Percutaneous fixation of pelvic fractures—introduction
General principles—the role of minimally invasive osteosynthesis in pelvic fractures
Conventional techniques of internal fixation have generally required extensive surgical exposure of the deep structures of the pelvis, which can be associated with problems of wound healing, damage to major vessels or nerves, and increased incidence of infection up to 25% [ 1– 3]. Most of these complications are related to the surgical exposure itself, rather than to the initial injury. It therefore seems reasonable to consider less invasive alternatives whenever possible.
To overcome the complication of extensile surgical approaches, percutaneous fixation of the pelvis has been receiving increasing attention. Routt et al described percutaneous fixation with iliosacral screws, for sacroiliac dislocation, and sacral fractures, demonstrating it to be a safe, reproducible method which is biomechanically stable with reduced blood loss and infection [ 4– 6]. Subsequently, percutaneous fixation with iliosacral screws has become increasingly common for treating complex injuries of the pelvic ring. Apart from the percutaneous iliosacral screw, a few other types of screws have been described and eventually added to the orthopaedic armamentarium for the treatment of pelvic fractures, such as antegrade and retrograde intramedullary pubic ramus screws [ 7, 8], iliac wing, and transverse screws [ 9] ( Fig 14.1-1 ).
Rationale: indications and contraindications
Unstable pelvic ring injuries, especially in polytraumatized patients, require anatomical reconstruction and stable fixation to allow for early function. The surrounding anatomical vicinity is characterized by vital and vulnerable structures, and therefore the percutaneous surgical approach becomes an attractive option for the treatment of these injuries. Percutaneous techniques may offer a shorter surgical time, reduce exposure-related hazards and decrease soft-tissue disruption. The soft-tissue planes remain undisturbed. In patients with severe comminution and osteopenia, the percutaneous technique is useful as a means of preserving bone stock. It does not decompress the pelvic hematoma and therefore surgical stabilization is possible without the risk of additional hemorrhage.
Early and accurate closed reduction in association with stable fixation utilizing percutaneous techniques may be an ideal treatment for specific disruptions of the pelvic ring, especially in polytrauma cases. Blood loss is significantly reduced, and due to decreased tissue trauma and the lack of a large open wound, a lower risk of infection may be anticipated. Patients are allowed to start weight bearing within 2 weeks after percutaneous fixation and do not have to recover from a major operation.
Percutaneous fixation is recommended when a number of essential criteria are met and only after an accurate reduction has been achieved, avoiding residual displacement which can endanger the adjacent neural and vascular structures associated with compromised outcomes and function. The use of the technique is precluded in displaced fractures which are irreducible by closed means, sacral dysmorphism, and other unusual pelvic anatomical variations. Safe insertion of an iliosacral screw is impossible in such patients and is determined by the preoperative radiological studies. The method cannot be used if intraoperative image intensification is inadequate because of morbid obesity or intraabdominal contrast agents.
The indications for percutaneous pelvic surgery are controversial among orthopaedic trauma surgeons. Significant displacements of the fractured or dislocated pelvic fragments on x-ray images are generally associated with pelvic instability. Wide fragment displacements reflect high-energy injuries and related instability. The mechanical instability of pelvic injuries is best identified by obtaining an accurate injury history along with a compressive manual stress examination of the injured pelvic ring, either with or without anesthesia and real-time image intensification. In alert patients, pelvic ring instability is flagged by severe pain in the pelvic area with any attempted movements. Consequently, patients with unstable pelvic ring injuries will attempt to remain motionless. On physical examination, manual compression applied to each iliac crest simultaneously will cause notable displacement of the unstable segments and pain. Mechanical instability is best assessed in the anesthetized patient using compressive manual examination while observing the injured areas with real-time image intensification ( Fig 14.1-2 , Fig 14.1-3 ). This identifies the unstable regions and quantifies their displacements. Since it is a ring structure, each injured site of instability impacts the other injury sites. When using percutaneous fixation techniques especially, reduction and stable fixation of each unstable site improves the overall ring stability and allows each implant to absorb some of the effect of ring stability. The indications for percutaneous fixation are any unstable pelvic ring component injury that can be well aligned or reduced and includes an osseous fixation pathway sufficient for the selected implant(s).
Ramus instability is identified using both radiographic displacement and clinical manual examination. The radiographic appearance and actual displacement does not always correlate; minimally displaced ramus fractures can be quite unstable. Similarly the examination for pelvic instability can be hindered in alert patients due to associated pain and other factors, such as obesity. In such situations, a manual pelvic stability examination under anesthesia and real time image intensification allows the surgeon to visualize the anterior pelvic instability without causing the patient excessive pain ( Fig 14.1-2 , Fig 14.1-3 ).
Despite this debate, the percutaneous approach to pelvic fractures has gained popularity and has been adopted by many pelvic surgeons due to the following rationale:
In spite of the pelvis‘s complex structure, a pelvic ring fracture is not an intraarticular fracture in which a perfect reduction needs to be achieved by almost all means. The surgeon often gives up absolute anatomical reconstruction to avoid extensive exposure, and might accept “near anatomical” reconstruction without significantly affecting the clinical outcome.
The percutaneous approach does not entirely eliminate the need for a more “open” traditional approach but rather complements it and can be used to minimize open approaches in certain areas where it can be safely implemented.
In case of percutaneous surgery of pelvic fractures, the same rules apply as for percutaneous long bone fracture fixation; surgery should be performed according to a combination of the following three stages: understanding the different fracture components including preoperative planning, indirect reduction techniques, and percutaneous fixation.
The pelvis is a three-dimensional (3-D) complex structure and percutaneous surgery requires a profound understanding of its anatomy as well as the utilization of imaging and percutaneous reduction and fixation techniques. These are totally different and more complex than those required for long bone fixation.
The pelvis is composed of the anterior ring of the pubic and ischial rami connected with the symphysis pubis. A fibrocartilagenous disc separates the two pubic bodies. Posteriorly, the sacrum and the two innominate bones are joined at the sacroiliac joint by the interosseous sacroiliac ligaments, the anterior and posterior sacroiliac ligaments, the sacrotuberous ligaments, the sacrospinous ligaments, and the associated iliolumbar ligaments. This ligamentous complex provides stability to the posterior sacroiliac complex because the sacroiliac joint itself has no inherent bone stability. Tile has compared this relationship of the posterior pelvic ligamentous and bone structures to a suspension bridge with the sacrum suspended between the two posterior superior iliac spines .
Pelvic stability is determined by ligamentous structures in various planes. The primary restraints to external rotation of the hemipelvis are the ligaments of the symphysis, the sacrospinous ligament, and the anterior sacroiliac ligament. Rotation in the sagittal plane is resisted by the sacrotuberous ligament. Vertical displacement of the hemipelvis is controlled by all the mentioned ligamentous structures, but if other ligaments are absent, it may be controlled by intact interosseous sacroiliac and posterior sacroiliac ligaments, along with the iliolumbar ligament. Frequently, a rotationally unstable hemipelvis may remain vertically stable because of these intact ligamentous structures.
Together with understanding the 3-D structure of the pelvis, the surgeon performing minimally invasive pelvic surgery must recognize the adjacent susceptible organs found within the pelvis and around it. Percutaneous surgery demands total comprehension and recognition of the specific safe zones of each one of the screws. The concept of osseous fixation pathway (OFP) ( Fig 14.1-4 ) determines the specific safe zones of each part of the pelvic ring and helps the surgeon to recognize not only dysmorphic pathways but also to plan the direction of an implant and its possible dimensions Fig 14.1-5 .
The normal sacral ala ( Fig 14.1-5 ) has an inclined anterosuperior surface, the sacral alar slope which extends from proximal-posterior to distal-anterior. Anterior to the sacral ala in this region runs the L5 nerve root and the iliac vessels. The cortex of the alar slope forms the anterior boundary of the “safe zone” for the passage of iliosacral screws into the body of S1. The posterior boundary of the safe zone is formed by the foramen of the S1 nerve root. The inclination of the alar slope can be more acute in patients with sacral dysplasia, narrowing the safe zone for screw passage ( Fig 14.1-6 , Fig 14.1-7 ). Routt et al [ 10] detected sacral dysplasia in 28 of 80 patients with pelvic fractures evaluated by inlet/outlet and true lateral images. Preoperative CT scanning was useful to determine the dimensions of the safe zone and to identify recessed sacral alae. A recessed sacral ala in a dysmorphic S1 may cause the screw to leave the safe osseous pathway (“in-out-in” screws) that can injure the L5 nerve root.
The retrograde or antegrade pubic screw fixation is also technically demanding and risks screw misplacement even with intraoperative image intensification and should be performed with caution. When the canal diameter at the acetabulum is extremely narrow, this type of surgery should not be performed. The organs at risk include the bladder, iliac artery, and iliac vein that are close to the pubis. Placement of a urinary catheter affects the distance from the pubis to the bladder. To avoid injuring the iliac artery or vein, the screw should not protrude posteriorly in the parasymphyseal area and superiorly around the medial margin of the acetabulum.
While using image intensifier control for percutaneous pelvic fixation it is imperative that the screws are inserted with a reliable and safe technique. It is essential that image intensifier guidance is used to ensure the safe placement of these screws. To ensure that the procedure is performed safely the surgeon must meet the following criteria:
Understand the 3-D anatomy of the pelvis of the specific patient and specific fracture.
Study the x-rays and CT scan to determine the safe zones and make sure that the specific anatomy of the patient allows percutaneous fixation ( Fig 14.1-8 , Fig 14.1-9 , Fig 14.1-10 , Fig 14.1-11 , Fig 14.1-12 ).
Ensure prior to surgery via high-quality image intensification (mandatory throughout surgery) that there is no visual obstruction which might interfere with the comprehension of the bone anatomy and pathology.
Have all the required instrumentation for carrying out a percutaneous surgery of the pelvis, in particular long screws and cannulated screws with 3.5, 4.5, and 7.0 or 7.3 mm diameters and of lengths up to 190 mm.
Be able to reduce the fracture, either closed or open.
Be able to perform open surgery if necessary.
A careful analysis including medical history and physical examination is essential for obtaining the correct diagnosis of pelvic instability. The patient should be undressed and the examiner should check all of the wounds carefully to confirm the presence or absence of an open pelvic fracture. Wounds around the pelvic disruption are considered to be associated with the fracture, until proven otherwise. The physical examination should also include the genitalia since the presence of bleeding from the urethra suggests an occult open pelvic fracture. Deformation of the pelvic ring may sometimes be indefinable; therefore signs for this deformation, such as a shortened or rotated leg, should be searched for. Stability should be checked by pushing the iliac crest and searching for abnormal movement. Direct palpation reveals the presence of a large symphyseal gap or further injuries. Both rectal and vaginal examination is essential for achieving a complete patient assessment.
Type of x-ray and CT scans
A single AP x-ray, commonly used in most trauma centers, is often sufficient to determine the presence or absence of pelvic ring instability. This x-ray is sufficient to initiate resuscitation in an unstable patient. However, such x-rays may be misleading. The best way to ensure the existence of a posterior displacement is the inlet view, and the best way to ensure superior displacement is the outlet view. Therefore these three projections: AP, inlet, and outlet are considered standard to plan a definitive treatment of pelvic fractures.
CT scan provides an accurate 3-D picture which provides further information about the bone as well as the soft tissue. The CT scan will show the direction of the displacement, the posterior elements’ morphology, the safe zones, and the extent of the hematoma and soft-tissue damage. Three-dimensional reconstruction images contribute another layer to the understanding of the fracture pattern and to the planning of the treatment. The usage of CT angiography, an innovative technique, provides information about arterial bleeding which is one of the causes for hemodynamic instability that is difficult to handle. Needless to say, percutaneous definitive treatment demands the acquisition of all the information mentioned above to achieve satisfying reduction and fixation.
Choice of implants
A prerequisite for the performance of pelvic surgery is the availability of a complete armamentarium (a complete pelvic set with reduction instruments and implants). Especially in percutaneous surgery of pelvic ring disruptions, 3.5 mm cortex screws and up to 130 mm long are the most commonly used screws for the treatment of anterior lesions of the pelvic ring. Alternative techniques are based on 7.3 mm cannulated screws for the posterior ring or sometimes 4.5 mm cortex screws for the anterior and posterior ring.
Timing of surgery
The percutaneous treatment of displaced pelvic ring injuries is based primarily on the ability to reduce the fracture. Only after establishing a satisfactory reduction, can the surgeon go on to perform fixation. Usually, closed reduction (explained in detail in 5.2.2 Reduction technique), is possible only within the first few days following the injury.
Preoperative planning is mandatory in pelvic surgery and is a critical step while using a percutaneous approach. A major problem in such surgeries is the difficulty in understanding the 3-D construction of the pelvic pathology. Recently, specific software has been developed allowing segmentation of the various fracture components, virtual reduction, and preoperative planning of fracture fixation. This software is based on the preoperative CT scan. Section 4.3 The role of navigation is dedicated to this issue as a basis for computerized navigated percutaneous pelvic surgery.
Operating room setup
Minimally invasive percutaneous surgery of the pelvis can be integrated into the acute trauma management phase or as a definitive treatment after the patient is hemodynamically stable. The pelvic fracture can be characterized by the patient‘s hemodynamic stability and by the mechanical stability of the injury. There can be different variations of these factors that would determine the scenario of treatment in general and the type of anesthesia in particular. It should be emphasized that from the surgeon‘s point of view the percutaneous surgery depends on the ability to achieve reduction of the fracture, whereas the reduction depends on the patient‘s full relaxation.
In percutaneous pelvic surgery the setup of the operating room is an integral part of the preoperative planning ( Fig 14.1-13 ). The use of a radiolucent table is mandatory and although there is a weight limit in using such a table, solutions must be found to accommodate obese patients. The patient‘s position on the table is also preplanned, according to the procedure to be performed.
The role of navigation
In cases where the surgeon uses computerized navigation systems, the operating room setup is even more meticulously planned since there is a need to take into account an unobstructed line of vision for the infrared camera in addition to the surgeon observing the image intensifier and the monitor ( Fig 14.1-14 , Fig 14.1-15 , Fig 14.1-16 ).
Injuries of the anterior pelvic ring
Anterior pelvic injuries that allow percutaneous reduction and fixation techniques include parasymphyseal fractures, midpubic superior ramus fractures, and lateral superior ramus fractures. Inferior ramus injuries are difficult to stabilize because of fracture comminution and displacement patterns, and their normal medullary osteology is often quite narrow and curved. Pubic symphyseal disruptions can be treated using percutaneous reduction and external fixation techniques, but open reduction and plate fixation remain the standard. Some parasymphyseal fractures require transymphyseal fixation to attain sufficient stability. Some symptomatic hypertrophic superior and inferior pubic ramus nonunions are amenable to percutaneous stabilization as long as the bone fragments are well aligned ( Fig 14.1-17 ).
Optimal anterior pelvic manipulation and percutaneous fixation is achieved with the patient positioned supine. Anterior pelvic external fixation and either retrograde or antegrade medullary superior ramus screws can be inserted when the patient is supine. Prone patient positioning does not allow direct access to the anterior pelvis, but antegrade superior pubic ramus medullary screws can still be inserted if the reduction is satisfactory.
The incisions for reduction and fixation are dependent on the planned reduction maneuver(s) and the implants necessary to stabilize the injury.
For anterior pelvic external fixation, the incisions are applied either over the iliac crest or anterior inferior iliac spine (AIIS) ( Fig 14.1-18 , Fig 14.1-19 ).
Medullary screw fixation of the superior pubic ramus is inserted either “retrograde” from the pubic tubercle directed posterior-cranial-lateral, or “antegrade” beginning in the superior-posterior acetabular area and directed anterior-caudal-medial. The incision is made only after the perfect starting point and aim are established, using a small-diameter wire (1.6 mm) and image intensifier guidance. The skin incision for a retrograde screw is located on the contralateral side, lateral to the midline and caudal to the pubic tubercle ( Fig 14.1-20 , Fig 14.1-21 ).
Antegrade screw incisions are located on the posterolateral flank between the ASIS, greater trochanter, and posterior-superior iliac spine. The incision locations are affected by obesity. These incisions should be several millimeters longer than the planned screw diameter. The retrograde incisions are oriented superior-inferior. The skin is incised and then blunt dissection to the injured pubic tubercle is performed using a hemostat. A protective soft-tissue sleeve and oscillating drill technique are used to avoid deep-tissue injuries ( Fig 14.1-22 ).