A nationwide cohort study of slipped capital femoral epiphysis

Abstract

Objectives: To describe the epidemiology of slipped capital femoral epiphysis (SCFE), to examine associations with childhood obesity and socioeconomic deprivation, and to explore factors associated with diagnostic delays.

Design: Historic cohort study using linked primary and secondary care data from the Clinical Practice Research Datalink and Hospital Episode Statistics.

Setting: All contacts with healthcare services, including emergency presentations, outpatient appointments, inpatient admissions and primary care visits, within the UK National Health Service.

Patients: All individuals <16 years old with a diagnosis of SCFE and whose electronic medical record was held by one of 650 primary care practices in the UK between 1990 and 2013.

Main outcome measures: Annual incidence, missed opportunities for diagnosis and diagnostic delay.

Results: Over the 23-year period the incidence remained constant at 4.8 (95% CI 4.4 to 5.2) cases per 100,000 0-16-year-olds. There was a strong association with socioeconomic deprivation. Predisease obesity was also strongly associated with SCFE; mean predisease z-score of body mass index was 1.43 (95% CI 1.20 to 1.68) compared with the UK reference mean. Diagnostic delays were common, with most children (75.4%) having multiple primary care contacts with relevant symptomatology, and those who presented with knee pain having significantly longer diagnostic delay (median 161 (IQR 27-278) days) than those with hip pain (20 (5-126)) or gait abnormalities (21 (7-72)).

Conclusions: SCFE has a strong association with both area-level socioeconomic deprivation and predisease obesity. The majority of patients with SCFE are initially misdiagnosed and those presenting with knee pain are particularly at risk.

Keywords: delayed diagnosis; descriptive epidemiology; misdiagnosis; slipped capital femoral epiphyses.

Figure 1

Flow diagram showing number of SCFE cases and missing data. BMI, body mass index; SCFE, slipped capital femoral epiphysis.

Figure 2

Histogram of age of onset of slipped capital femoral epiphysis. Each bar represents the incidence rate for age with 95% Poisson CIs.

Figure 3

Scatter plot of disease incidence of slipped capital femoral epiphysis by year. Each point represents the annual incidence rate with 95% Poisson CIs.

Figure 4

Scatter plot of disease incidence of slipped capital femoral epiphysis by quintile of patient-level socioeconomic deprivation. Individual quintiles of deprivation were available for 392 patients from practices within England.

Figure 5

BMI prior to diagnosis, using the most recent BMI recorded in primary care before slipped capital femoral epiphysis diagnosis. Red diamonds represent the standard deviation (z-) score and error bars represent 95% CIs. z-Scores derived using British 1990 data set. BMI, body mass index.