Pre-contoured Plate Fit Assessment for Acetabular Fractures

Abstract

Purpose: Insufficient fitting of pre-contoured plates for acetabular fractures might lead to inadequate fracture reduction, but it is unclear in which patients pre-contoured plates fit adequately. The aims of this study were to assess plate fitting in sex- and height-specific anatomical variations of the hemipelvis, and categorizing the outcomes as moderate or good fit.

Methods: 3D models from computed tomography (CT) scans were obtained from a dataset of 200 patients with an intact left hemipelvis. This dataset was divided into eight subgroups, based on sex and body height, and the plate was virtually fitted on each shape. Plate fitting was assessed by computing the iliopectineal line, the quadrilateral slope, and the root mean square distance (RMSD) between each coordinate of the plate and its closest coordinate on the hemipelvis.

Results: The mean age was 56 ± 16 years, and the mean height was 173 ± 10 cm. All female pelves had a moderate fit, mainly because the plate length either exceeded the iliopectineal line length, or the plate's anterior aspect was directed too ventrally. Three out of four male pelves had a good fit. Only the small height subgroup (<175 cm) showed a moderate fit due to the plate length exceeding the iliopectineal line length and a relatively high median RMSD value (1.5 [0.8-2.0] mm) in mid-section of the plate.

Conclusions: In acetabular fracture surgery, both visual and quantitative evaluation of suprapectineal plate fitting in sex- and body height-specific subgroups showed moderate fitting in female pelvic shapes, indicating a need for substantial intraoperative bending. This suggests the need for different sizes and contours of future suprapectineal plates in acetabular fracture surgery.

Keywords: Acetabular fracture; Implant fitting; Suprapectineal quadrilateral surface plate.

Fig. 1

Workflow from construction of shapes to plate fitting analysis. a A dataset of 200 patients was used to construct different shapes. A mean shape was constructed from all 200 patients. Accordingly, the dataset was divided by sex, resulting in 100 female and 100 male patients. Then, for each sex-specific group, four subgroups were defined based on the patients’ body height distribution (quartile 1-4; Q1-Q4) within each sex-specific group. b Plate fitting of the quadrilateral suprapectineal (QLS) plate was performed on all nine hemipelvis shapes. c Evaluation of plate fitting by computation of clinically relevant parameters, including iliopectineal line (black dots) (1) length, (2) radius, and (3) the quadrilateral slope (pink dots), and distance between the plate and the hemipelvis, represented by the green lines between the plate and the bone

Fig. 2

Plate fitting performed according to virtual surgical operative technique as described in the surgical guide by Stryker [25]. a The first anchor point of the plate is the third hole of the suprapectineal part of the plate. b The infrapectineal part of the plate was aligned utilizing this anchor point. c The anterior part of the plate can be finetuned and adjusted to align the anterior part of the hemipelvis.

Fig. 3

Visualization of the computation of the clinically relevant parameters. a Iliopectineal line length, b iliopectineal line radius and c quadrilateral slope

Fig. 4

a Obturator oblique view and b inlet view of the mean shape and the fitted plate. c To compute the root mean square distance (RMSD) for specific parts of the plate, four regions of the plate were defined. Region 1 (blue) represents the anterior part of the plate, region 2 (yellow) represents the suprapectineal part of the plate, region 3 (red) represents the posterior part of the plate, and region 4 (green) represents the infrapectineal part of the plate

Fig. 5

Visualization of plate fitting for the mean shape a obturator oblique view and b inlet view, c a zoom-in of the obturator oblique view d and a zoom-in of the inlet view. The root mean square distance (RMSD) of the whole plate with the mean shape is 0.6 (0.0–1.5) mm. In regions 2 and 4, an RMSD of 0.0 (0.0–0.6) mm and 0.0 (0.0–0.5) mm was reported, respectively

Fig. 6

Assessment tool for clinical interpretation of plate fitting of the male and female subgroups. When a patient is presented with an acetabular fracture, he or she could be allocated to a sex-specific group. Accordingly, the patient’s height determines in which Q-subgroup the patient belongs. For each subgroup, the plate fitting is evaluated by means of the visual inspection, with bounding boxes indicating reasons for a moderate fit. A moderate fit requires significant additional pre- or intraoperative bending adjustments, whereas a good fit allows the pre-contoured plate to be utilized without bending adjustments. An orange colour box highlights the plate length exceeding the length of the iliopectineal line and a blue coloured box highlights ventral protrusion of the plate relative to the iliopectineal line of the hemipelvis, both contributing to a moderate fit assessment