Leg length Discrepancy (LLD) is a controversial subject amongst chiropractors, physical therapists, podiatrists, and medical doctors.
In the medical community, there are two main types of LLD. Functional LLD occurs when alignment or dysfunction of a joint causes an appearance of a short leg. For instance, the pelvic bone can rotate and cause the femur to move up or down, creating an apparent short or long leg. Another common functional cause can be hip rotator tightness and/or psoas tightness which, for lack of a better word, sucks up the femur giving the appearance of a short leg.
Structural LLD occurs when the tibia (shin bone) or femur (thigh bone) is literally shorter than the other side. This can be congenital, but it can also be caused by a healed fracture.
Many of you are told you have a long leg or a short leg from various techniques such as: The practitioner measures your legs while you are lying on your back or stomach. Some look at the height of your pelvis while standing. Some will have you lie on your back and bend your knees to see if the femur or tibia are longer. Some of you even have had x-rays.
But how do we know if a patient REALLY has a so-called Leg Length Discrepancy. And, how do we know if the LLD is the actual cause of pain.
Unfortunately, research shows that there are errors between examiners and even in x-ray machines. (2005 Terry, 2002 Gurney, 1995 Rhodes.)
Errors of the machine = 0.9cm
Intra-examiner (reading the x-ray) error = 0.4cm
Inter-examiner error = 1 cm
Measurement error between lying down and standing = up to 12mm
Intra-evaluator error = 2cm
Inter-evaluator error = 2.5cm
Research also shows that LLD is universal and that 90% of the population has it with an average of 5.2mm. (Knutson, 2005) Two literature reviews have concluded that 20mm of a LLD is necessary to negatively affect the patient with regard to pain, function, and biomechanics. (Knutson, 2005 and Gurney, 2002.) That is very significant. Personally, I don't believe I have ever come across such a LLD in a patient who has not fractured a leg bone.
Given the errors in x-ray machines, in reading x-rays, in evaluating legs in the clinic, AND that 90% of the population has a LLD, AND 20mm of LLD is significant to cause pain and affect biomechanics, do we really need to put a lift in shoes or build up orthotics? Are we barking up the wrong tree?
As clinicians, we often find that some patients display anthropometric asymmetries, but are asymptomatic while other patients have equal flexibility, leg length, and ranges of motion, yet are in chronic pain. Yet, many clinicians are very quick to put in a heel lift or beef up an orthotic to create symmetry in leg length.
Let's review why repetitive stress injuries in running occur: 80% of the injuries are caused by an overload to soft tissue. In other words, soft tissue becomes injured/inflamed if the stress applied is greater than it's ability to adapt. This is usually due to training errors and too much too soon. The rest of the 20% is divided among intrinsic and extrinsic factors. Intrinsic factors include muscle strength, flexibility, and biomechanics. Extrinsic factors include shoes, orthotics, surface.
Given that 80% of running injuries are caused by soft tissue overload, we may need to look more closely at training errors in addition to biomechanics and shoes and less into leg length discrepancies.
Dubois, Blaise. New Trends in the Prevention of Running Injuries. Conference September 2010, Saskatchewan, SK, CN.
Gurney, B. Leg Length Discrepancy. Gait Posture. 2002 Apr;15(2):195-206.
Terry, Michael et al. Measurement Variance in Limb Length Discrepancy: Clinical and Radiographic Assessment of Interobserver and Intraobserver Variability. Journal of Pediatric Orthopaedics:March/April 2005 - Volume 25 - Issue 2 - pp 197-201.