  HISTORY: A 39-year-old man fell. FINDINGS: Axial, T2-weighted fat-suppressed MR image (Fig. 2.1.1) shows bone contusions in the medial patella and the lateral femoral condyle (arrows) with an associated tear of the medial retinaculum (arrowheads). DIAGNOSIS: Acute patellar dislocation-relocation (PDR) Acute PDR is a common injury that occurs with a variety of activities and accounts for 2% to 3% of knee injuries overall, but has a higher incidence in active populations . It characteristically occurs with internal rotation of the femur on a fixed and externally rotated tibia or a direct blow to the medial side of the knee. In PDR, the patella dislocates laterally, and the medial patellar facet impinges on the lateral femoral condyle, producing bone contusions at both sites. Because the bone contusions result from direct impaction as they are in the transient dislocation of the knee associated with ACL tears, the contusions may also be called “kissing contusions.” Clinical evaluation of the patient with PDR is often difficult because of the large knee joint effusion and because the patella is usually relocated to its near anatomic position at the time of presentation. The patient may not realize that patellar dislocation has occurred. Notes: 1. patella /pə'tɛlə/ 髌骨 2. contusions /kən'tjʊz/ vt. 撞伤；挫伤 3. femoral /ˈfɛmərəl/ adj. 股骨的,大腿骨的,大腿的 4. condyle /'kɑndəl/ n. 骨节；髅状突起 5. retinaculum /ˌrɛtə'nækjələm/ n. 支持带,韧带 6. tibia /'tɪbɪə/ n. 胫骨 7. effusion /ɪ'fjuʒn/ n. 流出,喷出 8. ACL=anterior cruciate ligament 前交叉韧带 来源：每天朗读一段医学影像学英语文章 圈主 深圳市人民医院放射科副主任医师杨敏洁 |
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