Preparation of cement spacer in treatment of segmental bone defects in children by the induced membrane technique: A technical note

Abstract

The Masquelet Induced Membrane Technique (IMT) is one of the tools in the surgeon’s armamentarium for the management of segmental bone defects. The first stage of the IMT includes the insertion of a cement spacer, which is typically fashioned by the free-hand technique. We propose a novel technique for preparation of the cement spacer using a split syringe barrel as a mould. This technique produces a uniformly cylindrical spacer with minimum cement spillage, while also minimizing thermal damage to the surrounding soft tissues. It is a simple and cost-effective method that can be adapted for use in any long bone in children.

1. Introduction

The Masquelet Induced Membrane Technique (IMT) is an extremely useful method for the staged reconstruction of segmental bone defects due to a variety of causes such as infection, trauma, tumor, resection of pseudoarthrotic tissues etc., in children as well as in adults.¹ The first stage of the Masquelet technique consists of debridement of devitalized bone and soft tissues, insertion of a cement spacer, skeletal stabilization and soft-tissue reconstruction if necessary. The second stage consists of spacer removal with careful preservation of the induced membrane, repeat debridement of the bone edges, placement of autologous bone graft in the defect and closure of the membrane over the graft without tension, with definitive stabilization of the bone.

Traditionally, the cement spacers are fashioned by the free-hand technique, however, in long defects, it can be difficult to prepare a uniformly cylindrical spacer by this technique. Additionally, the heat generated during cement setting can cause thermal necrosis of surrounding soft tissues. To overcome these difficulties, we describe a simple alternative technique of in-vivo cement spacer preparation using a slit syringe barrel as a mould.

2. Surgical technique

• 1.As per standard procedure, in the first stage, the osteomyelitic bone is exposed, all sequestra and infected tissue are excised, the bone ends are debrided until bleeding bone is seen, the medullary canal is opened on either side, and copious lavage is given. The length of the bone defect is measured (Fig. 1b).
• 2.A syringe is selected that has a diameter similar to that of the affected bone (the size required depends on the age and build of the child, for example, 5 cc and 10 cc syringes are usually required in toddlers for the tibia and femur respectively).
• 3.The plunger is removed, the flange and nozzle at the two ends of the syringe are cut and discarded and the central barrel is retained. The length of the barrel should be at least 1–2 cm greater than the measured length of the defect, to allow for overlap of the cement at both bone ends. The barrel is split longitudinally along its entire length (Fig. 1c).
• 4.The syringe barrel is inserted into the defect such that its ends are wrapped around the bone fragments on either side. Care is taken to ensure that the ends of the syringe barrel overlap at least 5–10 mm of the bone fragments at both ends (Fig. 1d).
• 5.The cement mixed with appropriate antibiotics is then prepared and inserted into the slit barrel while in the doughy state, typically 3–4 minutes after mixing of the cement and solution. Insertion is made easier by an assistant opening out the barrel by means of Kocher forceps attached on either side of the slit (Fig. 1d).
• 6.The slit is then closed and any excess cement that spills out is removed. The syringe barrel is held in the closed position until the cement sets and hardens (Fig. 1d).
• 7.Once the cement has hardened, the syringe barrel is easily pulled out (Fig. 1e).
• 8.The bone is stabilized if necessary, and closure is performed in the routine manner.

Fig. 1.

Step-wise surgical technique in stage 1 of IMT, demonstrated in a case of left tibial diaphyseal chronic osteomyelitis with pathological fracture and gap non-union in a nine-months-old boy.

a Pre-operative anteroposterior and lateral view radiographs of the left tibia. b Left tibial shaft exposed. The was a 2 cm gap non-union at the mid-distal 1/3rd junction, and a large part of the anterior tibial cortex was sequestered. The fracture site was debrided of all infectious tissue, medullary canal opened on both sides and all sequestra excised. c Preparation of the syringe for use – plunger removed; nozzle and flange ends cut off; barrel slit longitudinally and stretched open. d Syringe barrel inserted into the defect enclosing both bone ends and overlapping them; insertion of doughy cement into defect while the barrel is being held open by two artery forceps; slit ends of the barrel being held in apposition to mould the spacer into a cylindrical shape, excess cement extruding through the silt has been removed. e Cement has hardened; syringe barrel being removed; final appearance of the spacer. f Post-operative radiographs.

See Fig. 1(a–f) for clinical photographs demonstrating the steps in the surgical technique outlined above. Fig. 2(a–d) follows the same case until spacer removal and bone grafting. Clinical photographs and radiographs of another similar case, followed-up until one year after the second-stage surgery are given in Fig. 3(a–e).

Fig. 2.

Spacer removal and bone grafting during stage 2 of IMT in the same case as in Fig. 1, surgery being performed six weeks after the first stage.

a Spacer exposed, the induced membrane has been incised and retracted. b Appearance of the spacer after removal en masse, and of the wound bed after re-debridement. c Reconstruction with fibula strut graft harvested from the opposite limb. d Post-operative radiograph. The graft was fixed using and intramedullary Kirschner wire spanning the ankle and subtalar joints.

Fig. 3.

Case example of a two-years-old male child with infective gap non-union of right tibial diaphysis.

a Pre-operative anteroposterior and lateral view radiographs of the right leg. b Intra-operative photographs during first stage of IMT surgery – Right tibial diaphysis debrided exposing 3 cm defect; syringe barrel placed in defect; cement filled into barrel and allowed to set. c Anteroposterior and lateral view radiographs of the right leg after spacer insertion. d Intra-operative photographs during second stage surgery (six weeks later) – Induced membrane incised and retracted to reveal the spacer; spacer removed and autologous fibula strut placed in defect; morselized iliac crest added around the fibula graft. e Anteroposterior and lateral view radiographs of the right leg - immediately after surgery and at one-year follow-up. The fracture united well and there was no further infection.

3. Discussion

The IMT is a reliable method for reconstruction of bone defects in children. The presence of a cement spacer incites a foreign body inflammatory reaction, leading to the formation of a biologically active membrane rich in inductive molecules and mesenchymal stem cells.¹

Numerous authors have studied the effect of the type of spacer used on the quality of the induced membrane.¹ Alterations in the texture of the cement (surface roughness) do not appear to have an effect on later bone formation. Presence of antibiotics in the spacer appear to promote higher osteogenic gene expression. Although cement beads are equally effective in local control of infection, they are not as effective as spacers for inducing healing in large bone defects.

Although the exact biological mechanisms underlying the IMT remain unknown, long-term follow-up of more than 100 patients has led to the identification of several technical rules which need to be strictly followed for successful bone reconstruction.^1,2

• •The spacer should overlap the periosteum at both ends of the bone defect for at least 1cm. This allows membrane induction away from the defect area and reduces the risk of non-union between the graft and the bone ends.
• •The cement must invaginate into the medullary canal so as to give better stability.
• •While the cement is setting, the surrounding soft tissues must be protected from the heat generated by using a piece of glove and by continuous saline irrigation.

Traditionally, the antibiotic-laden cement is prepared, and when it is of a doughy consistency, it is shaped by hand and placed into the defect. In case skeletal fixation is not being applied, as is often the case in very young children, the gap between the bone ends is highly unstable, and inadvertent movement of the limb as the cement sets can produce a misshapen angulated spacer. It can be difficult to keep the soft tissues separated from the cement, due to which loose cement particles often end up in the soft tissues, and some heat damage to the soft tissues invariably occurs during the exothermic phase. It is also difficult to obtain invagination of the cement into the medullary canal by the freehand insertion technique. The size of the spacer is often mis-judged, and over-sized spacers may lead to difficulty in obtaining soft tissue closure.

The novel technique proposed helps to overcome a number of these difficulties. Placement of the cement into the mould formed by the syringe barrel facilitates shaping of the spacer. As the barrel overlaps the bone edges, it gives some degree of stability to the bone ends while the cement is setting, and also ensures overlap of the spacer at the bone ends. Holding the barrel closed applies gentle pressure to the doughy cement allowing it to invaginate into the medullary cavity. Excess cement can extrude out only through the longitudinal slit in the syringe barrel, thus minimizing soft tissue spillage. Also, the syringe protects the surrounding soft tissues from thermal damage as the material from which it is made (polypropylene) is a poor conductor of heat. Finally, with the range of sizes of syringes available, and given their malleability, the spacer can be easily customized to the dimensions of the bone, and problems associated with oversizing are avoided. We thus propose this technique as a simple alternative method for the in-vivo preparation of a cement spacer.

A literature review revealed that we were not the first to make use of a syringe for fabricating cement spacers. A similar technique was described by Pauchot et al.³ in which, a syringe body was cut in half lengthwise, one half was introduced into the defect, the cement was poured into it in a semi-liquid state, and the other half of the syringe barrel was then placed over it. The authors described this technique to be similar to the use of ‘formworks’ in construction. Silk et al.⁴ recently described another technique using a syringe as a mould to create a cement spacer with a spigot at one end to insert into the medullary canal and a broad surface at the other end for greater bone contact. The spacer is prepared outside the wound and inserted into the bone defect after it has set. Two groups of authors^5,6 have even described the use of a piece of disposable syringe itself as a spacer, and have reported outcomes similar to those seen with cement spacers.

Disposable syringes offer several advantages when used as moulds for cement spacer preparation. The syringe barrel is made from polypropylene which has a melting point of 130–171 °C.⁷ Studies have shown that the heat produced during polymerization of bone cement produces surface temperatures of 37–70 °C and central temperatures of up to 122 °C.⁸ Thus, the surface temperatures being well below the melting point of the polypropylene, there is no risk of the plastic melting as the cement sets. The cylindrical shape of syringes makes them very suitable as moulds for defects in tubular bones. Syringes are also inexpensive and universally available, in an array of sizes (Table 1). A possible limitation is that the length of the available syringes may fall short for large defects in adults; however we have not encountered any such problems in children.

Table 1.

Relevant dimensions of commonly used syringes.

Syringe volume (cc)	Inside diameter (cm)	Barrel lengtha (cm)
2 (2.5)	0.8	4.9
5 (6)	1.2	5.5
10 (12)	1.5	7.1
20	2.0	8.5
50 (60)	2.7	11.0

^aBarrel length measured along the portion of the syringe body that can be used for spacer preparation only (nozzle and finger grip excluded).

The senior author has used this technique in five cases – including two tibiae, two femora and one radius/ulna – and has had satisfactory results in all cases. An example of one such case is given in Fig. 3.

4. Conclusions

We have described a novel technique to create a uniformly cylindrical cement spacer, with no soft tissue spillage, that can be customized to the bone. This is a simple and cost-effective technique, using an ordinary syringe as a mould. We have found this technique to be very useful during the first stage of the Masquelet technique for treating segmental bone defects in children.

Funding

This study has no funding support.

Consent to publish

The authors affirm that participants provided informed consent for publication of the images in Fig. 1, Fig. 2, Fig. 3.

CRediT authorship contribution statement

Deepika A. Pinto: Investigation, Writing - original draft. Sandeep V. Vaidya: Conceptualization, Methodology, Writing - review & editing, Supervision. Mandar V. Agashe: Conceptualization, Methodology, Supervision.

Declaration of competing interest

The authors declare that they have no conflict of interest.