12.14 Principles of monolateral external fixation

Monolateral external fixation is a system for the stabilization, reduction, and manipulation of bone segments by means of bone anchorage consisting of pins fastened to an external frame. Monolateral external fixators in their various forms have the advantage that they allow the use of half-pins (bicortical pins that do not penetrate both sides of the soft tissue envelope), thereby avoiding major damage to the neurovascular structures contralateral to the insertion point. The simple structure of monolateral systems permits rapid application and simplified preoperative planning, both of which are features particularly appreciated in traumatology.

The external construct may present different configurations according to the type of fixator used or the application for which it is designed (Box 12.14.1).

We can distinguish between two major types of monolateral fixators: one-plane monolateral fixators (Figure 12.14.1) in which clusters of pins are placed practically in the same plane, and two-plane monolateral fixators (Figure 12.14.2) in which pin clusters are placed in different planes and joined by the frame in two planes.

Monolateral fixators can also be differentiated on the basis of how the pins are connected to the frame. Simple fixators (Figure 12.14.3) have independent articulations which connect each pin with a rigid longitudinal rod, and clamp fixators (Figure 12.14.4) have pin clusters connected to a clamp which introduces the option of adjustments between the clamp and fixator body.

In addition, external fixators can be subdivided into static fixators and dynamic fixators on the basis of their intrinsic dynamization capability. This characteristic will be considered in the section on the biology of healing.

Simple fixators have the distinct advantage that each pin can be placed at a different angle in relation to the fixator rod, and that the distance between two pins in a bony fragment can be freely chosen in relation to the soft tissue lesion and depending on the mechanical needs of the frame bone construct. A disadvantage is the need for reduction of the fracture prior to fixator application and the fact that external manipulation manoeuvres, particularly rotation, can only be performed by replacing one or more pins.

Advantages of clamp fixators are that they allow fracture reduction after the fixator has been applied and that subsequent adjustments can be performed fairly easily by loosening the universal articulations between the fixator body and the clamps. Disadvantages are the need to resort to supplementary external systems whenever gradual multiplanar adjustments are required; pin cluster placement and spread are strictly dictated by the clamp configuration.

The basic elements to be considered in the mechanics of a monolateral fixation system are as follows:

The pins play the most important role in the stability of the entire system. When assessing the ideal type of pin, the following parameters must be considered:

The pin diameter must be such as to minimize the risk of breakage at the pin entry point. At the same time the pin must possess a sufficient degree of stiffness to ensure adequate implant stability. A pin hole greater than 30% of the diameter of the bone results in a 45% reduction in the torsional strength of the bone. The bending stiffness of the pin increases as a function of its radius by the power of four. If we know the diameter of the bone, the thickness of the cortex, the elastic modulus of the bone, the number of pins to be applied, the elastic modulus of the pin material, and the load applied, we can calculate the minimum pin diameter allowed in order to obtain a stable implant in relation to different bone–fixator distances.

In adult bone, a pin of diameter 6mm enables this requirement to be satisfied for bone–fixator distances up to 6cm, while maintaining the specific pressure at the entry cortex below one-third of the tensile strength of the bone tissue.

The load distribution in a monolateral implant is asymmetric, being greater at the entry cortex than at the exit cortex. For this reason a tapered conical pin can be employed and proves particularly useful. The taper ratio produces a gradual increase in radial preload. Pin–bone contact is optimized and the micromovements typical of a straight cylindrical pin inserted in a predrilled hole are avoided.

Increasing the number of pins leads to an increase in implant stability, as does spreading the pins across the bony segment. Maximal stability for a construct with two pins per segment occurs when one pin is close to the fracture site and one is as far away as possible. With a sufficiently rigid frame two or, at most, three pins per fracture segment will be enough to ensure adequate stability regardless of their spread.

The type of pin thread is determined by the shape, pitch, and pitch height. Various types of pins with different morphological characteristics are commercially available. The pin design must make allowance for the quality of the bone to which the pin is applied, with different designs being necessary for cancellous and cortical bone. The pitch vertex angle and the curvature radius at the base of the pin will have an effect on the insertion torque and thus on the temperature generated during pin insertion.

The pin insertion technique influences the bone–pin interface and thus the stability of the entire system over time. The use of self-drilling pins is associated with microfractures (particularly in cortical bone) and with the development of temperatures above 50°C which may cause thermal necrosis. Pre-drilling using very sharp drills minimizes thermal necrosis and bone damage, allowing the use of self-tapping conical pins which afford optimal bone purchase in that each thread cuts its own path as the pin advances. The advantage of such pins consists in their easy removal, often in the outpatient clinic, while the disadvantage is related to the fact that they cannot be backed out, even partially, without complete loss of bone purchase.

The pins must be made of biocompatible material and have substantial stiffness, making the use of stainless steel preferable. Titanium pins have been shown to be more elastic and this reduces pin loosening.

Pin coating with hydroxyapatite improves bone purchase by providing a better pin–bone interface. This reduces pin loosening and pin tract infection. They are recommended in implants applied for a long time and osteoporotic bone.

As the bone–fixator distance increases, implant stability decreases. This must always be borne in mind when deciding on the number of pins to be used and the initial weight-bearing load that the patient is to be allowed. In particular, in applications at the femoral level, the number of pins applied per fracture segment needs to be increased and the patient allowed to bear only a partial load for the first 2–4 weeks.

The weakest part of any system is the junction between the fixator body and the clamp, or directly between the fixator body and the pins. Here, one needs to know the mechanical yield characteristics of these elements through adequate information which should be provided by the manufacturers. In order to avoid secondary fracture displacements, the yield point of each system must be established in relation to the clinical bone–fixator distance, the load applied, and the fracture conditions.

The stability of simple and/or clamp fixators can be enhanced by increasing the number of pins or external rods. An example of this may be the delta or triangular configurations that can be created. In practice, increasing the number of components is less effective and clinically less desirable than increasing the size of the individual components, which increases the bending stiffness to the power of 4 and resistance to torsion to the power of 3. A greater pin diameter, particularly in the entry cortex, is also known to enhance implant stability in monolateral fixation. For these reasons, the latest types of monolateral systems tend have larger pin diameters and to use conical pins and fixator bodies of fairly large size compared with the rods used in the past.

However, stability must not be confused with rigidity, which is a condition which causes delays in consolidation, pseudoarthrosis, increased screw loosening, and pin-tract infections. Excessively rigid constructs should be avoided and the latest generation of stable fixators should incorporate fracture-stimulation systems such as dynamization.

The natural healing of a fracture proceeds through the well-known phases of inflammation, repair by periosteal callus formation, and remodelling, which depend on numerous variables such as the degree of soft tissue involvement, the reduction obtained, the type of fracture and the stability of the fixation. The type of healing obtainable with external fixation depends on the mechanical characteristics of the device used and the stability of the implant.

In a transverse fracture anatomically reduced and fixed with a rigid external fixation device in such a way that the weight-bearing forces are fully absorbed by the fixation system, healing is of the direct type, without callus formation, via a biological process akin to that associated with the use of rigid compression plates. Direct-type or contact healing requires lengthy time periods to restore the mechanical stability of the bony segment.

When an external fixator has been applied it is always necessary to consider the behaviour of the pin–bone interface, which deteriorates over time, in relation to the healing process. Thus the type of healing that should be achieved by external fixation must be of the periosteal type, as occurs without rigid fixation, which is quicker and stronger. It is only in this way that consolidation can be achieved in a relatively short period of time, which is essential for minimizing the most feared complications of external fixation such as pin loosening and pin-tract infection which in turn result in instability of the bone frame construct and may be a possible cause of pseudoarthrosis.

The conditions necessary for achieving periosteal healing with external fixation are as follows:

Sparing the fracture site can be achieved by placing the pins at an adequate distance from the fracture site (at least 1.5cm) and by seeking preferably a closed reduction solely by means of external manipulation of the segments. It has been demonstrated that the combination of external fixation with internal fixation with interfragmentary lag screws at diaphyseal levels to contain and reduce segmental fractures leads to an increased incidence of pseudoarthrosis. This is related to the different types of repair biology which the two systems create: interfragmentary—direct healing; external fixation—periosteal healing.

The reduction must be adequate and avoid large gaps which may indicate interposition of soft tissues, and axial alignment must be accurate. However, the reduction does not have to be anatomical where interfragmentary movements might be inhibited.

Micromovements are of fundamental importance for the development of the periosteal callus and distinctions need to be made in terms of quality, extent, and time of application. In this sense we can distinguish between static and dynamic fixators.

Lastly, from the biological standpoint, external fixation allows formation of new bone starting from an osteotomy or fracture site, when a gradual progressive distraction force of varying proportions depending to the bone response is applied. Distraction induces bone formation with an intramembranous-type ossification when the frame is stable; the newly formed bone eventually becomes mature and normally corticalized. This characteristic of bone repair under distraction can be exploited to remedy limb discrepancies and loss of bony substance as well as to perform gradual angular adjustments.

The term dynamization indicates converting a static fixation into a fixation which allows the passage of forces and/or the possibility of stimulating the fracture site with controlled micro movements. In a monolateral fixation, dynamization may be of three types:

Passive dynamization is achieved when the fixator is placed in a static configuration and the patient applies a load to the limb in such a way as to exert a significant force (usually above 200N). In this case the micro movements are cyclic and are applied in an asymmetric manner on the fracture callus through the bending of the pins, which, in modern monolateral fixators, are the most elastic elements in the entire frame. In the long run, this type of dynamization will lead to asymmetric callus formation, thereby facilitating pseudoarthrosis (Figure 12.14.5).

Active dynamization is achieved by releasing the telescopic slides on the bodies of fixators possessing these features, hence the term dynamic fixators (Figure 12.14.6). When bearing weight or applying a load, the patient brings about the progressive closure of the fracture gap; tissue stimulation is of the concentric type and is conducted mainly along the longitudinal axis of the telescopic element, which at the time of assembly must lie parallel to the main axis of the bony segment. This kind of dynamization may be of the free or controlled type. In the latter case, the fixator is equipped with systems which limit the excursion capability of the telesystem and at the same time provide for an elastic recoil after the loading phase.

It has been demonstrated that when all of the fixator joints were allowed to adjust simultaneously during dynamization, exact axial movement or uniform compression at a complicated fracture site was achievable. This study revealed that significant non-axial movements may occur during dynamization, and that such a deficiency can be corrected by relaxing certain fixator joints in addition to the sliding mechanism. The same modelling technique can also be applied in bone lengthening application to assure desirable limb alignment during the distraction process. These analysis results can aid the performance assessment of an external fixator and facilitate appropriate application of such a device to achieve either active or controlled axial movement.

Induced dynamization may be manual or mechanical and is applied according to known quantities and frequencies via external actuators. Kenwright and colleagues applied this type of controlled mechanical stimulation to tibial fractures, starting with a 1-mm movement at 0.5Hz for 30min daily a week after application of the fixator until a load of at least 200N was reached by ambulation. The patient group submitted to dynamization healed earlier than a control group treated with static fixation.

Induced dynamization can also be applied manually, with micromovements induced from the first week after surgery with the purpose of achieving early stimulation of callus formation even in bedbound patients or patients incapable of bearing weight on the limb.

The biological effects of dynamization have been demonstrated in a number of studies.

From the anatomical standpoint monolateral fixation presents no limitations and as a result of the versatility and apparent simplicity of application it may be regarded as indicated for most traumatic or orthopaedic injuries.

In practice, however, it is necessary to define the limitations related to considerations of a mechanical nature, such as the stability of the fixation construct, the durability of the pin–bone interface, complications directly associated with external fixation, biological and clinical considerations, such as patient tolerance and the quality of the bone tissue or of the adjacent soft tissues, and the feasibility of adequate patient surveillance in the outpatient setting.

Therefore it is useful to define relative contraindications to external fixation (Box 12.14.5):

There are also a number of relative contraindications related to the bony segment treated. Application of a fixator to the femur entails crossing soft tissues of such thickness as to create a bone–fixator distance which makes the fixation construct comparatively less stable than in other segments and leads to more serious extension–flexion disorders of the knee.

The indications for external fixation in traumatology are as follows:

In orthopaedic surgery, monolateral fixation is used in the following cases:

Monolateral fixation affords definitive treatment of open fractures. The systems currently employed achieve optimal stability, and frame stiffness can be adjusted over time to adapt to biological needs.

The prognosis of an open fracture depends mainly on the degree of soft tissue injury, the extent of the bone comminution, and the degree of bacterial contamination. Immediate stabilization of the bone lesion, administration of adequate broad-spectrum antibiotic prophylaxis (it is mandatory to perform a bacteriology specimen at the beginning of the debridement and at the end of the procedure in order to assess the pathogenic flora and adjust the antibiotic therapy), elimination of necrotic tissue with repeated debridements, and subsequent coverage of bone by replacing soft tissue substance losses as quickly as possible are necessary to optimize results. These manoeuvres are facilitated by the use of monolateral external fixators. Stability is achieved without interference at the fracture site. In particular, it is of paramount importance that the fracture be adequately reduced. A partial load is permitted as soon as the patient’s general condition allows and the soft tissue lesions are healing. Further fracture callus stimulation is subsequently applied by dynamization. A stable dynamizable monolateral external fixation should be generally regarded as a definitive form of treatment and not merely as a form of temporary stabilization.

Reports have demonstrated the possibility of achieving a healing rate of more than 90% with a malunion rate of less than 5% by the use of monolateral fixators. One study reported the outcomes of 101 open tibial fractures treated with axial dynamic fixators, including 63 grade III fractures, with pseudoarthrosis occurring in five cases and infection in six.

Recently there is a tendency to perform a temporary stabilization by external fixation in deep soft tissues lesions. After thorough care of the local damage, when there is evidence of recovery of the external mantle and absence of contamination, the external fixation, used for bony stabilization, can be substituted by internal synthesis as a definitive treatment. This is used following the principles of ‘local damage orthopaedics’ and it is intended to minimize the incidence of osteomyelitis and infected non-union. For this reason, the conversion must be performed only when the earlier mentioned conditions are contemporarily present, unless external fixation can be used as a definitive method of treatment.

In diaphyseal open fractures of the lower extremity, an alternative treatment to monolateral external fixation is intramedullary nailing, which has a decreased rate of angular malunion. External fixation should be favoured when there is greater contamination or more severe soft tissue injury (Figure 12.14.7).

A monolateral external fixator allows rapid closed reduction which enables the surgeon to limit operative time and blood loss. This is useful in those patients with multiple trauma or at anaesthetic risk. Therefore this group of patients can be treated with external fixation even if the type of fracture would lend itself to other methods.

Femoral fractures in patients during growth, especially in multiple trauma, may be treated with external fixation. Other indications include unstable fractures, such as proximal-third fractures, and complex metaphyseal fractures, particularly those associated with a high-grade soft tissue injury.

The multiply traumatized patient, particularly when simultaneously presenting with a thoracic or cranial trauma, requires early stabilization of the long bones in order to reduce the risk of acute respiratory distress syndrome (ARDS), to decrease time in the intensive care unit, and to decrease the period of ventilatory support.

If the stabilization is performed within 24h, the incidence of ARDS is 7%, compared with 39% if more than 24h has elapsed. However, certain injury combinations may preclude lengthy internal fixation procedures.

External fixation in its monolateral form allows early stabilization with closed reduction, minimal blood loss, and short operative times compatible with the severity of the associated lesions. The benefits of early stabilization are achieved with minimal surgical result.

If external fixation is chosen in the acute period for long-bone stabilization, it is necessary to decide whether the external fixation needs to be kept in place until healing is achieved or whether there is scope for replacement with intramedullary nailing so as to reduce pin-tract problems, increase fixation stability, and afford a better range of movement. Replacement operations must be decided on the basis of the type of fracture (periarticular fractures prove difficult to treat with intramedullary nailing) and the patient’s general condition. Conversion from external to internal fixation should be done within 2 weeks of frame application to reduce the risk of osteomyelitis.

A definitive stable monolateral external fixator with a system for micromovement and subsequent dynamization is an alternative to internal fixation. Micromovement is necessary in the non-ambulant patient to ensure an adequate healing rate.

The stabilization of unstable pelvic fractures in both the horizontal and vertical planes by external fixation is part of the surgeon’s resuscitative armamentarium. Continuous blood loss and the resulting difficult haemodynamic compensation can be decreased by means of early stabilization with external fixation (Figure 12.14.8).

The retroperitoneal space can contain as much as 900–1000mL of blood which can collect in a very short period of time. External fixation can decrease pelvic volume and control motion which results in a reduction in mortality rates.

Pin insertion is possible either at the iliac crest level or below the anterior inferior iliac spine. In the former case, pin application is percutaneous, whereas in the latter it is open owing to the presence of the lateral femoral cutaneous nerve of the thigh. From the biomechanical point of view it is advisable to choose the anterior application in order to have a better grip of the pin–bone interface due to the thickness of the ileum in the area of insertion and a suitable mechanical performance of the frame in the horizontal plane. Associated posterior instability requires internal fixation after the patient stabilizes.

The ideal treatment of articular fractures entails anatomical reconstruction of the articular surface and adequate stabilization of the meta-epiphyseal lesion so as to permit early rehabilitation. In complex articular fractures, external fixation may be used as an adjunct to obtaining these goals. These fractures present two major problems, namely articular incongruence and metaphyseal comminution. The metaphysis can be treated by means of external fixation, which enables adequate alignment and good stability to be achieved. The treatment of articular incongruence is facilitated by the presence of the fixator distracting across the joint. The articular reconstruction is then obtained with an adjunctive percutaneous (closed reduction external fixation, CREF) or open minimal internal fixation (limited open external fixation, LOREF). In this case the open approach necessary for articular reduction is limited, stripping of periosteum is reduced, and the use of metallic elements is minimized, thus decreasing the risk of the serious complications, such as pseudarthrosis and infection, associated with wide open approach.

Most monolateral external fixators used for articular fractures are spanning fixators, i.e. they cross the involved joint. The external fixator is applied in distraction, utilizing ligamentotaxis with gripping elements placed at a considerable distance from the fracture site. Limited internal fixation of the articular surface is then applied secondarily. The external fixator may also serve as a tool for the definitive fixation of the articular lesion without additional internal fixation, when the reduction obtained is satisfactory, or when a ‘biological’ approach to the treatment of such lesions is adopted from the outset. Less commonly, the metaphyseal fracture may be treated by placing the monolateral fixator on the same side of the joint. This technique is useful in less comminuted cases, and has been utilized for the distal radius and proximal tibia (Figure 12.14.9).

These principles can be applied in various areas, such as the elbow, wrist, knee, or ankle. Experience with modern fixators spanning the elbow and fixing in the humerus and ulna, appears to be encouraging. A hinge articulated at the rotation axis of the elbow allows early mobilization of the joint, thus reducing the incidence of joint stiffness, which is a frequent and serious complication. This procedure appears to be particularly indicated for open or severely comminuted fractures. Furthermore it has been proved that a condition of fracture–dislocation is well addressed by the use of stable internal fixation to treat the bony lesions and an articulated fixator in order to achieve stability and to allow early motion while the ligaments are repairing. Ideally the fixator should be maintained for a period of 6 weeks.

Numerically, the greatest indication for monolateral fixation in traumatology is for fractures of the distal radius using a spanning fixator with or without limited internal fixation. Occasional extra-articular distal radius fractures are amenable to fixation on the same side of the joint.

The following principles must be applied in external fixation of the wrist:

The role of joint mobilization via articulated fixators for the wrist is still controversial. Prospective studies have demonstrated that with the Pennig dynamic external fixator there are no differences between the dynamized and the static group.

Similar principles apply to the treatment of intra-articular fractures of the knee. Complex fractures with meta-epiphyseal comminution or major involvement of soft tissues benefit most from external fixation. Knee stiffness is avoided by limiting transarticular external fixation to 40–50 days (Figure 12.14.10).

Twenty-one complex fractures of the tibial plateau were treated with closed reduction, application of a monolateral fixator, and fixation of the articular fragments. A range of movement of 115 degrees in 19 of the 21 fractures was reported, and the authors concluded that this procedure yields satisfactory outcomes. In this series most cases were treated with the external fixator on the tibia only, not spanning the knee joint.

High-energy fractures of the tibial plafond are a frequent indication for spanning external fixation. Pins can be applied across the ankle joint using an articulated clamp along the rotation axis of the tibiotalar joint. Release of this articulation at 3–4 weeks helps rehabilitation of the joint. The technique is safe and effective, and significantly decreases the treatment-related complications when compared with internal fixation with plates and screws.

Recent studies have demonstrated that the use of circular fixator for high-energy bicondylar tibial plateau fractures have marginal benefits over the use of plates and significant reduction of infections.

External fixation is a means not only of achieving stabilization and healing of fractures, but also of subjecting bony segments to gradual progressive distraction of an osteotomy area so as to obtain bone-segment lengthening.

The basic prerequisites for achieving such results are stability of the lengthening device and respect for the biological conditions which allow new bone formation, such as sparing of the periosteum, adequate waiting time prior to distraction, and customized distraction in relation to individual osteogenic capabilities.

Equally important is the preoperative patient assessment in order to minimize or prevent possible complications.

The joints adjacent to the segment to be lengthened must be stable and display normal functional capacity. Any muscular contracture must be evaluated in order to avoid aggravating it during lengthening. If necessary, tenotomies must be planned at the time of the first operation or to resolve unresponsive contractures during surgery. The amount of distraction possible must be assessed so as to plan a lengthening in one or more stages. In particular, congenital diseases are more prone to complications related to difficult muscle and tendon extension with the result that lengthenings often need to be done in several stages.

It is equally important to assess the coexistence of associated angular defects in order to be able to plan simultaneous angular adjustments or subsequent adjustments to the lengthening via manipulation of the callus.

Lastly, factors such as bone quality, the possible presence of endocrine–metabolic diseases, and neurovascular function must be carefully considered when establishing indications for lengthening.

The lengthening process is not merely confined to the actual surgery, but requires thorough monitoring by an integrated team of surgeons, physiotherapists, and paramedic staff throughout the distraction and consolidation period until the fixator is removed.

Osteotomies for adjustment of axial or rotational defects can be stabilized in various ways. Often internal fixation is preferred because of the intrinsic stability of the method and the resulting possibility of early rehabilitation. However, the degree of adjustment has to be precise in order to obtain a good long-term outcome, and sometimes it is not simple to achieve the desired result intraoperatively. In this context, external fixation, especially with fixators which allow gradual adjustments, yields precise results with less surgical trauma.

In osteoarthritic genu varum, precision in realigning the load axis appears to be of fundamental importance for achieving clinically acceptable results in the medium to long term with less surgical trauma (Figure 12.14.11).

Bone loss can be treated using the principles applied in lengthening. Bone transport may be used where a segment of bone previously osteotomized above or below the gap is gradually transported across the gap to ‘dock’ against the opposite segment (Figure 12.14.12). Alternatively, a compression–distraction can be used where the gap is immediately closed by shortening, followed, either in the same operating session or later, by an osteotomy at another site which allows a lengthening to be performed to restore limb length (Figure 12.14.13).

The bone-transport procedure is indicated when the loss of substance is more than 4cm in the tibia or more than 6cm in the femur. It is subject to the frequent complication of delayed consolidation or non-consolidation of the docking site, so that an additional procedure is needed to stimulate union.

Compression–distraction allows immediate contact between two viable contact surfaces. If the fracture site is clean and there is no risk of infection for the other sites of the same segment, a lengthening osteotomy can be performed concomitantly in a site which may be proximal or distal to the previously bridged gap. Shortening must not exceed 5cm to avoid vascular or soft tissue problems, although this depends on the characteristics of the injury. The fibula, if intact, should be resected 2cm more than the shortening distance.

The advantage of segment-shortening over bone transport is that it allows consolidation of the contact area without any additional intervention.

When assessing whether such surgical reconstruction is indicated, the surgeon must bear in mind the patient’s age, the condition of the soft tissues, neurovascular function, and degree of patient compliance. The treatment is lengthy (on average 40 days per centimetre of gap to be bridged) and complications are common. For this reason, appropriate patient selection is mandatory and patients must be adequately informed and monitored.

The experience of the University of Verona Orthopedic Clinic is based on 38 cases, 15 treated with bone transport and 23 with compression–distraction for substance losses ranging from 3–11cm. All segments healed. The following complications have been reported: 11 (75%) pseudarthroses of the docking site, two axial deviations of 5–10 degrees (with compression–distraction), and seven (18.4%) pin loosening (with reinsertion).

The problems and complications relating to external fixation can be avoided or minimized by using scrupulous surgical technique and codified rules for patient follow-up, and having an adequate understanding of mechanics as applied to bone biology.

Problems are defined as mishaps which stand in the way of the realization of a given objective, without jeopardizing the final outcome.

Complications are defined as obstacles to the realization of a given objective which require treatment and may undermine or impair the final outcome.

For this reason, we regard as problems only those deriving from minor pin-tract problems (grades 1 and 2 of the Checketts classification), which require improved nursing and closer cooperation between surgeon and patient.

Complications can be classified as follows:

The latter group are specifically related to the type of trauma or the type of orthopaedic condition treated and will therefore be addressed elsewhere in this book.

Complications due to monolateral external fixation can be further subdivided as follows:

Complications due to bone-gripping elements are as follows:

Vascular or neurological damage from a pin can be avoided by adequate care in placement. The monolateral system involves the use of pins whose entry point is well controlled and which penetrate only a few millimetres beyond the contralateral exit cortex.

The complications of pin-tract infection, osteolysis, and sequestrum are defined as major pin-tract complications and occur for the following reasons:

Some systems require different types of pins for cortical bone and cancellous bone. Therefore it is necessary to choose the correct type of pin for the anatomic area to which it is to be applied. The total length of the pin must be based on the thickness of the soft tissues and on the size of the frame to which it is applied so as to allow adequate pin–fixator contact and at the same time care of the pin tracts. The length of the thread will depend on the diameter of the bone and must be selected so as to ensure adequate contact with both bone surfaces. The pin diameter must never exceed one-third of the diameter of the bone in order to avoid secondary fractures, and must never be undersized in order to avoid bending or breakage of the pin itself. The choice of hydroxyapatite-coated pins is recommended in order to reduce the incidence of pins loosening and the rate of pin infections.

The release of soft tissues at the point of insertion must be sufficient to prevent friction during articular excursion. In those cases where different types of pins are required for cancellous and cortical bone, care must be taken to ensure the drill diameter matches the type of pin used. The drill must always be equipped with a sharp bit in order to minimize damage due to thermal necrosis. Both bone surfaces must be drilled so as to guarantee correct insertion, avoiding any risk of the pin taking the wrong route through the bone. In those cases where it is recommended, the use of a template is essential to maintain parallelism of the pins and thus reduce preload bending at the bone–pin interface. It is recommended to apply the pins after pre-drilling using a sharp drill at a speed of 800rpm/min and the stop and go technique in order to reduce the thermal bone interface necrosis.

The load must be graduated in relation to the type of fracture or condition treated, the type of bone segment to which the fixator is applied, the mechanical characteristics of the fixator, and the patient’s weight. In dynamizable fixators, the dynamization must be implemented at the right time in order to limit pin stress and facilitate healing with a view to reducing total fixation time, which is directly proportional to the incidence of pin loosening.

A preliminary investigation is necessary in order to establish whether the patient is allergic to any of the constituent materials of stainless steel. In such cases, the use of titanium pins or hydroxyapatite-coated steel pins is indicated.

The methods of cleaning pin tracts must be properly explained to the patient. During the period in hospital after surgery, checks must be performed to make sure that the patient complies with the instructions given.

There is a close correlation between the complications related to muscular stiffness and the bony segment and condition treated. Such complications, which are almost non-existent in tibial and humeral injuries, are significant in injuries of the femur because the pins pass through the fasciae lata and the quadriceps muscle.

Soft tissue release should be carried out intraoperatively, checking for any residual tension by means of extension–flexion movements while the patient is still under the anaesthetic. Maintenance of an adequate range of movement in the postoperative period may require postoperative release of any residual tension not previously identified.

This complication is unlikely to occur when using fixators with ball-joints, since the loads needed to bend pins are higher than the yield strength of the joint. However, pin bending is possible if the pin diameter is undersized and during lengthenings following early consolidation of the callus.

This is possible if the pin diameter is undersized, particularly in cases of acute trauma when combined with breakage of the fixator body.

Generally speaking, there may be complications related to failure of the frame depending on the geometry of the fixator and on the loads to which it is subjected. For this reason we need to have an exact knowledge of the mechanical characteristics of the device and relate them to the conditions of use so as to avoid breakage of the frame or, more frequently, yielding failure with consequent misalignment.

The fixator body composed by anodized aluminium may also be subject to breakage due to tension–corrosion phenomena relating to the effects of certain disinfectants, the use of which should be expressly banned.

One possible complication of dynamizable fixators is jamming of the dynamization system when the fixator is subjected to excessive torsional stress. For this reason new jam-free dynamization systems are currently being produced.

The fixation system may be a contributory cause of malunion. Some fixators require reduction prior to application. However, all the latest monolateral fixators allow reduction adjustment with the fixator in place. It should be noted that whenever a rotatory adjustment is made with any type of monolateral fixation system, we invariably create a displacement in another plane, with the result that it is essential that limb rotation in particular should be reduced prior to application of the pins. This enables us to avoid positioning the pins in planes which are so different as to prevent subsequent reduction. If this should happen, the only way to overcome the problem is to reposition the pins.

Malunion may also be due to secondary loosening of the pins or frame. Therefore it is essential to monitor the patient over time with serial radiographs and give precise weight-bearing instructions, checking that the patient adheres to them scrupulously. If loss of reduction occurs, the fracture must be reduced by means of external manipulation of the segments, which can be done under anaesthetic or, depending on the degree of patient cooperation and the extent of the adjustment, may be performed without an anaesthetic.