DDH: Screening, Diagnosis, and Treatment Guidelines

Developmental Dysplasia of the Hip (DDH) represents the most common orthopaedic disorder in newborns, affecting approximately 1 in 100 to 1 in 1000 infants depending on the population and diagnostic criteria. For the orthopaedic surgery trainee preparing for fellowship exams, mastering DDH is non-negotiable. It is not a static condition but a dynamic spectrum of pathology—ranging from a shallow acetabulum (dysplasia) to a subluxatable hip, and ultimately to a frankly dislocated, teratologic hip.

The overarching goal of screening and treatment is elegantly simple in theory but nuanced in practice: achieve and maintain a concentric, stable reduction to stimulate normal acetabular and proximal femoral development. The acetabulum and femoral head develop in tandem; they need each other for normal morphology. Failure to achieve this symbiotic reduction leads to abnormal joint mechanics, labral tears, early-onset osteoarthritis, and lifelong disability requiring complex adult reconstructive procedures.

The Etiology and Risk Factors (The "4 F's" and Beyond)

Understanding the etiology of DDH is crucial not just for clinical practice, but because it forms the foundation of all selective screening protocols tested in orthopaedic surgery training. While many cases are considered idiopathic, the classic risk factors are well-established.

The Classic "4 F's"

1. Female Sex: Females are affected at a 6:1 ratio compared to males. The prevailing theory is that female infants are uniquely sensitive to maternal relaxin and estrogens circulating in the third trimester, leading to increased ligamentous laxity.
2. First Born: Primigravida pregnancies feature a tighter, unstretched uterus and abdominal musculature, increasing mechanical constraint on the fetus.
3. Feet First (Breech Presentation): This is the most significant mechanical risk factor for DDH. A frank breech position (hips flexed, knees extended) places immense mechanical stretch on the hamstrings, which in turn pull the femoral head out of the acetabulum. The left hip is more commonly affected (60%) because the most common intrauterine position is Left Occiput Anterior (LOA), where the left fetal hip is compressed against the maternal sacrum.
4. Family History: A positive family history significantly increases risk. If one sibling has DDH, the risk to the next child is 6%. If one parent has DDH, the risk is 12%. If a parent and a sibling are affected, the risk jumps to 36%.

Packaging Disorders and Associated Conditions

Mechanical constraints in utero often manifest with multiple "packaging" issues. Infants with DDH have a higher incidence of:

• Congenital Muscular Torticollis (CMT): Up to 20% of infants with CMT have DDH.
• Metatarsus Adductus: Associated with a 1-10% rate of DDH.
• Oligohydramnios: Decreased amniotic fluid amplifies the mechanical constraints of the uterus.

Pathoanatomy of the Dislocated Hip: Obstacles to Reduction

For the fellowship exam, you must be able to eloquently list the pathoanatomic changes that occur when a hip remains dislocated. These are the specific "obstacles to reduction" that you will encounter during an open reduction.

1. Extra-articular Obstacles:

   • Iliopsoas Tendon: Becomes contracted and compresses the joint capsule, creating an "hourglass" constriction that blocks the femoral head from re-entering the true acetabulum.
   • Adductor Longus: Becomes contracted, severely limiting abduction.

2. Intra-articular Obstacles:

   • Pulvinar Hypertrophy: The fibrofatty tissue in the cotyloid fossa hypertrophies and fills the empty acetabulum.
   • Ligamentum Teres: Becomes severely elongated, thickened, and hypertrophic, occupying critical space.
   • Transverse Acetabular Ligament (TAL): Contracted and pulled superiorly, blocking the inferior aspect of the acetabulum.
   • Inverted Limbus/Labrum: The superior labrum is pushed down and inverted into the joint by the migrating femoral head, acting as a mechanical block.
   • Capsule: Elongated, redundant, and adherent to the false acetabulum.

Screening Guidelines: The Global Debate and Evidence

The optimal screening strategy remains a topic of international debate. As a trainee, you must understand both sides of the coin and your local jurisdiction's standard of care.

Clinical Screening (Universal)

Every newborn must undergo a meticulous clinical examination.

• Barlow Test: The provocative test. The hip is flexed and adducted, with gentle posterior pressure applied. You are attempting to push a subluxatable or dislocatable hip out of the socket.
• Ortolani Test: The therapeutic test. The hip is abducted and lifted anteriorly. You are attempting to reduce a dislocated hip back into the socket. The classic "clunk" (not a click) is the sensation of the femoral head slipping over the posterior labrum into the acetabulum.
• Galeazzi Sign: Evaluates for apparent limb length discrepancy. With the infant supine, hips and knees flexed, unequal knee height suggests a unilateral dislocated hip. This is ineffective in bilateral dislocations.
• Limited Abduction: This becomes the most reliable clinical sign after 2-3 months of age. As the infant grows, the provocative instability (Barlow/Ortolani) disappears due to soft tissue contracture, and limited, asymmetric abduction becomes the hallmark sign of a missed DDH.

Ultrasound Screening: Selective vs. Universal

• Universal Ultrasound (e.g., Austria, Germany): Screens every infant. This leads to early diagnosis and drastically reduces the late presentation rate. However, it is highly resource-intensive and leads to significant "over-treatment" of physiologic immaturity (Graf 2a hips), causing parental anxiety and unnecessary costs.
• Selective Ultrasound (e.g., UK, USA, Australia, POSNA/AAOS guidelines): Recommends ultrasound only for "High Risk" infants—those with a positive family history, breech presentation, or an abnormal or equivocal clinical exam.
• Timing is Critical: Routine screening ultrasounds should be performed at 6 weeks of age (corrected for prematurity). Before 4-6 weeks, maternal relaxin causes physiologic laxity that usually resolves spontaneously. Performing the scan too early leads to high false-positive rates.

The Graf Classification: The Language of Hip Sonography

Professor Reinhard Graf revolutionized the diagnosis and management of DDH with standard infant hip sonography. You cannot pass a fellowship exam without speaking this language fluently.

A diagnostic ultrasound requires a standard coronal plane. The three critical landmarks that must be visible to calculate angles are:

1. The lower limb of the os ilium (must be straight).
2. The chondro-osseous junction (where the ilium meets the triradiate cartilage).
3. The labrum.

Treatment: The Pavlik Harness and the "Safe Zone"

For infants under 6 months of age with reducible hips, the Pavlik harness is the gold standard. It is a dynamic flexion-abduction orthosis. Unlike rigid spica casts, it relies on the infant's active movement to achieve and maintain reduction.

The biomechanical secret is the "Principle of Reciprocal Action". When the infant kicks and extends their legs, the posterior straps act as a tether, pulling the hip into flexion. When the infant relaxes or adducts, the anterior straps check the motion, guiding the femoral head directly toward the triradiate cartilage, stimulating acetabular remodeling.

Precise Application Technique

Correct application is frequently tested in clinical exams:

• Chest Strap: Positioned at the nipple line. You must be able to fit two fingers beneath it to allow for normal respiratory excursion.
• Anterior (Flexion) Straps: Adjusted to hold the hip at 90-100° of flexion.
• Posterior (Abduction) Straps: Adjusted to prevent adduction past the midline, allowing for relaxed, gravity-assisted abduction.

Ramsey's "Safe Zone"

Dr. Paul Ramsey defined the "Safe Zone" for DDH reduction, a concept vital to preventing iatrogenic complications.

• Limit of Adduction: The precise angle of adduction at which the hip slips out of the acetabulum (redislocates).
• Limit of Abduction: The maximal angle of comfortable abduction.
• The Danger Zone: Forcing the hip into excessive, rigid abduction (the "frog-leg" position) compresses the retinacular branches of the medial femoral circumflex artery (MFCA) against the cartilaginous posterior acetabular rim. This ischemia leads directly to Avascular Necrosis (AVN) of the femoral head—the most devastating complication of DDH treatment.
• The Goal: The harness must maintain the hip comfortably within the middle of this safe zone.

Complications of the Pavlik Harness

1. Femoral Nerve Palsy: Caused by hyperflexion (anterior straps too tight). The nerve is compressed under the inguinal ligament. Clinically, the infant stops actively extending the knee. Treatment: Loosen or temporarily remove the harness; recovery is usually rapid and complete.
2. Avascular Necrosis (AVN): Caused by hyperabduction.
3. "Pavlik Disease": This occurs when a harness is continually used on an irreducible hip (e.g., Graf Type IV with an inverted labrum). The femoral head repeatedly grinds against the posterior-superior acetabular rim, causing erosion of the cartilage. This posterior wall deficiency makes future open reduction significantly more difficult.

Management of the Late Presenter (> 6 Months)

Once the ossific nucleus of the femoral head appears (typically between 4 to 6 months of age), ultrasound becomes unreliable due to acoustic shadowing. At this point, AP pelvis radiographs become the primary diagnostic modality.

Essential Radiographic Lines for the Trainee

You must be able to draw and interpret these lines on a standard AP pelvis film:

• Hilgenreiner’s Line: A horizontal line drawn through the bilateral triradiate cartilages.
• Perkin’s Line: A vertical line drawn perpendicular to Hilgenreiner's, intersecting the lateral margin of the ossified acetabular roof.
  • Normal: The femoral head ossific nucleus must sit in the inferomedial quadrant created by these two lines.
• Shenton’s Line: A smooth, continuous arc drawn along the inferior border of the femoral neck and the superior border of the obturator foramen. A broken Shenton's line indicates proximal migration of the femur (subluxation or dislocation).
• Acetabular Index (AI): The angle formed between Hilgenreiner's line and a line drawn along the sclerotic acetabular roof.
  • Normal: <25° at 1 year of age.
  • Dysplastic: >30° requires close monitoring or intervention.

Age-Based Treatment Algorithm

6 to 18 Months: Closed vs. Open Reduction

The primary goal shifts from bracing to surgical reduction under general anesthesia.

1. Closed Reduction (CR): An Examination Under Anaesthesia (EUA) is performed. An arthrogram is mandatory to confirm concentric reduction and identify any radiolucent obstacles (like the "rose thorn" sign of an inverted labrum or pooling of dye medially indicating pulvinar hypertrophy). If a stable, concentric reduction is achieved within Ramsey's safe zone, a hip spica cast is applied (usually for 12 weeks). A percutaneous adductor longus tenotomy is frequently performed to widen the safe zone and decrease the risk of AVN.
2. Open Reduction (OR): Indicated if closed reduction fails, requires excessive force, or if the safe zone is incredibly narrow. The approach can be:
   • Medial Approach (Ludloff or Ferguson): Excellent direct access to the psoas and inferior capsule. Less blood loss, but higher risk of medial circumflex vessel injury if careless. Often used in younger children (< 12-18 months) without the need for concurrent pelvic osteotomy.
   • Anterior Approach (Smith-Petersen): Provides comprehensive exposure of the capsule, allowing clearance of all intra-articular obstacles and concurrent pelvic osteotomy if needed.

18 Months to 8 Years: The Reconstructive Era

In this older cohort, soft tissue contractures are severe, and bony deformity is established. Treatment usually involves a comprehensive, single-stage reconstruction:

1. Open Reduction: Essential to clear the joint.
2. Femoral Shortening / Varus Derotation Osteotomy (VDRO): Shortening the femur decompresses the joint, significantly lowering the risk of AVN. Correcting the excessive valgus and anteversion (VDRO) mechanically redirects the femoral head into the socket.
3. Pelvic Osteotomy: Required to correct acetabular dysplasia and provide definitive coverage.

Conclusion: The Long Game

DDH is profoundly time-sensitive. The natural history of untreated dislocation is a cascade of joint deterioration. A hip diagnosed and treated effectively at 2 weeks of age is often cured permanently with a simple fabric strap. A hip diagnosed at 2 years requires major pelvic and femoral reconstructive surgery with a lifelong risk of residual dysplasia. A hip diagnosed at 20 years will almost certainly require complex total joint arthroplasty in a young, active patient.

For the orthopaedic surgeon, vigilance during neonatal screening, mastery of the Graf ultrasound criteria, strict adherence to safe harness principles, and a deep understanding of the pathoanatomy of the late-presenting hip are the foundational pillars of success. Protect the blood supply at all costs, ensure concentric reduction, and respect the developmental biology of the hip joint.