Hip Impingement

HIP IMPINGEMENT

Within the hip joint the head of the femur and the acetabulum (socket) are coated with articular cartilage to permit smooth movement.

Around the rim of the acetabulum sits a lip of fibrous cartilage that is triangular in cross-section, called the labrum. The labrum improves the stability of the hip and, along with the joint capsule, helps to ‘seal’ the hip joint.

Both the labrum and the articular cartilage can be damaged by injury to the hip. However, the most common cause of damage to the labrum and articular cartilage is as a result of impingement, or to give it it’s proper name femoroacetabular impingement (FAI).

FEMOROACETABULAR IMPINGEMENT

This is a condition that has only recently been recognised as a cause of hip symptoms. It is thought to be the underlying cause for >75% of all cases of osteoarthritis of the hip. Impingement results either because the femoral head (ball) is not quite spherical or because the acetabulum (socket) is too deep; thus when the hip is flexed fully the neck of the femur is pushed against the labrum and acetabulum at the front of the hip, causing damage to these structures. There are 2 basic types of Hip Impingement. CAM impingement occurs when the femoral head is not spherical. PINCER impingement occurs when the acetabulum is too deep (or points slightly backwards – retroverted). If both types of impingement are present it is termed MIXED impingement.

Symptoms are of groin pain which is related to activity. Sports, sitting and driving aggravate symptoms. There may also be mechanical symptoms such as catching, locking and pain when pivoting. Examination reveals pain when the hip is flexed, adducted (brought across the body) and internally rotated. This is termed a positive impingement test.

INVESTIGATION AND TREATMENT

X-rays can identify the sphericity of the femoral head and depth of the acetabulum but abnormalities can be very difficult to spot as the changes are subtle.

An MR arthrogram may be helpful in identifying labral tears and articular cartilage damage associated with impingement and can also be used to measure specific parts of the patient’s hip anatomy. This can be important when planning further surgery.

The use of Hip Arthroscopy as an investigation tool for impingement allows the assessment & treatment of any associated cartilage damage (both the labrum and articular cartilage) and the identification of significant osteoarthritis. If the hip does not have any significant arthritis but has evidence of impingement, the patient’s symptoms may be improved by a hip resculpting procedure. Recent advances in arthroscopic hip surgery have shown that the abnormal bump on the femoral neck can be removed via the arthroscope. This is known as Hip Resculpting. Early results are very encouraging in terms of symptom relief and safety (i.e. low complication rate). We do not know yet whether or not this sort of surgery lowers the risk of subsequent development of osteoarthritis or whether the need for hip replacement will be avoided.

LABRIAL TEARS

Tears of the labrum are usually caused by sudden pivoting or twisting actions but can also occur as a result of developmental hip problems such as Perthes’ disease, slipped upper femoral epiphysis or developmental dysplasia. Most labral tears occur as a result of hip impingement.

The symptoms of a labral tear include groin pain, catching, clicking or locking of the hip.

Examination may be relatively unremarkable but if the hip is flexed fully, brought across the body (adducted) and rotated internally, pain and catching may be felt. There may be an audible ‘clunk’.

INVESTIGATION AND TREATMENT

Investigation should begin with a plain x-ray which may show evidence of previous hip disorders such as Perthes’ disease or dysplasia, but are frequently normal. There may be evidence of impingement.

MRI scanning is useful but can be improved in terms of its accuracy by the injection of contrast into the hip by the radiologist; this is called an MR Arthrogram. The best method of diagnosing and treating labral tears is by Hip Arthroscopy. Unstable fragments of labrum can either be removed or repaired depending on the degree of damage.

ARTICULAR CARTILAGE TEARS

These are also known as Chondral Injuries. They are frequently found along with labral tears, osteoarthritis, dysplasia and avascular necrosis, but are also caused by trauma, especially by a direct blow to the outer part of the thigh (‘lateral impact injury’). Most chondral injuries occur as a result of hip impingement. Symptoms of chondral injuries are similar to those of a labral tear but they are usually more painful and the patient may have a significant limp with a very irritable hip on examination.

INVESTIGATION AND TREATMENT

Plain x-rays and MR arthrogram are useful investigations but arthroscopy is the most accurate way of diagnosing a chondral injury. Treatment can be carried out at the same time; unstable areas of chondral damage can be trimmed to a stable margin and if necessary, microfracture can be performed.

Microfracture is where a small, sharp pick is used to perforate the underlying bone and encourage healing of the cartilage defect. A good outcome can result, but does not replace the damaged area with normal cartilage.

If microfracture is performed, a period of 4-6 weeks on crutches is necessary afterwards.

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