Normal bony anatomy of the hip joint

The hip joint is a ball-and-socket joint.  The socket, called the acetabulum, is part to the pelvic bone and is shaped like a hemisphere and composes the weight-bearing surface of the hip joint.  The socket is covered in a layer of cartilage, which acts to cushion and lubricate the joint, allowing for smooth motion.    The rim of the socket is covered by a ring of specialized cartilage that goes all the way around the socket, called the labrum. The labrum is an important structure for normal hip function, as it adds depth to the joint, creates a seal that maintains joint fluid within the hip and adds stability to the hip socket. The labrum contains many nerve fibers and causes pain when it is torn.  The labrum is frequently torn in pre-arthritic conditions such as hip impingement and hip dysplasia.  In a normally shaped hip joint, the labrum is almost never torn without a traumatic event causing the ball to come out of the socket.  The ball of the ball-and-socket joint is called the femoral head, and it is the top part of the thigh bone (femur).  The ball is covered in a layer of cartilage that contacts the cartilage layer of the socket, again allowing for smooth weight-bearing and movement.

Normal hip

In a normal hip, the socket should cover the ball to the appropriate extent and the ball should be perfectly round (spherical). Too much coverage of the socket causes impingement (pincer impingement), where the bones of the ball and socket knock against each other.  Alternatively, if the ball is not perfectly round, a different type of hip impingement can occur (cam impingement), and when the hip joint moves, it’s like to forcing a square peg into a round hole.  While hip impingement results from excessive or abnormal contact of the ball and socket, hip pain can also result from a socket that has too little coverage, or a shallow hip socket, which is called hip dysplasia. Both hip impingement, also called FAI (femoroacetabular impingement), and hip dysplasia can result in damage and tears to both the labrum and cartilage. Labral tears frequently cause groin pain which becomes worse with high-demand activities (running, jumping, cutting, squatting, rotating) and normal daily activities (sitting, using stairs, putting on socks and shoes, etc.). If left untreated for many years, the repeated injury to the labrum and cartilage can result in osteoarthritis.

Femoroacetabular impingement (FAI) - Left: socket overcoverage (pincer); Middle: aspherical ball (cam); Right: combined hip impingment (both cam and pincer simultaneously)
Dysplastic hip (shallow hip socket)

 Osteoarthritis (arthritis) is a loss of the cartilage surface in a joint, and when it becomes advanced and painful enough, the only available option is a hip replacement, which removes the arthritic parts of the joint and replaces them with metal, ceramic and/or plastic.  Arthritis can be delayed or prevented if hip impingement or hip dysplasia is diagnosed and treated properly and in a timely fashion.  Hip surgeries aimed at treating hip injuries before arthritis begins are called hip preservation.  Hip preservation surgeries include hip arthroscopy, periacetabular osteotomy (PAO), surgical dislocation of the hip (SDH) and others, discussed below.

There are several other hip injuries that involve the soft tissues (muscle, tendon, ligament) surrounding the hip joint.  These include gluteus tendon tears, hamstring tendon tears, hip snapping (internal and external), bursitis, ligamentum teres tears, hip joint instability and growth plate injuries, all of which can cause pain and functional limitation.  These injuries and their respective treatments are listed below. If you have any of the following conditions or undiagnosed hip, groin or buttock pain, please contact us for an appointment.