Hip-healthy swaddling international hip dysplasia institute hip bone surgery

There are many ways to swaddle babies by using blankets or commercial products designed for swaddling. In order for swaddling to allow healthy hip development, the legs should be able to bend up and out at the hips. This position allows for natural development of the hip joints.

Some parents choose to wrap their babies in sleepsacks specifically designed for swaddling, instead of using a simple cloth or blanket. Commercial products for swaddling should have a loose pouch or sack for the baby’s legs and feet, allowing plenty of hip movement. However, even some of these commercial products can confine the legs if they are tightened around the thighs.

It’s especially important to allow the hips to spread apart and bend up. In the womb the legs are in a fetal position with the legs bent up across each other.

Sudden straightening of the legs to a standing position can loosen the joints and damage the soft cartilage of the socket.

Summary Statement: Swaddling infants with the hips and knees in an extended position increases the risk of hip dysplasia and dislocation. It is the recommendation of the International Hip Dysplasia Institute that infant hips should be positioned in slight flexion and abduction during swaddling. The knees should also be maintained in slight flexion. Additional free movement in the direction of hip flexion and abduction may have some benefit. Avoidance of forced or sustained passive hip extension and adduction in the first few months of life is essential for proper hip development.

Scientific Rationale: There are many benefits of swaddling,[1, 2] but improper swaddling increases the risk of hip dysplasia and hip dislocation.[3, 4] A leading proponent of swaddling, Harvey Karp, M.D., has stated, “Contemporary swaddling techniques…permit infants to be snugly wrapped with their hips being safely flexed and abducted.”[5] This position should be encouraged. An alternative method is to swaddle only the upper extremities and allow the lower limbs to move freely.[1, 2]

Mechanical factors in development of hip dysplasia The etiology of hip dysplasia in otherwise healthy infants is multifactorial, but mechanical factors play an important role.[6] Studies of hip development have been conducted using ultrasonography during late stages of fetal development prior to delivery and also in pre-term infants.[7, 8] These studies indicate that the normally developing hip is well-formed prior to birth. An unpublished study by Judy Estroff, M.D. at Harvard evaluated 451 fetal hip ultrasound studies. All hips were noted to be mature and well-formed near term. A published study of fetal ultrasonography also reported, “Prenatally, the mean ?-angles were above the level that corresponds to a mature hip joint.”[8] The acetabular roof angle decreased after birth in normal infants suggesting post-natal influences on developmental dysplasia. The same study evaluated pre-term infants and noted that ß-angles were greater in term infants than pre-term infants. This suggests that mature infants had greater displacement of the lateral soft tissues than pre-mature infants.[7] Dissections in deceased newborn infants with hip dislocation have not always demonstrated primary acetabular dysplasia.[9] Thus, the concept of “immature hip” should be re-considered with regards to anatomical development. These observations suggest that the hip may be more “mature” prior to birth and become more dysplastic around the time of birth. Gardiner, Clarke and Dunn postulated that transient ligamentous laxity from maternal relaxin and greater mechanical pressures around the time of birth may contribute to soft tissue deformation in the mature infant.[7] It is known that normal infants have an average hip flexion contracture of 28° that decreases to 19° at six weeks and 7° at three months of age.[10, 11] Hip flexion contractures of 50° to 120° and knee flexion contractures of up to 35° have also been noted in otherwise healthy newborn infants.[12] These improve rapidly in the newborn period and gradually resolve following the assumption of upright posture.[11, 12] Several authors have cautioned against extension of the hip during the neonatal period as this may contribute to subluxation, dislocation, or dysplasia of the joint.[11, 13, 14] Also, hip dysplasia has been shown to develop in animal studies, when the lower extremities were immobilized with the hips or knees in extension.[14-16] In these studies the incidence of hip dislocation was also increased by addition of maternal progesterone that promotes hip joint laxity and the effect was greater on females than males.[15, 16] There is evidence in humans that post-natal positioning influences the development of hip dysplasia. Hip dysplasia has been associated with abduction contracture of the contralateral hip.[17] Positioning the thighs together uncovers the femoral head and stretches of the hip capsule on the side opposite the abduction contracture. Protecting both hips with abduction bracing while implementing stretching exercises resulted in resolution of dysplasia.[17] It has also been noted that hip dysplasia is rare in cultures that carry their infants with the hips abducted.[4, 13] A study of Canadian First Nations demonstrated a ten-fold increase in the incidence of hip dislocation in tribes that carry babies on a “cradle board” with the hips strapped in an extended and adducted position.[13]. A high incidence of hip dislocation was noted in Navajo Indians who strapped their infants to a cradle board.[18] However the incidence of complete dislocation in Navajo Indians decreased dramatically in the 1940s when diapers were introduced instead of moss to absorb excreta. The reduction in the rate of dislocations was attributed to the use of diapers that kept the hips slightly abducted and flexed even when strapped in the cradle board. A somewhat similar experience has been documented in Japan.[15] In 1975 a national program was initiated in Japan to avoid swaddling infants with the hips and knees in extension. Prior to that initiative, the incidence of infantile dislocation of the hip was as high as 3.5%. Following that initiative, the incidence dropped to less than 0.2%.[15] A significant relationship between swaddling and hip dysplasia has also been found in Turkey.[19] Swaddling is increasing in frequency in the USA to promote improved sleep habits.[1] The benefits of this practice may be offset by higher rates of developmental hip dysplasia and dislocation if infants are swaddled incorrectly. Caution when swaddling has been recommended to allow the hips to move freely to avoid increasing the risk of developmental dysplasia.[1, 3]