Paediatric Protocol

For Medical Students

What It Shows

A paediatric knee protocol images a joint whose bones are still forming, so the physis, the secondary centres and the marrow all look different from an adult's. 5.15.1 covers the normal paediatric anatomy.

It is adapted for a smaller joint, a shorter attention span and a different set of expected injuries. 5.15.5 covers paediatric cruciate injury.

It matters because most paediatric knee imaging error is normal development read as pathology. 5.15.7 covers developmental variants.

How It Is Acquired

Use a smaller field of view and a coil matched to the limb, which maintains resolution in a smaller joint. 5.5.1 covers the standard protocol.

Shorten the protocol where possible, because movement is the dominant technical problem. 5.2.19 covers artefacts.

Include the physis in the coverage, since physeal injury is a paediatric specific question. 5.15.2 covers the growth plates.

Expect red marrow and know its normal distribution for the age. 5.2.13 covers T1 imaging.

Avoid contrast unless the question requires it, which it usually does not. 5.2.21 covers advanced magnetic resonance techniques.

What Normal Looks Like

An open physis with its characteristic signal, which is not a fracture. 5.15.2 covers the growth plates.

Red marrow in the metaphyses, darker than adult fatty marrow on the unsuppressed sequences. 5.2.13 covers T1 imaging.

Irregular ossification at a secondary centre, which is development rather than disease. 5.15.7 covers developmental variants.

Thicker cartilage than in an adult, with the expected high signal. 5.5.7 covers the cartilage.

What Abnormal Looks Like

Physeal widening or a fracture line crossing it. 5.15.2 covers the growth plates.

A bony avulsion at a ligament attachment, which is the paediatric equivalent of a ligament tear. 5.3.14 covers avulsion injuries.

An osteochondral lesion at the classic site. 5.15.3 covers paediatric OCD.

Marrow replacement rather than red marrow, which needs distinguishing on distribution and symmetry. 5.13.7 covers bone tumours.

MRCS Level

How It Is Acquired

In a viva this is the protocol to name when asked what differs in imaging a child's knee.

The expected points are the field of view and coil, the shorter protocol, the physeal coverage, the red marrow, and avoiding contrast.

Say that normal development is the main source of error. 5.15.7 covers developmental variants.

Say that a bony avulsion replaces a ligament tear at this age. 5.3.14 covers avulsion injuries.

Say that physeal injury is a question only this age group has. 5.15.2 covers the growth plates.

What Normal Looks Like

The reasoning expected is that a growing bone has a cartilaginous physis and haematopoietic marrow, both of which carry signal an adult's does not, so the normal reference is age dependent. 5.15.1 covers the normal paediatric anatomy.

Red marrow is cellular, so it is darker on unsuppressed sequences than fatty marrow, which is why normal marrow in a child resembles infiltration in an adult. 5.2.13 covers T1 imaging.

The physis is the weakest link in a growing skeleton, so the same mechanism produces a physeal or avulsion injury in a child and a ligamentous one in an adult. 5.15.5 covers paediatric cruciate injury.

That also means an injury here carries a growth consequence as well as a structural one, which is a consideration no adult study has. 5.15.2 covers the growth plates.

How Good It Is

Magnetic resonance imaging in a child is as capable as in an adult and is read against a moving normal.

Its best contribution is the physis and the cartilaginous structures, which no other modality shows. 5.15.2 covers the growth plates.

It is limited by movement, by the age dependent normal, and by sedation considerations in the youngest patients. 5.2.19 covers artefacts.

No figures appear for accuracy on this page, under decision 028, and no age ranges or physeal closure timings appear either: those are published quantities and this environment cannot check them.

FRCS Level

How Good It Is

At decision level this protocol supports decisions no adult protocol has to make.

A physeal injury's extent determines the growth risk, which is the decision no other imaging informs. 5.15.2 covers the growth plates.

A cruciate injury in a skeletally immature patient is a different operation, and the imaging contributes the skeletal maturity as well as the injury. 5.15.5 covers paediatric cruciate injury.

A bony avulsion is repairable with an intact ligament, which is a better situation than the adult equivalent. 5.3.14 covers avulsion injuries.

A marrow question in a child should raise the threshold for calling abnormality, because the normal is wide. 5.13.7 covers bone tumours.

Where It Misleads

The commonest error is reading normal red marrow as infiltration. 5.2.13 covers T1 imaging.

An open physis is read as a fracture. 5.15.2 covers the growth plates.

Irregular secondary centre ossification is read as an osteochondral lesion. 5.15.7 covers developmental variants.

An adult protocol is run on a child's knee, losing resolution in a smaller joint. 5.5.1 covers the standard protocol.

Movement artefact is reported rather than the study repeated. 5.2.19 covers artefacts.

Fellowship Level

Where It Misleads

At fellowship level the paediatric knee is where the normal reference does the most damage.

The normal appearance changes continuously with age, so the reference is not a single standard but a trajectory, and no report states the age dependent expectation it was read against. 5.15.1 covers the normal paediatric anatomy.

Red marrow distribution varies with age and with factors such as athletic training and anaemia, which widens the normal further in exactly the population being imaged for sport. 5.2.13 covers T1 imaging.

Physeal injury's growth consequence depends on the proportion of the physis involved, and measuring that from a routine study is not reliable. 5.15.2 covers the growth plates.

Automated reading is trained predominantly on adult knees, so a paediatric study is the setting where it should be trusted least and where normal variation is greatest. 5.18.8 covers artificial intelligence in imaging.

The honest practice is to read a child's knee against the age rather than against an adult, and to say when the appearance is within normal development. 5.15.7 covers developmental variants.