Patel Preemal, Little Zoe, Beak Phillip, Williams Rachel, Trompeter Alex
Department of Trauma and Orthopaedics, St George's University Hospital NHS Foundation Trust, St George's University, London, UK.
Trauma and Orthopaedics, Kingston Hospital, London, UK.
Indian J Orthop. 2024 Jan 22;58(3):250-256. doi: 10.1007/s43465-023-01066-3. eCollection 2024 Mar.
To facilitate the posterolateral approach to the posterior malleolus patients are often positioned prone initially, then turned supine to complete fixation at the medial malleolus. We sought to define observed differences in the radiographic appearance of implants relative to the joint line, in prone and supine positions.
A 3.5 mm tubular plate and a 3.5 mm posterior distal tibial periarticular plate were applied sequentially to 3 individual cadaveric legs, via a posterolateral approach. The tubular plate was positioned to simulate buttress fixation and the posterolateral plate placed more distally. Each limb was secured on a custom jig and radiographs were taken on a mobile c-arm fluoroscopy machine with a calibration ball. A series of prone AP, supine PA and mortise radiographs were taken. Prone radiographs were also taken in different degrees of caudal tilt to simulate knee flexion which occurs in practice, during intraoperative positioning. Plate tip-joint line distances were measured and Mann-Whitney tests performed.
There was no statistically significant difference in plate tip-joint line distance when comparing equivalent prone and supine views (PA/AP or mortise). However, significant differences in apparent implant position were noted with alterations in caudal tilt. When taking a prone image, when the knee is flexed to 20 degrees, the plate tip will appear 6.5-8.5 mm more proximal than in the equivalent supine image where the knee is extended and the fluoroscopy beam is orthogonal to the anatomic axis of the tibia.
Observed differences in radiographic appearance of metalwork in the prone and supine position are most likely due to knee flexion and the resulting variation in the angle of the fluoroscopy beam, rather than projectional differences between supine and prone views. Surgeons should be alert to this when analysing intraoperative images.
为便于采用后外侧入路治疗后踝骨折，患者通常先取俯卧位，然后转为仰卧位以完成内踝固定。我们试图确定在俯卧位和仰卧位时，植入物相对于关节线的影像学表现的差异。
通过后外侧入路，依次将一块3.5毫米的管状钢板和一块3.5毫米的胫骨干骺端后侧关节周围钢板应用于3条尸体下肢。将管状钢板放置以模拟支撑固定，后侧钢板放置在更靠远端的位置。将每条下肢固定在定制夹具上，并用带有校准球的移动C形臂荧光透视机进行X线摄影。拍摄一系列俯卧位前后位、仰卧位后前位和斜位X线片。还在不同程度的尾侧倾斜下拍摄俯卧位X线片，以模拟术中定位时实际发生的膝关节屈曲。测量钢板尖端与关节线的距离，并进行曼-惠特尼检验。
比较等效的俯卧位和仰卧位视图（后前位/前后位或斜位）时，钢板尖端与关节线的距离无统计学显著差异。然而，随着尾侧倾斜的改变，植入物的表观位置存在显著差异。在拍摄俯卧位图像时，当膝关节屈曲至20度时，钢板尖端将比膝关节伸直且荧光透视束与胫骨解剖轴正交的等效仰卧位图像中更靠近近端6.5 - 8.5毫米。
俯卧位和仰卧位时金属植入物影像学表现的差异很可能是由于膝关节屈曲以及荧光透视束角度的相应变化，而非仰卧位和俯卧位视图之间的投影差异。外科医生在分析术中图像时应注意这一点。
