Masquelet Technique: Visualization of Cement Spacer Utilizing Methylene Blue

Abstract

The Masquelet’s induced membrane technique remains an effective method for reconstruction in the setting of substantial bone loss. In fact, segmental bone defects that span nearly 50% of the total bone length have been restored.1 The technique was first described by a French Orthopedic surgeon, Dr Alain Charles Masquelet, in 1986 to reduce problems associated with graft containment and malnutrition hindering the growth of nonautogenous bone grafts.2 For many surgeons, Masquelet’s technique has become the first-choice management for segmental bone defects and allows for decreased monitoring or need for advanced training or facilities compared with other widely recognized treatments, including the Ilizarov bone transport.2 Although potential limitations in graft volume may be an obstacle, the technique remains viable. During the procedure, a cement spacer is interposed in the first stage and then removed, leaving a membrane of highly vascularized tissue in the defect. The graft is then placed into the defect, and the membrane is closed.2 However, distinguishing between cement and the bone itself during the removal of the cement from the defect may be difficult. The incomplete removal of cement may further complicate the reconstruction process by leaving debris in a previously open site causing damage to the membrane or inadvertent resection during a difficult spacer removal and postoperative complications. Therefore, the addition of methylene blue to bone cement, providing a contrast between the cement and bone, may aid in cement removal, thus, increasing the likelihood of successful reconstruction. The present study presents the Masquelet technique supplemented with methylene blue and outlines the benefits of our approach. SURGICAL TECHNIQUE Masquelet’s induced membrane technique allows for the reconstruction of segmental bone loss in 2 surgical stages (See Fig. 1).FIGURE 1: Radiographs of a 29-year-old patient who has a long-standing bone defect after unsuccessful treatment of a previous injury with an external fixator.First Surgical Phase When beginning the procedure, the area of bone loss needs to be cleaned of any necrotic or infected tissue. Careful attention must be paid to the muscle and fasciocutaneous environment of the segmental bone defect, as its condition is essential in the first step of this surgical procedure. Local and free flaps should be considered to optimize the reconstruction conditions if soft tissue defects are present. The borders of the flap should be marked with nonabsorbable sutures, and the position of the pedicle should be clearly noted to limit risks to the soft tissues during grafting. Placement of Cement Spacer Depending on the nature of the defect, temporary external fixation in the operating room (OR) may be helpful for spacer placement. Once mechanical stabilization is achieved, the surgeon must prepare the cement spacer and site for insertion. Surgeons must plan for a spacer that is more voluminous than the bone to reconstruct with adequate coverage of the segmental bone loss. The cement used to create the spacer is primarily composed of polymethylmethacrylate (PMMA) and allows for molding and hardening within 10 minutes through an exothermic reaction. For this reason, surgeons need to be cautious when applying cement directly to the area of bone and then molding appropriately, as the cement may burn the soft tissue. The authors recommend ensuring a smooth texture for ease of removal after the membrane has formed. Furthermore, a mixture of 2 to 3 milliliters (ml) of methylene blue per bag of cement/monomer helps contrast the cement from bone, allowing for easy removal without compromising cement structure, stability, or affecting surgical outcomes. The mixture of antibiotics with cement is highly debatable. In Dr Masquelet’s experience, the cement was not impregnated with antibiotics, thus allowing for postoperative detection of possible reinfection.2 In contrast, other surgeons have suggested the use of antibiotic-mixed cement to reduce infection risk, especially for those undergoing chemotherapy. In the authors’ experience, antibiotics (1–2 grams vancomycin, 1.2–2.4 grams tobramycin) may be mixed with the cement for specific infection related cases, and a nonantibiotic cement mixture can be used for noninfection cases. After preparation of the cement and site, the surgeon may now prepare to apply the cement to the area of bone loss. Several volumes of cement are then mixed accordingly depending on the zone to be filled. When the cement can be handled easily and is not sticky, it is molded with an increased diameter than the initial bone and adequate coverage for the bone ends (See Fig. 2). During polymerization, regular irrigation with saline solution cools the surgical field.FIGURE 2: Postoperative as well as 3-week follow-up radiographs and clinical photographs of spacer placement.Spacer Stabilization Mechanical stability is essential for successful reconstruction. Factors for stability depend heavily on the bone segment needing resection. Assuming the availability of adequate and healthy skin coverage, it is common to use plate stabilization with interlocking screws (See Fig. 2). The authors place the cement spacer, and then a plate and screw construct is utilized through the same approach. The screws are placed through the cement as it is necessary for the plate and screw construct. First, a drill bit and drill is utilized to create a hole into which a screw is then screwed into. Extensive bone loss, particularly tibia or distal humerus, require stabilization by way of external fixation. Alternatively, the cement spacer may be pinned into place through Kirschner wires, or an intramedullary nail (IMN) or similar implant can be used. There have been reports of IMNs being the superior option by the final stage, but to the authors’ knowledge, the timing of optimal IMN placement has not been demonstrated. When necessary, the authors prefer to place an intramedullary nail after cement spacer removal. Placing an IMN during initial spacer placement complicates spacer removal, potentially putting the membrane at increased risk. If necessary, the authors would use a hemicylinder shape of cement around the nail. This is because when removing cement from the nail after the membrane is formed, there is a high risk of destroying the membrane. Placing an IMN concomitant to graft or spacer removal may offer the advantage of intramedullary reaming at the time of new graft placement. These fixation methods primarily create stability by preventing excessive motion. Of note, micromotion does not impact the production of the induced membrane. The Second Stage The second surgical phase comprises the essential grafting procedure and spacer removal. It consists of placing the morselized bone graft in the induced membrane that is formed around the cement spacer after the removal of cement. In most cases, the second surgical procedure comes 6 to 8 weeks after the first procedure. Cement Removal Removal of cement without disrupting the surrounding membrane may be difficult. Further, difficulty in preserving the membrane may arise if an intramedullary nail is used in the initial stabilization process. After incising the previous surgical incision and dissecting the soft tissue around the area of the bone defect, the membrane is incised in the axis of the bone. Self-retaining retractors may be used to retract the induced membrane, as the membrane adheres to soft tissue and not cement. Cement removal may prove to be tedious, but patience is warranted. The addition of methylene blue during the first step of the technique allows adequate visualization of any cement remaining within the segmented bone loss. Therefore, the surgeon may inspect the surgical site and remove any remaining cement. Larger defects may require splitting the spacer into fragments, which is easiest with a multiple drill hole or osteotome technique. The pieces are subsequently removed manually or with instruments. Grafting Substantial bone loss involves using a large quantity of autograft material, which is often the limiting factor, particularly in young children. The site selected for harvesting graft material is determined by the amount needed for the bone defect. Classically (in adults), with the patient in lateral decubitus position, graft material is obtained from a single posterior iliac crest filling up to 5 centimeters (cm) of diaphyseal bone loss.3 The use of a reaming-irrigation-aspirator (RIA) system is an option for femurs that can accommodate a 10.0 mm diameter RIA 2 (DePuy Synthes, Warsaw, Indiana) reamer. All soft tissues are debrided, and canals are opened with intramedullary reamers. The autograft obtained from the RIA should be “aerated” with the cancellous chips (allograft) during the grafting procedure (See Fig. 3). Other cortical autograft sources include the tibia. In addition, the graft may be expanded by using allograft chips; however, allografts do not contain growth factors or stem cells and, therefore, should not exceed 30% to 50% of the total volume as this may cause a decrease in integration. The iliac crest, through an apophyseal splitting approach, may be used in skeletally immature patients. The membrane is sutured closed after bone grafting with either a 3-0 or 0 Vicryl (Ethicon, Bridgewater, New Jersey), depending on how robust it seems.FIGURE 3: Postoperative radiographs of the grafting procedure with an intramedullary rod.Expected Outcomes of Utilizing Methylene Blue Methylene blue is a thiazine dye commonly used to treat methemoglobinemia and, in rare cases, cyanide poisoning and urinary tract infections. Generally, patients suffering from this condition are given fifty milligrams once every 4 hours until symptoms resolve. In the setting of cement placement/removal, methylene blue may be used off-label as a dye to distinguish between bone and cement. In this technique, 1 ml of 1% of aqueous methylene is injected into the cement. This allows for visualization and distinction between cement and bone during the removal process while being well below precautionary measures. Of note, Methylene Blue exposure to patients with G6PD (glucose-6-phosphate dehydrogenase) deficiency should be avoided as it can cause severe hemolysis. In addition, those who have hypersensitivity to methylene blue or renal insufficiency should also have limited exposure to this dye. In all, 1 to 3 cc of methylene blue is injected per pack of PMMA during the initial mixing. Postoperative Complications The postoperative phase is usually uneventful. In small children, cast immobilization is advised until bone union. The bone union necessary for weight-bearing remains challenging to determine. In the context of a pure morselized graft, corticalization of the graft indicates that weight-bearing can be resumed without risk. Time to full weight-bearing will vary depending on the stabilization method and often patient factors. DISCUSSION Incomplete removal of cement during the second stage may predispose to postoperative infection. The primary component of cement, PMMA, does not trigger the host immune response; however, it is not biodegradable either. The porous surface of PMMA may harbor biofilm-forming bacteria, thus serving as a nidus for infection. Therefore, another surgery may be required to remove the undifferentiated cement. While the potential risks for infected cement are unknown, the authors recommend the addition of methylene blue to the cement for adequate visualization and differentiation of cement from bone. This aids in the debridement during the second surgical phase without postoperative complications. Few studies suggest mixing dye or methylene blue with cement but have not described the technique.4,5 For example, Hoit et al4 suggested mixing methylene blue with cement for identification and removal during the second phase. In contrast, Chloros et al5 found no difficulties in separating cement from bone, thus not recommending methylene blue. However, to the authors’ knowledge, the present study is the first to detail the technique using methylene blue for spacer placement. Our altered Masquelet technique has shown success in treating bone defects. Methylene blue allows for ease in visualization and removal of cement from the bone without an increase in postoperative complications. This technique holds promise and may serve as a safe alternative when treating bone defects.