Ochenjele George, Ho Bryant, Switaj Paul J, Fuchs Daniel, Goyal Nitin, Kadakia Anish R
Department of Orthopaedic Surgery, Northwestern University, Chicago, IL, USA.
Department of Orthopaedic Surgery, Northwestern University, Chicago, IL, USA
Foot Ankle Int. 2015 Mar;36(3):293-301. doi: 10.1177/1071100714553467. Epub 2014 Sep 24.
Jones fractures occur in the relatively avascular metadiaphyseal junction of the fifth metatarsal (MT), which predisposes these fractures to delayed union and nonunion. Operative treatment with intramedullary (IM) screw fixation is recommended in certain cases. Incorrect screw selection can lead to refractures, nonunion, and cortical blowout fractures. A better understanding of the anatomy of the fifth MT could aid in preoperative planning, guide screw size selection, and minimize complications.
We retrospectively identified foot computed tomographic (CT) scans of 119 patients that met inclusion criteria. Using interactive 3-dimensional (3-D) models, the following measurements were calculated: MT length, "straight segment length" (distance from the base of the MT to the shaft curvature), and canal diameter.
The diaphysis had a lateroplantar curvature where the medullary canal began to taper. The average straight segment length was 52 mm, and corresponded to 68% of the overall length of the MT from its proximal end. The medullary canal cross-section was elliptical rather than circular, with widest width in the sagittal plane and narrowest in coronal plane. The average coronal canal diameter at the isthmus was 5.0 mm. A coronal diameter greater than 4.5 mm at the isthmus was present in 81% of males and 74% of females.
To our knowledge, this is the first anatomic description of the fifth metatarsal based on 3-D imaging. Excessive screw length could be avoided by keeping screw length less than 68% of the length of the fifth metatarsal. A greater than 4.5 mm diameter screw might be needed to provide adequate fixation for most study patients since the isthmus of the medullary canal for most were greater than 4.5 mm.
Our results provide an improved understanding of the fifth metatarsal anatomy to guide screw diameter and length selection to maximize screw fixation and minimize complications.
琼斯骨折发生于第五跖骨相对血供较差的干骺端交界处，这使得这些骨折易于延迟愈合和不愈合。在某些情况下，建议采用髓内（IM）螺钉固定进行手术治疗。螺钉选择不当可导致再骨折、不愈合和皮质爆裂骨折。更好地了解第五跖骨的解剖结构有助于术前规划、指导螺钉尺寸选择并减少并发症。
我们回顾性地确定了119例符合纳入标准患者的足部计算机断层扫描（CT）图像。使用交互式三维（3-D）模型，计算以下测量值：跖骨长度、“直段长度”（从跖骨基部到骨干曲率的距离）和髓腔直径。
骨干有一个向外侧足底的弯曲，髓腔在此处开始逐渐变细。直段平均长度为52 mm，相当于跖骨从近端起总长度的68%。髓腔横截面为椭圆形而非圆形，矢状面最宽，冠状面最窄。峡部的冠状髓腔平均直径为5.0 mm。峡部冠状直径大于4.5 mm的情况在81%的男性和74%的女性中出现。
据我们所知，这是基于三维成像对第五跖骨的首次解剖学描述。通过使螺钉长度小于第五跖骨长度的68%，可避免螺钉过长。由于大多数研究患者的髓腔峡部直径大于4.5 mm，可能需要直径大于4.5 mm的螺钉来提供足够的固定。
我们的结果有助于更好地理解第五跖骨的解剖结构，以指导螺钉直径和长度的选择，从而使螺钉固定最大化并减少并发症。
