Lower limb dysmetria: what does it consist of?

By Cristiano Antonino On Apr 16, 2023

The term dysmetria indicates a bone defect that results in a different length of the limbs: dysmetria can be congenital and thus present from birth, or acquired, as in the case of traumatic events, accidents or pathologies, which can lead to skeletal abnormalities

What is dysmetria of the lower limbs?

Lower limb dysmetria, or more precisely heterometria, is a medical condition that indicates a difference in length of the bone segments of the lower limbs.

Two forms of heterometria can be distinguished: a structural form proper, and a functional form.

Functional dysmetria: also known as false dysmetria, it is due to joint contractures or other defects that may result in an apparent difference in leg length, or an alteration in the mechanical axis of the limbs.
Structural dysmetria: this is due to congenital defects or bone abnormalities at both lower limb and pelvic levels.

Precisely because of this duality, the diagnosis and treatment of dysmetria of the lower limbs can entail several difficulties for the medical team: the type of intervention best suited to resolve the condition, in fact, can vary depending on whether it is a real bone abnormality or a false shortening due to other components.

Furthermore, dysmetria can be congenital and thus be due to hereditary defects malformed from birth, or it can be acquired, as a consequence of traumatic events, infections or inflammatory processes developed during an individual’s lifetime.

Heterometria is also referred to as short leg syndrome, and has a higher incidence in children, who make up approximately 30% of cases.

What can be the causes?

There are a number of conditions that can lead to alteration in the lower limbs, these include:

Abnormal ossification of the pelvis during growth spurts.
Rotation of the pelvis.
Basculature of the iliac bone, i.e. an incorrect alignment of the pelvic bones.
Visceral fixation: the musculoskeletal system and internal organs are wrapped in connective tissue called fascia. In this way, the internal organs (viscera) are connected to the spinal column and consequently to the skeletal system. Different types of pathologies of the internal organs can consequently affect the morphological conformation of the spinal column.
Muscle retraction, i.e. shortening and permanent injury to muscle tissue.
Scoliosis and other postural defects.
Piriformis syndrome, a condition caused by compression of the sciatic nerve by the piriformis muscle.
Calcaneal valgism.
Knee valgism.

Real dysmetria of the limbs is relatively less common: in most cases, the real dysmetria is of an acquired type, and generally it can be the result of traumatic events such as accidents and fractures, a consequence of surgery, or it can be due to infectious and tumour processes.

In the case of congenital dysmetria, it can be due to various conditions:

Pathological growth, in which case one speaks of hyperplasia.
Delayed growth of one of the limbs, a process referred to as hypoplasia or aplasia.
Genetic malformations, such as hemihypertrophies, hypoplastic limbs or skeletal dysplasias.
Osteopathies, such as Legg-Calvè-Perthes disease, i.e. an osteochondritis characterised by necrosis of the femoral head, or osteosarcomas affecting the mesenchymal cells responsible for the production of osteoid substance.
Neurological or neoplastic diseases.

If no associated abnormality or apparent cause can be detected, one can speak of idiopathic forms of dysmetria.

How does dysmetria of the lower limbs manifest itself?

As already mentioned, dysmetria of the lower limbs is a condition that is not always easy to detect: in addition to the diagnostic difficulties linked to the type of dysmetria, the course of the disease is often symptomless, unless it is a consequence of other ongoing pathological processes.

Symptomatology naturally varies from case to case depending on the type of disorder, however, in general, the main symptoms may include swelling, joint and muscle pain, motor difficulties and functional impotence of the affected limb.

It should be pointed out that in these cases, it is necessary to first treat the triggering condition in order to then be able to resolve the dysmetria.

The difference in length between the limbs in itself does not imply symptoms and is therefore difficult to notice, but there are certain elements that can be taken into account to detect heterometry.

In addition to leg malformations, dysmetria affects the balance of the entire body structure, and can therefore lead to posture defects, an asymmetry of the trunk and shoulders, or walking difficulties with an unstable and awkward gait.

Diagnosis

The first step in diagnosing a dysmetria of the lower limbs is a careful orthopaedic examination, during which, first of all, it will be determined whether it is functional or structural:

Structural measurement: to determine whether the patient has a structural form of dysmetria, the orthopaedist measures the distance from the anterior superior iliac spine (SIAS) to the midpoint of the median internal malleolus; the length of the femur and tibia are also measured, and the mechanical axes of the entire limb and individual bone segments are traced.
Functional measurement: in cases of functional dysmetria, the skeletal structure is intact, so abnormalities should be looked for in the biomechanical functions of the limb; for example, in patients with a rotated pelvis or tilted iliac bones, it will be possible to find a pronounced difficulty in standing up straight or maintaining balance.

Having an accurate and quick diagnosis of the pathology is very important in order to be able to plan an appropriate treatment and prevent the patient from developing other problems related to bone unevenness, such as posture defects or underdevelopment of the limb.

For the correct measurement of dysmetria, some specific investigations are necessary; these may include:

Plumb line measurement: this is a non-invasive test using a special medical device needed to measure the height difference of the iliac crests and highlight the difference between the limbs.
X-rays: In order to accurately determine the heterometry of the lower limbs, it is necessary to take an X-ray under load, i.e. the patient must remain upright with the kneecaps placed frontally, and an X-ray in lateral position; the X-ray must frame the pelvis and hip area, legs, ankles and feet. A comparison X-ray should also be taken, using a compensatory elevation for the shorter limb.

In the case of paediatric patients who have not yet completed the bone growth phase, at least two x-rays must be taken six months apart in order to calculate what the limb length difference will be at the end of growth.

In congenital forms, the worsening, i.e. the increase in the difference in length between one limb and the other, occurs constantly and it is not difficult to predict the course of the condition; in acquired forms, on the other hand, heterometry is extremely variable, depending on the age at which it appears, the triggering causes and the severity of the condition.

Treatment

Several treatment options are available to resolve dysmetria conditions.

The most suitable approach varies depending on the specific case and the form of the disorder encountered.

Functional dysmetria

In the case of functional dysmetria, only osteopathic manipulative therapy combined with targeted postural exercises and physiotherapy can be used.

For more pronounced heterometry, proprioceptive insoles or orthopaedic insoles may be prescribed.

Structural dysmetria

Generally, to resolve dysmetria defects, the most adopted solution is the use of orthopaedic insoles and elevations; this can be useful to compensate for differences between limbs of up to 3 centimetres.

For more severe cases, however, it may be necessary to intervene surgically with so-called ‘controlled growth techniques’: epiphyseodesis is a micro-invasive approach involving the insertion of a metal device inside the cartilage, which allows the growth of the longer limb to be temporarily slowed down or stopped permanently, so that the shorter limb has time to compensate for the difference.

Epiphyseodesis is the most indicated treatment for dysmetria between 2 and 4 cm, especially for patients who are close to skeletal maturity.

When the limb length difference exceeds 5 cm and a controlled growth intervention would excessively compromise adult stature, bone lengthening treatment with external fixation can be used.

This is a more invasive approach that consists of the interruption of the outermost part of the bone, which is followed by a reparative process with a gradual distraction of the bone ends.

More recently, internal fixation methods involving the implantation of an elongated nail in the bone marrow have been developed: although this approach offers the advantage of avoiding an external device and allows very satisfactory results to be achieved, unfortunately it has reduced applicability and only selected cases can benefit from this treatment.

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