Hip Instability

Hip instability can be the result of bony instability due to hip dysplasia.  A subtler form of instability, called microinstability, is a more recently described entity that can be present in adult hips and lead to hip dysfunction and pain. 

Hip Dysplasia

Hip dysplasia is a condition in which the hip socket (acetabulum) is shallow and does not fully cover or support the femoral head (the “ball” of the hip joint). This structural abnormality causes the hip joint to be loose or unstable, which can lead to joint pain, abnormal movement, and eventual degeneration of the joint.

Hip dysplasia is commonly measured on an x-ray by the lateral center edge angle (LCEA).  The LCEA is the angle between the center of the femoral head and the outside edge of the acetabulum.  A LCEA between 25° and 40° is considered normal (above left).  A LCEA less than 18-20° is often associated with dysplasia and instability (above right).  A LCEA between 18-20° and 25° is considered borderline dysplasia and associated with microinstability

Causes and Risk Factors:

• Congenital (Developmental Dysplasia of the Hip or DDH): Hip dysplasia can be present at birth or develop in infancy and early childhood. In infants, the hip joint forms abnormally, and the hip socket remains shallow as a child grows.
• Genetic Factors: Family history of hip dysplasia increases the risk.
• Other Risk Factors: Breech position during pregnancy and female gender are also associated with a higher risk.

Symptoms: In infants and young children, hip dysplasia may cause limited hip range of motion, leg-length discrepancy, or a "click" sound when moving the hip.

In older children and adults, hip dysplasia may lead to:

• Hip or groin pain (20% of children report only knee pain with hip pathology)
• A sensation of hip instability or "catching"
• Reduced range of motion
• Development of osteoarthritis, often in early adulthood due to abnormal wear and tear in the joint

Diagnosis and Treatment:

• Diagnosis is usually made through physical exams and imaging tests like X-rays or MRI.
• Treatment for infants may include bracing to help the hip form correctly as they grow. In older children and adults, surgical options, such as a periacetabular osteotomy (PAO), can correct the joint alignment and deepen the hip socket to restore hip stability and prevent further damage.

Early diagnosis and intervention are important to help prevent joint deterioration and improve hip function.

View the helpful video below, "Understanding Hip Dysplacia":

Microinstability

Hip microinstability is a condition where the hip joint lacks the stability needed to maintain proper alignment and function. Unlike hip dislocation or major instability due to dysplasia, hip microinstability involves subtle looseness or excessive movement in the joint, which can lead to pain, discomfort, and potential joint damage over time. This instability usually occurs when the supporting structures around the hip — such as the joint capsule or ligaments and the labrum (the ring of cartilage around the socket) — are compromised or weak.

Marc Safran and colleagues at Stanford have summarized the etiology of microinstability in young athletes as being multifactorial with contributions from: bony deficiency (borderline dysplasia), capsular and ligamentous laxity, and labral deficiency or tearing.

Causes and Risk Factors

• Trauma or Injury: Repetitive hip movements, particularly in sports like gymnastics, dance, or soccer, can strain the ligaments and lead to microinstability.
• Bony Deficiency: borderline dysplasia is the result of mildly shallow hip socket (LCEA 18-25°).  This can contribute to “extra-physiologic” or abnormally increased motion between the femoral head and the acetabular socket.
• Capsular or Ligament Laxity: Some individuals naturally have more flexible ligaments, making their joints more prone to instability. Patients with connective tissue disorders such as Ehlers-Danlos syndrome (EDS) would also be at higher risk for hip microinstability. EDS is a group of inherited connective tissue disorders characterized by defects in collagen, a key protein that provides strength and elasticity to joints and other tissues.
• Labral Tears: A torn labrum can destabilize the hip joint, as the labrum provides important stability by creating a suction seal.  Labral deficiency may also result from chronic wear due to primary microinstability (bony and capsular deficiency) and further exacerbate the underlying microinstability.
• Iatrogenic: Hip arthroscopy surgery requires the use of a capsulotomy, in which the joint capsule is cut in order to access the joint.  If the capsulotomy (capsule defect) does not heal adequately after surgery, the integrity of the joint capsule and ligaments may be compromised and lead to microinstability (below left).

Symptoms

• Hip or Groin Pain: Often worsens with activities involving rotation or prolonged weight-bearing, such as running, jumping, or climbing stairs.
• Sensation of Hip Looseness or Giving Way: Some people describe the feeling that their hip is slipping or slightly out of place.
• Reduced Range of Motion: Activities that involve hip extension, rotation, or flexion may become uncomfortable or limited.
• Clicking or Popping Sensation: This can occur when the joint is unstable or when tissues in the joint are irritated.

Diagnosis and Treatment

• Diagnosis typically involves a combination of patient history, physical examination, and imaging studies like MRI or ultrasound. Special tests may also be done to assess hip stability and detect any ligament or labral issues.
• Treatment starts conservatively, with options like physical therapy to strengthen the hip muscles, improve stability, and reduce strain on the joint. If conservative treatments fail and symptoms persist, arthroscopic surgery may be considered to restore hip stability by repairing damaged structures, such as the labrum and joint capsule.

Hip microinstability is an evolving area of study, and early diagnosis and intervention can help improve outcomes and prevent long-term joint damage.