There are many more adaptations to LLI than 10, but these are a few visual signs that might help you recognise asymmetry in leg length. I’ll write more about the associated over-use injuries and treatment planning for LLI in follow-up posts: PART 2 & 3. These are based on my own experiences over 30-years in MSK, and I would encourage you to do further reading and look at the evidence should you find these areas of interest.

  1. Excessive pronation on the longer-limb side.

I often find that there is excessive pronation on the longer-limb side, but this is not a ‘hard-and-fast’ rule. Other researchers have found similar findings (Blake Rl, 1993; McCaw ST, 1991; Lustein SM, 1985).

If there is concurrent increased hip, knee and ankle flexion in the longer-limb, there may be an increase in peak loading and/or increase ‘pressure-time’ integral on the ipsilateral side creating increased pronation moments.  However, I can also see excessive pronation on the shorter-limb side especially if the centre of mass (CoM) is displaced to the shorter side increasing downward load on the foot. Rothbart, 2006 found a positive correlation between functional LLI, an anterior pelvis and excessive pronation.

This is obviously dependent on subtalar joint (STJ) morphology and whether the foot can excessively pronate at all. You may find bilateral excessive pronation, or no pronation because of the individualistic nature of how we adapt. The key is to understand where the majority of the weight is displaced to.

2. Ankle inversion sprains on the shorter-limb side.

Depending on the magnitude of the LLI, coupled with the morphology of the STJ i.e. if the STJ axis is laterally deviated and the CoM is displaced to the shorter-limb side then this can increase the risk of ankle inversion sprains. More rarely you can see ankle inversion sprains on the longer-limb side, especially if the person is mesomorphic  in body type and pulls their CoM back upright for stability. This creates a momentary over-balance and can displace the CoM to the longer-limb.

3. Delayed heel-lift on the longer-limb side and/or early heel-lift on the shorter-limb side.

One of the fundamentals of gait is to stabilise the body to maintain smooth vertical and medio-lateral sinusoidal curves of the CoM. In the presence of LLI the longer-limb can adapt with concurrent increased flexion of the hip, knee and ankle with a resultant lowering of the pelvis on the ipsilateral side. This is caused due to the downward pressure of the CoM coupled with resultant upward pressure from ground reaction forces (GRF), creating a lever-effect within the joints which act as a sagittal plane facilitator. This is both useful as a height adjustment mechanism, but also potentially damaging due to increased joint moments. Increased flexion at the ankle joint therefore delays heel lift and increases the ‘pressure-time’ integral and potentially increasing the risk of over-use injury on the longer-limb side.

The opposite can also be true on the shorter-limb side, but this time the joints extend more in order to maintain height at the pelvis. There is usually less weight on a shorter-limb within the lever-mechanism and therefore less leverage on the heel to remain on the ground. If the magnitude of LLI is great enough, then the ‘levers’ can extend so much that it creates a straight ‘pull’ of the shorter-limb from the ground causing early heel lift. This increases the ‘pressure-time’ integral on the forefoot and is often coupled with an adduction motion of the heel creating shearing forces under the metatarsals, and can lead to pathology. Note: Increased knee flexion can also create early heel lift if there is ‘sagittal plane blockage’ at the ankle joint on the same side.

4. Weakened quadriceps muscles on the shorter-limb side.

Normal flexion of the knee after heel strike requires eccentric muscle activation to stabilise and decelerate the knee. It is not uncommon for a shorter-limb to extend more during the contact phase of gait to maintain height, and this can weaken the quadriceps muscle group. This is because  reduced flexion requires less eccentric contraction of the anterior thigh muscles and they become weak. When the quad muscles are weak they cannot absorb as well, with resultant stress in the connective and fascia around the knee joint.

5. Posterior rotation of the innominate bone on the longer-limb side.

The pelvis has multiple ways to adjust height in the presence of asymmetry in order to stabilise the CoM. These are evolved mechanisms to adapt to either external changes in the under-foot environment or internal asymmetries in the skeletal system. These adaptations are instant ‘in-the-moment’ changes in order stabilise the body as part of survival, but in a modern context can often lead to longer term damage in the system. Think of our early ancestors unshod bipedal gait and their need to survival in a harsh natural world. The body would have used a wide range of musculoskeletal (MSK) adaptations to navigate the environment.

One such adaptation is posterior rotation of the whole innominate on the longer-limb side which can lower and internally rotates the acetabulum by a few millimetres. Long-term posterior innominate adaptation can lead to pain and dysfunction in the  lower-back, weaken gluteal muscles, and increased internal rotation of the leg etc. Posterior rotation on the long-limb side has also been shown to be lose related (Cooperstein R, Lew M 2009; Cummings GS, Scholz JP & Barnes k 1993).

6. Anterior rotation of the innominate bone on the shorter-limb side.

The opposite can also be true for the shorter-limb. The innominate can adapt with an anterior rotation orientation, which can raise and externally rotate the acetabulum by a few millimetres. Anterior adaptation on the shorter-side has also been shown to be dose related (Cummings GS, Scholz JP & Barnes k 1993). Anterior innominate rotations are more likely to occur in an individual with a naturally flexed (nutated) sacrum. This may because the easiest route to adapt is forward rotation because nutation moves the sacrum base upwards and forwards. It may also be because there is less GRF under a shorter limb and innominates are more likely to rotate forward with less weight on them. An example of this is if you stand on a step with one leg, and hang the other leg over the edge in mid-air. The innominate of the hanging limb will rotate forwards. Concurrently, the innominate of the single leg standing on the step has increased GRF into the acetabulum and it is more likely to rotate backwards. This effect is due to where the upward force is positioned relative to a downward force along a  lever-arm created between the acetabulum and the sacral base i.e. a bit like a seesaw with two unevenly weighted children on it. Depending on the weight relative the pivot point the lever-arm will either rotate one way or the other.

Anterior innominate rotation can also have a number of MSK consequences and can lead to a number of over-use injuries with long-term consequences. In a study by Zabjek KF & Leroux MA et al 2001, found that raise of 5, 10 and 15mm under the left foot to simulate LLI created anterior innominate rotation on the contralateral side. Does this suggest that the short leg can adapt to the effects and forces created by a longer? I have observed this myself for many years.

7. Sacroiliac joint (SI joint) restriction on the shorter-limb side.

As described above a common adaptation on the shorter-limb side is an anterior innominate rotation. Over many years I have found that this can cause some issues in the SI joint on the side of most anterior rotation. If the innominate rotates forward higher than 15 degrees +ve (measured as a sagittal plane angle between the posterior superior iliac spine (PSIS) and anterior superior iliac spine (ASIS), horizontal being zero degrees) I would consider this an excessive angle. Because of the oblique angle of the SI joint from sacrum to innominate – anterior rotation compresses the joint creating sacroiliitis characterised by acute pain behind the PSIS. This is more common on in shorter-limb; on the right side; and more common in women. Because the sacrum is basically triangular in shaped with the apex at the lowest margin, the SI joints are tilted towards the shorter-limb side. This results in increased compressive forces (because the SI joint becomes more horizontal) within the joint on the shorter-limb side, while increasing shearing forces (because the SI joint becomes for vertical) within the joint on the longer-limb side. This is far from ideal for pelvic function.

8. Increased muscle activity and/or spasm in the paraspinals on the shorter-limb side.

It is not uncommon to see increased muscle activity above the pelvis on the shorter limb side. Muscles that become particularly active are Quadratus lumborum (QL) and Erector spinae (ES), which are vital for spinal movement and stability. Their origin and insertion also make them ideally suited to correct deviations in orientation of the pelvis in the frontal plane. QL is an oblique muscle and quadrangular in shape, perfectly positioned from its origin at the iliac crest to its insertion on the transverse process of lumbar one through five and the lower part of the twelfth rib, to exert an oblique pull upwards on the shorter-limb pelvic side. ES is a vertical muscle that originates from pelvic, vertebral, and rib bones located in the lower-to-mid back and then extend upward and insert on vertebral and rib bones located higher up in the back and neck. It is ideally suited to hold the pelvis up on the shorter limb side. Palpation of these muscle on your patient can often reveal that they are in hyper-tone or even spasm on the side of the shorter limb as they support other adaptive mechanism to stabilise the CoM during stance and ambulation.

9. Tension along the fascia of the posterior oblique sling (POS) from the ipsilateral shorter-limb side, to the contralateral longer-limb side.

If any of you are familiar with the book ‘Anatomy Trains’ by Thomas W. Myers you will understand how important the fascial slings are in normal gait. There is an antagonistic reciprocal relation between the posterior and anterior (AOS) slings. In the presence of an LLI, the POS consisting of the latissimus dorsi muscle, the opposite side gluteus maximus muscle, and the interconnecting thoracolumbar fascia – can be pulled asymmetrically from the shorter-limb side to the longer-limb side obliquely across the body. For example, with a longer left leg the POS will be pulled from right-lower to left-upper creating a specific pattern of injury that we will discuss is the Part 2 of this three-part series. This sling crosses at the level of the lumbosacral junction and provides what is known as force closure to the SI joint. Typically, a patient with an oblique pull across the POS in this way will complain of lower limb issues in the shorter-limb; lower back pain and upper body issues on the longer limb-side.

10. Functional scoliosis to the shorter-limb side.

A functional scoliosis is a very common occurrence with an LLI. This is because of the L5-S1 lumbosacral joint where the lumbar spine ends and the sacral spine begins. Any deviation from the ‘normal’ orientation of the lumbosacral joint in any plane will result in deviation of the L5, L4, L3 and so on until correction is made further up the spine. It seems obvious to have eyes that are level with the horizon for normal sight, however a complex sequence of corrections between each vertebral body are necessary in order to achieve this when an LLI is present. When the lumbosacral joint is deviated due to LLI, it will be dropped on the shorter-limb side which means that the L5 vertebra sitting at  90 degrees to the sacral will be angled the shorter-limb. In order to establish a horizontal shoulder line, each successive vertebra are corrected away from the short-limb towards the contralateral side at a slightly less angle than the vertebra below, in a cephalic direction. This will result in an observable longitudinal curve in the frontal plane that we call a functional scoliosis. If treated early enough by levelling the sacral base, a functional scoliosis can be corrected with in-shoe orthotics. Unlike an idiopathic scoliosis – not caused by LLI and can often only be corrected with complex spinal surgery. Papaioannou et al, 1982 reported significant scoliosis in patients with LLI greater than 22mm, however from my own experience I have seen many functional scoliosis in patient with 10mm and above.