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Three Techniques for the Fabrication of Cement Spacers in the Treatment of an Infected Total Hip Arthroplasty

Zawadsky, Mark W. M.D.; Pearle, Andrew D. M.D.; Sculco, Thomas P. M.D.

TIPS AND PEARLS
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Summary Two-stage exchange arthroplasty has become the treatment of choice for chronic infection of total hip arthroplasty in North America based on the improved eradication rates compared to single-stage exchange. A temporary cement spacer is used during the intervening treatment period to deliver antibiotics locally, maintain length and alignment, and provide some degree of mobility and comfort for the patient. This paper reviews three types of antibiotic-loaded cement spacers that meet these criteria and are simple and easy to fashion. The first technique uses spherical molding of cement over a Steinman pin; the second uses a spherical molding technique over a 4.5 dynamic compression plate; the third technique uses a prefabricated mold device to produce a cement spacer for implantation.

From the Hospital for Special Surgery, Cornell University Medical College, New York, New York, U.S.A.

Address correspondence and reprint requests to Mark W. Zawadsky, MD, Hospital for Special Surgery, 535 East 70th Street, New York, NY 10021 USA.

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INTRODUCTION

Deep infection in total hip arthroplasty remains a potentially devastating complication, even though the incidence has been successfully reduced from historical rates of 7% to 10% in the 1960s to the current levels of 0.5% to 1% using modern techniques. 2 Except in early perioperative infections, or rare late infections such as hematogenous seeding with a nonvirulent organism, the treatment of infected total hip arthroplasty necessitates the removal of the prosthetic components. While a single stage, direct exchange arthroplasty may be indicated in select cases, 4 a two-stage exchange arthroplasty has become the treatment of choice for chronic infection of total hip arthroplasty in North America. 3 This is based on the reported eradication rates of 90% or better for two-stage exchange compared with a success rate of approximately 80% in primary exchange. 1

In a two-stage exchange procedure, the prosthetic components are removed along with all cement, nonviable osseous and soft tissue is debrided, the acetabulum and femur are gently reamed, and a temporary spacer is placed into the acetabulum. The spacer is used to deliver antibiotics locally, to maintain length and alignment, and to provide some degree of mobility and comfort for the patient during the intervening treatment period.

The ideal temporary spacer should be inexpensive, provide concentric elution of antibiotic to endosteal bone and tissue, allow ease of implantation and removal, provide a smooth load bearing surface to preserve bone stock, provide adequate and physiologic tension of the soft tissues, and allow for mobilization of the patient. This paper reviews three types of antibiotic loaded cement spacers that meet these criteria and are simple and easy to fashion. The first technique uses spherical molding of cement over a Steinman pin; the second uses a spherical molding technique over a 4.5 dynamic compression plate (DCP); and the third technique uses a prefabricated mold device to produce a cement spacer for implantation.

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Spherical Molding Over a Steinman Pin

In this technique, a spacer is prepared by hand molding a ball of cement over a smooth Steinman pin (Figs. 1, 2, and 3). The length and thickness of the pin can be modified to match the size of the femur; alternatively, a larger rush rod or similar device can be used. The acetabular shell or trials can be used as a template to help produce a uniform shape, as well as appropriate size for the spacer head. An alternative and simple technique is to use a bulb syringe to shape the proximal cement head (Fig. 4). 5 Cement is poured into the bulb portion while in the liquid phase and the pin is held in the cement as it cures. Once the cement has set, the bulb can easily be cut away with a scalpel. This produces a spacer head with a smooth, uniform surface and a diameter of approximately 51 mm. A limitation of this technique is that only one size of bulb syringe is commonly available.

FIG. 1

FIG. 1

FIG. 2

FIG. 2

FIG. 3

FIG. 3

FIG. 4

FIG. 4

Cement can be shaped to fit in the femoral canal for added rotational stability. We have found, however, that this is not necessary and can lead to difficulty in removal, as well as retained cement at the time of reimplantation. The placement of a smooth pin of sufficient diameter and length provides good stability for the spacer construct. If cement is placed to fit in the femoral canal, it is important that the cement be molded in the femur while still in a “doughy” phase and removed prior to final hardening so that the mantle matches the contours of the femoral canal, yet has sufficient play to allow for ease of removal.

This technique has the advantage of being a simple, flexible, and inexpensive means of producing a cement spacer. It provides for easy placement and removal, limits stress on the femoral shaft, and reduces bone loss due to secondary erosion. The disadvantage is that, in rare cases, the pin can fracture or a fracture of the neck portion of the cement spacer can occur if cement is extended into the femur.

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Spherical Molding Over a 4.5 mm DCP Plate

This second technique is similar to the first in that the proximal cement head can be hand molded or shaped with a bulb syringe; however, a contoured 4.5 mm DCP plate is used as the intramedullary device (Figs. 5 and 6). This produces a stronger mechanical construct of the spacer and also provides an added degree of rotational stability, due to the wider geometry when compared with a smooth pin or rod. The smooth surfaces of the plate help to minimize bone erosion while the holes in the plate produce a more secure attachment to the cement. The width of the plate facilitates molding of the cement over the proximal portion to gain a better fit in the proximal aspect of the intramedullary canal of the femur. This allows for easier adjustment of the soft tissue tension because the length of the proximal aspect of the spacer can be better controlled with this method. Again, this is an easy, flexible, and reproducible technique that requires no special equipment.

FIG. 5

FIG. 5

FIG. 6

FIG. 6

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Prefabricated Mold Device: ANTILOCH Technique

This technique uses a prefabricated teflon mold cast in the shape of a Austin Moore-type hemiarthroplasty prosthesis (Figs. 7, 8, and 9). This has been labeled the ANTILOCH component for antibiotic loaded cement hemiarthroplasty (mold manufactured by Implex Corp., Allendale, NJ). The cement is injected into the mold while in the liquid phase. One or two Steinman pins can be contoured and placed in the mold to increase the strength of the spacer. Once the cement has fully hardened, the spacer is removed from the mold and the rough surfaces are trimmed with an oscillating saw and rongeur. Currently, three mold sizes are available which provide a better fit in the femur and more accurate soft tissue tensioning. Partial weight bearing is routinely allowed and most patients are able to ambulate with crutches. This technique has the advantage of being easy and reliable to use, it has no uncovered metal or polyethylene components as with the PROSTALAC device, (University of British Columbia, British Columbia, Canada) 6 and it accurately matches the shape of the femur and acetabulum. Additionally, it is stable while implanted, easy to retrieve, and provides a large surface area to deliver a concentric volume of antibiotics.

FIG. 7

FIG. 7

FIG. 8

FIG. 8

FIG. 9

FIG. 9

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CONCLUSION

These techniques provide a wide degree of flexibility when constructing a cement spacer for the staged treatment of an infected total hip arthroplasty. All are easy to construct, inexpensive, and allow increased patient mobility and comfort while maintaining soft tissue tension and minimizing loss of bone stock during the treatment period.

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REFERENCES

1. Antoniou J. Revision of the Infected Total Hip Arthroplasty. In: Paprosky WG, ed. Revision Total Hip Arthroplasty Rosemont, Il: American Academy of Orthopedic Surgeons Monograph Series; 2001; 53–59.
2. Fitzgerald RH. Infected total hip arthroplasty. Diagnosis and treatment. JAAOS 1995; 3: 249–262.
3. Garvin KL, Hanssen AD. Infection after total hip arthroplasty: past, present, and future. J Bone J Surg Am 1995; 77: 1576–1588.
4. Jackson WO, Schmalzried TP. Limited role of direct exchange arthroplasty in the treatment of infected total hip replacements. Clin Ortho Related Res 2000; 381: 101–105.
5. Ries MD, Jergesen H. An inexpensive molding method for antibiotic impregnated cement spacers in infected total hip arthroplasty. J Arthroplasty 1999; 14: 764–765.
6. Younger AS, Duncan CP, Masri BA, McGraw RW. The outcome of two-stage arthroplasty using a custom-made interval spacer to treat the infected hip. J Arthroplasty 1997; 12: 615–623.
Keywords:

Total hip arthroplasty; Infection; Two-stage exchange; Temporary spacer

© 2001 Lippincott Williams & Wilkins, Inc.