2.3 Pathoanatomy and classification of acetabular fractures
1 Introduction
Full credit must be given to Emile Letournel, whose initial human anatomical specimen studies of the acetabulum provided surgeons with an understanding of the anatomy, the injury, the diagnostic plan including radiographic evaluation, and the guidelines for managing these difficult fractures [1]. Compared with the pelvic ring, there are no cadaveric studies after acetabular fractures to confirm Letournel’s suppositions [2]. Cadaveric testing after impacts in the biomechanical laboratories and surgical experience over the last 25 years has provided an insight into the fracture’s pathoanatomy, mechanisms, and hence fractures patterns and classification of the injury.
2 Mechanism of injury
Classic acetabular fractures have been difficult to produce in the laboratory (Pennal GF, Garside H, unpublished data); however, there is good clinical correlation between the type of fracture and the force that created it [2]. Fractures of the acetabulum are caused by forces that drive the femoral head into the acetabulum. For this reason, damage to the articular surface of both the femoral head and acetabular surface must always be suspected. The type of acetabular fracture depends on the position of the femoral head in the acetabulum at the moment of impact as well as the direction of the force ( Fig 2.3-1 ). Dakin et al [3] showed that acetabular fracture patterns associated with motor vehicle crash correlated to the type of impact. This study verified the biomechanical concepts proposed by Letournel [2]. Many variables can cause the different types of fracture: sitting position, impact, and load of the impact. The sitting position is important because the position of the femoral head while sitting can affect the type of fracture. The amount of internal rotation/external rotation, abduction/adduction, or flexion/extension at the time of injury can produce different types of fractures. This accounts for numerous possible fracture types. The injurious force may be applied to the flexed knee and along the femoral shaft—as in the dashboard injury or to the greater trochanter (lateral force), to the foot, or to the lumbosacral area ( Fig 2.3-2 ). As the type of injury depends on the precise position of the femoral head at the moment of impact, the number of specific fracture types appears to be infinite.
The following general statements may be made [3]: Dashboard injuries with the hip flexed and in some degree of internal rotation cause a preponderance of posterior wall fractures of all types, including those associated with posterior column. An associated posterior dislocation of the hip is also prevalent with this injury.
The resolution of forces applied directly to the great trochanter will determine the following type of acetabular fracture:
In neutral rotation, it will cause an anterior column posterior hemitransverse fracture
With external rotation of the head, the anterior part of the acetabulum is involved leading to anterior type fractures
With internal rotation of the head, more transverse fractures with a posterior wall or column component occur
With an abducted head, the inferomedial acetabular area will fracture and with an adducted head the superolateral acetabular area wall will fracture
With the hip in extension, forces along the leg will usually cause transtectal transverse fractures of the acetabulum
Another variable is the size of the individual—the effect of an impact is different in a petite woman than a large truck driver. The impact also depends on frontal, lateral, or off-axis loading. Dakin et al [3] evaluated 83 patients with fractures, 41 women and 42 men, who had a combined average age of 32.8 years. Femoral shaft axis-loading fractures (frontal impact) correlated significantly with male gender and trucks. Greater trochanter-loading fractures occurred statistically more frequently in side impacts (the typical transverse fracture). Women received a higher rate of off-axis−loading fractures in smaller vehicles with an increase of the transverse posterior wall type [3].
The type of passenger restraint may also affect the fracture pattern. Preliminary results show that the worst fracture patterns are with front airbags alone without wearing seatbelts. Although the airbag averts death by preventing head or thoracic injuries, the passenger who is not held in place by the seatbelt can slide under the airbag and sustains severe injuries to the pelvis and lower extremities. The load is also important. A high load in a short period results in worst injuries. Finite modeling of the acetabulum with lateral impacts has shown that it takes just 55 ms to produce an acetabular fracture.
As acetabular fractures are high-energy injuries, other structures are at risk for injury. Because the energy is often delivered through the flexed knee, injuries to the patella and the posterior cruciate ligament are common and may often be overlooked. More recently with the advent of more stable passenger restraint systems, such as airbags, forces are transmitted through the foot and extended knee that increase the incidence of associated foot and ankle injuries as well as periarticular knee fractures. Not only is the acetabulum injured but also the remainder of the pelvic ring—especially the sacroiliac joint—may suffer from the force applied to cause the fracture. A close evaluation of the symphysis and sacroiliac joint should always be considered when pelvic pain exists after acetabular repair. Good reconstructions of the acetabular fracture have been performed but when the hip is painful 3–4 years after surgery, even though excellent x-rays and range of motion exist, the reaction is to perform a total hip arthroplasty. These patients do not get pain relief, and were evaluated later and diagnosed with sacroiliac arthritis. The pain subsided after injection and arthrodesis.
3 Diagnosing the fracture
The assessment of the total acetabular injury will define the personality of the injury. This includes the history and physical examination of the patient as well as assessment of the patient functional demands (see Chapter 2.4). Included in this assessment is the process of acetabular fracture diagnosis when the surgeon determines the fracture pattern, displacement, and associated articular involvement through radiographic evaluation. This diagnostic process determines the treatment plan and in particular the operative approach and fixation methods. The diagnostic process is part of the classification determination. However, one cannot finally classify a fracture until the postoperative period when the tentative diagnosis is confirmed by direct visualization. Nonoperative cases are classified at the time of the final choice of the treatment method. The classification determination allows surgeons to compare similar groups of patients treated by different methods.
The variables that make up the personality of the fracture must be considered in the decision-making process because the prognosis of an individual fracture pattern depends on them. These variables include anatomical types, the degree of the causative force (low energy versus high energy), the direction of displacement, the presence or absence of a dislocation, the number of fragments, the presence of marginal impaction, and damage to the articular surface of the femoral head and/or the acetabulum. All these factors are important in decision making as they define the injury. This is clearly different than classifying the injury because all the present classifications are anatomically based and do not factor in all these elements. For example, a T-type fracture may be undisplaced or displaced. If displaced, one column may be more displaced than the other and may be associated with a wall fracture plus/minus a dislocation. Also, the fracture may be caused by high energy, with severe fragmentation, or by low energy in an older individual with osteoporotic bone. The prognosis of any given T-type fracture varies widely, even though the present anatomical classifications regard them all the same. The AO/OTA modification of the Letournel-Judet classification added modifiers to try and capture the anatomical variables; however, these are not widely used in clinical practice because of their complexity but are helpful for final documentation of operative cases.
For a classification to be useful clinically it must have face value, meaning the classification represents what is seen and relates to clinical practice. It also must be reliable in its interpretation from observer to observer. As to observer reliability, it has been shown that the Letournel-Judet classification has substantial reliability [4]. O’Toole et al [5] have confirmed that this system is reliable especially if plain x-rays are supplemented by CT scans. However, no acetabular classification has been completely validated as having content reliability and validity [6]. Patel et al [7] have shown that nonacetabular surgeons have difficulty assessing factors that will predict outcome. Therefore, at best, the LetournelJudet classification that is anatomically based can be used as an acceptable guide to compare cases among centers and as a guide to treatment. Individualized decision making is mandatory for all patients with an acetabular fracture and is best undertaken by surgeons experienced in the field of acetabular fracture treatment [7].
3.1 Acetabular fracture classifications
The importance of Letournel-Judet classification cannot be underestimated as it rendered the description of these fractures—previously identified as central dislocation of the hip—more precise and led to a new understanding of these challenging fractures [1]. The Letournel-Judet system is anatomically based and all fractures are divided into two major types, elementary and associated or complex, each with subgroups. This system provides a useful clinical system for determining approach, reduction, and fixation methods. However, the system does not address other variables, such as dislocation, marginal impaction, displacement, and fragmentation. These variables are significant in the outcome of these fractures, thus may be useful in a more complete classification system. For the purpose of case comparison, the ideal is the development of a universal classification of all fractures that allows all surgeons to “speak the same language.” In the last two decades, the AO Foundation has attempted to attain this goal by collaborating with Société International Chirurgie Orthopèdique et de Traumatologie and the Orthopaedic Trauma Association. Based on the principles of the AO/OTA Fracture and Dislocation Classification (described in the Müller comprehensive classification of long bone fractures) [8] and working with members of these organizations, including Letournel, Helfet, achieved consensus on a classification for fractures of the acetabulum that is extremely complex but provides more detail and also an alphanumerical code for research purposes [1]. However, note that the AO/OTA Comprehensive Classification is an adaptation of the anatomical classification of Letournel-Judet rearranged to fit the articular classification scheme of Müller [8]. The type A fractures are rim fractures or avulsion-type injuries of the articular surface. The type B fractures are partial articular fracture and the type C fractures involve the complete joint ( Fig 2.3-3 ). Within each group is a progression from simple patterns to more complex fragmented fracture patterns. Both classification systems are needed: Letournel-Judet for clinical decision making and the AO/OTA Fracture and Dislocation Classification for documentation and research.
3.2 Letournel-Judet classification
This system [2] divides the acetabular fractures into elementary and associated or complex (see detailed description in topic 4 of this chapter). The elementary fractures consist of one fracture line that can involve the anterior segment, posterior segment, or both. This leads to posterior wall, posterior column, anterior wall, anterior column, and transverse fractures. The associated fractures are defined by two or more fractures through the acetabulum and pelvis. These are T-shaped fractures, both-column fractures plus variations of wall and column fractures associated with each other or the transverse fracture or T-type fracture. This system informs the surgeon where the fracture is located and usually indicates what surgical approach to use ( Table 2.3-1 ).
Elementary fractures |
Posterior wall |
Posterior column |
Anterior wall |
Anterior column |
Transverse |
Associated fractures |
T-shaped |
Posterior wall plus posterior column |
Posterior wall with transverse |
Anterior column or wall with transverse |
Anterior column or wall with posterior hemitransverse |
Both columns |
3.3 Classification according to direction of displacement
In describing various fracture patterns of Letournel-Judet system, the direction of displacement or locale of the fracture is used. This focus figures largely in the decision-making process. For example, all posterior-type fractures, whatever their type, share some characteristics. Fractures of the posterior wall, the posterior column, some transverse, or T-type with posterior wall displacement are usually caused by a blow to the flexed knee (eg, dashboard injury); therefore, associated knee injuries are common. Posterior dislocation of the hip is common if an associated posterior wall fracture is present. Almost invariably this leaves the hip potentially unstable after closed reduction. Therefore, posterior fracture types usually require open reduction and internal fixation (ORIF) to restore hip stability. Finally, the addition of a posterior dislocation affects the prognosis significantly because the prevalence of avascular necrosis and sciatic nerve lesions is significantly increased.
The direction of the displacement is important for deciding what surgical approach to use. For example, transverse fractures may rotate anteriorly or posteriorly. T-type fractures may be displaced in only one column (anterior or posterior), while the other remains undisplaced. The correct surgical approach should be obvious to a surgeon who has all this information.
3.4 AO/OTA pelvic and acetabular fracture classification
The AO/OTA modifications [9] and alphanumerical code of the Letournel-Judet classification [2] allows more in-depth description and ease for documentation. The nomenclature is similar between the two systems but additional modifiers have been added in the AO/OTA systems. Brandser and Marsh [10] have suggested a further modification based on the same anatomical types but divide them into wall, column, and transverse fractures. Their suggestion has merit for radiologists; however, we will not adopt it because it does not appreciably change existing classifications; rather, it just rearranges the types.
The AO classification is based on the anatomical site, the segment, the type, group and subgroup, and modifiers [8]. An alphanumerical code is used for its suitability for computers [11]. The acetabulum is anatomical location 62. The fractures may be divided into type A (partial articular fractures), type B (transverse or T-type fractures in which a portion of the articular surface of the acetabulum is still connected to the intact ilium, and, therefore, to the axial skeleton), and type C (both-column fracture, in which no portion of the acetabulum is connected to the intact ilium, nor to the axial skeleton). In effect, pattern C is a “floating acetabulum.” This classification with subgroups is described in Table 2.3-2 . Although, in order of severity, it attempts to follow the principles of the AO/OTA Fracture and Dislocation Classification for long bones, it must make some compromises because of the complexity of these fractures. For example, a T-type fracture, although it is a type B lesion, often is a much more severe injury than a type C both-column fracture.
3.5 How to use the classification for individual decision making?
Although a comprehensive classification is necessary for investigational purposes, such as prognosis and outcome studies, it is less important for making decisions on individual cases. In trauma, every case is different. The surgeon must know the basic fracture types, but even more important he/she must be able to interpret the x-rays and draw the fracture lines on a dry skeleton. Even experienced acetabular surgeons do this before every operation; consequently, it is absolutely essential that all surgeons adopt this preoperative practice.
The acetabulum is much less of a mystery than is commonly believed. A study of its anatomy reveals that it is made up of two columns and two walls. The two columns meet at the dome, tectum, or roof of the acetabulum ( Fig 2.3-4 ). All anatomical fracture types are variations and combinations of that anatomy. Therefore the possibilities include fractures of the anterior, posterior, and/or both columns plus wall fractures. The anterior or posterior wall may either be fractured alone or in association with an anterior or posterior column and/or dislocation. If both columns are fractured together, then we call that a transverse fracture.
If both columns are fractured (transverse) and also separate from each other, then we call that a T-type fracture. The femoral head also may be centrally dislocated through the quadrilateral plate or either anterior or posterior if there is an associated wall fracture. The both-column fracture, termed by Letournel and Judet, is actually a variant of the T-type fracture in which the transverse break runs through the ilium above the acetabulum; thus, disconnects all articular cartilage from the axial skeleton (the floating acetabulum). In this type, the posterior column is usually separated and displaced and may be associated with a posterior wall fracture.
Therefore, simply by applying thorough knowledge of anatomy, the surgeon can outline all possible fracture types without having to memorize a complex classification. Furthermore, various landmarks on the x-rays can lead the surgeon to logical treatment decision making for each patient.
Other factors must be assessed carefully to define the personality of the fracture. The surgeon must define not only the type of fracture but also the factors that affect the prognosis; namely (1) the degree of displacement; (2) the degree of comminution or impaction; (3) the exact position of the fracture, especially involvement of the acetabular dome; and (4) the presence of a dislocation—posterior, central, or (rarely) anterior.
A logical management decision should follow further assessment of the limb, the patient, and the surgeon’s own experience. Therefore, the treatment of a patient depends most on the assessment of each specific case by an experienced surgeon.
4 Letournel-Judet classification (AO/OTA Fracture and Dislocation Classification)
This section describes in detail the fractures of Letournel-Judet system and in parentheses adds the AO/OTA universal code and further description as needed.
4.1 Elementary fractures (one fracture line that can involve the anterior segment, posterior segment, or both)
4.1.1 Posterior wall fractures (A1)
All posterior wall fracture types share the following common characteristics:
They are usually caused by a blow to the flexed knee (dashboard injury); therefore, associated knee injuries are common.
Posterior dislocation of the hip is common, and usually associated with a posterior wall fracture.
The addition of a posterior dislocation seriously affects the prognosis because the prevalence of avascular necrosis and sciatic nerve lesions are markedly increased.
If the posterior wall fracture is associated with any other fracture type, eg, a posterior column (A2), transverse (B1), T-type fracture (B2), or associated both-column (C), it dictates the behavior of the pattern because it signifies potential posterior instability of the hip following closed reduction. The presence of a posterior wall fracture usually directs the surgeon to ORIF of the fragment, unless the fragment is so small that the hip remains stable in all positions.
Posterior wall fractures always involve the posterior articular surface but usually avoid the posterior horn or roof, cotyloid fossa, and quadrilateral plate. The fragment may be single or multiple, large or small, and high or low. Impaction of the acetabular margin is not infrequent as the head dislocates ( Fig 2.3-5 ). This impaction is equivalent to the depressed component of a tibial plateau fracture. It must be recognized; otherwise it will block the wall reduction and create joint incongruity. However, it is a factor in predicting a poor result if present. If the fragment or fragments are large, reduction of the dislocation may not be followed by reduction of the fracture; therefore, the hip joint may remain unstable. Another important aspect of the posterior wall fracture is its capsular attachments, which provide the bony wall fragment with a blood supply ( Fig 2.3-6 ). If the capsule is torn from the fragment at injury or during surgery, the prognosis for healing will be jeopardized. On occasion, the fragment contains a large portion of the superior weightbearing surface. This fragment may include part of iliac wing but does not involve the iliopectineal line, so is not an anterior fracture ( Fig 2.3-7 ). Accurate open reduction is compulsory to avoid repeated dislocation and instability and essential to restore joint congruity and prevent early degenerative arthritis. Excellent results should be achieved if the fragment is anatomically reduced and stabilized, and no marginal impaction is present.
To account for all these variables, groups and subgroups have been added to the AO/OTA classification of this fracture.
One fragment fracture (A1.1)
Type A1.1 is a pure fracture dislocation with one large fragment posteriorly. The fragment may be posterior (1), posterosuperior (2), or posteroinferior (3). The posterior and posteroinferior types may leave the hip unstable in flexion and internal rotation; the posterosuperior type is extremely unstable, even when the hip is extended. Often, the hip cannot be kept in the reduced position, and this particular type requires emergency surgery ( Fig 2.3-8 ).
Related posts:
2.2 Biomechanics of acetabular fractures
2.6 General assessment and perioperative management of acetabular fractures
2.5 Decision making: nonoperative and operative indications for treatment of acetabular fractures
2.1 Anatomy of the acetabulum
2.4 Defining the injury: assessment and principles of management of acetabular fractures
1.8.4 The management of the injured pelvic ring: internal fixation of the anterior pelvic injuries—open book (type B1)
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