Developmental Hip Dysplasia

Developmental Hip DysplasiaDevelopmental hip dysplasia (DDH) is a generic term describing a spectrum of anatomic abnormalities of the hip that may be congenital or develop during infancy or childhood. The spectrum covers mild defects such as a shallow acetabulum to severe defects such as teratologic dislocations. Teratologic dislocations occur before birth and include severe deformity of both the acetabulum and proximal femur.

Incidence

DDH incidence depends on how much of the spectrum is included. At birth, hip instability is noted in 0.5–1% of joints, but classic DDH occurs in about 0.1% of infants. The incidence of mild dysplasia contributing to adult degenerative arthritis is substantial. It is thought that half of the women who develop degenerative arthritis have preexisting acetabular dysplasia.

Etiology of Developmental Hip Dysplasia

DDH is considered to be inherited by a polygenic mode. DDH is more common in breech deliveries, in children with joint laxity, and in girls.

Pathology

The acetabulum is often shallow and maldirected. The proximal femur shows antetorsion and coxa valga. Structural interpositions between the displaced femoral head and acetabulum are common. The iliopsoas tendon causing a depression in the joint capsule. This gives the capsule an hourglass configuration. The acetabular labrum is inverted into the joint, the ligamentum teres is enlarged, and the acetabulum may contain fat (pulvinar).

Natural History

Residual acetabular dysplasia is common in DDH. This may occur even following an apparently good early reduction. The disability from dysplasia is related to the degree of displacement. Greater displacement causes more function disability. Pain is most common with severe subluxation or articulation in a false acetabulum.

Diagnosis

The early diagnosis of DDH is critical to a successful outcome. Acetabular development is abnormal if a hip is subluxated or dislocated. Delays in management result in residual abnormalities and eventual degenerative arthritis.

Neonatal examination Use no force. Test for instability in several positions.

Changing manifestations of DDH The signs of developmental hip dysplasia change with the infant’s age. For example, the incidence of hip instability declines rapidly, 50% within the first week. The classic findings of stiffness and shortening increase over the first few weeks of life. These signs become well established in the older infant.

Mother’s intuition Although not proven, a common clinical experience is the accuracy of the mother’s sense that something is wrong. Take the mother’s intuition seriously.

Hip-at-risk factors The presence of several factors increase the risk of DDH. When risk factors are present, the infant should be examined repeatedly and the hip imaged by ultrasound or radiography.

Hip “clicks” and asymmetrical thigh folds Hip clicks are fine, high-pitched sounds that are common and benign. These are to be differentiated from “clunks,” the sensation of the hip being displaced over the acetabular margin. Clicks and asymmetrical thigh folds are common in normal infants.

Radiography Radiographs become progressively more diagnostic with increasing age. By 2–3 months of age, radiography is reliable and this is the optimum age for screening by this method. A single AP radiograph is adequate. Draw the reference lines and measure the acetabular index. Normally, the AI in early infancy falls below 30°, is questionable in the 30°–40° range, and abnormal if above 40°. Hip subluxation or dislocation may often be demonstrated by the metaphysis of the femur positioned lateral to the lateral acetabular marginal line.

Ultrasound imaging The effectiveness of ultrasound imaging depends upon the skill and experience of the examiner. A skillful ultrasound evaluation is an effective screening technique for DDH. The major problem with this screening is in the interpretation of the findings. If the hip is unstable, imaging is unnecessary. Imaging is appropriate to evaluate a suspicious finding, when hip-at-risk factors are present, and to monitor the effectiveness of treatment.

Documentation Document your hip evaluation. The failure to diagnose developmental hip dysplasia is a common cause of suits against physicians. If the diagnosis is delayed, a record showing that appropriate examinations of the hip were made provides the best defense. DDH may be missed by even the most skilled examiners. Failure to screen for DDH is not acceptable by current standards.

Treatment of Developmental Hip Dysplasia

The management of DDH is challenging. Delays in diagnosis or problems in management often lead to residual anatomic defects and subsequent degenerative arthritis. The objectives of management include early diagnosis, reduction of the dislocation, avoidance of avascular necrosis, and correction of residual dysplasia.

Birth to 6 Months

Pavlik harness This widely used orthosis allows motion in flexion and abduction. Be certain that it is fitted properly, both initially and as applied by the parents. Advise the family on ways of transporting the infant.

See the infant weekly in the brace. Make certain the brace is being fitted properly and progress is being made. The hip should become progressively more stable.

If harness treatment is successful, continue full-time bracing for 6 weeks to allow the hip to become stable. Monitor with ultrasound imaging or by AP radiographs of the pelvis every 2 weeks. Continue the brace at night until the radiographs are normal.

If a dislocated hip has not reduced by 4 weeks, abandon Pavlic treatment. Persisting with this treatment may cause head deformity and posterior fixation, making closed reduction difficult or impossible. Proceed with closed or open reduction. Manage as is described for infants over 6 months of age.

Night splinting After the hip is reduced and stable, continue with night splinting to facilitate acetabular development. Continue until the radiographs are normal. A simple abduction splint is inexpensive and is well accepted by the infant.

Closed Reduction of developmental hip dysplasia

Closed reduction is appropriate management for most infants under about 18 months of age with DDH. Management involves several steps.

Arthrographic Evaluation

This step can be omitted if the hip easily reduces, is stable, and the conventional radiograph shows satisfactory reduction. If reduction or pathology is uncertain, perform an arthrogram. Fill a 20-cc syringe with diluted dye. Attach flexible tubing and fill the tubing with dye. Advance a 3-inch #20 needle through the adductor approach under fluoroscopic guidance into the empty acetabulum. This step is facilitated by filling a second syringe with saline to be used to confirm joint entry. Once the joint is thought to be entered with the needle, inject a few cc of saline. Remove the syringe and medially rotate the leg. Joint entry is confirmed if saline drips from the needle hub. Repeat if necessary. Once entry is confirmed, attach the tubing and inject a few cc of dye while imaging the joint. Avoid excessive dye injection. Image in the position of dislocation and reduction. Note any obstacles to reduction. The labrum (red arrow) is interposed but the medial dye pool (yellow arrow) is not excessive. Unless the hip is stiff, an interposed limbus often is accepted because the limbus will remodel with time.

Stability of Reduction

The second step is to determine the stability of reduction. If an adductor contracture limits abduction, narrowing the arc of stability (green or safe zone), perform a percutaneous adductor tenotomy.

Percutaneous Adductor Tenotomy

This procedure is performed with a pointed blade through a stab incision just distal to the inguinal crease.

Indications for an Open Reduction

If the limbus is interposed but the hip is stable, allow the interposition to be resolved by remodeling. If the interposition results in an unstable reduction or if the dislocation cannot be reduced or cannot be maintained without excessive abduction, perform an open reduction.

Immobilize in a Spica Cast

Most reductions may be safely maintained with the hip positioned in about 80° of flexion, 45° of abduction, and neutral rotation. While maintaining this position, place the infant on a spica frame and apply first the liner and padding and then the cast. Be aware of the natural tendency for the person holding the position to allow the thighs to fall in greater abduction and less flexion during the cast application, making the reduction less stable and increasing the risk of AVN.

Post-Reduction Management

Document the reduction by an AP radiograph in the cast. If the quality of reduction is uncertain, confirm the reduction by a CT scan prior to discharge. Plan to change the cast under anesthesia in 4–6 weeks. If limbus interposition was present, repeat the arthrogram during the second cast change to confirm that the reduction remains concentric. Remove the second cast in the clinic. Follow with shielded AP pelvic radiographs following cast removal. Some advocate night splinting until age 3 years, but no data confirm the value of this splinting.

Medial Approach Open Reduction (Ludloff)

This procedure was described by Ludloff to provide a direct approach for open reduction of the hip in DDH. This procedure is one of several approaches for open reduction.

Indications

The procedure is useful for management of dislocations of the hip due to DDH and arthrogryposis in infants under about 18 months of age.

Technique

Preparation Place a folded towel to elevate the pelvis. If necessary both hips may be reduced at one operative setting. Perform an arthrogram if indicated. Prepare the skin, and drape with the limb(s) free. Abduct the hip.

Approach
Make a 3 cm skin incision. On the lateral aspect of the incision, identify and avoid the long saphenous vein. Identify the interval just lateral to the adductor longus muscle and tendon. Through this interval, identify the lesser trochanter. This is best done by palpation. Bring the trochanter into profile by flexing and laterally rotating the thigh. Extend the finger dissection until the prominence of the trochanter is palpated. Place retractors to visualize the trochanter and free overlying soft tissue.

Psoas tenotomy Place a curve clamp around the psoas tendon just above its insertion. Divide the tendon completely. Free the hip capsule. Apply traction to approximate the femoral head within the capsule and rotate the thigh to feel the rotation of the femoral head.

Reduction Incise the capsule and extend the capsulotomy medially to include the transverse acetabular ligament. Perform a tendinotomy of the adductor longus tendon. Remove the ligamentum teres and pulvinar to allow a concentric reduction. To confirm that division of the ligament is complete, slide a curved clamp over the medial acetabular margin. Reduce the dislocation.

Stability Determine the arc of stability and the degree of flexion, abduction, and rotation that provides optimum stability while remaining within the safe zone. Obtain an AP radiograph with the hip reduced. The surgeon should maintain this position of stable reduction while an assistant performs the subcutaneous skin closure and applies the spica cast. To ensure maintenance of the reduction, make a second comparable AP radiograph in the cast. If any loss of reduction is demonstrated, remove the cast, re-reduce the hip, and apply a new cast.

Postoperative Care

Confirm the reduction with a CT scan. Expect considerable swelling about the perinenum. The patient may be discharged the next day. Reschedule for cast change in 6 weeks. Continue cast immobilization for 12 weeks. Maintain afterwards in a night splint. About a third of the hips show persisting dysplasia and require a pelvic osteotomy.

Complications

Redislocation is best prevented by thorough release and careful positioning and follow-up in the cast. Avascular necrosis is the most common complication, as with other methods of reduction. Try to avoid by careful dissection for exposure and positioning in the cast without excessive abduction.

6 to 18 Months

Most cases of developmental hip dysplasia can be managed by closed reduction and spica cast immobilization.

Traction The need for traction is controversial. The current practice is to omit traction in most cases. Traction may be useful if the hip is stiff and closed treatment is planned. Use home traction when possible. Maintain for about 3 weeks with the legs flexed and abducted about 45° with 2–3 pounds of traction applied to each limb.

Scheduling Schedule and obtain consent for a closed, or possibly open, reduction.

Reduction by closed means is first tried. If unsuccessful, open reduction is required. These procedures are outlined on the previous page.

Arthrography is useful when the quality of reduction is uncertain or the decision regarding management is difficult.

Follow-up After reduction, the infant should be followed carefully to assess the effect of time on growth, reduction, and acetabular development. Follow with AP radiographs made quarterly through infancy, yearly though early childhood, and then about every third year during middle and late childhood.

18 to 30 Months

Operative management is usually required. Occasionally, an infant with a “loose dislocation” can be managed as described in the flowchart for infants 6–18 months of age. If the hip is unusually stiff, be prepared to add femoral shortening, as described for management of children over 30 months of age.

Management Manage with an open reduction through an anterolateral approach and perform a concurrent Salter or Pemberton osteotomy. The open reduction is technically challenging. Add the pelvic osteotomy to improve results and save the child a second procedure.

Open reduction is the most difficult part of the procedure. The pelvic osteotomies are relatively simple, but the reduction can sometimes be difficult. The open reduction requires good exposure, careful dissection to minimize the risk of necrosis, and a concentric reduction. The obstacles to reduction must be corrected.

Iliopsoas tendon This tendon is interposed between the femoral head and acetabulum and must be released.

Capsular constriction Open the capsule widely to ensure a complete release.

Transverse acetabular ligament This structure lies across the base of the acetabulum and will block a deep concentric reduction unless released.

Pulvinar is fatty fibrous tissue that often fills the depth of the acetabulum. Remove with a rongeur.

Ligamentum teres is elongated and sometimes hypertrophied. Removal is usually required. The vascular contribution through this ligament is minimal.

Limbus is often inverted and hypertrophied. Do not excise this structure. Once the hip is concentrically reduced, the limbus will remodel and form the labrum, an important structure for hip stability and longevity.

Concurrent osteotomy This choice may be based on the pathology and on the experience and preference of the surgeon.

Femoral osteotomy Proximal femoral varus osteotomy is becoming less commonly used because the acetabular dysplasia is the more significant deformity. Include only minimal rotational correction.

Salter innominate osteotomy is suitable for unilateral mild to moderate dysplasia. The procedure is simple, risks are few, and results good.

Pemberton pericapsular osteotomy is more versatile because it can be performed bilaterally, does not destabilize the pelvis, provides greater correction, and requires no internal fixation. Avoid overcorrection. Stiffness is more common with this procedure, as the operation changes the shape of the acetabulum.

Postoperative care is determined by the treatment. If closed or open reduction is performed with an osteotomy, plan at least 12 weeks of spica cast immobilization. Usually, the cast is changed once or twice during this period. If a concurrent osteotomy is performed, stability is improved and only 6 weeks of immobilization are necessary.

Follow-up must be continued until the end of growth. Usually, a single AP radiograph of the pelvis is made every 6 months for 3 years, then yearly for 3 years, then every 3 years until maturity. At each visit, compare the current study with previous radiographs to determine the effect of time and growth on the development of the hip.

30+ Months

In this older age group, the opportunity to achieve an early reduction has passed. Avascular necrosis is still a threat and dysplasia is a certainty. Management is much more difficult and controversial, and a poor outcome with degenerative arthritis in early adult life is likely.

Indications for reduction Consider the child’s age, bilaterality, the family’s values, and the experience of the surgeon.

Early childhood In early childhood, reduction is usually appropriate. This requires a femoral shortening, open reduction, pelvic osteotomy. If the dislocations are bilateral, correct one side at a time. Allow 6 months between procedures to allow the child to recover. Reduction improves function, reduces the limp, and may make performing some salvage procedure more effective.

Mid or late childhood In the older child, leaving the hip unreduced is a reasonable option, especially when the condition is bilateral. The child will limp but is less likely to have pain. Hip arthroplasty may be elected after maturity.

Pelvic ostoeotomy Select the type of osteotomy based on the severity and the age at the time of treatment. Select the Salter osteotomy for mild dysplasia. This procedure can be performed at any age and it does not change the shape of the acetabulum. Select the Pemberton osteotomy if dysplasia is moderate or severe.

Femoral osteotomy Femoral shortening osteotomy is nearly always necessary. If the deformity is severe, the femoral shortening is performed first, then the open reduction, followed by the pelvic osteotomy. The femoral fragments are then aligned, with gentle traction on the limb. The overlap is then determined and the overlapping distal femoral segment is resected. The procedure is primarily a shortening osteotomy with little or no varus or rotational components required.

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