1. Bone loss in relation to open fractures may arise directly from extrusion of fragments at the time of injury or after surgical excision (debridement).
2. Safe and effective management requires expertise of both plastic and orthopaedic specialists in reconstruction. These cases are particularly challenging and should be managed in units with relevant expertise and experience.
3. The options for reconstruction will depend on the shape and size of the defect, the location within the bone, the condition of the local soft tissue, and the patient’s general physical and mental health.
4. Bone defects can be reconstructed through autogenous bone grafts (with or without augmentation), vascularised free transfer of bone (usually the fibula), or by distraction osteogenesis (according to the methods described by Ilizarov).
This chapter deals with the management of bone loss in open fractures with particular reference to the tibia. This is a challenging problem and requires input and expertise from orthopaedic and plastic surgery specialists in limb reconstruction. The different sizes, shapes, and location of the defect will have diverse implications and management must be individualised.
Aetiology of bone loss
Bone loss can occur from the initial injury (extrusion of bone fragments or segments at the time of impact) or following wound excision in open fractures. High-energy trauma to the metaphysis of osteoporotic bone can lead to crushing with impaction of cancellous bone that, in effect, creates a defect even without there being any physical removal of bone. Pathological fractures, too, may present with bone loss consequent to both the pathological process and the injury.
Cavitary or contained
This type of defect is a closed cavity seen after impaction in cancellous bone of the metaphysis of long bones or in the calcaneum.
Partial defects occur when a proportion of the circumference of a bone has been lost. Amenable to replacement by bone grafting when small, these are more challenging if involving an articular surface. After wound excision if most of the circumference has been lost, the surgeon may choose to create a true segmental defect in order to facilitate techniques such as bone transport.
Modes of treatment
Expectant or non-surgical (conservative)
Spontaneous restoration may be seen in young children, usually under the age of 6 years. In adults this phenomenon is observed occasionally in those patients who have had significant head trauma associated with the limb injuries. This pattern of spontaneous replacement happens more frequently in the femur than the tibia. The key in any expectant approach is a serial evaluation of clinical and radiological signs. The absence of continued progress should prompt intervention.
Autogenous bone graft remains a benchmark for treating bone defects against which other methods are compared. It is used for defects from open fractures after satisfactory wound healing; use at the time of index wound excision or before definitive wound healing may potentially increase the risk of infection through the introduction of non-vascularised material into a contaminated bed. Bone grafting procedures carry some donor site morbidity and have limitations in terms of volume and biological activity (particularly in older patients and those with immune suppression). Consequently, different methods of augmenting the volume and activity of autogenous bone graft have been proposed:
The induced membrane by Masquelet is a method for augmenting bone grafting procedures (1). An antibiotic-loaded polymethylmethacrylate (PMMA) cement spacer is placed and moulded to cover the bone at both ends of the defect at the time of soft tissue cover or wound closure. This induces a foreign body reaction producing a biologically active membrane around it that is highly vascular and has cells producing osteogenic growth factors. The cement spacer maintains the length of the limb, provides effective dead space management, and delivers a high concentration of antibiotics locally. The technique is illustrated in Figure 9.1.
Maturation of the membrane (from 6–12 weeks) is followed by a second procedure to remove the cement spacer and replace this with autogenous bone graft. The membrane is incised and protected when the cement spacer is extracted so that closure will facilitate containment of the graft material within the defect. The bone edges at either end of the defect are inspected, excised further if needed, and sharply ‘petalled’ (osteoperiosteal and cortical leaves are elevated from the surface of bone to stimulate a new inflammatory response) before the graft is placed.
Bone graft is obtained from the iliac crest or femoral canal (using the RIA—reamer irrigator aspirator—technique) as large volumes may be required (2, 3). Whilst the induced membrane technique is itself an augmentation procedure for autogenous bone graft, some parties advocate addition of further adjuncts such as bone morphogenetic proteins or bone marrow aspirate-concentrated osteoprogenitor cells.
Good results have been reported using this technique, particularly in the upper limb and femur (1, 4). In the tibia, Masquelet has encouraged creating cross-unions between the tibia and fibula at levels proximal to and distal to the level of the defect especially when external fixation is utilised for stabilisation. This is said to reduce refractures after fixator removal.
The induced membrane technique, especially when used in combination with internal fixation, may be more acceptable than prolonged external fixation and bone transport. It is helpful for partial or oblique defects where, if bone transport were performed, docking of bone ends might be troublesome. However, complications do occur and some centres have reported less favourable results in the tibia (5).
Where complex plastic surgery has been performed for definitive wound cover, and the induced membrane technique is considered, some pre-emptive discussions with plastic surgical colleagues will help in planning for access through this cover for bone grafting.
These are natural, synthetic, and animal-derived osteoconductive scaffolds and are available in many forms including structural blocks, chips, pellets, granules, and injectable cements (6). Some have been employed effectively for contained periarticular defects in closed fractures but using inert material in open fractures where the surgical field may, despite the best excision and lavage, still hold elements of contamination increases the risk of deep infection.
Bone graft substitutes can serve as a volume expander when using autogenous bone graft in the Masquelet method; the field is unlikely to be contaminated owing to the period of exposure to local antibiotics and the observation of satisfactory wound healing (1, 4).
Bone graft adjuncts
Various commercially available products have been developed to act as biological response modifiers to bone healing. Whilst some have been used in isolation for other indications, it is more usual to combine these with autogenous bone grafts when managing critical-sized segmental defects. Examples include the bone morphogenic proteins (BMPs), bone marrow and blood derivatives, and demineralised bone matrix.
BMPs are signalling proteins in the recruitment of osteoprogenitor cells during fracture healing. Originally described by Urist (7), commercial preparations of recombinant BMP-2 promoted fracture healing and bony union (8, 9) including in open tibial fractures (10, 11). The Food and Drug Administration (FDA) in the US thus approved BMP use in the treatment of acute tibial fractures managed with intramedullary fixation (12). However, recent studies have failed to find conclusive evidence for clinical effectiveness (13, 14); calls for adequately powered randomised trials to validate its continued use have occurred (12).
Bone marrow aspirate concentrate (BMAC) enables a harvest and concentrate of mesenchymal stem cells (MSCs), usually from iliac crest bone marrow, for clinical application. Laboratory studies suggest that MSCs can provide both a source of bone-healing cells and relevant cellular signalling molecules (15), with some clinical studies suggesting a use in augmenting bone healing during distraction osteogenesis and bone grafting procedures (15).
Platelet-rich plasma (PRP) is a blood derivative obtained by centrifugation of the patient’s blood. It contains very high concentrations of growth factors relevant to bone healing but preclinical work assessing the effectiveness of PRP in bone healing is limited. Whilst both BMAC and PRP procedures appear safe and research activity into potential clinical application is ongoing, specific recommendation for use in open fractures is premature (15, 16).
Demineralised bone graft is allogenic bone processed to remove mineral and cellular components. It contains bone matrix proteins and osteo-inductive cellular signalling molecules including BMPs. Although some studies describe its use as a bone graft substitute and expander, clinical evidence for effectiveness is weak and no studies for a role in open fracture defects exist. It is thus not recommended at the current time (17).
Vascularised bone grafting
The fibula, with its peroneal artery pedicle and hence vascular supply intact, is the most common bone transferred for tibial bone defects. It can be transferred ipsilaterally through a proximal and distal osteotomy and the intermediate segment slowly moved across from posterolateral to anteromedial to bridge the gap created from a tibial defect (18). This technique of slow transfer is achieved usually in an Ilizarov fixator and is termed transverse bone transport to distinguish it from longitudinal bone transport (described in further detail later in the chapter). The gradual transfer preserves the vascularity of the fibula segment. Alternatively, the fibula can be transferred as a vascularised graft from the contralateral leg; microsurgical anastomosis of the peroneal artery of the fibula to a suitable vascular bundle in the host (recipient) leg is required to re-establish the blood supply (19). An example of a free fibula microvascular transfer is shown in Figure 9.2.
This form of bone replacement for tibial defects carries the advantage of long defects being adequately filled by a corresponding length of fibula. It is also suited for partial defects of the tibia in which a small circumference of the tibia remains but over a long length; the fibula can be inserted and fixed to the remaining circumference thereby avoiding conversion of the defect into a segmental type by excising the remaining viable part (Figure 9.2).
This method of replacement requires the expertise of either a surgeon trained in transverse bone transport or one in free vascularised bone transfer. In the latter, considerations should be made for the impact of loss of the fibula from the contralateral leg (there can be restrictions on sports activities and problems with a deformity of the great toe) and the period of protection and activity modification required (usually 18 months or longer) until the transferred fibula has hypertrophied and is capable of load transfer equivalent to the intact tibia.
Distraction osteogenesis (DO)
DO is the most established method of bone regeneration for large segment bone loss (20). The technique employs the ‘tension stress effect’ whereby gradual traction on biological tissues induces metabolic activity, cellular proliferation and tissue synthesis (21). The technique has found multiple applications in orthopaedic surgery for bone regeneration in various situations (22). An example of bone restoration by distraction osteogenesis is shown in Figure 9.3.
DO is carried out usually with a circular (Ilizarov) external fixator. A stable arrangement of rings is applied and a low-energy corticotomy (technique of osteotomy) undertaken. This is followed by a latent phase of usually 7–14 days which allows for the formation of early repair tissue that is biologically active and that will respond favourably to mechanical stimulus. During the subsequent distraction phase, traction is applied usually at a rate of 0.25 mm four times a day (1 mm in total). This rate of distraction has been associated with the most reliable bone formation. Once the desired length has been achieved it is necessary to hold the bone segment in position with sufficient stability to allow the newly formed bone to consolidate. The external fixator is maintained in situ (or replaced with alternative forms of internal stabilisation) during this consolidation phase; the average total time in the external fixator is between 1 and 2 months per centimetre of bone regeneration.
The ability to solve the problem of bone defects by a percutaneous technique and external fixation, and avoid the use of internal implants in an at-risk environment for infection, is particularly attractive in open fractures (20). This must be balanced against the incumbency of prolonged external fixation and the potential for adverse events such as pin-site infections, joint contractures, and fixation failure.
Modifications to the standard technique of DO are used in order to improve patient experience and outcome whilst reducing complications. These include multifocal transport (using multiple distraction sites), acute shortening across the bone defect and lengthening from a distant site in the same bone, and combining the technique with internal fixation (20). Intramedullary devices that allow distraction osteogenesis without the need for external fixation have also been developed (23). There is insufficient evidence currently for specific recommendations using these modified techniques for bone defects in open fractures.
Bone loss in open tibial fractures—recommendations for management
Cavitary or contained (metaphyseal areas)
If the area of loss is small or unlikely to compromise support of the subarticular scaffold then an expectant approach is justified. If the area is large or replacement needed in the metaphyseal area to maintain articular stability or reinforce fixation, autogenous bone graft is used. Bone graft substitutes have been used successfully in this situation for closed periarticular fractures. Caution is advised against use of this in open fractures; if used, the clinical indications would follow those as suggested for the use of internal fixation in open tibial injuries.
This describes an area of subcritical bone loss judged unlikely to compromise union, usually less than 25% the circumference of the tibia. Complete healing will depend not only on the size but the geometry, location, and patient factors (including age and co-morbidities) that may affect union and stability. An expectant approach can be taken initially and if there is failure to progress after serial observations, autogenous bone graft is used.
Critically sized defects are those felt likely to compromise union either from their location and influence on stability or through the lack of bone contact. There is a greater than 50% chance that additional procedures are required to accomplish fracture union if the defect is greater than 1 cm and the circumferential loss greater than 50% (24). The method of dealing with such a defect in an open tibial fracture can be through:
1. The induced membrane technique (see previous description).
2. Converting the partial defect to a complete segmental void and to reconstruct using distraction osteogenesis.
3. Vascularised bone graft (fibula).
4. Partial segment bone transport (hemi-callotasis).
Hemi-callotasis is a variant of bone transport but here, instead of a complete segment of bone that is gradually moved across a defect, a large fragment from division of part of the cortex of the tibia (usually the anterior circumference) is transported gradually across the defect, leaving a trail of new bone in its wake (Figure 6.4).
Small (<3 cm)
Defects less than 15 mm may be left to heal by obliterating the defect through shortening the limb to facilitate contact between the bone ends and subsequent union. Some patients are better suited to achieving early fracture union without resorting to reconstruction of the bone defect as this may prolong the treatment period and recovery. The shortened limb may then be managed by orthotic means or not at all if less than 15 mm. However, larger defects towards 3 cm may be amenable to management by bone grafting after the soft tissues have recovered well or through use of the Masquelet technique as a planned procedure.
The management of bone defects from open tibial trauma requires the expertise of orthopaedic and plastic surgeons trained in reconstruction. There are a variety of techniques available to solve the problem. Individualisation of treatment entails an assessment of the local, systemic, and patient-related factors such that the optimum mode of treatment is chosen.
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