, an older person with wear to the back, hips and knees. It is therefore always important to look at the total picture.

An asymmetrical gait arises from a difference of 2 cm. Complaints usually arise when physical activities increase such as a change in training at athletes, or a construction project. The load on the leg, pelvis and back will increase on one side. A familiar picture in runners is the friction syndrome, in which the muscle tendon leaf (tract iliotibialis) on the side of the upper leg (from pelvis to below the knee) is irritated and can cause pain in the hip, thigh or knee. The complaints first arise just after walking, later at the start of walking, and later during and after walking. Foot complaints can be a result of leg length difference. The hip on the long side often turns outwards so that the leg becomes a bit shorter. The foot is thus loaded differently. This may cause fractures in the foot of runners.

When there is a considerable leg length difference, say more than 2 cm, there is evidence that this can give accelerated hip and knee wear. And possibly low back pain. There is no evidence that there are other complaints such as neck pain, headaches or shoulder complaints.

Bone length difference in musculoskeletal medicine

In musculoskeletal medicine a picture is known under the name 'twisted pelvis'. This image can be recognized in a sitting position. This eliminates a leg length difference. In standing this is difficult (you measure leg length and pelvis), but there is a functional leg length difference to see. Lifting the twisted pelvis normalizes again the leg length. Also a hip that is in a rotated position (recognizable by a foot that is turned outwards or inwards) can give a leg length difference. This can not always be corrected. See the next section for the reason.

Adaptability

The idea that we humans are mirror-like on the left and right is no longer tenable and therefore the idea that leg length differences are not good. A living being, such as man, has a physical capacity for adaptation. The body conforms to what you do with it through continuous renewal: when I train the biceps of my left arm, it increases in size and strength, but my right one does not. Since we carry out all movements and postures asymmetrically, our body develops in all respects asymmetrically: posture, mobility, and also the position of the hip, the leg length and so on. The 'correcting' of this to symmetry is thus a step back in the development of that person. Sometimes more complaints will arise. In any case, the body will try to start the adjustments again. See also the artcle on symmetry and asymmetry.

Conclusions

- Leg length differences are common without complaints
- Many leg length differences are normal adjustments
- To assess whether a leg length difference is problematic, measuring the leg length alone is insufficient.

References
Friberg O. The incidence of LLI in 653 patients with chronic low-back pain and 359 symptom-free conscript soldiers. Spine 1986;6:643-651.

Harvey WF et al. Association of leg-length inequality with knee osteoarthritis: a cohort study. Ann Intern Med. 2010 Mar 2;152(5):287-95.

Cursusklappers Marsman Stichting. Marsman Stichting, Haarlem, 2000.
Gurney B. Leg length discrepancy. Gait & Posture 2002;15:195-206.
Pakvis DFM, et al. Bepaling van beenlengteverschil met de plankjesmethode: nauwkeurige uitkomsten, onafhankelijk van de ervaring van de onderzoeker. Ned Tijdschr Geneesk 2003(147):443-6.
Pereira CS, et al. Is structural and mild leg length discrepancy enough to cause a kinetic change in runners’ gait? Acta Ortop Bras 16.1(2008):29-31.