Anteroposterior pelvis X-ray.
Lateral view X-ray.
A 35-year-old woman presents with right hip pain, which she has had for several months. She stopped running recently due to the pain and feeling that the hip was “popping out of place.” On examination, she has groin pain with passive hip flexion and internal rotation. She has no lower back pain and no motor weakness in the right lower extremity. Anteroposterior pelvis and lateral X-rays of the right hip (Figures 1 and 2) show a shallow acetabulum, an increased femoral neck-shaft angle, and an abnormal lateral center edge angle consistent with developmental hip dysplasia (DDH).
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Developmental hip dysplasia (DDH) is one of the most common causes of hip pain in patients younger than 50 years of age. Risk factors include female gender, breech position at birth, and a positive family history. DDH is a development disorder in which the hip fails to form in a normal shape. In DDH, the acetabulum is typically shallow, lateralized, and deficient anteriorly and superiorly. On the femoral side, the femoral neck is usually in a valgus position (increased neck-shaft angle), and the femoral head is usually small. These anatomic abnormalities cause a decreased contact area between the femoral head and acetabulum, which leads to increased motion of the head in the socket. Increased motion leads to early cartilage wear and a higher prevalence of labral tearing. DDH is often missed during infant screening and is most commonly diagnosed when symptoms arise in adulthood. DDH is the most common cause of hip arthritis in women younger than 50 years of age, and up to 10% of all total hips performed in the US are due to DDH.1,2
Anteroposterior pelvis and lateral view X-rays are diagnostic of DDH. A common radiographic measurement to diagnose and quantify the severity of DDH is the lateral center edge angle. The angle is formed between a line drawn from the center of the femoral head to the lateral edge of the acetabulum and a vertical line drawn from the center of the femoral head. An angle greater than 25 degrees is considered normal, and an angle less than 20 degrees is associated with dysplasia. An angle greater than 39 degrees indicates acetabular overcoverage, which is seen in pincer type acetabular impingement.1
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor-in-chief of the Journal of Orthopedics for Physician Assistants (JOPA).
- Gala L, Clohisy JC, Beaulé PE. Hip dysplasia in the young adult. J Bone Joint Surg Am. 2016;98:63-73.
- International Hip Dysplasia Institute. Hip dysplasia. http://hipdysplasia.org. Accessed October 17, 2017.