🥵 HARD

Most of us are familiar with neck of femur fractures, osteoarthritis and Paget’s disease, which may affect older adults, but how much do you know about lower limb problems in children? Take this quiz to find out; it’s more than just broken bones and twisted ankles…

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Lower limb paeds

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Question 1

Stem 1 - Question 1

A toddler is brought into A&E with a fever and unable to bear weight on its right leg. You suspect septic arthritis of the right hip.
What position would you expect the leg to be at rest?
A
Abducted
B
Externally rotated and flexed
C
Hyperextended
D
Hyperextended, internally rotated and adducted
E
Internally rotated and flexed
Question 1 Explanation: 
The hip is held in this position to relieve the pressure.
Question 2

Stem 1 - Question 2

What is the most likely causative organism?
A
Chlamydia trachomatis
B
Mycobacterium tuberculosis
C
Salmonella sp.
D
Staph. aureus
E
Strep. pyogenes
Question 2 Explanation: 
S. aureus accounts for up to 70 percent of cases of septic arthritis. Salmonella sp. may be more common in patients with osteomyelitis and sickle cell anaemia[1]. You'd also want to consider Salmonella or Chlamydia in cases of reactive arthritis; the latter might be your first thought in a sexually active teenager presenting with joint pain and fever. Of course, if Chlamydia was identified in this case, your safeguarding alarm bells should be firing.
Question 3

Stem 1 - Question 3

The following day you see another patient who is diagnosed with osteomyelitis. What is the definitive imaging technique for osteomyelitis?
A
CT scan
B
PET scan
C
MRI
D
USS
E
X-ray
Question 3 Explanation: 
An MRI is the definitive imaging technique for osteomyelitis. Osteomyelitis will cause pus to build up around the bone; this might not be observable on X-ray, but will show up on MRI.

Both osteomyelitis and septic arthritis are common causes of joint problems in children and should be suspected when a child has fever. The incidence of septic arthritis declines as children get older, while osteomyelitis stays pretty constant [2]. Symptoms may be a bit slower onset in osteomyelitis compared to septic arthritis, and not as severe.

Question 4
A 5 year old boy with a limp is brought to their GP one afternoon. The limp started two days ago. The child refused to walk in the morning. He is afebrile and has no rashes but their mother explains they had a bad cough a couple of weeks ago. What is the most likely diagnosis?
A
Developmental dysplasia of the hip
B
Juvenile arthritis
C
Perthes’ disease
D
Reactive arthritis
E
Transient synovitis
Question 4 Explanation: 
Transient synovitis is a self-limiting condition that often follows a respiratory tract infection. The child will be systemically well but may struggle to weight-bear in the morning.
Question 5
During the NIPE screen, a midwife detects an abnormality in the Barlow and Ortolani tests for developmental dysplasia of the hip. What should be ordered next?
A
CT scan
B
Frog-leg AP levic X-ray
C
MRI
D
Physiotherapist review
E
USS of hips
Question 5 Explanation: 
In children under 6 months, an USS is the investigation of choice for suspected developmental dysplasia of the hip. After 6 months, an AP lateral frog-leg X-ray is preferred. [3]

Remember the risk factors for DDH are the 4 F's: female, family history, funny birth and first born. An USS is indicated if a child is born breech, is in breech position after 36 weeks, if there is family history or if detected during NIPE screening.

A Pavlik harness is used to treat newborns with DDH. [4] In children who are diagnosed later, they may require surgery, after which they will be need to use a hip spica cast to keep their hip joints at the right angle.

Question 6

Stem 2 - Question 1

A seven year old boy is brought to their GP by their parent. On a couple of occasions over the past three months he has been limping after PE classes at school. On examination, one leg is longer than the other and there is loss of abduction of the hip on the affected side.
What is the most likely diagnosis?
A
Juvenile arthritis
B
Late onset development dysplasia of the hip
C
Perthes’ disease
D
Slipped upper femoral epiphysis
E
Transient synovitis
Question 6 Explanation: 
Perthes' disease is a type of avascular necrosis of the head of the femur causing it to flatten out. This makes it harder for the patient to abduct and internally rotate the affected limb. It is painful but, as noted in the stem, can be intermittent. It tends to affect boys more than girls and may lead to limb shortening.
Question 7

Stem 2 - Question 2

The paediatric orthopaedic surgeons recommend a varus osteotomy. What is the purpose of this procedure?
A
Adjust the neck of the femur to improve weight distribution
B
Create a fracture in the leg and hold it apart with pins to encourage bone growth to lengthen the leg
C
Replace the femoral head of the affected hip
D
Reposition the femoral head in the acetabulum
E
Straighten the leg
Question 7 Explanation: 
In a varus osteotomy, a wedge of bone is cut out of the femur and the bone is pinned in a new position so that the head of the femur is maintained within the acetabulum. This is meant to help the head of the femur develop a more rounded shape as it heals.
Question 8
A five year old girl is brought to see her GP. For the past couple of weeks she has been limping. The mother says that most days the child has had a mild temperature that lasts a couple of hours. Initially their hip hurt, but now their knee hurts too. The GP notes that a month ago the child was taken to A&E because the mother spotted a purple rash on the girl’s leg. Apart from the rash, the girl has had no other illnesses of note in the last few months. What is the most likely diagnosis?
A
Osteomyelitis
B
Neoplasia
C
Juvenile idiopathic arthritis
D
TB
E
Rheumatic fever
Question 8 Explanation: 
There is a lot of information here but it most likely points to JIA. The age of onset if before 16, but usually before the age of 6. It tends to affect females more than males (in males you should consider enthesitic related arthritis - pain where the tendons attach to the bone). They have a 'quotidian' fever (a fever that happens once a day) for at least two weeks. Rashes (including petechiae and echymoses) can precede the joint condition or be associated with the fever or joint pain. The joint pain is also 'summative' i.e. one joint hurts, then a second joint hurts as well.

Rheumatic fever would have a 'migratory' pattern of joint pain, where the pain moves from limb to limb. It is also associated with recent Strep infections.

Neoplasia and osteomyelitis are both important differentials to consider, and you would certainly do blood tests to rule these in or out. However, neoplasia would be associated with constant, escalating pain that doesn't go away at night.

Question 9

Stem 3 - Question 1

A 13 year old girl with a BMI of 27 with a painful knee is being assessed. Their pain began a couple of days ago and they struggle to bear weight. On examination, the affected leg is externally rotated.
What is the most likely diagnosis?
A
Developmental dysplasia of the hip
B
Slipped upper femoral epiphysis
C
Perthes' disease
D
Transient synovitis
E
Septic arthritis
Question 9 Explanation: 
SUFEs are a type of Salter-Harris Type 1 fracture. The epiphysis of the head of the femur has slid across the growth plate. It is common in obese children. They tend to affect boys more than girls, although tall girls, and those with endocrine disorders are at a higher risk. The external rotation is a classic sign.

Note how the child experienced knee pain but the injury was in the hip. Don't forget that pain from one joint can refer to another, which is why we always tell the OSCE examiner we would also examine the joint above and below.

Question 10

Stem 3 - Question 2

What sign would you look for on x-ray to confirm this diagnosis?
A
Increased acetabular index
B
Klein line does not intersect epiphysis
C
Fracture in neck of femur
D
Lightbulb sign
E
Shenton’s line
Question 10 Explanation: 
Klein's line is a line drawn along the lateral border of the neck of the femur and it should intersect the epiphysis (see Radiopedia). When it doesn't intersect the epiphysis, this is referred to as Trethowan's sign and indicates a SUFE. Let's look at some of the options:
  • Acetabular index - used to diagnose development dysplasia of the hip
  • Lightbulb sign - indicates a posterior shoulder dislocation
  • Shenton's line - this is used to tell if there has been a dislocation of the hip joint, and while the movement of the epiphysis could lead to a slight disruption of Shenton's line, it is Klein's line that is more specific for SUFE

See https://www.startradiology.com/internships/general-surgery/hip/x-hip/index.html for some other really useful pointers in interpreting hip X-rays.

Question 11

Stem 3 - Question 3

How is this condition managed?
A
Hemiarthropathy
B
Internal fixation with surgical screw
C
Intramedullary nail
D
Total arthropathy
E
Varus osteotomy
Question 11 Explanation: 
According to BMJ Best Practice, in situ fixation with a surgical screw is the widely accepted first line treatment. Prophylactic pinning of the opposite epiphysis may also be necessary. The child should not weight-bear until after treatment to prevent further slippage and a risk of avascular necrosis.
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References

  1. https://pubmed.ncbi.nlm.nih.gov/32890008/
  2. Nelson JD. Adv Pediatr Infect Dis. 1991
  3. https://radiopaedia.org/articles/developmental-dysplasia-of-the-hip and Am Fam Physician. 2017 Aug 1;96(3):196-197
  4. https://www.nhs.uk/conditions/developmental-dysplasia-of-the-hip/ 

NICE also lists some other differentials to consider: https://cks.nice.org.uk/topics/acute-childhood-limp/diagnosis/differential-diagnosis/

With thanks to Cardiff University Surgical Society and Miss Clare Carpenter for their webinar that inspired these questions.

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