New aspects of cerclage: improved technology applicable to MIO with special reference to periprosthetic fractures
1 Introduction 33
2 Functions of cerclage 34
2.1 Cerclage as a reduction tool 34
2.2 Cerclage as permanent fixation implant 35
2.3 Exclusive wire stabilization 35
2.4 Assisting wire stabilization 35
3 Biological aspects of cerclage 36
3.1 Biological damage at insertion of the cerclage loop 36
3.2 “Strangulation” of blood vessels 36
3.3 Pressure necrosis 39
3.4 Formation of grooves beneath the cerclage 39
4 Technical aspects of cerclage 39
4.1 Types of stability 39
4.2 Cerclage configuration 40
4.3 Cerclage types 41
4.4 Locking cerclage loops 42
5 Common errors 47
5.1 Technical aspects 47
5.2 Biological aspects 47
5.3 Biomechanical aspects 47
6 Summary 47
7 References 48
8 Acknowledgment 48
Introduction
Surgical fracture treatment aims to restore the function of bone, limb, and patient. Cerclages, which were conceived as simple periosteal loops for internal fixation, seem to be an attractive and simple method of fracture fixation. When used on their own, cerclages lack sufficient strength to maintain enough stability to allow functional aftertreatment. Historically, therefore, cerclage was used routinely in combination with a protective plaster cast. This procedure combined the disadvantages of both surgical and conservative methods. Furthermore, the loose coupling between plaster cast and bone did not significantly protect cerclage from overload. With the development of stable and strong fixation using plates, nails, or fixators the cerclage technique fell into disrepute and was infrequently used. Its application was limited to the treatment of long oblique or spiral fractures.
Recently, the use of cerclage has seen a revival due to the increasing incidence of periprosthetic fractures where the intramedullary cavity is not available for penetrating implants ( Fig 2.2-1 ). Today, when cerclages are used, they are protected by internal splinting (plate, nail, or stem of the prosthesis), avoiding the need for the plaster treatment mentioned above. Frequently, periprosthetic fractures are also multifragmented explosion fractures. Fragments are displaced centrifugally. In such cases cerclage offers help because it provides simple, safe, and efficient centripetal reduction and, when using up-to-date technology, adequate fixation.
In recent decades, our understanding of the way bone reacts to forces, strain, and blood supply has evolved. Furthermore, recent studies have demonstrated improvements in fixation technology [ 1]. The use of cerclage in the treatment of periprosthetic fractures will benefit from the application of these new insights into the reaction of bone to trauma [ 2]. These studies suggest it is now time to reconsider conventional cerclage technology and to discuss possible improvements with special reference to their use in minimally invasive osteosynthesis (MIO) and the treatment of periprosthetic fractures.
The term “cerclage” will be used here for any type of loop circling the bone while other uses of wires, such as tension bands or wire sutures, will not be considered. The term “stability” will be used in its orthopaedic sense describing the degree of relative mobility of the fracture fragments. Cerclage wiring is a simple technique and has been practiced widely since the advent of surgical treatment of fractures. A cerclage technique, using solid wires locked with a knurled twist, was described by Götze in 1933 [ 3]. Since then many studies have reported the use of various cerclage technologies using wires, cables, and straps which were connected to form closed loops in a variety of ways. The results and resultant conclusions in the literature differ widely. Leemann [ 4] addressed the lack of strength of the Götze [3] cerclage and proposed a new technology (“cerclage by folding”) that offered superior strength. This technique improved results but this was generally not convincing for many surgeons (see 2.1 Cerclage as a reduction tool). As late as 1985 Rütt and Beck [ 5] proposed the use of a simple wire twisted knot cerclage as a useful technology especially suited to spiral fractures. All these techniques had limited indications and results which do not match those of today‘s technology. In addition they could not, as a rule, forego protection by a plaster.
The indications for cerclage were limited, the results were generally disappointing, and other technologies offered a better outcome. Therefore, today cerclage is used rarely as an exclusive implant even for its most popular indication: the treatment of middiaphyseal spiral fractures of the tibia. Newer technologies, such as plates, nails, and fixators have been used in preference to cerclage for over 50 years despite the fact that their use is generally more demanding. Their results are far better than those of cerclage [ 6, 7].
The increasing numbers of periprosthetic fractures, where technologies with penetrating implants are of limited use has led to a revival of interest in cerclage. The shortcomings of the cerclage are outweighed by its benefits and cerclage is now frequently used for this indication. (Clamp-on plates [ 8] are not discussed here as they are considered incompatible with minimally invasive technology.)
Functions of cerclage
The cerclage may function in different ways: cerclage may be used temporarily as an instrument during surgery ( Fig 2.2-2 ) or can be used long-term as an implant ( Fig 2.2-3 ). Cerclage can either reduce or fix fracture fragments. When used temporarily the wire loop is used as a tool for reduction. When used long term the cerclage functions as an implant.
Cerclage as a reduction tool
Cerclage allows the reduction of several fracture fragments with a single cerclage loop. Cerclages applied for reduction of complex fractures function best when the instrument allows intermittent tensioning. If a fracture cannot be properly reduced on the first attempt, releasing tension and shaking the wire and fragments during retensioning may be a solution.
With reduction using temporary cerclage fixation, the fracture is ready for final stabilization, such as with a splinting plate. Once the fracture is splinted by the plate the cerclage wires are removed. The temporary use of cerclage as a reduction tool is generally accepted because it offers a good balance between the technical performance of reduction on the one hand and the biological disadvantages on the other hand.
Cerclage is an efficient reduction tool when used for reduction of long, shallow fracture planes and/or for reduction of fragments around an intramedullary implant. When carefully applied using appropriate instruments to avoid stripping the periosteum, the balance between mechanical advantage and biological damage is favorable. Today‘s MIO cerclage procedure takes advantage of the MIO wire passer (see Fig 2.2-9 ). This is a special forceps with two connectable cannulated semicircles which can be inserted around the bone, allowing the insertion of a wire loop with minimal soft-tissue damage (see Fig 2.2-7 ).
Cerclage as permanent fixation implant
When cerclages are used as the exclusive fixation element for long-term maintenance of reduction, the balance between advantages and disadvantages is questionable. The use of cerclage as a long-term implant is limited to specific indications. To clarify the nature of real or perceived disadvantages the following aspects deserve discussion.
Exclusive wire stabilization
The use of cerclage as an exclusive implant for fixation ( Fig 2.2-3 ) is of questionable value because other technologies offer far more advantages with respect to regaining early and complete bone function. When treating long spiral fractures in the past, the surgeon tried to compensate for the insufficient strength of exclusive wire loops by adding a plaster cast. A plaster cast does not abolish displacements of the fragments, due to the inherently loose coupling between plaster and bone through skin and soft tissues. The plaster is meant to act as an external splint but it does not prevent high loads exerted on a comparably stiff cerclage fixation. The cerclage is not sufficiently protected from functional load by the additional plaster cast. On the contrary the additional weight of the plaster may even increase the load exerted on the cerclage.
Callus-free healing, mostly described in the cerclage literature as endosteal healing, may be direct healing. Absolute stability is provided very rarely by cerclage.
Assisting wire stabilization
Cerclage can effectively assist in the treatment of periprosthetic fractures ( Fig 2.2-4 ). With the stem of the prosthesis in place, fixation can rarely be achieved with conventional locked plates. The screw all too often hits the stem or does not achieve sufficient anchorage in the bone fragments. A special design of the plate including angled locked screws may offer a solution but hitherto these plates do not offer sufficient locking strength when applied in a nonperpendicular inclination. New improved designs of VAL screws provide strong locking at inclined positions. When treating a periprosthetic fracture the addition of cerclage not only improves the reduction of the fragments but also adds strength to the fixation. When cerclage is used in this way it is combined with two splinting elements, the plate and the stem of the prosthesis. This is, overall, a good indication for cerclage.
Biological aspects of cerclage
Rhinelander and Stewart [ 9] observed in a dog model that cerclage wires and bands are mechanically compatible with fracture healing. They also studied the effect of cerclage contact upon periosteal blood supply. Wires and straps behaved differently. The effect of wires on blood supply was minimal; bands and straps produced a more noticeable effect. The local elevation of straps with undercuts or the like, did not, in the hands of Rhinelander improve the periosteal blood supply. According to Wilson [ 10], such undersurfaces of the straps rendered the reduction and fixation more difficult. Nyrop et al [ 11] confirmed the limited damage of cerclage upon periosteal blood supply while Geiser [ 12] reported major damage to the periosteum and impaired fracture healing.
The pilot experiments by Fernandez et al [ 13] confirmed that cable and wire applied to femora of sheep had minimal effect on bone periosteal blood supply as shown in Fig 2.2-5 .
Biological damage at insertion of the cerclage loop
Inserting the cerclage around the bone without creating soft-tissue damage is challenging, especially when performing MIO. As Fig 2.2-6 visualizes schematically, the exposure required during application of the conventional (Beranger) instrument is not compatible with the goals of MIO. To bring the tip of the semicircle within range to grab the end of the wire involves a fairly wide displacement of the skin and soft tissue on the inserting side. The method referred to by Rütt and Beck [5] (see Fig 2.2-8 ) consists of an insertion tool and a hocked wire-catching tool. Once again this procedure is not compatible with MIO technique because of the extent of the exposure required. Tissue damage is likely to occur when trying to find the wire and pull the hook back.
“Strangulation” of blood vessels
It is obvious that a wire placed around the periosteum seemed/would block blood vessels, which run along the bone. This was be thought of as local contact strangulation. The question is, whether the interruption of longitudinal blood supply has an important effect on the vitality of periosteum and bone.
Examples from literature [9] and the authors’ own experience ( Fig 2.2-5 ) prove that the interruption of longitudinal blood vessels has no major consequences because there is ample centripetal vascular supply to the periosteum.
When passing the wire around the bone the surgeon must ensure that the tip of the wire passer is always in direct contact with the bone, especially when closing the forceps, otherwise larger blood vessels and nerves of the limb may be caught and strangled [ 14, 15] (see Fig 2.2-7 , Fig 2.2-9 ). Careful use of proper tools should avoid this major complication.
Pressure necrosis
The amount of radial pressure has been calculated by Bandi and Sommer [ 16]:
Where F is the amount of tension in the wire, r is the radius of the loop, and b the contact width of the wire or band. As an example they calculated that the pressure exerted onto bone by the cerclage was 150 kp/cm2 (~15MPa) assuming a tension force in the wire of 60 kp (~600N), a diameter of the loop of 2 cm and a contact width of 0.2 cm.
The footprint of the wire and cable according to Fig 2.2-5 may be only 0.2–0.4 mm wide [13]. Static compression exerted by plates (up to 1400N) [ 17] as well as by 4.5 mm cortex screws (up to 1800N) [ 18] has not induced pressure necrosis. Today, based on these observations, it can be assumed that radial pressure and pressure necrosis are not the cause of any bone resorption that may be seen in cerclage fixations as long as the stability of the fixation is maintained.
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