Slipped capital femoral epiphysis — formative SAQs

SAQ 1 (10 marks) — The overweight adolescent with knee pain and a limp

Stem: A thirteen-year-old boy presents to the emergency department with a two-week history of left knee pain and a worsening limp. He is unable to bear weight on the left leg as of this morning. His body mass index is above the ninety-fifth percentile. On examination, the left leg is held in external rotation, and passive flexion of the left hip produces obligatory external rotation. A frog-lateral radiograph shows posteroinferior displacement of the capital femoral epiphysis with a Southwick angle of forty-five degrees. Outline your classification, immediate management, and definitive treatment. [1] [7]

Model answer

Classification (3 marks). This child has a slipped capital femoral epiphysis of the left hip. The Loder stability classification is the critical first determination: because he cannot bear weight even with crutches, the slip is unstable, and this classification predicts an avascular necrosis risk approaching fifty per cent — the finding from the Loder 1993 study that reported forty-seven per cent avascular necrosis in the unstable group and zero per cent in the stable group. The Southwick angle of forty-five degrees grades the severity as moderate, between the thirty-degree mild and the fifty-degree severe thresholds. The temporal pattern is acute-on-chronic, with the two-week history of knee pain and the acute worsening overnight. [1]

Immediate management (3 marks). The child is made strictly non-weight-bearing from the moment of diagnosis — transported by wheelchair or stretcher, never allowed to walk — because every step across the unstable physis worsens the displacement and threatens the retinacular blood supply. Intravenous analgesia is given for the acute pain. The unstable slip is an orthopaedic emergency: the child is kept fasting, bloods are drawn for the group and save, and the consent is obtained for the urgent reduction and fixation. The surgical team is informed and the theatre is arranged as an emergency case, because the window for the gentle reduction that protects the retinacular vessels narrows with every hour of delay. [1] [10]

Definitive treatment (4 marks). The unstable slip is taken to theatre for urgent management. The two options are gentle reduction under anaesthesia — achieved by traction and internal rotation, never by forceful manipulation — followed by single-screw fixation, or the modified Dunn procedure, a surgical hip dislocation with a subcapital osteotomy and capital realignment that restores the normal anatomy and directly visualises and protects the retinacular vessels. The choice depends on the severity, the timing, and the surgeon. The contralateral hip is assessed for the bilateral risk, which is between twenty and forty per cent, and the prophylactic pinning is considered if the child is young with an open triradiate cartilage. The child is followed for the avascular necrosis, which may declare radiographically over the months after the fixation, and the weight management programme is initiated as the secondary prevention. [7] [10]

SAQ 2 (10 marks) — The atypical child with bilateral slips and a nodular neck

Stem: An eight-year-old boy presents with bilateral hip pain and a limp that has developed over three months. He is short for his age, his weight is below the fiftieth percentile, and his mother has noticed a lump on the front of his neck. A frog-lateral radiograph shows bilateral slipped capital femoral epiphyses. Discuss your diagnostic reasoning and the additional work-up this child requires. [3] [7]

Model answer

Diagnostic reasoning (4 marks). This child has bilateral slipped capital femoral epiphyses in the atypical age-weight category, and the presentation is the classic clue to a systemic endocrinopathy. The Loder age-weight test flags any child below ten years or above sixteen, or whose weight is below the fiftieth percentile, as atypical rather than idiopathic, and this eight-year-old boy with a weight below the fiftieth percentile and a short stature meets both criteria. The nodular neck is the thyroid goitre or the thyroid nodule that points to the underlying endocrine disease, and the bilateral nature of the slips in a young, thin child is the hallmark of the biochemically weakened physis that slips at a low mechanical load. The fellowship skill is to recognise that the slip is the local manifestation of the systemic disease, and the work-up extends far beyond the orthopaedic fixation. [3]

Additional work-up (6 marks). The endocrine work-up is the priority alongside the orthopaedic management. Thyroid function tests are sent to screen for hypothyroidism, the commonest endocrine association, and the nodular neck warrants the thyroid ultrasound and the thyroid antibody panel. The growth hormone axis is assessed with the insulin-like growth factor one and the growth hormone stimulation testing, and the sex hormone axis with the follicle-stimulating hormone, the luteinising hormone, and the testosterone, because growth hormone deficiency and hypogonadism are the other leading endocrine associations. The pituitary axis is imaged with a magnetic resonance imaging of the brain and the pituitary if the hormonal screen is abnormal, because a pituitary adenoma or panhypopituitarism may present with the slip as its first manifestation. The renal function and the bone profile are checked to exclude the renal osteodystrophy. The orthopaedic management proceeds in parallel — both hips are stabilised with the single-screw in-situ pinning — and the endocrinologist is involved early to guide the systemic treatment that protects every physis in the growing skeleton. The weight and the growth are monitored, and the contralateral vigilance is maintained because the risk of the further slip is high in the atypical child. [3] [7]