Femoral morphology in Ortolani’s anatomical collection of developmental dysplasia of the hip: Anteversion is unrelated to severity of infantile dysplasia

Abstract

Purpose:

This study evaluated and quantified femoral anteversion and femoral head sphericity in healthy and dysplastic hips of post-mortem infant specimens from Ortolani’s collection.

Methods:

Healthy hips and hips with cases of dysplasia, with a large variety of severity, were preserved. Morphological measurements were taken on 14 specimens (28 hips), with a mean age of 4.68 months. The degree of dysplasia was classified as mild (A) to severe (D); 11 hips were Grade A, 6 hips were Grade B, 7 hips were Grade C, and 4 hips were Grade D. The femoral anteversion angle, the minimum femoral head diameter, and the maximum femoral head diameter were measured. The minimum and maximum femoral head diameters were used to estimate femoral head sphericity.

Results:

The mean femoral anteversion angle was 30.81 degrees ± 11.07 degrees in cases and 29.69 degrees ± 12.69 degrees in controls. There were no significant differences between the normal-to-mild group and moderate-to-severe group when comparing the femoral anteversion angle (p = 0.836). The mean estimated sphericity was 1.08 mm ± 0.50 mm in cases and 0.81 mm ± 0.65 mm in controls, with no statistically significant difference between the groups (p = 0.269).

Conclusion:

Ortolani’s collection showed no significant differences between healthy and dysplastic hips in specimens under 1 year of age. While the femoral head appeared slightly more flattened in dysplastic hips, it was not statistically significant. The findings in the unique collection add to the knowledge of the pathoanatomy of infantile hip dysplasia.

Clinical Relevance:

Femoral anteversion may not play a role in the etiology and pathogenesis of DDH.

Introduction

Many studies reporting increased anteversion are based on surgical findings, anatomical specimens from stillborn infants, or infants with multiple congenital anomalies, including hip dislocation.^1–3 Ortolani’s collection is a unique collection of post-mortem infant specimens that were dissected and evaluated by Ortolani, who evaluated them to identify the cause of the “jerk sign” or “segno dello scatto.” ⁴ Ortolani and his son preserved the collection until it was donated to the Institute of Anatomy at the University of Padua in 2008. ⁵ This unique collection allowed the study of the anatomy of non-teratological infant hips with varying degrees of hip dysplasia.

The pathogenesis of developmental dysplasia of the hip (DDH) is considered the result of both endogenous and exogenous factors. ⁶ Endogenous factors include primary alterations in the joint morphology, such as acetabular dysmorphism, excess femoral anteversion, and joint hyperlaxity. ⁶ Exogenous factors consist of abnormal forces acting on the hip in utero (i.e. oligohydramnios and feto-maternal disproportion), during delivery (i.e. vaginal breech delivery), or after birth (i.e. swaddling).^6,7 Reduced amniotic fluid and first childbirth can be associated with increased abdominal pressure. Breech presentation is thought to lead to extreme hip flexion and knee extension with consequent impairment of the fetus’s ability to move. The plasticity of the femoral head also makes it susceptible to mechanical factors. ⁸ Predisposing factors include the shallow neonatal cartilaginous acetabulum and soft tissue laxity accompanying the labor and delivery process.^9,10

A less understood factor is the variation of the femoral anteversion angle. This angle at birth averages approximately 30 degrees in otherwise healthy infants and gradually decreases to an average of 10–20 degrees in adulthood.^11,12 An increase in femoral anteversion, particularly when combined with increased acetabular anteversion, may contribute to hip instability. ¹³ Inconsistent findings regarding femoral anteversion have been reported for patients with DDH. Some authors reported increased femoral anteversion angles in patients with hip dysplasia.^11,13–15 Others found comparable anteversion angles between healthy infants and children and those with DDH.^6,13,16–18 Jia et al., ¹³ in a computed tomography (CT) study, found no differences in femoral anteversion angle between healthy and dysplastic hips in Tönnis Type II and III hips, while the anteversion angle was increased in Tönnis Type IV dysplastic hips.

Reports of pathoanatomy of DDH have described severe dislocations in stillborn infants or infants with additional congenital abnormalities.^1–3 However, a limited number of studies have described the femoral morphology of otherwise healthy infants under 1 year of age. The study seeks to add to the literature on femoral morphology in infants with DDH by adding Ortolani’s collection to the current state of knowledge. Therefore, the purpose of this study was to report anatomical findings from Ortolani’s collection. Specifically, the range of femoral anteversion in these untreated infants was evaluated, providing the basis for this study. Femoral head sphericity was also measured and included in this report.

Materials and methods

The specimens evaluated in this study are from infants who died of infectious diseases, such as influenza and gastroenteritis, that were common in children during the pre-antibiotic era. The specimens include healthy hips, those with varying cases of dysplasia, ranging from mild to severe, and those with and without hip instability. ¹⁹ A total of 14 of the 16 specimens from Ortolani’s collection were used in the study. Two of the 16 specimens (or 4 hips) from the collection did not meet the study’s inclusion criteria due to poor conservation. The age of the specimens (Table 1) was estimated using measured femoral lengths and growth charts.^20,21 The calculated ages were consistent with age-related femoral head diameter measurements in the literature.^20,22 There were 13 full-term specimens and one pre-term specimen.

Table 1.

Specimen estimated age.

Specimen	Femoral length (mm)	Approximate age
1	–	–
2	110.40	6.5 months
3	104.27	6 months
4	98.63	5 months
5	61.00	32 weeks gestation
6	99.35	5 months
7	–	–
8	79.83	3 weeks
9	–	–
10	110.00	6.5 months
11	90.50	3.5 months
12	94.87	4 months
13	90.46	3.5 months
14	103.10	6 months

For all specimens, the degree of hip dysplasia was assessed based on the rounding of the acetabular rim, the acetabular shape and depth, the development of a false acetabulum, and the morphology of the femoral head. The specimens were independently classified by two orthopedic surgeons, and they were confirmed with the previous classifications made by Ortolani. They were classified as Grade A (normal hips), Grade B (hips with mild alterations), Grade C (moderate, but clearly visible alterations), and Grade D (severe alterations). Table 2 shows the measurements used to assess normal and dysplastic hips. Pelvic measurements were also taken from the samples for completeness purposes (Figure 2(a)), but these measurements were not used in the analysis.

Table 2.

Femoral and acetabulum morphological measurements.

Femur measurements	Acetabulum measurements
Anteversion angle	Depth
Maximum femoral head diameter	Width
Minimum femoral head diameter	Height
Length	Anteversion angle
	Inclination angle

Figure 2.

The width of the iliac crests (a), the left and right femurs from Specimen 1 did not have intact femoral condyles; thus, the length of the femurs and the femoral anteversion angles were not measured (b), the acetabulum depth (c), and the acetabulum width (d) were measured using a digital caliper.

The femoral anteversion angle was measured using two different methods: the photographic method^23,24 and the direct method. ¹² The anteversion angle was measured using the photographic method in 8 of the 14 evaluated specimens (or 16 hips). For the photographic method, the femurs were placed on a table with both condyles in contact with the table. A photograph was taken from the proximal end parallel to the shaft axis and was used to measure femoral anteversion. The femoral anteversion angle was expressed as the angle between the projections of the axis of the femoral neck and the femoral condyles (Figure 1).

Figure 1.

A visual representation of how the femoral anteversion angle ( $\theta$ ) was measured using a photographic method.

Note: This is for visualization purposes only, and measurements from the figure may not be accurate.

For 3 of the 14 specimens (or 6 hips), the anteversion angle was measured using the direct method (i.e. a goniometer). Two independent observers confirmed all femoral anteversion measurements, and the mean value was determined. The femoral anteversion angle could not be measured for the last three specimens (six hips) because the distal femoral condyles were absent (Figure 2(b)). The maximum and minimum femoral head diameters were measured using a digital caliper on all 14 specimens (28 hips) because all specimens had intact proximal femurs. ⁹ The difference between the diameters was used to estimate femoral head sphericity. For comparison purposes, the specimens were then organized into two main groups. The control group consisted of normal hips (Grade A) and hips with mild hip dysplasia (Grade B). The cases group included hips with moderate to severe cases of hip dysplasia (Grades C and D). A summary of all measurements is shown in Tables 3 and 4.

Table 3.

Summary of the measurements for the controls.

Specimen	Grade	FAV ( $o$ )	D_min (mm)	D_max (mm)	Sphericity (mm)
2L	A	17.50	17.00	17.90	0.90
2R	A	11.75	16.95	17.72	0.77
4R	A	42.25	13.29	14.10	0.81
5L	A	14.00	4.75	4.99	0.24
6L	A	21.00	16.50	18.11	1.61
6R	A	12.50	16.98	18.37	1.39
10L	A	37.50	16.30	16.70	0.40
10R	A	24.00	16.90	17.70	0.80
11L	A	32.00	10.80	11.00	0.20
13L	A	33.50	14.40	14.40	0.00
14L	A	38.00	13.50	15.80	2.30
1R	B	–	17.00	17.10	0.10
4L	B	48.00	12.50	13.68	1.18
7R	B	–	20.60	21.40	0.80
9L	B	–	15.00	16.70	1.70
12R	B	37.50	15.36	16.00	0.64
13R	B	46.10	14.40	14.40	0.00

FAV: femoral anteversion angle; D_min: minimum femoral head diameter; D_max: maximum femoral head diameter; L: left femur; R: right femur.

Table 4.

Summary of the measurements for the cases.

Specimen	Grade	FAV ( $o$ )	D_min (mm)	D_max (mm)	Sphericity (mm)
1L	C	–	14.10	15.60	1.50
3L	C	26.60	15.46	16.77	1.31
3R	C	32.90	16.15	16.57	0.42
7L	C	–	19.30	19.90	0.60
9R	C	–	14.78	15.68	0.90
11R	C	32.50	10.10	11.00	0.90
12L	C	38.00	14.60	15.80	1.20
5R	D	10.50	7.60	8.10	0.50
8L	D	22.00	7.50	9.50	2.00
8R	D	46.50	9.00	9.90	0.90
14R	D	37.50	13.70	15.30	1.60

FAV: femoral anteversion angle; D_min: minimum femoral head diameter; D_max: maximum femoral head diameter; L: left femur, R: right femur.

All statistical analysis was performed using IBM SPSS Statistics 27. ²⁵ The study used a two-tailed independent samples t-test, with a statistical significance set to p < 0.05, to assess the between-group differences in the measurements of the femoral anteversion angles and sphericity. Descriptive statistics are presented as the mean value ± standard deviation.

Results

In this study, 28 hips with severity grades ranging from Grade A to Grade D were assessed. The mean estimated age of the 14 specimens (28 hips) was 4.68 months ± 1.80 months. The mean femoral anteversion was 30.10 degrees ± 11.87 degrees. The mean minimum and maximum femoral head diameters were 14.09 mm ± 3.65 and 15.01 mm ± 3.69, respectively. The mean estimated femoral sphericity was 0.92 mm ± 0.60 mm. Table 5 summarizes the measured parameters for the 14 specimens. The distribution of the femoral anteversion angle, the minimum and maximum femoral head diameter, and the sphericity for the cases and the controls are shown in Figure 3.

Table 5.

Summary of data: estimated age, femoral length, femoral anteversion angle (FAV), minimum femoral head diameter (D_min), maximum femoral head diameter (D_max), and sphericity.

Parameter	Unit	Mean	SD
Age	Months	4.68	1.80
FAV	Degrees	30.10	11.87
D_min	mm	14.09	3.65
D_max	mm	15.01	3.69
Sphericity	mm	0.92	0.60

SD: standard deviation; FAV: femoral anteversion angle; D_min: minimum femoral head diameter; D_max: maximum femoral head diameter.

Figure 3.

The distribution of femoral anteversion (FAV), minimum femoral head diameter (D_min), maximum femoral head diameter (D_max), and sphericity for the cases and the controls are given.

For the femoral anteversion analysis, there were 8 hips for the cases and 14 hips for the controls since femoral anteversion could not be measured in 3 specimens (6 hips) without femoral condyles. The mean femoral anteversion angle was 30.81 degrees ± 11.07 degrees in cases (moderate-to-severe group) and 29.69 degrees ± 12.69 degrees in controls (normal-to-mild group). The femoral anteversion angles did not show a statistically significant difference between the two groupings based on severity (p = 0.836).

There were 11 moderate-to-severe cases and 17 normal-to-mild hips (controls) when measuring the minimum and maximum femoral diameters since all specimens had intact proximal femurs. The mean maximal femoral head diameter in the cases was 14.01 mm ± 3.75 mm compared to 15.65 mm ± 3.62 mm in controls. The mean minimum femoral head diameter in the cases was 12.94 mm ± 3.83 mm and 14.84 mm ± 3.43 mm in controls. The difference between the maximum and minimum femoral head diameter was 1.08 mm ± 0.50 mm in cases and 0.81 mm ± 0.65 mm in controls. The difference in sphericity between cases and controls was not statistically significant (p = 0.269).

Discussion

Ortolani’s collection is unique because of its noteworthy number of specimens and historical value. The collection includes the original specimens on which Professor Ortolani studied the morphological alterations typical of DDH and the anatomical explanation of the “segno dello scatto,” which he pointed out as a pathognomonic “jerk sign” of dysplastic hips. A major value of this anatomical collection is that it includes all DDH grades instead of focusing solely on hip dislocations. The specimens were from babies ranging from birth to 1 year of age, which allows evaluation of the early characteristics of the untreated condition before the onset of weight-bearing. The specimens were from otherwise healthy babies who died of unrelated reasons, primarily infectious diseases common during the pre-antibiotic era, allowing DDH to be studied without confounding factors related to associated conditions. The collection includes the variations of typical hip dysplasia cases before intervention as a valid substrate for the characterization of anatomical alterations during the development of hip dysplasia.

Based on the findings of femoral anteversion in Ortolani’s collection, our analysis suggests that increased femoral anteversion is not part of the etiology or pathogenesis of DDH. The results also suggest that femoral anteversion has some individual variability in healthy and dysplastic hips. The mean femoral anteversion angle for all 28 hips was 30.1 degrees and showed no significant difference between moderate to severe cases (30.8 degrees) and normal to mild cases (29.69 degrees). The results of the femoral anteversion of Ortolani’s collection are consistent with research findings of infants with DDH that are otherwise healthy. The average values found in both groups agree with the findings from CT scans obtained by Edelson et al. ¹⁶ In addition, Mootha et al. ¹⁸ found no differences in femoral anteversion between healthy and dysplastic hips in an magnetic resonance imaging (MRI) study of children aged 12–48 months. Li et al. ¹⁷ found similar femoral anteversion between cases and controls in adult dysplastic hips. Our results are also in agreement with normal mean anteversion angles of 30–32 degrees reported in the literature in infants without DDH.^11,14 There are studies where increased femoral anteversion was found in infants, ¹⁴ children, ¹¹ and adults^17,26–28 with dysplastic hips. McKibbin based his findings on a single full-term, frank breech infant who died shortly after a difficult extraction and found the increased femoral anteversion present in an infant with bilateral hip dislocations. ¹⁴ Fabry et al. ¹¹ found a 17 degree increase in femoral anteversion in dysplastic hips of children older than 1 year of age when compared with a similar group of non-dysplastic hips. In addition, femoral anteversion increased in subjects with unilateral dislocation of the unaffected hip with an average value of 44.62 degrees. ¹¹ In adult dysplastic hips, Li et al. ¹⁷ reported increased femoral anteversion only for dysplastic hips with the onset of osteoarthritis, which may play a role in developing anomalous joint stresses.

Femoral anteversion in older infants may vary, ¹⁵ which may explain why osteotomy is no longer routinely performed during an open reduction in older children. A study of older children undergoing corrective surgery also found increased femoral anteversion, although there was great individual variability. ¹⁵ The variability was such that the authors cautioned that femoral derotation should only be performed when increased anteversion was present. ¹⁵ Although femoral derotation osteotomy is often part of the surgical procedure for hip dysplasia, there is no general agreement about its necessity. Sankar et al. ¹⁵ advised an individualized treatment with derotation osteotomy for anteversion greater than 50 degrees. Jia et al. ¹³ suggested derotation osteotomy in Tönnis IV type deformities in cases with concomitant increased acetabular anteversion and in cases where the hip is still unstable after pelvic osteotomy. It is widely accepted that increased anteversion angles of untreated dislocated hips in older children may reflect a remodeling failure secondary to an altered hip position. ¹⁸ The gradual decline in anteversion angle from birth to maturity is unlikely to occur when the hip remains dislocated. Our results suggest that the increase in femoral anteversion may be a secondary phenomenon or the result of an increased risk of failure of reduction in infants under 1 year of age.

One explanation for the increased femoral anteversion found in older children with dislocated hips is that increased anteversion may interfere with successful reduction. A biomechanical model has also suggested that increased femoral anteversion may affect the successful reduction of dislocated infant hips. ²⁹ Hunter et al. ³⁰ suggested that increased anteversion could lead to difficulty reducing unstable hips with the Pavlik harness. The increase in femoral anteversion in infants of walking age may be due to an increase in anteversion that inhibits spontaneous or guided reduction. The spontaneous reduction of untreated infantile dislocation has been reported along with spontaneous improvement of stable dysplasia cases.^31,32 The forces that influence the spontaneous reduction of anteversion derive primarily from muscle by their active contraction and elastic connective tissues. Abnormally oriented muscle forces could be associated with an abnormal anteversion angle, ³³ which could be another possible explanation for the increase in anteversion in older infants.

The sphericity, or the difference between the maximum and minimum diameters of the femoral head, is slightly larger in cases of DDH than in normal to mild hips. This finding suggests that dysplastic femoral heads are more ovoidal during infancy and before treatment. However, these findings do not explain if it is a cause or consequence of hip dysplasia. Ortolani considered head flattening a secondary change due to impingement against the acetabular rim during natural hip movements. ³⁴

Important limitations of this study include the small number of examined specimens, the uncertainty of morphological to clinical findings, and the absence of otherwise healthy control specimens from the same time. This study did not investigate the effects of intra- and inter-observer variability, although more than one observer confirmed the measurements. In addition, the effect of acetabular orientation combined with femoral anteversion was not evaluated as a potential factor for instability or pathogenesis of hip dysplasia. Regardless of these limitations, the femoral anteversion angle in Ortolani’s collection is consistent with anteversion angles found in anatomical studies of otherwise healthy infants. Our findings suggest that femoral anteversion alone is an unlikely factor in the pathogenesis of hip dysplasia. Future research on infantile hip dislocations may help determine whether the increased prevalence of femoral anteversion found in older children is due to failure of remodeling or whether increased anteversion predisposes to reduction failure. Either possibility could help explain the increased femoral anteversion found by Jia et al. ³⁵ in Tönnis Type IV dislocations but not in Tönnis Types I, II, or III dysplasia.

Ortolani’s anatomical collection allows a unique overview of the premature pathological anatomy of hip dysplasia. The findings can contribute to understanding DDH in infants and provide information on possible anatomical alterations. Measurements on the samples identified angles and variability of femoral anteversion that were comparable with anteversion angles in otherwise healthy infants. The increase in femoral anteversion does not appear to be a primary pathogenic factor in the development of DDH, and the degree of femoral anteversion varies considerably among samples.