Displasia Panggul

01Pathophysiology

Developmental dysplasia of the hip (DDH) refers to a spectrum of abnormalities in which the acetabulum fails to develop adequate depth and coverage, resulting in a femoral head that is unstable within or displaced from the hip joint. The term "developmental" replaced "congenital" because the condition can be present at birth or evolve during the first months of life as the hip continues to mature.

The neonatal hip is largely cartilaginous, which makes it vulnerable to mechanical forces. In utero crowding, particularly in breech presentation, forces the hips into sustained extension and adduction. This abnormal positioning prevents the femoral head from applying the normal concentric pressure on the acetabulum that stimulates its growth and deepening. Without that mechanical stimulus, the acetabulum remains shallow and the labrum stretches, allowing the femoral head to sublux or dislocate.

Ligamentous laxity plays a compounding role. Maternal estrogen and relaxin cross the placenta and increase capsular laxity in the newborn, which is why females are affected roughly four to eight times more often than males. The left hip is more commonly involved because the most common intrauterine position places the left hip against the mother's sacrum, restricting its abduction.

If the femoral head remains displaced, the acetabulum progressively loses its concave shape due to loss of the normal modeling stimulus. Over time, fibrofatty tissue (the pulvinar), a thickened ligamentum teres, and an inverted labrum fill the acetabular space, creating mechanical obstacles to reduction. This is why early detection and treatment are essential: the longer the hip remains dislocated, the more structural changes accumulate, and the less likely a nonsurgical reduction will succeed.

In a child who walks with an undetected bilateral dislocation, the gluteus medius cannot stabilize the pelvis because its lever arm is shortened. This produces the classic Trendelenburg gait (waddling gait), where the pelvis drops on the unsupported side during single-leg stance.

02Classification and Clinical Manifestation

03Diagnostic Workup

The clinical exam is the first step. Ortolani maneuver is performed by gently abducting the flexed hip while lifting the greater trochanter anteriorly. A palpable "clunk" indicates that a dislocated femoral head has been reduced back into the acetabulum. Barlow maneuver is the reverse: the examiner adducts the flexed hip while pushing posteriorly. A clunk here means the femoral head can be dislocated out of the acetabulum. These maneuvers test two different things and should not be confused. Ortolani asks "Is it out and can I put it back?" while Barlow asks "Is it in and can I push it out?"

A common exam trap is the distinction between a "clunk" and a "click." A clunk is pathologic and represents the femoral head moving over the acetabular rim. A click is a benign ligamentous or tendinous snap and does not indicate DDH.

Ultrasound is the imaging modality of choice in infants younger than 4 to 6 months because the femoral head is still cartilaginous and not visible on plain radiographs. The Graf classification system divides hips by the alpha angle (formed by the acetabular roof and the iliac line). A normal hip (Type I) has an alpha angle greater than 60 degrees. An alpha angle less than 50 degrees with femoral head displacement indicates a dislocated hip (Type III or IV).

After 4 to 6 months, the ossification center of the femoral head becomes visible, and a plain radiograph replaces ultrasound as the primary imaging tool. Key radiographic findings include a disrupted Shenton line (the smooth arc from the inferior border of the superior pubic ramus to the medial femoral neck), an increased acetabular index (greater than 30 degrees suggests dysplasia), and the femoral head ossification center located in the superolateral quadrant of the Perkin and Hilgenreiner lines grid (normally it should be in the inferomedial quadrant).

Routine screening ultrasound for all newborns is not recommended. Selective ultrasound is indicated for infants with risk factors (breech, family history) or an abnormal or equivocal clinical exam. If the exam is equivocal at birth, ultrasound should be deferred to approximately 4 to 6 weeks of age because physiologic laxity in the first few weeks can produce false-positive results.

04Management and Treatment

The Pavlik harness is the cornerstone of early treatment and the most tested management point. It works by holding the hip in a position of flexion and abduction, which centers the femoral head into the acetabulum and allows the acetabulum to remodel around it. The harness is typically worn full-time (removed only for bathing) for 6 weeks, confirmed with ultrasound, and then gradually weaned over an additional 6 weeks. Success rates exceed 90% when treatment is initiated before 6 weeks of age.

A critical teaching point is that the Pavlik harness should not be used if the hip is irreducible (i.e., Ortolani-negative but Barlow-negative with a fixed dislocation). Forcing an irreducible hip into a harness increases the risk of avascular necrosis of the femoral head because the femoral head compresses against the posterior acetabular wall rather than seating properly. This condition is called Pavlik harness disease and is the most feared complication of improper harness use.

If the harness fails (defined as no stable reduction by 3 to 4 weeks of treatment), the next step is closed reduction under anesthesia with arthrographic confirmation, followed by application of a hip spica cast. The hip is immobilized in the "human position" (approximately 100 degrees of flexion, 40 to 50 degrees of abduction, neutral rotation) for about 3 months, often changed at 6 weeks under anesthesia.

Open reduction becomes necessary when soft tissue interposition prevents concentric reduction, or when presentation is delayed beyond 18 months. In children older than 18 months to 2 years, an acetabular osteotomy (such as Salter innominate osteotomy) or femoral shortening osteotomy is frequently added to achieve stable concentric reduction and correct residual deformity.

Avascular necrosis (AVN) is the most important complication to understand. It results from excessive abduction or pressure on the femoral head that compromises the blood supply from the medial femoral circumflex artery. Avoiding forced or extreme abduction positions is the primary preventive measure.

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The most common way students lose points on DDH questions is by confusing the age-appropriate imaging modality. If the vignette describes an infant younger than 4 to 6 months, the correct answer for initial imaging is always ultrasound, not radiograph. A plain film in this age group is useless because the femoral head has not yet ossified. Conversely, for an older infant with a visible ossification center, ultrasound is no longer the preferred study; the answer shifts to an anteroposterior pelvis radiograph.

A second common trap involves the Ortolani versus Barlow distinction. The exam tests whether you know that Ortolani reduces a dislocated hip (you feel the head slide back in) while Barlow dislocates a reducible hip (you feel it slide out). Do not reverse these.

Another tested scenario is the "late-presenting DDH." When a vignette describes a toddler with a waddling gait, bilateral limited abduction, and hyperlordosis, the diagnosis is bilateral DDH that was missed during infancy. The clue is the Trendelenburg gait pattern and the radiographic findings of bilateral femoral head displacement.

Finally, remember that the Pavlik harness is only appropriate for a hip that is reducible (Ortolani-positive) and in an infant younger than 6 months. If the vignette describes a fixed, irreducible dislocation or a child older than 6 months, the Pavlik harness is the wrong answer. Selecting it in these scenarios leads to AVN, which is the most feared iatrogenic complication.

The core competency being tested is the ability to match the patient's age and exam findings to the correct diagnostic study and the correct initial treatment. The sequencing logic (clinical exam, then age-appropriate imaging, then age-appropriate intervention) is what the question writer is evaluating.