Due to the anatomic situation of the pelvis and acetabulum, management of an acetabular fracture is a technically demanding procedure. The close relationship to the iliac vessels and the complex construction of the acetabulum make it challenging to achieve reduction and fixation of the anterior and posterior acetabular column.
Demographic changes in industrial societies with overaging of the population have led to a shift in the typical fracture distribution. Large registry-based epidemiologic studies have demonstrated a rising number of acetabular fractures involving the anterior column over the last 20 years [
The infra-acetabular screw following Letournel’s [
The purpose of the study is to investigate if a plate-referenced drill guide can provide save placement of an infra-acetabular screw over a precontoured suprapectineal quadrilateral buttress plate (SQBP).
A total of 12 adult cadaveric acetabular specimens (6 pelvises) preserved by Thiel’s method [
The specimens were dissected and stripped of the surrounding soft tissue. The hip joint capsule was dissected at level of the capsule-labral junction (Figure
Fixation of the plate and drill guide construct to a left acetabulum (a) and image showing the infra-acetabular screw (white arrow) after removal of the plate (b).
We matched a 3D-CAD model of the anatomically precontoured plate to a mean 3D surface model of 516 pelvises (SOMA, Stryker Orthopaedic Modeling and Analytics, Stryker Inc. Selzach, Switzerland). The shape of the surgical drill guide used in this study reflected the surface of the anatomically precontoured plate and had an optimal fit to the plate to assure a stable attachment of drill guide and plate. The drill guide was designed to contain the measurements determined in a recently published study on the ideal position of the infra-acetabular screw. Accordingly, the ideal entry point was 10.2 mm below and 10.4 mm medial to the highest point of the convexity of the plate reflecting the IPE. The angulation of the drill guide was in 10.4° to the axial plane and 71.4° to the sagittal plane of the pelvic inlet plane of the 3D model. The drill guide was constructed by additive manufacturing in a 3D-printing process.
For referencing of the drill guide position, we used a suprapectineal quadrilateral buttress plate (SQBP) (PRO pelvis supra-pectineal plate, Stryker Inc., Selzach, Switzerland). The plate was placed aiming for an optimal fit of the anatomical precontoured shape and fixed starting with a parasymphysial screw and pressing the plate laterally to achieve an adequate fit on the pelvic brim to assure alignment with the pelvic inlet plane (Figure
Therefore, we added a radiopaque spiral to the drill guide to assure the correct position of the plate-drill-guide construct in relation to Koehler’s teardrop (Figure
Fluoroscopy image for fine adjustment of the plate position (a) and an image showing the relation of Koehler’s teardrop (center of the metal ring) and the drill guide (b) in a combined inlet oblique view along the infra-acetabular canal. Drill guide with a radiographic marker on a left acetabulum (c).
After insertion of the screw, the plate and the screws through the plate were removed leaving only the infra-acetabular screw in place to reduce material artifacts of the computed tomography (CT) scan. Since the screw does not go through a plate hole, the plate could be removed without the risk of malplacement when reinserting the infra-acetabular screw.
After drill guide-assisted placement of the infra-acetabular screw, we conducted a CT scan of all specimens to assess the actual position of the screw in relation of the infra-acetabular corridor and the acetabular joint surface. The position of the screw was measured using a picture archiving and communication system (PACS) software (Osirix 5.9, Pixmeo SARL, Bern, Switzerland). The infra-acetabular corridor was evaluated in a CT reconstruction plane centered at level of the infra-acetabular corridor with an inlet angulation of 25° according to Kanezaki and Miyazaki [
The measurement of the relation of the femoral head and the infra-acetabular screw was identified by generating a multiplanar reformation (MPR) centered through the core of the screw and the center of the femoral head according to Egli et al. [
Screenshot illustrating software-based measurements of the CT-based MPR.
The distance of the center of the screw to the medial wall of the infra-acetabular corridor at level of the center of the femoral head (SCD: screw-corridor distance): To measure the distance of the center of the screw to the virtual cartilage surface of the femoral head (SFHD: screw femoral head distance), we drew a virtual circle along the chondral border of the acetabulum to simulate the cartilage border of the head. All measurement results were recorded in mm.
The cadaveric specimens were donated to the university anatomy program. Donors gave their informed written consent for the donation and anatomical dissection during lifetime. No further prehumous data like medical records were used in this study. Therefore, there was no necessity for an approval by an ethics committee.
Statistical analysis was performed using the software package SPSS (Version 25, SPSS Inc, Chicago, Illinois). Since there is no previous data, this preliminary study was designed as an exploratory pilot study without any
The position of the screw was within the infra-acetabular corridor in all cases. We did not see any intra-articular or intrapelvic screw penetration. Table
Results of the computed tomography-based multiplanar reformation measurements given in mm.
Specimen No. | Infra-acetabular diameter (IAD) | Center cartillage distance (CCD) | Infra-acetabular corridor length (IACL) | Screw corridor distance (SCD) | Screw femoral head distance (SFHD) | Femoral head diameter (FHD) |
---|---|---|---|---|---|---|
1L | 7.90 | 6.96 | 79.6 | 3.62 | 7.01 | 42.7 |
1R | 8.06 | 7.12 | 80.7 | 3.24 | 6.52 | 42.3 |
2R | 6.56 | 8.30 | 84.9 | 3.13 | 7.74 | 43.4 |
2L | 6.68 | 8.34 | 81.1 | 2.41 | 6.70 | 43.4 |
3R | 6.53 | 7.90 | 85.7 | 3.14 | 7.68 | 49.6 |
3L | 6.89 | 7.31 | 99.9 | 2.72 | 6.99 | 50.1 |
4R | 5.83 | 6.36 | 99.8 | 2.98 | 6.72 | 43.0 |
4L | 7.08 | 7.39 | 85.9 | 3.29 | 6.80 | 42.8 |
5R | 6.19 | 7.61 | 98.5 | 3.14 | 7.17 | 46.4 |
5L | 5.87 | 4.15 | 92.0 | 2.66 | 3.73 | 46.2 |
6R | 8.12 | 9.30 | 85.9 | 4.95 | 9.98 | 45,2 |
6L | 7.44 | 9.57 | 86.9 | 5.05 | 10.50 | 45.8 |
Mean | 6.72 | 7.62 | 90.1 | 3.35 | 7.40 | 45.6 |
Range | 0.71 | 1.54 | 7.0 | 0.91 | 1.87 | 2.6 |
Min | 5.83 | 4.15 | 81.1 | 2.41 | 3.73 | 2.6 |
Max | 8.12 | 9.57 | 99.9 | 5.05 | 10.50 | 50.1 |
The mean corridor length measured at level of the screw (IACL) was 88.4 mm (±7.4). The mean distance of the core of the screw to the medial wall of the infra-acetabular corridor (SCD) was 3.36 mm (±0.83). The secure distance between screw and the virtual femoral head cartilage surface (SFHD) was 7.30 mm (±1.71).
This feasibility study demonstrated that a save placement of an infra-acetabular screw is possible by a plate-referenced drill guide over a precontoured SQBP. The entry point and angulation of the drill guide enabled save advancement of the drill directly into the infra-acetabular corridor. However, radiographic fine adjustment of the plate-drill-guide construct is indispensable to assure correct placement of the plate along the pelvic brim.
The secure distance between screw and the virtual femoral head cartilage surface was 7.30 mm (SFHD).
Demographic changes lead to an overaging of industrial societies and a rising number of geriatric fractures with a typical fracture pattern due to reduced bone quality in elderly [
Based on the quadrilateral screw described by Letournel [
In cases of reduced bone quality, a simple fall can cause a fracture of the anteromedial acetabulum or the quadrilateral surface by load transmission through the major trochanter [
Intra-articular screw penetration can cause a cartilage damage of the femoral head. We did not see any intra-articular screw position. The CT measurements revealed a secure distance of the screw to the femoral cartilage surface of 7.30 mm (SFHD). The diameter of the infra-acetabular corridor at level of the femoral head center was 6.72 mm.
Recently, a large biomorphometric CT-based study identified a viable infra-acetabular corridor with a diameter over 5 mm in 93% of specimens [
Instead of referencing the drill guide to the bony surface that might vary between each patient, the drill guide was referenced to a SQBP with a standardized surface. Using the plate as a reference, the interface between drill guide and plate allows an accurate fit without any deviation of the drill. Altering the level of patient-specific adjustment to the interface between plate and bone surface enlarges contact surface minimizing the risk of discrepancy of drilling direction in regard of the infra-acetabular corridor. In addition, conducting the drill process after insertion of the plate allows more room of action for the surgeon. The window of the intrapelvic approach provides a good overview and access to the anterior column and the quadrilateral surface. However, it can be difficult to manipulate with bulky instruments in the depth of the pelvis. Assembling the plate drill guide like a modular construct in situ might have an advantage over a large monobloc drill guide detecting the bone surface directly. The plate is constructed of annealed stainless steel which allows bending of the plate according to the bony surface. This implies the risk of mismatch of the drill guide and the plate when adaption by bending. His bending can also occur unintentionally by screw insertion and compression of the plate bone interface This has to be taken into account as a potential cause of mismatch of the plate-drill-guide interface and consequentially misguidance of the drill. However, most of the deflection of the plate takes place on the edges of the plate and the triangular shape of the plate at level of the drill guide prevents bending at this area. We did not observe any deflection of the plate at level of the plate-drill-guide interface leading to a mismatch or deviation of the drill. There is also a trend towards personalized medicine. Several pilot studies have proven advantages of preoperative 3D model-based plate bending for acetabulum fractures [
There is an ongoing debate about “safe zones” and “un-safe zones” in acetabular fracture management [
This study has some limitations. We manufactured the drill guide based on the SQBP that is adapted to a mean pelvic model based on 516 pelvic 3D CT scans of healthy subjects. This construction might not be suitable for patients with extreme skeletal dysplasia or degeneration of the hip joint. However, the pelvises used in this cadaveric study were of geriatric subjects with degenerative changes with a deep acetabular fossa narrowing the infra-acetabular canal. Even in these cases, we did not record any intra-articular screw penetration. Another limitation is that the drill guide was applied in not fractured acetabular cadavers. Incongruence of the infra-acetabular corridor due to insufficient reduction in a fracture situation can lead to occlusion of the designated screw canal or discrepancy of the reference at level of the quadrilateral surface. The limited number of cadavers that we used in this study reduces generalizability. Intention of this preliminary pilot study was to prove the principle of SQBP-based drill guide screw placement and to gain practical experience.
Detection of longitudinal displaceability of the SQBP along the pelvic brim in direction of the linea terminalis was one of the major findings that can only be detected in practical application. Although we did not observe any deformation of the plate, this could lead to a mismatch of the plate and drill guide leading to deviation of the drill.
Further studies are necessary to proof reliability in a large number of cases and in clinical application.
A plate-referenced drill guide can provide safe placement of an infra-acetabular screw for treatment of acetabular fractures. Radiographic fine adjustment is necessary to access the optimal entry. The secure distance between screw and the virtual femoral head cartilage surface was 7.30 mm (SFHD). Further studies are needed to proof reliability in clinics.
Center cartilage distance
Computer tomography
Infra-acetabular corridor length
Infra-acetabular diameter
Iliopubic/Iliopectineal eminence
Multiplanar reformation
Picture archiving and communication software
Screw corridor distance
Screw femoral head distance
Suprapectineal quadrilateral buttress plate.
Please contact the author for data requests.
The cadaveric specimens were donated to the university anatomy program. No further prehumous data like medical records were used in this study. Therefore, there was no necessity for an approval by an ethics committee.
Donors gave their informed written consent for the donation and anatomical dissection during lifetime.
Level of evidence is the level V cadaveric study.
The authors declare that they have no conflicts of interest.