Evaluation and Management of Limb Length Discrepancy

Limb length difference or discrepancy (LLD), occurs when one leg is noticeably shorter than the opposite. The prevalence rates of LLD range anywhere between 40 to 90 per cent of the population.

The effects of limb length differences are related to many painful orthopaedic concerns. In the literature, researchers have noted a correlation with LLD either causing or exacerbating foot, knee, hip and back issues. There also are significant kinematic and kinetic ramifications of LLD on, how it contributes to both static stance and dynamic gait asymmetry.

Some orthopaedic texts claim that any limb length discrepancy of less than one-half cm up to 2 cm is inconsequential. However, there’s quite a bit of literature to support the likelihood that an LLD of even less than five mm can indeed cause or exacerbate many musculoskeletal issues. During pressure mapping analysis, LLDs as little as three mm affect gait symmetry. Therefore, LLD should be one of the first conditions podiatrists look for when performing a comprehensive biomechanical examination.

Structural And Functional LLDs’

Limb length discrepancies are usually classified as either being structural or functional. Structural LLDs are due to bony abnormalities or asymmetry somewhere between the talus and therefore the lumbar spine. These structural issues may be congenital but may also result in a childhood growth plate injury, other trauma or result from joint replacement surgery later in life. Functional LLDs usually result from physiologic changes in the body or biomechanical compensatory changes that occur anywhere from the foot to the lumbar spine.

Scoliosis, an abnormal lateral curvature of the spine, may be an explanation for structural or functional LLD, depending on the kind of deformity. Some patients can functionally compensate for a scoliotic LLD, which would then qualify as a functional LLD in most cases. Those patients who are unable to compensate for their scoliosis usually have a structural LLD.

Causes of LLD

• Congenital
• Infection
• Post-traumatic
• Neoplasms
• Irradiation
• Skeletal Dysplasia’s
• Others

Diagnosing Limb Length Discrepancy

There are two ways to see if a patient has an LLD. one way is via clinical or physical examination. The second way is via radiographic imaging. One may accomplish this with a conventional full-length lower body standing X-ray, a three-part standing scanogram X-ray, magnetic resonance imaging (MRI) or computed tomography (CT). The latter two modalities require the patient to be in a very supine position.

Radiographic imaging is the most numerically reliable method for assessing LLD in line with the literature. The suggestion here is that the clinician should perform a clinical assessment irrespective of what the radiology report suggests about the scale of a patient’s deformity.

Clinical Examination

Clinical examination for LLD can involve two different methods: direct and indirect. For the direct way, one utilizes a tape measure to determine the distance between the anterior superior iliac spine (ASIS) and the fibular malleolus. The clinician performs this measurement with the patient supine but may do so with the patient standing. Patient body structure, weight and issues with unilateral muscle atrophy yet clinician error can all impact the outcome of direct method measurement of LLD.

Indirect method clinical measures occur with patients standing. The clinician will assess either the anterior superior iliac spine, the posterior superior iliac spine (PSIS) or both still at the level of the pelvis to determine which leg is long and which leg is short. Studies have shown that the indirect clinical LLD measure is more accurate and reproducible between clinical users than the direct measure. The indirect method also often incorporates the utilization of various thickness blocks of wood, felt or ethylene-vinyl acetate (EVA) foam to help in determining what proportion of a measurable difference, in centimetres or inches, there is between the short and long limbs.

While one usually performs this method of measure statically, combine the utilization of adhesive felt in three mm thicknesses and connect the felt to the patient’s heel(s) for a dynamic evaluation as the patient walks or runs. This process may determine if there is a mitigation of the usual clinical signs of LLD.

Clinical Signs

The other clinical signs of LLD the clinician should regularly assess beyond the methods mentioned above. for instance, one should compare shoulder height to pelvic level during gait. The high shoulder and low hip are to be on the short limb as opposed to the low shoulder and high hip on the longer limb. Checking for unilateral early heel-off during gait, even though it is not always easy to see in patients with more subtle LLDs, may be helpful. Standing hip hike testing is when the patient attempts to hike one leg and hip at a time up into their body without leaning medially or laterally away from the respective limb. The limb that he or she “feels” lifts higher towards their torso is on the short-sided limb.]

The real issue is LLDs’ create the potential for multi-level compensation throughout the upper and lower extremities. Limb length discrepancies create asymmetrical structure and performance throughout the kinetic chain. These issues can minimally or significantly affect static stance and/or dynamic gait and might result in or exacerbate the pain issues. LLDs’ and the other functional or structural conditions, of the lower extremity, are that regardless of where the primary deforming force may originate, the resulting pain will not always be in that same location. I hope that the reasons for the multi-level effects of LLD below will help clarify why this may be the case.

• Spine

Examination of the spine is crucial during the physical exam and when the patient is in ‘stance’. Merely tracing the vertebral column as the patient faces away from you and as he or she begins to flex forward can provide you with a cursory but usually accurate idea if there are any scoliotic curvatures to take into account regarding a possible LLD.

• Pelvis

One of the primary areas that most clinicians will seek to examine in patients whom they suspect of having an LLD is the hips or pelvic plateau. Pelvic obliquity, a tilting of the pelvis up toward the long side limb and down toward the short side limb, is characteristic for clinicians to see when examining for LLD.

• Innominate bones

Single-sided sagittal plane rotation of the bilateral innominate bones (anterior superior iliac spine or posterior superior iliac spine) often occurs in patients with LLD. In most instances, the anterior superior iliac spine and the posterior superior iliac spine will be short on the short limb side and higher on the long limb side, causing the sacral base to become unlevel and cause functional scoliosis.

• Hips

There can be significantly increased pressure and forces through the acetabulum of the long-sided hip joint, due to the foot and limb compensations, usually external rotation. These compensations, can uncover the head of the femur in the acetabulum and lead to a much more concentrated area of force or pressure on the smaller functioning area of the femoral head cartilage.

• Knee

The knee on the long side may flex easily or hyperextend as compensation for LLD. The short-sided limb will usually be fully extended in ‘stance’ and can tend to flex less in ‘stance’ phase gait than the long-sided knee. Often in older patients, the knee that tends to flex easily is associated with weak quadriceps. Some older patients with knee osteoarthritis may present to the clinic with fixed knee flexion. In these circumstances, the patient has developed a structural LLD. Therefore, one should treat this deformity as the short limb in this instance.

• Ankle

The ankle on the short limb side tends to plantarflex early to seek contact with the ground during the swing phase and into the first stance phase of gait. The chronic swing phase plantarflexion can cause weakness of the tibialis anterior, resulting in a functional restriction of dorsiflexion on the short limb side ankle.

• Foot

The foot also pronates on the long-sided limb while the short-sided limb’s foot will tend to stay more rectus or at times be more supinated. Blake states about 80 per cent of his participants with an LLD had more calcaneal valgus on the long limb side, but 20 per cent had more calcaneal valgus on the short limb side.

• External rotation

The foot and lower leg on the long leg side often externally rotate and exhibit a valgus heel both in ‘stance’ and in dynamic gait. during a caveat to the current, Subotnick says the short limb and foot will at times externally rotate and have a valgus heel as much or more so than the typical long sided foot or leg.

When one sees abnormal signs of LLD, sort of a high anterior superior iliac spine and low posterior superior iliac spine on the identical side, or increased rearfoot valgus on the short limb foot, the clinician will often see that other expected signs of traditional LLD aren’t in alignment either.

• Early Heel-Off During Gait: Sign Of LLD?

Using pressure mapping to assess gait, the observation of an early unilateral heel-off isn’t always indicative of LLD. There are many other factors in a patient’s biomechanics which will mimic an early heel-off during gait. In general, during gait, patients with LLD tend to “step down” onto the short limb and “vault” over the long-sided leg. One will often see decreased stance times, step length and an increased cadence on the short-sided leg. When examining pressure mapping data, the accelerations on the short-sided limb are usually faster along with an early heel off and shorted stance phase.

One of the primary causes of an early heel-off not always associated with a short limb is a limitation of dorsiflexion range of motion of the ankle joint. Once the ankle joint has hit its functional or structural limit of dorsiflexion, then the foot rarely has the other option but to begin to off-weight the heel. the foremost reliable test for assessing ankle joint dorsiflexion range of motion is the ankle joint lunge test. Testing LLD on the table is extremely unreliable between testers. However, we should understand that repeatability of tests does matter.

• Ankle Range of Motions causing Early Heel-Off

Van Gheluwe, Dananberg and colleagues reference functional hallux limitus causing midfoot collapse, which can also cause an early heel-off. The functional restriction of the first MPJ’s ability to dorsiflex promptly can cause a retrograde midfoot collapse, resulting in an early heel off. Clinicians regularly see this deformity with the use of pressure mapping devices. Adding modifications to a foot orthotic and an accompanying initial heel lift to alleviate the functional hallux limitus will usually also reduce this midfoot collapse.

Another potential cause of early heel-off observed in pressure mapping data is when the patient has a chronically flexed knee position or weak quadriceps that will result in the knee giving out early in the stance phase of gait.

All of those conditions can show differing degrees of heel-off during gait. they can also occur with or without a unilateral functional or structural LLD. Many foot and ankle practitioners automatically assume that any detectable LLD is related to functional LLD and that this is a result of the patient having more pronation in one foot than the other. They also wrongfully assume that merely correcting for the forefoot and rearfoot pronation via a custom orthotic prescription will make sure of this issue. Subotnick has discussed this, but there are no empirical studies to show that this approach works for all patients.

A study by Cornwall and McPoil showed that a “slight to moderate limitation of ankle passive dorsiflexion range of motion significantly alters the timing, but not the magnitude, of frontal plane rearfoot motion during walking.” I feel that one should use heel lifts to treat the ankle equinus or ankle dorsiflexion range of motion restriction to change the impaired timing. Then treat the heel position separately with varus posting. do not assume that one will always affect the other as the studies don’t necessarily show that they will every time.

Customised Orthotics In Treating LLDs

Many studies on LLD discuss the primary use of heel lifts inside shoes. In general, heel lifts alone don’t fulfil their potential for the patient. it’s probably best in most instances to use a heel lift in conjunction with a foot orthotic, AFO and/or directly add it to a shoe to maximize treatment of the LLD and overall foot function during gait.

In a 2018 article in Podiatry Today, Richie discussed the utilisation of heel lifts. one of Dr Richie’s conclusions was that the literature strongly points to the combined use of heel raise with a custom-moulded, prescription foot orthotic for issues that require the use of a heel lift.

Ultimately, using heel lifts with custom foot orthotics won’t change the actual measurable range of motion of any of the affected joints in the kinetic chain. However, the use of the custom foot orthotic with a heel lift will nearly always cause an increase in a joints’ functional range of motion, especially at the ankle joint, and to a more symmetrical functioning gait.

Summary

Limb length discrepancies are related to many different types of orthopaedic pain issues from the foot to the low back. Accordingly, clinicians must regularly assess patients for LLD during their comprehensive biomechanical examination. Using the indirect method of clinical assessment has proven to be the most reliable approach, short of radiographic studies.

Once you diagnose what variety of LLD a patient is probably going to experience, you may then often have a greater appreciation for why he or she could also be compensating up and down his or her entire kinetic chain. The kinetic and kinematic compensations can also explain other orthopaedic complaints that your patients could also be experiencing.

Finally, it’s best to treat these issues with a heel lift in conjunction with a custom-moulded prescriptive foot orthotic device and/or directly add it onto a shoe. This method of treatment is the most likely to lead to the desired outcome for your patients.

References

1. Article in Podiatry Today by Dr Williams 
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