LLD is an abbreviation that stands for “Leg Length Discrepancy,” which describes a situation in which one leg is significantly shorter than the other. LLD affects anywhere from 40% to 90% of the population. However, a limb length difference of less than 2 centimeters is typically ignored. A pressure map can reveal LLDs as small as 3 mm that have an impact on gait symmetry. So, when a podiatrist does a full biomechanical exam, one of the first things they should look for is LLD.
Assessment of Limb Length Discrepancy
There are two ways to determine whether a patient has LLD. A physical exam is one method. The second way is radiography. This can be done with a common standing X-ray of the whole length of the lower body, a three-part standing scanogram X-ray, magnetic resonance imaging (MRI), or computed tomography (CT).
Radiographic imaging is the most accurate way to measure LLD, according to scientific literature. No matter how bad the radiology report says the deformity is, the clinician is still encouraged to do a clinical assessment.
There are two types of clinical tests for LLD: direct and indirect. In the direct method, you measure the distance between the anterior superior iliac spine (ASIS) and the fibular malleolus, which is the end of the tibial tubercle.
Clinical measurements utilizing indirect methods are performed with patients in a standing position. The doctor will measure either the anterior superior iliac spine (ASIS) or the posterior superior iliac spine (PSIS), or both, at the level of the pelvis to figure out which leg is longer.
Signs and symptoms
The main issue is that LLDs can cause a wide variety of compensatory movements in the arms and legs. Because of the different lengths of the limbs, there are differences in how the kinetic chain is built and how it works.
The main thing that sets LLDs apart from other functional or structural conditions of the lower extremities is that the pain is not always in the place where the force that caused the deformation is acting. If you need further clarification, please read on.
When doing a physical exam on a patient, it is very important to pay close attention to the spine. Tracing the vertebral column while the patient is facing away from you and bending forward is a quick and, most of the time, accurate way to check for scoliosis curves related to a possible LLD.
One of the first places a doctor will look for signs of LLD is in the hips and pelvic plateau. Clinically, the most common sign of LLD is pelvic obliquity, which is when the pelvis tilts up toward the long-side limb and down toward the short-side limb.
Patients with LLD often have one of their two innominate bones (the anterior superior iliac spine or the posterior superior iliac spine) rotate in the sagittal plane. Most of the time, the anterior superior iliac spine and the posterior superior iliac spine will be shorter on the side with the shorter limb and longer on the side with the longer limb. This makes the sacral base uneven and causes functional scoliosis.
The forces and pressures that go through the acetabulum of the long-sided hip joint can get a lot worse when the foot and leg try to make up for something by rotating the thigh outward. These changes could make the femoral head more visible in the acetabulum, putting more force or pressure on the femoral head cartilage’s smaller area of use.
Those with LLD may experience hyperextension or excessive bending of the long knee. The knee of the shorter limb will be less likely to bend during the stance phase of gait but will still be fully extended most of the time. The elderly often have trouble moving their knees because their quadriceps are too weak. Knee osteoarthritis is a common reason why older people who come to the clinic can’t bend their knees. This case illustrates the development of a structural LLD in the patient. In this case, the short limb should be thought of as the deformity in question.
The ankle on the short limb side tends to plantarflex early to make contact with the ground during the swing phase and the first stance phase of walking. Constant plantarflexion during the swing phase can weaken the tibialis anterior, making it harder for the ankle on the short limb side to dorsiflex.
The foot also pronates on the long-sided limb, whereas the foot on the short-sided limb tends to be more rectus or, at times, supinated.
Customized Orthotics for the Treatment of LLD
A lot of research on LLD has focused on the main way heel lifts are used in shoes. Heel lifts on their own, in most cases, are not enough to help patients reach their full potential. In most cases, a heel lift is most effective when used in conjunction with a foot orthotic, an AFO, or when added directly to a shoe in order to treat LLD and improve gait.
Recent research has shown that problems that need a heel lift can be fixed by using the heel lift along with a custom-made foot orthotic.
Most people notice an improvement in their gait and a greater range of motion in their joints after using a custom foot orthotic with a heel lift, especially in the ankle. After receiving a diagnosis of LLD, patients should consult an orthopedic shoe modification specialist, such as American Heeler, to have a heel lift added to their shoes.