A 28 year old man was brought to hospital after a road traffic incident. He described hearing a “pop” as his right knee impacted against the dashboard at the time of collision, and he subsequently experienced extreme pain. On examination in the emergency department, his knee was swollen and tender, and range of movement was severely limited. After initial management in the emergency department, he was admitted under the orthopaedic team. Once the swelling was resolved, his knee was re-examined, and was found to be grossly unstable (fig 1⇓). Fig 1  Clinical photograph of the patient’s right knee ### 1. What sign is shown in the clinical photograph? #### Short answer Posterior sag sign suggesting injury to the posterior cruciate ligament. #### Discussion The posterior cruciate ligament serves as the main restraint to posterior displacement of the tibia relative to the femur. Secondary functions include resisting excessive valgus, varus, and external rotation movements. Disruption of the posterior cruciate ligament can be seen via posterior draw testing or by assessing for posterior sag (fig 2⇓). Normally, the anterior surface of the tibia lies around 1 cm anterior to the femoral surface when the knee is held in 90° of flexion. Any …

中文翻译：

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膝盖不稳定

道路交通事件发生后，一名28岁的男子被送往医院。他描述听到的“砰砰声”是因为他的右膝盖在碰撞时撞击在仪表板上，随后他感到极度疼痛。在急诊室检查时，他的膝盖肿胀和触痛，活动范围受到严重限制。在急诊室进行初步管理后，他被接纳为骨科团队成员。一旦肿胀消退，他的膝盖将被重新检查，并被发现严重不稳定（图1⇓）。图1患者右膝的临床照片### 1.临床照片显示什么体征？####简短答案后垂征表明后十字韧带受伤。####讨论十字交叉韧带是限制胫骨相对于股骨向后移位的主要约束力。次要功能包括抵抗过度的外翻，内翻和外部旋转运动。后十字韧带破裂可通过后屈试验或评估后下垂来观察（图2⇓）。通常，当膝盖保持90度屈曲时，胫骨的前表面位于股骨表面的前1 cm处。任何 … 当膝盖保持90度屈曲时，胫骨前表面位于股骨表面前1 cm处。任何 … 当膝盖保持90度屈曲时，胫骨前表面位于股骨表面前1 cm处。任何 …