This paper reports the changing incidence of slipped capital femoral epiphysis (SCFE) in South Australia over the last twenty years. It is a timely report in that obesity is now recognised as an important socio-economic issue. It seeks to show a clear relationship between the incidence of SCFE and obesity in the adolescent population.
The authors report that the incidence of SCFE has increased from 2.8 to 8.2 per 100,000 from 1985 and 2007. They consider that the most part of this is due to increasing obesity although the local indigenous population has a greater increase. In general, the mean weight of the adolescent population has increased from 47 kg to 51.2 kg during the same period while in those presenting with SCFE it has risen from 58 kg to 64 kg. This is a dramatic increase. The data is similar to the report by Murray and Wilson1 on the changing incidence in Scotland over approximately the same time period. The real question, which must be met and answered, is whether this increase in weight is the sole cause of this increase in shear forces on the upper femoral growth plate , or whether the growth plate itself weakened by the onset of the pubertal growth is further weakened by other factors.
It is known that obesity in childhood will reduce the age of onset of the pubertal growth spurt in girls but may delay it in boys. The current study confirms the known age difference between boys and girls, but also a lowering of the mean age at presentation from 13.5 years to 12.6 years in the study period. This might suggest that other factors are present in addition to simple obesity. They also note that no cases presented under the age of ten years prior to 1993 and that eight of the ten patients who presented after this time were girls. This raises the possibility of an earlier onset of the pubertal growth spurt in girls, or that other factors may be weakening the growth.
Another factor in this equation is the known association between obesity in childhood and low levels of Vitamin D.2,3 It is known that low levels of Vitamin D are found in obese adolescent patients particularly obese girls and that there is a seasonal variation with lower levels in the autumn and winter.. A recent study from Southampton4 has shown that nearly 40% of children with routine orthopaedic problems have low or seriously low levels of Vitamin D; 8% were in the rachitic range. Could low levels of Vitamin D result in a failure of the primary ossification in the growth plate further weakening it to the shear forces and result in an increased risk of epiphyseal displacement ?. This observation opens up interesting lines of research for the future. In a study by Harel et al5 of 68 obese adolescents low levels of Vitamin D were found in 100% of the girls and 90% of the boys. Vitamin D therapy resulted in only 28% reaching normal levels. This suggests that there may be a change in Vitamin D metabolism in these patients. Could this be an additional factor?
It is interesting that the incidence of acute massive displacement is not quoted in this paper although other studies quote between 9 and 14%. Acute massive displacement or the Unstable Slip has a serious risk of Avascular Necrosis of the epiphysis (AVN), which is seldom seen in Stable presentations. There were 7 cases of AVN in this report, which suggests that a number of unstable presentations have been included. Do these cases have the same weight increase as the Stable presentations Recent data6,7 has shown that this condition is in fact more common in girls, who in addition may be lighter than those with Stable slips. This raises the question of whether there is a different aetiology to those presenting with unstable displacements compared with the more common stable ones. The authors should comment on their findings. Further research is required.
In conclusion this is an important and timely report which raises a number of questions with regard to the aetiology of Slipped Upper femoral epiphysis. A number of opportunities now exist for future research into interesting condition.
1.Murray AW, Wilson NIL. Changing incidence of slipped upper femoral epiphysis: a relationship to obesity? J Bone Joint Surg [BR] 2008;90-B:744-46.
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3.Burt Solorzano C M, McCartney C R. Obesity and pubertal transition in girls and boys. Reproduction 2010;140:399-410.
4.Davies JH, Reed JM, Black E, Priesseman M, Jackson AA, Clarke NM. Epidemiology of Vitamin D deficiency presenting to a paediatric orthopaedic service in the UK. J Pediatr Orthop 2011;31:798-802.
5.Harel Z, Flanagan P, Harel D. Low vitamin D status among obese adolescents: prevalence and response to treatment. J Adolesc Health 2011;48:427-8.
6.Rosenfeld M, Van Niekirk M, Bevan W. Outcome of unstable slipped upper femoral epiphysis in Aukland. J Bone Joint Surg [Br] 2011;93-B(Suppl III):375 [abstract].
7.Eastwood D. Personal Communication