骨科英文书籍精读（332）｜髌骨脱位（2）
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Mechanism of injury
While the knee is flexed and the quadriceps muscle relaxed, the patella may be forced laterally by direct violence; this is rare. More often traumatic dislocation is due to indirect force: sudden, severe contraction of the quadriceps muscle while the knee is stretched in valgus and external rotation. Typically this occurs in field sports when a runner dodges to one side. The patella dislocates laterally and the medial patellofemoral ligament and retinacular fibres may be torn. Predisposing factors are anatomical variations such as genu valgum, tibial torsion, high-riding patella (patella alta) and a shallow intercondylar groove, as well as patellar hypermobility due to generalized ligamentous laxity or localized muscle weakness.
Clinical features
In a 'first-time’ dislocation the patient may experience a tearing sensation and a feeling that the knee has gone 'out of joint’; when running, he or she may collapse and fall to the ground. Often the patella springs back into position spontaneously; however, if it remains unreduced there is an obvious (if somewhat misleading) deformity: the displaced patella, seated on the lateral side of the knee, is not easily noticed but the uncovered medial femoral condyle is unduly prominent and may be mistaken for the patella. Neither active nor passive movement is possible (Fig. 30.16). In the rare intraarticular (downward) dislocation the patella is stuck between the condyles and there is a marked prominence on the front of the knee.
If the dislocation has reduced spontaneously, the knee may be swollen and there may be bruising and tenderness on the medial side. If there is fluid in the joint, aspiration may show that it is bloodstained; the presence of fat droplets suggests a concurrent osteochondral fracture.
With recurrent dislocation the symptoms and signs are much less marked, though still unpleasant. After spontaneous reduction the knee looks normal, but the apprehension test is positive.
---from 《Apley’s System of Orthopaedics and Fractures》
重点词汇整理：
dodge to one side.躲到一边。
dodge /dɑːdʒ/v. 躲开；迅速让开
Predisposing factors 发病诱因
/,pridɪs'poz/v. 使倾向于；容易诱发（predispose 的现在分词）
/ˌpriːdɪˈspoʊz/vt. 预先处置；使…偏向于
genu valgum/'vælɡəm/膝外翻；叉形腿
patella alta高位髌骨
bloodstained /ˈblʌdsteɪnd/v. 血染（bloodstain 的过去式和过去分词）adj. 有血污的，血腥的；犯杀人罪的
osteochondral fracture.(膝)骨软骨骨折
apprehension/ˌæprɪˈhenʃn/n. 理解；恐惧；逮捕；忧惧
有道翻译（仅供参考，建议自己翻译）：
损伤机制
当膝盖弯曲，股四头肌放松时，髌骨可能会受到直接暴力的侧向压迫；这种情况很少见。更常见的外伤性脱位是由于间接的力量：突然，严重的收缩股四头肌，而膝盖是在外翻和外旋拉伸。通常情况下，这发生在野外运动时，一个跑步者闪避到一边。髌骨外侧脱位，髌股内侧韧带和支持带纤维可能撕裂。易感因素包括膝外翻、胫骨扭转、高位髌骨（高位髌骨）和髁间沟浅，以及由于全身韧带松弛或局部肌肉无力导致的髌骨过度活动。
临床特征
在“首次”脱臼时，患者可能会有撕裂感和膝关节“脱臼”的感觉；跑步时，患者可能会摔倒在地。通常情况下，髌骨会自发地弹回原位；然而，如果髌骨未复位，则会出现明显的畸形（如果有点误导）：移位的髌骨位于膝盖外侧，不易被发现，但裸露的股骨内侧髁过度突出，可能会被误认为是髌骨。不可能进行主动或被动移动（图30.16）。在罕见的关节内（向下）脱位中，髌骨卡在髁突之间，膝关节前部有明显的突起。
如果脱位自行减轻，膝关节可能肿胀，内侧可能有瘀伤和压痛。如果关节内有液体，抽吸可能显示有血迹；脂肪滴的存在表明并发骨软骨骨折。
复发性脱位的症状和体征不明显，但仍令人不快。自然复位后膝关节看起来正常，但恐惧测试呈阳性。