The superior pubic ramus/anterior column anterior pelvic osseous fixation pathway (OFP) is the curved medullary bone conduit that extends from the symphysis pubis to the supra-acetabular lateral ilium that is cranial and posterior to the acetabular dome and has been well described.1–9 This corridor of cancellous bone is contained within the curved superior ramus and the irregular cortical surfaces of the anterior pubic ramus. The variable cortical surfaces include the curved posterior ramus flat surface, pubic tubercle, pectineus muscle sloped surface, iliopectineal eminence, and the iliopsoas muscle and obturator neurovascular gutters. The superior pubic ramus OFP is narrowest between the iliopsoas muscle and obturator neurovascular gutters. This complex osseous topography produces similarly complex cross-sectional pubic ramus anatomy. It is elliptical at the parasymphyseal region, triangular at the mid-ramus medial to the iliopectineal eminence, circular at the iliopectineal eminence, ovoid at the iliopsoas gutter, and triangular near the anterior wall of the acetabulum (Fig. 1).1 Understanding these cortical surface undulations, cross-sectional anatomy, and their imaging is mandatory to reliably insert safe intraosseous implants. If the osseous gutters, indentations, prominences, oblique cortical surfaces, and slopes are not recognized, drills and screws that seem to be safely located within the intraosseous pathway on intraoperative imaging could actually be extraosseous and risk damage to neurovascular and musculotendinous structures.1
The superior pubic ramus osteology dictates that the cranial–posterior cortical bone (the pelvic brim), the acetabular dome subchondral bone, the mid-ramus caudal bone, and the flattened curved posterior cortical surfaces are the reliable landmarks for routine radiographic imaging. Obtaining the appropriate fluoroscopic views of these landmarks allows the surgeon to visualize the cortical limits of the OFP and thereby locate implants within the various cortical confines of the medullary pathway. Although recent studies have advocated for additional views,10 the cortical limits of the superior pubic ramus OFP are reliably imaged intraoperatively using 2 fluoroscopic views: the pelvic inlet (PI) and the combination obturator oblique–outlet view (COOO).1 Due to the variability of each patient's pelvic orientation and changes with positioning, there is no standard degree of C-arm tilt. Instead, the tilt for each fluoroscopic image is adjusted to appropriately demonstrate the landmark cortical limits. These specific images can be obtained in either the supine or the prone position.
Intraoperative pelvic imaging begins with an anteroposterior (AP) pelvic view, with the symphysis pubis centered on the coccyx. If the image appears off center, the overall rotation is adjusted accordingly by slightly rotating the patient or by adjusting the C-arm to ensure the appropriate alignment. Once obtained, the fluoroscope is then tilted to obtain the PI view centered on the desired side so that the surgeon can visualize the start site and the entire superior pubic ramus OFP. The optimal PI view is achieved when the C-arm beam is completely tangential to the flat cortical surface of the posterior superior pubic ramus. Excessive C-arm tilt will produce superimposition of the superior pubic ramus and inferior pubic ramus posterior cortical surfaces. The C-arm tilt is adjusted until the posterior cortical surface of the superior ramus is identifiable just posterior to the inferior ramus posterior cortical surface and not overlapped (Fig. 2). The proper amount of C-arm tilt for the PI view may be estimated before surgery using the sagittal computed tomography images of the pelvic injury. These sagittal images help the surgeon to identify the anticipated C-arm tilt necessary for tangential intraoperative imaging of the superior pubic ramus posterior cortical surface. The intraoperative C-arm tilt for PI imaging can range from 15 to 35 degrees based on the patient's underlying sagittal plane orientation and any positioning modifications. Although the PI view demonstrates the AP limits of the superior ramus OFP, surgeons should remember the cortical surface osteology as the image will not demonstrate the posterior–cranial to anterior–caudal slope and triangular cross-sectional area of the mid-ramus. Implants that are anterior and cranial through this region are in jeopardy of being extraosseous while appearing intraosseous on the imaging.
The COOO view is obtained by combining the C-arm tilt of a pelvic outlet image with the roll of an obturator-oblique image. The C-arm directions depend on whether the patient is positioned supine or prone. The COOO image usually has 30–40 degrees of pelvic outlet tilt and 20–30 degrees of obturator-oblique roll. The COOO image is optimal when the tilt and roll are adjusted so the beam is tangential to the lateral iliac cortical bone of the supra-acetabular area and demonstrates the osseous pathway between the cranial cortical edge of the superior ramus and the subchondral bone of the acetabular dome. The COOO also reveals the caudal cortical limit of the superior ramus and the lucency of obturator neurovascular gutter (Fig. 3). The COOO view demonstrates the cranial, caudal, and lateral limits of the superior ramus OFP. Similar to the PI view, the surgeon must remember that the cranial–posterior to caudal–anterior cortical slope of the medial ramus as well as the iliopsoas and obturator neurovascular gutters.
Once the optimal PI and COOO views are obtained, the table height, C-arm unit position, and the degrees of tilt and roll required for each view are noted by the surgeon and radiological technician. This is done so the same views can be easily repeated as drilling and instrumentation progress requiring serially alternating views. Attention to the specifics of each will minimize the amount of errant fluoroscopic views and unnecessary radiation exposure to the surgeons, patient, and operating room staff.
Once the underlying osteology is understood and the appropriate PI and COOO views are obtained, medullary superior pubic ramus screws can be placed in either an antegrade or a retrograde direction with the patient positioned supine. Prone positioning restricts the surgeon to use antegrade screws only. The amount of curvature in both the AP and the cranial–caudal directions vary between patients and must be appreciated. The decision of which direction a screw is placed is influenced by many factors, including fracture location, the proximity of the external genitalia, and the impact of thigh girth.11,12 Ramus fractures at the middle or medial to the obturator foramen are often stabilized by retrograde screw insertion.11 It can be challenging to fully engage the screw through the small parasymphyseal segment from an antegrade approach due to the curvature of the OFP and technical proficiency. Especially in younger patients, the proximity of patient's external genitalia to the pubic symphysis may impede a surgeon from obtaining the correct retrograde start site. This is often less of a clinical issue with older patients as the external genitalia are generally more caudal from the parasymphsyeal start site but it is still patient specific. Retrograde screws can be successfully placed in younger patients with and without technique augmentations as detailed below (Fig. 4). Thigh girth also impacts screw placement as patients with large thighs can prevent the appropriate hand/drill placement required to achieve the desired aiming vector (Fig. 4).12
Although different methods of screw insertion have been previously described,11–15 a simple and reproducible technique for both antegrade and retrograde screw insertion using solid 4.5-mm screws is described below. The 4.5-mm screws used are ideally nondrilling and are not self-tapping. These blunt-tipped screws are beneficial as they tend to remain contained within the cortical limits of the curved superior ramus instead of creating a new, unintended, extraosseous, and potentially dangerous path. If a larger caliber screw (6.5, 7.0, 7.3, or 8.0 mm) is desired, a brief technique modification is described below. Additional modifications of the technique required due to suboptimal technique or soft tissue obstruction as mentioned above are also described below.
Antegrade Screw Insertion
For routine screw insertion, the necessary equipment is a 2.0-mm Kirschner wire, a 4.5-mm cannulated drill, a long 2.5-mm calibrated drill, and 4.5-mm cortex screws. For antegrade screw insertion, the C-arm is positioned contralateral to the side of injury and surgeon performing the instrumentation. The appropriate osseous start site for an antegrade screw is typically several centimeters cranial to the acetabular dome in the supra-acetabular region near the base of the gluteus medius pillar. It is ultimately determined by assessing the curvature of the superior ramus OFP on the PI and COOO views. Within limits, a straight line is envisioned extending from the supra-acetabular surface to the parasymphyseal bone (Fig. 5). A 2.0-mm Kirschner wire is placed percutaneously onto the appropriate start site. The skin start site for the wire is variable but is often located by triangulating to the base of the gluteus medius pillar. The gluteus medius pillar starts 4–6 cm posterior to the anterior superior iliac spine on the iliac crest and extends caudally and anteriorly toward the acetabulum. The wire should be inserted in the anticipated vector as the screw to minimize any hindrance from the soft tissue envelope. Once the appropriate skin and osseous start sites and aim are obtained on both views, the wire is inserted into the supra-acetabular bone. Using an oscillating technique, the wire is placed into bone (1 cm) and a 1-cm oblique skin incision is made. A 4.5-mm cannulated drill is then placed over the wire collinearly and the drill is then oscillated and advanced over the wire 1 cm into bone. Next, working between the PI and COOO views, the drill is advanced through the superior ramus OFP in the appropriate direction. If a trajectory correction is needed, the drill aim is changed appropriately and a quick pulse or oscillation of the drill is given to etch the bone and permit the improved trajectory (Fig. 6). Such corrections are made early in the OFP as any significant changes are difficult once the drill is further in. The drill is typically advanced to the fracture. Once there, the 4.5-mm cannulated drill bit is removed and a long, solid, 2.5-mm calibrated drill bit is placed into the path (Fig. 7). The drill bit can be used to palpate the drill tunnel to ensure an intraosseous position. The common areas of concern are the psoas gutter and just medial to the pectineal eminence. Once the drill is confirmed to be intraosseous, the drill is advanced to the parasymphyseal bone and then drilled through the medial cortex and left in situ with the drill tip 1–2 mm out of the cortex. Accurate depth measurement is performed using another long 2.5-mm calibrated drill and the subtraction method (Fig. 8). Note, the tip of the second drill is placed in a caudal and anterior position for this measurement as this replicates the final screw head position. If the second drill is placed cranial and posterior, the screw length will typically be overestimated. We typically use non–self-tapping 4.5-mm cortex screws (DePuy Synthes, Paoli, PA). The blunt tip of the non–self-tapping screw allows the screw to maintain an intraosseous position in tight OFPs and may minimize the chance of screw cut-out than can happen with self-tapping screws. Once the desired screw length is confirmed, the drill bit is removed and the screw is inserted using both views to ensure appropriate insertion vector and final screw depth (Fig. 9). This is typically done with power at first and final tightening done by hand. The screw head is confirmed to be down fluoroscopically and by the increased resistance felt when the screw head engages the cortical bone. The screwdriver can also be used to verify that the screw is seated by palpating the position of the screw on the cortex. When fully seated, the screw head will feel set under the cranial and posterior cortex and is flush to the caudal and anterior cortex. The incision is irrigated and closed with either 3-0 nylon or staples.
Retrograde Screw Insertion
The technique described above for antegrade screw insertion can also be used for retrograde screw insertion. Surgeons must be cautious when using the 4.5-mm drill on small parasymphyseal segments. If initially malpositioned at all, the 4.5-mm drill can be aggressive with any sort of vector correction. If too much bone is removed by etching, the purchase of the screw in the parasymphyseal segment will be compromised. Due to this, we advocate for a small modification of the technique. The required equipment is a 2.0-mm Kirschner wire, a long 3.5-mm drill and accompanying soft tissue guide, a long 2.5-mm calibrated drill bit, and 4.5-mm cortex screws.
For retrograde screw insertion, the C-arm is positioned ipsilateral to the side of injury and the surgeon performing the instrumentation is positioned on the contralateral side. The appropriate osseous start site for a retrograde screw is in the parasymphyseal bone medial to the pectineal tuberosity. It is ultimately determined by assessing the superior ramus OFP on the PI and COOO views (Fig. 10). As with the antegrade method, the curvature of the superior ramus OFP is assessed and a straight line is drawn within the confines of the curve. Typically, the osseous start site is on the anteromedial corner of the parasymphyseal bone. Start sites and drilling must not be lateral to the pubic tubercle as the spermatic cord and genital branch of the genitofemoral nerve are immediately lateral to the tubercle.16,17 With the same anatomical concerns, care must also be taken with the skin start site. If the wire is started too lateral on the contralateral side, injury to these structures can also occur. To minimize this, the wire is oscillated into bone 1 cm from anterior to posterior, with the skin site no further lateral than the contralateral parasymphyseal bone.17 A 1-cm skin incision is made and the 3.5-mm soft tissue guide is placed over the wire and advanced down onto the parasymphyseal bone (Fig. 11). Once the soft tissue guide is firmly in place, the wire is removed and the 3.5-mm drill is inserted. The drill is advanced in retrograde direction alternating between the PI and COOO views. Any desired vector changes are performed with the drill in a superficial position (Fig. 12). Attempting changes with the drill deeper in bone requires more force and the parasymphyseal footprint could be jeopardized. The 3.5-mm drill is advanced to the fracture or to the superomedial aspect of the acetabular dome on both the PI and the COOO views. The 3.5-mm drill is then removed and the long 2.5-mm calibrated drill is inserted into the tunnel. As noted above, the drill can be used to palpate the drill tunnel and confirm an intraosseous position in all areas of concern and the drill location is verified fluoroscopically before further advancement. The 2.5-mm calibrated drill is advanced to the cortex of the supra-acetabular lateral ilium, drilled bicortically, and left in situ with the drill tip 1–2 mm out of the cortex. Accurate depth measurement is performed with a similar 2.5-mm drill and subtraction method, with the second drill tip medial and posterior to the initial (Fig. 13). Once the appropriate screw length is determined, the 2.5-mm drill is removed and the screw is inserted. Both the PI and the COOO views are used to verify insertion vector. The PI view is used to verify if the head of the screw is appropriately down on the parasymphyseal bone (Fig. 14). The incision is irrigated and closed with either 3-0 nylon or staples.
Larger Caliber Screw Placement
If an implant larger than a 4.5-mm screw is desired and the superior ramus OFP can safely accommodate the larger implant, the techniques described above are easily modified to use a larger cannulated implant. For either an antegrade or retrograde insertion, the 2.0-mm Kirschner wire is placed onto the appropriate start site as described. The 4.5-mm cannulated drill is placed over the wire and advanced to the desired depth. The drill is then removed and the larger guidewire is then placed into the drill tunnel. We typically use 7.0-mm screws (Zimmer, Warsaw, IN) and the accompanying 3.2-mm threaded guidewire. Screws from alternative vendors and the corresponding guidewires can also be used. If the 3.5-mm drill is used for the retrograde start as described above, the 3.2-mm guidewire can still be placed. The guidewire is manually advanced through the OFP, typically using gentle mallet taps, until cortical bone is reached. The guidewire is then advanced just out of the cortex. Measurement is performed using the standard cannulated screw depth gauge or subtraction method with a similar guidewire. The screw is inserted over the guidewire and seated appropriately and is verified using both fluoroscopic views. A washer is typically not used for either screw direction due to the obliquity of the ilium and the soft tissue present on the parasymphyseal bone.
Bent Tip Guidewire Adjunct
When drilling for intramedullary ramus screw placement, close monitoring of the drill location and vector on both views is crucial to maintain intraosseous implants. If the drill is noted to be off the desired vector once it is fairly deep in to the OFP, attempts can be made to adjust the vector either by redrilling a new path or in situ vector correction as described above requiring more exaggerated hand positioning. Performing the latter should be done cautiously with retrograde screw placement in small parasymphyseal start sites to avoid removing excessive parasymphyseal bone. Alternatively, a bent tip guidewire technique has been described that can successfully correct and salvage an initially incorrect drill vector or help improve fracture alignment.18
Briefly, a 2.0-mm guidewire can be used to correct the vector. The guidewire is used as it is notably longer than a 2.0-mm Kirschner wire. On the blunt end of the guidewire, the distal 1 cm is bent 15–20 degrees similar to bending the tip of the guidewires used for intramedullary nailing of the femur and tibia. The guidewire is not bent more than this as it can prevent wire removal through the upcoming drill or screw. The bent tip guidewire is then inserted into the OFP and manipulated carefully using both the PI and the COOO views into a more appropriate position and vector. The guidewire can be further advanced until it is sufficiently into a new and more appropriate location. Once there, an appropriately sized cannulated drill is advanced over the guidewire up to the new position. If a 4.5-mm solid cortical screw is to be used, the cannulated drill is removed and the 2.5-mm calibrated drill is inserted and the standard technique continues as described above. If a cannulated 4.5-mm screw is desired (Zimmer), the 2.4-mm guidewire is placed back into the path and advanced to the appropriate depth. Accurate depth measurement is performed with the calibrated depth gauge or with subtraction technique and the appropriate screw is inserted (see Figure 1, Supplemental Digital Content 1, http://links.lww.com/JOT/A428). Care is taken to not drill completely over the initial bent tip guidewire to prevent guidewire tip amputation, binding, or advancement of the guidewire into an undesired position.
Although standard instrumentation techniques are successful for most patients requiring retrograde implant insertion, a small number of patients require augmentation with the bent tip guidewire technique as noted above. There is an even smaller number of patients where both the standard and the bent tip guidewire techniques do not allow for safe placement of an intramedullary implant. In these patients, a retrograde-antegrade-retrograde technique has been described that allows placement of a cannulated screw through the entire OFP.19
Briefly, once a retrograde intramedullary screw is determined to not be feasible and initial adjuncts were unable to successfully alter the drill path, a 2.0-mm Kirschner wire is then placed at the appropriate start site for an antegrade screw as detailed above. Once obtained, this is oscillated 1 cm into bone and a 1-cm skin incision is made. If a 4.5-mm screw is going to be placed, a 3.2-mm cannulated drill is placed over the wire and inserted into bone. If a 6.5- to 8.0-mm cannulated screw is planned, a 4.5-mm cannulated drill is used. The correct drill is advanced through the OFP in the appropriate vector using the PI and COOO views to the prior retrograde drill site. The cannulated drill is removed and an appropriately sized guidewire is placed in an antegrade direction down the antegrade drill path until reaching the retrograde start site (see Figure 2, Supplemental Digital Content 2, http://links.lww.com/JOT/A429). This can be a standard guidewire for the desired cannulated screw, or a bent tip 2.0-mm guidewire depending on the size and curvature of the OFP and the degree of manipulation needed. The wire is advanced to the desired depth in the parasymphyseal bone and screw length measurement occurs either with the corresponding cannulated screw depth gauge or with a similar length guide wire using subtraction technique. The wire is then passed out of the retrograde start site and retrieved through the previous skin incision. Depending on the surrounding soft tissues, this can be performed with a small clamp or a cannulated screw depth gauge. The cannulated screw is then inserted in retrograde fashion and seated appropriately with fluoroscopic verification (see Figure 3, Supplemental Digital Content 3, http://links.lww.com/JOT/A430). The guidewire is removed, both incisions are irrigated with saline, and closed in normal fashion.
Finally, there are patients with severe parabolic anatomy in which placement of an intramedullary implant through the entire length of the superior ramus OFP is not possible, even with the technical adjuncts described above (Fig. 15). In these patients, a shorter screw can be placed in either an antegrade or a retrograde approach with the techniques described above depending on the fracture location and surrounding soft tissues. The possible biomechanical differences of a shorter screw in comparison with a longer screw are not currently clearly defined. If further stability is required, an open approach for reduction and fixation with an intrapelvic or pelvic brim plate can be performed.
In summary, surgeons must first understand the baseline irregular osseous anatomy of the superior ramus OFP. Besides this undulating anatomy, there is a significant amount of variability to the inherent size and the curvature of the superior ramus OFP in both the AP and the coronal planes. Surgeons must grasp the osseous morphology and then obtain and correctly interpret the appropriate fluoroscopic views to demonstrate the cortical limits of the OFP. Adding this knowledge to a complete understanding of the pelvic ring injury allows the surgeon to develop an appropriate preoperative surgical plan. When intramedullary ramus screw fixation is desired, implants can be placed in either an antegrade or a retrograde direction. The size of the implants is surgeon dependent but is ultimately dictated by the size of implant the OFP can safely accommodate. Standard instrumentation techniques as described above are successful for the large majority of patients. There are technical adjuncts that can be performed if the osseous corridor or external anatomy is prohibitive of standard techniques. A thorough understanding of each patient's anatomy, injury, and precise surgical technique are required to safely place intraosseous intramedullary implants.
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