Novel modification of second generation intramedullary PMMA cementing technique for narrow upper and lower extremity canals

Abstract

Purpose

It is very difficult to cement intramedullary canals smaller than 10 mm with standard commercially available cement syringes due to mismatch in canal and syringe diameters. This is often encountered in children and in the upper limb. We describe a simple method of cementing, using cement gun with size-matched plastic endotracheal tube (ET).

Methods

The medullary canal is prepared and the size determined. ET with outer diameter 0.5–1 mm smaller than the canal diameter is chosen. The standard cementing syringe nozzle is cut at the middle and fitted to Portex^® tube with the adaptor connector, which comes with the ET. The plastic ET is cut to an appropriate length depending on canal length to be cemented. The nozzle is fitted to the syringe and cementing done in the usual way. We applied this new modification in the method to cement narrow canals of ulna, humerus, tibia and femur.

Results

The method has proven to be consistently reliable and useful in cases of cementing stems into bones with narrow intramedullary diameters. Apart from femur and tibia in children, humerus and ulna in adults were also cemented. The cement mantle by this technique is uniform and uninterrupted. Special care should be taken to fit the connector properly to the syringe nozzle and to hold it firmly while cementing.

Conclusions

In our experience, this new technique has proven to be very useful, easy to use, reproducible and effective in cementing narrow canals.

1. Introduction

With the evolution of cementing technique, retrograde high pressure cementing with a gun has shown to improve the quality of cement mantle and delay loosening.¹ Commercially available cement guns have pre-sized disposable nozzles, which have a diameter of 12 mm at the narrowest taper and 14–15 mm at the proximal end. This is unsuitable for narrower canals encountered in children and the forearm bones, as well as lower limb bones in the Asian population. Lack of options may force surgeons to choose inferior methods like thumb packing/pouring the cement in its liquid form, which can significantly compromise bonding interface and impact longevity of the construct.^{2, 3}

We describe a novel modification to the existing second generation technique of cementing, which allows cement filling in narrow intramedullary canals of virtually all sizes ranging from 3 mm to 12 mm inclusive of upper and lower extremities using cement gun with size-matched plastic endotracheal tube (ET).

2. Technique

All patients had prosthesis inserted for reconstruction after resection of bone or joint for a tumour and a canal size less than 13 mm (this is the minimum required with the advantage nozzle). Keeping the above advantages of second generation/contemporary cementing techniques in mind, the focus of our technique was to improve cementing in narrow intramedullary canals and in the absence of appropriately sized nozzles for the Indian population as explained above.

The technique exploits the universal availability of all sizes of ET in every operating theatre.

The first step is to fetch a tube where the outer diameter (OD) matches closest to the canal diameter after satisfactory reaming to allow the ET to comfortably slide into the canal [Fig. 1], e.g., if the ulna canal is reamed to allow a 4 mm component to fit, an ET with an OD of 3.9 mm or slightly lesser could be used.

Fig. 1.

Endotracheal tube with OD smaller than prepared/reamed canal diameter.

The next step is to cut the cuff and trim the length to suit the length of the stem to be inserted [Fig. 2]. If the stem length is 8 cm, a 1–2 cm margin of cement plug (restricted by a canal centraliser or cement restrictor where required) demands that the ET be cut at 10 cm from its proximal connector end.

Fig. 2.

Cut endotracheal tube to desired length, to allow retrograde cementing.

The commercially available nozzle (for example, Advantage nozzle) is cut at 8.5 cm from the shoulder of the nozzle [Fig. 3]. This allows the ET adaptor to fit snugly on to the nozzle so they act as one long passage for the cement. This assembly is fit as usual to the cementing gun and could now be used to inject cement under pressure into the desired canal size [Fig. 4]. The cut is made with a knife blade or with a saw. The loose plastic particles are removed by wiping with wet gauze.

Fig. 3.

Advantage gun nozzle cut at 8.5 cm from the shoulder.

Fig. 4.

Endotracheal tube fitted to the cement-gun nozzle and loaded onto the cement-gun assembly.

The advantage lies in the fact that even a 4 mm ulnar canal could be cemented under pressure by adapting a 3.5 or a 3.9 OD ET to the native nozzle. The snugness of the fit ensures that the assembly does not disengage while cementing under pressure. For any other system, it is possible to work out where the nozzle should be cut to obtain a tight fit with the adaptor.

Downsized ET diameter allows entry well into the intramedullary canal up to desired thereby allowing retrograde cementing, and also the flexibility of the ET, which tends to align itself in the intramedullary canal – allows cementing without having to be perfectly in line with the intramedullary canal (Fig. 5) – which are the key highlights of the cementing technique using ET.

Fig. 5.

Insertion of the endotracheal tube into canal for cementing.

Table 1 lists the various sizes of Portex^® endotracheal tubes available with their respective OD as a ready reckoner for use. If a different manufacturer were used, the only change would be the distance from the shoulder where the native nozzle is cut so as to allow a snug adaptation with the ET.

Table 1.

Various sizes of Portex^® endotracheal tubes available (with their respective OD) as reference for use in corresponding canal diameters.

Intramedullary diameter (mm)	Cuffed endotracheal tube		Un-cuffed endotracheal tube
	ID (mm)	OD (mm)	ID (mm)	OD (mm)
4			2.5	3.4
4.5			3.0	4.2
5			3.5	4.8
6			4.0	5.5
6.5			4.5	6.2
7	5.0	6.8	5.0	6.9
8	5.5	7.4	5.5	7.6
8.5	6.0	8.2	6.0	8.2
9	6.5	8.8	6.5	8.9
10	7.0	9.6	7.0	9.6
11	7.5	10.2	7.5	10.3
11.5	8.0	10.9	8.0	11.0
12	8.5	11.6	8.5	11.6
12.5	9.0	12.3	9.0	12.3
13.5	9.5	13.0	9.5	13.0
14	10.0	13.7

ID: inner diameter of endotracheal tube; OD: outer diameter of endotracheal tube.

The bone was thoroughly cleaned before cement insertion, in most cases using a pulsatile lavage, an intramedullary centraliser plug was used where advocated, and canal packed with roller gauze until we were ready to cement the canal. The cement was inserted retrograde to reduce blood lamination and voids. Because of high resistance, the cement was injected early in the polymerisation process. Maintaining proximal pressurisation to improve the penetration of cement into the cancellous bone enhances the mechanical interlock and the interface fixation strength while the implant stem is gradually inserted into the canal. Final position is maintained until the cement sets.

3. Results

The method has proven to be consistently reliable and useful in cases of cementing stems into bones with narrow intramedullary diameters. Apart from femur and tibia in children, humerus and ulna in adults were also cemented. The cement mantle by this technique is uniform and uninterrupted. No voids were noticed.

4. Drawbacks

While the described modification can easily be applied into practise directly, there is always a possibility of leakage/breakage or disengagement at the nozzle–tube junction if the assembly is not snugly fit or under high pressurisation if cement is injected in its doughy phase. Special care should be taken to fit the connector properly to the syringe nozzle and to hold it firmly while cementing.

While there are no major pitfalls of this method as it is only an extension of the currently existing cementing technique, the outcomes are only a matter of effective use of the technique while following the general principles of cementing.

5. Discussion

The goal of modern cementing technique in general is to improve both the long-term properties of the cement itself and the cement–bone interface.

No ideal system exists on the market, which offers both excellent mixing and a well-designed, efficient cement-gun assembly, especially for the Indian scenario where cost is an important deciding factor and difference in the skeletal structure with narrower intramedullary canals restricts us from using most cementing systems available globally.

Therefore, our modification to an already accessible cement-gun system available at any particular centre with the only requirement of an ET allows cementing of intramedullary canals ranging from 3.5 mm to 14 mm, which would have otherwise required thumb packing or the first-generation cementing technique. While the surgeon continues to remain familiar with the cement-gun assembly, the principles of modern cementing technique can be effectively applied even in narrowest canals.

In addition to the easy availability and limited/low cost of the ET, it allows this method to be easily and conveniently reproduced/practised at most centres.

6. Requirements

• 1.Cement gun
• 2.Advantage nozzle (cut at 8.5 cm from the shoulder)
• 3.Bone cement (preferably low viscosity)
• 4.ET (Cut to desired length)
• 5.Pulsatile lavage
• 6.Roller gauze
• 7.Cement restrictor (where required)

Conflicts of interest

The authors have none to declare.