6.5 Acetabulum
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1 Introduction—epidemiology
Acetabular fractures commonly occur in young and active individuals involved with high-energy trauma, although the number of elderly patients with acetabular fractures has increased during the last few decades. Acetabular fractures result from indirect trauma, transmitted via the femur. They occur after a blow to the greater trochanter, to the flexed knee, or to the foot with the knee extended [1].
The treatment of acetabular fractures has rapidly evolved over the past three decades, leading to decreased morbidity and improved outcomes. To a great extent this can be attributed to the revolutionary techniques introduced by Judet and Letournel [2–4]. Accurate diagnosis and appropriate surgical approach, technique and instruments are essential to offer the patient the best chance of a good outcome.
2 Anatomy and classification
The hemipelvis is a complex 3-dimensional shape. The three primary bones that fuse at the triradiate cartilage and form the acetabulum are the ilium, ischium, and pubis. From its lateral aspect, the acetabulum is cradled by the arms of an inverted Y ( Fig 6.5-1 ).
The posterior column begins at the dense bone of the greater sciatic notch and extends distally through the center of the acetabulum to include the posterior wall of the acetabulum, ischial spine, and ischial tuberosity. The anterior column extends from the iliac crest to the symphysis pubis and includes the anterior wall of the acetabulum.
The superior articular surface is often referred to as the dome, roof or tectum. This dome extends from the strong bone just posterior to the anterior inferior iliac spine to the posterior column. This area provides the weight-bearing surface. The two columns cradle the acetabulum and meet medially to form the medial surface, the quadrilateral plate. It is best considered an accessory structure preventing medial displacement of the hip.
Judet and Letournel [2] proposed a classification system for acetabular fractures based on the anatomical concept that the acetabulum is composed of two pillars or columns and two walls, each termed anterior and posterior ( Fig 6.5-2 ). This classification system ( Fig/Animations 6.5-3 – 4 ) has five elemental fracture types and five associated fracture types. To define each fracture pattern, six fundamental radiological landmarks should be identified: the posterior wall of the acetabulum, the anterior wall, the roof (dome or tectum), the teardrop, the ilioischial line (posterior column) and the iliopectineal line (anterior column). The integrity of these lines should be evaluated not only in the AP view but also on the 45° oblique projections as described below ( Fig 6.5-5 ).
This system has also been incorporated into the more detailed AO/OTA Fracture and Dislocation Classification defining acetabular fractures as 62 and separating then into types A, B, and C ( Fig 6.5-6 ) [5].
Both the Letournel and the AO/OTA classifications have additional subgroups, which can be studied in more detail in the literature on acetabular fractures.
3 Evaluation and diagnosis
3.1 Examination
Life-threatening injuries take priority when treating a patient with an acetabular fracture. A secondary survey is mandatory as these high-energy fractures are often associated with pelvic ring and long-bone fractures, spinal and head trauma, and abdominopelvic visceral injuries, all of which are potentially fatal [4]. Contusions and abrasions in the area of the greater trochanter or iliac crest may herald the presence of a Morel-Lavallée lesion. This is an area of degloved skin with fluctuance due to a large underlying hematoma and fat necrosis. Although technically a closed injury, secondary bacterial contamination is common and surgical debridement and drainage is needed before definitive fracture care.
Rectal and vaginal examinations are mandatory to rule out the presence of an open fracture. Hematuria must be carefully assessed. Injuries to the superior gluteal artery can occur in association with fractures that enter the sciatic notch and this vessel may also be damaged during surgery [4]. This may result in life-threatening hemorrhage and patients with unexplained hemodynamic instability or a drop in hemaglobin level should have a computed tomographic (CT) scan with intravenous contrast or pelvic angiography. Hemorrhage may require urgent control by surgery or embolization.
An accurate neurological examination is mandatory.
Following a fracture of the acetabulum, the incidence of sciatic nerve compromise detected preoperatively ranges from 12–38% [6]. Because the peroneal division is most at risk, foot dorsiflexion and eversion should be tested and recorded in the medical records both before and after surgery.
An associated hip dislocation should be considered an orthopedic emergency and requires prompt reduction followed by evaluation of stability.
If there is any joint instability, traction is indicated. The traction weight should be no more than 1/6 of the patient′s body weight and applied skeletally if there is to be a delay before definitive surgery. Posterior hip dislocations are more common; the hip must be kept extended and externally rotated to assist in maintaining reduction.
3.2 Radiology
An AP view of the pelvis is required for all patients having sustained significant trauma. If an acetabular fracture is suspected, three additional views are necessary:
AP view of the involved hip ( Fig 6.5-5a–b ).
Iliac oblique view is used to assess the posterior column and anterior wall. The patient is rolled 45° toward the injured side. This provides a view of the iliac wing and a profile of the obturator ring ( Fig 6.5-5c–d ).
Obturator oblique view is used to assess the anterior column and posterior wall. The pelvis is rotated 45° toward the uninjured side, providing a view of the obturator ring, and a profile of the iliac wing ( Fig 6.5-5e–f ).
Axial ( Fig 6.5-7 ) and 3-D computed tomography (CT) improve understanding of the injury [7]. They are especially useful in measuring articular comminution and step off, the size and number of posterior wall fragments, marginal impaction, rotation and displacement of the columns, and the presence of intraarticular fragments or femoral head fractures. A CT scan can also identify injuries to the posterior aspect of the pelvis, such as sacroiliac joint disruption or a sacral fracture.
A better understanding of fracture line orientation will facilitate preoperative planning, surgical approach, reduction maneuvers, and proper placement of implants during surgery.
4 Surgical indications and decision making
The decision to proceed with nonoperative management versus surgical stabilization depends upon the personality of the injury [8]. Patient factors include age, comorbidities, mobility, and treatment of associated visceral and skeletal injuries. The soft tissues must be carefully examined and the fracture pattern evaluated by completion of all imaging studies necessary for preoperative planning. The surgical facilities and experience of the surgical team are also important factors. Surgery can be delayed for a few days to obtain all necessary information and allow transfer to the appropriate facility.
Indications for operative intervention include displacement of the articular surface, joint incongruity, and unacceptable roof arc measurements [8]. These indications are based on the principle that performing an accurate reduction of the articular surface to obtain a congruous hip joint will restore normal joint mechanics and reduce the risk of posttraumatic arthritis; long-term clinical outcomes closely correlate with the quality of the surgical reduction [4, 8–10]. Malreduction or subluxation of the hip joint will lead to abnormal loading of the articular cartilage and subsequent joint arthritis. It is generally accepted that displacement or incongruity greater than 1–2 mm is unsatisfactory [9–11].
Because most nondisplaced fractures will have a stable and concentric hip joint, surgery is not required. Nonoperative management is also indicated for some displaced fractures. These include:
Fractures not extending into the weight-bearing dome
Low anterior column fractures
Small (stable) posterior wall fractures not associated with a dislocation or not involving the posterosuperior portion of the acetabulum
Low transverse fractures with roof arc angles of more than 45° on all three radiographic views
Both-column fractures with secondary congruity in patients with low functional demand
5 Preoperative planning
5.1 Timing of surgery
Acute open reduction and internal fixation is rarely indicated. Exceptions to this include dislocations that cannot be reduced by closed means, an incarcerated intraarticular fragment following closed reduction, and unstable posterior dislocations that cannot be held in the reduced position because of the marked deficiency of the posterior wall. Progressive or sciatic nerve palsy that develops after reduction of the dislocation also should be considered a surgical emergency.
In all other circumstances, the timing of surgery is more dependent on stabilization of associated injuries, the completion of all imaging studies, and the availability of an experienced surgeon. A difficult procedure then can be performed on an elective basis with a more experienced operating team. Delays of over a week should be avoided if possible as anatomical reduction becomes progressively harder to obtain.
5.2 Preoperative preparation
Complete fracture images are mandatory for surgical planning. Prophylaxis for deep vein thrombosis [12] is effective but to date there is no evidence base that it is also effective in reducing the risk of fatal pulmonary embolism. It is appropriate to consider screening the pelvic veins with duplex ultrasound, magnetic resonance venography, or contrast enhanced CT scans in high-risk patients. When findings are positive, vena cava filter placement is indicated.
The patient is placed on a radiolucent operating table that allows intraoperative traction and image intensification. A urinary catheter is always used. An intraoperative cell saver permits recycling of about 20–30% of the effective blood loss and minimizes blood transfusion.
Nerve monitoring with both somatosensory-evoked potentials and electromyography may provide a degree of protective surveillance against intraoperative sciatic nerve injury. Although it has not been demonstrated that the use of nerve monitoring yields better results than appropriately performed surgery alone [6], intraoperative monitoring may prove most beneficial among less experienced surgeons.
5.3 Implant and instrument selection
The complex anatomy and fracture patterns of the pelvic ring and acetabulum has required the development of specific reduction tools and techniques. Usually reconstruction plates 3.5 and corresponding cortex screws (especially longer than 70 mm) are used in this area but larger size implants, like 4.5 or 6.5 mm screws, are sometimes required.
5.4 Operating room set-up
5.4.1 Kocher-Langenbeck approach (prone position)
The patient is prone on the radiolucent operating table, the knee flexed to reduce tension on the sciatic nerve. The exposed area from above the iliac crest of the injured side down to the foot and the leg draped free ( Fig 6.5-8 ).
The surgeon stands on the injured side of the patient and the assistant opposite the surgeon. The operating room personnel sets up adjacent to the surgeon. The image intensifier comes in from the side opposite the surgeon. The image intensifier display screen is placed in full view of the surgical team and the radiographer ( Fig 6.5-9 ).
5.4.2 Ilioinguinal appraoch (supine position)
The patient is supine on the radiolucent operating table, the exposed area from midthorax to include the whole abdomen and the lower limb of the injured side is draped free and prepped with the appropriate antiseptic ( Fig 6.5-10 ).
The surgeon stands on the injured side of the patient and the assistant opposite the surgeon. The operating room personnel set up adjacent to the surgeon. The image intensifier comes in from the side opposite the surgeon. The image intensifier display screen is placed in full view of the surgical team and the radiographer ( Fig 6.5-11 ).
6 Surgery
6.1 Surgical approaches
Thorough preoperative evaluation of the fracture will allow most acetabular fractures to be managed through a single surgical approach to either the front or back of the acetabulum [13].
For more complex fracture patterns involving both acetabular columns, the extended iliofemoral or a combined anterior and posterior approach may be necessary for exposure and reduction [3, 4, 14] although the requirement for this seems to decrease with surgical experience. Compared with single anterior or posterior approaches, extensile exposures involve greater patient morbidity, including increased operative time and blood loss, increased risk of infection, nerve injury, abductor weakness, joint stiffness, and heterotopic ossification [4, 14, 15]. The extensile approach may be preferred in the presence of nearby suprapubic catheters and colostomies, where infection rates with the ilioinguinal approach are high, and when surgical treatment of the acetabular fracture is delayed beyond 2–3 weeks [4].
The approach utilized is often dictated by the experience of the operating surgeon but should provide the greatest chance of anatomical reduction and stabilization of the joint surface.
6.1.1 Posterior: Kocher-Langenbeck
The patient may be positioned in the lateral decubitus position for posterior wall or column fractures but the weight of the leg often hinders the reduction of T-fractures, so prone positioning may be preferred in this instance ( Figs 6.5-8 – 9 ).
The maintenance of knee flexion (at 90°) and hip extension throughout the procedure reduces tension on the sciatic nerve.
The incision is centered over the posterior half of the greater trochanter, extends distally along the shaft of the femur for approximately 8 cm, and curves proximally toward the posterior superior iliac spine for another 8 cm ( Fig 6.5-12 ). The fascia lata and fascia over the gluteus maximus muscle are incised and the muscle gently split by blunt dissection. The sciatic nerve can consistently be identified along the medial aspect of the quadratus femoris fascia. A portion of the gluteus maximus insertion on the femur may require release to decrease tension.
The short external rotators, the piriformis, obturator internus, and the gemelli muscles are identified by internal rotation of the hip, tagged, and reflected from their femoral insertions. To protect the medial femoral circumflex artery, which provides the blood supply to the femoral head, they should be released 1.5 cm proximal to their insertion on the femur and the quadratus femoris muscle must not be violated. Retraction of the obturator internus tendon provides access to the lesser sciatic notch and protects the sciatic nerve, which passes superficially to the tendon. Retraction of the piriformis tendon provides access to the greater sciatic notch but fails to protect the sciatic nerve, which exits underneath the tendon. Blunt retractors are carefully placed into these two locations to provide a view of the entire retroacetabular surface. Care should be taken to identify and protect the superior gluteal neurovascular pedicle as it exits the greater sciatic notch. For fractures, such as high transtectal transverse or T-type fractures, an osteotomy of the greater trochanter is occasionally required to gain access to the superior weight-bearing surface of the acetabulum. However, this carries the disadvantage of potential nonunion and an increased risk of heterotopic ossification.
At closure, the external rotators are sutured to the cuff of tissue on the posterior aspect of the greater trochanter or are reattached through drill holes. If a release of the gluteus maximus insertion has been required, this too is repaired. Deep drains are placed as needed. The fascia lata and fascia over the gluteus maximus are repaired followed by the superficial closure.
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