1.1 Lumbosacral pelvic ring anatomy

The sacrum acts as a keystone for the spinopelvic junction as well as provides the posterior link in the pelvic ring. In an intact situation, load transmission from the axial skeleton to the pelvis proceeds from the lower lumbar spine to the sacrum and then on into the iliac wings [6]. The sacrum is stabilized in the pelvis by the anterior and posterior sacroiliac ligaments as well as the sacrotuberous and sacrospinous ligaments that make up the floor of the true pelvis [7] ( Fig 1.10-2 ).

1.2 Ligaments in lumbosacral spine

The soft-tissue stabilizers of the lumbosacral region are of paramount importance and must be understood as they are not well imaged by CT. Predicting the stability of the lumbosacral junction must include an understanding of these ligamentous relationships and how they may contribute to operative indications and approaches. The most frequently injured ligaments in pelvic ring injuries are the iliolumbar ligaments ( Fig 1.10-2 ). Injury to iliolumbar ligaments is predicted by transverse process fractures of lowest lumbar vertebrae. Probably the most important ligamentous disruptions to recognize are the anterior and posterior sacroiliac ligaments, as they provide essential information about the pelvic ring stability and may indicate a necessity to consider anterior pelvic ring stabilization. Injury is best demonstrated by either anterior or posterior sacroiliac joint widening on the CT scan. The sacroiliac joint is an intrinsically unstable joint in the absence of intact ligamentous support. The low lumbar spine also has important elements of stability provided by the facet capsules, anterior longitudinal and posterior longitudinal ligaments, as well as the intervertebral connections such as the interspinous and supraspinous ligaments. The broad muscle attachments of the dorsal paraspinal musculature also contribute to the stability of the lumbopelvic junction and spine itself.

1.3 Classification of injury

Sacral fractures are classified by the orientation and location of the fracture line in relation to the neural foramen, the lateral facet, and by descriptive classification of the fracture lines.

Denis et al [1] reviewed vertically oriented sacral fractures and their relationship to neurological dysfunction. Dividing the fractures by their location relative to the neural foramen allowed for an estimate of neurological impact of the fracture. Fractures lateral to the foramen are classified as alar fractures or zone I and have just over 6% associated nerve symptoms. Fractures exiting the neural foramen are zone II injuries and those exiting centrally through the sacrum central to the neural foramen are in zone III ( Fig 1.10-3 ). Sacral nerve root injury and bladder dysfunction with zone III injury occurred in nearly 60% of patients.

Roy-Camille [8] looked at sacral fractures in a suicide-jumping population and classified horizontal sacral fractures by the position of the proximal segment along with the flexion or extension in relation to the distal segment, with or without translation. They divided displaced fractures into three types, with type 1 being flexion deformity; type 2, flexion deformity with horizontal posterior displacement; and type 3, fractures having an extension deformity. Despite this division by fracture displacement and angulation, the primary operative indication in this series for all types of fracture was the presence of neurological deficit. Strange-Vognsen and Lebech [9] further classified the horizontal sacral fractures with the addition of a type 4. This fracture pattern consists of a fragmented upper sacral segment fracture without significant translation or angulation [8, 9] ( Fig 1.10-4 ).

One study [10] reviewed the experience with lumbosacral pelvic ring injuries, specifically looking at the transition from rotationally unstable pelvic ring injuries to translationally unstable injuries. It was found that the injury pattern in relation to the L5/S1 articulation was the factor leading to increased instability at the lumbopelvic junction. Isler [10] devised a classification system based on the location of the fracture line in relation to the articular facet of S1. Type 1 fractures had the fracture line exit lateral to the cephalad articular surface. Type 2 fractures involved the S1 superior end plate articular surface but did not involve the pedicles or laminae at the L5/S1 articulation. Type 3 fractures involved the S1 articular facet as well as the lamina and pedicles of the L5/S1 articulation [10] ( Fig 1.10-5 ).

Descriptive classification of sacral fractures has also been presented and was illustrated by Vaccaro et al [2] in 2004. The U, H, T, and lambda types are all fractures that cross the central canal of the sacrum and correspond to type 3 fractures in the Denis classification [2] ( Fig 1.10-6 ).

1.4 Management

Initial management is directed at restoring hemodynamic stability. Awareness of the high frequency of associated injuries is essential in the management of these complex pelvic injuries. In one series [3], associated injuries to the lumbar and cervical spine were present in more than one-third of patients with sacral U-type fractures. Use of pelvic sheeting or temporizing external fixation may improve hemostasis and assist resuscitative efforts [11]. Initial evaluation and treatment by interventional radiology with embolization may also help decrease hemorrhage from intrapelvic in terms of injury [2, 3].

Evaluation of the patient needs to include a careful neurological examination. Specific attention should be paid to the L5 root, which controls extensor hallucis longus function, as the L5 root is frequently injured. It is hypothesized that fracture displacement occurs at the time of injury, as the L5 root courses anterior to the sacrum and sacroiliac joint that is proximal to the fracture level. Sacral nerve root function should also be documented with particular focus on cauda equina symptoms of perineal numbness and bladder or anal sphincter dysfunction. Digital rectal examination is essential for documentation. Urinary dysfunction, usually in the form of retention, is more difficult to assess as most patients will have a Foley catheter placed immediately upon arrival for fluid monitoring or may have a direct genitourinary injury. If urinary function cannot be assessed preoperatively, it is essential to discuss with the patient and/or family the high likelihood of urinary dysfunction with this injury pattern.

Any neurological deficit is a relative indication for surgical intervention. The surgeon should attempt to correlate any neurological compression or fracture displacement with the patient′s symptoms and should tailor the planned operation to address these potential areas of ongoing neurological compression. Potential management options include sacral decompression and fracture realignment.

Further operative indications for lumbosacral injury include open fractures, progressive neurological injury, and vertical instability [2, 7]. To our knowledge, specific operative criteria based on angulation or displacement have not been studied nor published [2, 7]. Lumbopelvic fixation has been advocated for sacral fractures involving the L5/S1 articulation as well as for bilateral vertically unstable fracture patterns [4, 12]. In general, injury involving the L5/S1 articulation in conjunction with transforaminal sacral fractures results in significant instability of the lumbopelvic junction. This instability is a relative indication for surgery after hemodynamic stability has been obtained.

Due to the incidence of concomitant injuries clear communication with other departments, such as urology and trauma surgery, should take place before proceeding to the operating room. Unless there is a progressive neurological deficit, hemodynamic instability, or open fracture, it is usually safe to postpone lumbopelvic stabilization until more pressing injuries, such as long-bone fractures have been stabilized.