Digital anatomical measurements of safe screw placement at superior border of the arcuate line for acetabular fractures

Special screw corridors and imaging in pelvic ring trauma

Adequate intraoperative visualization is mandatory for implant application in pelvic ring injuries. Several fluoroscopic X-ray views are in practical use. The gold standard primary X-ray is the anteroposterior view of the pelvis. In addition to this view, oblique views for pelvic ring instabilities and acetabular fractures are well defined. Combinations of these views allow better identification of osseous corridors for screw applications. These corridors are based on the 3-ring concept of the hemipelvis. For pelvic ring stabilization the main osseous corridors include the retrograde and antegrade superior ramus/anterior column corridor, the supraacetabular corridor and the gluteus medius pillar corridor. The radiographic anatomy of these corridors is described in detail for screw applications with definition of image intensifier angulations, risk zones and corridor parameters. This allows for intraoperative safe implant application.

Extra-articular screw placement strategy in Stoppa approach based on three-dimensional reconstruction model

The study aimed to explore an extra-articular screw placement strategy in Stoppa approach. Radiographic data of patients who underwent pelvic computed tomography from January 2016 to June 2017 were imported into Materiaise's interactive medical image control system software for three-dimensional reconstruction. Superior and lower margins of acetabulum and ipsilateral pelvic brim could be observed simultaneously through inlet-obturator view. A horizontal line from superior acetabular margin intersected pelvic brim at point "A" and another vertical line from lower margin intersected pelvic brim at point "B" were drawn, respectively. Lengths form sacroiliac joint to "A" (a), "A" to "B" (b), and "B" to pubic symphysis (c) were measured. Patients were divided into four groups depending on gender and side difference of measured hemi-pelvis: male left, male right, female left, and female right. Lengths of adjacent holes (d) and spanning different holes (e) of different plates were also measured. Mean lengths of a, b, c in four groups were 40.94 ± 1.85 mm, 40.09 ± 1.93 mm, 41.78 ± 3.62 mm, and 39.77 ± 2.23 mm (P = 0.078); 40.65 ± 1.58 mm, 41.48 ± 1.64 mm, 40.40 ± 1.96 mm, and 40.66 ± 1.70 mm (P = 0.265); 57.03 ± 3.41 mm, 57.51 ± 3.71 mm, 57.84 ± 4.40 mm, and 59.84 ± 4.35 mm (P = 0.165), respectively. Mean d length of different plates was 12.23 mm. Average lengths spanning 1, 2, 3 and 4 holes were 19.33 mm, 31.58 mm, 43.80 mm, and 55.93 mm. Our data showed that zones a and c could be safely inserted three and four screws. Penetration into hip joint could be avoided when vacant 3-hole drilling was conducted in zone b. Fracture line in zone b could serve as a landmark for screw placement.

Excessively long interfragmentary screws for posterior wall acetabular fractures can predict intra-articular penetration

BACKGROUND

The fixation of posterior wall acetabular fractures often utilizes interfragmentary screws with varying length. Intricate pelvic anatomy and overhanging greater trochanter make obtaining proper screw trajectory difficult. A large measurement may represent aberrant trajectory and breach of the articular surface. This study aims to identify a preferred maximum screw length that avoids intra-articular penetration.

HYPOTHESIS

We hypothesized that a screw measured 40 millimeters or longer has a high likelihood of being intra-articular.

PATIENTS AND METHODS

A retrospective review included CT scans of 151 consecutive patients collected at a level-1 trauma center was analyzed by two observers. On axial imaging, a straight line was measured at the largest extraarticular portion of the posterior wall simulating ideal screw placement. Another line was measured tangent to the articular surface simulating longest possible extraarticular screw. Measurements were taken at 2-millimeter increments.

RESULTS

The intra-class correlation coefficient between both observers was excellent (0.75-1.00) for most recorded values. The maximum mean length for straight line measured (m=32.18mm, SD=3.74) which was smaller than the mean length for tangent line (m=38.44, SD=4.29). Exploratory multivariate logistic regression analyses demonstrated increased height, age, and acetabular version were associated with larger measurements greater than 40mm (p<0.05).

DISCUSSION

This study demonstrates that most acetabular posterior walls cannot accommodate a 40 millimeter lag screw. If the measured drill hole is greater than this length, then careful reconsideration of the screw trajectory is warranted to ensure the screw is not intra-articular. Older and taller patients may be able to accommodate longer screws.

LEVEL OF EVIDENCE

III.

Digital anatomical study and clinical application of screw placement for quadrilateral plate fractures in the danger zone

BACKGROUND

Direct screw placement for quadrilateral plate fractures in the danger zone of the acetabulum is very difficult. This study was performed to simulate the surgical procedure and try to obtain effective and safe screw angles through the middle window of the ilioinguinal approach in Chinese patients.

METHODS

We randomly collected the pelvic computed tomography (CT) scans of 100 adults. DICOM-formatted CT-scan images were imported into Mimics software. The three-dimensional reconstruction (3D) digital model of the semi-pelvis was established. A 3.5 mm cylinder was used to simulate the pathway of the screw from the designated insertion point. The angles of insertion and intersex differences were explored by statistical analyses.

RESULTS

The screws could be inserted via three angles: medial inclination, anterior inclination and posterior inclination. The mean minimum medial inclination angle (MIMIA) of insertion point A was 4.96° ± 1.11° in males and 8.66° ± 3.40° in females, and the intersex difference was significant. The mean minimum medial inclination angle (MIMIA) of insertion point B was - 5.31° ± 3.69° in males and 1.75° ± 8.95° in females, and the intersex difference was significant. There were no differences between any of the angles for males and females at insertion point O.

CONCLUSIONS

Preoperative measurement and calculation by digital tools before screw placement for quadrilateral plate fractures of the acetabulum are feasible. Double cortical screws could be placed safely in the danger zone through the middle window of the ilioinguinal approach to increase the stability of the acetabulum.

Development of generic Asian pelvic bone models using CT-based 3D statistical modelling

Background/Objective

Artificial bone models (ABMs) are used in orthopaedics for research of biomechanics, development of implants and educational purposes. Most of the commercially available ABMs approximate the morphology of Europeans, but they may not depict the Asian anatomy. Therefore, our aim was to develop the first Asian ABM of the pelvis and compare it with the existing pelvic ABM (Synbone®; Caucasian male).

Methods

One hundred clinical computed tomography (CTs) of adult pelvises (male n ​= ​50, female n ​= ​50) of Malay, Chinese and Indian descent were acquired. CTs were segmented and defined landmarks were placed. Three 3D statistical pelvic model and mean models (overall, male, female) were generated. Anatomical variations were analysed using principal component analysis. To measure gender-related differences and differences to the existing ABM, distances between the anterior superior iliac spines (ASIS), the anterior inferior iliac spines (AIIS), the promontory and the symphysis (conjugate vera, CV) as well as the ischial spines (diameter transversa, DT) were quantified.

Results

Principal component analysis displayed large variability regarding the pelvic shape and size. Female and male statistical models were similar in ASIS (225 ​± ​20; 227 ​± ​13 ​mm; P ​= ​0.4153) and AIIS (185 ​± ​11; 187 ​± ​10 ​mm; P ​= ​0.3982) and differed in CV (116 ​± ​10; 105 ​± ​10 ​mm; P ​< ​0.0001) and DT (105 ​± ​7; 88 ​± ​8 ​mm; P ​< ​0.0001). Comparing the unisex mean model with the pre-existing ABM, the ASIS (226; 275 ​mm; P ​< ​0.0001), the AIIS (186; 209 ​mm; P ​< ​0.0001) and the CV (111; 105 ​mm; P ​< ​0.0001) differed significantly. Both models were similar regarding DT (97; 95 ​mm; P ​= ​0.6927). The analysis revealed notable gender- and size-dependent anatomical variations within the Asian population. Chinese, Malay and Indian descents did not differ notably. The overall Asian model was smaller than the existing ABM.

The translation potential of this article

Owing to the large differences between the Asian ABM and the pre-existing ABM, as well as differences between genders, the use of an Asian- and gender-specific ABM is important to consider in research, biomechanics and implant development for this population.

The "safe zone" for infrapectineal plate-screw fixation of quadrilateral plate fractures: An anatomical study and retrospective clinical evaluation

Extra-articular screw placement in the true pelvis for fixing quadrilateral plate fractures remains challenging. We aimed to define the "safe zone" on the quadrilateral surface to facilitate safe plate-screw placement.Twenty cadaveric hemipelves were sectioned and assembled to define the projection of the acetabular boundary on the quadrilateral surface. Three lines (X, Y, and Z) were drawn tangent to the projection, with X parallel to the iliopectineal line, Y perpendicular to the iliopectineal line, and Z parallel to the posterior border of the ischial body. Then, the distances between X and the iliopectineal line (D1), Y and the sacroiliac joint (D2), and Z and the posterior border of the ischium (D3) could be used to determine a "safe zone" on the quadrilateral surface for screw insertion. We included 15 patients whose conditions satisfied the definition of a comminuted quadrilateral plate fracture and applied two-ended buttress plates for treatment in accordance with this "safe zone."The average D1 was 50.0 mm, the average D2 was 30.6 mm, and the average D3 was 12.4 mm. For all 15 patients with comminuted quadrilateral fracture who were treated, no intraoperative or postoperative screw penetration of the acetabulum was identified, and no loss of reduction was observed during an average follow up of 17.7 months.The "safe zone" established in this study simplifies extraarticular screw placement for managing quadrilateral plate fractures in the true pelvis. As a result, two-ended buttress plate fixation in the true pelvis becomes safe, therefore, treatment with two-ended buttress plates may represent a viable alternative to single-ended elastic fixation in the management of comminuted quadrilateral fractures.

The safe screw path along inferior border of the arcuate line at acetabular area: an anatomical study based on CT scans

BACKGROUND

Misplaced screw during the internal fixation of acetabular fractures may penetrate the hip joint which might cause chondrolysis and traumatic osteoarthritis in the future. This study aims to acquire the safe path for screw insertion along inferior border of the arcuate line fixation route at acetabular area.

METHODS

Computed tomography (CT) scans of 98 patients without pelvic trauma were rebuilt for three-dimensional models of pelvis. After depicting the fixation route curve, five cross-sections perpendicularly to the curve were established from the anterior of pelvis to the posterior along inferior border of the arcuate line. The safe screw lengths for section 1 and 5 were measured from the computer models. In section 2, 3 and 4, a line from the screw entry point tangent to the inferior edge of the acetabulum was depicted and the measurements of minimum safe direction of screw insertion were performed then marked with angle θ.

RESULTS

The safe screw lengths for section 1 and 5 were 22.29 ± 4.41 mm and 32.64 ± 4.70 mm (n = 98). The minimum safe angles of screw insertion for the middle three sections 2, 3, and 4 were 65.38 ± 10.23°, 74.20 ± 10.20°, and 57.88 ± 11.11°(n = 98), respectively. The results for the male group (n = 98) indicated smaller minimum safe angles in these three sections compared with the female (n = 98).

CONCLUSIONS

Compared to male, the minimum safe angles of screw placement at acetabular area for female should be more away from inferior edge of acetabulum and tilt to the bottom of pelvis along inferior border fixation route in surgical management of acetabular fractures.

A novel electromagnetic navigation tool for acetabular surgery

BACKGROUND

Acetabular fracture surgery is demanding and screw placement along narrow bony corridors remains challenging. It necessitates x-ray radiation for fluoroscopically assisted screw insertion. The purpose of this cadaver study was to evaluate the feasibility, accuracy and operation time of a novel electromagnetic navigation system for screw insertion along predefined acetabular corridors.

METHODS

A controlled laboratory study with a total of 24 electromagnetically navigated screw insertions was performed on 8 cadaveric acetabula. 3 peri-acetabular bony corridors (QSS, Quadrilateral Surface Screw; IAS, Infra-Acetabular Screw; PCS, Posterior Column Screw) were defined and screws were placed in a defined order without fluoroscopy. Operation time was documented. Postoperative CT scans were performed to analyse accuracy of screw placement.

RESULTS

Mean cadaver age was 70.4 ± 11.7. Successful screw placement was accomplished in 22 out of 24 (91.7%) cases. The overall mean time for all 3 acetabular screws was 576.6 ± 75.9s. All 3 complications occurred during the placement of the IAS due to an impassable narrow bony corridor. QSS mean length was 50 ± 5mm, IAS mean length was 85 ± 10mm and PCS mean length was 120 ± 5mm.

CONCLUSION

In this cadaver study the novel electromagnetic navigation system was feasible to allow accurate screw placement without fluoroscopy in defined narrow peri-acetabular bony corridors.