History
A 35-year-old man presents with hip pain for multiple years.
35岁男性，髋关节疼痛数年。
Axial oblique T1- and coronal proton density-weighted images are shown below.
1.There is a labral tear（髋臼盂唇撕裂）.
True
False
2.There is a hip fracture（髋关节骨折）.
True
False
3.The hip is dislocated（髋关节脱位）.
True
False
4.There is an abnormal contour of the femoral neck（股骨颈轮廓异常）.
True
False
Angle Measurement
Measurements were performed on the axial oblique images.
5.What is being measured here?
Acetabular angle
Alpha angle
Beta angle
Center-edge angle
Wiberg angle
6.The measured angle is 58°. What is the unifying diagnosis?
Ankylosing spondylitis
强直性脊柱炎
Developmental dysplasia of the hip
发育性髋关节发育不良
Femoral acetabular impingement (FAI) – cam type
股骨髋臼撞击综合征（FAI）-凸轮型
FAI – pincer type
股骨髋臼撞击综合征（FAI）-钳夹型
Primary osteoarthritis of the hip
髋关节原发性骨关节病
答案：
-
True
The superior labral tear is seen best on coronal images
-
False
No fracture line is seen on these images
-
False
The hip is normally aligned.
-
True
An osseous “bump” is noted best on the axial oblique images.
-
Alpha angle
The alpha angle is being measured. The other angles listed are also important in assessing for hip anomalies
-
Femoral acetabular impingement (FAI) – cam type
While there is osteoarthritis present, the best unifying diagnosis, given the osseous bump in the femoral neck and the alpha angle greater than 50°, would be cam-type FAI.
Findings
-
Axial oblique T1 and coronal proton density-weighted fat-saturated images of the right hip show a tear of the superior, anterior labrum. The axial oblique image shows the contour abnormality of the femoral neck, with an osseous bump creating an abnormal convexity at the head/neck junction. There is also cartilage loss and subchondral cystic changes beginning over the lateral acetabulum.
右髋关节斜横断位T1WI及冠状位脂肪抑制质子加权像示髋臼前上方盂唇撕裂。斜横断位示股骨颈轮廓异常，骨性撞击致股骨头颈交界处异常突起。髋臼侧可见软骨磨损、软骨下囊性变。
-
The alpha angle, measured as shown, is 58° (normal less than 50°).
如图所示，alpha角测量值58°（正常值小于50°）。
Differential Diagnosis
-
Cam type femoral acetabular impingement (FAI)
股骨髋臼撞击综合征-凸轮型
-
Pincer-type FAI
股骨髋臼撞击综合征-钳夹型
-
Primary osteoarthritis of the hip
原发性髋关节骨关节炎
Diagnosis
Cam-type femoral acetabular impingement (FAI)
股骨髋臼撞击综合征-凸轮型
Discussion
Femoral acetabular impingement (FAI) is a spectrum of congenital morphologic abnormalities of the acetabulum and proximal femur that represent a major etiology of osteoarthritis of the hip in young patients. The etiology is believed to be repetitive microtrauma to the labrum due to the abnormal biomechanics involved with the congenital abnormality. Two major types are recognized, cam type and pincer type, and they usually present in some combination of the two (86% of patients have both). While a distinct entity, developmental dysplasia of the hip can lead to FAI.
股骨髋臼撞击综合征（FAI）是一组先天性股骨近端及髋臼形态异常，是年轻患者髋关节骨性关节炎的主要原因。其主要病因机制为先天性异常引起生物力学改变，使髋臼盂唇受到反复的微创伤。
FAI主要分为凸轮型（cam type）和钳夹型（pincer type），以及二者混合型（约86%的患者为混合型）。
部分发育性髋关节发育不良可进展为FAI。
Cam type, which is illustrated in this case, describes an abnormal morphology of the femoral head-neck junction. In this type, the abnormal “bump” in the proximal femur impinges on the labrum, which, over time, leads to damage of the cartilage at hip joint and subsequent findings of osteoarthritis. Typical imaging findings include the following:
本例所示的凸轮型FAI,股骨头-颈交界区形态异常，股骨近端突起反复撞击盂唇，引起髋关节软骨损伤，形成骨性关节炎。典型的影像学表现包括：
-
“Pistol grip” deformity on Dunn angle or frog-leg lateral radiographs.
Dunn侧位或蛙式侧位像可见“手枪柄样”畸形。
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Visualization of the femoral “bump” near the head-neck junction on x-ray and MRI.
X线片或MRI可见股骨头-颈交界区撞击。
-
Labral tears are best seen on MR arthrography.
MR关节造影可清晰显示盂唇撕裂。
-
Eventually, typical signs of osteoarthritis can occur, including osseous spurring on x-ray and cartilage loss and subchondral cyst formation on MRI.
病变最终可形成骨性关节炎的典型表现，包括X线可见骨刺形成、MRI可见软骨损伤及软骨下骨质囊变。
-
Paralabral cysts are seen in 15% of cases.
约15%的FAI病例可见盂缘囊肿。
The alpha angle can be measured on axial oblique MR sequences. The MRI should be performed with oblique axial images parallel to the plane of the femoral neck. A circle is first drawn conforming to the femoral head contours, but not including the femoral or acetabular cartilage. A line is drawn from the center of the circle, which travels perpendicular to the femoral neck, bisecting its plane. Then another line is drawn from the center of a circle to the point at which the contour of the femoral head begins to diverge from the circle. This angle is less than 50° in normal patients. Angles greater than 55° are suggestive, but not diagnostic, of cam-type FAI. Alpha angles can also be calculated from x-ray or CT imaging if images are acquired or manipulated into the correct planes.
Alpha角可以通过MRI斜横断位测量，扫描层面需与股骨颈平行。首先沿股骨头轮廓画一个圆，圆内不包括股骨和髋臼软骨。通过圆心和股骨颈横轴中的做一条直线，再通过圆心和股骨头开始偏离圆周处做一条直线，两线之间的夹角即为alhpa角。正常人alpha角小于50°，当大于55°时考虑凸轮型FAI，但尚不能肯定诊断。如果采集层面准确，alpha角也可以通过X线或CT来测量得到。
FAI generally affects younger patients, ages 15 to 50. Presentation later in life usually involves secondary osteoarthritis, and, thus, if undiagnosed it can be difficult to distinguish from primary osteoarthritis.
FAI多发生于年轻人，好发年龄15-50岁。病变后期可引起继发性骨关节炎，所以如果诊断不清的话，可能与原发性骨关节炎相混淆。
Treatment involves correction of the abnormal biomechanics by surgical resection of the osseous abnormality. If present, secondary osteoarthritis may require arthroscopic repair of cartilage damage or, in some cases, hip replacement.
治疗方法包括通过手术切除异常骨性结构从而改变生物力学异常。继发性骨关节病则需要关节镜手术修复损伤的关节软骨。部分患者则需要行髋关节置换术。