x Labral Tears of the Hip and Femoroacetabular Impingement JB (3).docx
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Labral Tears of the Hip and Femoroacetabular impingement
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The acetabular labrum is a rim of cartilage surrounding the socket of the hip joint. Damage to the labrum can result from various causes, including trauma and degeneration. Labral tears can be painful, but also may be found incidentally on imaging studies. Femoroacetabular impingement is a clinical syndrome associated with labral tears. This syndrome is characterized by bony overgrowth of either the femur, the pelvis or both (Figure 1). These morphological abnormalities are thought to produce (or at least reflect) abnormal contact between the proximal femur and acetabulum during hip flexion and rotation. It has been proposed that this contact damages the labrum as well as the articular cartilage of the hip joint itself.
Figure 1: Schematic tracing of the bones of the hip joint, showing the normal femur and pelvis in red. The bony overgrowth impingement is shown in black. (The green arrow points to so-called “cam impingement” and the blue arrow to “pincer impingement” [see text]).
Structure and Function
The labrum is a fibrocartilaginous structure surrounding the rim of the acetabulum (Figure 12). In cross section, the labrum is triangular with an articular and capsular surface. The labrum rim functions to deepen the acetabulum, increasing the contact area of the hip joint and thereby reducing cartilage contact pressure and increasing hip stability.
Figure 12: The labrum, outlined in red, serves to deepen the socket of the acetabulum.
Trauma is a common cause of labral tears. Usually, this involves a mechanism which results in forceful resistance of hip flexion (e.g. tackled while kicking or running).
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Femoroacetabular impingement anatomy is broadly defined by bony overgrowth of the femur at the femoral head-neck junction, termed “Cam impingement” (Figure 23), or overgrowth of the acetabular rim, termed “Pincer impingement” (Figure 34). Both Cam and Pincer impingement may be found concurrently (Figure ).
Figure 2Figures 3a and 3b: Cam impingement. The outline of a normal femur Figure 2 is an ray of cam impingement [MF1]
In figure 3b, the normal contour of the femur shown in figure 3a is shaded in purple. The red arrow points to the excess bone (not outlined) seen in causing cam impingement. (Case courtesy of Dr. Kenny Sim, Radiopaedia.org, rID: 30914)
Figure 34: Pincer impingement. The outline of a normal pelvis is shaded in red. The yellow arrow points to the excess acetabular bone (not outlined) seen in pincer impingement.
(Case courtesy of A.Prof Frank Gaillard, Radiopaedia.org, rID: 2738)
Figure 4: Schematic view of the hip joint showing the femur in blue and the pelvis in red. The bony overgrowth of cam and pincer impingement is shown in pink and yellow, respectively.
Cam impingement is characterized by a non-spherical femoral head and decreased head-neck offset. During hip flexion, the aspherical femoral head can make contact that shears the acetabular cartilage and the labrum. Labral damage in Cam deformity most often occurs anterosuperiorly, at the transition zone where the labrum blends into the hyaline cartilage.
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Patients may make a “C sign” –grasping the affected hip with their hand indicating both anterior and posterior hip pain (Figure 5).
Figures of C sign NEED CLINICAL PHOTOS
Figure 5: of the “C sign” Patients [MF2] with labral tears, when asked to “point” to the area of pain will not point but rather grasp the hip, as shown
On physical exam, flexion, adduction, and internal rotation (FAIRFigure 6) can provoke the symptoms of an anterior-superior tear whereas hyperextension, abduction , and external rotation (Figure 7) tend to elicit pain in those with posterior labral tears.
Figures of hip flexion, adduction, and internal rotation NEED CLINICAL PHOTOS
Figure 6: Patients with an anterior-superior labral tear will report pain if the examiner passively flexes (red arrow), slightly adducts (white arrow) and internally rotates (green arrow) the hip.
Figure 7: Patients with posterior labral tears will report pain if the examiner abducts (white arrow) and externally rotates (green arrow) the hip.
These tests are performed when the patient is supine and the hip and knee are flexed to 90 degrees.
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MRI is the most sensitive method of imaging and study of choice to evaluate for chondral or labral damage (figureFigure 8).
Figure 78: A labral tear seen on hip MRI. (Case courtesy of Dr Roberto Schubert, Radiopaedia.org, rID: 13826)
Nonetheless, MRI may miss clinically significant findings. MRI arthrogram, (MRI with contrast material injected into the joint), is the study of choice to identify labral tears.
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In Cam impingement, alpha angle is a commonly used quantitative measure of the deformity. This angle is determined by placing a circle over the femoral head with a line from the center to the center of the femoral neck and another line from the center of the circle to the first point of the superior head-neck junction (Figures 8 9 and 910).
Figure 89: The alpha angle is formed by two lines emanating from the center of the femoral head: one bisecting the femoral neck and second drawn to the point where the neck meets the head. Normal anatomy is shown here
Figure 910: In this drawing, there is bony overgrowth from a cam lesion (green) which changes the point where the neck meets the head, leading to a larger alpha angle.
The higher the angle between these two lines, the larger and more severe the Cam lesion. However, there is no precise criterion value for alpha angle that defines pathological abnormality and (interestingly) the original paper in Clinical Orthopaedics and Related Research describing femoroacetabular impingement did not mention the alpha angle.
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Because of the high prevalence of femoroacetabular impingement morphology in asymptomatic patients, it is speculative at best to suggest that any treatment should be employed in the name of altering the risk of arthritis later in life. It may be more reasonable to address femoroacetabular impingement bony deformities when surgery is undertaken to repair the labrum: osteoplasty of the Cam deformity or resection of the Pincer lesion may be chosen. (Optional figure??)
Figure: surgical treatment of hip labrum?? NEED CLINICAL PHOTOS Fotios—if you have access to eye candy, we can put a piece here
Risk Factors and Prevention
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Perform physical examination to suggest or exclude the diagnosis of labral disease.
[MF1]What are you trying to say here?
[MF2]What are you trying to say here?
[Ed.3]Cutting this. Figure is not edifying.
