Who is at Risk?
The hip is considered a generally stable joint, unlike the shoulder, which is more pre-disposed to instability. However, hip instability can occur and is generally seen in patients who have:
- sustained prior trauma – such as a traumatic dislocation
- generalized ligamentous laxity, or loose joints
- hip dysplasia – or a poorly formed hip socket
Normal Hip Anatomy?
The hip is a ball and socket joint. The femur bone has a cartilage-covered femoral head (ball) which fits into the pelvis acetabulum (socket). The acetabulum is a deep socket – deeper than the shoulder socket, thereby creating a more stable joint. Yet the hip is similar to the shoulder joint in that it has many degrees of motion in many different planes, unlike a knee or elbow joint, which only bends and extends. To add to the stability, there is a ring of cartilage, called the acetabular labrum which further deepens the socket and creates a suction-seal to keep the ball in the socket. Furthermore, there is a ligament inside the hip called the ligamentum teres connecting the acetabulum and the femoral head which provides stability. Finally, there are three extremely strong ligaments that surround the hip and form a capsule to hold the hip in place called the iliofemoral ligament, ischiofemoral ligament, and pubofemoral ligament.
Traumatic Hip Instability
Instability of the hip joint is most often seen in three situations:
- High-energy trauma such as a motor vehicle accident
- Fall from height
- Significant collision during contact sports
In these cases the ball may completely dislocate (come out) of the socket. This may require immediate medical attention to reduce the hip (put it back in place). After these traumatic events, the patient may be left with symptoms of instability of the hip after a dislocation. In athletes and those patients who participate in repetitive motion in the hips (twisting and rotating as is the case in golf, baseball, tennis, soccer) further damage can occur to the labrum and acetabular cartilage.
Non-Traumatic Hip Instability
There are several types of non-traumatic instability of the hip.
- generalized ligamentous laxity (loose joints)
- hip dysplasia (poorly formed hip socket)
- femoroacetabular impingement
Patients with femoroacetabular impingement can develop tears of the hip labrum and articular cartilage which can eventually lead to microinstability of the hip. Hip instability may also develop in patients who are born with hyper-ligamentous laxity (loose joints) or those whose hips do not develop properly (called hip dysplasia).
Patients with hip instability can develop many symptoms including:
- Sensation that the hip will dislocate during weight bearing on the leg
- Deep aching in the hip joint
- Palpable or audible clicking or shifting of the hip during activities such as walking or sports
- Ability to voluntarily bring the hip out of joint and place it back into joint
Diagnosis and Treatment
Patients who present with symptoms of hip instability must undergo a thorough evaluation through a detailed history, physical examination and diagnostic studies. An MRI scan may be ordered to determine the status of the articular cartilage, labrum, impingement lesions, ligamentum teres and capsular structures. In most cases, the recommended treatment will be conservative in nature with specific physical therapy instructions to strengthen the dynamic hip stabilizers as well as taking anti-inflammatories and modifying activities that place the hip at risk.
If the hip instability is severe or fails a period of conservative management, then surgery may be necessary. Generally, this may be performed with an arthroscopic procedure through small skin incisions using a camera and special instruments. The type of surgery depends largely on the specific injury and cause of instability. Usually, the labrum is repaired or reconstructed and any underling femoroacetabular impingement (FAI) is addressed. Then the hip capsular ligaments are tightened and the ligamentum teres may be tightened (or in severe cases reconstructed). The end-goal of surgery is to stabilize the hip, allow for more normal motion, and in most cases prevent future instability.