HIP IMPINGEMENT – A BRIEF INTRODUCTION
What is it?
- Recent concept. Common cause of hip pain in young adults.
- Proposed to be one of the causes of arthritis of the hip at younger age.
What are the mechanisms?
- Cam impingement (bony bump at the head neck junction damages the labrum and cartilage with flexion)
- Pincer impingement (over-
coverage of the acetabular wall – the labrum gets pinched between the acetabulum and femoral neck and gets damaged)
What are the symptoms?
- FAI usually presents in active young adults with slow onset of deep groin pain that may start after a minor trauma. During the initial stages of the disease, the pain is intermittent and may be exacerbated by excessive demand on the hip, such as from athletic activities including deep flexion of the hip or prolonged walking. The pain also may present after sitting for a prolonged period.
- Mechanical symptoms from the hip such as painful locking or giving way are common presenting feature if labral tear is present.
Whom does it affect?
- Cam impingement – more common in young active males (M:F 14:1, age range 21-
51, mean 32)
- Pincer impingement – More common in middle-
aged active females (M:F 1:3, age range 40- 57, mean 40)
(Tannast M, Siebenrock KA, Anderson SE. Femoroacetabular Impingement: Radiographic Diagnosis—What the Radiologist Should Know AJR 2007; 188:1540-
- Often many have mixed type of impingement
What are the clinical signs?
- Anterior Impingement test –
Hip is flexed to 90 degrees. Hip then passively flexed further, adducted and internal rotation – Positive if it reproduces the pain similar to that experienced by the patient.
- Posterior impingement (uncommon) – The hip is passively hyperextended by hanging the leg over the end of the couch while keeping the opposite limb in neutral position. Pain is reproduced if passive external rotation of the extended leg.
Differential diagnosis of hip pain in young adults
- Acetabular dysplasia
- Avascular necrosis
- Snapping iliopsoas tendon
- Non hip causes like inguinal hernia etc.,
How do we investigate?
- Plain radiographs
Cam impingement: Bump over the anterolateral aspect of the femoral neck. Often obvious only in the horizontal beam lateral – hence the need to do both AP pelvis Xray and horizontal beam lateral when impingement syndrome is suspected. Various measurements like alpha angle etc.,
Pincer impingement: Cross over sign in standardised AP pelvis Xray – due to overcoverage of the anterior acetabular wall.
- MRI arthrogram – evaluates cartilage damage and labral tear. Also may show pathology like avascular necrosis.
An initial trial of nonsurgical treatment, which may include activity modification including restriction of athletic activities, and nonsteroidal anti-
- Surgical treatment:
1. Through open dislocation of the hip
2. Combined arthroscopy and mini-
3. Arthroscopic treatment
- Encouraging early results for symptomatic improvement in recent literature.
- Less optimal result when there is large area of cartilage damage or presence of early arthritis
- Still an evolving concept
- No long term studies are available to show that surgical treatment can prevent the progression of arthritis
Hip impingement is a recently recognised condition which can cause hip pain in young adults. Essentially in this condition, the clearance between the ball (femoral head) and the cup (socket) of the hip joint is less than adequate. Often this is due to an abnormal shape of the ball of the hip joint (CAM impingement) or over coverage of the cup of the hip joint (Pincer impingement). Often it is due to a combination of both factors. Hip impingement can also occur if the socket is deeper than normal and also if there is joint laxity allowing abnormal movement. Hip impingement can lead to damage to labrum (could be considered like a soft tissue bumper for the hip joint) and subsequently the articular cartilage (surface lining of the hip joint) can get damaged leading to arthritis in young adults.
In a normal hip, the “ball” moves inside the cup without any restriction (impingement).
CAM impingement can occur when the shape of ball of the hip joint is not a sphere and more like a rugby ball on one side or with a “impingement bump” on one side. This leads to less clearance and with repetitive bending movements of the hip the labrum (a special cartilage at the rim of the cup of the hip joint) and the articular cartilage (surface lining of the hip joint) gradually get damaged.
Pincer impingement occurs when there is over coverage of the cup of the hip joint and this leads to impingement. With repetitive bending movements of the hip, the labrum gets damaged initially followed by the articular cartilage.
Progressive damage to the cartilage can gradually lead to arthritis of the hip in young adults.
The most common symptom in hip impingement is pain in the region of the groin (front of the hip joint). It may start following a minor injury or often without any injury. The pain increases with activities which involve bending of the hip joint. Activities which increase the pain include sitting for a prolonged period, getting up from a seated position, getting in and out of the car, walking up and down slopes, climbing stairs, getting in and out of the bath tub, squatting, heavy work including push/pull, carrying heavy objects, putting on shoes and socks, twisting etc., Sporting activities may also be affected. While many of the above symptoms can also be present in patients with hip arthritis, the arthritic pain also increases with activities like walking and sometimes there may be pain even at rest. The patients with impingement can also have a sensation of the hip coming out of the hip joint and also a feeling of clicking sensation. This can be due to a labral tear although in some patients this could be due to dysplasia (shallow cup).
While the preliminary diagnosis of hip impingement is based on the symptoms and the clinical finding on examination, further radiological investigation including plain x-
rays showing CAM type impingement
rays showing the removal of the CAM (bump) from the femoral head
ray showing relatively normal looking hip but closer inspection
reveal calcification in the labral area and impingement cyst
suggesting possible impingement.
ray showing cross- over sign suggesting pincer impingement
(“figure of 8” sign, shaded area representing the overcoverage
of the acetabulum)
CT scan with 3 D reconstruction showing
CAM type impingement (shaded in green for
MR arthrogram showing labral tear
and impingement cyst
The following are some relevant selected scientific references:
1.Femoroacetabular impingement syndrome: an under recognized cause of hip pain and premature osteoarthritis?
2. Efficacy of Surgery for Femoroacetabular Impingement: A Systematic Review.
3. Combined hip arthroscopy and limited open osteochondroplasty for anterior femoroacetabular impingement.
4. Open treatment of femoroacetabular impingement is associated with clinical improvement and low complication rate at short-
5. Combined arthroscopic and modified open approach for cam femoroacetabular impingement: a preliminary experience.
6. Arthroscopic femoroplasty in the management of cam-
7. Femoroacetabular impingement treatment using arthroscopy and anterior approach.
As the condition (hip impingement) is only being recently recognized as a cause of hip pain which can progress to hip arthritis in young adults, the treatment strategies are still evolving. In the initial stages, it would be appropriate to consider conservative treatment including physiotherapy, painkillers and activity modification.
If the symptoms persist, it would be appropriate to consider surgical option. When Ganz initially suggested this condition as a cause of hip pain, he advised surgery using a technique known as “surgical dislocation” of the hip. In this exposure, the hip joint is completely exposed (see picture below). While this still may be needed in some cases, the surgical exposure is extensive and carries certain morbidities including non-
Exposure of the femoral head with Ganz “surgical dislocation” of the hip
(the picture also shows the bony bump the so called “CAM lesion” to be excised)
Hip arthroscopy is a technically more challenging procedure when compared with a knee arthroscopy. However, with the advances in the technique of hip arthroscopy and instrumentation, treatment strategies are also evolving which makes it possible for at least some impingement pathologies to be treated entirely through hip arthroscopy.
CAM impingement resection through hip arthroscopy
Whatever the surgical technique may be, the treatment essentially entails creating better clearance for the ball of the hip joint. The bump in the anterolateral aspect of the ball is removed and/or the over covered part of the acetabulum is excised. The labral tear is often debrided but in some cases, the labrum could be repaired.
While studies have shown that many patients gain short term improvement in their symptoms, the symptom relief is not universal. One of the main negative predictors of symptoms relief is presence of arthritic changes or damage to the surface lining of the hip joint.
At this stage, there is lack of data to say whether surgical treatment of hip impingement can delay or prevent the progression to hip arthritis.