Lower Limb Disorders in Children MCQ

The hip is held in this position to relieve the pressure.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.