避免第五跖骨髓内钉头骰骨撞击：负重 CT 解剖研究。
Avoiding Fifth Metatarsal Intramedullary Screw Head Cuboid Impingement: A Weightbearing Computed Tomography Anatomic Study.
机构信息
Department of Orthopaedic Surgery, University of California San Francisco, San Francisco, CA, USA.
Department of Orthopaedics, The Warren Alpert Medical School of Brown University and Rhode Island Hospital, Providence, RI, USA.
出版信息
Foot Ankle Int. 2022 Jul;43(7):880-886. doi: 10.1177/10711007221084624. Epub 2022 Apr 11.
BACKGROUND
Multiple case reports of fifth metatarsal (MT) intramedullary fixation highlight symptomatic hardware with screw head impingement on the cuboid. We developed a fifth MT intramedullary screw trajectory model using weightbearing computed tomography data. The goal was to assess for cuboid impingement with simulated intramedullary screw position.
METHODS
For 20 weightbearing foot computed tomographs (CTs), an automated tool was used to simulate fifth MT screw fixation in the ideal trajectory down the shaft and with a 7-mm screw head. (1) The closest distance from the simulated ideal trajectory to the cuboid in 3 dimensions was measured. A measurement less than 3.5 mm (the radius of the screw head) indicated screw head impingement on the cuboid if not countersunk into the metatarsal. (2) In 3 dimensions, a simulated screw head was then advanced from the proximal tip of the metatarsal distally into the metatarsal until it was entirely avoiding the cuboid.
RESULTS
In this model, 95% (19/20) of the patients would have cuboid impingement if the screw was not countersunk. The average ideal pin start distance was 0.15 mm (SD 2.4 mm) inside the cuboid. In this cohort, the screw head would have to be countersunk an average of 8.1 mm (SD 2.7 mm) relative to the proximal tip of the metatarsal to avoid cuboid impingement. For all cases, the simulated fluoroscopic oblique view was a reliable indicator of cuboid impingement, demonstrating visible overlapping of the screw with the cuboid. The overlap resolved on the oblique foot view once the screw was sufficiently countersunk, confirmed on 3-dimensional imaging.
CONCLUSION
The ideal guidewire placement for fifth MT intramedullary fixation is directly against the cuboid. Approximately 95% of patients would have cuboid impingement if the screw is not countersunk. The oblique fluoroscopic view of the foot is a reliable assessment of screw head impingement on the cuboid.
LEVEL OF EVIDENCE
Level III, retrospective study.
背景
多篇关于第五跖骨（MT）髓内固定的病例报告强调了带有螺钉头撞击骰骨的有症状内固定物。我们使用负重 CT 数据开发了一种第五 MT 髓内螺钉轨迹模型。目的是评估模拟髓内螺钉位置是否存在骰骨撞击。
方法
对 20 例负重足部 CT 进行分析，使用自动工具模拟沿骨干的理想轨迹和 7mm 螺钉头进行第五 MT 螺钉固定。（1）测量模拟理想轨迹与骰骨在三维空间的最近距离。如果螺钉未沉入跖骨而小于 3.5mm（螺钉头半径），则表明螺钉头撞击骰骨。（2）在三维空间中，模拟螺钉头从跖骨近端向远端推进，直到完全避开骰骨。
结果
在该模型中，如果不沉头，95%（19/20）的患者会发生骰骨撞击。理想的钉起始距离平均为 0.15mm（SD 2.4mm），位于骰骨内。在该队列中，螺钉头相对于跖骨近端需要沉头平均 8.1mm（SD 2.7mm），以避免骰骨撞击。对于所有病例，模拟透视斜位是骰骨撞击的可靠指标，显示螺钉与骰骨明显重叠。一旦螺钉充分沉头，斜位足部视图上的重叠就会消失，在三维成像上得到证实。
结论
第五跖骨髓内固定的理想导丝放置位置直接靠在骰骨上。如果螺钉不沉头，大约 95%的患者会发生骰骨撞击。足部斜透视是评估螺钉头撞击骰骨的可靠方法。
证据等级
III 级，回顾性研究。
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