2.11.1 Cerclage wires and cable fixation for an acetabular fracture
1 Introduction
The conventional application of pelvic and acetabular screw fixation is sometimes hampered by markedly osteopenic bone, comminution, or peculiar orientation of the fracture. Pelvic bone consists of three layers of bone: two thin layers of dense cortical bone separated by a thicker layer of cancellous bone. A cancellous bone screw achieves its principal fixation by anchoring into the cancellous layer and potentially by fixation in a thicker layer of distal cortex. As osteopenia progressively compromises the structural integrity of the pelvis, the cancellous layer softens so that a screw achieves steadily less fixation in bone. The outer layers of cortical bone diminish in thickness, which further compromises screw fixation. In this situation, a cerclage wire engages the densest surface of available bone to optimize fixation [1].
Effective screw fixation also is markedly impeded by certain structural features of the acetabulum. For example, in the medial eminence of the acetabulum the principal central portion of the bone is extraordinarily thin. Although thickness varies by patient, the medial eminence typically is less than 3 mm. In the presence of an acetabular fracture, such as a typical T-type injury in which the central acetabular region is comminuted, effective screw fixation may be compromised by limitations of the available bone [2]. Another example is the anterior column, anterior wall, or quadrilateral surface fracture pattern [3]. This injury generally occurs in elderly patients with osteopenia who land on the outside of the ipsilateral hip in a simple fall. The large displaced quadrilateral surface fragment is separated from all thicker portions of the acetabulum. The fragment usually is displaced in a hinge-like fashion from the base of the intact rim of quadrilateral surface with maximum superior displacement. A third example is a comminuted segment of acetabulum in a thin portion of the bone. In all three situations, the use of one or more cables in a cerclage fashion may be an effective form of fixation. Cerclage wire fixation can be applied as a rapid technique for both reduction and fixation of an acetabular fracture [4]. In selective clinical situations, application of cerclage wires may be a valuable time saver compared with screw and plate fixation.
A somewhat similar fixation technique involves the use of braided cables [5]. Compared with a wire used for fixation, a cable possesses superior tensile strength, notch susceptibility, and fatigue life. When a cable is used as a reduction tool, it can be progressively tightened to approximate the fracture. Another attribute of a cable is its ability to be tightened and released for repetitive tightening. If the initial reduction is not properly aligned, the tension on the cable can be released so that the reduction can be repeated with the use of an altered position of the cable and potentially a modification in the alignment of bone reduction forceps. A wire used as a tool for reduction is limited to a single tightening. If the reduction is not properly aligned, the wire has to be removed and replaced. Another asset of a braided cable is that its outside diameter is larger than that of a 16- or 18-gauge wire. In the presence of markedly osteopenic bone, the larger diameter of the cable has superior load-sharing capabilities compared with that of a wire. With the use of a cable, tightening is less likely to provoke its displacement into the osseous surface. Multiple cabling systems are accompanied by a tool kit with effective passage and tightening instruments. Some specialized cable-passing instruments have been adapted to facilitate safe passage of a cable along the inner pelvic wall to minimize the risk of associated neurovascular injury.
2 Instrumentation for cable fixation of the acetabulum
2.1 Braided cables and wires and tightening instrumentation
Various commercially available braided cables and 16- or 18-gauge wire can be used to immobilize an acetabular fracture. Single-strand stainless steel wire is readily available and has a modest degree of intrinsic stiffness that may permit passage of the material across shorter distances without use of a passing tool. The wire can be braided to form a stiffer material with improved strength. A favored application for a cerclage wire is a transverse fracture in which the posterior end of the fracture extends high into the greater sciatic notch. The wire can be positioned deep to a bone plate, augmenting fixation even after the plate has been positioned on the bone. This attribute of a wire permits its application in a secondary way as a supplement to a plate, both to improve the reduction and augment the fixation. However, the wire is vulnerable to inadvertent kinking that may weaken it or impede optimal placement and positioning. When tightening a wire by twisting the two free ends, meticulous technique is needed in which a symmetrical twist is created to optimize the force of tightening. When the wire begins to change from a metallic luster to a whitish sheen the tightening must be stopped before the wire breaks, causing a premature loss of fixation. A braided cable has a free sleeve to apply to the cable after it has been passed. The free cable permits independent passage of both ends with passing tools. When a cable is passed through multiple foramina (ie, the greater and lesser sciatic notches and the obturator foramen), the passage of each end of the cable markedly simplifies the procedure.
2.2 Cable-passing tools
A cable passer is essential to permit controlled passage of the cable along the opposing surface of the pelvis. If the surgical exposure provides direct visualization of the outer pelvic table, then the passing tool is needed to advance the cable along the inner pelvic table ( Fig 2.11.1-1 ). With an ilioinguinal approach, the cable passer is used to pass the cable along the outer pelvic table. Traditional cable passers consist of curved metallic tubes with a hemispherical configuration and an ergometrically suitable handle. A cable is passed through the tubular part of the tool. Various diameters of cable passers are available for application around tubular bones of varied diameters. Such a configuration, however, is suboptimal for use on the pelvis. When the hemispherical style of the passer is manipulated from the inner table to the outer, or vice versa, the passer protrudes extensively into the soft tissues, potentially causing an iatrogenic injury such as a neurovascular injury or impalement of an intraabdominal organ. As a replacement for a conventional cable passer, a Statinski vascular clamp was modified to grasp a cable [5]. The Statinski design has multiple angles rather than a continuous curved profile. These angulations permit the close approximation of the cable passer to the pelvic table, thereby minimizing the risk of iatrogenic injury to neighboring soft tissues. The jaws of the modified Statinski clamps were reconfigured with cylindrical recesses so that a cable could be firmly gripped ( Fig 2.11.1-2 ). Larger and smaller Statinski clamps were modified for application on various regions of the pelvis and acetabulum.
2.3 Tightening of a cable
For tightening of the original free braided cable, a tensioning device grips both ends of the cable and imposes a symmetrical tensile load. This type of tension device is bulky; thus, a substantial surgical exposure is required. The principal sites that provide sufficient exposure are the roof of the acetabulum or the adjacent high posterior column. Most recent cabling instrumentation devices use a cable with a beaded end to support the sleeve. This type of cable can be passed solely from the nonbeaded end that fits into a passer. The ability to pass a single end of the cable is a disadvantage for complex cable passing through multiple foramina.
Nevertheless, the single-ended design tightening tool displaces the one free end of the cable directly away from the bony surface while it immobilizes the other end of the cable ( Fig 2.11.1-2 ). For pelvic applications, this design minimizes the space needed to tighten the cable and extends the anatomical sites in which a cable can be applied. To secure the tensioned cable, the sleeve is crimped with a crimping tool. As a cable is tightened, the sleeve may subside into the underlying soft tissue or into osteopenic bone. Such subsidence can hamper or prevent the use of a crimping tool on the sleeve. This potential problem is minimized if the sleeve is positioned on denuded bone. If the exposed bone is markedly osteopenic, a thin osteotome can be positioned under the sleeve as the cable is being tightened, thereby minimizing subsidence. Once the sleeve is crimped, the osteotome is removed. Excessive cable beyond the site of the crimp is removed with a cable cutter. Cables are available with larger and smaller outside diameters. The larger 1.7 mm cable is appropriate for most pelvic applications.
2.4 Special considerations
For certain applications, the direction of the cable is critical so that the tightening process tends to compress the fracture surfaces in a particular direction. When the cable is passed from the acetabular roof around the front of the pelvis, the cable tends to rest either between the anterior superior and the anterointerior iliac spines or immediately inferior to the anterior interior iliac spine. If the tightening vector needs to be modified, the cable is passed through a small drill hole in the neighboring pelvis ( Fig 2.11.1-3 ). A secondary role for a drill hole is to prevent a cable from sliding down an oblique edge on the bone. During the tightening phase, the cable tends to slide along an oblique surface to rest on the site of the minimal width of the bone. A drill hole can be used to anchor the cable so that it does not slide along the bone during the tightening phase.
Related posts:
2.11.3 Use of bone substitutes
2.11.2 Intrapelvic approach in acetabular fractures
2.9.2 Image intensifier-assisted closed techniques of reduction and fixation
2.10.2 Surgical management of wall and column fractures (type A)
2.10.4 Surgical management of associated both-column fractures (type C)
2.7 Specific surgical approaches and technique
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
