JBJS | Acetabular Development in Developmental Dysplasia of the Hip Complicated by Lateral Growth Disturbance of the Capital Femoral Epiphysis*

The Journal of Bone & Joint Surgery, Volume 82, Issue 12

Articles | December 01, 2000

Acetabular Development in Developmental Dysplasia of the Hip Complicated by Lateral Growth Disturbance of the Capital Femoral Epiphysis*

Hyun Woo Kim, M.D., Ph.D.†; Jose A. Morcuende, M.D., Ph.D.‡; Lori A. Dolan, R.N., M.A.‡; Stuart L. Weinstein, M.D.‡

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Investigation performed at the Department of Orthopaedic Surgery, University of Iowa Hospitals and Clinics, Iowa City, Iowa
A complete video supplement complementing this article ("Management of DDH for Children Two Years of Age and Older: Open Reduction Employing an Anterior Approach," by Dennis Wenger, M.D., San Diego, California) is available from the Video Journal of Orthopaedics. A video clip is available at the JBJS web site, www.jbjs.org. The Video Journal of Orthopaedics can be contacted at (805) 962-3410, web site: www.vjortho.com.
*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.
†Department of Orthopaedic Surgery, Yonsei Medical Center, Severance Hospital, Yonsei University College of Medicine, C.P.O. Box 8044, Seoul, Korea.
‡Department of Orthopaedic Surgery, University of Iowa College of Medicine, Iowa City, Iowa 52242-1088. E-mail address for S. L. Weinstein: stuart-weinstein@uiowa.edu.

The Journal of Bone & Joint Surgery. 2000; 82:1692-1692

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Abstract

Background: Lateral growth disturbance of the capital femoral epiphysis is the most common type of physeal arrest complicating the treatment of developmental hip dysplasia. Although this type of physeal damage has been assumed to result in poor acetabular development, the natural history of dysplastic hips affected by this pattern of growth disturbance is still unclear. To investigate this issue, we evaluated acetabular development in a retrospective study of fifty-eight hips in forty-eight patients who had lateral physeal arrest after management of developmental hip dysplasia.

Methods: Of the fifty-eight hips, thirty-six were reduced closed and twenty-two were reduced open. The average age of the patients was twenty-two months (range, three to ninety-seven months) at the time of the reduction and twenty-one years (range, ten to fifty-five years) at the time of the latest follow-up evaluation. Hips rated as Severin class I (an excellent result) or II (a good result) were defined as having a satisfactory result, and those rated as Severin class III (a fair result) or IV (a poor result) were considered to have an unsatisfactory result. Specific femoral head changes were sought in the complete radiographic files on all hips. Various radiographic parameters of hip integrity, including the degree of lateral tilt of the capital femoral epiphysis, were measured over time, and comparisons were made between hips classified as satisfactory and those classified as unsatisfactory at four time-points: before the reduction, at two years after the reduction, at six to eight years of age, and at the time of the final follow-up.

Results: Lateral growth disturbance of the capital femoral epiphysis was first evident by an average of ten years of age (range, four to fourteen years of age). There was no consistent early pattern of changes in the epiphysis, physis, or metaphysis related to later development of valgus tilt of the epiphysis. Thirty-four hips (59 percent) were rated as satisfactory and twenty-four were rated as unsatisfactory at the latest follow-up evaluation. Hips classified as unsatisfactory exhibited poor acetabular development by an average age of seven years. The inclination of the epiphyseal plate became progressively more horizontal or even reversed over time; however, serial measurements of inclination were not significant predictors of Severin classification.

Conclusions: Lateral growth disturbance of the capital femoral epiphysis is not necessarily associated with poor acetabular development, as when dysplasia does occur it is generally evident prior to the identification of the physeal arrest. It is important to monitor acetabular development after reduction rather than search for radiographic changes of physeal arrest, which are difficult to detect in young children.

Figures in this Article

Introduction

Introduction | Materials and Methods | Results | Discussion | References

Growth disturbance of the capital femoral epiphysis, commonly referred to as aseptic necrosis of the femoral head, remains the major complication following treatment of developmental hip dysplasia^{4,5,7,8,10,12,15,18,36}. Its potential sequelae include femoral head deformity, poor acetabular development, and osteoarthritis in later life. Once a growth disturbance has developed, the extent of the damage to the femoral head as well as the degree of acetabular development should be assessed because persistent acetabular dysplasia has been regarded as a major contributing factor in early degenerative joint disease of the hip^{4,7,8,10,12-14,18,30,32,36}. Bucholz and Ogden⁵ and Kalamchi and MacEwen¹⁵ examined and classified patterns of growth disturbance in the capital femoral epiphysis after the treatment of developmental hip dysplasia. They suggested that early recognition of growth disturbance patterns, based on the degree of involvement of the physis rather than the changes in the ossific nucleus alone, allows more accurate anticipation of subsequent problems and residual deformities of the proximal part of the femur and thus can be helpful in planning additional treatment. However, the deformity seen at maturity cannot be predicted during the earlier stages of aseptic necrosis in certain patterns of physeal arrest^{6,15,19,24,32}.

Development of a lateral growth disturbance of the capital femoral epiphysis (type II^5,15) is unpredictable; hence, follow-up to skeletal maturity is important. Although type II, the most common type of growth disturbance^{5,15,16,18,31}, usually is not evident until nine to ten years of age^{6,15,19,24,32}, it is characterized by retarded growth in the lateral aspect of the physis or by premature lateral fusion, resulting in the subsequent development of valgus deformity of the head on the neck. Problems associated with femoral coverage, as a result of progressive valgus deformity and subsequent poor acetabular development, are assumed to occur more frequently in patients with this type of growth disturbance. However, we are not aware of any studies providing quantitative data or with sufficiently long-term follow-up to support the relationship between type-II growth disturbance and acetabular development, and the natural history of hips with developmental dysplasia affected with this pattern of growth disturbance is still unknown. The present retrospective study was performed to evaluate acetabular development in patients with a type-II growth disturbance after reduction for the treatment of developmental hip dysplasia.

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Fig. 1:: Anteroposterior radiograph of the pelvis and hips of a thirteen-month-old child with a right hip dislocation. The patient was treated by adductor tenotomy and closed reduction.

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Fig 1-B:: Anteroposterior radiograph made at six years of age. There is fairly good development of the proximal femoral epiphysis without evidence of ossification irregularities. The Shenton line is intact.

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Fig 1-C:: Anteroposterior radiograph made at thirty-four years of age. On the right side, there is a slight valgus deformity of the femoral head on the neck associated with minimal residual acetabular dysplasia and evidence of subchondral bone sclerosis.

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Fig 2-A:: Anteroposterior radiograph of the pelvis and hips of a forty-five-month-old child with a high right hip dislocation. The patient was treated by adductor tenotomy and closed reduction.

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Fig 2-B:: Anteroposterior radiograph made at nine years of age. There is lateral tilting of the proximal femoral epiphysis on the neck with a bone bar located on the superior-lateral aspect of the neck. The Shenton line is broken, the head is slightly flattened, and the acetabulum is dysplastic.

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Fig 2-C:: Anteroposterior radiograph made at eleven years of age. There is a severe valgus deformity of the femoral head on the neck with residual acetabular dysplasia, poor development of the teardrop figure, and subluxation of the right hip.

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TABLE I: Radiographic Data Before Reduction and at Two Years After Reduction*

*The values are given as the average and the standard deviation, with the number of hips in parentheses.

	Before Reduction			Two Years After Reduction
Severin Class I or II at Follow-up*	Severin Class III or IV at Follow-up*	P Value	Severin Class I or II at Follow-up*	Severin Class III or IV at Follow-up*	P Value
Acetabular index (degrees)	36.5 ± 6.1 (32)	37.8 ± 5.3 (24)	0.38	26.0 ± 5.6 (30)	27.2 ± 4.2 (23)	0.40
Centering ratio
Lateral	1.06 ± 0.11 (27)	1.07 ± 0.10 (21)	0.71	0.72 ± 0.03 (26)	0.74 ± 0.03 (19)	<0.05
Superior	-0.06 ± 0.19 (27)	-0.11 ± 0.15 (21)	0.31	0.11 ± 0.09 (26)	0.12 ± 0.04 (19)	0.95
Acetabular quotient				216.6 ± 24.0 (24)	211.3 ± 21.9 (20)	0.51

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TABLE I: Radiographic Data Before Reduction and at Two Years After Reduction*

*The values are given as the average and the standard deviation, with the number of hips in parentheses.

	Before Reduction			Two Years After Reduction
Severin Class I or II at Follow-up*	Severin Class III or IV at Follow-up*	P Value	Severin Class I or II at Follow-up*	Severin Class III or IV at Follow-up*	P Value
Acetabular index (degrees)	36.5 ± 6.1 (32)	37.8 ± 5.3 (24)	0.38	26.0 ± 5.6 (30)	27.2 ± 4.2 (23)	0.40
Centering ratio
Lateral	1.06 ± 0.11 (27)	1.07 ± 0.10 (21)	0.71	0.72 ± 0.03 (26)	0.74 ± 0.03 (19)	<0.05
Superior	-0.06 ± 0.19 (27)	-0.11 ± 0.15 (21)	0.31	0.11 ± 0.09 (26)	0.12 ± 0.04 (19)	0.95
Acetabular quotient				216.6 ± 24.0 (24)	211.3 ± 21.9 (20)	0.51

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TABLE II: Radiographic Data at Six to Eight Years of Age and at the Final Follow-up Evaluation

*The values are given as the average and the standard deviation, with the number of hips in parentheses.

	Six to Eight Years of Age			Final Follow-up Evaluation
Severin Class I or II at Follow-up*	Severin Class III or IV at Follow-up*	P Value	Severin Class I or II at Follow-up*	Severin Class III or IV at Follow-up*	P Value
Acetabular index (degrees)	19.6 ± 4.7 (30)	25.7 ± 3.3 (18)	<0.0001
Acetabular angle (degrees)	46.5 ± 4.1 (32)	49.3 ± 2.6 (17)	<0.01	41.7 ± 6.8 (34)	46.9 ± 3.7 (24)	<0.0005
Acetabular quotient	266.2 ± 35.4 (30)	231.1 ± 19.6 (17)	<0.0001	293.8 ± 48.4 (32)	231.4 ± 47.5 (24)	<0.0001
Acetabular roof (ACM) angle (degrees)	61.4 ± 3.0 (28)	64.9 ± 1.9 (17)	<0.0001	58.4 ± 7.0 (28)	65.0 ± 4.5 (24)	<0.0001
Epiphysis-femoral neck (KE) angle (degrees)	21.6 ± 6.3 (30)	21.4 ± 7.5 (18)	0.89	30.2 ± 8.7 (34)	29.6 ± 9.3 (24)	0.79
Epiphyseal index	38.9 ± 8.3 (29)	35.6 ± 6.9 (18)	0.17
Femoral head spherical index	31.4 ± 28.0 (29)	19.4 ± 25.5 (17)	0.15	49.2 ± 29.7 (23)	51.5 ± 28.7 (14)	0.82
Femoral head uncoverage (percent)	18.3 ± 7.5 (27)	29.0 ± 7.4 (18)	<0.0001	16.5 ± 8.9 (33)	36.9 ± 11.4 (24)	<0.0001
Articulotrochanteric distance (cm)				2.3 ± 0.7 (28)	2.6 ± 0.9 (24)	0.20

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TABLE II: Radiographic Data at Six to Eight Years of Age and at the Final Follow-up Evaluation

*The values are given as the average and the standard deviation, with the number of hips in parentheses.

	Six to Eight Years of Age			Final Follow-up Evaluation
Severin Class I or II at Follow-up*	Severin Class III or IV at Follow-up*	P Value	Severin Class I or II at Follow-up*	Severin Class III or IV at Follow-up*	P Value
Acetabular index (degrees)	19.6 ± 4.7 (30)	25.7 ± 3.3 (18)	<0.0001
Acetabular angle (degrees)	46.5 ± 4.1 (32)	49.3 ± 2.6 (17)	<0.01	41.7 ± 6.8 (34)	46.9 ± 3.7 (24)	<0.0005
Acetabular quotient	266.2 ± 35.4 (30)	231.1 ± 19.6 (17)	<0.0001	293.8 ± 48.4 (32)	231.4 ± 47.5 (24)	<0.0001
Acetabular roof (ACM) angle (degrees)	61.4 ± 3.0 (28)	64.9 ± 1.9 (17)	<0.0001	58.4 ± 7.0 (28)	65.0 ± 4.5 (24)	<0.0001
Epiphysis-femoral neck (KE) angle (degrees)	21.6 ± 6.3 (30)	21.4 ± 7.5 (18)	0.89	30.2 ± 8.7 (34)	29.6 ± 9.3 (24)	0.79
Epiphyseal index	38.9 ± 8.3 (29)	35.6 ± 6.9 (18)	0.17
Femoral head spherical index	31.4 ± 28.0 (29)	19.4 ± 25.5 (17)	0.15	49.2 ± 29.7 (23)	51.5 ± 28.7 (14)	0.82
Femoral head uncoverage (percent)	18.3 ± 7.5 (27)	29.0 ± 7.4 (18)	<0.0001	16.5 ± 8.9 (33)	36.9 ± 11.4 (24)	<0.0001
Articulotrochanteric distance (cm)				2.3 ± 0.7 (28)	2.6 ± 0.9 (24)	0.20

Materials and Methods

Introduction | Materials and Methods | Results | Discussion | References

We reviewed the medical records and radiographs of all children with developmental hip dysplasia treated at our institution between July 1935 and June 1991. We identified all patients with radiographic evidence of type-II growth disturbance according to the systems of Bucholz and Ogden⁵ and Kalamchi and MacEwen¹⁵. Patients were excluded if they had subluxation of the hip without dislocation; dislocation due to neuromuscular disease, arthrogryposis, or a teratological condition; type-II growth disturbance in the contralateral, nondysplastic hip; growth disturbance following primary or secondary osteotomy of the femur or acetabulum; lack of regular radiographic follow-up; or a final follow-up evaluation before the age of ten years. Fifty-eight hips in forty-eight patients were included. There were forty-two female and six male patients. Thirty-five patients had a unilateral dislocation and thirteen, a bilateral dislocation. Eleven of the patients with a bilateral dislocation had the type-II growth disturbance bilaterally, and two had it unilaterally. Data on one hip in a patient with bilateral type-II growth disturbance were excluded because an acetabular procedure had been performed at the age of five years and, thus, our criterion for duration of follow-up was not met.

Thirty-six hips underwent closed reduction, and twenty-two underwent open reduction through an anteromedial approach¹⁹. Fourteen hips had been treated with skin or skeletal traction before the reduction. After removal of the cast, all patients wore a flexion-abduction brace full-time for two months and then at night and while napping for several years. The average age was twenty-two months (range, three to ninety-seven months) at the time of the reduction and twenty-one years (range, ten to fifty-five years) at the time of the latest follow-up evaluation. Five hips were treated with a secondary reconstructive operation at an average age of fifteen years (range, ten to twenty-seven years) because of persistent acetabular dysplasia and subluxation. These operations included a Chiari acetabular osteotomy in two hips, a Staheli slotted acetabular augmentation in one hip, and a femoral varus derotation osteotomy in two hips. For these hips, only data until the secondary operation were included to exclude subsequent changes in acetabular development caused by that operation.

The Severin classification²⁶ was used to evaluate the hip at the most recent follow-up evaluation or immediately before a secondary procedure was performed. We defined a satisfactory result as Severin class I (an excellent result) or II (a good result) and an unsatisfactory result as Severin class III (a fair result) or IV (a poor result). To increase the accuracy and reliability of the diagnosis of type-II growth disturbance and of the Severin classification, the radiographs were independently reviewed in chronological order by three of us and the consensus diagnosis was recorded.

All radiographs were examined for early specific changes in the epiphysis, physis, and metaphysis thought to be related to later development of valgus tilt of the epiphysis^5,15,16,31. These included irregular fragmentation or ossification in the lateral part of the epiphysis, lateral physeal irregularity and premature fusion, and a defect in the lateral portion of the metaphysis. We also examined the radiographs for evidence of inverted L-shaped growth lines in the metaphysis²⁰ - that is, lines in which the short horizontal arm of the L corresponded to the central limb of the physis and the long vertical arm of the L appeared subjacent to the greater trochanter.

Radiographic measurements were made over time by one of us (H. W. K.) with the use of a digitizer program. Comparisons were made between hips with satisfactory results and those with unsatisfactory results at four time-points: before the reduction, at two years after the reduction, at six to eight years of age, and at the time of the final follow-up. Not all measurements could be made for all hips because of difficulty defining some anatomical landmarks and the lack of consistently reproducible parameters for assessing consecutive radiographic changes through skeletal maturity. Normal values for angles and indexes were derived from the literature^1,3,35 and from the contralateral, normal hips.

Femoral head displacement before the reduction was evaluated with use of the Tönnis grading system³⁴ and the centering ratios of Smith et al.²⁹. Parameters used to assess acetabular development and the head-acetabulum relationship included the acetabular index of Hilgenreiner^33,35; acetabular angle of Sharp²⁷; acetabular depth, width, and quotient^8,35; acetabular roof angle (ACM angle of Idelberger and Frank³⁵); percentage of uncoverage of the femoral head⁸; center-edge angle of Wiberg³⁷; and articulotrochanteric distance^10,31. The epiphysis-femoral neck (KE) angle³⁵ was measured to assess inclination of the epiphyseal plate relative to the perpendicular axis of the femoral neck and to characterize the degree of valgus tilt of the capital epiphysis. Coxa magna¹⁰ was evaluated as present or absent. The epiphyseal index of Eyre-Brook³⁵ and the femoral head spherical index^11,35 were calculated to evaluate flattening of the femoral head. Femoral head sphericity was also evaluated according to Mose's criteria⁸. The degree of relative proximal migration of the greater trochanter¹⁶ was assessed by measuring the distance between the tip of the greater trochanter and the most proximal point of any portion of the physis on the anteroposterior radiograph; it was defined as mild when the tip of the greater trochanter did not reach the physeal line and as moderate when the tip reached or passed just proximal to the physeal line. Degenerative changes were classified with use of the criteria of Boyer et al.².

The association between the independent variables and the dependent variable (the Severin class [Severin class I or II compared with Severin class III or IV]) was assessed at each time-point with use of the Student t test, analysis of variance, or the Fisher exact test as appropriate. Alpha was set at 0.05. The relationship between the independent variables was assessed with use of Pearson correlation coefficients.

Results

Introduction | Materials and Methods | Results | Discussion | References

Radiographically, lateral tilting of the capital femoral epiphysis, a hallmark for the diagnosis of type-II growth disturbance, was evident by an average age of ten years of age (range, four to fourteen years of age). In general, inclination of the epiphyseal plate became progressively more horizontal or even reversed over time, as reflected by grade-3 or 4 deviation from the age-related normal range at the time of the final follow-up³⁵. The average epiphysis-femoral neck angle in the dislocated hips was not significantly different from that in the contralateral, normal hips until the final follow-up evaluation, when it measured 30.0 degrees in the dislocated hips compared with 25.7 degrees in the normal hips (p < 0.002). Serial examination of all radiographs failed to identify any consistent early patterns of change in the epiphysis, physis, or metaphysis that could be related to later development of valgus tilt of the epiphysis. Although various early radiographic findings could be recognized, those findings were not present in all hips and occasionally even changes in the ossific nucleus were absent altogether. Within one year after the reduction, complete irregular fragmentation of the femoral epiphysis, the so-called type-I change described by Salter et al.²⁵, was observed in seventeen hips (29 percent). Early detection of premature physeal closure was difficult in many hips. With regard to the metaphyseal changes, a growth line described by O'Brien et al.^20,21, whether normal or abnormal, could be detected in eighteen hips (31 percent) within one year after the reduction.

All hips initially were completely dislocated; fifteen hips (26 percent) were Tönnis³⁴ grade III, and forty-three (74 percent) were Tönnis grade IV. The ossific nucleus was present in forty-nine (84 percent) of the fifty-eight hips before the reduction. The average acetabular index was 37.1 ± 5.7 degrees (range, 20.7 to 53.1 degrees) in the dislocated hips compared with 21.8 ± 4.3 degrees (range, 11.7 to 28.2 degrees) in the contralateral, normal hips.

With use of the most recent follow-up radiographs, thirty-four hips (59 percent) were rated as satisfactory (three, as Severin class I, and thirty-one, as Severin class II) and twenty-four were rated as unsatisfactory (fourteen, as Severin class III, and ten, as Severin class IV). According to Mose's criteria, four (7 percent) of fifty-seven hips had no deformity of the femoral head, forty-four (77 percent) had mild deformity, six (11 percent) had moderate deformity, and three (5 percent) had severe deformity; we were unable to evaluate deformity in one hip. Four hips (7 percent) showed degenerative changes (average age, thirty-four years; range, twenty-five to thirty-seven years). The degree of relative proximal migration of the greater trochanter was normal in twenty (34 percent) of the fifty-eight hips, mild in thirty (52 percent), and moderate in eight (14 percent). Coxa magna was present in six (17 percent) of the thirty-five hips for which it was possible to perform this evaluation.

Association Between Parameters Before Reduction and Final Severin Classification (Table I)

With the number of hips available for study, we did not find gender, age at reduction, side of involvement, bilateral involvement, type of reduction, or preoperative traction to be significantly associated with the final Severin classification. The presence or absence of the ossific nucleus, the acetabular index, and the degree of preoperative displacement of the femoral head (Tönnis grade and superior and lateral centering ratios) also were not significant factors differentiating between the satisfactory and unsatisfactory groups.

Association Between Parameters at Two Years After Reduction (Table I) and Those at Six to Eight Years of Age (Table II) with Final Severin Classification

At two years after the reduction, the lateral centering ratio was within the reported normal range (0.60 to 0.85³⁵) in all hips. All but fifteen hips had a normal superior centering ratio (range in series, -0.09 to 0.25; reported normal range³⁵, 0.10 to 0.20). There was a small but significant difference in the average lateral ratio between the satisfactory and unsatisfactory hips (0.72 ± 0.03 compared with 0.74 ± 0.03, p < 0.05). With the number of hips available for study, we did not detect any significant association between the superior centering ratio or acetabular development (as measured by the acetabular index and the acetabular quotient) and the Severin classification at the most recent follow-up examination.

By six to eight years of age (average, seven years of age), there was a significant difference in acetabular development between the satisfactory and unsatisfactory hips (Table II). There were significant differences in the acetabular index (p < 0.0001), acetabular angle (p < 0.01), acetabular quotient (p < 0.0001), acetabular roof angle (p < 0.0001), and percentage of femoral head uncoverage (p < 0.0001). There was no significant difference between the satisfactory and unsatisfactory hips in terms of the femoral head spherical index, the epiphyseal index, or the epiphysis-femoral neck angle.

Correlations between the epiphysis-femoral neck angle and the other independent variables ranged from -0.21 (epiphyseal index) to 0.15 (center-edge angle).

Comparison of Radiographic Parameters with Severin Classification at the Latest Follow-up Evaluation (Table II)

At the final follow-up evaluation, the acetabular angle (p < 0.0005), acetabular quotient (p < 0.0001), acetabular roof angle (p < 0.0001), and percentage of femoral head uncoverage (p < 0.0001) were significantly different between the satisfactory and unsatisfactory hips. There was no significant difference in the articulotrochanteric distance, femoral head spherical index, or epiphysis-femoral neck angle between the two groups. Correlations between the epiphysis-femoral neck angle and the other independent variables ranged from -0.30 (articulotrochanteric distance) to 0.20 (acetabular quotient).

Discussion

Introduction | Materials and Methods | Results | Discussion | References

Several articles discussing growth disturbance (aseptic necrosis) of the capital femoral epiphysis after reduction for the treatment of developmental hip dysplasia have been mainly concerned with the extent of involvement^5,15,16,34. Of the various types of disturbance, type II is considered the most prevalent (average, 25 percent of cases). The pathogenesis of a type-II growth disturbance is unknown, but several hypotheses suggest mechanical or ischemic insults. The medial femoral circumflex artery may become occluded between the femoral neck and the posterior part of the acetabular rim as the hip is abducted, resulting in ischemic necrosis leading to lateral growth impairment of the femoral neck⁵. Another possible explanation is a growth disturbance of the germinal layer of the lateral part of the femoral physis or an abnormally sustained compressive force transmitted through the epiphysis⁶. The fact that this type of growth disturbance often is not evident until a bar develops when the cartilage ossifies^6,28, and the fact that the ossification of the subcapital growth plate normally begins on the lateral side and progresses medially^9,28, may explain the late appearance of valgus tilt of the femoral head.

Several early radiographic signs are thought to predict later appearance of valgus tilt of the epiphysis^5,15,16,31. Regarding epiphyseal changes, Bucholz and Ogden⁵ observed that the secondary ossification center always demonstrates changes at some point following reduction. However, twelve (21 percent) of the hips in our series did not show any changes in the ossific nucleus, a finding that is consistent with other observations^6,15. Seventeen hips (29 percent) in our series showed complete irregular fragmentation after reduction²⁵. Whether this represents damage to the epiphyseal cartilage or merely multiple ossification centers that eventually coalesce could not be determined. We agree with others^{5,15,16,21,31} that ossific nucleus changes alone have no prognostic importance. A variable degree of localized premature fusion or even irregularity in the lateral aspect of the physis and adjacent metaphysis could be detected. In addition, substantial osseous bridging across the superior portion of the physeal plate could not be clearly identified early after reduction in many hips.

Another area of uncertainty is the issue of the inverted L-shaped growth lines detected in the metaphysis²⁰. O'Brien et al.²¹ suggested that abnormal growth lines would be present only in patients who subsequently manifested abnormal patterns of growth of the proximal physis and that flattening of the L-shaped line is associated with lateral physeal arrest. However, we observed hips that demonstrated normal growth lines but nonetheless had a type-II growth disturbance later. Moreover, the intensity of these lines was variable. Many of the anteroposterior radiographs in our series were not made with the hip in full internal rotation, which may account for some of these lines being overlooked.

Growth disturbance of the capital femoral epiphysis and its associated problems are serious concerns in the treatment of developmental hip dysplasia^{4,5,7,8,10,12,15,18,36}. It has been associated with relative trochanteric overgrowth, limb-length discrepancy, and, most importantly, acetabular dysplasia. However, the majority of hips in this series demonstrated only mild relative proximal migration of the greater trochanter, and the articulotrochanteric distance was not found to be a factor distinguishing between satisfactory and unsatisfactory results.

Of particular concern in this context is the presence of persistent acetabular dysplasia, a major contributing factor in osteoarthritis^{4,7,8,10,12-14,18,30,32,36}. In general, residual acetabular dysplasia has been associated with poor reduction, older age at reduction, and femoral head deformity. We found no evidence that any of these factors were responsible for dysplasia in this series. Maintenance of concentric reduction and equivalent acetabular development between the satisfactory and unsatisfactory hips at two years eliminate the possibility of detrimental effects of early incongruency or residual subluxation on acetabular development. Although it should be noted that femoral heads were mildly flattened, this deformity was not sufficient to produce a corresponding acetabular deformity (Fig. 1-A, Fig. 1-B, and Fig. 1-C).

Type-II growth disturbance is believed to lead to acetabular dysplasia as a result of progressive valgus tilt of the femoral head^5,6,15,16 and secondary subluxation. By definition, all hips in this study had an abnormal degree of valgus tilt of the femoral head (Fig. 2-A, Fig. 2-B, and Fig. 2-C), but only ten (17 percent) of the fifty-eight were classified as Severin class IV, indicating that subluxation is not inevitable in hips with this type of disturbance. In addition, the epiphysis-femoral neck angle was not associated with the percentage of femoral head uncoverage, the center-edge angle, or the acetabular quotient at any point in this series.

Acetabular dysplasia did develop in 41 percent of the hips in our series, but it appears that the dysplasia preceded the appearance of a lateral growth disturbance of the capital femoral epiphysis. Although the depth of the acetabulum is increased at puberty by the development of three centers of secondary ossification in the hyaline cartilage surrounding the acetabular cartilage, the majority of acetabular development occurs by eight years of age^17,22,23. After this age, accommodation of acetabular shape to a deformed femoral head may not be possible. Our radiographic results show that acetabular development was already inadequate in the Severin class-III and IV hips by an average of seven years of age, prior to the appearance of the growth disturbance, which was noted at an average of ten years of age. At no time during the development of the acetabulum was the degree of valgus tilt of the femoral head prognostic of outcome.

Long-term studies of hip growth after a growth disturbance of the capital femoral epiphysis have demonstrated that careful follow-up and observation of growth and the head-acetabulum relationship are necessary so that preventive measures can be taken to correct hip deformity^7,8,18,30-32. However, many of the patients with a type-II growth disturbance in these reports had not been followed to skeletal maturity. In addition, the amount of acetabular development prior to the appearance of valgus tilt of the femoral head, which may have a greater influence on the final shape of the acetabulum than the later-appearing femoral head growth disturbance, was not assessed. Also, although classification systems based on physeal involvement are very helpful for comparing patients treated by various methods, valid evaluation requires follow-up radiographs over a considerable period of time. Radiographic evidence of aseptic necrosis usually appears within the first or second year following reduction^5,15; however, evidence of a type-II growth disturbance may appear at any time until skeletal maturity. Substantial growth abnormalities, especially in hips with a type-II growth disturbance, may not be manifest before the second growth-spurt period, when the capital femoral epiphysis becomes the dominant growth center of the proximal part of the femur. There is also the possibility of the hip classification changing over time. For example, involvement of the lateral portion of the physis can induce central or total involvement, resulting in a reclassification to a type-III or type-IV growth disturbance^15,31.

In conclusion, a lateral growth disturbance of the capital femoral epiphysis is not necessarily associated with poor acetabular development. In many of the hips in our series, the femoral head was deeply seated within a well developed acetabulum despite extreme valgus tilt of the femoral head. The residual acetabular dysplasia at the time of the final follow-up is more reflective of an already poorly developed acetabulum prior to any evidence of lateral physeal arrest. Our results emphasize the importance of monitoring acetabular development rather than searching for radiographic changes of physeal arrest, which are difficult to detect in young children.

References

Introduction | Materials and Methods | Results | Discussion | References

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Fig. 1:: Anteroposterior radiograph of the pelvis and hips of a thirteen-month-old child with a right hip dislocation. The patient was treated by adductor tenotomy and closed reduction.

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Fig 2-A:: Anteroposterior radiograph of the pelvis and hips of a forty-five-month-old child with a high right hip dislocation. The patient was treated by adductor tenotomy and closed reduction.

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TABLE I: Radiographic Data Before Reduction and at Two Years After Reduction*

*The values are given as the average and the standard deviation, with the number of hips in parentheses.

	Before Reduction			Two Years After Reduction
Severin Class I or II at Follow-up*	Severin Class III or IV at Follow-up*	P Value	Severin Class I or II at Follow-up*	Severin Class III or IV at Follow-up*	P Value
Acetabular index (degrees)	36.5 ± 6.1 (32)	37.8 ± 5.3 (24)	0.38	26.0 ± 5.6 (30)	27.2 ± 4.2 (23)	0.40
Centering ratio
Lateral	1.06 ± 0.11 (27)	1.07 ± 0.10 (21)	0.71	0.72 ± 0.03 (26)	0.74 ± 0.03 (19)	<0.05
Superior	-0.06 ± 0.19 (27)	-0.11 ± 0.15 (21)	0.31	0.11 ± 0.09 (26)	0.12 ± 0.04 (19)	0.95
Acetabular quotient				216.6 ± 24.0 (24)	211.3 ± 21.9 (20)	0.51

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TABLE I: Radiographic Data Before Reduction and at Two Years After Reduction*

*The values are given as the average and the standard deviation, with the number of hips in parentheses.

	Before Reduction			Two Years After Reduction
Severin Class I or II at Follow-up*	Severin Class III or IV at Follow-up*	P Value	Severin Class I or II at Follow-up*	Severin Class III or IV at Follow-up*	P Value
Acetabular index (degrees)	36.5 ± 6.1 (32)	37.8 ± 5.3 (24)	0.38	26.0 ± 5.6 (30)	27.2 ± 4.2 (23)	0.40
Centering ratio
Lateral	1.06 ± 0.11 (27)	1.07 ± 0.10 (21)	0.71	0.72 ± 0.03 (26)	0.74 ± 0.03 (19)	<0.05
Superior	-0.06 ± 0.19 (27)	-0.11 ± 0.15 (21)	0.31	0.11 ± 0.09 (26)	0.12 ± 0.04 (19)	0.95
Acetabular quotient				216.6 ± 24.0 (24)	211.3 ± 21.9 (20)	0.51

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TABLE II: Radiographic Data at Six to Eight Years of Age and at the Final Follow-up Evaluation

*The values are given as the average and the standard deviation, with the number of hips in parentheses.

	Six to Eight Years of Age			Final Follow-up Evaluation
Severin Class I or II at Follow-up*	Severin Class III or IV at Follow-up*	P Value	Severin Class I or II at Follow-up*	Severin Class III or IV at Follow-up*	P Value
Acetabular index (degrees)	19.6 ± 4.7 (30)	25.7 ± 3.3 (18)	<0.0001
Acetabular angle (degrees)	46.5 ± 4.1 (32)	49.3 ± 2.6 (17)	<0.01	41.7 ± 6.8 (34)	46.9 ± 3.7 (24)	<0.0005
Acetabular quotient	266.2 ± 35.4 (30)	231.1 ± 19.6 (17)	<0.0001	293.8 ± 48.4 (32)	231.4 ± 47.5 (24)	<0.0001
Acetabular roof (ACM) angle (degrees)	61.4 ± 3.0 (28)	64.9 ± 1.9 (17)	<0.0001	58.4 ± 7.0 (28)	65.0 ± 4.5 (24)	<0.0001
Epiphysis-femoral neck (KE) angle (degrees)	21.6 ± 6.3 (30)	21.4 ± 7.5 (18)	0.89	30.2 ± 8.7 (34)	29.6 ± 9.3 (24)	0.79
Epiphyseal index	38.9 ± 8.3 (29)	35.6 ± 6.9 (18)	0.17
Femoral head spherical index	31.4 ± 28.0 (29)	19.4 ± 25.5 (17)	0.15	49.2 ± 29.7 (23)	51.5 ± 28.7 (14)	0.82
Femoral head uncoverage (percent)	18.3 ± 7.5 (27)	29.0 ± 7.4 (18)	<0.0001	16.5 ± 8.9 (33)	36.9 ± 11.4 (24)	<0.0001
Articulotrochanteric distance (cm)				2.3 ± 0.7 (28)	2.6 ± 0.9 (24)	0.20

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TABLE II: Radiographic Data at Six to Eight Years of Age and at the Final Follow-up Evaluation

*The values are given as the average and the standard deviation, with the number of hips in parentheses.

	Six to Eight Years of Age			Final Follow-up Evaluation
Severin Class I or II at Follow-up*	Severin Class III or IV at Follow-up*	P Value	Severin Class I or II at Follow-up*	Severin Class III or IV at Follow-up*	P Value
Acetabular index (degrees)	19.6 ± 4.7 (30)	25.7 ± 3.3 (18)	<0.0001
Acetabular angle (degrees)	46.5 ± 4.1 (32)	49.3 ± 2.6 (17)	<0.01	41.7 ± 6.8 (34)	46.9 ± 3.7 (24)	<0.0005
Acetabular quotient	266.2 ± 35.4 (30)	231.1 ± 19.6 (17)	<0.0001	293.8 ± 48.4 (32)	231.4 ± 47.5 (24)	<0.0001
Acetabular roof (ACM) angle (degrees)	61.4 ± 3.0 (28)	64.9 ± 1.9 (17)	<0.0001	58.4 ± 7.0 (28)	65.0 ± 4.5 (24)	<0.0001
Epiphysis-femoral neck (KE) angle (degrees)	21.6 ± 6.3 (30)	21.4 ± 7.5 (18)	0.89	30.2 ± 8.7 (34)	29.6 ± 9.3 (24)	0.79
Epiphyseal index	38.9 ± 8.3 (29)	35.6 ± 6.9 (18)	0.17
Femoral head spherical index	31.4 ± 28.0 (29)	19.4 ± 25.5 (17)	0.15	49.2 ± 29.7 (23)	51.5 ± 28.7 (14)	0.82
Femoral head uncoverage (percent)	18.3 ± 7.5 (27)	29.0 ± 7.4 (18)	<0.0001	16.5 ± 8.9 (33)	36.9 ± 11.4 (24)	<0.0001
Articulotrochanteric distance (cm)				2.3 ± 0.7 (28)	2.6 ± 0.9 (24)	0.20