Pelvic & Acetabular Trauma MCQs

In an APC-II injury, there is widening of the symphysis pubis > 2.5 cm, with tearing of the anterior sacroiliac (SI) ligaments, sacrotuberous, and sacrospinous ligaments. The posterior SI ligaments remain intact, providing vertical stability but allowing rotational instability ('open book'). An APC-III injury involves disruption of both anterior and posterior SI ligaments.

An APC II injury involves disruption of the anterior sacroiliac ligaments with an intact posterior SI hinge. An APC III injury implies complete dissociation of the hemipelvis due to concurrent disruption of the robust posterior sacroiliac ligaments, severely increasing pelvic volume and instability.

Anteroposterior compression (APC) injuries, specifically APC-II and APC-III (open book pelvis), are associated with a significant increase in pelvic volume and major disruption of the posterior venous plexus and branches of the internal iliac artery. APC-III injuries, which involve complete disruption of the anterior and posterior sacroiliac ligaments (complete spinopelvic dissociation), historically carry the highest risk for massive, life-threatening retroperitoneal hemorrhage.

While arterial bleeding (such as from the superior gluteal or internal pudendal arteries) can cause rapid, life-threatening exsanguination and is the target for pelvic angioembolization, the most common overall source of hemorrhage in pelvic ring fractures is venous bleeding from the presacral venous plexus and the exposed cancellous bone surfaces. This low-pressure bleeding is typically managed initially by reducing pelvic volume (e.g., pelvic binder) to promote tamponade.

Chronic Morel-Lavallée lesions develop a fibrous pseudocapsule that prevents fluid resorption. Definitive treatment requires excision of this capsule via open debridement, frequently combined with sclerodesis.

A Morel-Lavallée lesion is a closed degloving injury caused by severe shearing forces that separate the skin and subcutaneous tissue from the underlying deep fascia. This tears the trans-fascial perforating vessels, leading to a hemolymphatic fluid collection.

A pelvic binder or sheet must be centered over the greater trochanters to effectively reduce pelvic volume and stabilize the pelvic ring. Placement over the iliac crests is incorrect and can paradoxically worsen pelvic opening or fail to control hemorrhage.

To effectively reduce pelvic volume and provide stability in an open-book pelvic ring injury (such as an APC-III), a pelvic binder must be applied directly over the greater trochanters. Placement over the iliac crests or ASIS can paradoxically open the pelvis further or fail to provide adequate closure of the posterior ring.

Anteroposterior Compression Type III (APC III) injuries are characterized by complete disruption of the anterior ring (symphysis diastasis) AND complete disruption of the posterior ring, including both the anterior AND posterior sacroiliac ligaments. This results in complete hemipelvic instability (external rotation). The key distinguishing factor between APC II and APC III is the disruption of the posterior SI ligaments in APC III. While it mentions vertical displacement, the primary vector described by the 4cm diastasis and complete anterior/posterior widening fits an APC III. (Note: True vertical shear requires cranial displacement of the hemipelvis, but extreme APC forces cause massive diastasis and total SI disruption).

In the Young-Burgess classification, APC-II injuries involve a disrupted symphysis pubis (or vertical rami fractures) along with disruption of the anterior sacroiliac, sacrotuberous, and sacrospinous ligaments, while the posterior sacroiliac ligaments remain intact (opening of the anterior SI joint). An APC-III injury involves the additional complete disruption of the posterior sacroiliac ligaments, leading to complete hemipelvic instability.

An APC-III injury involves complete anterior and posterior disruption. This includes the symphysis pubis, the sacrotuberous/sacrospinous ligaments, and both the anterior and posterior sacroiliac ligaments, leading to complete global instability.

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.

DISCUSSION: When a trochanteric osteotomy is performed with the desire to maintain vascularity to the femoral head, as in the approach for a surgical hip dislocation, the deep branch of the medial femoral circumflex artery must be maintained. This branch courses along the posterior aspect of the greater trochanter, posterior to the tendon of obturator externus, and anterior to the tendons of superior gemellus, obturator internus, and inferior gemellus. It perforates the capsule above the superior gemellus and distal to the tendon of piriformis, before dividing into two to four terminal retinacular branches. Maintaining the attachment of the external rotators maintains the blood supply to the femoral head. Additionally, the superior-lateral retinacular vessels must also be maintained during femoral neck osteoplasty.

In pelvic ring injuries, particularly those involving disruption of the posterior elements (like APC-III and vertical shear patterns), the most common source of major hemorrhage is venous bleeding, accounting for up to 80% of cases. The presacral venous plexus and prevesical venous plexus are the primary venous sources. Arterial bleeding (e.g., superior gluteal, internal pudendal) accounts for approximately 10-20% of cases.

To effectively reduce pelvic volume in an open-book (Anteroposterior Compression) pelvic ring injury, a pelvic binder or sheet must be centered directly over the greater trochanters. Placing the binder too proximally over the iliac crests is a common error that can paradoxically widen the pelvic outlet or fail to adequately close the symphyseal diastasis.

Discussion for questions 77 and 78: It has been demonstrated on a cadaver model that screw fixation of moderate and severe slipped capital femoral epiphyses may result in screw impingement upon the acetabulum and labrum. This is likely when the screw head on the anteroposterior view is seen to lie medial to the intertrochanteric line. Femoral artery pseudoaneurysm has been reported when the screws are left long (projecting far from the bone) to ease removal. Chondrolysis is associated with persistent penetration into the hip joint; both screws stop well short of the articular surface. Many in vitro studies of slip models have demonstrated increased strength of construct of two screws compared to one, although the clinical relevance can be questioned. The radiographs show the screw heads firmly in the femoral head, with loss of fixation in the femoral neck. Sanders and associates reported a series of 7 such failures and hypothesized that acute-on-chronic slips may develop osteopenia of the femoral neck. All patients reported continued pain postoperatively rather than the relief typically seen following surgical stabilization of the epiphysis. There is no radiographic evidence of osteonecrosis or chondrolysis.

Pelvic binders are most effective at reducing pelvic volume and stabilizing the ring when centered directly over the greater trochanters. Placement over the iliac crests is a common error and provides suboptimal reduction.

The obturator oblique view of the pelvis profiles the anterior column and the posterior wall of the acetabulum. Conversely, the iliac oblique view profiles the posterior column and the anterior wall.

The clinical presentation describes a Morel-Lavallée lesion, which is a closed degloving injury. It is characterized by the traumatic separation of the subcutaneous fat and skin from the underlying deep fascia. This creates a potential space that fills with blood, lymph, and necrotic fat (hemolymphatic fluid). If unrecognized or improperly treated, it carries a high risk of soft tissue necrosis and deep infection.

To effectively reduce pelvic volume and provide hemostasis in an 'open book' (APC) pelvic ring injury, a pelvic binder or sheet must be centered directly over the greater trochanters. This directs the compressive force through the femoral heads and into the acetabula, effectively closing the anterior diastasis at the pubic symphysis and reducing the posterior sacroiliac joints. Placing the binder higher (e.g., iliac crests) can actually flare the true pelvis and exacerbate the deformity.