Henry Claude Sagi
DEFINITION
Pelvic fractures are serious injuries associated with a diverse assortment of morbidities and mortality rates ranging from 0% to 50%.
Fractures and dislocations of the pelvis involve, in broad terms, injuries to the anterior and posterior structures of the pelvic ring.
Injuries to the anterior pelvic ring include symphyseal disruption and pubic body or rami fractures.
Injuries to the posterior pelvic ring involve iliac wing fractures, sacroiliac (SI) joint dislocations and fracturedislocations, and sacral fractures.
The implications and treatment of damage to these structures vary widely with the broad spectrum of injury patterns, combinations of injuries, and degree of displacement.
This chapter will focus on treatment of displaced sacral fractures and type 3 SI joint dislocations.
ANATOMY
The pelvis is a ring structure composed of the two hemipelves, or innominate bones, and the sacrum. Each innominate bone is formed as the result of fusion of the three embryonic bony elements: the ilium, the pubis, and the ischium (FIG 1A).
The two innominate bones are joined anteriorly at the pubic symphysis, a symphyseal joint. Posteriorly, the two innominate bones articulate with the wings, or alae, of the sacrum via the strong SI joints to complete the ring (FIG 1B).
The sacrum represents the terminal structural segment of the spinal column that connects the pelvis and extremities to the trunk and spine.
As the sacrum is essentially a spinal element, it is subject to segmentation abnormalities and dysmorphisms.
Most commonly, segmentation anomalies such as a lumbarized S1 and a sacralized L5 will be present (FIG 2).
The only true way to be sure which defect, if any, is present, is to count down from the first thoracic vertebrae, which is the first vertebra to have transverse processes that are inclined cephalad.
As a general rule of thumb, however, the top of the iliac crest is usually at the same level as the L4/5 disc space. This rule can be used to judge the presence of dysmorphism (see Fig 2A).
These issues are pertinent to interpretation of the radiographic landmarks required to safely place iliosacral screws (see later).
Being wedge-shaped, the sacrum forms a keystone articulation with the innominate bones.
By virtue of this shape and their orientation, the SI joints are inherently unstable and the maintenance of posterior pelvic ring integrity is wholly dependent on the support provided by the ligamentous structures for stability (see Fig 1B and FIG 3).
With axial loading, the natural tendency is for each hemipelvis to externally rotate and translate in a cephalad and posterior direction. The pelvic ligaments are structured and positioned to resist these deformations as static stabilizers of the pelvis. There are no specific dynamic stabilizers of the pelvic ring.
FIG 1 • A. The three embryonic bones (pubis, ischium, ilium) fusing to form the innominate bone or hemipelvis. B. The two innominate bones and sacrum forming the pelvic ring with supporting ligaments.
FIG 2 • A. Outlet radiograph of the pelvis demonstrating failure of segmentation of the right side, giving a sacralized L5. The left side is normally segmented. The crest, despite the segmentation anomaly, remains at the L4–5 disc level. B. Threedimensional CT reconstruction of the same pelvis.
The SI ligaments (anterior, posterior and intra-articular ligaments) are the strongest ligaments in the body, with the posterior SI ligaments being the most important in resisting posterior and cephalad displacement (see Fig 3).
FIG 3 • Sacroiliac joint ligaments.
The symphyseal ligaments (themselves contributing no more than 15% to pelvic ring stability), the sacrotuberous ligaments, and the sacrospinous ligaments resist external rotation.13,32
The bladder is immediately posterior to the pubic bodies and symphysis, separated only by a thin layer of fat and the potential space of Retzius.
The intimate relationship of the L5 nerve root to the superior aspect of the sacral ala as it courses to join the lumbosacral plexus is a key anatomic feature that must be kept in mind during reduction and stabilization of posterior pelvic ring injuries (FIG 4).
The superior gluteal artery is immediately lateral to the inferior aspect of the SI joint as it arises from the internal iliac artery to exit the greater sciatic notch with the superior gluteal nerve. The obturator nerve and artery course along the quadrilateral plate (medial wall) of the acetabulum as they exit the superior and lateral quadrant of the obturator foramen (see Fig 4).
FIG 4 • A. Neurovascular structures around the posterior pelvic ring. B. Note intimate relationship of L5 nerve root to sacral ala.
PATHOGENESIS
Because the SI ligaments are the most resilient in the human body, SI dislocations occur purely as a result of high-energy traumatic injuries.
Anteroposterior compression of the pelvic ring causing external rotation of the innominate (which may or may not be coupled with a vertical shearing force) is the most common cause of SI joint dislocation.
Sacral fractures, however, can occur in three distinctly different situations.
Insufficiency fractures of the sacrum arise secondary to failure through excessively osteoporotic or ostepenic bone.
Stress fractures of the sacrum result from fatigue and cyclic failure of normal bone in high-level athletes or military recruits.
Traumatic disruptions result from high-energy lateral or anteroposterior compression or vertical shear injuries such as (in order of decreasing frequency) motorcycle crashes, auto–pedestrian collisions, falls from height, motor vehicle accidents, or crush injuries.13,32
NATURAL HISTORY
Pelvic fractures occur in at least 20% of blunt trauma admissions, most frequently in young males.
They can result in small insignificant fractures of the pubic rami with no compromise of pelvic ring stability, or major injuries and disruptions that can be associated with life-threatening bleeding or visceral injury.
The pelvic ring encloses the true pelvis (organs contained below the pelvic brim, extraperitoneal) and the false pelvis (organs contained above the pelvic brim, both peritoneal and retroperitoneal).
The most commonly associated injuries to structures contained within the true pelvis are the internal iliac arterial and venous systems and branches, the bladder (20%) and urethra (14%), the lumbosacral plexus, and the rectum and vaginal vault (open pelvic fractures).
Injuries to structures within the false pelvis as a direct result of the pelvic fracture are uncommon, but severe iliac wing fractures with abdominal wall disruption can result in intestinal injury and even entrapment.
Morbidity and mortality from pelvic fractures can be high and are most commonly secondary to pelvic hemorrhage.
The mortality rate associated with pelvic fracture with an associated bladder rupture approaches 35% in some series, and the mortality rate of open pelvic fractures involving the perineum used to be as high as 50%.
Fortunately, this has decreased to about 2% to 10% with the liberal use of diverting colostomies and more advanced stabilization techniques.
Neurologic injury to the lumbosacral plexus can lead to significant sensorimotor dysfunction involving the extremities, bowel, bladder, and sexual functions.
Because of these associated neurovascular and visceral injuries, pelvic fractures often result in prolonged recovery periods, significant chronic pain, permanent disability, and loss of psychological and socioeconomic structure.5,7,9,21–29
PATIENT HISTORY AND PHYSICAL FINDINGS
Any patient presenting with a history of trauma or satisfying criteria for a Trauma Alert in the emergency department should be suspected of having a pelvic fracture until otherwise ruled out by radiologic and physical examination.
The physical examination should follow the primary and secondary survey of the Advanced Trauma Life Support protocol.1
Examination of a patient suspected of having a pelvic fracture should be divided into the examination of the abdomen, pelvic ring, perineum, rectum, vagina, and lower extremities.
The abdominal examination should elucidate:
Tenderness, fullness, or rigidity
Abdominal wall disruptions, defects, or open wounds
Flank ecchymosis
Presence of internal degloving or a Morel-Lavalle lesion (separation of the subcutaneous tissues from the underlying fascia). This can be recognized by subcutaneous fluctuance or a fluid wave and, later, extensive ecchymosis.
The rectal and vaginal examination should consider:
The position of the prostate (a high-riding prostate may be a sign of urethral injury)
Palpable bony fragments perforating the rectal or vaginal mucosa
Defects or tears in the wall of the rectum or vagina indicating possible bony penetration
Rectal or vaginal bleeding indicating possible tears or bony penetration
Urethral bleeding at the meatus indicating possible urethral or bladder disruption
Scrotal or labial swelling and ecchymosis indicating pelvic hemorrhage (FIG 5)
Rectal tone, perianal sensation, voluntary sphincter control, and bulbocavernosus reflex to assess for the presence of cauda equina syndrome or lower sacral nerve root injury
Examination of the pelvic ring and extremities should focus on the following key factors:
Palpable internal or external rotation instability of the pelvic ring with manually applied anteroposterior and lateral compressive forces on the iliac wings and crests
Leg-length discrepancy with asymmetrical internal or external rotation
Neurologic status in patients able to comply can be assessed as follows:
L1/2: iliopsoas (hip flexors) and upper anterior thigh sensation
L3/4: quadriceps (knee extensors) and lower anterior thigh and medial calf sensation
L5: extensor hallucis longus, digitorum longus (toe dorsiflexion), peroneal eversion (although this can have a strong L4 component) and lateral calf and dorsum of foot sensation
FIG 5 • Scrotal ecchymosis from internal pelvic hemorrhage.
S1: gastrocsoleus complex (ankle plantarflexion) and posterior calf sensation
S2/3: flexor hallucis and digitorum longus (toe plantar flexion) and sole of foot sensation
IMAGING AND OTHER DIAGNOSTIC STUDIES
Plain Radiographs
The standard anteroposterior (AP pelvis) view should be part of the initial trauma series screening. With enough experience, many of the injuries to the posterior pelvic ring can be diagnosed with this single projection (FIG 6A,B).
A good AP radiograph should have the pubic symphysis co-linear with the sacral spinous processes.
This allows side-to-side comparison of bony landmarks to aid in diagnosis of subtle displacements of the sacrum or SI joint.
The cortical density of the pelvic brim and iliopectineal line should be traced back to its intersection with the lateral margin of the sacral ala.
This intersection should be at the same level (usually the inferior margin of the S2 foramen) bilaterally.
Asymmetry in the SI joint space and the appearance of the sacral foramina should alert the surgeon to the presence of an SI joint dislocation or sacral fracture.
Fractures of the L5 transverse process may be a clue to a vertical shear injury that has avulsed the transverse process via the iliolumbar ligament.
Symphyseal diastasis or displaced rami fractures should alert the examiner to additional injuries in the posterior ring, even though they may not be readily apparent on first glance.
The inlet projection is taken with the x-ray beam directed caudally about 45 degrees to the radiographic film.
A true inlet view of the pelvis, however, may require variations on this degree of angulation because of the normal variations in sagittal plane pelvic obliquity.
This view simulates a direct view into the pelvis from above along its longitudinal axis (FIG 6C,D).
The inlet view is helpful in imaging:
External or internal rotation of the hemipelvis
Opening of the SI joint or an impaction fracture of the sacrum
“AP” displacement or translation of the hemipelvis (see below)
The outlet projection of the pelvis is obtained by directing the x-ray beam about 45 degrees cephalad to the radiographic film.
This view simulates looking at the sacrum and SI joints directly en face (FIG 6E,F).
The outlet view is helpful in imaging:
Cephalad or “vertical” shift of the hemipelvis
Sacral fractures relative to the foramina
Flexion–extension deformity of the hemipelvis
These radiographs are taken at about 45 degrees to the long axis of the patient's body.
Therefore, a given amount of translation or displacement seen on the inlet or outlet view is in fact the sum of displacement vectors in both the coronal and axial planes. For example, “posterior” shift seen on the inlet projection is in fact a combination of both posterior and cephalad translation.
Another important point to bear in mind is the appearance of the sacrum on the AP projection.
If one sees a paradoxical inlet view of the upper sacrum and outlet view of the distal sacrum, a lateral radiograph and CT scan with sagittal reconstruction must be performed to rule out an occult sacral fracture-dislocation (a U-shaped sacral fracture otherwise known as spinal-pelvic dissociation; FIG 7).
FIG 6 • A,B. AP pelvis radiographs. Ideal film should have symphysis aligned with sacral spinous processes. C,D. Inlet pelvic radiographs. Note sacral promontory and alar regions. E,F. Outlet pelvic radiographs. Note sacral foramina and sacroiliac joints. Ideal image should have top of symphysis–rami at the S2–3 level.
FIG 7 • A. AP radiograph of patient with a U-shaped sacral fracture. Note inlet view of proximal sacrum but outlet appearance of caudal sacrum. Axial (B) and sagittal (C) CT scan reconstructions of the same patient with a U-shaped sacral fracture. The fracture almost always occurs at the level of the vestigial disc space at S1–2.
Computed Tomography
CT is imperative in any suspected pelvic ring injury.
As the pelvis is a ring structure, any disruption in one location (no matter how seemingly insignificant) must (by virtue of ring structure mechanics) be accompanied by disruption in another location.
Three-millimeter axial sections (or 3 mm of vertical travel per 360-degree rotation of the gantry in a spiral CT) are recommended to disclose the majority of significant injuries and to allow for good-quality three-dimensional reconstructions (FIG 8).
FIG 8 • A. Axial CT scan of transforaminal (Denis zone 2) sacral fracture. B. Axial CT scan of sacroiliac joint dislocation. Note diastasis of anterior and posterior joint.
Retrograde Urethrography and Cystography
Retrograde urethrography and cystography are mandatory in pelvic fractures with ring disruption to rule out urethral and bladder injury.
The Foley catheter is partially inserted into the urethra, and the balloon is inflated with 2 to 3 mL of sterile saline to occlude the urethra. Ten to 15 mL of water-soluble contrast is then injected into the urethra and the outlet view of the pelvis is repeated.
If no extravasation is seen, the catheter is advanced into the bladder with injection of a further 300 mL of water-soluble contrast to rule out a bladder rupture. If no contrast extravasation is noted, the bladder is drained with the Foley, and any residual dye is noted.
If passage of the catheter is not possible or there is a tear of the urethra or bladder neck, suprapubic catheterization should be performed well above the umbilicus if possible (to avoid contamination of potential future anterior pelvic operations).
Pelvic Angiography
Angiography is indicated in patients with persistent hemodynamic instability despite10:
Adequate volume resuscitation
Other sources of hemorrhage being ruled out (abdomen, thorax, and long bone fractures)
Attempts to “close” the pelvic ring (see below) have failed to stop pelvic hemorrhage
Most cases of pelvic hemorrhage (85%) arise from venous bleeding, which is not amenable to angiographic embolization.
Arterial bleeding is usually from branches of the internal iliac system (median sacral, superior gluteal, pudendal, or obturator arteries; FIG 9).
FIG 9 • Angiograms showing extravasation and embolization of superior gluteal artery. (Courtesy of Prof. Johannes Reuger.)
If diagnostic peritoneal lavage is being performed to rule out abdominal hemorrhage, then it must be performed above the umbilicus and arcuate line to avoid false-positive results from pelvic hemorrhage.
NONOPERATIVE MANAGEMENT
As a general rule, traumatic type 3 SI dislocations should not be managed nonoperatively.
Progressive cephalad displacement of the hemipelvis will result in pelvic malunion. Leg-length inequality, chronic mechanical low back and buttock pain, pelvic obliquity with sitting imbalance, and dyspareunia are common complaints when the hemipelvis and ischial tuberosities are positioned medially or cephalad.
For patients in extremis or those with sepsis or critical medical comorbidity, nonoperative therapy may be the only option.
In these cases, the pattern of deformity dictates the maneuvers to be used to minimize the malunion.
Patients with any evidence of vertical instability should be placed into balanced longitudinal skeletal traction in an attempt to reduce or prevent further cephalad displacement.
Distal femoral traction is preferable.
Patients with external rotation deformity of the pelvic ring (ie, “open book” pelvis) should be initially treated with some form of temporizing pelvic binder (ie, the T-POD pelvic binder, Bio-Cybernetics, LaVerne, CA) or an external fixation clamp.
This helps to reduce the external rotation deformity, stabilize the pelvic hemorrhage and clot, and improve patient comfort in the acute resuscitative period.2
Ideally, circumferential devices such as pelvic binders (FIG 10) should be applied over the greater trochanters, and frequent skin checks are mandatory to prevent full-thickness pressure ulceration. As such, they are rarely if ever indicated for definitive treatment. Anterior pelvic external fixators can be applied either in the iliac crest or the anterior inferior iliac spine and supra-acetabular bone.
FIG 10 • TPOD pelvic binder. (Courtesy of MidMed, Queensland, Australia.)
Anterior external fixators are good for controlling external and internal rotation of the anterior pelvic ring. Thus, the surgeon may elect to use them definitively if the SI joint is disrupted only through the anterior SI ligaments (a type 2 injury with no vertical or sagittal plane instability) or with certain lateral compression injuries where the sacral fracture is stable by virtue of its impaction.
By themselves, however, anterior external fixators are not effective in controlling the posterior pelvic ring, and if applied incorrectly they can make some pelvic deformities worse.16,30
For external fixation control of the posterior ring, external C-clamps and pelvic clamps are used on occasion, but expertise is required in their use to prevent serious complications from misplacement.8,18
In contrast to SI joint dislocations, most traumatic sacral fractures can be treated successfully with nonoperative care.
Although vertical shear sacral fractures represent the far end of the spectrum of unstable sacral fractures needing operative stabilization, impacted sacral fractures resulting from lateral compression mechanisms can be relatively stable injuries (FIG 11A,B).
If the radiographic and CT scanning evaluation reveals an impacted sacral alar fracture without significant displacement in other planes, a trial of nonoperative therapy is warranted. The patient must comply with the weight-bearing restrictions and close radiographic follow-up to prevent gradual shift that will result in a pelvic malunion and leg-length inequality with sitting imbalance (FIG 11C).
Often, the presentation of the patient in bed can help to predict success with nonoperative treatment of impacted sacral fractures.
Patients able to roll in bed on their own and help with hygienic care with only minimal or moderate discomfort often have a relatively stable pelvis and will be able to mobilize with physical therapy.
Some patients, however, will not be able to tolerate even log-rolling in the bed with nursing care.
They may be found on examination under anesthesia to have an unstable pelvis despite innocuous-appearing imaging studies.
FIG 11 • A,B. Impacted sacral fracture from lateral compression mechanism with internal rotation. C. Nonoperative treatment of vertical shear sacral fracture with resultant malunion and leg-length inequality.
If a patient with an impacted sacral fracture is deemed to be a candidate for nonoperative treatment, he or she is mobilized with physical therapy in 3 to 5 days so long as all other injuries permit.
The patient is instructed in touch-down weight bearing on the affected extremity.
If the patient can successfully mobilize, then AP, inlet, and outlet radiographs are repeated within a week to assess for any further displacement and increasing leg-length inequality.
If no further displacement occurs, the patient is instructed to continue touch-down weight bearing for another 8 to 10 weeks, with repeat radiographs every 4 weeks.
SURGICAL MANAGEMENT
Treatment Options
Iliosacral Screws
In general, all complete SI joint dislocations and unstable displaced nonimpacted sacral fractures should be treated with operative stabilization.
The choice of fixation in most instances for both SI joint dislocations and sacral fractures will be with iliosacral screws (SI screws).
Biomechanical studies have validated the strength of this technique in comparison to more traditional anterior SI plating and transsacral bars and plates.11,26
Also, SI screws can be applied with the patient in either the prone or supine position, and in either an open or closed percutaneous fashion.
SI screw placement, however, does require an exacting knowledge of the radiographic correlates of anatomic landmarks to prevent neurologic and vascular injury.3,6,15,22,31,33
Transforaminal sacral fractures with comminution and vertical instability treated with standard SI screw fixation alone may be suboptimal and have a high reported failure rate.
In these instances, the surgeon may elect to place alternate forms of fixation to augment the SI screw (such as with transsacral screws or with some form of spinal pelvic construct to better resist the tendency for vertical displacement).12,24,27
Spinal Pelvic Fixation
Also known as lumbopelvic fixation and triangular osteosynthesis, spinal pelvic fixation is done to augment an SI screw for a very unstable posterior ring injury that has been reduced and temporarily stabilized but remains at risk for failure of fixation and subsequent redisplacement.
This usually arises in the case of extensively comminuted transforaminal sacral fractures.
Sacral Nerve Decompression
Sacral nerve decompression is indicated in either of two situations:
The patient has a neurologic deficit attributable to sacral radiculopathy and preoperative imaging shows fracture fragments within the sacral foramen.
The patient is neurologically intact, but preoperative imaging studies disclose a large bone fragment within the foramen that during reduction will further compress the nerve root and stenose the foramen, resulting in iatrogenic nerve root injury (FIG 12).
Zone 3 Sacral Fractures
Vertically oriented zone 3 sacral fractures are usually the result of wide anteroposterior compression forces and are associated with anterior ring disruption.
Generally, they can be treated with internal rotation and anterior ring fixation alone.
If residual sacral gapping persists, however, an SI screw with short threads can be placed into the contralateral S1 body to close the residual gap.
U-Shaped Sacral Fractures
Otherwise known as spinal-pelvic dissociation, this fracture is essentially a sacral fracture-dislocation.
It tends to occur through the vestigial disc space and result in kyphosis.
FIG 12 • Axial CT scan of a sacral fracture showing large intraforaminal bony fragment.
FIG 13 • U-shaped sacral fractures can be difficult to detect on standard AP pelvis views (A) but are more evident on sagittal CT reconstruction (B).
These fractures can be easily missed on the standard AP pelvis view (FIG 13A) and even axial CT scans, but they are quite evident on the sagittal CT reconstruction (FIG 13B).
These injuries generally do not result in pelvic ring instability, as the SI joints and distal surrounding sacrum are intact; they are more commonly associated with spinal instability.
They can be associated with cauda equina syndrome and significant spinal instability and should be treated by an experienced spinal surgeon.
Although some trauma surgeons have advocated bilateral SI screw fixation alone for these injuries, they more commonly require reduction, decompression, and some form of posterior lumbopelvic fixation to control kyphotic deformity.
Preoperative Planning
Proper preparation and preoperative planning for any major pelvic surgery are mandatory.
These operations can be associated with prolonged anesthetics, lengthy prone positioning, extensive blood loss, and complex reduction maneuvers that can pose serious risk to the patient with other medical or traumatic comorbidities.
Having a detailed understanding of the deformity and the reduction and fixation strategy can help to significantly decrease operative time and blood loss.
All patients should have had anticoagulation started within 24 hours of admission.
If there are contraindications to anticoagulation, inferior vena caval filter placement should be requested.29
If an open reduction is predicted to be necessary, waiting for 3 to 5 days is prudent to allow the pelvic clot to stabilize and diminish intraoperative bleeding.
Patients should have at least three units of typed and cross-matched blood on hold.
The surgery should be booked semielectively if possible, with a surgical team that is familiar with complex pelvic surgery.
Positioning
Patients should be positioned on a radiolucent table that allows traction to be applied in some fashion.
Regarding the standard OSI (Orthopaedic Systems Inc., Union City, CA) fracture table with the perineal post, adequate caudal translation cannot be obtained as long as the perineal post is in place because the ischial tuberosity and pubis tend to abut the post, preventing further caudal translation of the hemipelvis.
This problem can be overcome by stabilizing the contralateral extremity in a traction boot without applying traction to provide some vertical support for the contralateral side while traction is applied to the affected extremity.
Another alternative in cases with severe vertical displacement is to rigidly fix the contralateral pelvis to the OR table with Schanz pins and an external fixator with a frame supplied by OSI.
Patient positioning will be in either the prone or supine position, depending on the surgeon's assessment of the ability to achieve reduction using closed (supine) or open (prone) means.
In some cases, initial reduction of the anterior pelvic ring will facilitate reduction of the posterior ring, allowing the entire procedure to be performed in the supine position.
However, an imperfect reduction of the anterior pelvic ring and subsequent rigid stabilization may actually impair reduction of the more important posterior ring. In this case, anterior fixation would have to be removed to allow for an exact reduction of the posterior ring.
For the patient positioned in the prone position (FIG 14), the surgeon must ensure proper padding and support for the chest to allow adequate ventilation.
FIG 14 • Positioning and setup of patient for posterior approach and reduction of sacral fracture or sacroiliac joint dislocation. Note the pelvis hanging freely, traction setup, and rigid stabilization frame on contralateral stable hemipelvis.
It is preferable to use longitudinal chest rolls that come short of the pelvis, allowing the lower trunk to hang freely and not rest on the anterior superior iliac spine.
If the pelvis is permitted to rest on the anterior superior iliac spine, posterior translation of the unstable hemipelvis may result or reduction may be impaired.
The extremity ipsilateral to the unstable hemipelvis should be draped free to allow longitudinal traction and internal–external rotation.
It should be placed in either boot or skeletal (distal femoral or proximal tibial) traction that allows for rotation and abduction–adduction.
Extension of the hip and extremity will help to indirectly reduce the hemipelvis as well, since some degree of flexion deformity exists in vertically displaced pelvic fractures.
Draping of the operative field should include the entire flank on the affected side.
The field should continue to include the buttock and upper thigh, with free draping of the affected extremity.
The natal cleft and contralateral buttock are excluded from the field.
For the patient positioned in the supine position, a small folded sheet or pad should be placed under the sacrum or buttock on the affected side to lift the pelvis away from the table. Again, the affected extremity should be placed into traction to aid in reduction, as detailed above.
If there is posterior displacement of the hemipelvis, placing the bump under the buttock will help to anteriorly translate the pelvis when traction is applied.
If there is anterior translation of the hemipelvis, placing the bump directly midline will help to lift the pelvis away from the table and also let the affected hemipelvis hang freely to allow posterior translation during reduction maneuvers.
Approach
Approach to the SI joint can be either anterior or posterior.
If significant displacement exists and a difficult open reduction is predicted, the posterior approach should be chosen.17
The anterior approach does not afford good visualization of the entire SI joint, only the superior aspect at the top of the ala.
Also, placement of reduction clamps anteriorly across the SI joint, while possible, is cumbersome and places the L5 nerve root at risk.28
The anterior approach to the SI joint is advocated only in situations in which:
The soft tissues do not permit the posterior approach.
The patient will not tolerate prone positioning because of poor pulmonary status.
A close-to-anatomic closed reduction of the SI joint can be obtained with traction and manipulation and only minor adjustments need to be made.
TECHNIQUES
POSTERIOR APPROACH
For the posterior approach to the SI joint dislocation and sacral fracture, the incision is vertical and paramedian, centered directly over the involved SI joint. The incision is not carried directly over the bony prominence of the posterior superior iliac spine; rather, it is placed just medial to the posterior superior iliac spine (TECH FIG 1A).
The tissues that bridge the SI joint posteriorly in the intact state include the lumbodorsal fascia, the transverse fibers of the gluteus maximus (TGM), the paraspinal erector spinae muscles, the iliolumbar ligament, and the posterior SI ligaments (TECH FIG 1B).
TECH FIG 1 • A. Skin incision for posterior approach to sacrum and sacroiliac joint. B. Diagram of fascial fibers and muscular layers for posterior approach to sacrum and sacroiliac joint. C. Posterior exposure for sacral fracture reduction.
With SI joint dislocations, some or all of these fascial, muscular, and ligamentous layers may be completely disrupted, and no further dissection is needed.
Often, however, to visualize the inferior aspect of the SI joint posteriorly, the TGM needs to be mobilized. The TGM attachment to the sacral spinous processes and thoracolumbar fascia is released and the TGM is reflected laterally and inferiorly to expose the inferior aspect of the SI joint. To prevent wound complications, the attachment and origin of the gluteus maximus must be preserved.
Occasionally some of the lumbodorsal fascia will need to be released from the posterior iliac crest.
This allows dissection up over the superior aspect of the SI joint and sacral ala to permit digital palpation to assess reduction of the anterior SI joint.
Once exposure is complete, it is usually necessary to evacuate a significant amount of blood clot and hematoma from the joint.
On occasion, loose fragments of denuded articular cartilage will require removal.
Routine removal of articular surfaces for a primary SI joint fusion is not performed, however, unless there is significant cartilaginous destruction to begin with.
During removal of blood clot and debris, specific attention must be paid to the superior gluteal vessels and the internal iliac vascular system.
Removal of clot may restart arterial bleeding that was initially controlled by tamponade and spasm, or direct iatrogenic injury may occur with dissection through the fracture hematoma and clot.
All sacral fractures that necessitate an open reduction require a posterior approach.
Anterior approaches are not recommended as it is not possible to dissect onto the anterior aspect of the sacrum without posing excessive risk to the lumbosacral nerve roots and iliac vessels.
The posterior approach for sacral fracture reduction varies depending on the fracture location and the need for sacral nerve root decompression.
In general, however, most sacral fractures and foraminal decompressions can be performed through the same paramedian approach as described above for SI joint dislocations. The only alterations in technique would be as follows:
Subperiosteal elevation of the paraspinal muscles from the dorsal aspect of the sacrum to the spinous processes is required to expose the whole posterior surface of the sacrum (TECH FIG 1C).
Proximal extension in the intermuscular plane of the paraspinal muscles exposes the L4–L5 facet joint in the manner described by Wiltse, if a spinal pelvic construct is to be applied.
Open Reduction of the SI Joint and Sacrum via the Posterior Approach
Reduction of the dislocated SI joint is complex and requires a good knowledge of the three-dimensional anatomy of the sacrum, ilium, and SI joint.
Although some anteroposterior translation and lateral–medial translation may be necessary to reduce the SI joint, longitudinal traction is the single most important indirect maneuver to perform.
Adequate longitudinal traction can be assessed intraoperatively with direct visualization, digital palpation, and the image intensifier.
Reduction of the superior aspect of the SI joint can be assessed with digital palpation, ensuring that the superior–anterior aspect of the SI joint is flush.
Final confirmation with inlet, outlet, and AP radiographs will help disclose subtle rotational deformities not appreciated by direct visualization or palpation.
Only once adequate length has been restored can the need for additional anteroposterior or medial-to-lateral translation be assessed.
Fine-tuning of the SI joint reduction will require the placement of one or two reduction clamps to medially translate and internally rotate the hemipelvis. Large pointed reduction clamps (eg, Weber clamp or offset Matta clamps) are used.
Posteriorly, a clamp can be placed over the sacral spinous process or into the posterior cortex of the sacrum inferiorly and into the cortical bone of the medial aspect of the greater sciatic notch. This can help close the inferior aspect of the SI joint (TECH FIG 2A).
TECH FIG 2 • A. Weber reduction clamp positioned to reduce inferior aspect of sacroiliac joint, from posterior approach. B,C. Matta offset clamp reducing superior and anterior aspect of sacroiliac. The clamp is positioned from over the top between iliac crest and L5 transverse process. D,E. Matta offset clamp reducing anterior aspect of sacroiliac. The clamp is positioned through the greater notch onto the lateral aspect of the ala, lateral to the L5 nerve root.
A second clamp can be used superiorly, with one tine placed carefully over the top of the joint onto the sacral ala anteriorly and the second tine placed just lateral to the posterior superior iliac spine (TECH FIG 2B,C).
Alternatively, this second clamp can be placed through the greater notch, with one tine on the sacral ala and the other on the posterior cortex of the ilium (TECH FIG 2D,E).
While these clamps are being closed to reduce the superior SI joint, internal rotation of the extremity or pushing on the anterior iliac wing with a ball-spike pusher (picador) can help to close down the anterior aspect of the SI joint.
ANTERIOR APPROACH
The anterior approach to the SI joint uses the upper limb of the Smith-Peterson approach, taking the external oblique fibers off the iliac crest and elevating the iliacus muscle subperiosteally from the inner table of the ilium.
When the SI joint is encountered, careful mobilization of the tissue on the sacral ala using a blunt periosteal elevator and finger dissection helps to move the L5 nerve root medially out of harm's way.
Once this tissue is mobilized and the sacral ala is seen under direct vision, a sharp Hohmann retractor is driven into the alar cortex and used to protect the L5 nerve root, which lies medial (TECH FIG 3).
Open Reduction of the SI Joint via the Anterior Approach
Once the SI joint and sacral alae have been exposed, reduction can be carried out.
Similar to the posterior approach, longitudinal traction is applied with internal rotation of the extremity.
If there is wide diastasis of the SI joint and symphysis, the surgeon may elect at this stage to expose the symphysis and temporarily reduce it with a clamp to aid in internal rotation and reduction.
However, permanent fixation of the symphysis at this time is not indicated, as it may impede anatomic reduction of the SI joint by limiting motion of the unstable hemipelvis.
If open reduction of the symphysis is performed, it is held temporarily with a clamp so that it can be removed or adjusted if the SI joint does not reduce satisfactorily.
Should persistent diastasis of the SI joint exist despite these indirect maneuvers, a Verbrugge or Farabeuf reduction clamp can be used to complete the reduction.
A single cortical screw is placed on either side of the SI joint into the ilium and sacral ala, respectively.
The heads of the screws are left proud off the cortex, allowing the reduction clamp to engage the screw heads.
The clamps can be rotated and twisted in any direction while closing the gap to achieve reduction of the joint (TECH FIG 4).
Alternatively, an offset reduction clamp or King Tong reduction clamp can be placed on the ala and external iliac wing, as in Techniques Figure 2B, but from the front.
TECH FIG 3 • Diagram of incision (A) and view of sacroiliac joint from the anterior approach (B). Note position of sharp Hohmann retractor in the ala to protect the L5 nerve root.
TECH FIG 4 • Farabeuf pelvic reduction clamp reducing the sacroiliac joint from the anterior approach using the two-screw technique.
PLACEMENT OF ILIOSACRAL SCREWS
Entry Points
Large cannulated partially threaded screws are used (7.3 or 8.0 mm).
The entry point externally is typically 10 to 20 mm anterior to the crista glutea two thirds of the way from the iliac crest (posterior superior iliac spine) to the greater sciatic notch, or 2 cm up and 2 cm posterior to the notch (TECH FIG 5A).
Percutaneously, the external landmark for choosing the correct entry site is the point of intersection between a line extending proximally from the greater trochanter and a horizontal line extending laterally from the posterior superior iliac spine (TECH FIG 5B).
In percutaneous procedures, the surgeon must be wary of injury to the superior gluteal neurovascular bundle since the entry point is close to the neurovascular bundle as it exits the greater sciatic notch.4,23
“Safe” placement is maximized by careful attention to radiographic bony landmarks.6,33
TECH FIG 5 • A. Entry point for sacroiliac screw on outer table of the ilium. Note proximity to the superior gluteal neurovascular bundle. B. Superficial landmarks for percutaneous sacroiliac screw placement.
Safe Placement and Trajectory
The three critical projections for placing an SI screw are:
The lateral projection to center the guidewire on the sacrum anterior to the canal and to ensure that the guidewire is below the iliac cortical density and sacral alar slope to prevent injury to the L5 nerve root (TECH FIG 6A)
The outlet projection to ensure that the guidewire passes above the S1 sacral foramen (TECH FIG 6B)
The inlet view to ensure that the guidewire is at the proper trajectory and coming to rest in the anterior aspect of the sacral body–promontory for maximal purchase (TECH FIG 6C)
The surgeon should be attentive to sacral dysmorphism and segmentation defects that give rise to altered anatomy, such as lumbarized S1 or sacralized L5 vertebral bodies.
The case shown in TECHNIQUES FIGURE 7A,B demonstrates a unilateral sacralized L5 on the right. The left side is normal. The iliac crest is in line with the L4–5 disc space.
The safe corridor for the SI screw is between the valley of the ala anteriorly (L5 nerve root), the sacral canal posteriorly (cauda equina), and the sacral foramen inferiorly (S1 nerve root).
In the normal situation (no segmentation abnormality), the corridor is well defined (TECH FIG 7C), but in the case of a sacralized L5, the safe corridor is either exceedingly narrow or nonexistent (TECH FIG 7D,E).
If this abnormality is not recognized and an SI screw is placed into L5 assuming it is S1, the L5 nerve root is likely to be injured.
If the surgeon is unsure, the lateral projection with the iliac cortical densities is key in determining the correct level to place the screw, since they are constant with their relationship to S1 even in segmentation abnormalities (TECH FIG 7F).
TECHNIQUES FIGURE 7G shows a reduced SI joint dislocation with a safely placed SI screw.
For SI joint dislocations, the screw trajectory should be from inferior to superior on the outlet view, and from posterior to anterior on the inlet view (perpendicular to the plane of the SI joint).
TECH FIG 6 • A. Lateral projection of pelvis showing the iliac cortical density (ICD) or sacral alar slope line. The tip of the sacroiliac screw and guidewire must be below this line when the screw is at the level of the foramen on the outlet projection. Outlet (B) and inlet (C) projection showing path of iliosacral screw for sacroiliac joint dislocation.
For sacral fractures, the screw trajectory should be straight across from lateral to medial on the inlet view (perpendicular to the fracture plane).
The tip of the SI screw should come to rest in the contralateral side of the S1 body and promontory.
Carrying the screw into the ala provides weaker purchase secondary to poor bone quality and increased risk to the contralateral L5 nerve root.
In situations of comminuted transforaminal sacral fractures, the theoretical risk of overcompression and iatrogenic sacral nerve root injury exists. To gain stability with the construct and avoid a nonunion, some compression is necessary, however.
If this risk exists, sacral nerve root decompression should be performed before placing the SI screw, or an alternative form of fixation such as spinal pelvic fixation or a transsacral screw should be placed.
TECH FIG 7 • Outlet projection (A) and three-dimensional reconstruction (B) showing the segmentation anomaly (in this case a unilateral sacralized L5). C. Safe corridor for placement of an S1 iliosacral screw into the ala of S1. D,E. Lack of safe corridor into “S1” demonstrated on this axial CT of the patient with the unilateral sacralized L5. On some cuts and the lateral projection this may appear as S1 when it is in fact L5. There is no safe corridor at this level. F. Safe placement of an iliosacral screw into S1 under the iliac cortical densities (red arrow). G. AP projection demonstrating a reduced sacroiliac joint with a well-placed sacroiliac screw.
SPINAL PELVIC FIXATION
Through a posterior approach as described above, the L4–5 facet joint is exposed, taking care not to disrupt the capsule.
A 6.2-mm titanium Schanz screw is placed into the L5 pedicle, with the entry point at the junction of the transverse process and the lateral border of the facet joint.
A second Schanz screw is placed into the ilium at the posterior superior or inferior iliac spine, and then directed between the inner and outer tables of the ilium.
The trajectory should be aiming for the ipsilateral greater trochanter as an external landmark. The screw should be directed to pass through the region of the sciatic buttress as seen on the iliac oblique view.
Placement out of the SI joint and within the confines of the inner and outer tables can be confirmed on the obturator and iliac oblique views (TECH FIG 8A,B).
These two screws are then connected with fixed-angle clamps and a 5.0-mm rod, supplementing the SI screw to resist vertical displacement (TECH FIG 8C).
Sacral fracture reduction and fixation with clamps and an SI screw as described above should be performed before placing any spinal pelvic construct.
This avoids rigid fixation with residual sacral gap and subsequent nonunion or delayed union.
TECH FIG 8 • Judet obturator (A) and iliac oblique (B) views to show the path of the iliac screw for triangular osteosynthesis. This path is between the inner and outer tables (outlined with red hashmarks) on the obturator oblique view and just above the sciatic buttress on the iliac oblique view. C. AP radiograph of the pelvis after spinal pelvic fixation (triangular osteosynthesis).
SACRAL NERVE ROOT DECOMPRESSION
In most transforminal fractures, the incriminating fragment of bone can be found and removed by working directly through the fracture in the sacrum.
A laminar spreader can be placed into the fracture to spread the respective portions of the fracture.
After the clot is removed, careful dissection along the exposed surface of the medial sacral fragment will disclose some portion of the foramen.
Tracing the nerve root anteriorly will usually lead to the bone fragment.
Occasionally, a Kerrison and pituitary rongeur will be needed to remove some portion of the sacral lamina to find the nerve root, so these instruments should always be readily available.
POSTOPERATIVE CARE
Provided that all other injuries permit, the patient is mobilized the first postoperative day.
The patient is instructed to be touch-down weight bearing on the ipsilateral extremity for 10 to 12 weeks for SI dislocations and sacral alar fractures stabilized with SI screws.
Patients with spinal pelvic fixation can be allowed to bear full weight within 4 to 6 weeks.
All patients are given a regimen of pelvic, core trunk, hip, and knee range-of-motion exercises.
Common early postoperative problems in patients with severe pelvic fractures include ileus and urinary retention; these need to be addressed early.
The Foley catheter is usually not removed until the patient can mobilize well with physical therapy.
Diet is not advanced until flatus and normal bowel sounds have returned.
Anticoagulation is administered in all patients for 6 weeks, with low-molecular-weight heparin or Coumadin for deep venous thrombosis and pulmonary embolism prophylaxis.
OUTCOMES
Outcome studies after fixation of pelvic fracture-dislocations are difficult to interpret because of poor follow-up, heterogeneity of the injury pattern, associated visceral and neurologic injury, and the lack of reliable outcome measures for pelvic ring injuries.
Improved short-term patient outcomes with early stabilization and mobilization as well as numerous reports citing improved outcomes with anatomic reduction of the posterior ring continued to provide the impetus to develop more rigid and stable posterior fixation constructs.
Earlier outcome studies support the position that the longterm functional results are improved if reduction with less than 1 cm of combined displacement of the posterior ring is obtained, especially with pure dislocations of the SI complex.
Fractures of the posterior ring, as opposed to pure SI dislocations, tend to display superior outcomes, presumably because bony healing can restore initial strength and stability.
In contrast, SI dislocations rely purely on ligamentous healing and scar formation; as a result, these patients tend to have worse functional outcomes in the short term and long term with pain and ambulation compared to patients with other injury patterns.
More recent detailed clinical outcome studies have shown that with current fixation techniques, many patients continue to have poor outcomes with chronic posterior pelvic pain despite seemingly anatomic reductions and healing, with less than 50% returning to previous level of function and work status.
This disparity in results is likely related to multiple confounding factors, such as:
Poor financial and psychosocial and emotional status of trauma patients
Extensive soft tissue damage and associated long bone and extremity fractures
Associated neurologic, visceral, and urogenital injuries, resulting in dyspareunia, sexual dysfunction, and incontinence
Prolonged recovery and rehabilitation time, with loss of job, home, and family roles
COMPLICATIONS
Blood loss and the need for transfusion is common with any open procedure on the posterior pelvic ring, particularly with open reduction of the SI joint and sacral fracture, where injury to the superior gluteal artery is always a danger.
Wound infection occurs surprisingly infrequently given the medical condition of these patients, prolonged ICU and hospital admission, and associated soft tissue injury.
Infection and wound complications occur in about 3% of all patients.
Patients with internal degloving injuries (a Morel-Lavalle lesion), where the skin and subcutaneous fatty layer are sheared and separated from the underlying musculofascial layers, are particularly prone to severe wound complications, with dehiscence, necrosis, and slough.
Patients who have been identified as having an internal degloving lesion in the area of operative approach should first have drainage and débridement of the lesion, and the reduction and placement of fixation should be performed through an alternate approach.
Neurologic injury from manipulation of fracture fragments or placement of SI screws is also a possibility.
Careful attention to the radiologic landmarks and clear appropriate imaging should allow the surgeon to avoid these iatrogenic complications, although even smooth, gentle reductions of widely displaced fractures and dislocations can result in neuropraxic injury to the nerve roots and postoperative deficits.
Patients need to be informed of this risk preoperatively.
The risk of misplaced SI screws varies widely with surgeon and individual experience.
Loss of reduction and failure of fixation can occur in very comminuted and unstable fracture-dislocations, particularly in patients with poor bone quality.
These situations should be recognized preoperatively and intraoperatively, and the appropriate supplemental fixation (additional SI screws or spinal pelvic fixation constructs) should be applied.
Nonunion of sacral fractures and SI dislocations is rare and not reported specifically in the literature.
Rigidly stabilizing a sacral fracture with a residual gap predisposes to malunion and nonunion.
Some patients with SI dislocations continue to have chronic SI joint pain, requiring SI joint fusion.
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