骨科英文书籍精读（70）｜肩关节后脱位（1）
POSTERIOR DISLOCATION OF THE SHOULDER
Posterior dislocation is rare, accounting for less than 2 percent of all dislocations around the shoulder.
Mechanism of injury
Indirect force producing marked internal rotation and adduction needs be very severe to cause a dislocation. This happens most commonly during a fit or convulsion, or with an electric shock. Posterior dislocation can also follow a fall on to the flexed, adducted arm, a direct blow to the front of the shoulder or a fall on the outstretched hand.
Clinical features
The diagnosis is frequently missed – partly because reliance is placed on a single anteroposterior x-ray (which may look almost normal) and partly because those attending to the patient fail to think of it. There are, in fact, several well-marked clinical features. The arm is held in internal rotation and is locked in that position. The front of the shoulder looks flat with a prominent coracoid, but swelling may obscure this deformity; seen from above, however, the posterior displacement is usually apparent.
X-Ray
In the anteroposterior film the humeral head, because it is medially rotated, looks abnormal in shape (like an electric light bulb) and it stands away somewhat from the glenoid fossa (the ‘empty glenoid’ sign). A lateral film and axillary view is essential; it shows posterior subluxation or dislocation and sometimes a deep indentation on the anterior aspect of the humeral head. Posterior dislocation is sometimes complicated by fractures of the humeral neck, posterior glenoid rim or lesser tuberosity. Sometimes the patient is too uncomfortable to permit adequate imaging and in these difficult cases CT is essential to rule out posterior dislocation of the shoulder.
---from 《Apley’s System of Orthopaedics and Fractures》
重点词汇整理：
convulsion/kənˈvʌlʃn/n. [医] 惊厥；动乱；震撼；震动
outstretched /ˌaʊtˈstretʃt/adj. 伸开的；扩张的v. 伸出；扩大；伸展得超出…的范围（outstretch的过去分词形式）
internal rotation内旋转
obscure /əbˈskjʊr/adj. 昏暗的，朦胧的；晦涩的，不清楚的；隐蔽的；不著名的，无名的vt. 使…模糊不清，掩盖；隐藏；使难理解
indentation /ˌɪndenˈteɪʃn/n. 压痕，[物] 刻痕；凹陷；缩排；呈锯齿状
rim /rɪm/n. 边，边缘；轮辋；圆圈
百度翻译：
肩关节后脱位
后脱位很少见，占肩关节周围所有脱位的不到2%。
损伤机制
产生明显内旋和内收的间接力需要非常严重才能引起脱位。这通常发生在发作、抽搐或触电时。后脱位也可能发生在手臂弯曲、内收、肩部前部受到直接打击或伸直的手摔倒之后。
临床特征
这种诊断经常被漏掉，部分原因是依赖于一次前后x光片（看起来几乎正常），另一部分是因为那些看护病人的人没有想到。事实上，有几个明显的临床特征。手臂保持内部旋转，并锁定在该位置。肩部前部看起来平坦，喙突突出，但肿胀可能掩盖了这种畸形；然而从上方看，后方移位通常很明显。
X射线
在正位片中，肱骨头由于向内侧旋转，外形异常（像一个电灯泡），它离关节盂窝有点远（即“空盂征”）。侧位片和腋位片是必要的，它显示后半脱位或脱位，有时在肱骨头前部有一个深的凹陷。后脱位有时合并肱骨颈、关节盂后缘或小结节骨折。有时病人太不舒服，无法进行充分的影像学检查，在这些困难的病例中，CT是排除肩关节后脱位的关键。