Anterior Approach for Open Reduction of the Developmentally Dislocated Hip
DEFINITION
Developmental dysplasia or dislocation of the hip (DDH) is a disorder that may affect the development and stability of the hip joint during the critical period of growth, either in utero or after birth.
This may lead to dysplasia, subluxation, or frank dislocation of the hip joint.
ANATOMY
Growth of the hip joint is genetically and mechanically determined.
In the first trimester, the structures of the joint begin as a single mass of scleroblastema with a globular femoral head that becomes cartilage at 6 weeks.
By 8 weeks' gestation, the start of the fetal period, vascular invasion leads to endochondral ossification.
The joint space develops by degeneration at 7 to 8 weeks, and the structure of the joint is well apparent by week 11.
A round and reduced femoral head influences the concave shape of the acetabulum to develop.
Acetabular growth depends on interstitial, appositional, periosteal new bone and secondary centers of ossification growth.
In the first two trimesters of fetal life, the acetabulum is a hemisphere with a depth 50% of its diameter. However, by the time of birth, the depth is only 40% of its diameter, which may contribute to instability at birth.
The acetabular labrum, which resembles an O ring (FIG 1A), contributes considerable mechanical stability and proprioceptive feedback (FIG 1B).
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FIG 1 • A. Femoral head and acetabulum of newborn hip. Note the concentric nature of the acetabular labrum, resembling in form and function an O ring. B. Acetabular labrum in a second trimester human fetus.
S100 stain shows nerve tissue extending to the tip of the labrum. This is evidence of the proprioceptive function of the labrum. C. Coronal section of a third trimester fetal hip joint showing the extensive cartilaginous nature of the femoral chondroepiphysis and the acetabular cartilage. (A: Courtesy of Gene Mandell, MD.)
By 8 years of age, the acetabular shape is for the most part determined and thus surgical reduction is less advised, especially if the dislocation is bilateral.
There is continued growth into adolescence, with the triradiate cartilage fusing by 13 years in girls and 15 years in boys.
Closure of the triradiate cartilage may occur earlier in the dysplastic hip. By adulthood, the acetabular depth is 60% of its diameter.
The proximal femur is formed initially as a single chondroepiphysis (FIG 1C), with the ossific nucleus typically appearing in infancy at 2 to 8 months of age.
There may be some side-to-side size discrepancy in appearance.
The greater trochanter nucleus appears at about 3 years in girls and 5 years in boys, with the lesser trochanter appearing by age 6 to 11 years.
The femoral head vascularity is mostly from the medial and somewhat from the lateral femoral circumflex arteries. Because it is an intra-articular dome-shaped structure, this blood supply is susceptible to injury.
PATHOGENESIS
Around the time of birth, capsular laxity, a normally shallow acetabulum, and abnormal mechanical forces, such as those seen in breech presentation, may cause the hip capsule to be lax and to dislocate.
An absent or subluxated femoral head eventually leads to a flat, egg-shaped acetabulum, which is a consistent finding on three-dimensional computer modeling performed of the acetabulum (FIG 2A).
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FIG 2 • A. Three-dimensional computer-generated hip model of adolescent with long-standing left hip developmental dysplasia. The acetabulum is shallow and elongated in its superior aspect, resembling an egg.
B. Intraoperative left hip arthrogram of a dislocated femoral head (FH). Arrowhead shows the neolimbus (NL) contributing to blocking the reduction of the femoral head. LT, ligamentum teres.
With time, the neolimbus, which is abnormally formed articular cartilage, can develop at the edge of the acetabulum. It can be a barrier to reduction (FIG 2B).8
A steep, maloriented growth plate; intra-articular obstructions; and stunting of periosteal new bone formation all in time contribute to further deformity.
Mechanical blocks to reduction include the anteromedial capsule, ligamentum teres, psoas tendon, neolimbus, transverse acetabular ligament (which is an inferior medial extension of the acetabular labrum), and intra-articular pulvinar tissue.
An inverted labrum is rarely a block to reduction.
The average unit load of human and animal joint cartilage is 25 kg/cm2.
Hips with acetabular dysplasia, and particularly with subluxation, have about 25% less contact area and more unit load (stress) per area of contact.
There is an inverse relationship between greater contact pressures and the onset of osteoarthritis.
NATURAL HISTORY
Newborn period
About 1 in 60 infants have instability at birth, with 60% of cases resolving in the first week of life and 88% by the first 2 months. Thus, about 1.5 in 1000 have a true dislocation.2
Muscle activity is considered important for recovery and is the basis of the Pavlik harness success.
Untreated acetabular dysplasia with subluxation or dislocation
The natural history of hip dysplasia when subluxation or dislocation is present is predictable. The long-term outcome is worse than with acetabular dysplasia without subluxation.13
The onset of symptoms and radiographic deterioration is directly related to the degree of subluxation and dysplasia.
Clinical symptoms, typically pain, may antecede the radiographic deterioration by 10 years.
If the hip is completely dislocated, limb length discrepancy and back and knee pain are common, whereas painful arthritis correlates with the presence of a false acetabulum and its adverse effect on the femoral head articular cartilage.
Acetabular dysplasia with no subluxation
The natural history of acetabular dysplasia is much less predictable when subluxation or dislocation is absent.13
During childhood, hips that are well centered improve their acetabular dysplasia, although not always to normal, whereas the hip that is radiologically eccentric typically does not improve.
If the center-edge angle in the mature hip is less than 20 degrees, the hip will likely develop arthritis sometime during the patient's lifetime. However, it is difficult to determine how early in life the deterioration will occur.
Although hips with acetabular dysplasia can spontaneously improve, this improvement is not predictable or necessarily complete.10
A hip with a persistently upsloping lateral margin seen on an anteroposterior (AP) radiograph generally develops arthritis by late adulthood.11
PATIENT HISTORY AND PHYSICAL FINDINGS
Because 75% of DDH occurs in female infants with no other risk factures, clinical examination of all infants is the most important method of detecting hip dysplasia.
All newborn infants should receive a gentle and focused examination of the hips, including range of motion and Ortolani maneuver.
The physical examination of the newborn, rather than imaging studies, should determine the diagnosis of DDH and the need for treatment.
An Ortolani-positive hip is dislocated or subluxated and the examiner perceives that the hip partially reduces with abduction. After several months of age, the hip may appear stable on examination but may still be
dislocated due to tightening of the soft tissue structures about the hip.
The child is examined for any abnormal skin creases (FIG 3). Proximal skin creases may indicate a dislocated hip or a short femur. The examiner should also note the
level of the popliteal skin crease, the position of the knee, and any lateral displacement of the hip.
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FIG 3 • A,B. Abnormal skin creases.
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A simple, high-pitched and commonly felt “hip click” is not a sign of instability or dislocation.
Hip instability decreases with time, whereas deformity, such as limited hip abduction, increases with time.
The young infant with a dislocated hip may have normal abduction until several months of age. There may be limited abduction in developmental coxa vara. Abduction may appear to be normal if both hips are dislocated.
The upper extremities, spine, and feet are always inspected to evaluate for possible generalized conditions such as arthrogryposis or neuromuscular conditions.
In the child of walking age, a delay of walking may be the first indicator that the hip is dislocated.
Dipping of the pelvis and shoulder (Trendelenburg gait), female profile (pelvic widening from the dislocation), and shortening of the thigh (Galeazzi sign) are classic signs of a dislocated hip in the older child.
The Galeazzi test may also be abnormal if the child has a congenital short femur.
Additional signs of Trendelenburg gait include side-to-side waddling, indicating weak hip abductors, or the examiner may see lurching, indicating weak hip extensors. The child may stand or walk with hyperlordosis. These are proximal compensations for a hip dislocation and the resulting inadequate muscle strength to support the pelvis.
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FIG 4 • A. Coronal section ultrasound imaging through the most posterior aspect of the acetabulum. The femoral head is well visualized dislocated from the acetabulum. B. Seven-month-old child with a dislocated left hip. The acetabulum is steep. The femoral ossific nucleus is not present. There is a break in the Shenton line on the left and it is normal on the right. C-E. Radiographs of young adult with high-grade right acetabular dysplasia. C. On the AP pelvic view, the center-edge angle (CEA) on the left is low normal (26 degrees); on the right, it is 10 degrees. The Shenton line is intact, indicating that there is no subluxation. D,E. Right hip false-profile views.
Right hip CEA is 0 degrees and left hip CEA is 22 degrees. F. Left hip intraoperative arthrogram shows concentric reduction. There is no pooling of the intra-articular contrast medially.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Ultrasound is a useful imaging method up to 6 months of age (FIG 4A).
The two most common indications for ultrasound imaging are for screening the asymptomatic infant considered to be at high risk for hip dislocation (girls born breech have a 133/1000 risk of DDH) and for following an infant with proven DDH, especially during Pavlik harness treatment.
The AP radiograph is most useful in infants older than 6 months of age.
In children older than 3 years of age, the Shenton line is a reliable indicator of subluxation (FIG 4B). The Von Rosen view in abduction and internal rotation shows the ability of the femoral head to reduce.
In the adolescent or adult hip, a standing AP pelvis view is obtained with measurement of the center-edge angle, as well as standing false-profile views of each hip joint (FIG 4C-E).
The normal center-edge angle on the AP pelvic radiograph is greater than 24 degrees.
Decision analysis model indicates that the most effective way to prevent hip arthritis by age 60 years is to do physical examination screening on the hips of all infants and to use ultrasound selectively on those infants
with high risk factors.5
Intraoperative arthrography can show whether the femoral head is fully reducible with no medial pooling of contrast (FIG 4F).
If the femoral head does not easily reduce and remain stable without excessive hip abduction, an open reduction
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is used to address the extra-articular and intra-articular blocks to reduction.
Computed tomography (CT) scanning is commonly used to evaluate the adequacy of a closed or open reduction after surgery and for preoperative planning of pelvic or femoral osteotomy.
However, even a limited CT scan can deliver over 100 times the radiation of daily background or that from a single chest radiograph. If using CT for a child, it is important to child size the peak kilovoltage and milliam-
pere and scan only the indicated area with one scan.11
For imaging after closed reduction and casting, magnetic resonance imaging (MRI) can replace the use of CT and be accomplished with a limited study and no radiation.3
DIFFERENTIAL DIAGNOSIS
Septic hip dislocation: This is the most important diagnosis to consider in the young infant. Teratologic hip dislocation (arthrogryposis)
Neuromuscular dislocation (most commonly cerebral palsy and spina bifida) Traumatic hip dislocation
Developmental coxa vara: easy to mistake as DDH before the ossific nucleus is present Congenital short femur
Instability and dysplasia related to underlying condition (Down syndrome, Ehlers-Danlos syndrome, Charcot-Marie-Tooth disease); commonly bilateral
NONOPERATIVE MANAGEMENT
The basic principles of treatment are to obtain a concentric, stable reduction while avoiding osteonecrosis; to promote normal growth of the hip; and to achieve normal long-term function.
The treatment of DDH depends on the age of the child and thus the stage of development of the hip joint.
Generally, the earlier that treatment is initiated, the more likely that less invasive treatment will be successful and that a better outcome will result.
Treatment options range from observation to a Pavlik harness (FIG 5) or other brace treatment in the young infant, to closed or open reduction and hip spica casting, pelvic or femoral osteotomies, and salvage procedures in older patients.
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FIG 5 • Pavlik harness. This infant is comfortable in the harness; hips and knees are flexed with abduction provided by gravity, not from the lateral straps.
By the time of skeletal maturity, as normal as possible, acetabular anatomy should be restored.8 Ideally, reconstructive surgery should be performed during early childhood, when the results are believed to be better and the risks acceptable.
SURGICAL MANAGEMENT
If the hip remains dislocated or subluxated despite conservative treatment with a Pavlik harness or abduction orthosis, or if a concentric and stable reduction cannot be achieved with closed reduction and casting, open surgical reduction is appropriate.
Preoperative Planning
For the infant who has not achieved walking age, an open reduction without associated femoral shortening or pelvic osteotomy is generally sufficient.
With age and walking, the deformities in and around the hip become more fixed and require a more aggressive surgical approach.
Prereduction traction is less frequently used than in the past for the infant and is not recommended for the older child.1
Generally, a child older than age 2 to 3 years requires a femoral shortening osteotomy if the femoral head is displaced proximally.9
Epidural or caudal regional anesthesia may be helpful to supplement the general anesthesia. A type and screen is obtained, but blood transfusion is rarely required.
An indwelling bladder catheter is used during the surgery because much of the surgery is intrapelvic.
Positioning
A radiolucent table is used in case an intraoperative radiograph will be obtained. The child is placed in a semilateral position (FIG 6).
The entire limb is draped free.
Approach
Several variations of the medial approach to the hip joint have been described. These are very useful in the infant if the femoral head is not excessively high and for bilateral instability surgery done the same day.
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FIG 6 • Semilateral position. The anterior hip and lateral thigh incisions are generally parallel when the hip is flexed about 30 degrees.
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For the older infant and child, an anterior approach to the hip joint allows more extensile exposure.
The anterior approach is especially useful if there is a false acetabulum with a high dislocation and for fixed dislocations in which the hip capsule is adherent to the hip abductors and pelvic wall.
The anterior approach allows for an associated pelvic osteotomy through the same incision.
The decision to perform a medial approach or an anterior approach to the hip joint will depend on the child's age, the location and severity of the pathology, and the surgeon's experience.
TECHNIQUES
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Anterior Hip Exposure
A modified anterior Smith-Petersen exposure with the incision placed in the inguinal crease just below the anterior superior iliac spine is cosmetically appealing.
Sharp dissection is carried deep until no more fat can be identified.
This is the deep fascia, which can then be further exposed distally by using a sponge on the fascia.
If femoral shortening is anticipated, a separate direct lateral approach to the proximal femur is used.
Both exposures should be completed before osteotomies are performed because of increased bleeding from the bone.
The tensor-sartorius internervous interval is easier to identify distally where the muscles are divergent (TECH FIG 1A).
The fascia of the tensor muscle is entered slightly lateral to the fatty interval between the two muscles. The lateral femoral cutaneous nerve is identified and protected.
Army-Navy retractors are used to separate the tensor and sartorius muscles until the rectus femoris
muscle is identified.
This dissection is continued proximally and the prow of the pelvis is exposed between the anterior superior and anterior inferior iliac spines.
The external oblique muscle is gently separated off the iliac crest.
The iliac crest apophysis is divided exactly in the middle with a single cut using a no. 15 blade down to iliac bone (TECH FIG 1B).
Periosteal elevators are used to expose the inner and outer tables of the iliac crest (TECH FIG 1C).
Laparotomy sponges are used to help dissect deep near the sciatic notch and to pack the surgical site for hemostasis.
Perforating vessels into the iliac bone on the inner table are consistently present and require bone wax for hemostasis.
Smooth Lane retractors are used to further dissect the sciatic notch both medially and laterally. The reflected and straight heads of the rectus femoris muscle are identified (TECH FIG 1D).
TECH FIG 1 • A. Tensor-sartorius interval. Note the lateral femoral cutaneous nerve (arrow). B. The external oblique muscle has been detached off the iliac crest apophysis, which is being divided by a no. 15 blade. C. Subperiosteal dissection of the iliac inner and outer tables. D. Superior view of the left hip (patient's head is to the right) showing the rectus femoris (RF), its straight head attachment to the anterior inferior iliac spine (AIIS), and the reflected head attaching to the hip capsule (RH). E. The iliopsoas tendon is identified, dissected distally, and divided at the iliopectineal eminence. (continued)
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TECH FIG 1 • (continued) The reflected head of the rectus femoris is lifted off the hip capsule (F) and divided (G). H. Deep muscles of the iliacus, rectus femoris, and gluteus medius are reflected off the hip capsule. The capsule must be separated from any false acetabulum on the lateral iliac wall. I. The capsule is exposed, particularly the inferior medial aspect.
It is extremely important for the dissection to continue medially onto the pubis by opening the interval between the iliacus and the rectus femoris muscles (TECH FIG 1E).
By opening the medial periosteum at the level of the pubis, the iliopsoas tendon is identified, which lies deep on the iliacus muscle.
The tendon is followed distally so that the interval between the iliacus muscle and the rectus femoris muscle is separated more deeply.
The iliopsoas tendon is brought into the superficial surgical site with a right-angled clamp and divided at the level of the iliopectineal groove on the pubis.
The femoral nerve is close by, superficial and medial to the psoas tendon.
The reflected and straight heads of the rectus femoris muscle are identified and divided. This allows skeletonization of the femoral head by separating the iliacus, rectus femoris, and hip abductor muscles off the capsule (TECH FIG 1F-H).
A Cobb elevator is useful for separating these muscles off the hip capsule.
It is extremely important to carry the dissection around to the deep inferior medial aspect of the hip capsule (TECH FIG 1I).
With a Kocher clamp, grasp the proximal aspect of the reflected head of the rectus femoris tendon to further expose the capsule. The capsule must be detached from the false acetabulum if present and exposed superiorly and posteriorly.
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Open Reduction
A T-shaped capsulorrhaphy is made with the redundant proximal limb eventually removed.
The incision parallels the acetabular rim but is about a centimeter away so that the labrum is not injured (TECH FIG 2A).
The femoral head is examined for deformity (TECH FIG 2B).
The ligamentum teres is divided off the femoral head (TECH FIG 2C).
The stump of the ligamentum teres is grabbed with a Kocher clamp and it is followed into the depths of the acetabulum.
It is essential to visualize the entire acetabulum and the transverse acetabular ligament.
The ligamentum teres is removed with Mayo or cartilage scissors at its deep acetabular attachment.
Under direct vision, a pituitary rongeur is used to remove the pulvinar tissue that lies within the acetabulum.
The transverse acetabular ligament is divided. At this point, the femoral head should be reducible.
For children older than 2 to 3 years of age, especially if the reduction is tight or unstable, a femoral shortening osteotomy is performed before the capsule is closed.9
If an acetabular osteotomy is performed, it is also completed before the capsulorrhaphy sutures are tied.
An adductor longus and gracilis tenotomy is generally not needed but can be included if these muscles feel excessively tight.
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TECH FIG 2 • A. A T-shaped capsulorrhaphy is performed. The upper limb is generally excised. B. The hip capsule has been opened, exposing the deformed femoral head. C. The ligamentum teres is divided off its femoral head attachment. The vascular contribution of the ligamentum teres to the femoral head is minimal. D. After any associated femoral and acetabular osteotomies are performed, the capsule is advanced medially. E. Nonabsorbable sutures are placed and tied after osteotomies have been completed.
A capsulorrhaphy is performed by advancing the superolateral capsule to the inferior medial aspect of the capsule on the pubis (TECH FIG 2D).
Nonabsorbable no. 0 sutures are all placed and tagged and then sequentially tied (TECH FIG 2E).
The iliac crest apophysis is reapproximated with heavy suture, and the external oblique muscle is reattached.
The rectus femoris can be repaired, but the iliopsoas muscles are left divided. A surgical drain is not required.
A one-and-a-half spica cast is applied with the hips in a safe “human” position with no more than 30 degrees of flexion and abduction.
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Proximal Femoral Shortening Osteotomy
A straight lateral approach to the proximal femur is used. The tensor fascia is divided longitudinally.
The anterior edge of the gluteus medius muscle is identified where it attaches to the greater trochanter. Several millimeters of the gluteus medius muscle is detached off the trochanter.
This allows palpation of the anterior aspect of the femoral head to estimate the amount of femoral torsion (TECH FIG 3A).
The vastus lateralis muscle is detached off the femur by dividing its proximal attachment in the transverse plane at the trochanteric ridge, leaving enough cartilage attached to the muscle to allow secure fixation during closure (TECH FIG 3B).
The vastus lateralis muscle should be divided off the posterior intermuscular septum so that the muscle innervation is left completely intact.
Stiff Steinmann pins are inserted in the proximal and distal femur to ensure that a proper amount of femoral rotation is provided.
A third pin is placed up the neck of the femur to judge femoral head-neck antetorsion, and a fourth pin is placed just below the lesser trochanter to guide the osteotomy.
A one-third tubular small fragment plate or a 2.7-mm minifragment dynamic compression plate is generally sufficient in a young child (TECH FIG 3C). A 3.5-mm dynamic compression plate is used for an older child.
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The proximal aspect of the plate is fixed loosely.
A subtrochanteric osteotomy is believed to be less hazardous to the hip vascularity than an intertrochanteric osteotomy.
The femur is shortened by the amount that the cut ends of the femur overlap when the femoral head is reduced (TECH FIG 3D).
The shortened fragment of femur can be used for holding open a pelvic osteotomy.
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TECH FIG 3 • A. About 5 mm of the most anterior edge of the gluteus medius muscle is detached from the greater trochanter so that the femoral neck can be palpated and visualized (shown on a left hip). B. The vastus lateralis muscle is detached from the trochanteric ridge (TR) and the posterior intermuscular septum (IS) to expose the proximal femur (F). C. A one-third tubular plate has been attached to the proximal femur, and a 2-cm segment of bone has been removed from the subtrochanteric aspect of the femur. D. The femur has been shortened, rotated into less antetorsion, and compressed. E. The tension
band of the vastus lateralis muscle is reestablished with 0 absorbable suture.
The plate is prebent slightly and is secured with some compression applied.
The Steinmann pins are used to judge any rotation that is desired.
If excessive femoral torsion was noted, some of this can be judiciously corrected. The tension band effect of the vastus lateralis muscle is restored (TECH FIG 3E). The incision is closed with absorbable suture. No drain is necessary.
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PEARLS AND PITFALLS |
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Diagnosis ▪ A painful dislocated hip in a newborn or young infant could be a septic dislocation.
Long term ▪ Operatively treated hips should be followed until skeletal maturity. Late growth |
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arrest may affect the end result.
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POSTOPERATIVE CARE
A spica cast is applied at the time of surgery.
A Gore-Tex liner protects the skin from excoriation. The cast is removed at 6 weeks.
A night brace can be used until the acetabulum has remodeled sufficiently. Physical therapy is generally not needed.
Follow-up radiographs are obtained.
The acetabulum will remodel the most in the first year after surgery.
If the acetabular shape does not normalize within several years, a pelvic osteotomy may be indicated.
OUTCOMES
Patients treated with a Pavlik harness may have persistent acetabular dysplasia in adulthood and should be followed until skeletal maturity.
The younger the age at reduction, the better the final Severin grade at maturity. This in turn predicts the need for total hip arthroplasty in later adulthood.1
About 50% of hips that underwent closed reduction in childhood had residual acetabular dysplasia as adults.6
The best results occur if there is no osteonecrosis, femoral growth disturbance, or residual subluxation.12
Persistent acetabular dysplasia, if present past age 7 years, is associated with a poor late outcome.4 A persistent upsloping sourcil and a centering discrepancy suggest a need for surgical correction in the
younger child.7
Early measurements of the acetabular index (AI) are also predictive for Severin grade at maturity.
In particular, an AI of 35 degrees or higher at 5 or more years after reduction has an 80% association with Severin grade III or IV at maturity.1
COMPLICATIONS
Osteonecrosis
Late physeal and lateral femoral growth arrest
Inadequate reduction with persistent subluxation Loss of reduction and redislocation
Stiffness
Lack of remodeling after reduction Infection
Arthritis
REFERENCES
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Albinana J, Dolan LA, Spratt KF, et al. Acetabular dysplasia after treatment for developmental dysplasia of the hip: implications for secondary procedures. J Bone Joint Surg Br 2004;86(6):876-886.
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Barlow TG. Early diagnosis and treatment of congenital dislocation of the hip. J Bone Joint Surg Br 1962;44(2):292-301.
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Desai AA, Martus JE, Schoenecker J, et al. Spica MRI after closed reduction for developmental dysplasia of the hip. Pediatr Radiol 2011;41(4):525-529.
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Kim HT, Kim JI, Yoo CI. Acetabular development after closed reduction of developmental dislocation of the hip. J Pediatr Orthop 2000;20:701-708.
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Mahan ST, Katz JN, Kim YJ. To screen or not to screen? A decision analysis of the utility of screening for developmental dysplasia of the hip. J Bone Joint Surg Am 2009;91(7):1705-1719.
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Malvitz TA, Weinstein SL. Closed reduction for congenital dysplasia of the hip. Functional and radiographic results after an average of thirty years. J Bone Joint Surg Am 1994;76(12):1777-1792.
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Murphy SB, Ganz R, Müller ME. The prognosis in untreated dysplasia of the hip. A study of radiographic factors that predict the outcome. J Bone Joint Surg Am 1995;77(7):985-989.
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Ponseti IV. Morphology of the acetabulum in congenital dislocation of the hip. Gross, histological and roentgenographic studies. J Bone Joint Surg Am 1978;60(5):586-599.
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Schoenecker PL, Strecher WB. Congenital dislocation of the hip in children. Comparison of the effects of femoral shortening and of skeletal traction in treatment. J Bone Joint Surg Am 1984;66(1):21-27.
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Schwend RM, Pratt WB, Fultz JF. Untreated acetabular dysplasia of the hip in the Navajo. A 34-year case series follow-up. Clin Orthop Relat Res 1999;(364):108-116.
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The Alliance for Radiation Safety in Pediatric Imaging. One size does not fit all … so when we image, let's image gently! Available at: http://imagegently.dnnstaging.com/Home.aspx. Accessed March 20, 2014.
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Weinstein SL. Congenital hip dislocation. Long-range problems, residual signs and symptoms after successful treatment. Clin Orthop Relat Res 1992;(281):69-74.
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Weinstein SL. Natural history of congenital hip dislocation (CDH) and hip dysplasia. Clin Orthop Relat Res 1987;(225):62-76.
