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What is Os Acetabuli?

An Os Acetabuli is a lesion of the acetabular rim commonly seen in patients with Femoral Acetabular Impingement (FAI) and hip dysplasia. It is an unfused secondary ossification (process of creating bone) center of the acetabulum and is an area in the acetabulum where bone has not properly formed.

Bones are initially cartilage and slowly transform into bone at ossification centers that slowly spread until no cartilage is left. Different ossification centers spread and fuse with other ossification centers but sometimes fusion does not take place leaving a separate unfused bone. In the acetabulum, this can happen in the anterior superior margin and that isolated bone is called the os acetabuli.

Os acetabuli improves the surface and contact area of the acetabulum and is crucial for maintaining congruity of the hip joint. Hence, preservation of these ossicles, secondary ossification centers that remain separate from the adjacent bone, is significant to prevent loss of contact area and ensure containment of the femoral head in the acetabulum.

Risk Factors for Os Acetabuli

A risk factor is something that is likely to increase a person’s chance of developing a disease or condition. Risk factors for developing os acetabuli may include the following:

  • Hip dysplasia
  • Degenerative or post-traumatic bone fragments
  • Femoroacetabular impingement (FAI)
  • Osteochondrosis dissecans
  • Structural/anatomical abnormalities of the hip
  • Congenital hip conditions
  • Male gender

Signs and Symptoms of Os Acetabuli

Some of the signs and symptoms of os acetabuli include:

  • Hip impingement
  • Reduced range of hip motion
  • Groin pain associated with hip activity
  • Complaints of pain in the front, side, or back of the hip
  • A locking, clicking, or catching sensation in the hip
  • Pain in the inner hip or groin area after prolonged sitting or walking
  • Pain in the buttocks or outer thigh area

Diagnosis of Os Acetabuli

Os Acetabuli is diagnosed based on a review of your medical history, a thorough physical examination to check for any abnormality in hip motion, and diagnostic studies, such as X-rays, MRIs, and three-dimensional CT scans to check for any anatomical differences in the acetabulum which confirms the diagnosis.

Treatment for Os Acetabuli

Os acetabuli can be successfully managed through a minimally invasive arthroscopic surgery technique in which an arthroscope, a narrow tube with a tiny camera and light source on the end, and miniature instruments are inserted through small incisions over the hip to access the acetabulum and remove the os acetabuli to relieve pain and other associated symptoms. However, care should be taken in removing unfused secondary ossification centers, as removal of a large os may result in iatrogenic dysplasia. Additionally, any damage to the soft-tissue structures such as the cartilage and labrum are also repaired during the operation.

Surgery is immediately followed by rehabilitation and involves a focused physical therapy program under the guidance of a physical therapist to improve hip movement and strength.