Anatomical and physiological background
The newborn's hip joint differs fundamentally from that of an adult: the articular surfaces are underdeveloped and represented mainly by cartilaginous tissue.
- The acetabulum (acetabulum) has an oval shape and a sloped upper rim. It is formed by three ossification centers separated by the Y-shaped cartilage (ossifying only by 15–18 years). The depth of the socket increases due to the cartilaginous labrum — the limbus (limbus).
- The proximal femur (femur) is entirely cartilaginous, including the head, neck, and greater trochanter. On infant radiographs, these structures are not visualized.
The newborn's femoral head is always larger than the size of the acetabulum. This natural mismatch (incongruence) of the articular surfaces and insufficient coverage of the head create prerequisites for the development of pathology.
Pathogenesis: from subluxation to dislocation
The main cause of the disease is a delay in the normal intrauterine development of the joint. An unfavorable fetal position (especially sharp adduction of the legs in breech presentation) leads to the articular surfaces forming without close contact. This causes dysplasia.
Stages of pathological development:
- Preadluxation. The joint capsule is severely stretched, the femoral head easily slips out of the socket and returns back. May end in spontaneous recovery with proper infant care.
- Subluxation. The head is displaced and decentered, but does not extend beyond the limbus.
- Dislocation. Complete loss of contact between the head and the socket occurs, often with interposition of the limbus (it becomes trapped between the articular surfaces).
Before walking begins, the femoral head is displaced upward by the muscles. When the child starts walking, the displacement progresses—the head moves under the anteroinferior iliac spine and further toward the posterior surface of the iliac wing.
Symptoms in infants in the first year of life
Examination of the infant requires muscle relaxation (best during sleep or when the child is calm). Main clinical signs:
- Ortolani sign (click sign). Detected by flexion and abduction of the legs. Due to the stretched capsule, the femoral head "rolls" over the edge of the socket. In newborns, there is no sound; the sign is only felt by the physician. As the child grows, the capsule tightens, and the sign disappears (after 2–3 weeks, it occurs in only 25% of cases).
- Limited hip abduction. Normally, a newborn's thighs can be abducted to the table surface (or to an angle of at least 60° at an older age). In pathology, abduction is limited due to high tone of the adductors or the head resting against bone.
- Asymmetry of folds. On the affected side, the inguinal and gluteal-femoral folds become deeper and asymmetric.
- External rotation sign. Detected by the mother predominantly during sleep.
- Axis asymmetry and shortening. If the legs of a child lying on their back are bent at the knees and hips at a 90° angle, the knee on the side of the dislocation will be positioned lower.
Clinical presentation after the onset of walking
In children over one year old, gait disturbance becomes the leading symptom. With unilateral lesions, a "dipping" limp occurs; with bilateral lesions, a "waddling" gait appears.
Additional signs:
- Trendelenburg sign: if the child is asked to stand on the affected leg, the pelvis tilts toward the healthy (unsupported) leg, and the gluteal fold on that side drops.
- The greater trochanter is palpable above the Roser–Nelaton line.
- Relative limb shortening and limited abduction persist.
- In bilateral involvement, lumbar lordosis is significantly increased.
Radiodiagnostics: Hilgenreiner's scheme
In newborns, the clinical picture can be subtle, so radiography plays a decisive role. For accurate interpretation of radiographs, Hilgenreiner's scheme is used, which evaluates three parameters:
- Acetabular angle. Formed by a horizontal line passing through the Y-shaped cartilages and a tangent to the upper rim of the acetabulum. Norm: in children under 3 months — less than 30°, by 1 year — about 20°.
- Indicator $h$ (vertical displacement). The distance from the horizontal line to the middle of the femoral metaphyseal plate. Norm: 9–12 mm strictly symmetrical. In dysplasia, the indicator decreases and becomes asymmetric.
- Indicator $d$ (lateral displacement). The distance from the bottom of the acetabulum to the vertical line $h$. Norm: no more than 15 mm on both sides.
Briefly: answers to topical questions
Which radiographic lines are used to diagnose congenital hip dislocation?
Hilgenreiner's, Perkin's, and Shenton's lines are used to diagnose congenital hip dislocation and dysplasia.
- Hilgenreiner's line (Hilgenreiner's line) — a horizontal line passing through the Y-shaped (triradiate) cartilages.
- Perkin's line (Perkin's line) — a vertical line dropped from the lateral edge of the acetabular roof perpendicular to Hilgenreiner's line.
- Shenton's line (Shenton's line) — an arched line passing along the medial edge of the femoral neck and the lower edge of the superior pubic ramus.
Also, in Hilgenreiner's scheme, a tangent line passing along the upper edge of the acetabulum is used to measure the acetabular angle.
What orthopedic devices are used for the conservative treatment of congenital hip dislocation in children under one year old?
At 1–2 months of age, wide swaddling is supplemented with Pavlik harness. Treatment is carried out strictly in a specialized institution under the supervision of an orthopedic doctor with regular X-ray control. Children treated for hip dysplasia are prohibited from walking until 1 year of age.
What are the indications for surgical treatment of congenital hip dislocation?
The critical age to achieve congruence of the articular surfaces is up to 4 years. After 4 years, surgical correction is indicated. The scope of surgery depends on the degree of dysplasia and includes correction of the femoral and/or pelvic components: corrective osteotomies, acetabuloplasty, and pelvic osteotomies. In advanced cases in children over 6 years old with high iliac dislocations, palliative interventions aimed at stabilizing the joint, eliminating contractures, and removing pathological symptoms are indicated.
Through which anatomical landmarks does the Roser–Nelaton line pass?
The Roser–Nelaton line passes through the anterior superior iliac spine and the ischial tuberosity.
- Anterior superior iliac spine (spina iliaca anterior superior) — the upper anatomical landmark of the line.
- Ischial tuberosity (tuber ischiadicum) — the lower anatomical landmark of the line.
Normally, with the hip flexed at a 135° angle, the apex of the greater trochanter of the femur is located on this line. In congenital hip dislocation, the greater trochanter is palpable above this line.
Class and exam questions
Why is the proximal femur of a newborn not visible on radiographs?
In infants, the femoral head, neck, and greater trochanter consist entirely of cartilaginous tissue, which is radiolucent. The ossification center appears only by 3–4 months of age.
How to reliably detect leg shortening in an infant?
The child is placed on their back, legs are bent at the hip and knee joints at a right angle, resting the feet on the table. On the side of the dislocation, the level of the patella will be lower.
What conditions should limitation of hip abduction be differentiated from?
Limited abduction is not a strictly specific symptom for dislocation. It can be a consequence of neurological disorders causing muscle spasticity. In such cases, a neurologist's consultation is required.
What else to study on this topic
- The impact of breech presentation and fetal posture on the incidence of dysplasia
- The mechanism of formation of the Trendelenburg sign
- Limbus interposition and its effect on dislocation reduction
- Biomechanics of femoral head displacement after the onset of walking
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