Extract
A twenty-year-old woman was struck by an automobile, sustaining an open (Gustilo type-IIIB) diaphyseal fracture of the left tibia (AO-OTA 42-C3). There was extensive loss of the soft-tissue envelope over the medial, anterior, and posterior aspects of the leg. On admission, the wound was debrided and an external fixator was applied for temporary immobilization. Two more debridements were necessary to remove all contamination. Subsequently, the soft-tissue defect was covered with a vascularized rectus abdominis muscle flap six weeks after initial presentation. The recovery of the patient was complicated by wound infection with Klebsiella pneumoniae and Escherichia coli, for which she was treated with imipenem. Six months after the injury, she was referred to our institution for the treatment of an infected tibial nonunion. The external fixator was still in place. The muscle flap was viable, but there was persistent serous discharge from a sinus. Radiographs showed a large diaphyseal segmental bone defect in the tibia (Fig. 1). The two remaining problems were fracture site infection and a lack of skeletal continuity in an area where a severe, nearly circumferential, soft-tissue degloving injury had occurred and for which a free muscle flap had already been performed.
A twenty-year-old woman was struck by an automobile, sustaining an open (Gustilo type-IIIB) diaphyseal fracture of the left tibia (AO-OTA 42-C3). There was extensive loss of the soft-tissue envelope over the medial, anterior, and posterior aspects of the leg. On admission, the wound was debrided and an external fixator was applied for temporary immobilization. Two more debridements were necessary to remove all contamination. Subsequently, the soft-tissue defect was covered with a vascularized rectus abdominis muscle flap six weeks after initial presentation. The recovery of the patient was complicated by wound infection with Klebsiella pneumoniae and Escherichia coli, for which she was treated with imipenem. Six months after the injury, she was referred to our institution for the treatment of an infected tibial nonunion. The external fixator was still in place. The muscle flap was viable, but there was persistent serous discharge from a sinus. Radiographs showed a large diaphyseal segmental bone defect in the tibia (Fig. 1). The two remaining problems were fracture site infection and a lack of skeletal continuity in an area where a severe, nearly circumferential, soft-tissue degloving injury had occurred and for which a free muscle flap had already been performed.
Diaphyseal defects too long to be bridged by conventional cancellous bone-grafting need complex reconstruction. One option, distraction osteogenesis, requires specialized equipment and expertise and is associated with a high rate of complications. Vascularized bone-grafting also needs special expertise, is associated with donor-site morbidity, and requires a long time for osseous incorporation and consolidation. Moreover, the recipient site may not have appropriate vessels left to allow anastomosis, as was the situation in this patient. The induced membrane technique is a relatively simple method that can restore segmental bone loss without the need for sophisticated equipment or special expertise.
In this staged technique, the external fixator and pins are removed and the limb is placed in a plaster cast for two weeks to allow the pin tracks to heal. The patient is then brought to the operating room after the pin tracks are healed (Fig. 2). Surgery is performed with the patient in the supine position. We apply a thigh tourniquet, but it is not inflated unless we have difficulty securing hemostasis in the surgical field. Prophylactic antibiotics are not given until intraoperative cultures have been obtained. The limb is cleaned and draped in a standard aseptic manner as for intramedullary fixation of the tibia.
The fracture site is opened posteromedially between the junction of the muscle flap and the remaining intact soft tissue; the discharging sinus is excised. Soft-tissue handling must be gentle, and self-retaining retractors are not used. The fracture gap is then debrided, removing all of the intervening fibrous and granulation tissue (Fig. 3). Nonviable bone and unhealthy surrounding soft tissue are also debrided. The proximal and distal fracture ends of the tibia are also debrided with rongeurs and osteotomes until bleeding can be seen from the bone ends. If a tourniquet is in use, it should be temporarily deflated at this point to identify bleeding from the bone ends and the surrounding soft tissue. Debridement must be radical as the goal is to eliminate any residual infection. There should be no apprehension toward creating an excessively large segmental bone defect with the radical debridement. In this case, the defect created was 8 cm in length between the cortical bone ends.
Next, tibial intramedullary nailing is performed in the standard manner. We prefer the use of an unreamed interlocking nail. The nail is locked while the length of the leg, axial alignment, and rotation are all maintained. The nail should then be clearly seen, traversing the defect, and occupying the central space of the defect (Fig. 4).
Methylmethacrylate cement that has been mixed with imipenem is then prepared and circumferentially packed around the exposed intramedullary nail. Together with the nail, the cement should completely occupy the space created by the segmental bone defect (Fig. 5). The cement coverage should extend slightly beyond the cortical ends of the tibia rather than only abutting them. This is to ensure that fibrous tissue does not grow into the space between the cortical ends and the cement spacer. While the cement is setting, constant irrigation is performed to ensure that the heat generated does not cause thermal necrosis of the surrounding soft tissue and bone. The surgical wound may then be closed.
Postoperatively, the patient is allowed to bear up to 15 kg of weight on the affected limb as cement is stable in axial loading. On the basis of the cultures obtained intraoperatively, therapy with appropriate intravenous antibiotics is commenced and continued for at least six weeks and until the C-reactive protein level and the erythrocyte sedimentation rate normalize. A period of between two and three months is needed to allow the induced membranes to form before the next procedure is done. In the present case, our patient underwent the second so-called bone-grafting stage of the reconstruction two months after the index procedure. Surgery is performed with the patient in the supine position. Again, we apply a thigh tourniquet as a precaution, but it is typically not inflated. The limb and the ipsilateral iliac crest are repaired and draped for bone-grafting. Culture-specific prophylactic antibiotics are given after the induction of anesthesia.
The surgical approach is through the same incision as that used in the index procedure. Again, careful and gentle soft-tissue handling is important. Sharp dissection is carried directly onto the cement spacer without damaging or shredding the sleeve of induced membranes. The cement spacer is then carefully removed with use of osteotomes and rongeurs in a piecemeal fashion without damaging the circumferential sleeve of the induced membranes (Fig. 6). The induced membranes have the appearance of very thin fascia and are intimately apposed to the surrounding soft tissue (Fig. 7).
Next, cancellous bone is harvested from the iliac crest and introduced into the space that was previously occupied by the cement spacer. The intramedullary nail actually occupies the central space in the defect and thus less cancellous bone graft volume is required. The bone graft should be placed circumferentially around the nail. The surgical wounds are then closed.
Postoperatively, the patient should not be allowed to bear weight on the limb. Radiographs are made immediately postoperatively for baseline comparison and then subsequently at six weeks, three months, and six months. Because of the properties of the induced membranes, bone formation is expected to be fairly rapid. The commencement of weight-bearing depends on the rate of new bone formation, which is based on the radiographic appearance. Follow-up radiographs for our patient are presented in Figures 8, 9, and 10.
INDICATIONS:
- Long segmental bone defects that are too large to be bridged by simple cancellous bone-grafting, typically those that are >6 cm.
- Infected nonunion of a long bone for which the procedure is a means of simultaneously eradicating the fracture site infection and reconstructing the defect.
CONTRAINDICATIONS:
- Second-stage bone-grafting should not proceed if the infection has not been cleared.
- The intramedullary nail might compromise tissue planes if used to reconstruct the defect following tumor resection.
- Uncertain patient compliance.
- Poor general health of the patient is a relative contraindication.
PITFALLS:
- Not extending the cement slightly beyond the cortical bone ends so as to "wrap" the ends. Failing to extend the cement allows unwanted fibrous tissue to grow into the cement-cortical bone interface and into the bone defect site.
- Rough handling damages or tears the induced membranes.
- Sometimes it can be difficult to place the cement optimally behind the nail.
- Careful closure after the second-stage bone-grafting is important to ensure that the induced membrane envelope is completely closed.
AUTHOR UPDATE:
There has been no substantive change in the procedure since it was reported in the original article.