Sonography of the infant hip (synonyms: sonography according to Graf; ultrasound of the infant hip) is a screening procedure for the early detection of hip maturation disorders as well as congenital deformities of the infant hip. This ultrasound examination was established by R. Graf in the 1980s and is part of the U3 screening examination. The so-called congenital hip dysplasia (synonym: hip joint dysplasia; hip dysplasia, developmental dysplasia of the hip, congenital dysplasia of the hip; abbreviations: CDH, DDH; collective term for congenital or acquired deformities and disorders of ossification of the hip joint in the newborn) is one of the most common congenital anomalies of the musculoskeletal system, with an incidence (frequency of new cases) of 2 to 4%. It can be detected by early sonography. Congenital hip dislocation is the most severe manifestation of congenital hip dysplasia (hip joint malformation). In this condition, the acetabulum is not deep enough to adequately enclose the condyle (acetabular dysplasia). Together with a loosening of the hip joint capsule, this malformation can lead to subluxation or luxation (dislocation of the joint). The cause is a disturbance in the maturation of the hip joint, which is due to delayed formation of the acetabulum in particular. The following are risk factors for the development of hip dysplasia:
- Positive family history – hip dysplasia or osteoarthritis of the hip in the family.
- Oligohydramnios (insufficient amniotic fluid; amount of amniotic fluid: < 200 to 500 ml).
- Premature birth
- Breech presentation
- Positive clinical examination with suspected hip dysplasia.
- Further skeletal anomalies
At birth, there is usually no dislocation hip but only the acetabular dysplasia. In the course develops a dislocation with load and pull by the muscles. While dislocation hip can be diagnosed on clinical examination, mild hip dysplasia can be detected with sonography. If a dislocated hip is not treated, contractures (restriction of function and movement of joints) lead to a positive Trendelenburg sign (“waddling gait”; patient cannot keep his pelvis in balance while standing on one leg – whereby the muscles of the stance leg are affected) and subsequently to a walking disability, among other things via leg shortening. Another risk is the development of secondary osteoarthritis (osteoarthritis that develops due to an event that itself has disease value and is causative, while primary osteoarthritis is to be seen as age-related wear and tear) of the hip in middle adulthood; hip dysplasia is thus to be seen as a prearthrotic deformity. Screening allows early treatment and subsequent cure of congenital conditions of the infant hip.
Indications (areas of application)
Graf sonography is used as a screening examination for early detection of congenital hip dysplasia (congenital maldevelopment of the hip joint).
Contraindications
Sonography (examination with ultrasound) does not result in radiation exposure and is not invasive. Therefore, there are no contraindications for this examination.
The procedure
Because the structures of the infant hip are predominantly hyaline (cartilaginous) rather than osseous (bony) in organization, sonography, but not radiography, is suitable for visualizing a possible malformation with disease significance. In particular, the acetabular roof is composed of hyaline cartilage at this time. The results of sonography are subsequently classified according to Graf and treated accordingly, with only an immature type IIb hip requiring treatment according to Graf:
- Type I according to Graf (a, b) – mature hip joint.
- Type II according to Graf (a, b, c) – hip dysplasia with the head remaining in the socket.
- Type III according to Graf (a, b, + type D) – migration of the femoral head out, so-called subluxation.
- Type IV according to Graf – Complete dislocation or luxation of the joint.
Graf established a standard plane that allows safe reproduction of sonography of the infant hip. Furthermore, Graf introduced the angles alpha and beta, according to the width of which hip dysplasia can be classified. The angles indicate the position of the anatomical structures in relation to each other.The classification according to Graf also takes into account the age of the patient and the bony oriel of the acetabulum: the so-called oriel normally presents itself as low in echo in sonography; if the echo increases, this corresponds to a compression in the area of the acetabular roof, which can result from the incorrect loading (pressure load) caused by an already subluxated femoral head. The following anatomic structures are seen on the standard plane:
- Oriel
- Joint capsule
- Femoral head
- Labrum acetabulare (acetabular lip)
- Cartilaginous acetabular roof
- Osseous acetabulum
- Cartilage-bone boundary
- Envelope fold
Dynamic ultrasound examination (movement of the hip during the examination) allows assessment of possible instability of the hip joint. Technical requirements for sonography of the infant hip is an ultrasound machine with frequencies from 7.5 MHz upwards. Documentation should be provided by two time-shifted images per side examined. One of the images must contain the acolytes with α and β angles. The following possible sources of error should be considered:
- Insufficient bearing (use of bearing is obligatory).
- No or incomplete anatomical identification
- Inadequate measurement technique (angles α and ß are incorrect due to incorrect anatomical identification).
- Incongruence of findings and angle measurement.
Possible complications
No complications are expected for this examination.
