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impingement, CAM and PINCER pathology » impingement, CAM and PINCER pathology



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impingement, CAM and PINCER pathology

Femoral Acetabular Impingement and the development of arthritis of the hip

Femoroacetabular impingement (FAI) occurs when there is abnormal contact between the neck of the femur and the rim of the acetabulum.  This abnormal contact occurs during activities that result in movements to the extreme limits of the normal range of motion of the hip (such as martial arts, yoga, or kick boxing), or when there is an abnormal anatomic configuration to the bone such that contact is produced even with motion in the normal range.  This disease is thought to be a precursor to hip arthritis and its early recognition MAY give us the opportunity to preserve the patient’s joint for longer.

There have been two types of FAI described, [Cam] and [Pincer] types.  Although they are described as separate entities, most patients have components of both types of impingement.  Cam type femoroacetabular impingement occurs when a femur with an abnormal head neck junction and insufficient head-neck offset creates shear forces on the acetabular cartilage and labrum.  This kind of impingement often occurs in patients with post-traumatic deformities, slipped capital femoral epiphysis (SCFE), coxa vara, and avascular necrosis (AVN).  Many patients are males who are physically active or heavy laborers.

History, Past Medical History, and Physical Exam

This part of the consultation is used to determine if the pain is due to trauma, arthritis, or some other entity.  The past medical history can give clues to possible causes, such as AVN due to glucocorticoid use, and the physical exam is extremely important to identify the possible causes of hip pain and exclude other conditions such as low back pain or other causes of pelvic pain.  There are a number of physical examination tests that can be use to reproduce the patients pain and verify that the hip is the source of the discomfort, such as the FADDIR, FABER, and scour tests.

Diagnostic Imaging

Xrays, MRI scans, and CT scans are extremely useful in understanding the causes of hip pain and possible treatment options.  In our office, we will obtain the appropriate xrays and if we need advanced imaging, such as an MRI scan or a CT scan, we will make arrangements to have these tests performed.  Some of the measurements that we use in evaluating patients for hip pain include the following:

Joint space: measures the amount of cartilage between the femoral head and acetabulum.

Tonnis Angle: measures the degree of acetabular overcoverage or undercoverage.

The Crossover sign: measures acetabular retroversion or anteversion.

The Alpha angle: measures cam impingement and lack of roundness of the femoral head.

Coxa Profunda: measures how deep the femoral head sits inside the acetabulum.

The following xrays show some examples of the xrays of patients with femoral acetabular impingement and demonstrate the use of these measurements.

xray of bilateral cam impingement of the hip joint

This is the AP weight bearing xray of a 40 year old male with bilateral hip pain, good preservation on the joint space and cam impingement with a relatively large alpha angle.  The alpha angle is considered to be normal when it is less than 40 to 50 degrees, and abnormal when it is more than 60 degrees.  In this case it measures approximately 75 degrees.  This patient has sharp catching pain in his groin, is still very active — playing pickup basketball — and is an excellent candidate for hip arthroscopy and femoral head debridement / osteoplasty.

This xray is of a 40 year old female with mixed cam and pincer impingement and with joint space narrowing.

xay of cam and pincer impingement

She has acetabular overcoverage as measured by a low Tonnis angle, calcification of the acetabular labrum, and a large alpha angle.  Unfortunately, she also has loss of joint space and so she is not a candidate for a joint preserving procedure but instead will require a joint replacement procedure to alleviate her hip pain.

Non-operative Treatment

A course of non-operative treatment for most hip pathology is usually the first line of treatment. Patients presenting with femoroacetabular impingement or labral disease may try modification of activity, avoiding excessive hip movement and regular non-steroidal anti-inflammatory medication such as Advil, Tylenol, or Ibuprofen.

Selective injections and a pain journal

Injections inside the hip joint can be used help diagnose and manage the symptoms of patients with hip pain, especially if there is any question as to whether or not the patient could have disease in other areas, such as the back.  During this procedure, an intra-operative xray machine called a fluoroscope to accurately identify the correct area to inject medicine.  Typically, two different types of medications are injected.  One is an anesthetic agent that results in immediate pain relief lasting for 2 to 3 hours.  The other medication is an anti-inflammatory medicine that takes 2 to 3 days to work and then lasts for a much longer time.  These injections have two purposes: they are DIAGNOSTIC and they are THERAPEUTIC.

The diagnostic component of the injection helps us to confirm that we are working towards a correct diagnosis.  For example, if the patient’s hip is injected and all of the patient’s pain goes away, we know that we have identified the source of the pain.  If the injection results in no pain relief or only partial pain relief, then we suspect that another anatomic area may be contributing to the patient’s pain.

The therapeutic component of the injection helps the patient to manage their pain and possibly avoid having surgery.

A pain journal is often used to help document the effects of selective injections and demonstrate to the patient and the doctor that the correct source of the pain has been identified.  This journal begins on the day of the injection and then covers the next 7 days.  It is important that you fill this document out on a daily basis for the 1st week after then injection and then bring it to your follow-up visit when in order to discuss the results of the injection and what it means in terms of future treatment decisions.   You can download a copy of a sample pain journal by clicking here:

pain journal

Arthroscopy — Joint Preservation

Arthroscopic surgery for femoral acetabular impingement is an emerging treatment for hip disease.  With arthroscopic surgery, we can repair tears in the labrum around the edge of the acetabulum, remove delaminated cartilage, and remove the abnormal bone spur that causes cam impingement.  This type of surgery is typically performed as an outpatient at a surgery center with an overnight stay.

Here are a series of xrays and intra-operative arthroscopic pictures of a 50 year old woman with classic findings of cartilaginous delamination caused by femoral acetabular impingement.  The first row of pictures includes her pre-operative xray of the hip, the fluoroscopic picture taken by the radiologist after injection of the contrast material for the MRI arthrogram, and the last two pictures demonstrate the MRI findings of femoral acetabular impingement.

left hip early OA AP pre hip scope left hip early OA arthrogram pre MRI left hip early OA coronal bilateral T1 MRI left hip early OA axial MRI with reactive osteophyte

Here we have the intra-operative pictures at the time of hip arthroscopy.  In the first image the torn and degenerative part of the acetabular labrum is being removed.  In the second image the bent probe is indicating the area of delaminated cartilage, and in the third picture the femoral head osteoplasty is being performed.

arthroscopic debridement of a torn degenerative labrun arthroscopic view of delaminated cartilage in the acetabulum after debridement arthroscopic femoral osteoplasty for impingement



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  1. cartilage degeneration explained » anteriorhipreview

    [...] There are certain morphological conditions that seem result in a predisposition towards early arthritis of the hip, and this is one of the most fascinating areas of research currently in orthopedics.  The mechanism, implications, and successful treatment of CAM and PINCER impingement have not been completely worked out yet, but there is the suggestion that abnormal forces, especially shear forces across the surface of the cartilage, may be particularly detrimental.  Shear forces seem to develop when there is some sort of structural abnormality of the joint, such as instability, or in the case of CAM impingement, when there is a mismatch or an incongruity between the shape of the femoral head and the socket.  For more on femoral acetabular impingement, click here. [...]

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