Aetiology of Legg-Calvé-Perthes disease: A systematic review

Table 1 Main findings of the included case-control studies

Ref.	Subjects	Association/molecule studied	Results
Perry et al[12] (2017)	A hospital case-control study (n = 149/146)	Tobacco smoke exposure during pregnancy	The odds of Perthes' disease significantly increased with reported in utero exposure after adjustment for socioeconomic deprivation (maternal smoking OR = 2.06, 95%CI: 1.17-3.63; paternal smoking OR = 2.09, 95%CI: 1.26-3.46).
Daniel et al[13] (2012)	128 children with LCPD and 384 children attending the hospital for other orthopaedic complaints	environmental tobacco smoke, firewood smoke and socioeconomic status and the risk of LCPD	The main risk factors for LCPD were indoor use of a wood stove (adjusted OR, 2.56) and having a family member who smoked indoors (adjusted OR, 2.07).
García Mata et al[15] (2000)	90 patients with LCPD and 183 normal children, as controls, selected at random to determine whether the condition of passive smoking is related to the disease	LCPD and passive smoking	The association between LCPD and passive smoking, after controlling for age and gender, became significant (p = 0.0000). Thus the risk of LCPD in passive smoking children is more than five times higher than in children who are not exposed to smoke.
Bahmanyar et al[17] (2008)	The Swedish Inpatient Register identified 852 individuals with a diagnosis of LCPD from 1983 to 2005, individually matched by year of birth, age, sex and region of residence with 4432 randomly selected control subjects.	Maternal smoking pregnancy and LCPD	Maternal smoking during pregnancy was associated with an increased LCPD risk, and heavy smoking was associated with a risk increase of almost 100%. Very low birth weight and caesarean section were independently associated with approximately 240% and 36% increases in the risk of LCPD, respectively.
Wiig et al[29] (2006)	402 patients with a matched control group of non-affected children (n = 1025952) from the Norwegian Medical Birth Registry	Epidemiology and possible aetiology of LCPD	Applying Sartwell's log-normal model of incubation periods to the distribution of age at onset of Perthes' disease showed a good fit to the log-normal curve. Our findings point toward a single cause, either genetic or environmental, acting prenatally in the aetiology of Perthes' disease.
Perry et al[32] (2013)	146 cases of LCPD and 142 hospital controls, frequency matched by age and sex	LCPD and hyperactivity	Significant associations (P < 0.05) existed with the majority of the psychological domains captured by the Strength and Difficulties Questionnaire [OR for "high" level of difficulties-Emotion OR 3.2, Conduct OR 2.1, Inattention-Hyperactivity OR 2.7, Prosocial behaviour OR 1.9]. Hyperactivity was especially marked among individuals within 2 years of diagnosis (OR = 8.6; P < 0.001), but not so among individuals over 4 years from diagnosis.
Berman et al[34] (2016)	16 children with LCPD (age 9.1 ± 3.3, 75% males) were compared with their closest-aged siblings (age 9.3 ± 2.6, 30% males).	LCPD and ADHD	Our findings in a small cohort of children with LCPD and their comparably aged siblings do not support an association between LCPD and ADHD
Hailer et al[35] (2012)	2579 patients with LCPD in Sweden during the period 1964-2005. 13748 individuals without LCPD were randomly selected from the Swedish general population	LCPD and risk of injury	Patients with LCPD are vulnerable to injuries that could be interpreted as a marker of hyperactive behaviour.
Hailer et al[36] (2014)	4057 individuals with LCPD in Sweden during the period 1964-2011. 40570 individuals without LCPD were randomly selected from the Swedish general population	LCPD and ADHD	Compared to the control group, individuals with LCPD had a raised HR of 1.5 (95%CI: 1.2-1.9) for ADHD.
Türkmen et al[37] (2014)	The study included 3 groups of patients: Perthes patients, trauma patients and orthopaedic patients without Perthes disease or history of trauma. Each group was comprised of 56 males and 4 females.	LCPD and ADHD	ADHD was diagnosed in 7 patients in the Perthes group. The findings are not significant
Lee et al[39] (2013)	38 male and 3 female patients with LCPD, and an equal number of age (range was 4-12) and sex-matched control patients with healthy fractures.	LCPD and leptin	Leptin, disease severity and treatment outcomes were associated. This correlation suggests that leptin might play an important role in LCPD pathogenesis.
Srzentić et al[51] (2014)	37 patients with Perthes disease and 50 healthy controls	LCPD and IL-6	Our study revealed that heterozygote subjects for the IL-6 G-174C/G-597A polymorphisms were significantly overrepresented in the control group than in the Perthes patient group.
Kamiya et al[52] (2015)	28 patients with matched controls	LCPD and IL-6	In the synovial fluid of the affected hips, IL-6 protein levels were significantly increased (LCPD: 509 ± 519 pg/mL, non-LCPD: 19 ± 22 pg/mL; P = 0.0005) on the multi-cytokine assay.
Perry et al[76] (2012)	149 cases and 146 controls	Vascular abnormalities in LCPD patients	Children with Perthes disease exhibit small artery calibre and reduced function, which is independent of body composition. These data imply that that Perthes disease may reflect a wider vascular phenomenon that could have long-term implications for the vascular health of affected individuals.
Kitoh et al[78] (2003)	125 children (105 boys, 20 girls) with unilateral LCPD	Delayed ossification in LCPD	Our findings support the hypothesis that a delay in endochondral ossification in the proximal capital femoral epiphysis may be associated with the onset of Perthes' disease.
Kocjančič et al[79] (2014)	135 adult hips of patients who had been treated for Perthes disease in childhood with matched controls	Hip stress distribution in LCPD	No differences were found in resultant hip force and in peak contact hip stress between the hips that were in childhood subject to Perthes disease and the control population, but a considerable (148%) and significant (P < 0.001) difference was found in the contact hip stress gradient index, expressing an unfavourable, steep decrease of contact stress at the lateral acetabular rim.
Neidel et al[83] (1992)	59 consecutive children with Perthes' disease and 59 matched controls	IGF-1 and LCPD	Our data may reflect an impaired synthesis or release of IGF I relative to age in Perthes' disease or changes in the affinity or metabolism of IGF binding proteins. The observed changes seem to be of a temporary nature.
Kim et al[82] (2009)	56 immature pigs	HIF-1α and LCPD	Acute ischemic injury to the immature femoral head induced severe hypoxia and cell death in the bony epiphysis and the deep layer of the epiphyseal cartilage. Viable chondrocytes in the superficial layer of the epiphyseal cartilage showed HIF-1α activation and VEGF upregulation with subsequent revascularization occurring in the cartilage.
Matsumoto et al[84] (1998)	27 children with Perthes' disease and 10 age-matched control subjects	IGF binding protein-3 and LCPD	The bone age was delayed 2 years or more compared with the chronological age in 7 of 18 patients, and all of them, except 1, showed decreased levels of IGFBP-3 on WLB.
Graseman et al[85] (1996)	23 children with unilateral LCPD and in 23 sex and age matched controls	IGF binding protein-3 and LCPD	Data confirm that most children with LCPD are skeletally immature. However, IGF-I measured with IGF-II-blocked IGFBP binding sites, and IGFBP-3 serum concentrations analysed with respect to bone age showed no evidence for a disturbance of the hypothalamo-pituitary-somatomedin axis in these children.
Neidel et al[86] (1993)	55 children with Perthes' disease and 55 age- and sex-matched controls	IGF and LCPD	Our findings indicate that low levels of circulating IGF I in Perthes' disease, as we have reported previously, are caused neither by altered concentrations of the principal IGF-binding protein, IGFBP-3, nor by an underlying growth hormone deficiency.

LCPD: Legg-Calvé-Perthes disease; OR: Odds ratio; CI: Confidence interval; ADHD: Attention deficit hyperactivity disorder; IL-6: Interleukin 6; IGF: Insulin-like growth factor; IGFBP: Insulin-like growth factor binding protein; HR: Hazard ratio: HIF: Hypoxia-inducible factor.

Table 2 Main findings of included cohort studies

Ref.	Subjects	Association/molecule studied	Results
Gordon et al[14] (2004)	60 patients with LCPD	Smoking and socio-economic status and the severity of LCPD	A significant association was noted between living with a smoker and LCPD as well as between increasing smoke exposure and increased risk of developing LCPD. No significant association was noted between lower income and LCPD. There was no association between increased smoke exposure and increased severity of LCPD as measured by the lateral pillar classification.
Glueck et al[16] (1998)	39 children with Legg-Perthes disease	Second-hand smoke exposure	Second-hand smoke exposure had no significant effects on other measures of coagulation. Second-hand smoke exposure while in utero and during childhood appears to lower stimulated tissue plasminogen activator activity and additionally may depress heritable low stimulated tissue plasminogen activator activity, leading to hypofibrinolysis. Hypofibrinolysis may facilitate thrombotic venous occlusion in the head of the femur, leading to venous hypertension and hypoxic bone death, Legg-Perthes disease.
Sharma et al[18] (2005)	240 children (263 hips) who presented with Perthes' disease in Greater Glasgow	Socio economic deprivation and LCPD	There was no significant evidence of a preponderance of Perthes' disease in the most deprived groups.
Pillai et al[19] (2005)	40 LCPD patients and the Southwest Scotland registry	The incidence of LCPD in Southwest Scotland	The incidence of LCPD increases with deprivation and poor living standards.
Kealey et al[20] (2000)	313 children with LCPD and Northern Ireland registry	Socio economic deprivation and LCPD	While the incidence of Perthes' disease was found to be associated with indicators of the level of deprivation for areas, there was no evidence to suggest that there was an increased risk in urban areas; the highest rate was found in the most deprived rural category
Perry et al[21] (2012)	The General Practice Research database was analysed to identify incident cases between 1990 and 2008 in children aged 0-14 years	LCPD incidence in United Kingdom	The incidence was declining in the study period. The declining incidence, along with the geographic variation, suggests that a major etiologic determinant in LCPD is environmental and closely linked to childhood deprivation.
Perry et al[22] (2012)	Scottish Morbidity Record, based in Scotland, United Kingdom using data from 2000-2010. A total of 443 LCPD patients	Socio economic deprivation and LCPD	The occurrence of Perthes' disease within urban environments is high, yet this appears to be a reflection of higher socioeconomic deprivation exposure. Disease rates appear equivalent in similarly deprived urban and non-urban areas, suggesting that the determinant is not a consequence of the urban environment.
Perry et al[23] (2011)	1082 children with Perthes' disease (682 from a geographically defined area). Regional disease register in Merseyside, United Kingdom, 1976-2009	Social deprivation and the declining incidence of LCPD	There was a marked decline in disease incidence over the study period, particularly in more deprived areas. The magnitude of the association with deprivation, and the changing incidence, strongly suggest that environmental factor(s) are a major aetiological determinant in Perthes' disease.
Hall and Barker[24] (1989)	Yorkshire region registry	Perthes incidence over the region	There were large geographical differences in incidence that could not be explained by urban-rural or social class differences.
Hall et al[25] (1983)	Case registry in Liverpool and adjacent parts of Knowsley and Sefton during 1976-81	Incidence of LCPD in the region	The inner city of Liverpool, which has been shown to be underprivileged, had the highest yearly incidence of the disease ever reported: 21.1 cases/100000 children aged 14 years and under. The associations with poverty support the hypothesis that undernutrition is a causative factor in the disease.
Margetts et al[26] (2001)	Registry of Liverpool (1982-1995)	Incidence and distribution of LCPD in Liverpool	We suggest that environmental influences may come into play some years before a child presents with pain in the hip. There may be a genetic predisposition to the disease.
Metcalfe et al[27] (2016)	All twin pairs from the Danish Twin Registry (DTR) in which at least 1 individual had LCPD (81 twin pair)	Twin study of LCPD	This study found evidence of familial clustering in LCPD but did not show a genetic component. The absolute risk that a co-twin of an affected individual will develop LCPD is low, even in the case of monozygotic twin pairs.
Lappin et al[28] (2003)	320 patients on the Northern Ireland Perthes' database	Birthweight and LCPD	We observed that the low birthweight twin in each case was the affected child. It is proposed that environmental factors associated with low birthweight are involved in the aetiology of Perthes' disease.
Loder et al[30] (1993)	24 LCPD patients	LCPD and ADHD	One third (33%) of the children had abnormally high scores in profiles associated with ADHD (impulsive, hyperactive and psychosomatic categories), much higher than the 3%-5% incidence of ADHD in the general population.
Perry et al[31] (2012)	General Practise Research database in United Kingdom	LCPD comorbidities	The risk of Perthes' disease was significantly increased with the presence of congenital anomalies of the genitourinary and inguinal region, such as hypospadias (OR = 4.04, 95%CI: 1.41-11.58), undescended testis (OR = 1.83, 95%CI: 1.12-3.00) and inguinal herniae (OR = 1.79, 95%CI: 1.02-3.16). Attention deficit hyperactivity disorder was not associated with Perthes' disease (OR = 1.01, 95%CI: 0.48-2.12), although a generalised behavioural disorder was (OR = 1.55, 95%CI: 1.10-2.17). Asthma significantly increased the risk of Perthes' disease (OR = 1.44, 95%CI: 1.17-1.76), which remained after adjusting for oral/parenteral steroid use.
Podeszwa et al[33] (2015)	11 LCPD patients	Psychological finding in patients undergoing surgery	A significant presence of depression and anxiety symptoms was reported.
Neal et al[38] (2016)	150 patients (172 hips) with LCPD	LCPD and obesity	Obesity is common in patients with LCPD and is associated with a later stage of disease presentation.
Srzentić et al[48] (2015)	37 LCPD patients	Markers of coagulation, inflammation and apoptosis in LCPD	The results presented indicate that apoptosis could be one of the factors contributing to the lack of balanced bone remodelling process in Perthes patients.
Calver et al[56] (1981)	50 children with “irritable hip”	Radionuclide scanning in LCPD	Five of the 50 children seen during the one year had areas of ischemia in the capital femoral epiphysis demonstrated on the scan. All five developed radiological signs of Perthes' disease within 6 mo. The remaining 45 had radiographically normal hips at one year.
Royle and Galasko[60] (1992)	192 patients with a typical transient synovitis syndrome	Scintigraphy in LCPD patients	Fifteen patients had evidence of ischemia of the femoral head, but only four patients went on to develop the typical radiographic features of Perthes' disease. The other 11 patients are thought to represent a minor, radiographically silent form of Perthes' disease.
Lamer et al[61] (2002)	26 DGS MRI and bone scintigraphies of 25 hips in 23 children	Blood supply in LCPD	DGS MRI allows early detection of epiphyseal ischemia and accurate analysis of the different revascularisation patterns. These changes are directly related to the prognosis of LCPD
Atsumi et al[62] (2000)	28 hips in 25 patients with LCPD	Blood supply in LCPD	We suggest that in Perthes' disease the blood supply of the LEAs is impaired at their origin and that revascularisation occurs from this site by ingrowth of small vessels into the femoral epiphysis. This process may be the result of recurrent ischemic episodes.
de Camargo et al[63] (1984)	30 patients, including 26 aortographies and 6 selective angiographies	Blood supply in LCPD	The major angiographic alterations were: general decrease of blood flow in the affected hip, lack of a patent medial circumflex artery, an atrophic medial circumflex artery or obstruction of its branches, distended vessels in subluxations of the hip joint and almost complete absence of the obturator artery
Theron et al[64] (1980)	11 cases of LCPD	Blood supply in LCPD	The balance between the respective vascular territories of the dilated superior and inferior capsular arteries is variable and seems to affect the position of the sequestrum and the centering of the femoral head.
Kitoh et al[78] (2003)	125 children (105 boys, 20 girls) with unilateral LCPD	Delayed ossification in LCPD	Our findings support the hypothesis that a delay in endochondral ossification in the proximal capital femoral epiphysis may be associated with the onset of Perthes' disease.

LCPD: Legg-Calvé-Perthes disease; ADHD: Attention deficit hyperactivity disorder; OR: Odds ratio: CI: Confidence interval; MRI: Magnetic resonance imaging.

Table 3 Main findings of the included animal studies

Ref.	Subjects	Association/molecule studied	Results
Suehiro et al[49] (2005)	Mouse model	Osteonecrosis in rat model	Repetitive mechanical stress on the femoral heads from 5 wk to 9 wk of age played an important role in the aetiology of osteonecrosis
Gershuni et al[59] (1983)	Hip of the immature pig	Joint tamponade in LCPD animal model	The data from this experiment do not support the theory that tamponade of the femoral capital epiphysis is the cause of osteonecrosis in Legg-Calvé-Perthes syndrome
Cheon et al[66] (2015)	10 piglets	Quantitative MRI in piglet model of LCPD	The epiphyseal ADC values of the ischemic hip decreased immediately (1 hour) after embolization. However, they increased rapidly at 1 wk after embolization and remained elevated until 4 wk after embolization. Perfusion MRI of ischemic hips showed decreased epiphyseal perfusion with decreased Kep immediately after embolization.
Li et al[67] (2006)	20 femoral heads of 10 piglets	MRI in piglet model of LCPD	Gadolinium-enhanced MRI can identify early ischemia and its reversal of the capital femoral epiphysis induced by hip hyper-abduction
Babyn et al[68] (1998)	Piglet model	MRI in piglet model of LCPD	High resolution MRI can demonstrate changes in the CE associated with ischemic injury and may have a role in the assessment of the CE and its development after ischemic injury.
Li et al[69] (2008)	25 piglets models	Diffusive MRI in a model of LCPD	Histological study revealed necrosis of chondrocytes and osteocytes and abnormal thickening of the epiphyseal cartilage in the ischemic femoral head.
Levin et al[70] (1999)	Rat model	Epiphysis studies in a rat model	Thickening and condensation of the subchondral bone, leading to increased stiffness of the subchondral zone, result in the osteoarthritis-like disorder. Mimicking the well-known phases of human osteonecrosis, the model readily allows for preclinical studies of therapeutic regimens.
Kandzierski et al[71] (2004)	Calf femurs	Calf femur experimental study	The author concludes that impaired blood flow within the growth layers additionally weakens the immature bone tissue of the femoral head and neck, which may lead to mechanical damage of the bone tissue itself, as well as to the epiphyseal blood vessels entering bony epiphysis.
Suehiro et al[72] (2000)	Twenty femora from 10 Wistar Kyoto rats	Standing and induction of OA	Repetitive mechanical stress on the femoral heads from 5 wk to 9 wk of age played an important role in the aetiology of osteonecrosis
Naito et al[74] (1992)	Canine femoral head	Acute effect of traction, compression, and hip joint tamponade on blood flow of the femoral head	These experimental data may have important implications for the pathogenesis of iatrogenic avascular necrosis in the treatment of congenitally dislocated hip, Legg-Perthes disease and avascular necrosis following nondisplaced femoral neck fracture
Kim et al[77] (2013)	56 immature pigs	MRI in the initial stage of LCPD	Acute ischemic injury to the immature femoral head induced severe hypoxia and cell death in the bony epiphysis and the deep layer of the epiphyseal cartilage. Viable chondrocytes in the superficial layer of the epiphyseal cartilage showed HIF-1α activation and VEGF upregulation with subsequent revascularization occurring in the cartilage.
Zhang et al[81] (2015)	6-wk-old Sprague Dawley rats	HIF-1α and LCPD	Hypoxia might be an etiological factor for femoral head necrosis. HIF-1α, VEGF as well as apoptotic genes participated in the pathophysiological process of ischemic osteonecrosis.
Kim et al[83] (2009)	56 immature pigs	HIF-1α and LCPD	Acute ischemic injury to the immature femoral head induced severe hypoxia and cell death in the bony epiphysis and the deep layer of the epiphyseal cartilage. Viable chondrocytes in the superficial layer of the epiphyseal cartilage showed HIF-1α activation and VEGF upregulation with subsequent revascularization occurring in the cartilage.

LCPD: Legg-Calvé-Perthes disease; HIF-1: Hypoxia-inducible factor; VEGF: Vascular endothelial growth factor; MRI: Magnetic resonance imaging.

Table 4 The main findings of the included in vitro human studies are reported

Ref.	Subjects	Association/molecule studied	Results
O’Sullivan et al[40] (1985)	A family in which Legg-Calvé-Perthes disease (LCPD) occurred in four members	Genetic factors and LCPD	This unusually high incidence in one family raises questions about the genetic versus the environmental factors in the aetiology of LCPD.
Livesey et al[41] (1998)	Case report of three family with three female first-degree relatives affected by LCPD	Genetic factors and LCPD	First case of three first-degree relative affected
Miyamoto et al[42] (2007)	A Japanese family with an autosomal dominant hip disorder manifesting as LCPD	LCPD and COL2A1	This is the first report of a mutation in hereditary LCPD. COL2A1 mutations may be more common in LCPD patients than currently thought, particularly in familial and/or bilateral cases.
Al-Omran and Sadat-Ali[43] (2013)	2 generations of 4 male family members with LCPD-like features and mutation of the COL2A1 gene of the 12q13 chromosome	LCPD and COL2A1	If LCPD occurs in any family member, we recommend genetic analysis and counselling as well as early radiological screening of related children.
Kannu et al[44] (2011)	Two children who presented with abnormal development of both hips and in whom novel mutations in the COL2A1 gene were found	LCPD and COL2A1	The purpose of our report is to alert clinicians to the possibility that children who present with bilateral Perthes-like disease of the hip might have an underlying mutation in the gene encoding type II collagen.
Su et al[45] (2008)	Forty-two members of a 5-generation family	LCPD and COL2A1	The p.Gly1170Ser mutation of COL2A1 in the family described is responsible for pathology confined to the hip joint, which presents as isolated precocious hip OA, AVN of the femoral head, or Legg-Calvé-Perthes disease.
Li et al[46] (2014)	Forty-five members of a four-generation family	LCPD and COL2A1	In our research, we identify a heterozygous mutation (c.1888 G>A, p. Gly630Ser) in exon 29 of COL2A1 in the Gly-X-Y domain, in a Chinese family affected by LCPD and ANFH.
Woratanarat et al[47] (2014)	Twelve case–control studies met inclusion criteria and had sufficient data for extraction	Hypercoagulability and LCPD	The factor V Leiden mutation is significantly related to Perthes disease, and its screening in at‐risk children might be useful in the future.
Srzentić et al[48] (2015)	37 LCPD patients	Markers of coagulation, inflammation and apoptosis in LCPD	The results presented indicate that apoptosis could be one of the factors contributing to the lack of balanced bone remodelling process in Perthes patients.
Liu et al[50] (2015)	Age- and sex-matched serum samples from 10 control subjects and 10 patients with LCPD were compared using the isobaric tags for relative and absolute quantification (iTRAQ) technique.	Serum proteomes in LCPD	The complement and coagulation cascades, and abnormal lipid metabolism may be involved in the pathogenesis of LCPD.
Srzentić et al[51] (2014)	37 patients with Perthes disease and 50 healthy controls	LCPD and IL-6	Our study revealed that heterozygote subjects for the IL-6 G-174C/G-597A polymorphisms were significantly overrepresented in the control group than in the Perthes patient group.
Kamiya et al[52] (2015)	28 patients with matched controls	LCPD and IL-6	In the synovial fluid of the affected hips, IL-6 protein levels were significantly increased (LCPD: 509 pg/mL ± 519 pg/mL, non-LCPD: 19 pg/mL ± 22 pg/mL; P = 0.0005) on the multi-cytokine assay.
Su et al[55] (2010)	a five-generation family with 42 members with a new type II collagenopathy	LCPD and COL2A1	Our study demonstrated that the p.Gly1170Ser mutation of COL2A1 caused significant structural alterations in articular cartilage, which are responsible for the new type II collagenopathy.
Matsumoto et al[84] (1998)	27 children with Perthes' disease and 10 age-matched control subjects	IGF binding protein-3 and LCPD	The bone age was delayed, 2 years or more compared with the chronological age in 7 of 18 patients, and all of them, except 1, showed decreased levels of IGFBP-3 on WLB.
Graseman et al[85] (1996)	23 children with unilateral LCPD and in 23 sex and age matched controls	IGF binding protein-3 and LCPD	Our data confirm that most children with LCPD are skeletally immature. However, IGF-I measured with IGF-II-blocked IGFBP binding sites, and IGFBP-3 serum concentrations analysed with respect to bone age show no evidence for a disturbance of the hypothalamo-pituitary-somatomedin axis in these children.
Neidel et al[86] (1993)	55 children with Perthes' disease and 55 age- and sex-matched controls	IGF and LCPD	Our findings indicate that low levels of circulating IGF I in Perthes' disease, as we have reported previously, are caused neither by altered concentrations of the principal IGF-binding protein, IGFBP-3, nor by an underlying growth hormone deficiency.

LCPD: Legg-Calvé-Perthes disease; COL2A1: Collagen type II gene; IGF: Insulin-like growth factor.