6.6 Lumbosacral spine trauma classification systems
1 Introduction to lumbosacral spine classification systems
Sacral fractures have been long overlooked or compiled into the area of pelvic ring fractures. The introduction of improved skeletal and neuroimaging has opened the door to a more detailed visualization of sacral injuries.
Lumbosacral fracture-dislocations and fractures at the lum-bosacral junction with functional instability are most often classified in terms of sacral and pelvic ring fracture classifications. In more descriptive terms, these are either longitudinal sacral fractures, which extend into or medial to the L5/S1 facet joint, or bilateral vertical sacral fractures connected by a transverse fracture line. This fracture pattern results in a U-type fracture, or, if the vertical fracture lines extend and exit caudal to the sacroiliac joint, in an H-type (bilateral pelvic instability) and Y-type (unilateral pelvic instability) fracture. H- and Y-type fracture patterns result in a disrupted posterior pelvic ring and an unstable pelvis. They are typically associated with an anterior pelvic ring injury as well. Less commonly encountered fracture patterns include L, T, and ? types [1].
2 Current lumbosacral fracture classification systems
Müller AO/OTA Classification
The Müller AO/OTA Classification, which is the most commonly used fracture classification in orthopedic and trauma surgery, describes vertical sacral fractures as 61-C1.3, C2.3, C3.2, and C3.3 fractures depending on overall pelvic ring stability in the horizontal and vertical planes [2]. C1.3 fractures are unilateral unstable injuries, while C2.3 lesions are ipsilat-eral complete unstable and contralateral incomplete unstable injuries, and C3.3 lesions are bilateral complete unstable fractures. This classification does not take into account unilateral or bilateral lumbosacral fractures and fracture-dislocations, which are associated either with L5/S1 facet injuries or with a horizontal fracture line typically at the level of S1 or S2. Horizontal sacral fracture lines are only described in frame of a stable pelvic ring as A3.1, A3.2, or A3.3 fractures, with A3.1 being a sacrococcygeal dislocation, A3.2 being a horizontal undisplaced sacral fracture, and A3.3 being a horizontal displaced sacral fracture distal to S2.
Denis Classification
The Denis classification of sacral fractures correlates anatomic factors with neurologic injury risk in a progressive severity scale. It differentiates between alar fractures (zone I), trans-foraminal fractures (zone II), and central fractures, which include any fracture extending into the spinal canal (zone III) [3]. However, this classification system as well fails to take lumbosacral stability into account. Nevertheless, it may be used to describe the vertical sacral fracture lines associated with lumbosacral injuries.
Isler Classification
Isler recognized that vertical sacral fractures extend rostral-ly either lateral to, through or medial to the S1 facet [4]. Fractures that involve or extend medial to the L5/S1 facet result in lumbosacral instability. This classification is of specific value in unilateral lumbosacral injuries and should then be combined with the Denis classification to fully describe the injury pattern at the lumbosacral junction.
“Letters”, Roy-Camille and Strange-Vognsen Classification
U- and H-type fracture-dislocations at the lumbosacral junction are only marginally summarized i n AO/OTA type 61- C3.3 pelvic fractures (see above). According to the Denis classification, these fracture-dislocations are Zone III injuries, since they all involve the sacral canal. Unfortunately, these classi-fications do not take into account the mechanism of injury, nor the type, magnitude or direction of displacement. Roy-Camille et al. have added a helpful subclassification system of Denis Zone III injuries and lumbosacral fracture-dislocations, describing three types of transverse sacral fractures that are classified according to injury severity and presumed likelihood of neurologic injury[5]. Type 1 injuries consist of a simple flex-ion deformity of the sacrum, and are thought to be the result of axial loading injury with the spine in flexion; Type 2 injuries are characterized by flexion and posterior translation of the upper sacrum, also presumably caused by axial loading injury with a flexed spine; Type 3 injuries demonstrate complete anterior translation of the upper sacrum, typically caused by an axial loading force in extension. A Type 4 injury was later added by Strange-Vognsen and Lebech, consisting of a segmen-tal comminuted S1 vertebral body caused by axial implosion of the lumbar spine into the upper sacrum [6]. All these injuries are caused by indirect forces to the lumbosacral junction. A direct impact force as in impalement orgun shot injuries c a n result in a completely disrupted sacrum with lumbosacral instability [7]. These injuries may be classified as Type 5 injuries. While the Roy-Camille subclassification of Denis Zone 3 injuries is somewhat helpful in expressing injury severity and mechanism it too fails to identify the level of the sacral injury or reflect upon neurologic injury.
3 Summary
Generally, the severity or type of spinal cord injury has been effectively classified according to the American Spinal Injury Association (ASIA) based upon the original work of Frankel [8]. Since it is based primarily on sensorimotor function of the extremities, the ASIA classification is of limited value in sacral injuries, where a combination of root injuries can produce a variety of deficits and are more likely to affect bowel and bladder function lower extremity sensorimotor function. Gibbons addressed this by differentiating patients into those having (1) no injury, (2) lower extremity paresthesias only, (3) lower extremity motor deficit with intact bowel and bladder function, or (4) impaired bowel and/or bladder control [9]. This simple and meaningful classification, however, has not found widespread clinical acceptance. As these brief reviews illustrate the area of sacral fractures is confounded by multiple variables in form of fracture patterns, neurologic injury and soft-tissue disruption. Especially in the area of neurologic injury greater awareness of the various stages of sacral plexus injury is a long overdue step for ward. It is safe to say that more systematic review of larger patient cohorts is necessary to refine present day classification systems of these injuries.
4 References
1. Nork SE, Jones CB, Harding SP, et al (2001) Percutaneous stabilization of U-shaped sacral fractures using iliosacral screws: technique and early results. J Orthop Trauma; 15:238–246. 2. Committee for Coding and Classification (1996) Fracture and Dislocation Compendium Orthopaedic Trauma Association. J Orthop Trauma; 10 Suppl 1:66–70. 3. Denis F, Davis S, Comfort T (1988) Sacral fractures: an important problem. Retrospective analysis of 236 cases. Clin Orthop Relat Res; 227:67–81. 4. Isler B (1990) Lumbosacral lesions associated with pelvic ring injuries. J Orthop Trauma; 4:1–6. 5. Roy-Camille R, Saillant G, Gagna G, et al (1985) Transverse fracture of the upper sacrum. Suicidal jumper’s fracture. Spine; 10:838–845. 6. Strange-Vognsen HH, Lebech A (1991) An unusual type of fracture in the upper sacrum. J Orthop Trauma; 5:200–203. 7. Schildhauer TA, Chapman JR, Mayo KA (2005) Multisegmental open sacral fracture due to impalement: a case report. J Orthop Trauma; 19:134–139. 8. American Spinal Injury Association (1996) International standards for neurological classification of spinal cord injury American Spinal Injury Association: Chicago. 9. Gibbons KJ, Soloniuk DS, Razack N(1990) Neurological injury and patterns of sacral fractures. J Neurosurg; 72:889–893.1 Denis Three-Zone Classification of Sacral Fractures
Denis F, Davis S, Comfort T (1988) Sacral fractures: an important problem. Retrospective analysis of 236 cases. Clin Orthop Relat Res; 227:67–81.
SCALE DESCRIPTION
Fractures classified based on the direction, location, and level of sacral fractures. Fractures are divided into the following three zones:
Zone 1—Region of the ala
Zone 2—Region of the foramina
Zone 3—Central sacral canal region
Interpretation:
Descriptive of fracture location. One type not necessarily more severe than the next.
SCALE ILLUSTRATION
METHODOLOGY
No predictive validity or reliability studies were identified.
Predictive validity
Population tested in | Outcome | Predictive validity |
Not tested |
Reliability
Population tested in | Interobserver reliability | Intraobserver reliability |
Not tested |
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