Anatomical Study of Lateral Compression II Screw Path and Entry Parameters Based on Three-Dimensional CT Image Reconstruction Techniques

Abstract

Objective: Lateral compression II (LC-II) fractures, a common type of pelvic injury, often require closed reduction and percutaneous screw fixation due to posterior pelvic ring instability. However, existing methods fail to adequately account for the internal structure of the screw path and lack precise anatomical guidance, increasing surgical risks. This study utilized digital medical software to analyze the LC-II screw path and entry parameters, providing the anatomical references.

Methods: This retrospective study enrolled 43 adult patients (21 males and 22 females) who underwent a complete computed tomography (CT) scan examination from February 2017 to February 2019. The digital three-dimensional (3D) pelvic model was reconstructed, and the ideal LC-II screw path was designed by the cross-section method. The primary evaluation parameters included the screw path length (D _AP), maximum diameter (D _max), distances at narrow points (D1 and D2), bone thickness parameters (OW1 and IW1; OW2 and IW2), and screw entry angles (∠α, ∠β, ∠γ).

Results: Of 43 patients, 42 successfully completed LC-II screw path construction. Among 21 female patients, 5 (23.8%) could accommodate screws with a maximum diameter of < 6.5 mm. Compared with female patients, male patients exhibited significantly higher D _AP, D _max, D ₂, OW₁, IW₁, IW₁/OW₁, and IW₂/OW₂ (p < 0.05). The ∠γ was significantly lower in male patients. Furthermore, digital 3D pelvic model observations revealed that LC-II screws bone entry points in the anterior iliac region were all located posterior to the anterior inferior iliac spine (AIIS). The angles between the LC-II screw and coronal plane were 48.06° in males and 45.10° in females, while the angles between the LC-II screw and sagittal plane were 27.14° and 25.60°, respectively.

Conclusion: This study utilized digital medical software to construct the LC-II screw path and analyze sex-based differences, highlighting the importance of individualized preoperative path planning and providing essential anatomical evidence for the precise and safe percutaneous insertion of LC-II screws.

Keywords: anatomy; fracture fixation; lateral compression II screw; mimics software; pelvic fracture.

FIGURE 1

The process of establishing the LC‐II screw path of the left hip bone in 3‐Matic13.0 software. (A) A platform passing through ASIS, PSIS, and the vertex of the greater sciatic notch was established and defined as platform 1; a platform that passed through AIIS and PSIS and was perpendicular to platform 1 was constructed and defined as platform 2. (B) The left iliac bone was divided along platform 2 to obtain the cross‐section of the LC‐II screw path. (C) The inner margin line, lateral margin line, and central axis of the LC‐II screw were divided. (D) A cylinder passing through the central axis of the LC‐II screw was built, taking the distance between the inner and lateral margin lines of the LC‐II screw as its diameter; (E) The left hip bone was treated transparently, and the cylinder representing the LC‐II screw was observed from all directions to be located in cancellous bone. AIIS, anterior inferior iliac spine; ASIS, anterior superior iliac spine; LC‐II, lateral compression II; PSIS, posterior superior iliac spine.

FIGURE 2

Schematic diagram of the measurement for the parameters of the LC‐II screw path of the left hipbone. P_as and P_ps were the intersection points of the central axis of the LC‐II screw with the AIIS area and PSIS, respectively; D _AP was the maximum length of the LC‐II screw path; D ₁ was the distance from the first narrow of the screw path to the PSIS; D ₂ was the distance from the second narrow of the screw path to the PSIS; OW₁ and IW₁ were the outer and inner diameters of the first narrow of the screw path, respectively; OW₂ and IW₂ were the outer and inner diameters of the second narrow of the screw path, respectively. AIIS, anterior inferior iliac spine; LC‐II, lateral compression II; PSIS, posterior superior iliac spine.

FIGURE 3

Measurement for the lateral compression II screw entry parameters of the left hipbone. (A, B) ∠α, ∠β, and ∠γ indicate the included angles of the lateral compression II (LC‐II) screw with the coronal plane, sagittal plane, and horizontal plane. (C) P_as, the bone intersection point of the central axis of the LC‐II screw in the anterior iliac region; P_sn, the skin intersection point of the central axis of the LC‐II screw in the anterior iliac region; D _v1, the vertical distance between the anterior iliac bone intersection point of the LC‐II screw and anterior superior iliac spine (ASIS); D _h1, the horizontal distance between the anterior iliac bone intersection point and ASIS; D _v2, the vertical distance from the anterior iliac skin intersection point to ASIS; D _h2, the horizontal distance from the anterior iliac skin intersection point to ASIS.