By Eva Briggs
It turns out that there are three scenarios that lead to hip dislocation: after hip replacement, following trauma or in infants with developmental dysplasia of the hip.
The hip joint consists of a ball at the top of the thigh bone (femoral head) that fits into a socket (acetabulum) in the pelvis. The joint surfaces are covered by cartilage to provide a smooth gliding surface. A ring of fibrocartilaginous tissue, the labrum, surrounds the hip joint and helps seal the joint and keep the bones stabilized in the proper position.
Traumatic hip dislocations require a high force injury such as a motor vehicle accident or fall from a significant height. The hip is pushed and forced out of the socket. About 90 percent of the time the hip is pushed backward leading to a posterior dislocation. Less often the hip dislocates forward, an anterior hip dislocation.
This is a serious, painful injury. The ligaments, labrum, muscles and nerves may be damaged. The patient won’t be able to move his leg. If the nerves are damaged the patient may lose feeling in the foot or leg. Often there are broken bones, such as a piece of the acetabulum broken off when the hip is forced out of the socket.
Because hip dislocations occur in high force accidents, there may be breaks to other bones in the leg or pelvis, spine injuries, or head trauma.
When there are no other injuries, an orthopedic surgeon may be able to reduce (manipulate into place) the dislocation after the patient receives anesthesia or sedation. Sometimes this is done in the operating room. If broken bits of bone or torn soft tissues are in the way, surgery might be required to maneuver the hip back into place.
Complications include injury to the sciatic nerve in about 10 percent of patients, causing pain, numbness or weakness. Damage to blood vessels within the hip can lead to bone death (osteonecrosis) of the femoral head. This produces pain and rapid development of severe arthritis, often necessitating hip replacement. Damage to the smooth cartilage lining the hip joint during hip dislocation also leads to arthritis.
Hip dislocation after hip replacement usually occurs in the first few months after surgery, when the soft tissues surrounding the hip joint haven’t fully healed. It can usually be reduced without surgery. Rarely the hip dislocations are recurrent, requiring additional surgery.
Developmental dysplasia of the hip (DDH) occurs when the hip joint hasn’t formed properly and the ball is loose within the hip socket. Typically it is present at birth, but can develop in the first year of life. Pediatricians check for this in newborns and at each well child exam. When DDH is suspected, the doctor can order an ultrasound or X-ray, depending on the child’s age.
Risk factors for DDH include family history of DDH in parents or siblings, female sex, first born, breech position, and decreased amniotic fluid.
Most infants identified with DDH can be treated with a soft brace such as a Pavlik harness worn for a few months. This keeps the hips flexed and the legs rotated outward. It positions the ball within the socket allowing the hip to form properly.
It turns out that improper swaddling, with the baby’s legs out straight, can cause DDH. For example, an educational program about correct swaddling in Japan reduced DDH from 3 percent of infants to less than 1 percent. A good video (although a bit dry) from the International Hip Dysplasia Institute can be found at https://hipdysplasia.org/developmental-dysplasia-of-the-hip/hip-healthy-swaddling/
The speaker explains how improper swaddling might cause an infant’s hips to dislocate, then shows video examples of three ways to properly swaddle an infant.
Eva Briggs is a medical doctor who works at two urgent care centers (Central Square and Fulton) operated by Oswego Health.