A 7-year-old male presents with his father to General Practice with a 3-week history of left-sided hip pain. His father states the pain has been progressively worsening since onset and the boy has now developed a limp.

The young patient is normally very active and plays football regularly, but has not been able to recently due to his hip problems.

Examination of the hip reveals limited internal rotation, a limping gait and some wasting of the quadriceps and gluteal muscles.

The child is otherwise fit and well.

Which of the following is the most likely underlying pathology?

Options:
explanation: Transient hip inflammation describes transient synovitis. Transient synovitis is an idiopathic inflammation of the synovium, causing self-limiting pain and a limp. Transient synovitis would not present as progressively worsening hip pain over 3 weeks, as transient synovitis typically resolves with rest after 7-10 days. This is therefore an unlikely underlying pathology.
name: Transient hip inflammation
label: d
answer: no
explanation: This pathology describes septic arthritis, an infection of the joint space caused by the direct or haematogenous invasion. This is a very unlikely underlying cause in this patient. Septic arthritis typically presents with severe joint pain, joint swelling, extremely limited joint movement, non-weight bearing, and systemic illness. This patient is systemically healthy, without fever and can weight bear but with a limp. Septic arthritis is therefore a far less likely diagnosis than Perthes' disease.
name: Infection of the hip joint
label: c
answer: no
explanation: This pathology describes a condition called slipped upper femoral epiphysis (SUFE) but is not the most likely diagnosis here. SUFE typically presents in a slightly older age group, with diagnosis most common in the 11-13 age group. SUFE occurs due to the weakening of the growth plate due to stressors such as obesity or a period of sudden growth. SUFE can present acutely or chronically, and typically presents with hip pain or pain referred to the knee or groin. The most important differentiating factor here is the age at presentation. This patient is too young to have undergone the growth spurts of puberty and is not obese, therefore SUFE is an unlikely diagnosis.
name: Displacement of the upper femoral epiphysis
label: b
answer: no
explanation: This patient suffers from Perthes' disease, which occurs due to impaired blood supply to the femoral head. This results in avascular necrosis and remodelling of the femoral head, which can lead to collapse and flattening. Perthes' disease is most common in males aged 4-8 and presents with progressively worsening hip pain and limited joint movement, which can lead to the wasting of leg muscles due to underuse. These three factors contribute towards the development of a limp.
name: Avascular necrosis of the femoral head
label: a
answer: yes
explanation: This pathology describes developmental dysplasia of the hip (DDH), in which abnormal development of the hip joint results in an abnormal relationship between the femoral head and the acetabulum. This condition is usually picked up through the use of the Barlow and Ortolani tests in screening and then confirmed by ultrasound. In cases where DDH slips through screening, it typically presents in children under 3 years as leg length discrepancy, limited hip abduction and toe-walking. DDH would not present as a 3-week history of progressive hip pain in a previously fit and active child.
name: Abnormal position and alignment of the femoral head
label: e
answer: no

Correct answer: a