What is the labrum?
The hip labrum is a horseshoe-shaped cartilage structure attached to the rim of the acetabulum (hip socket). It is triangular in cross section. It plays a key role in hip stability and cartilage consolidation with by providing a suction seal effect for the hip joint and helps spread the synovial (joint) fluid evenly between the ball and socket thereby reducing cartilage stress and strain.
What is a labral tear?
The hip labrum can be damaged due to dynamic forces acting across the hip joint. There are five common reasons identified causing labral tears. These include femoroacetabular (bony) impingement, dysplasia (shallow socket), trauma, laxity or hypermobility, and degeneration (predominantly arthritis). A labral tear can cause abnormal biomechanics of the hip joint by causing potential leakage of synovial fluid disrupting the suction seal. There may be some contributions from nerves to the labrum that are thought to cause pain from a labral tear. However, it is important to know that studies have also identified labral tears in the asymptomatic (non-painful) hip. Hence understanding the cause of the labral tear and whether or not it in and of itself is causing the pain in the hip is paramount before its management.
Labrum tears can occur in a large demographic of individuals. It can produce mechanical symptoms such as clicking and catching in the hip as well as pain that is frequently felt in the groin. The pain can be during activities such as walking or jogging but can also be felt at rest especially after a lot of activity or while sitting with the hip flexed such as while resting in a low chair. It is uncertain whether the labrum has any healing potential.
It is usual to rehabilitate the hip with physiotherapy for three to six months to see if symptoms abate.
How do you diagnose a labral tear?
The diagnosis of a labral tear requires a history, physical examination, and a review of radiographic imaging of the hip. The history may include mechanical symptoms and pain, predominantly in the anterior hip and groin region. This may or may not be incited with a specific traumatic event. Typically the hip pain is accentuated with motion of the hip, particularly in flexion and hence sitting or other deep flexion activities are more bothersome.
Physical examination often reveals a reduction in internal rotation and pain when the hip is flexed up, internally rotated and brought across the body. These maneuvers cause more stress on the labrum and bony impingement accentuating the pain. However, greater loss of motion in all directions often signifies the onset of more significant arthritis.
Radiographic imaging begins with a weightbearing x-ray of the pelvis, which is very useful and will always be required in the work up of patients with hip or groin pain. It will show the bony anatomy of the hip joint and some of the predisposing factors (listed above) that can lead to labral tears. Most importantly, it will indicate if overt arthritis is present, which could be a major cause of the hip pain.
Magnetic Resonance Imaging (MRI) with an arthrogram (where a dye/contrast agent is injected in the hip joint prior) is the best test to show a labral tear.
An MRI scan uses strong magnets rather than radiation and shows the soft tissues such as cartilage and muscle very clearly. The contrast agent is nontoxic and is excreted in the urine a short time after but can make the hip ache a little more over the next 24-48 hours.
The contrast fluid fills the gap between the edge of the socket and the torn labrum, thus outlining the tear. Despite its superior soft tissue visualization, an MRI is most effective only when performed with a clinical question in mind and after a thorough review of x-rays. This helps put findings in a proper context for the person interpreting the MRI.
Oftentimes x-rays identify obvious issues with the hip for which an MRI may not be necessary and may delay diagnosis and/or management. It should also be noted that multiple research studies in the literature have shown the presence of labral tears in upwards of 69-85% of asymptomatic volunteers and so finding one on an MRI may not always correlate to patients’ symptoms. Hence, judicious use of an MRI in the evaluation of hip pain is suggested.
The MR arthrogram may also show some of the bony abnormalities that can cause femoroacetabular impingement and are thought to contribute to labral tears. However, it is also sometimes necessary to obtain a CT scan which is the most accurate way to show any bony predisposing factors.
How do you manage a labral tear?
Prior to considering management of a labral tear, it is important to understand whether or not it is a contributing factor to the patient’s symptoms. When uncertain, a diagnostic injection can be performed with local anesthetic in the patient’s hip using x-ray or ultrasound guidance to ascertain the position of the injection within the hip joint.If determined to be a potential cause, labral tears can be managed non-operatively or operatively.