1 Incidence

The 3-D structure of the pelvis, composed of the two innominate bones and the sacrum, relies on a complex ligamentous network to provide stability. Pelvic ring injuries are rarely isolated to a single anatomical location and may involve ligamentous disruptions with associated dislocations, as well as fractures with or without displacement. Most patients also present with associated injuries to other organ systems. Associated injuries, the pattern of injury, and the amount of displacement all contribute to the initial management of a pelvic ring injury. Despite an increased understanding of these injuries, nonunion and malunion continue to occur. Malunion or pelvic instability may result secondary to fractures that heal with residual displacement or incomplete bony and ligamentous healing. This makes it difficult to separately discuss malunion and nonunion of the pelvic ring because the two entities may coexist in a single complex posttraumatic deformity. Regardless of initial treatment, as many as 5% of all pelvic fractures are believed to remain in an unsatisfactory position following injury [1].

2 Etiology

Malunion and nonunion of the pelvis can occur after any form of treatment but more commonly following nonoperative care [2–5]. Residual deformity results when the degree of stability or displacement is misunderstood on initial or subsequent radiographic and clinical evaluation. Pelvic stability depends on the mechanism of injury, type of injury (ie, fracture or dislocation), and the amount of displacement. A stable injury pattern is commonly referred to as one that can withstand physiological forces without further displacement, but defining the amount and duration of that force can be difficult [6]. Therefore, evaluation of deformity and stability are critical concepts to understand for those involved in the initial treatment of pelvic ring injuries.

Deformity may result following operative treatment of fractures or dislocations if reduction and/or fixation obtained at the time of surgery is inadequate [2]. The characteristics of an acceptable, stable reduction are important and are affected by the injury pattern, bone quality, and/or patient′s ability to cooperate with postoperative activity restrictions. Each of these characteristics is defined differently by the patient population and can affect the choice of fixation and the resulting outcome [7–9]. Delaying definitive internal fixation may be appropriate given a patient′s overall health but can make reduction more difficult. Thus, definitive treatment in this context requires a higher degree of surgical expertise [10].

Obtaining a near-anatomical reduction with appropriate fixation of unstable fractures is the most reliable way to maintain fracture position until union and decrease the incidence of malunion and/or ongoing instability [11]. Although the use of less invasive stabilization strategies for pelvic ring injuries may decrease acute morbidity under certain circumstances [12], the quality of reduction and degree of stability may be affected. External fixation may provide a degree of stability to the pelvis, particularly during initial resuscitation. However, use of this modality as the sole treatment of globally unstable pelvic fractures will likely result in deformity [5, 6, 13]. Emergent application of an external fixator has been associated with increasing posterior cephalad translation, despite apparent improvement anteriorly and the creation of an external fixator deformity (ie, flexion and internal rotation of the hemipelvis) [14].

Preventing deformity is the best treatment for a pelvic ring injury, and successful treatment requires radiographic monitoring until fracture union. Serial x-rays may reveal occult fractures, early displacement, or loss of fixation, and identifying those who may benefit from early revision may be less challenging than reconstruction at a later time. Patients with multiple trauma injuries or preexisting medical problems are candidates for transfer to surgeons and institutions well equipped for such complexity.

3 Deformity

Pelvic ring deformities can be complex and may include translational and/or rotational displacement. Deformities of the hemipelvis typically are described based on the posterior zone of injury (ie, ilium, sacrum, or sacroiliac joint), the point around which most deformity occurs. Anatomical descriptions of translational deformity include caudad/cephalad, anterior/posterior, and medial/lateral displacements. Rotational deformity also occurs around the posterior sacroiliac complex, resulting in flexion/extension, internal/external rotation, and abduction/adduction. Specific radiographic views of the pelvis provide extensive information regarding pelvic deformity ( Fig 1.19-1 ). The appearance of certain anatomical features of the pelvis, including the obturator foramen, can be particularly useful. Rotational displacements can be inferred from the AP view, with internal rotation or external rotation resulting in the appearance of the obturator oblique or iliac oblique view. Flexion and extension result in a more cephalad or caudad view of the hemipelvis, respectively.

Multiple translational and rotational displacements may exist within a single posttraumatic deformity, at times making it difficult to define the residual position of the hemipelvis following treatment. A typical deformity following an anteroposterior compression mechanism includes cephalad translation with external rotation and abduction of the hemipelvis. Lateral compression results in internal rotation with flexion and adduction of the hemipelvis. Additional deformity can occur within the innominate bone. Often occurring in the rami, these deformities may be a source of morbidity in posttraumatic deformity and complicate subsequent treatment.

4 Definition

Despite improved understanding of pelvic pathoanatomy [15], including factors contributing to instability [16, 17] and operative techniques required for restoring stability [18, 19], anatomical healing of pelvic ring injuries remains difficult. Many fractures heal with residual displacement. Initial radiographic evidence of cephalad displacement of 1 cm and/or 15–20° rotation of the hemipelvis is considered to be acceptable; however, dislocations of the hemipelvis may tolerate less displacement. These measurements approximate what may be acceptable deformity following fracture union. Displacements more than 1 cm or 15° rotation may represent malunion because healing outside these parameters has been associated with diminished clinical results [7, 20–28]. Although this view is not universally held [29, 30], evaluating displacement is difficult and existing techniques for evaluating displacement of the posterior pelvic ring are unreliable [31]. Radiographic assessment of the sacroiliac joint has been demonstrated to be both inaccurate and unreliable [32].

The diagnosis of nonunion may be difficult. Traditional x-rays may not reveal nonunion because it can be out of the radiographic plane or obscured by internal fixation devices. Some regions of the pelvis may require 6–12 months to unite. Areas of bridging bone may develop but are insufficient to provide stability to the pelvic ring. Progressive fracture healing should be demonstrated on serial x-rays, and the patient should show signs of clinical improvement with less pain or tenderness on examination. Persistent pain, loss of fracture reduction, hardware failure, lack of progressive radiographic healing, and residual sacroiliac joint or pubic symphysis diastasis provide clues of ongoing instability from nonunion or malunion. X-rays (AP and oblique views) centered on the area of interest and computed tomographic (CT) scans may help in evaluating the extent of fracture union. Residual instability may be demonstrated with stress x-rays, including single-leg standing views [33].

5 Symptomatology

Pain is the most common complaint following pelvic ring injury and is not limited to fractures deemed unstable at the time of injury [29]. It is common after nonoperative treatment of the unstable fractures [20, 34] and is also often reported following operative treatment [25, 27]. The etiology can be complex and related to surrounding soft-tissue trauma sustained in the initial injury. Lumbosacral articulations [35, 36] and neurological injury [37] have been implicated as sources of pain following pelvic trauma. Ongoing displacement or instability of the posterior pelvic ring, particularly sacral fractures, may result in persistent nerve root compression and pain.

Deformity can be a source of pain and dysfunction following injury. Specific fractures of the anterior ring have been associated with symptoms, and these so-called “tilt” fractures are commonly an indication for acute open reduction and internal fixation ( Fig 1.19-2 ). In addition to pain, residual displacement of anterior ring fractures can cause dyspareunia, urinary frequency, and chronic constipation. Although unlikely to biologically limit fertilization, pelvic injuries affect sexual function and in the presence of deformity may complicate subsequent vaginal delivery [38].

Typical posterior and cephalad displacement of the pelvic ring results in a prominence along the posterior buttock or flank, causing difficulty and pain with supine positioning. Residual cephalad and rotational displacement of the hemipelvis repositions the hip socket and ischial tuberosity, affecting limb length and rotation. Even in the absence of pain, these deformities may affect gait, sitting balance, and overall function. Prolonged deformity may alter sitting or gait, causing compensatory motion with resultant pain and disability.

Hemipelvic instability, whether occult or obvious, also can be a source of pain. The patient may describe a sensation of limb shortening or pistoning during weight-bearing activities. Loading pain is characteristic and occurs in the region of instability or nonunion.