The Journal of Bone & Joint Surgery

The Journal of Bone & Joint Surgery, Volume 87, Issue 3

Scientific Articles | March 01, 2005

Idiopathic Slipped Capital Femoral Epiphysis in Amish Children

Randall T. Loder, MD¹; Jeffrey Nechleba, MD²; James O. Sanders, MD²; Patricia Doyle, RN³

¹ James Whitcomb Riley Hospital for Children, Room 4250, 702 Barnhill Drive, Indianapolis, IN 46202. E-mail address: rloder@iupui.edu
² Erie Shriners Hospital for Children, 1645 West 8th Street, Erie, PA 16505
³ Twin Cities Shriners Hospital for Children, 2025 East River Parkway, Minneapolis, MN 55414

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The authors did not receive grants or outside funding in support of their research or preparation of this manuscript. They did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

Investigation performed at the Twin Cities Shriners Hospital for Children, Minneapolis, Minnesota, and the Erie Shriners Hospital for Children, Erie, Pennsylvania

The Journal of Bone and Joint Surgery, Incorporated

J Bone Joint Surg Am, 2005 Mar 01;87(3):543-549. doi: 10.2106/JBJS.D.01773

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Abstract

Background: Of the many studies of slipped capital femoral epiphysis, none have specifically addressed Amish children. The Amish reflect a small gene pool relative to the general white North American population. Additional knowledge of the demographics of this disorder in Amish children may provide genetic insights. The purpose of this study was to review the demographics of slipped capital femoral epiphysis in the Amish population.

Methods: A retrospective review of the cases of twenty-five Amish children with slipped capital femoral epiphysis treated at two institutions was performed. The child's gender, age, weight, height, and body mass index at the time of the diagnosis; duration of symptoms; laterality of the slip; birth weight; family history; and slip severity were recorded. The slip was classified as stable or unstable. Patients who had been included in a previously published multicenter study served as a control group.

Results: There were seventeen boys and eight girls with a total of thirty-three slipped capital femoral epiphyses; eight of the slips were bilateral. At the time of the diagnosis, the mean age (and standard deviation) was 13.4 ± 1.6 years, the mean weight and height were 55.6 ± 12.4 kg and 155.5 ± 10.2 cm, and the mean body mass index was 23.4 ± 5.4 kg/m². The mean duration of symptoms was 6.6 ± 9.0 months. There were thirty-one stable and two unstable slips with a mean slip angle of 38° ± 20°. Nine (39%) of twenty-three children for whom the information had been recorded had a positive family history of slipped capital femoral epiphysis, a rate that is higher than the 9% and 14.5% rates reported in two other series (p = 0.002). The Amish children were not as heavy as their non-Amish counterparts (55.6 ± 12.4 kg compared with 66.4 ± 17.7 kg, p = 0.0036).

Conclusions: Although the children in this study were moderately heavy, they could not be classified as obese on the basis of weight-for-age or body-mass-index percentiles. The high prevalence of family members with slipped capital femoral epiphysis may reflect either a genetic or environmental component, or an interaction between genetics and environment (for example, work load or common chores requiring particular physical positions) in the Amish population.

Level of Evidence: Prognostic Level II. See Instructions to Authors for a complete description of levels of evidence.

Figures in this Article

There have been previous studies of the demographics of slipped capital femoral epiphysis in different populations (whites, blacks, and Japanese)^1-14. Several of those studies documented differences in the prevalence and demographics of slipped capital femoral epiphysis that correlated with the child's weight and ethnic group^11,15-17. We observed that the body habitus of Amish children with slipped capital femoral epiphysis was different from that of the typical North American child with slipped capital femoral epiphysis. Amish children with the disorder seemed to be less obese but taller. Also, affected Amish children seemed to more often have family members with slipped capital femoral epiphysis than did other ethnic groups, such as blacks, Hispanics, and non-Amish whites. Thus, we thought that exploration of the demographics of slipped capital femoral epiphysis in Amish children might lead to areas of further research into its etiology, since the Amish comprise a small gene pool relative to the general white population in the United States¹⁸. Since there have been no studies of slipped capital femoral epiphysis in Amish children, to our knowledge, the purpose of this investigation was to address these questions.

Materials and Methods

Materials and Methods | Results | Discussion | Appendix | References

Aretrospective review of the charts and radiographs of all Amish children with slipped capital femoral epiphysis treated at the Twin Cities Shriners Hospital for Children, Minneapolis, Minnesota, and the Erie Shriners Hospital for Children, Erie, Pennsylvania, was performed. These two institutions are located in close proximity to many Amish communities. Institutional review board approval was obtained at both institutions. The child's gender; birth weight; family history of slipped capital femoral epiphysis; age, weight, and height at the time of the diagnosis; and duration of symptoms were recorded. When a patient had bilateral slipped capital femoral epiphysis, the time between the first and second slips was recorded as well. The slipped capital femoral epiphysis was classified as pre-slip, acute, acute-on-chronic, or chronic¹⁹ as well as stable (if the patient was able to walk, with or without crutches) or unstable (if the patient was unable to walk, with or without crutches)²⁰. A hip was considered to have a pre-slip when it had symptoms similar to those in the contralateral hip, which had a previously unilateral slipped capital femoral epiphysis, but did not have radiographic changes. The slip angle was calculated with the method described by Southwick²¹, in which the slip angle, or the lateral epiphyseal-shaft angle, is determined by drawing three lines on the frog-leg lateral radiograph of the pelvis. The first line connects the anterior and posterior tips of the epiphysis (epiphyseal line), the second line is perpendicular to the epiphyseal line (perpendicular line), and the third line is drawn along the femoral diaphysis (diaphyseal line). The Southwick angle is the angle created by the intersection of the perpendicular and diaphyseal lines. On the basis of this angle, the slip severity was classified as mild (=30°), moderate (31° to 50°), or severe (=51°)²².

The bone age was determined with use of the Oxford method on pelvic radiographs^23-25. The Oxford method was chosen rather than the Greulich and Pyle²⁶ method since most children did not have radiographs of the hand available.

The child's birth weight was classified according to the percentile standards of Battaglia and Lubchenco²⁷, and the child's height and weight at the time of the diagnosis were classified according to both 1979²⁸ and 2000²⁹ percentiles because norms specific to the Amish population do not exist. In order to compare the Amish children with slipped capital femoral epiphysis with non-Amish white children with the disorder, a control group of 302 North American white children with slipped capital femoral epiphysis was extracted from a previously published worldwide, multicenter, multiracial study¹¹. The percentiles used in that study¹¹ were based on the 1979 norms. The 2000 norms²⁹ include the newer concept of body mass index^30,31, which accounts for both height and weight and is a more reliable indicator of obesity. Body mass index = [body weight/(body height)²] where body weight and height are expressed in kilograms and meters (kg/m²), respectively²⁹. To classify the body mass index of the Amish children in this study, it was necessary to use the 2000 norms²⁹. Therefore, both the 1979²⁸ and the 2000²⁹ percentiles were used in the present study.

Statistical Analysis

Each child was counted only once for the calculation of means or proportions with the exception of hip laterality (right or left), hip presentation (chronic or acute, and stable or unstable), duration of symptoms, and slip severity (mild, moderate, or severe). Statistical analyses were performed with use of Systat 10 software (Systat Software, Chicago, Illinois). Continuous variables are reported as the mean and one standard deviation. The Pearson chi-square or Fisher exact test was used to analyze differences between groups of discrete data. Differences between groups of continuous data were analyzed with the Student t test (two groups) or analysis of variance (three groups). If the groups were small (less than ten patients) or non-normal in distribution, nonparametric tests were used (the Mann-Whitney U test for two groups, and the Kruskal-Wallis test for more than two groups). For all analyses, p < 0.05 was considered to be significant.

Results

Materials and Methods | Results | Discussion | Appendix | References

Twenty-five Amish children (seventeen boys and eight girls), all of whom were white, with a total of thirty-three idiopathic slipped capital femoral epiphyses were identified between 1985 and 2002. Seventeen children had unilateral and eight had bilateral involvement (Table I). At the time of the diagnosis (of the first slip in those with bilateral involvement), the mean age was 13.4 ± 1.6 years (range, 10.1 to 16.2 years), the mean weight and height were 55.6 ± 12.4 kg (range, 34 to 84 kg) and 155.5 ± 10.2 cm (range, 137 to 171.5 cm), and the mean body mass index (of the twenty children for whom both the weight and the height at the time of the diagnosis were known) was 23.4 ± 5.4 kg/m² (range, 15.8 to 36.1 kg/m²). There were thirty-one stable and two unstable slips. The duration of symptoms, which was known for twenty-eight hips, averaged 6.6 ± 9.0 months (range, zero to forty-seven months). Of these twenty-eight hips, two had an acute and twenty-six had a chronic slip. Another three hips were asymptomatic; the slip was noted on radiographs during routine follow-up of a child with a previously unilateral slipped capital femoral epiphysis. Another hip was considered to have a pre-slip. The duration of symptoms was not known for one hip. The mean slip angle of the twenty-three hips for which adequate frog-leg lateral radiographs were available was 38° ± 20° (range, 7° to 72°), with seven mild, eleven moderate, and five severe slips. The mean Oxford score (measured in seventeen hips) was 32.8 ± 3.6, which corresponds to a mean bone age of 14.3 ± 1.1 years²³. There was no significant difference between the chronologic and bone ages of these children, as the mean chronologic age fell within two standard deviations of the mean Oxford bone age.

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TABLE I Demographic Data on Twenty-five Amish Children with Thirty-three Slipped Capital Femoral Epiphyses

Parameter	All Children	Boys (N = 17)	Girls (N = 8)	P Value
Age at diagnosis^*(yr)	13.4 ± 1.6	13.6 ± 1.4	12.6 ± 1.8	0.671
Duration of symptoms^*(mo)	6.6 ± 9.0	4.6 ± 4.3	10.4 ± 13.9	0.28
	5.2 ± 4.7†	4.6 ± 4.3†	6.3 ± 5.5†	0.50
Unilateral/bilateral (no.)	17/8	11/6	6/2	1.00
Weight^*(kg)				0.671
Birth	3.7 ± 0.5	4.4 ± 3.7	3.8 ± 0.6
At diagnosis	55.6 ± 12.4	59.4 ± 12.7	47.8 ± 6.6	0.038
Height at diagnosis^*(cm)	155.5 ± 10.2	157.2 ± 10.0	151.6 ± 10.5	0.248
Body mass index at diagnosis^*(kg/m²)	23.4 ± 5.4	24.4 ± 5.7	21.1 ± 4.3	0.322
Laterality (R/L) (no.)	12/20	9/13	3/7	0.56
Acute/chronic slip at presentation (no.)	2/26/3/1‡	2/16	0/10	0.52
Stable/unstable at presentation (no.)	31/2	21/2	10/0	1.00
Oxford bone age^*
Score	32.8 ± 3.6	31 ± 2.1	35.3 ± 3.8	0.003
Years	14.3 ± 1.1	14.2 ± 0.9	14.3 ± 1.4	0.22
Slip angle^*(deg)	38 ± 20	35 ± 21	44 ± 17	0.41
Mild/moderate/severe slip (no.)	7/11/5	6/6/3	1/5/2	0.38

The values are given as the mean and standard deviation. †These means were calculated after exclusion of the one outlier case, a girl who had had symptoms for forty-seven months. ‡The last two values (3/1) refer to the number of asymptomatic, contralateral slips and the number of pre-slips.

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TABLE I Demographic Data on Twenty-five Amish Children with Thirty-three Slipped Capital Femoral Epiphyses

Parameter	All Children	Boys (N = 17)	Girls (N = 8)	P Value
Age at diagnosis^*(yr)	13.4 ± 1.6	13.6 ± 1.4	12.6 ± 1.8	0.671
Duration of symptoms^*(mo)	6.6 ± 9.0	4.6 ± 4.3	10.4 ± 13.9	0.28
	5.2 ± 4.7†	4.6 ± 4.3†	6.3 ± 5.5†	0.50
Unilateral/bilateral (no.)	17/8	11/6	6/2	1.00
Weight^*(kg)				0.671
Birth	3.7 ± 0.5	4.4 ± 3.7	3.8 ± 0.6
At diagnosis	55.6 ± 12.4	59.4 ± 12.7	47.8 ± 6.6	0.038
Height at diagnosis^*(cm)	155.5 ± 10.2	157.2 ± 10.0	151.6 ± 10.5	0.248
Body mass index at diagnosis^*(kg/m²)	23.4 ± 5.4	24.4 ± 5.7	21.1 ± 4.3	0.322
Laterality (R/L) (no.)	12/20	9/13	3/7	0.56
Acute/chronic slip at presentation (no.)	2/26/3/1‡	2/16	0/10	0.52
Stable/unstable at presentation (no.)	31/2	21/2	10/0	1.00
Oxford bone age^*
Score	32.8 ± 3.6	31 ± 2.1	35.3 ± 3.8	0.003
Years	14.3 ± 1.1	14.2 ± 0.9	14.3 ± 1.4	0.22
Slip angle^*(deg)	38 ± 20	35 ± 21	44 ± 17	0.41
Mild/moderate/severe slip (no.)	7/11/5	6/6/3	1/5/2	0.38

The mean body mass index of 23.4 kg/m² was in the eighty-fifth percentile. A child whose body mass index is in the ninety-fifth percentile or higher is considered to be overweight³¹. Adults with a body mass index of =30 kg/m² are considered to be obese, those with an index of between 25 and 29.9 kg/m² are considered to be overweight, and those with an index between 18.5 and 24.9 kg/m² are considered to be of healthy weight³⁰. Thus, on the average, these children were not obese by either adult or pediatric criteria. Of the twenty children for whom the body mass index at the time of the presentation of the first slipped capital femoral epiphysis was known, only three had a body mass index of =30 kg/m². The body-mass-index distribution for these twenty children was not skewed (skewness [g₁] = 0.70, p > 0.10). Detailed percentile data for body habitus are shown in Table II and the Appendix.

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TABLE II Comparison Between Amish and Non-Amish North American White Children with Slipped Capital Femoral Epiphysis

Parameter	Amish Group (N = 25)	Control Group¹¹ (N = 302)	P Value
Gender (M/F) (no.)	17/8	184/118	0.67
Age at diagnosis^*
All children	13.4 ± 1.6	13.1 ± 1.8	0.65
Boys	13.6 ± 1.4	13.6 ± 1.7	0.91
Girls	12.6 ± 1.8	12.1 ± 1.6	0.68
Duration of symptoms^*(mo)	6.6 ± 9.0	4.2 ± 5.0	0.13
Unilateral/bilateral (no.)	17/8	251/51	0.044
Weight at diagnosis^*(kg)
All children	55.6 ± 12.4	66.4 ± 17.7	0.0036
Boys	59.4 ± 12.7	71.4 ± 17.8	0.005
Girls	47.8 ± 6.6	47.8 ± 6.6	0.038
Laterality (R/L) (no.)	12/20	148/205	0.71
Acute/chronic slip at presentation (no.)	2/26	51/288	0.40
Percentile of body weight at diagnosis of first slip†(no.)
=95th	6 (29%)	150 (53%)	0.004
90th to 94th	2 (10%)	49 (17%)
50th to 89th	7 (33%)	65 (23%)
11th to 49th	5 (24%)	14 (5%)
<10th	1 (5%)	6 (2%)
=90th	8 (38%)	199 (70%)	0.006
<90th	13 (62%)	85 (30%)

The values are given as the mean and standard deviation. †1979 National Center for Health Statistics percentiles²⁸.

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TABLE II Comparison Between Amish and Non-Amish North American White Children with Slipped Capital Femoral Epiphysis

Parameter	Amish Group (N = 25)	Control Group¹¹ (N = 302)	P Value
Gender (M/F) (no.)	17/8	184/118	0.67
Age at diagnosis^*
All children	13.4 ± 1.6	13.1 ± 1.8	0.65
Boys	13.6 ± 1.4	13.6 ± 1.7	0.91
Girls	12.6 ± 1.8	12.1 ± 1.6	0.68
Duration of symptoms^*(mo)	6.6 ± 9.0	4.2 ± 5.0	0.13
Unilateral/bilateral (no.)	17/8	251/51	0.044
Weight at diagnosis^*(kg)
All children	55.6 ± 12.4	66.4 ± 17.7	0.0036
Boys	59.4 ± 12.7	71.4 ± 17.8	0.005
Girls	47.8 ± 6.6	47.8 ± 6.6	0.038
Laterality (R/L) (no.)	12/20	148/205	0.71
Acute/chronic slip at presentation (no.)	2/26	51/288	0.40
Percentile of body weight at diagnosis of first slip†(no.)
=95th	6 (29%)	150 (53%)	0.004
90th to 94th	2 (10%)	49 (17%)
50th to 89th	7 (33%)	65 (23%)
11th to 49th	5 (24%)	14 (5%)
<10th	1 (5%)	6 (2%)
=90th	8 (38%)	199 (70%)	0.006
<90th	13 (62%)	85 (30%)

The values are given as the mean and standard deviation. †1979 National Center for Health Statistics percentiles²⁸.

Differences by Gender (Table I)

The mean age at the time of the diagnosis was 13.6 ± 1.4 years for the boys and 12.6 ± 1.8 years for the girls. The mean weight and height were 59.4 ± 12.7 kg and 157.2 ± 10.0 cm for the boys and 47.8 ± 6.6 kg and 151.6 ± 10.5 cm for the girls. The difference in weight was significant (p = 0.038). The boys were in approximately the eighty-fifth percentile and the girls were in approximately the sixty-fifth percentile for weight, whereas both the boys and the girls were in approximately the thirtieth percentile for height. The mean body mass index of the boys and girls was 24.4 ± 5.7 and 21.1 ± 4.3 kg/m², respectively, or in approximately the ninety-second and eightieth percentiles, respectively.

With the numbers available, there were no significant gender differences in birth weight, symptom duration, proportion of bilateral slipped capital femoral epiphysis, height at diagnosis, body mass index at diagnosis, proportion of right and left hips, proportion of acute or chronic slipped capital femoral epiphyses, proportion of stable or unstable slipped capital femoral epiphyses, slip severity, or Oxford bone age in years.

Birth and Family History

Whether or not there was a family history of slipped capital femoral epiphysis was noted in the medical records of twenty-three of the twenty-five children. Nine children (39%) had a positive family history, with six having an affected sibling and three, an affected cousin. Birth history was recorded in the medical records of twenty-four children; twenty were born by vaginal delivery and four, by Cesarean section. The mean birth weight was 3.7 ± 0.5 kg. Assuming that all were full-term births, the birth weight corresponds to approximately the eightieth percentile for both boys and girls²⁷. Both birth weight and the weight at diagnosis were known for seventeen of the twenty-five children. The mean birth weight was in the eightieth percentile, and the mean weight at the time of the diagnosis of the slipped capital femoral epiphysis was in approximately the sixty-fifth percentile for the girls and the eighty-fifth percentile for the boys (see Appendix).

Comparison Between Amish and Non-Amish White Children with Slipped Capital Femoral Epiphysis (Table II)

There was no significant difference between the Amish and non-Amish children with regard to gender distribution or the mean age at the time of the diagnosis. There was a significant difference in the body weight at the time of the diagnosis, which was 55.6 ± 12.4 kg for the Amish children and 66.4 ± 17.7 kg for the non-Amish children (p = 0.0036). This difference in body weight between the Amish and non-Amish children was found for both boys and girls. Amish children with a slipped capital femoral epiphysis are thus lighter than their non-Amish counterparts (Table II and Fig. 1). The prevalence of bilaterality was 32% (eight of twenty-five) in the Amish children and 17% (fifty-one of 302) in the non-Amish children (p = 0.044). With the numbers available, there were no other significant differences between these two groups.

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Fig. 1: Distribution of body weight percentiles in three groups: the normal United States population, the Amish children with slipped capital femoral epiphysis in our study, and 284 non-Amish white North American children with slipped capital femoral epiphysis. Note that both groups with slipped capital femoral epiphysis are shifted toward the heavier body weight percentiles but that the Amish children are less heavy than the non-Amish children.

Data on family history were not gathered for the control group in the multicenter study¹¹. However, the rates of a positive family history were reported to be 9% and 14.5% in two literature studies^32,33, performed in Scotland and Sweden. These studies likely included all white children, similar to the control group in the present study. We believe that it is thus reasonable to conclude that Amish children have a higher familial incidence of slipped capital femoral epiphysis than do non-Amish white children.

Bilateral Slipped Capital Femoral Epiphysis (see Appendix)

Eight Amish children had bilateral involvement; three presented with both slips simultaneously, and five had sequential slips with an average of 0.9 ± 0.5 years (range, one to eighteen months) between the two events. In three of the five children with sequential slips, the second slip was asymptomatic. The children with bilateral slipped capital femoral epiphysis were, on the average, less heavy than those with a unilateral slip, with a mean body weight of 47.8 ± 7.6 kg compared with 60.1 ± 12.4 kg (p = 0.026) and a mean body mass index of 19.6 ± 2.5 kg/m² compared with 25.1 ± 5.6 kg/m² (p = 0.032). With the numbers available, there were no other significant differences between the children with unilateral involvement and those with bilateral involvement.

Discussion

Materials and Methods | Results | Discussion | Appendix | References

The Amish are descendants of the Anabaptist religious movement, which occurred during the Protestant Reformation^34-36. As a result of religious persecution, they fled to the mountains of Switzerland and southern Germany. They later emigrated to America in the eighteenth century and settled in southeastern Pennsylvania to take advantage of William Penn's religious tolerance. Additional migrations occurred from Pennsylvania to Ohio in 1808, to Indiana in 1830, and to Iowa in 1846. The Amish have a strong rural agriculture manual labor work ethic derived from their historical roots³⁷. Their present customs include a strict adherence to the use of horses on the farm and as transportation, refusal to allow electricity or telephones in their homes, and traditional standards of dress. Many chores are thus done by hand or with minimal machinery. The Amish population was estimated to be 168,000 in 1997³⁴. Presently, approximately 75% live in Ohio, Pennsylvania, or Indiana³⁴.

The three main findings in this study were that, compared with their white counterparts with slipped capital femoral epiphysis, Amish children with slipped capital femoral epiphysis had a higher familial prevalence, bilaterality was more common, and slipped capital femoral epiphysis occurred in less heavy children. Most series of children with slipped capital femoral epiphysis have demonstrated a strong tendency for obesity^1,4-11. However, Amish children with the disorder were significantly less heavy than non-Amish children with the same disorder (p = 0.0036). The mean body weight for age was in the eighty-fifth percentile for boys and in the sixty-fifth percentile for girls. Although the children in this study were moderately heavy, they could not be classified, on the average, as obese with use of weight-for-age percentiles. We believe that this is the first study to compare birth weight and weight at diagnosis of children with slipped capital femoral epiphysis. No differences between the percentiles for birth weight and the weight at diagnosis were noted, indicating that the child's birth weight reasonably predicted the child's weight in adolescence.

Does this difference in body weight between the Amish and non-Amish children simply reflect a difference in height? The heights of the children in the control group were not reported¹¹. However, Kelsey et al.¹⁵ did record the heights of children with slipped capital femoral epiphysis in Connecticut, a location with a geography and latitude similar to that of the states where Amish children reside. The height distributions of the Amish children and those in the study by Kelsey et al. were similar (Pearson chi-square = 2.85, degrees of freedom = 3, p = 0.42). The mean body mass index of the Amish boys in our study was in the ninety-second percentile and that of the Amish girls was in the eightieth percentile. Both were lower than the ninety-fifth percentile, which is the definition of obesity according to pediatric body-mass-index standards³¹. Thus, Amish children with slipped capital femoral epiphysis are as tall as but less heavy than their non-Amish white counterparts with slipped capital femoral epiphysis in North America.

The prevalence of bilateral slipped capital femoral epiphysis was higher in the Amish children (32%; eight of twenty-five) than in the non-Amish children (17%; fifty-one of 302) (p = 0.044). One possible explanation for this is that the Amish avoid traditional medical care for financial reasons, since they do not believe in third-party payers. Amish children may present for medical care only when they have substantial symptoms, which may be more likely in a child with bilateral involvement than in one with unilateral involvement. However, three of the eight children with bilateral slipped capital femoral epiphysis had no symptoms related to the second slip, making the medical access argument unlikely. The prevalence of bilaterality may actually increase if a second slipped capital femoral epiphysis develops in the children cared for in 2001 and 2002. Thus, it is appropriate to conclude that Amish children have a higher prevalence of bilateral slipped capital femoral epiphysis.

Little is known about the genetics of slipped capital femoral epiphysis. The first English-language description of familial slipped capital femoral epiphysis was in 1940³⁸, and there have been several more descriptions since then^32,33,39-46 (see Appendix). Proposed patterns of genetic transmission include X-linked dominant, autosomal dominant with variable penetrance, and autosomal recessive^33,42,43,45. If there is a hereditary factor in slipped capital femoral epiphysis, it has not yet been identified. Studies of HLA (human leukocyte antigen) phenotypes in children with slipped capital femoral epiphysis have not demonstrated any commonality^39,40,46-48.

The Amish reflect a small gene pool with a high prevalence of consanguinity relative to that in the general white United States population^18,49,50. If a genetic factor is responsible for slipped capital femoral epiphysis, it is likely to be more visible in the Amish population as a result of their restrictive culture and consanguinity. Consanguinity is specifically known to enhance the phenotypic expression of autosomal recessive disorders. Slipped capital femoral epiphysis is not, to the best of our knowledge, a standard autosomal recessive disorder, although it has been postulated to be autosomal recessive with low penetrance³³. The 39% prevalence of a positive family history (nine of the twenty-three children for whom a family history was recorded) in this study is much higher than the prevalences of 9% (four of forty-five)³² and 14.5% (thirty-one of 214)³³ in two other population studies (p = 0.002). Rennie postulated that inbreeding was the reason for the increased familial incidence of slipped capital femoral epiphysis in north-east Scotland³³. The rural, agricultural population of northeast Scotland at the time of his study had very definite geographical boundaries with a stable community, not unlike that seen in the Amish population in the United States today.

The fact that Amish children with slipped capital femoral epiphysis are more likely to have affected family members may also be due to environmental factors or a combination of both environment and genetics. The strenuous physical work performed by Amish people (including children) may increase stress on the proximal femoral physis and result in a slipped capital femoral epiphysis^51-54. If common chores (e.g., milking dairy cattle while assuming a particular posture) are shared by all members of a particular family, including children, and are enough to result in physeal slippage, then the strong familial tendency seen in this study may simply reflect physical stress and not a true genetic pattern. Alternatively, the hips of Amish children may have a lower load to failure because of an underlying genetic predisposition. Finally, there may be a combination of both genetic and mechanical factors: Amish children may be more susceptible to normal physeal stress because of an underlying genetic predisposition, and they also may be exposed to greater physeal stress than are non-Amish children. These issues require further investigation.

Appendix

Materials and Methods | Results | Discussion | Appendix | References

Tables showing the distribution of study patients according to body habitus percentiles, a comparison between the children with unilateral slipped capital femoral epiphysis and those with bilateral slipped capital femoral epiphysis, and a summary of the data from previous studies on slipped capital femoral epiphysis are available with the electronic versions of this article, on our web site at (go to the article citation and click on "Supplementary Material") and on our quarterly CD-ROM (call our subscription department, at 781-449-9780, to order the CD-ROM). ?

References

Materials and Methods | Results | Discussion | Appendix | References

Aronson DD, Loder RT. Slipped capital femoral epiphysis in black children. J Pediatr Orthop.1992;12: 74-9.1274 1992 [PubMed]

Bishop JO, Oley TJ, Stephenson CT, Tullos HS. Slipped capital femoral epiphysis. A study of 50 cases in black children. Clin Orthop.1978;135: 93-6.13593 1978 [PubMed]

Burrows HJ. Slipped upper femoral epiphysis: characteristics of a hundred cases. J Bone Joint Surg Br.1957;39: 641-58.39641 1957

Exner GU. Growth and pubertal development in slipped capital femoral epiphysis: a longitudinal study. J Pediatr Orthop.1986;6: 403-9.6403 1986 [PubMed][CrossRef]

Hägglund G, Hansson LI, Ordeberg G, Sandstrom S. Bilaterality in slipped upper femoral epiphysis. J Bone Joint Surg Br.1988;70: 179-81.70179 1988

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epiphyses, slipped

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Randall T. Loder, Jeffrey Nechleba, James O. Sanders, Patricia Doyle; Idiopathic Slipped Capital Femoral Epiphysis in Amish Children. The Journal of Bone & Joint Surgery. 2005 Mar;87(3):543-549.

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