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An inexpensive molding method for antibiotic-impregnated cement spacers in infected total hip arthroplasty
The Journal of Arthroplasty Vol. 14 No. 6 1999
An Inexpensive Molding Method for Antibiotic-Impregnated Cement Spacers in Infected Total Hip ArthroplasW Michael D. Ries, MD, and Harry Jergesen, MD
Abstract: Placement of an antibiotic-impregnated cement endoprosthesis facilitates patient mobilization and treatment of infection complicating total hip arthroplasty. Molds, particularly to form the spherical head of the cement endoprosthesis, are not readily available, however. We have found that the rubber bulb portion of an irrigation syringe can be conveniently used as a mold to shape the proximal end of a cement endoprosthesis during surgery. Key words: cement, spacer, antibiotic, infection, hip, arthroplasty.
Use of a prosthesis with antibiotic-loaded acrylic c e m e n t (PROSTALAC; University of British Columbia, British Columbia, Canada) or a spacer m a d e with use of antibiotic-impregnated c e m e n t placed a r o u n d an intramedullary rod can be beneficial in the t r e a t m e n t of infected total hip arthroplasty (THA) [1,2]. The PROSTALAC contains a m e t a l - o n p o l y e t h y l e n e bearing, however, which is not coated with antibiotics, and the proximal end of the intramedullary cement spacer is difficult to shape into a smooth surface to articulate with the bony acetabulum. We have found a simple, inexpensive method to form the cement on the head of an i n t r a m e d u l l a r y c e m e n t spacer into a spherical shape by using a bulb syringe as a mold.
al. [2]. The rod or pins, coated with d o u g h y cement, are introduced into the femoral canal to shape the stem portion of the c e m e n t endoprosthesis. Rather t h a n placing c e m e n t a r o u n d the p r o x i m a l end of the rod or pins, antibiotic-impregnated c e m e n t is packed inside the rubber bulb portion of an irrigation syringe (Fig. 1). The bulb containing c e m e n t is t h e n placed over the p r o x i m a l end of the rod and held until the cement sets. The rubber bulb is then indsed with a scalpel and removed, leaving an antibioticimpregnated cement endoprosthesis (Fig. 2).
Discussion Two-stage d~bridement, i n t r a v e n o u s antibiotic therapy, and delayed reimplantation THA is a successful m e t h o d of t r e a t m e n t for infected THA [1,3]. Use of an antibiotic-impregnated c e m e n t spacer permits early patient mobilization, delivers local antibiotics, maintains leg length, and facilitates exposure during the second-stage reimplantation operation. Molds to f o r m the c e m e n t into the shape of a prosthesis, however, m a y be expensive or unavailable in the United States because of Food and Drug Administration restrictions. Hand molding the c e m e n t a r o u n d an intramedullary rod or stacked pins to f o r m the i n t r a m e d u l l a r y portion of the spacer, w h i c h t h e n fits the irregular shape of the endosteal surface of the femur, m a y be beneficial in providing rotational stability of the c e m e n t endoprosthesis [41. H a n d molding the proximal end of the c e m e n t endoprosthesis that articu-
Surgical Technique One end of an intramedullary nail or stacked t h r e a d e d pins are p r e b e n t to 45 ° and autoclaved before surgery. After the infected prosthesis is rem o v e d and the hip d~brided, antibiotic-impregn a t e d c e m e n t is placed a r o u n d the rod using the same technique as that described by D e s h m u h k et From the Department of Orthopaedic Surgery, University of California, San Francisco, San Francisco, CA. Submitted July 16, 1998; accepted December 2i, 1998. Reprint requests: Michael D. Ries, MD, Department of Orthopaedic Surgery, UCSF Medical Center, 500 Parnassus Ave (MU 320-W), San Francisco, CA 94143. Copyright © 1999 by Churchill Livingstone® 0883- 5403199/1406-0019510.00/0
764
Antibiotic Cement Spacer Molding Method •
Fig. 1. Rubber bulb portion of an irrigation syringe used to mold a femoral cement endoprosthesis head.
lates with an irregularly shaped acetabular cavity, however, m a y cause crepitus during hip range of motion, pain, and erosion of the acetabular bone surface. Use of a s m o o t h hemispherical shape to
Ries and Jergesen
765
mold the articulating surface of an antibioticimpregnated cement endoprosthesis m a y permit more comfortable patient mobilization and preservation of bone stock than h a n d molding. The bulb portion of an irrigation syringe permits intraoperative fabrication of a s m o o t h hemispherically shaped cement endoprosthesis. The bulb is available in only one size, however, which molds an endoprosthesis of approximately 51 m m in diameter. To use this technique, the acetabular defect must be at least the same diameter as the inner diameter of the bulb syringe. We have f o u n d that the bulb syringe mold can be used in larger acetabular defects w i t h o u t compromising stability. Femoral head molds ideally should be available in multiple sizes. Alternatively, antibiotic-impregnated cement m a y be added by h a n d to the outer surface of the molded endoprosthesis to increase its size. We have used 1.2 g of tobramycin p o w d e r in each package of cement plus 1 g of v a n c o m y c i n p o w d e r if the infection m a y be caused by Staphylococcus epidermidis. Larger antibiotic concentrations have been recommended for use with the PROSTALAC [1,3]. Increased antibiotic concentrations may weaken the cement, however [5]. Recently, we have used 3.6 g of tobramycin in each package of cement and have not observed problems with cement fracture. The mechanical integrity of the cement in the spacer may also depend on the amount of proximal bone present, rod diameter, and biomechanical demands of the patient. Our current practice is to mix 3.6 g of tobramycin in each package of cement and use the largest diameter intramedullary rod that can be completely coated with cement and still fit inside the femoral canal.
References
Fig. 2. Anteroposterior radiograph of a 74-year-old man who presented with an infected periprosthetic hip fracture and was treated with d~bridement and insertion of an antibiotic-impregnated cement endoprosthesis spacer. The cement coats an 8-mm prebent Schneider intramedullary nail. The femoral head of the cement endoprosthesis measures 50.6 mm in diameter and had been molded from the interior surface of an irrigation syringe rubber bulb.
1. Younger ASE, Duncan CP, Masri BA: Treatment of infection associated with segmental bone loss in the proximal part of the femur in two stages with use of an antibiotic-loaded interval prosthesis. J Bone Joint Surg Am 80:60, 1998 2. Deshmukh RV, Thevarajan K, Kok CS, et al: An intramedullary cement spacer in total hip arthroplasty. J Arthroplasty 13:197, 1998 3. Younger ASE, Duncan CP, Masri BA, McGraw RW: The outcome of two-stage arthroplasty using a custommade interval spacer to treat the infected hip. J Arthroplasty 12:615, 1997 4. Kraay M J, Goldberg VM, Figgie HE: Use of an antibiotic impregnated polymethylmethacrylate intramedullary spacer for complicated revision total hip arthroplasty. J Arthroplasty 7:397, 1992 5. Flick AB, Herbert JC, Goodell J, Kristiansen T: Noncommercial fabrication of antibiotic-impregnated polymethylmethacrylate beads: technical note. Clin Onhop 223:282, 1987
An Inexpensive Molding Method for Antibiotic-Impregnated Cement Spacers in Infected Total Hip ArthroplasW Michael D. Ries, MD, and Harry Jergesen, MD
Abstract: Placement of an antibiotic-impregnated cement endoprosthesis facilitates patient mobilization and treatment of infection complicating total hip arthroplasty. Molds, particularly to form the spherical head of the cement endoprosthesis, are not readily available, however. We have found that the rubber bulb portion of an irrigation syringe can be conveniently used as a mold to shape the proximal end of a cement endoprosthesis during surgery. Key words: cement, spacer, antibiotic, infection, hip, arthroplasty.
Use of a prosthesis with antibiotic-loaded acrylic c e m e n t (PROSTALAC; University of British Columbia, British Columbia, Canada) or a spacer m a d e with use of antibiotic-impregnated c e m e n t placed a r o u n d an intramedullary rod can be beneficial in the t r e a t m e n t of infected total hip arthroplasty (THA) [1,2]. The PROSTALAC contains a m e t a l - o n p o l y e t h y l e n e bearing, however, which is not coated with antibiotics, and the proximal end of the intramedullary cement spacer is difficult to shape into a smooth surface to articulate with the bony acetabulum. We have found a simple, inexpensive method to form the cement on the head of an i n t r a m e d u l l a r y c e m e n t spacer into a spherical shape by using a bulb syringe as a mold.
al. [2]. The rod or pins, coated with d o u g h y cement, are introduced into the femoral canal to shape the stem portion of the c e m e n t endoprosthesis. Rather t h a n placing c e m e n t a r o u n d the p r o x i m a l end of the rod or pins, antibiotic-impregnated c e m e n t is packed inside the rubber bulb portion of an irrigation syringe (Fig. 1). The bulb containing c e m e n t is t h e n placed over the p r o x i m a l end of the rod and held until the cement sets. The rubber bulb is then indsed with a scalpel and removed, leaving an antibioticimpregnated cement endoprosthesis (Fig. 2).
Discussion Two-stage d~bridement, i n t r a v e n o u s antibiotic therapy, and delayed reimplantation THA is a successful m e t h o d of t r e a t m e n t for infected THA [1,3]. Use of an antibiotic-impregnated c e m e n t spacer permits early patient mobilization, delivers local antibiotics, maintains leg length, and facilitates exposure during the second-stage reimplantation operation. Molds to f o r m the c e m e n t into the shape of a prosthesis, however, m a y be expensive or unavailable in the United States because of Food and Drug Administration restrictions. Hand molding the c e m e n t a r o u n d an intramedullary rod or stacked pins to f o r m the i n t r a m e d u l l a r y portion of the spacer, w h i c h t h e n fits the irregular shape of the endosteal surface of the femur, m a y be beneficial in providing rotational stability of the c e m e n t endoprosthesis [41. H a n d molding the proximal end of the c e m e n t endoprosthesis that articu-
Surgical Technique One end of an intramedullary nail or stacked t h r e a d e d pins are p r e b e n t to 45 ° and autoclaved before surgery. After the infected prosthesis is rem o v e d and the hip d~brided, antibiotic-impregn a t e d c e m e n t is placed a r o u n d the rod using the same technique as that described by D e s h m u h k et From the Department of Orthopaedic Surgery, University of California, San Francisco, San Francisco, CA. Submitted July 16, 1998; accepted December 2i, 1998. Reprint requests: Michael D. Ries, MD, Department of Orthopaedic Surgery, UCSF Medical Center, 500 Parnassus Ave (MU 320-W), San Francisco, CA 94143. Copyright © 1999 by Churchill Livingstone® 0883- 5403199/1406-0019510.00/0
764
Antibiotic Cement Spacer Molding Method •
Fig. 1. Rubber bulb portion of an irrigation syringe used to mold a femoral cement endoprosthesis head.
lates with an irregularly shaped acetabular cavity, however, m a y cause crepitus during hip range of motion, pain, and erosion of the acetabular bone surface. Use of a s m o o t h hemispherical shape to
Ries and Jergesen
765
mold the articulating surface of an antibioticimpregnated cement endoprosthesis m a y permit more comfortable patient mobilization and preservation of bone stock than h a n d molding. The bulb portion of an irrigation syringe permits intraoperative fabrication of a s m o o t h hemispherically shaped cement endoprosthesis. The bulb is available in only one size, however, which molds an endoprosthesis of approximately 51 m m in diameter. To use this technique, the acetabular defect must be at least the same diameter as the inner diameter of the bulb syringe. We have f o u n d that the bulb syringe mold can be used in larger acetabular defects w i t h o u t compromising stability. Femoral head molds ideally should be available in multiple sizes. Alternatively, antibiotic-impregnated cement m a y be added by h a n d to the outer surface of the molded endoprosthesis to increase its size. We have used 1.2 g of tobramycin p o w d e r in each package of cement plus 1 g of v a n c o m y c i n p o w d e r if the infection m a y be caused by Staphylococcus epidermidis. Larger antibiotic concentrations have been recommended for use with the PROSTALAC [1,3]. Increased antibiotic concentrations may weaken the cement, however [5]. Recently, we have used 3.6 g of tobramycin in each package of cement and have not observed problems with cement fracture. The mechanical integrity of the cement in the spacer may also depend on the amount of proximal bone present, rod diameter, and biomechanical demands of the patient. Our current practice is to mix 3.6 g of tobramycin in each package of cement and use the largest diameter intramedullary rod that can be completely coated with cement and still fit inside the femoral canal.
References
Fig. 2. Anteroposterior radiograph of a 74-year-old man who presented with an infected periprosthetic hip fracture and was treated with d~bridement and insertion of an antibiotic-impregnated cement endoprosthesis spacer. The cement coats an 8-mm prebent Schneider intramedullary nail. The femoral head of the cement endoprosthesis measures 50.6 mm in diameter and had been molded from the interior surface of an irrigation syringe rubber bulb.
1. Younger ASE, Duncan CP, Masri BA: Treatment of infection associated with segmental bone loss in the proximal part of the femur in two stages with use of an antibiotic-loaded interval prosthesis. J Bone Joint Surg Am 80:60, 1998 2. Deshmukh RV, Thevarajan K, Kok CS, et al: An intramedullary cement spacer in total hip arthroplasty. J Arthroplasty 13:197, 1998 3. Younger ASE, Duncan CP, Masri BA, McGraw RW: The outcome of two-stage arthroplasty using a custommade interval spacer to treat the infected hip. J Arthroplasty 12:615, 1997 4. Kraay M J, Goldberg VM, Figgie HE: Use of an antibiotic impregnated polymethylmethacrylate intramedullary spacer for complicated revision total hip arthroplasty. J Arthroplasty 7:397, 1992 5. Flick AB, Herbert JC, Goodell J, Kristiansen T: Noncommercial fabrication of antibiotic-impregnated polymethylmethacrylate beads: technical note. Clin Onhop 223:282, 1987