Developmental Variants

For Medical Students

What It Tests

A growing limb passes through angular and rotational shapes that resolve on their own, and a child is often brought because of one of them. 4.3.10 covers the deformity.

The examination is deciding whether the shape is within the normal range for the age, whether it is symmetrical, and whether anything else is wrong. 4.3.3 covers standing alignment.

It matters because the commonest intervention here is reassurance, and the examination is what justifies it.

How It Is Performed

Establish the age, since the normal alignment changes direction during the first years of life. 4.19.1 covers the growth plate assessment.

Ask what changed and when, because a shape that is improving behaves differently from one that is worsening. 4.2.9 covers the onset.

Look at the child standing and walking, from the front and from the side. 4.3.1 covers observation from the door.

Record the alignment in both planes and whether it is symmetrical, since asymmetry is the finding that matters most. 4.3.3 covers standing alignment.

Record the rotational profile, since in toeing and out toeing are the common presenting complaints. 4.19.7 covers torsional assessment.

Measure the limb lengths, because a length difference alongside an angular shape suggests something other than a variant. 4.5.8 covers limb length assessment.

Assess generalised laxity, since hyperextension and apparent instability are often part of it. 4.23.3 covers the hypermobile patient.

What a Positive Means

A symmetrical angular shape that fits the age, with normal limb lengths, a normal rotational profile and no pain, is a variant and needs no treatment.

Asymmetry between the two limbs is the finding that argues against a variant and for a localised cause. 4.1.4 covers the structured approach.

An angular shape that is worsening rather than improving argues against a variant, whatever the measurement. 4.3.10 covers the deformity.

Pain in a child with an angular shape is not explained by the shape, so it is investigated separately. 4.2.1 covers pain.

Hyperextension and increased translation in a generally lax child are laxity rather than instability, and the distinction decides whether anything follows. 4.5.5 covers hyperextension.

MRCS Level

How It Is Performed

In a viva this is the bow legged or knock kneed child and the expected answer reassures with reasons rather than simply reassuring.

The expected points are the age, the history of change, the standing and walking observation, the alignment in both planes, the symmetry, the rotational profile, the limb lengths, the laxity assessment, and the absence of pain.

Say that you would ask whether the shape is improving or worsening, since that distinguishes a variant from a disorder. 4.2.9 covers the onset.

Say that you would measure limb lengths, because a difference points away from a variant. 4.5.8 covers limb length assessment.

Say that you would look for pain, a limp and asymmetry as the three findings that change the answer. 4.4.2 covers the antalgic gait.

What a Positive Means

The reasoning expected is that the growing limb remodels in response to load, so a shape within the normal range for the age corrects itself as the loading changes. 3.5.2 covers contact pressures.

Symmetry indicates a systemic developmental process rather than a local lesion, which is why asymmetry is the more serious finding. 4.3.3 covers standing alignment.

A worsening shape means the remodelling is not correcting it, so a localised or a metabolic cause is more likely. 4.3.10 covers the deformity.

Generalised laxity changes the normal range for translation and hyperextension, which is why it is assessed before any laxity is called abnormal. 4.23.3 covers the hypermobile patient.

How Good It Is

The examination is reliable for symmetry, for limb length and for the presence of pain, and those are the three findings the decision needs.

Its best contribution is excluding the things that are not variants, which is a negative result and the useful one here. 4.1.4 covers the structured approach.

It is imprecise about the magnitude of an angular shape, which radiographs measure when the question arises.

Long leg films quantify the deformity, so the examination decides whether a film is needed rather than replacing it. 4.1.6 covers that relationship.

No figures appear for any accuracy comparison on this page, under decision 023, and the comparison is the claim being made.

FRCS Level

How Good It Is

At decision level the examination separates the children who need nothing from the children who need imaging, and it does that well.

A symmetrical, painless, improving shape with equal limb lengths needs observation, and the examination establishes all four of those. 4.5.8 covers limb length assessment.

Asymmetry, pain, a limp or a worsening shape moves the child to imaging, and each is a clinical finding. 4.4.2 covers the antalgic gait.

A rotational component alongside an angular one changes the assessment, because the two can compensate for each other. 4.19.7 covers torsional assessment.

Generalised laxity in a child presenting with instability changes the diagnosis rather than the severity. 4.23.3 covers the hypermobile patient.

Where It Misleads

The commonest error is measuring an angular shape and comparing it against an adult normal rather than an age appropriate one. 4.3.3 covers standing alignment.

A variant is accepted in a child whose shape is worsening, because the single measurement looks acceptable. 4.3.10 covers the deformity.

Asymmetry is missed when the limbs are examined one at a time. 4.1.4 covers the structured approach.

Generalised laxity is read as ligament injury, and the family history is the question that separates them. 4.23.3 covers the hypermobile patient.

Pain is attributed to the shape, which it rarely explains. 4.2.1 covers pain.

Fellowship Level

Where It Misleads

At fellowship level the question is whether a shape will resolve, and the examination answers it only by repetition.

A single assessment cannot distinguish a resolving from a progressing shape, so the trajectory is the finding and it needs two visits. 4.2.9 covers the onset.

Angular and rotational components compensate for each other, so a child with both can present with a normal looking gait and an abnormal examination of each part. 4.19.7 covers torsional assessment.

The normal range for a given age is wide and is a population statement, so an individual child sits inside or outside it without that being decisive. 4.3.3 covers standing alignment.

Generalised laxity is a spectrum assessed by a scored test whose threshold is a convention, and a child near the threshold is not thereby normal or abnormal. 4.23.3 covers the hypermobile patient.

A metabolic or skeletal dysplasia can present as a symmetrical variant, and the examination findings that separate them are stature and proportion rather than anything at the knee. 4.5.8 covers limb length assessment.