Thursday, 8 October 2015

Limping child safari

Deciding the cause of a mysterious limp in a child involves a bit of detective work.  The history is often sketchy and there are a multitude of possibilities.  This guide is a fun way to think of all the possible causes, through the different age groups.  As we go, we will find out how the various causes of unexplained limp in children can be related to a different wild animal.

Imagine that you are going for a walk in the English countryside and you see an animal in the bushes.  You might expect to see a horse where you are but nothing more exotic than that.  What you didn’t know is that an animal has escaped from a nearby safari park.  So when you hear something rustling in the bushes it turns out to be something else.  When you notice that the animal is unusual and has stripes, you need to know whether to run or take photos.  The question is, like the limping child, what is it and how do you tell before it is too late?

Billy is a newborn Baby Zebra
Transient Synovitis or “Irritable Hip” because he is:
  • Wobbly but well
  • Happy if left alone and will get better if given time

Irritable hip is a condition that tends to affect children about 1-4 yrs old, causing them to have an unexplained limp.  The pain is caused by excess synovial fluid in the hip capsule, thought to be reactive to a recent viral illness.  They will either not walk at all or will have a limp which gets worse with activity.  They will not be systemically unwell.  Irritable hip is best diagnosed by a thorough history and examination (usually revealing restricted hip movements and nothing else) rather than by using blood tests or X-rays.  Like a baby Zebra, there is nothing dangerous about an irritable hip.
Management consists of analgesia and watchful waiting.  You can’t make a toddler rest any more than you can a baby Zebra so just let them determine their own activity level.  The most important thing is to make sure that you safety-net thoroughly so that the parent knows to come back if the pain is severe or the child is significantly febrile or unwell. If that happens, maybe you were wrong about the baby Zebra…

Wendy is a Wounded Baby Zebra:
a Toddler’s fracture because she is
  • In more distress
  • going to feel much better once she has the correct treatment

A toddler’s fracture is an undisplaced fracture of the tibia in a child usually aged 1-3.  It sometimes occurs with a seemingly insignificant mechanism of injury, so that the parents are surprised at how upset the child is after what seemed like a mundane slip or fall.  This is not to be confused with the finding of a significant injury without a good explanation, which is a red flag for non-accidental injury.  It may be difficult to localise findings in these children as they are in a lot of pain.  This, combined with the fear of strangers in that age group, results in a difficult assessment.  There will be normal hip movements if you are able to examine this and there may be a subtle warmth to the tibia.  The child will be systemically well.  So, if your "Baby Zebra" seems to be disproportionately distressed, look to see if they might be injured as it may not be easy to tell from the history or examination.  Suspected toddler’s fractures, like all other causes of limp, require other explanations to be ruled out clinically.
Even if the X-ray is normal, when a child has finding that suggest a toddler’s fracture, they are treated in a cast (soft cast if you can get one) regardless.  As soon as the cast is on, they feel much better.

Sam is a Striped Hyena: Osteochondritis of the hip - Perthe’s Disease because it...
  • Is difficult to spot and hard to remember
  • Will cause damage but safer if handled early on by a specialist

The cause of Perthe’s Disease is not known.  What is known is that it tends to present with a unilateral hip problem in a child aged 6-12 yrs old.  Like all hip problems, the pain may be referred to the knee which can distract the assessing clinician.  It is always advisable to examine the joint above and below a problem, which will stand you in good stead if this happens to you.  If a school aged child develops a mysterious limp, the possible diagnoses are much less likely to be benign than with the under five year olds.  Like a hyena, Perthe’s disease may not be what you are expecting but it needs to be identified as soon as possible because early intervention improves outcomes.

Tanya is a Tiger: Septic Arthritis or Osteomyelitis because it is...
  • Dangerous
  • Moves quickly
  • Best acted upon immediately

Any child with a fever and a limp must be considered carefully as possibly having a bone or joint infection.  Most children with irritable hips are well or able to weight bear reasonably.  Although transient synovitis often folows a viral illness, the fever is usually subsiding when the limp begins.  If a child is unwell and unable to weight bear, infection is likely and must be treated urgently.  Like finding a tiger, no-one wants to think that they have stumbled across septic arthritis or osteomyelitis but if you think you have possibly found one, you should not hesitate.  Get help according to your local pathways.

Obidiah is an Okapi: Slipped upper femoral  epiphysis (SUFE) because it...
  • Looks like something else to begin with
  • Is rare but does occur
  • Needs you to take a picture

Slipped upper femoral epiphysis (SUFE) is a debilitating condition that affects a small number of adolescents.  Often it presents as a sport injury and is mistaken for a groin strain.  In fact the femoral head has slipped off its perch and risks permanent necrosis.  Like an Okapi (which looks like a zebra from the back), SUFE can be mistaken for something else at first glance but if you know it exists you can look out for it.  Beware the limping adolescent, even if the pain came on during sport.  If in doubt, arrange for the patient to have a frog lateral X-ray of the hip with or an urgent orthopaedic opinion.   Sometimes even the picture can miss a SUFE so if the problem is not resolving, like recognising an Okapi, you may need to look again.

Karim is a King Cobra: Juvenile Idiopathic Arthritis because it is...
  • Unlikely but not to be missed
  • Difficult to be sure unless you look really carefully

Juvenile Idiopathic Arthritis (JIA) is uncommon but for that reason also easy to miss.  Children often present with isolated symptoms which may not be matched up with problems elsewhere in time or space.  The history should include other mysterious joint problems, and examination should include a full PGALS screen to detect other affected joints not reported (this only takes 2 minutes).  If you only see the tail of a snake, you don’t really know what you’ve got, so you have to see more to know what it is.  Episodes of joint inflammation may be isolated and disappear without intervention.  It is reasonable to observe a single, mildly inflamed joint in a well child as this may well resolve over the space of a few weeks.  If the inflammation is severe, involves multiple joints or makes the child unwell you should refer the child.  I wouldn’t take on a King Cobra so if an inflamed joint looks aggressive or won’t go away, get help.  Never treat a possible arthritis with steroids as you may mask another creature we won’t describe here – leukaemia.

Edward Snelson

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