Pelvic & Acetabular Trauma MCQs

In APC-II injuries, the symphysis opens and the anterior sacroiliac, sacrotuberous, and sacrospinous ligaments are disrupted. However, the strong posterior sacroiliac ligaments remain intact, providing vertical stability. In APC-III injuries, the posterior SI ligaments are also disrupted, leading to complete global (rotational and vertical) hemipelvic instability.

An APC-II injury is characterized by symphyseal diastasis and disruption of the anterior sacroiliac, sacrotuberous, and sacrospinous ligaments, resulting in a 'vertically stable but rotationally unstable' pelvis (opening like a book). The defining feature that differentiates an APC-III injury from an APC-II is the complete disruption of the posterior sacroiliac complex (posterior sacroiliac ligaments), rendering the hemipelvis both rotationally and vertically unstable.

An APC-II injury is characterized by symphyseal diastasis and disruption of the anterior sacroiliac, sacrotuberous, and sacrospinous ligaments. The posterior sacroiliac ligaments remain intact, providing rotational instability but maintaining vertical stability.

DISCUSSION: Though no gold standard exists, a reduction of concordant pain by at least 75 to 80% following an intra-articular, image-guided anesthetic injection is considered to be the most reliable method of identifying the SI joint as the cause of a patient's pain. Although provocation tests including the Gaenslen test, the compression test, thigh thrust, and Yeoman test are commonly used and can be helpful in diagnosing non-specific SI joint pain, individually they are not as reliable as the response to a diagnostic, anesthetic injection. Of note, the combination of all 4 maneuvers has proven to be more useful than any one individual test. An MRI of the SI joint showing bony erosion and bone marrow edema suggests inflammatory arthritis and may not necessarily be associated with pain.

DISCUSSION: The false profile view of Lequesne and de Seze is obtained with the patient standing with the affected hip on the cassette, the ipsilateral foot parallel to the cassette, and the pelvis rotated 65 degrees from the plane of the cassette. This view best assesses anterior coverage of the femoral head.

The degree of acetabular dysplasia and the age of the child are important considerations when choosing what type of osteotomy to perform. The ability to obtain concentric reduction is a prerequisite of all osteotomies that redirect the acetabulum. Procedures that cut all three pelvic bones allow more displacement and, therefore, correction of acetabular dysplasia. The closer the osteotomy is to the acetabulum, the greater the coverage of the femoral head. Compared with the other acetabular osteotomies, the Ganz periacetabular osteotomy provides the greatest potential for correcting acetabular deficiency because there are no bone or ligamentous restraints to limit correction, but it has the disadvantage of being a technically demanding procedure. The amount of coverage provided by the Salter osteotomy is limited.

Unstable anterior and posterior pelvic ring injuries are amenable to percutaneous treatment if reduction is able to be obtained in a closed manner and appropriate radiographic visualization is able to be achieved. Proper SI screw placement is described using pelvic inlet, outlet, and lateral sacral images. The iliac cortical density seen adjacent to the SI joint is the anterior edge of the insertion safe zone, and is only able to be seen on the lateral image. Failure to place the screw behind this radiographic line would lead to an "in-out-in" screw (in the ilium, and then exiting anterior to the sacral ala, only to re-enter in the sacral body), which would cause direct injury to the L5 nerve root. Safe SI screw insertion in the S1 body should be underneath the sacral ala line to minimize risk of an "in-out-in" screw that would come out in the area of the ala and injure the L5 nerve root that sits directly on top of this structure.

DISCUSSION: When substantial lengthening of a dysplastic hip will occur because a high dislocation is relocated into a considerably lower acetabulum, a femoral shortening may be necessary to reduce the hip and avoid a stretch injury to the sciatic nerve. No other choice specifically addresses the need for femoral shortening, and high offset stems and lateralized liners may exacerbate the problem if used alone and without femoral shortening.

DISCUSSION: Of the pelvic ring injuries, APC type III have the highest rate of mortality, blood loss, and need for transfusion. They also have a high rate of urogenital injury and abdominal organ injury. Lateral compression injuries (especially type III) have the highest rate of head injury.

DISCUSSION: The lateral sacral view is used to place percutaneous iliosacral screws. Sacral alar morphology has been shown to be variable from patient to patient. Therefore, intraoperative fluoroscopy is recommended. During placement of the screws, the L5 nerve root is at risk. Routt et al (1997) examined the sacral slope and sacral alar anatomy in cadavers and a series of patients. They determined that the pelvic outlet and lateral sacral plain films provide the best plain radiographic view of the sacral ala. They recommended routine usage of these views intraoperatively to guide screw placement. Routt et al (2000) reported on the early complications of percutaneous placement of iliosacral screws for treatment of posterior pelvic ring disruptions. While technically challenging, this technique leads to less blood loss and lower rates of infection compared to traditional open techniques. Barei et al described methods of anterior and posterior pelvic ring disruptions. They determined that successful placement depends on accurate closed reduction, excellent intraoperative fluoroscopic imaging, and detailed preoperative planning. Early treatment decreased hemorrhage, provides patient comfort, and allows early mobilization.

The radiograph reveals an anterior posterior compression injury to the pelvic ring which is commonly seen after horseback riding injuries. In a large series of patients with this type of injury, 18 of 20 patients had sexual dysfunction after sustaining this injury. Posttraumatic osteoarthritis of the sacroiliac joints may occur, but is less common in this type of injury. Chronic low back pain, gait abnormalities, and quadriceps weakness are not typically seen with this type of injury.

DISCUSSION: In a report of more than 70 hips treated by surgical dislocation, iatrogenic osteonecrosis failed to develop in any of the hips. REFERENCE: Ganz R, Gill TJ, Gautier E, Ganz K, Krugel N, Berlemann U: Surgical dislocation of the adult hip: A technique with full access to the femoral head and acetabulum without the risk of avascular necrosis. J Bone Joint Surg Br 2001;83:1119-1124.

In a normal AP pelvis radiograph, the anterior rim of the acetabulum runs medially and distally, diverging from the posterior rim which runs much more vertically. In excessive acetabular retroversion, the anterior rim (bold line in Figure 33b) and posterior rim start laterally, and as these lines progress medially and distally, the anterior line crosses the posterior line. This predisposes to femoral acetabular impingement.

The Chiari osteotomy is recommended for patients with inadequate femoral head coverage and an incongruous joint. The osteotomy shortens the affected leg. It also medializes the hip's center of rotation. The osteotomy involves cutting the ilium at a spot above the acetabulum, which in effect abducts the acetabulum into a more vertical and medial position. The iliac wing then serves as a superior buttress. The most frequent complication of subsequent total hip arthroplasty is inadequate anterior and posterior coverage.

In APC pelvic fractures, the anterior ring disruption most commonly injures anterior branches of the internal iliac artery, particularly the internal pudendal and obturator arteries. Conversely, lateral compression or vertical shear fractures more commonly injure the superior gluteal artery.

For effective reduction and stabilization of the pelvic ring, a pelvic binder or sheet should be centered directly over the greater trochanters. Placement over the iliac crests or ASIS can paradoxically open the pelvic ring further in certain fracture patterns and provides less effective mechanical advantage.

APC II injuries involve symphyseal diastasis and disruption of the anterior sacroiliac (SI) ligaments, as well as the sacrotuberous and sacrospinous ligaments. The critical distinction is that the strong posterior SI ligaments remain intact, providing vertical stability but allowing rotational instability (the 'open book' pelvic injury). APC III involves disruption of both anterior and posterior SI ligaments, resulting in both rotational and vertical instability.

In an APC III injury, the symphysis is widely disrupted, and the hemipelvis is completely unstable due to tearing of the anterior SI, sacrotuberous, sacrospinous, and posterior SI ligaments. The iliolumbar ligament attaches the L5 transverse process to the iliac crest and is typically disrupted in vertical shear (VS) injuries, not classically in APC injuries.

The L5 nerve root courses directly over the anterior aspect of the sacral ala as it joins the lumbosacral trunk. It is highly susceptible to stretch injury during significant SI joint disruptions or iatrogenic injury during placement of iliosacral screws if they breach the anterior cortex of the sacral ala. Injury presents with weakness in ankle dorsiflexion and great toe extension (foot drop).

The Ficat and Arlet classification for osteonecrosis of the femoral head is as follows: Stage I has normal radiographs but abnormal MRI/bone scan; Stage II shows cystic/sclerotic changes on radiographs but a spherical head; Stage III is characterized by subchondral collapse, which is radiographically visible as the 'crescent sign'; Stage IV involves complete collapse of the femoral head with secondary degenerative changes in the acetabulum (joint space narrowing).