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Pelvic & Acetabular Trauma MCQs

Practice Set 8 of 35

This practice set contains high-yield board review questions covering key concepts in Pelvic & Acetabular Trauma. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 141

Topic: Pelvic & Acetabular Trauma

A 7-year-old male presents with a complex left hip deformity following a prior Salter osteotomy for severe Developmental Dysplasia of the Hip (DDH). Preoperative planning requires establishing a reliable pelvic horizontal reference line. On the AP pelvis radiograph, the triradiate cartilages appear asymmetric due to premature closure on the previously operated side. Which of the following anatomical landmarks is the MOST reliable for establishing the pelvic horizontal line in this specific patient?

. Iliac crests
. Acetabular teardrops
. Center of the triradiate cartilages
. Inferior aspects of the sacroiliac (SI) joints
. Superior margins of the pubic symphysis

Correct Answer & Explanation

. Inferior aspects of the sacroiliac (SI) joints

Explanation

Correct Answer: DThe case explicitly states that in skeletally immature patients, the triradiate cartilage is an excellent landmark,provided the pelvis has not been subjected to a prior osteotomy or asymmetric premature closure. In complex revision cases, such as this patient with a prior Salter osteotomy leading to asymmetric triradiate cartilages, the surgeon must abandon the triradiate cartilage and revert to the more stable, universally applicable adult landmarks: the inferior SI joints or the sacral foramina. The inferior SI joints are described as the 'Gold Standard' due to their robustness, central location, and minimal affection by lateralized acetabular or iliac wing pathology. Iliac crests and acetabular teardrops are often distorted by the primary pathology or previous surgeries. The pubic symphysis is less reliable for a horizontal reference due to its variability and potential for rotation.

Question 142

Topic: Pelvic & Acetabular Trauma
In patients with Crowe types III and IV developmental dysplasia of the hip with high hip centers, acetabular reconstruction often requires lowering the acetabular component into the native acetabulum. In doing so, considerable risk for limb lengthening beyond 4 cm exists, making the hip difficult to reduce and raising the risk for nerve injury. Which technique is used to overcome this problem?
. Subtrochanteric osteotomy with femoral shortening
. An offset femoral component
. A lateralized liner
. Extended trochanteric osteotomy

Correct Answer & Explanation

. Subtrochanteric osteotomy with femoral shortening

Explanation

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.

Question 143

Topic: Pelvic & Acetabular Trauma
Figures 28a through 28c show the MRI scans of a 30-year-old woman who weighs 290 lb and has low back and left leg pain. She also reports frequent urinary dribbling, which her gynecologist has advised her may be related to obesity. Examination will most likely reveal
. ipsilateral weakness of the tibialis anterior.
. ipsilateral weakness of the peroneus longus and brevis.
. ipsilateral weakness of the extensor hallucis longus.
. a positive Beevor’s sign.
. a positive ipsilateral Gaenslen’s sign.

Correct Answer & Explanation

. ipsilateral weakness of the tibialis anterior.

Explanation

DISCUSSION: The patient will most likely exhibit ipsilateral weakness of the tibialis anterior. Gaenslen’s test is designed to detect sacroiliac inflammation as a source of low back pain. Beevor’s sign tests the innervation of the rectus abdominis and paraspinal musculature (L1 innervation). The extensor hallucis longus is predominantly innervated by L5. The peroneals are predominantly innervated by S1. REFERENCES: Hoppenfeld S: Physical Examination of the Spine and Extremities. Appleton, WI, Century-Crofts, 1976. Hollinshead WH (ed): Anatomy for Surgeons: The Back and the Limbs, ed 3. Philadelphia, PA, Harper & Rowe, 1982.

Question 144

Topic: Pelvic & Acetabular Trauma
Iliosacral screws placed for stabilization of posterior pelvic ring injuries (e.g., sacroiliac dislocation) that exit the sacrum anteriorly are most likely to injure which of the following structures?
. L4 nerve root
. L5 nerve root
. S1 nerve root
. Internal iliac artery
. External iliac artery

Correct Answer & Explanation

. L5 nerve root

Explanation

DISCUSSION: Iliosacral screws have gained popularity for posterior stabilization of pelvic ring disruptions, but complications attributed to incorrect placement are a clinical problem. The L5 nerve root is at greatest risk and is in closest proximity to a malpositioned screw (exiting the sacrum). The L4 root is more anterior at this level. The S1 root is still intraosseous at this level and is at risk but not from the screw exiting anteriorly at this level. The arteries are at risk but are more anterior and are at less risk than the L5 nerve root. REFERENCE: Ebraheim NA, Haman SP, Xu R, Stanescu S, Yeasting RA: The lumbosacral nerves in relation to dorsal SI screw placement and their locations on plain radiographs. Orthopedics 2000;23:245-247.

Question 145

Topic: Pelvic & Acetabular Trauma
In the treatment of acetabular dysplasia, what type of pelvic osteotomy leaves the teardrop in its original position and redirects the acetabulum?
. Steel
. Chiari
. Ganz periacetabular
. Dial or spherical
. Salter innominate

Correct Answer & Explanation

. Dial or spherical

Explanation

DISCUSSION: The dial or spherical osteotomy leaves the medial wall or teardrop in its original position and, as a result, is intra-articular. The other pelvic osteotomies (except Chiari) redirect the acetabulum, including the medial wall. The Chiari osteotomy improves coverage without redirecting the acetabulum within the pelvis, and it leaves the teardrop in the same place.

Question 146

Topic: Pelvic & Acetabular Trauma
A 40-year-old male is brought to the trauma bay following a motorcycle collision. He is hypotensive with a mechanically unstable anteroposterior compression (APC-III) pelvic ring injury. A pelvic binder is applied. To optimally reduce pelvic volume and stabilize the fracture, the binder should be centered over which of the following anatomical landmarks?
. Iliac crests
. Greater trochanters
. Anterior superior iliac spines
. Pubic symphysis
. Sacral promontory

Correct Answer & Explanation

. Greater trochanters

Explanation

Pelvic binders are most effective at reducing pelvic volume and controlling hemorrhage when centered directly over the greater trochanters. Placement over the iliac crests is less effective and may inadvertently cause paradoxical widening of the pelvic ring.

Question 147

Topic: Pelvic & Acetabular Trauma
According to the Young-Burgess classification, which of the following injury patterns is the anatomical hallmark of an Anteroposterior Compression Type III (APC III) pelvic ring injury?
. Symphysis diastasis < 2.5 cm with intact posterior ligaments
. Symphysis diastasis > 2.5 cm with disrupted anterior SI ligaments but intact posterior SI ligaments
. Complete disruption of both the anterior and posterior sacroiliac ligaments
. Sacral fracture with spinous process avulsion
. Internal rotation of the hemipelvis with a compression fracture of the anterior sacrum

Correct Answer & Explanation

. Complete disruption of both the anterior and posterior sacroiliac ligaments

Explanation

An APC III injury is characterized by the complete disruption of the anterior sacroiliac (SI) ligaments, the sacrospinous and sacrotuberous ligaments, AND the posterior SI ligaments. This results in complete global (rotational and vertical) pelvic instability.

Question 148

Topic: Pelvic & Acetabular Trauma

A patient with an unstable pelvic ring injury has just undergone an emergent laparotomy and currently has a packed abdomen. Stabilization of the pelvic ring is performed with an anterior external fixator. What is an advantage of using an external fixator with pins in the iliac crest rather than pins in the anterior inferior iliac spine?

. Greater pelvic ring stability
. Lower risk of pin tract infection
. Less reliance on fluoroscopy for pin placement
. Better ability to control a posterior pelvic injury
. Less likely to interfere with future incisions for definitive pelvic internal fixation

Correct Answer & Explanation

. Greater pelvic ring stability

Explanation

There are relative advantages to both types of these external fixators. A frame based on the iliac crest is oftentimes easier to place rapidly because it is less dependent on fluoroscopy. This is also advantageous in this clinical scenario because the patient may not be on a radiolucent table. A frame with pins in the anterior inferior iliac spines may be advantageous in that the pin sites will be away from any future needed incisions if an ilioinguinal approach is needed. There is, however, a higher risk of lateral femoral cutaneous nerve injury or intra-articular pin placement at the hip joint with this frame configuration. This technique is generally more dependent on fluoroscopy for pin placement. Some biomechanic studies have shown advantages to AIIS-based frames but this does not give a definite clinical advantage because neither frame alone is adequate to definitively treat an unstable associated posterior pelvic ring injury. There is no known difference in pin site infection rates between these frame types.

Question 149

Topic: Pelvic & Acetabular Trauma

Anterior penetration of an iliosacral screw through the sacral ala would most likely lead to weakness of which of the following movements?

. Hip flexion
. Hip adduction
. Knee extension
. Ankle plantarflexion
. Great toe dorsiflexion

Correct Answer & Explanation

. Great toe dorsiflexion

Explanation

DISCUSSION: Penetration of an iliosacral screw through the sacral ala would injure the ipsilateral L5 nerve root (great toe dorsiflexion). This can be avoided with proper understanding of the sacral anatomy as well as iliosacral screw starting points. The three required views for placement of this screw are: lateral sacral, pelvic inlet, and pelvic outlet. The referenced study by Ziran et al is an excellent review of fluoroscopic evaluation of screw placement. They reported that the anterior border of the S1 body is best seen with overlap of the S1 and S2 anterior cortex while the superior aspect of the S1 foramen is best seen with overlap of the S2 foramen on the superior pubic ramus.The referenced study by Routt et al reviewed 177 patients with pelvic ring injuries treated with these screws and found that quality triplanar imaging decreased intraoperative and postoperative complications. They also recommend supplemental fixation of iliosacral screws with posterior plating in noncompliant patients.

Question 150

Topic: Pelvic & Acetabular Trauma

The primary purpose of obtaining the radiograph shown in Figure 9 is to assess

. the anterior column of the acetabulum.
. the acetabular rim.
. the os acetabulae.
. anterior coverage of the femoral head.
. femoral anteversion.

Correct Answer & Explanation

. the anterior column of the acetabulum.

Explanation

DISCUSSION: The radiograph shows a faux profil view of the hip.  The primary purpose of this view is to evaluate anterior coverage of the femoral head.REFERENCES: Beaty JH (ed): Orthopaedic Knowledge Update 6.  Rosemont, IL, American Academy of Orthopaedic Surgeons, 1999, pp 455-492.Ganz R, Klaue K, Vinh TS, Mast JW: A new periacetabular osteotomy for the treatment of hip dysplasias: Technique and preliminary results.  Clin Orthop 1988;232:26-36.Lequesne M, deSez S: Le faux profil du bassin: Nouvelle incidence radiographique pour l’etude de la hance.  Son utilite dans les dysplasies et les differentes coxopathies.  Rev Rhum Mal Osteoartic 1961;28:643.

Question 151

Topic: Pelvic & Acetabular Trauma

The infection work-up is negative. What is the best next step?

. Revision of the acetabulum and evaluation of the femoral stem
. Conversion to a constrained liner
. Gluteus medius repair and application of a hip abductor brace
. Revision to an elevated acetabular polyethylene liner

Correct Answer & Explanation

. Revision of the acetabulum and evaluation of the femoral stem

Explanation

DISCUSSION:The cross-table lateral radiograph shows that the patient has decreased acetabular anteversion. She is likely impinging on her cup in flexion and levering the femoral component posteriorly. Given a well-fixed and well-aligned femoral component and a negative infection work-up, the preferred treatment is to revise the acetabulum with a goal of increasing acetabular anteversion to avoid prosthetic impingement. Conversion to a constrained or elevated rim liner is suboptimal in this setting, because the problem is impingement. Indications for a constrained liner are neuromuscular compromise, abductor deficiency, or instability despite well-fixed and well-placed components. Given her 5 of 5 abductor strength, gluteus medius repair is not indicated.

Question 152

Topic: Pelvic & Acetabular Trauma
Figure 36 shows the hip arthrogram of a newborn. Which of the following structures is enclosed by the circle?
. Limbus
. Pulvinar
. Ligamentum teres
. Transverse acetabular ligament
. Acetabular labrum

Correct Answer & Explanation

. Acetabular labrum

Explanation

DISCUSSION: The structure enclosed by the circle is the acetabular labrum. It is visible as the white point of tissue outlined by the darkly radiopaque contrast. The appearance of the contrast surrounding the sharp white point of a normal labrum is called the “rose thorn sign.” The limbus is the term reserved for a rounded, infolded labrum seen with arthrography. The pulvinar is the fatty tissue seen in the empty acetabulum when the hip is dislocated. The ligamentum teres is seen as a white stripe outlined by contrast coursing from the central acetabulum to the dislocated femoral head. The transverse acetabular ligament courses across the inferior portion of the acetabulum and is not clearly seen with arthrography. REFERENCES: Herring JA: Tachdjian’s Pediatric Orthopaedics, ed 3. Philadelphia, PA, WB Saunders, 2002, vol 1, pp 532-533. Severin E: Contribution to the knowledge of congenital dislocation of the hip joint. Acta Chir Scand 1941;84:1.

Question 153

Topic: Pelvic & Acetabular Trauma

A 35-year-old man who has had a 6-month history of low back pain and tenderness now reports worsening pain and stiffness in the hips and entire back. An AP radiograph of the pelvis demonstrates fusion of the sacroiliac joints bilaterally. What is the next most appropriate step in management? Review Topic

. Anesthetic injections in both sacroiliac joints
. Sacroiliac fusion with plate fixation
. Anti-inflammatory medications, physical therapy, and HLA-B27 testing
. Patient reassurance and follow-up as needed
. Immediate bilateral sacroiliac joint aspiration and culture

Correct Answer & Explanation

. Anesthetic injections in both sacroiliac joints

Explanation

The patient has a classic presentation of early ankylosing spondylitis. Sacroiliac joint fusion is the earliest radiographic finding and is typically followed by cephalad spinal progression. Early treatment of ankylosing spondylitis consists of nonsteroidal anti-inflammatory drugs and physical therapy to preserve spinal motion. HLA-B27 testing is positive in most (about 95%) patients; however, it is not pathognomonic because it can be positive with other conditions. Considering the progressive nature of thisdisease, further work-up in a patient with potential ankylosing spondylitis is not warranted. Sacroiliac joint anesthetic injections and sacroiliac fusion are not recommended treatments for early ankylosing spondylitis. Aspiration of the sacroiliac joints can be done if sacroiliac joint infection is suspected; however, in the absence of fever or other constitutional symptoms, infection is unlikely.

Question 154

Topic: Pelvic & Acetabular Trauma
A patient with severe rheumatoid arthritis reports progressive hip pain. Serial hip radiographs will most likely show which of the following findings?
. Asymmetric joint space narrowing
. Sacroiliac joint ankylosis
. Progressive superior and lateral migration of the femoral head
. Periarticular osteopenia
. Hip synovitis

Correct Answer & Explanation

. Periarticular osteopenia

Explanation

DISCUSSION: Radiographic findings in patients with rheumatoid arthritis include symmetric joint space narrowing, periacetabular and femoral head erosions, and diffuse periarticular osteopenia. In advanced stages, protrusio acetabuli is a common finding. Ranawat and associates have shown a rate of superior femoral head migration of 4.5 mm per year and medial (axial) migration of 2.5 mm per year. Asymmetric joint space narrowing is a classic radiographic finding of degenerative arthrosis. Sacroiliac joint ankylosis commonly occurs in ankylosing spondylitis. Hip synovitis is a pathologic diagnosis, not a radiographic finding. REFERENCES: Lachiewicz PF: Rheumatoid arthritis of the hip. J Am Acad Orthop Surg 1997;5:332-338. Stuchin SA, Johanson NA, Lachiewicz PF, Mont MA: Surgical management of inflammatory arthritis of the adult hip and knee, in Zuckerman JS (ed): Instructional Course Lectures 48. Rosemont, IL, American Academy of Orthopaedic Surgeons, 1999, pp 93-109.

Question 155

Topic: Pelvic & Acetabular Trauma
In patients with Crowe types III and IV developmental dysplasia of the hip with high hip centers, acetabular reconstruction often requires lowering the acetabular component into the native acetabulum. In doing so, considerable risk for limb lengthening beyond 4 cm exists, making the hip difficult to reduce and raising the risk for nerve injury. Which technique is used to overcome this problem?
. Subtrochanteric osteotomy with femoral shortening
. An offset femoral component
. A lateralized liner
. Extended trochanteric osteotomy

Correct Answer & Explanation

. Subtrochanteric osteotomy with femoral shortening

Explanation

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.

Question 156

Topic: Pelvic & Acetabular Trauma

Which of the following descriptions is true regarding APC-II (anterior-posterior compression) pelvic injuries as classified by Young and Burgess?

. Pubic symphysis diastasis, intact anterior sacroiliac ligaments, intact sacrotuberous ligament, intact posterior sacroiliac ligaments
. Pubic symphysis diastasis, torn anterior sacroiliac ligaments, intact sacrotuberous ligament intact posterior sacroiliac ligaments
. Pubic symphysis diastasis, intact anterior sacroiliac ligaments, torn sacrotuberous ligament, intact
. posterior sacroiliac ligaments
. Pubic symphysis diastasis, torn anterior sacroiliac ligaments, torn sacrotuberous ligament, intact posterior sacroiliac ligaments
. Pubic symphysis diastasis, intact anterior sacroiliac ligaments, torn sacrotuberous ligament, torn posterior sacroiliac ligaments

Correct Answer & Explanation

. Pubic symphysis diastasis, intact anterior sacroiliac ligaments, intact sacrotuberous ligament, intact posterior sacroiliac ligaments

Explanation

DISCUSSION: APC II injuries are unstable injuries and occur as a result of high-energy trauma. Anatomic structures which are injured or torn include the pubic symphysis, anterior iliosacral ligaments, and the sacrotuberous ligaments. The posterior sacroiliac ligaments are spared in APC-II injuries, and differentiate an APC-II injury from an APC-III injury, in which the posterior ligaments are also torn.Burgess et al review the classifications of pelvic ring disruptions and their association with mortality. They concluded that APC injuries required more blood replacement and were related to death more often than lateral compression, vertical shear, or combined mechanism pelvic injuries.Tile studied the anatomy of anterior to posterior pelvic ring injuries. Although the anterior structures, the symphysis pubis and the pubic rami, contribute to 40% to the stiffness of the pelvis, clinical and biomechanical studies have shown that the posterior sacroiliac complex is more important to pelvic-ring stability. The posterior sacroiliac ligamentous complex is more important to pelvic-ring stability than the anterior structures and therefore, the classification of pelvic fractures is based on the stability of the posterior lesion.

Question 157

Topic: Pelvic & Acetabular Trauma
In hip arthroplasty, the location of the medial femoral circumflex artery is best described as:
. superior to the piriformis tendon.
. superior to the anterior rim of the acetabulum.
. deep to the transverse acetabular ligament.
. deep to the quadratus femoris muscle.
. within the substance of the gluteus minimus.

Correct Answer & Explanation

. deep to the quadratus femoris muscle.

Explanation

The obturator artery lies closest to the transverse acetabular ligament. The femoral artery is closest to the anterior rim of the acetabulum. No named vessel lies within the substance of the gluteus minimus or superior to the piriformis tendon. The medial femoral circumflex artery lies medial or deep to the quadratus femoris muscle.

Question 158

Topic: Pelvic & Acetabular Trauma
  • Which of the following radiographic views best shows the size and displacement of a posterior wall fracture of the acetabulum?
. Inlet view of the pelvis
. Outlet view of the pelvis
. AP view of the hip
. Ilial oblique view (external oblique) of the hip
. Obturator oblique

Correct Answer & Explanation

. Obturator oblique

Explanation

This view best reveals the posterior acetabular wall and the anterior column of the pelvis. This view is best taken by elevating the affected hip 45 degrees to the horizontal by means of a wedge and directing the beam through the hip joint with a 15 degree upward tilt. The inlet view best delineates posterior displacement of the hemipelvis. The outlet view best views the sacrum, the sacroiliac joints, and the sacral foramina, caudad and cephalad displacement as well. The standard AP radiograph is used in the initial trauma series as a screening tool. Ilial oblique views best view the anterior wall of the acetabulum and the posterior column of the pelvis.

Question 159

Topic: Pelvic & Acetabular Trauma
Which of the following illustrations shown in Figures 21a through 21e correctly shows the projection of the sacroiliac joint on the outer table of the ilium?
. 21a
. 21b
. 21c
. 21d
. 21e

Correct Answer & Explanation

. 21c

Explanation

DISCUSSION: The projection of the sacroiliac joint on the outer surface of the ilium should be well understood to avoid violation of the joint during bone graft harvesting and to help in insertion of the screw across the joint. The sacroiliac joint has superior and inferior limbs. The average lengths of the superior and inferior limbs are 4.4 cm and 5.6 cm, respectively. The average width of each limb is 2.0 cm. The average distance from the longitudinal axis of the superior limb to the posterior superior iliac spine is 5.5 cm. The average longitudinal axis of the inferior limb is 1.2 cm superior to the inferior margin of the posterior inferior iliac spine. The average angle between the two axes is 93 degrees. Figure 21c most closely shows the projection of the sacroiliac joint on the outer table of the ilium.

Question 160

Topic: Pelvic & Acetabular Trauma
Based on the Young and Burgess classification of pelvic ring injuries, an anterior-posterior compression type II injury does not result in disruption of which of the following?
. pubic symphysis
. anterior sacroiliac ligaments
. posterior sacroiliac ligaments
. sacrospinous ligament
. sacrotuberous ligament

Correct Answer & Explanation

. posterior sacroiliac ligaments

Explanation

An APC type I involves slight widening of pubic symphysis and/or anterior sacroiliac (SI) joint. An APC II is a continuation of this force, and additionally involves a disrupted anterior SI joint, as well as sacrotuberous and sacrospinous ligaments. An APC III also involves disrupted posterior SI ligaments, causing complete SI joint disruption with potential translational and rotational displacement. An APC-II pelvic ring injury involves injury to all of these structures except the posterior sacroiliac ligaments.

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