Intraoperatively, the gold standard to analyze the results of reduction and fixation during acetabular fracture fixation is fluoroscopic X-ray views. Despite the ongoing discussion, if Judet views are still necessary for preoperative evaluation of acetabular fractures,1,2 their main value is for an intraoperative understanding of column reconstruction and safe localization of implants.
The gold standard primary X-ray is the anteroposterior (AP) view of the hip or pelvis (PAP). In addition to this view, no true radiological perpendicular plane is available. The understanding of the hemipelvic anatomy is the basis for further understanding of the acetabular column theory. The hemipelvis consists of an obturator segment and an iliac segment, and acetabular cavity is integrated at their connection area.
Oblique views of the hemipelvis are the basis for an additional radiography in two perpendicular planes. Considering the morphological anatomy of the hemipelvis, the iliac wing/fossa is rotated 90 degrees in relation to the obturator segment (▶ Fig. 22.1).
Fig. 22.1 Perpendicular orientation of the iliac and obturator segment for understanding different imaging techniques.
In the true frontal plane of a PAP, the obturator segment and the iliac wing have an angulation of approximately 45 degrees (see ▶ 3). Thus, oblique views are taken for two-plane analysis with the pelvis rotated either right or left by 45 degrees. These views were optimized and described by Judet based on ideas of Waller.3,4,5
To allow optimal comparison, preoperative X-rays of the whole pelvis should be performed, as one side shows an obturator oblique view (OOV) and the contralateral side shows an iliac oblique view (IOV) and therefore intraoperative comparison with the healthy side is possible. Alternatively, these views can be generated from CT data (▶ Fig. 22.2).
Fig. 22.2 Generated views and 3D imaging from standard CT scans.
Additionally, analysis of the pelvic ring can be performed by additional oblique views allowing better understanding of the ring structure of the pelvis and a better displacement analysis of pelvic ring injury deformity. Thus, inlet (PIV) and outlet (POV) views were introduced by Pennal.6
Historically, the angulation of pelvic inlet and outlet views in relation to the AP plane of the pelvis was described as being 40 degrees in each plane6 (▶ Fig. 22.3). Pohlemann already described different angulations: 40–60 degrees for the inlet view and 30–45 degrees for the outlet view.7
Fig. 22.3 Standard inlet and outlet projections from 3D CT data.
Recently, Ricci et al reevaluated these values and found that for the optimal inlet view, the X-ray plane is angulated 21 degrees to the true AP plane at the level of S1; and for the optimal outlet view perpendicular to the S1 body, the X-ray plane is angulated 63 degrees; and to the S2 body, the X-ray plane is 57 degrees to the true AP plane.8 No differences were observed regarding gender and age and for patients with normal and dysmorphic pelvises.
In a Korean analysis, the optimal inlet angles were reported to be 24.2 degrees at S1 and 27.9 degrees at S2 and the outlet angles at S1 was 54.8 degrees and at S2 52.3 degrees, respectively.9
A further CT analysis revealed—independent of gender—an optimal inlet angle of 26.7 degrees (25–29 degrees) using generated, virtual X-rays from CT data and 24.3 degrees (22–26 degrees) using three-dimensional (3D) reconstructions. The average outlet angles were 43.7 degrees (42–45 degrees) and 43.8 degrees (42–45 degrees), respectively. Sacral dysmorphism lead to an increase of the outlet angle of 5 degrees.10
For long time, five views (PAP; IOV and OOV Judet views; PIV and POV Pennal views) were the basis of evaluation of pelvic ring and acetabular injuries.
Together, these five views allowed for analysis of different bone corridors to analyze fracture location, displacement, intraosseous hardware, and intra- and postoperative results.
With increasing experience treating acetabular fractures, special views were generated to get an optimal understanding of safe screw placement in conventional or minimally invasive screw application together with navigation or two-dimensional (2D)/3D fluoroscopy.11,12,13,14,15 Pelvic and acetabular oblique views were combined for relevant intraoperative visualization of special bone corridors.
These bone corridors are relevant, especially for percutaneous screw insertion and to address special fracture lines using one-column approaches.
Percutaneous screw insertion can be performed using standard approaches supported by fluoroscopy or with the addition of 2D and 3D navigation. Crowl reported on the use of all three different techniques in 23 patients.16 These techniques are suitable, especially for anterior or posterior column screws as well as for the stabilization of peripheral fracture lines.
Even in percutaneous techniques, the primary goal of treatment is anatomical joint reconstruction. Steps and gaps of up to 2 mm are acceptable as larger displacement increases the risk of posttraumatic osteoarthritis. Additionally, percutaneous screws should achieve similar biomechanical stability as standard plate techniques, which has been shown in a cadaver study in T-type fractures.17
Since the first reports on percutaneous techniques in the early 1990s, numerous different procedures have been described. Both new instruments and technologies have been developed.11,15,18 Almost all authors use cannulated screw systems in which a wire is first placed under fluoroscopic imaging or navigation followed by screw insertion.11,12,13,14,15
Thus, the definition of relevant bone corridors is therefore essential and the knowledge of special intraoperative views helps to avoid implant malpositioning.
22.2 The Ring Structure of the Hemipelvis
The anatomy of the hemipelvis is the basis for understanding bone corridors. The hemipelvis can be interpreted as a three-ring structure (▶ Fig. 22.4).
Fig. 22.4 Three-ring structure of the hemipelvis.
22.2.1 First Ring = Iliac Ring
The iliac wing segment has a ring-shaped structure with a very thin bone plate central in the iliac fossa surrounded by dense bone. The iliac fossa has an anterior bony condensation, the gluteus medius pillar. Between the gluteus medius pillar and the posterior gluteal line, a thin central segment is present (▶ Fig. 22.5) sometimes a real hole is observed. On a true lateral hemipelvic view, four relevant landmarks are the basis for this ring segment:
The superior dense bone segment is represented by the iliac crest, reaching from the anterior superior iliac spine (ASIS) to the posterior superior iliac spine (PSIS).
The anterior border is the thick and strong bone segment from the ASIS to the pelvic brim superior to the joint just inferior to the anterior inferior iliac spine (AIIS); good bone quality is present in a 2- to 3-cm corridor.3
The base of this ring consists of the supraacetabular corridor superior to the greater sciatic notch starting at the AIIS and ending at the posterior inferior iliac spine (PIIS) or the PSIS; this AIIS–PIIS bone corridor has a length of approximately 85–100 mm, and the AIIS–PSIS bone corridor has a length of approximately 128–141 mm.19
The posterior part consists of the strong bone between the PIIS and the PSIS; this bone segment is approximately 2- to 3-cm thick and has an anterior enlargement of up to 2 cm up to the posterior gluteal line.
Fig. 22.5 Thin bone structure at the iliac fossa between the gluteus medius pillar and the posterior gluteal line. Bone thickness at the iliac crest and at the supraacetabular corridor.
22.2.2 Second Ring = Acetabular Ring
The second ring is the original joint, consisting of the facies lunata with the surrounding bone, divided into the anterior wall, the thicker posterior wall, and the superior dome with parts of the radiographical iliac cortical density. Centrally, a thin bone segment, the acetabular fossa, is present. Its thickness was reported to be 4 mm in male and 3 mm in female cadavers.20 The second ring shows an anterior (internal) rotation in relation to the first ring structure.
22.2.3 Third Ring = Obturator Ring
The third ring consists of the complete obturator segment, which has a classical ring-shaped structure with a true hole surrounded by the bony obturator ring. The third ring is slightly anteriorly (internally) rotated in relation to the second ring structure and consist of four parts:
The superior part consists of the infraacetabular corridor, described by Letournel and Culemann,21,22 for additional stabilization connecting the anterior and posterior column and to prevent a medial displacement of quadrilateral fracture fragments.
The anterior part consists of the superior pubis ramus and part of the inferior ramus; long screws can be inserted as in symphyseal plating.23
The posterior part consists of the ischial tuberosity extending into the true posterior column; thus, retrograde posterior column screws can be inserted at that part.
The inferior part of the third ring is a thin, innominate bone segment,4,22 where typically no stabilization is necessary; due to this thin bone structure, this region is in danger for inferior ramus fractures, which are often observed in anterior pelvic ring injuries.7
Overall, an inferior overlapping zone is present between each two rings (▶ Fig. 22.4). Letournel has already described important screw directions for isolated screw fixation of certain acetabular fracture lines.22 Isler summarized these screw directions and reported eight different theoretical screw positions for the fixation of components of acetabular fractures.24 Recently, these screw pathways were confirmed by Bishop.23
At the iliac ring anterior, superior and posterior hardware can be fixed. Periacetabular, four fixations regions are present, including both overlapping zones. At the obturator ring, only anterior and posterior fixation is useful. Inside the ring centers, adequate fixation is normally difficult or even impossible.
22.3 Iliac Ring
Anterior fixation at the iliac wing is possible and is sometimes performed in some special anterior column fractures in an oblique or anterior posterior direction (see ▶ Fig. 12.15).
The iliac crest corridor is often used as a bone corridor for stabilization of high anterior column fractures. Typical fracture types are high anterior column fractures, associated both-column fractures, and associated anterior column plus posterior hemitransverse fractures, in which the anterior column component of the fracture reaches the iliac crest. Typically, long 3.5-mm screws can be inserted according to the curvature of the crest, but larger diameter screws up to 7.3 mm are possible. For the application of iliac crest screws, screw lengths of 60–80 mm can be achieved (▶ Fig. 22.6).
Fig. 22.6 Schematic view of iliac crest screws.
The typical X-rays confirming placement of these screws are the PAP, the IOV, and, for axial determination of the screw, an OOV.
In the posterior part screw fixation is rarely an option in acetabular fractures. This area can be fixed using percutaneously inserted screws in crescent fractures.25
22.4 Acetabular Ring
Fixation around the acetabular ring is necessary in several fracture types. The most common fixation area is the posterior wall (for details, see ▶ 8).
In rare cases, fixation in the supraacetabular region and at the anterior wall is indicated. A further concept is the stabilization of the anterior against the posterior column at the inferior acetabular level. The concept of the inferior acetabular screw was already described by Letournel22 and the corresponding relevant intraoperative fluoroscopy views were recently defined by Culemann.21
22.4.1 Anterior Periarticular Safe Zones and Dangerous Zones
Letournel defined the dangerous zone of possible screw penetration, especially in the anterior wall region of the acetabulum. Two safe areas were described22:
Proximal to a line connecting the inferior pole of the AIIS and the superior border of the greater sciatic notch on the level of the pelvic brim (inlet view)
Anterior to a horizontal line tangential to the inferior part of the iliopectineal eminence
The segment in between these two lines is the dangerous zone, were screw penetration into the joint is possible (▶ Fig. 22.7). Thus, knowledge of screw orientation is of relevance (▶ Fig. 22.8).
Fig. 22.7 Dangerous area periacetabular at the anterior wall.
Fig. 22.8 Possible periacetabular screw direction.
Ji et al analyzed the direction of screws placed in the anterior periacetabular region.26 Perpendicular to the bone surface, five different angles were measured in the medial direction (away from the joint) with a safe area to the acetabular fossa or cartilage of 5 mm. Close to the joint, three positions were analyzed: anterior joint area, central joint area, and posterior joint area. The corresponding potential screw angles were 21.1, 30.4, and 23.8 degrees, respectively. The mean screw length at these points was 58.8 mm, 42.9 mm, and 72.4 mm, respectively.26
Bi et al analyzed the mean cortical thickness based on CT data in 75 cases at the medial pelvic brim.27 Periarticular, starting from anterior, the mean thickness was 23.0 mm, 19.9 mm, 13.2 mm, and 17.4 mm, respectively. Females showed a smaller cortical thickness than males.
A comparable analysis was performed by Wang et al in Chinese hemipelvises.28 A cross-sectional analysis of potential screw angulation in relation to the quadrilateral surface and the width of the nonarticular cortex in relation to the medial pelvic brim at three periarticular levels were performed: anterior quarter point (AQP), midpoint (MP), and posterior quarter point (PQP), respectively.
At these points, the maximum angulation (= most safe angulation) of AQP in relation to 5 mm, 10 mm, and 15 mm lateral to the pelvic brim border to avoid articular penetration was measured, resulting in 8.2, 14.9, and 26.1 degrees, respectively. At the MP level, these angles were 4.5, 13.2, and 23.6 degrees, and at the PQP level, these values were –15.2, –7.4, and 4.9 degrees, respectively. The average nonarticular width was 6.8 mm, 8.2 mm, and 12.1 mm, respectively.28
22.4.2 Supraacetabular Screw Corridor
The supraacetabular screw corridor (▶ Fig. 22.9, ▶ Fig. 22.10) can be used for antegrade pin placement in supraacetabular external fixation,29,30 retrograde screw placement in lumbopelvic fixations,19 and for stabilization of crescent fractures of the pelvic ring.25,31
Fig. 22.9 CT evaluation of the supraacetabular bone corridor and possible screw course with slight angulation projected onto a 3D model of the hemipelvis.
Fig. 22.10 Drawing and clinical example of the supraacetabular screw course.
The bone corridor starts at the AIIS, runs parallel and slightly lateral to the pelvic brim, and superior to the greater sciatic notch before reaching the PSIS or the PIIS (▶ Fig. 22.9). The borders of this corridor are lateral and medial the inner and outer iliac surfaces, the superior border is the thinning between both cortices and the base is the anterosuperior acetabulum, the greater sciatic notch with the iliac part of sacroiliac (SI) joint. This corridor therefore enables placement of an anterior-to-posterior directed screw, for fixing anterior column fractures.22
The starting point in posterior screw application during lumbopelvic fixation techniques is just inferior and anterior to the PSIS.32 The typical screw trajectory is orientated in a 15-degree lateral angle to the sagittal plane and in a 30-degree caudal orientation in relation to the transversal plane.33
Pichler et al analyzed the length, the anterior distance to the narrowest iliac zone, the maximal dimension of the narrowest zone, and the angles between the sagittal and transversal plane relative to the supracetabular screw, based on CT data; and 7.3-mm screws were simulated in 50 patients.34,35 The mean screw length was 148 ± 9.4 mm, the mean distance from the entry point to the narrowest zone was 17.5 ± 3.3 mm, and the overall narrowest superior ramus point was 16.0 ± 2.7 mm. The angle between the sagittal and coronal plane and the screw was 22.4 ± 3.4 degrees and 35.3 ± 4.6 degrees, respectively. Despite gender differences in the size of the anterior column screw corridor (ACSC), the angles showed no significant gender differences.34,35
Schildhauer defined the overall pathway and two narrow zones in this bony canal.19 The PSIS–AIIS length was 141.1 mm in male patients and 128.7 mm in female patients on average; the PIIS–AIIS length was 86.3 mm in male patients and 99.7 mm in female patients on average, respectively. The distance to the first narrow area starting from posterior was approximately 3 cm in men and 2.7 cm in women; the distance to the second narrow area was 86.3 mm in men and 84.1 mm in women on the superior pathway (PSIS–AIIS) and 60.3 mm in men and 52.8 mm in women on the inferior pathway (PIIS–AIIS), respectively. Thus, a three-point stabilization of a long screw is possible in this corridor. The analysis of the width of this corridor revealed possible screw diameters of 8 mm in men and 6–7 mm in women.
Additionally, in some fracture situations, a more anterolateral or lateral screw insertion is helpful to address oblique fractures or support superior marginal impactions. To confirm these supraacetabular screw placements, for posterior wall fractures, Tosounidis et al recommended the combined inlet and obturator oblique view (IOOV).36 The average screw direction is 22 degrees medially directed to the sagittal plane and 35 degrees cranial to the horizontal plane (▶ Fig. 22.11).34,35
Fig. 22.11 Image intensifier positioning for supraacetabular screw placement.
For the SASC, all possible standard views and their combinations were recommended including the standard PAP, OOV, IOV, COOO, inlet view, true lateral view, the combined obturator oblique inlet (COOI), and the combined iliac oblique outlet (CIOI) views.11,16,37,38,3,9
Radiographically, the most relevant view is the combined obturator oblique outlet view (COOO), where the corridor is imposed as a teardrop figure.19,29,31,40 The inferior aspect of the teardrop figure is optimally positioned directly tangential to the acetabular roof (sourcil) and the teardrop shape should be as small as possible for optimal identification of the screw entry point. The capsular insertion up to 16 mm proximal to the sourcil should be considered when inserting screws.41 The classical IOV confirms the optimal placement of the screw superior to the greater sciatic notch.
Intraoperative analysis of the screw pathway consists of four possible views (▶ Fig. 22.12):
The true lateral hemipelvic view (LV) confirms the screw superior to the greater sciatic notch19
The COOO confirms the axial screw orientation within the bony corridor from the PSIS to the AIIS; possible medial/lateral penetration can be excluded
The PIV confirms the screw path lateral to the SI joint
The IOV confirms the screw path superior to the greater sciatic notch and the length of the screw
Bishop recommends, beside the COOO view, the COOI and IOV.23
Fig. 22.12 Intraoperative projections for safe supraacetabular screw placement. From left to right: LV, COOO, PIV, IOV with marked screw corridor.
22.4.3 Quadrilateral Plate Screws
This screw has been referred to as magic screw and stabilizes the quadrilateral plate after reduction. The entry point is on the lateral side of the iliac wing slightly above and posterior to the acetabulum (▶ Fig. 22.13). It penetrates the medial cortex of the quadrilateral plate approximately at the level of the sciatic spine.14,15
Fig. 22.13 Magic screw course: 3D view and clinical example.
22.4.4 Infraacetabular Screw Corridor
Letournel already proposed an infraacetabular screw and reported three possibilities of screw positions relative to the joint ▶ Fig. 22.8, ▶ Fig. 22.14).22
Fig. 22.14 Clinical example of the infraacetabular screw.
The screw can be totally embedded in the floor of the acetabular fossa, when there is thick bone canal. Depending on the size of the bone corridor, slight to complete thread penetration at the lower acetabular fossa is possible without damaging the femoral head and acetabular cartilage.22 By palpating the quadrilateral surface, a strictly parallel screw orientation to the quadrilateral surface is possible.
Culemann recommended special intraoperative fluoroscopy views to detect the optimal screw position and reported the entry point relative to intraoperative bony landmarks.21
The entry point is described as 1 cm anterior to the top of the iliopectineal eminence in the midline of the upper pubic ramus.
Three views are recommended for screw position confirmation placing the image intensifier on the contralateral side:
Pelvic inlet view: 30-degree tilting of the C-arm, the extraarticular axial screw/drill bit position is confirmed; the tip of the drill should be in the center of the teardrop figure (▶ Fig. 22.15)
COOO: the C-arm is rotated to the fracture side, and additional 30-degree caudal tilting is performed allowing confirmation of the screw/drill bit path at the superior border of the obturator segment (▶ Fig. 22.16)
One-third iliac oblique outlet view (1/3 IOO): the C-arm is rotated 15 degrees to the uninjured side and a 30-degree caudal tilting is performed to control screw position lateral to the quadrilateral surface and medial to the joint line (▶ Fig. 22.17)
Fig. 22.15 Pelvic inlet view as the starting view for infraacetabular screw insertion and corresponding image intensifier position in the supine position.
Fig. 22.16 Combined obturator oblique outlet view as the classical view confirming the infraacetabular screw course and the corresponding image intensifier position.
Fig. 22.17 Image intensifier position for the one-third iliac oblique outlet view and the corresponding X-ray projections.
22.5 Obturator Ring
At the obturator ring, the main screw corridors are for application of anterior and posterior column screws. These screws are additionally part of the anterior and posterior acetabular ring region.
22.5.1 Anterior Column Screw Corridor
Knowledge of the ACSC is necessary to apply either anterior columns screws (ACS) or retrograde superior ramus screws (rSRS). The main screw course is antegrade, starting at the posterior gluteal area, at the gluteus medius pillar (▶ Fig. 22.18, ▶ Fig. 22.19, ▶ Fig. 22.20, ▶ Fig. 22.21, ▶ Fig. 22.22, ▶ Fig. 22.23). Additionally, this screw can be placed retrograde as a superior pubic ramus screw.42,43,45
Fig. 22.18 Drawing and clinical example of an anterior column screw.
Fig. 22.19 X-ray of the implant positions (screws replaced by metal rods): anterior column screw (left) and posterior column screw (right).
Fig. 22.20 Anterior column screw insertion close to the pubic symphysis (wrong) with risk of intraarticular penetration. Insertion close to the pubic tubercle (correct) reduces penetration risk.
Fig. 22.21 The optimal retrograde insertion point is caudal to the pubic tubercle. The drill direction follows the pecten ossis pubis.
Fig. 22.22 Drill direction of the anterior column screw in the inlet view: the green dotted lines are the anterior and posterior borders of the superior pubic ramus (in the inlet view, the posterior aspect of the inferior pubic ramus is projected superior to the superior pubic ramus). The relation of the drill axis and the pecten ossis pubis is shown.
Fig. 22.23 Drill direction of the anterior column screw in the obturator oblique view: angle of the drill axis (green) in relation to the radiopaque line starting from the pubic tubercle (violet, 111), and in relation to the lateral portion of the inferior border of the superior pubic ramus (blue, 111a)
Indications
The ACS is often used in acetabular fracture stabilization, especially in fractures with a transverse fracture component to address and fix the invisible contralateral column using the Kocher-Langenbeck approach. An additional posterior percutaneous approach using a step incision is often used for this screw,46 as this incision is not part of the Kocher-Langenbeck approach.
Alternatively, the retrograde superior ramus screw, as already described by Lambotte in 1913,42 can be used to fix displaced upper pubic ramus fractures, low anterior column fractures, or fractures with a transverse fracture component.
Osseous Morphology
The osseous corridor starts in the area of the symphysis pubis, and contains the entire upper pubic rami up to the anterior acetabular border, the anterior wall, and ends in the area of the pelvic brim near the SI joint.
Relevant surrounding anatomical structures include the corona mortis, the obturator canal with the obturator neurovascular bundle, and the iliac external vessels.
The superior border is extremely variable due to several bony landmarks.47 It starts at the pubic symphysis. The first few centimeters extend laterally to the pubic tubercle, the insertion of the inguinal ligament. Medially, a ridge on top of the superior ramus becomes visible (pecten ossis pubis), and is the origin of the strong superior periosteum. The pecten ossis pubis, together with the arcuate line medially, forms the iliopectineal line, which is the medial border of the anterior column. Lateral to the pecten ossis pubis, a groove is visible, where the iliac external vessels run along the upper pubic rami. Medial to the anterior acetabular rim, the iliopectineal eminence becomes prominent, the insertion of the iliopectineal fascia, which divides the muscular from the vascular lacuna. The iliopectineal eminence is a thickened bone part opposite to the anterior horn of the acetabulum. Posterior to the iliopectineal eminence, the iliopsoas groove (iliopsoas gutter) is present, which ends at the level of the AIIS. The superomedial part of the pelvic inlet forms the most proximal part of this superior border of the ACSC.
The medial part of the ACSC has a curved shape, consisting of different curvature values.27
The inferior border of the ACSC is irregular, starting with a triangle-shaped configuration at the upper pubic ramus extending into the obturator canal and the anterior horn and wall area.
There is an ongoing change in cross-sectional anatomy of the ACSC.23,26 At the upper pubic rami there is a change from triangular to circular.23,26 Around the joint area, the circular orientation changes to horizontal ovoid to superior-based small triangular at the mid anterior acetabulum to an acetabulum-based triangular configuration at the posterior part of the corridor until an oblique rhombus-like configuration posterior to the acetabulum.26
Entry Point
The optimal entry point is clinically difficult to find. The skin incision is recommended at the crossing point of two lines: the lateral femoral border junction line through the greater trochanter and a tangential line from the pubic tubercle symphysis to the AIIS on a pelvic AP view.48
The optimal entry point for the antegrade ACS at the outer iliac bone was described by several authors:
According to Letournel, the starting area is on the outer side of the ilium approximately 3–4 cm cranial to highest point of the acetabulum slightly posterior to the anterior gluteal line in a 2-cm circle.22
Ebraheim et al described the entry point as 46 ± 6 mm superior to the superior acetabular rim, and 16 mm superior to the midpoint of a line connecting the apex of the greater sciatic notch and the mid-distance between the ASIS and AIIS; sagittal angulation of 90.6 degrees and transversal angulation of 29 degrees were stated.49
Yi et al described the entry point as being “slightly superior to the acetabulum in the gluteus medius pillar, a thickening of bone that runs from the acetabulum to the iliac crest.”32
The insertion point landmark for an antegrade anterior column screw was found at the intersection between two perpendicular lines, one from the tip of the anterior inferior iliac spine and from the superior edge of the acetabulum.50 Depending on the size of the bony corridor, antegrade insertion had a possible area around the optimal entry point of 2.5 cm2 in patients with an 8.0 mm canal diameter and of 5.7 cm2 in patients with a 14.0 mm canal diameter.
An analysis of the distance between the center of the pubic symphysis and the entry point for the retrograde superior ramus screw found an average value of 27–28 mm.51 The distance between this entry point and the pubic tubercle was 14–17 mm.
The distance between the entry point for an antegrade anterior column screw and the apex of the greater sciatic notch was 37–42 mm.51
In a study on 164 hemipelvic CT models, the distance between the retrograde screw entry point and the mid symphysis was 18.4 ± 4.8 mm and the distance to the superior rim of the upper pubic ramus was 17.8 ± 2.6 mm.52
Length of the ACSC
Several authors reported on CT-based measurements of the length of the ACSC. Depending on their definition of this corridor, different results were stated. A mean length of approximately 120 mm is reported.
Chacko et al performed CT-based measurements and reported a length of 109.8 mm in male pelvises, and 108.8 mm in female pelvises. The ACSC was defined from 3 mm superior to the pubic tubercle through the superior pubic ramus to the posterior acetabular margin, on the obturator oblique view.53
Pichler et al in a CT-based measurement found a mean screw length was 127.2 ± 7.1 mm in a simulated corridor for a 7.3-mm screw.34,35
In a 2D CT analysis of 160 Japanese people, the overall screw lengths for men and women were 124.6 mm and 123.8 mm, respectively.50
Shahulhameed et al performed an anatomical analysis of the anterior column length and reported an average length of 12 cm (10.5–13.2 cm).54
In a study on 164 hemipelvic CT models, the mean length for a simulated screw was 109.39 ± 8.95 mm.52
Isthmus of the ACSC
There are several isthmus-like regions (superoinferior and mediolateral) in this corridor. The narrowest region is observed between the iliopsoas gutter and obturator neurovascular canal.54,55
The clinically most relevant isthmus is the superior distance between the joint and the superior corridor border.
Ji et al measured the thickness at the level of the facies lunata in 175 CT scans. A mean thickness of 14 mm was found (15.4 mm in male and 11.9 mm in female patients).47
For the mediolateral isthmus, a thickness of 12.5 mm (17.2 mm in male and 9.9 mm in female patients) was observed.27
In contrast, Chacko et al analyzed CT data and measured the narrowest point on the inlet view. The average width of this isthmus was 6.4 mm in males and 5.2 mm in females, whereas on the OOV the narrowest point at the mid-acetabular roof was 3.9 mm in males and 3 mm in females.53
Comparable data were reported by Attias et al, with a maximum diameter of 6.4 mm.2
Pichler et al analyzed, based on CT data, the overall narrowest superior ramus point.34,35 The mean distance from the entry point to the narrowest zone was 50.6 ± 6.3 mm and the overall narrowest superior ramus point was 14.6 ± 2.4 mm.
In a 2D CT analysis of 160 Japanese people, the size of the screw canal was determined.50 The pubic canal was narrowest at the parasymphyseal area with 13.5 mm (10–17.5 mm) in males and 10.7 mm (7.3–14.6 mm) in females, respectively.
Analyzing the axial anterior column screw (AACS) view showed an oval-shaped structure with a short diameter of 8.9 mm (range 7.7–10.6 mm).56
In a study on 164 hemipelvic CT models, the mean corridor diameter for a simulated screw was 8.16 ± 1.21 mm. The narrowest points of the ACSC were in the groove area of the muscular and vascular lacunae. Females showed overall smaller values.52
Thus, depending on the type of measurement, the narrowest part of the ACSC is between 10 mm and 14 mm.
Screw Orientation
The screw orientation is of clinical relevance. Therefore, beside fluoroscopy, intraoperative guidance is helpful for screw insertion and angulations of the drill bit can help to determine the optimal screw course.
Pichler et al analyzed, based on CT data, the antegrade angles between the sagittal and coronal plane relative to a simulated 7.3-mm screw corridor.34,35 The angle between the sagittal and coronal plane and the screw was 39.02 ± 3.17 degrees and 15.05 ± 4.01 degrees, respectively. No significant gender differences were observed.
In a 2D CT analysis of 160 Japanese people, the screw angle was determined for retrograde screw placement.50 The angles were 54.1 degrees in males and 55.9 degrees in females in the lateral direction to the sagittal plane and 66 degrees and 67 degrees in the vertical direction to the horizontal plane.
In a further study, the angulation between the anterior column screw and the sagittal plane was 33.6 degrees (range 29.6–36.5 degrees) and between ACS and the transverse plane was 59.1 degrees (range 56.4–63.2 degrees).56
In a study on 164 hemipelvic CT models, the angle between the potential screw and the transverse plane was 39.7 ± 3.9 degrees; the angle between the potential screw and the coronal plane was 20.8 ± 4.6 degrees and the angle between the potential screw and the sagittal plane was 42.7 ± 3.2 degrees.52
Overall, three angles can be defined:
A lateral-superior to medial-inferior directed angle of 33.6-39 degrees on the PAP34,35,56
A posterosuperior to anteroinferior directed angle of 15-22.3 22.3 degrees on the true lateral view34,35,50
A posteromedial to anterolateral directed supraacetabular angle of 55–59.1 degrees in the horizontal/transverse plane (inlet view)50,56
Recently, Peng et al proposed two different screw corridors for ACS, depending on the necessity of screw length, the localization of the fracture, and the chosen insertion point.57
ACS Fluoroscopic Projections
Screw placement is confirmed using different intraoperative X-ray views. Several views are recommended in the literature. For anterior column screws, all possible standard views and their combinations were recommended including the standard PAP, OOV, IOV, COOO, inlet view, the COOI, the CIOI, and the combined iliac oblique outlet (CIOO) views.11,15,37,39,58,59,60
The two main relevant views were the classical inlet and outlet views according to Pennal.6 Additionally, a modified OOV according to Judet61 was recommended. The modification consisted of a slight outlet configuration of this view, resulting in the COOO view. Further views were reported recently and combinations of these different views are potentially the most helpful intraoperative tool.32
Pelvic Inlet View
The pelvic inlet view (PIV) allows confirmation that the guidewire or drill does not penetrate the medial cortex.15 Disagreement exists whether an overlapping of the superior and inferior pubic rami, forming one column, is helpful62,63 or should be avoided.23 This overlapping view was described by Yi as an iliac inlet view (IIV).32 The guidewire should be targeted to the midline of the upper pubic rami from posterior (antegrade screw). A medial (posterior) guide wire orientation is proposed, as the vascular groove is responsible to the medially based triangular shape of the mid upper pubic rami. The resulting anterior and lateral slope starts directly lateral of the pectin pubis.
The entry point for retrograde superior ramus screws is typically at the pubic tubercle on the PIV. Variations are possible, depending on fracture localization and necessary screw length.
The Combined Obturator Oblique Outlet View
The COOO confirms avoidance of hip joint penetration and of a superior extraosseous pathway (▶ Fig. 22.24 and see ▶ Fig. 22.16). Outlet configuration of this view should be extended to the maximum width of the bone corridor between the joint and the iliopectineal eminence. Due to the upper pubic rami slope (vascular groove),23 the guidewire should be targeted to the superoposterior (most proximal) cortex.
Fig. 22.24 Combined obturator oblique outlet view (COOO) for analysis of the anterior column screw course.
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