Orthopedics

Feature Article 

Standardization of Acrylic Bone Cement Mixing Protocols for Total Knee Arthroplasty Results in Cost Savings

James R. Kee, MD; Simon C. Mears, MD; Paul K. Edwards, MD; Marty Bushmiaer, MSN; C. Lowry Barnes, MD

Abstract

Cost reduction is important in total joint replacement surgery. Bone cement is used to fixate implants in most knee replacement procedures. The authors instituted a 4-pronged approach to reduce the cost of cement. Their approach included reducing the cost of the cement powder, changing the type of mixing method, using less antibiotic cement, and decreasing the amount of cement required for smaller implants. The authors evaluated the implementation of this program and measured the overall costs of cementation during knee replacement. A retrospective review of total knee replacement cementation technique and cost was performed before and after the cost-reduction program was implemented. The type of cement and cement mixing equipment used, the amount of cement used, and the cost of cement and cement mixing equipment were examined. The authors also reported the short-term complication rate including 90-day readmission rate and 30-day revision rate. The program resulted in an overall decrease in cement-related costs from approximately $310 to $105 per case. Reductions in the amount of cement used and the use of antibiotic cement were shown. Among the 3 surgeons, adoption of the program varied. Bone cement is an expense of modern total knee replacement. Implementing a cost-reduction program can reduce cement costs without changing quality of cementation. [Orthopedics. 2018; 41(5):e671–e675.]

Abstract

Cost reduction is important in total joint replacement surgery. Bone cement is used to fixate implants in most knee replacement procedures. The authors instituted a 4-pronged approach to reduce the cost of cement. Their approach included reducing the cost of the cement powder, changing the type of mixing method, using less antibiotic cement, and decreasing the amount of cement required for smaller implants. The authors evaluated the implementation of this program and measured the overall costs of cementation during knee replacement. A retrospective review of total knee replacement cementation technique and cost was performed before and after the cost-reduction program was implemented. The type of cement and cement mixing equipment used, the amount of cement used, and the cost of cement and cement mixing equipment were examined. The authors also reported the short-term complication rate including 90-day readmission rate and 30-day revision rate. The program resulted in an overall decrease in cement-related costs from approximately $310 to $105 per case. Reductions in the amount of cement used and the use of antibiotic cement were shown. Among the 3 surgeons, adoption of the program varied. Bone cement is an expense of modern total knee replacement. Implementing a cost-reduction program can reduce cement costs without changing quality of cementation. [Orthopedics. 2018; 41(5):e671–e675.]

The increasing incidence of knee replacement1 and the increasing costs of implants2 have led to evaluation of cost-saving opportunities by government payers such as the Centers for Medicare & Medicaid Services, private payers, hospitals, and surgeons. Several studies have investigated systemic cost-saving measures such as bundled payments and standardized patient pathways following surgery.3–5 Implant costs are important within a bundled payment model6; however, a reduction in the cost or use of other instrumentation and equipment may also provide an opportunity for savings.

Polymethylmethacrylate bone cement (PMMA) is routinely used in total knee arthroplasties (TKAs) and provides several opportunities for cost savings. Like most biomedical technology, PMMA is provided to hospitals and surgeons by a handful of competing companies. Physicians and hospitals contracting with vendors may lead to decreased costs of implants. In addition to PMMA itself, there are many proprietary devices available to assist in the preparation and delivery of PMMA.

Polymethylmethacrylate bone cement is provided in discrete packets of a polymer powder and a monomer liquid, which are combined to form a certain amount of bone cement.7 Contemporary PMMA application techniques often involve specific predetermined amounts of PMMA and can lead to leftover PMMA and waste.8 The use of less PMMA has been shown to result in potential cost savings.9 Cement may also be mixed using different methods. Polymethylmethacrylate bone cement can be mixed in a vacuum and then extruded from a cement gun. Alternatively, the cement may simply be mixed in a bowl with a plastic spatula. Differences in outcomes have not been reported between these methods.10,11

Decreased use of antibiotic cement may also provide an opportunity for cost savings. Soares et al12 concluded that there is no difference in the rate of early revision using antibiotic cement in patients with osteoarthritis, a conclusion supported by several studies.13–17 Additionally, routine use of antibiotic cement may induce resistance and hinder the effectiveness of intravenous antibiotics in the infected knee. Hinarejos et al18 suggested that antibiotic cement be used only in patients at high risk for infection, including patients with inflammatory arthritis, obesity, compromised immunity, or a history of trauma or infection of the knee.

The pricing of cement may provide another opportunity for cost savings. Surgeons have become comfortable with specific brands of cement. Different brands of cement can have slightly different material properties and hardening rates. However, the clinical significance of these differences is unclear.19,20 Hospitals and other health care providers are increasingly using their purchasing power to negotiate rebates from specific pharmaceutical and implant companies.21 These rebate contracts have been shown to decrease costs of arthroplasty.22

To decrease costs of TKA, the authors instituted 4 changes in perioperative management of bone cement during primary TKA. The first change was the routine use of bowl mixing with spatula application instead of vacuum mixing and cement gun application. The second change was the use of only 1 pack of cement for smaller knee implants. The third change was restricting the use of antibiotic bone cement to only high-risk patients. The fourth change was to aggressively pursue lower price contracting for cement and cementation equipment. The authors hypothesized that these simple modifications in the perioperative management of PMMA would decrease the cost of knee arthroplasty. Additionally, the authors sought to determine the safety of these practices by examining length of hospital stay, 30-day complication rates, 30-day revision rates, and whether there were any intraoperative problems during surgery because of the cementation process.

Materials and Methods

On January 1, 2016, 3 fellowship-trained joint replacement surgeons at the authors' institution (S.C.M., P.K.E., C.L.B.) adopted a new protocol for perioperative management of bone cement during primary TKA. This protocol included the routine use of bowl mixing of cement, the application of cement with a spatula, the use of 1 pack of cement in cases of implants sized 4 or less (aMP Knee System; MicroPort Orthopedics, Arlington, Tennessee; and EMPOWR 3D Knee System; DJO Global Inc, Vista, California), and the restriction of antibiotic cement to patients at high risk for infection, including patients with inflammatory arthritis, obesity, compromised immunity, or a history of trauma or infection of the knee. This protocol also involved the use of less expensive cement and cement preparation products. Surgeons changed from Simplex Bone Cement (Stryker, Kalamazoo, Michigan) to Cobalt Bone Cement (DJO Global Inc). Preparation was changed from using a vacuum cement-mixing system such as MixeVac (Stryker) and SMARTMIX (DePuy Synthes, Warsaw, Indiana) to a hand-mixing technique using a bowl and spatula (Stryker).

All surgeons performed in the same 2 operating rooms. Storage temperature and procedures for the cement were the same for each surgeon. Surgeons placed the cement when at the consistency they each considered workable and easily placed appropriately. Pulsed lavage with normal saline to clear the bone was used before cementation during all total knee replacements. Additionally, sclerotic bone was routinely drilled with a 2-mm drill bit.

Once institutional review board approval was obtained, a retrospective review of the electronic medical records of all primary TKA cases performed by the 3 surgeons between August 1, 2015, and August 31, 2016, was conducted. A total of 256 primary TKAs met inclusion criteria. Twenty-eight cases were excluded because of previous surgery, hardware removal, or bone loss. Patients' age, height, weight, body mass index, American Society of Anesthesiologists score, complications, 90-day readmission rate, and 30-day revision rate were retrieved from the medical records.

This consecutive series of cases was divided into a group before and a group after the protocol change on January 1, 2016. A total of 170 cases were performed after the change in protocol (cement optimization group), and 88 cases were performed before the change in protocol (standard group). Amount of cement, whether antibiotic cement was used, and type of mixing equipment were compared between the 2 groups. The case series of each surgeon was analyzed. Additionally, the cost for cement and the amount of cement used were collected for knees, excluding implants sized 5 or greater. Values were compared using the Student's t test, chi-square test, or one-way analysis of variance when appropriate.

Results

No significant differences were observed between the standard and cement optimization groups regarding 90-day readmission rate, 30-day revision rate, age, height, weight, body mass index, American Society of Anesthesiologists score, or implant size (femur and tibia) (Table 1). Two patients returned to the operating room within 3 weeks for irrigation and debridement, 1 due to infection and 1 to drain a hematoma. Both cases occurred after the change in cement protocol. Six knees underwent manipulation under anesthesia for early arthrofibrosis, 2 before and 4 after the change in protocol.

Patient Demographics and Readmission and Revision Rates

Table 1:

Patient Demographics and Readmission and Revision Rates

Cases after the change in protocol had significantly lower total cement and mixing costs, cement costs, and mixing costs (Table 2). Additionally, the number of cases using 2 packs of cement and the more expensive cement mixing equipment decreased significantly. The use of a mixing bowl increased after the change in protocol. There was no change in the number of cases using antibiotic cement (Table 3).

Mixing and Cement Costs per Group

Table 2:

Mixing and Cement Costs per Group

Cement Application

Table 3:

Cement Application

When each surgeon was evaluated independently, variations were observed in compliance with the protocol. Surgeon compliance with the protocol is detailed in Table 4. Surgeon 1 had decreased cement use and antibiotic use. Surgeon 2 had no difference in cement or antibiotic use. Surgeon 3 had a decrease in cement use but no decrease in antibiotic use. When implantation of larger TKAs (femur size ≥5) was excluded, surgeons 1 and 3 had decreases in cement use, with surgeon 3 using only 1 pack of cement in 18 eligible cases.

Cement Optimization per Surgeon

Table 4:

Cement Optimization per Surgeon

Discussion

This study found a reduction in costs associated with adoption of a perioperative PMMA protocol. Although the surgeons did not implement the protocol equally, reductions in overall cost were still achieved. Further standardization between surgeons should lessen costs. Each portion of the protocol seemed to be effective. Forgoing vacuum mixing for hand mixing may provide the surgeon with a cost-saving measure that can be easily implemented. Several studies have shown no clinical effect in TKA from vacuum-mixed cement.8,10,11 Geiger et al10 showed that vacuum mixing has variable effects on cement properties dependent on cement brand. They concluded that vacuum mixing had no predictable effect on cement–bone interface porosity or mechanical properties of cement. Kopec et al11 compared cement mantle radiographic outcomes after total knee replacement in which cement was vacuum mixed and gun pressurized and in which cement was bowl mixed and applied by hand packing. They concluded that gun pressurization did not offer an advantage over hand packing. In fact, another study concluded that administration of cement with a gun resulted in excess cement in the tibia.8

Reducing the amount of cement used from two 40-g packs to one also was an effective technique for cost reduction without sacrificing outcome. This is in agreement with previous work showing good outcomes at 3 years after TKA with the use of only 1 pack of cement.9 In smaller implants, 1 pack of cement provides enough material to cover both the tibia and the tibial implant. Covering both the tibia and the tibial implant with cement has been found to achieve better penetration than simply covering the tibial implant.8 In this study, on the basis of the experiences of the 3 surgeons that 1 pack was enough to cover the smaller implants, the size of 4 was somewhat arbitrarily decided to be the cutoff for using a different amount of cement.

The restriction of antibiotic cement to high-risk patients also reduced costs. Applying standardized criteria for the use of antibiotic cement is a relatively easy protocol to institute. Although no difference in short-term periprosthetic joint infection rates was reported, the power of this study was not sufficient to detect a difference. However, other adequately powered studies have shown no benefit from such use of antibiotic cement.12–18 Given the expense of antibiotic cement and its questionable role in primary TKA, costs may be reduced with routine use in only high-risk patients.

Negotiating improved contractual pricing for cement and accessories leads to immediate cost savings. Standardization of cement manufacturer to a single source will provide the best opportunity for lowest pricing. Although the focus of cost reduction has been on knee arthroplasty implant costs, hospitals should not lose sight of other opportunities, such as cement, for cost savings.

A limitation of this study was the retrospective nature of the data collection from the electronic medical records; however, this provided a realistic view of a busy joint replacement practice by highlighting the difficulty obtaining compliance among surgeon partners for any newly instituted program. This study also showed variability of the adoption of this program among the participating surgeons. This variability highlights the importance of communication between surgeon, surgical technician, operating room circulator, and vendor representative. Not all of the smaller implants received only 1 pack of cement. Even after the protocol was implemented, 5% to 37% of the cases with small implants received 2 packs of cement. Additionally, only 1 surgeon showed a reduction in the use of antibiotic cement with the protocol. Another limitation was that the authors did not quantify operative time, which was not included in the electronic medical records. Although no surgeons perceived a change in operative time after the adoption of the program, this conclusion cannot be proven without measuring the operative time. The antibiotic cement was premixed and therefore did not add any operative time compared with nonantibiotic cement.

Conclusion

Joint replacement surgeons may further reduce costs in TKA by adopting a few easily implemented perioperative protocols for bone cement. These include reducing the amount of cement used for smaller implants, replacing vacuum mixing with less expensive hand mixing, and avoiding the use of antibiotic cement in routine primary TKA.

References

  1. Kurtz S, Mowat F, Ong K, Chan N, Lau E, Halpern M. Prevalence of primary and revision total hip and knee arthroplasty in the United States from 1990 through 2002. J Bone Joint Surg Am. 2005; 87(7):1487–1497.
  2. Zywiel MG, Ulrich SD, Suda AJ, Duncan JL, McGrath MS, Mont MA. Incidence and cost of intraoperative waste of hip and knee arthroplasty implants. J Arthroplasty. 2010; 25(4):558–562. doi:10.1016/j.arth.2009.03.005 [CrossRef]
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  5. Iorio R, Clair AJ, Inneh IA, Slover JD, Bosco JA, Zuckerman JD. Early results of Medicare's bundled payment initiative for a 90-day total joint arthroplasty episode of care. J Arthroplasty. 2016; 31(2):343–350. doi:10.1016/j.arth.2015.09.004 [CrossRef]
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  9. Maheshwari AV, Argawal M, Naziri Q, Pivec R, Mont MA, Rasquinha VJ. Can cementing technique reduce the cost of a primary total knee arthroplasty?J Knee Surg. 2015; 28(3):183–190. doi:10.1055/s-0034-1373740 [CrossRef]
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  13. Bohm E, Zhu N, Gu J, et al. Does adding antibiotics to cement reduce the need for early revision in total knee arthroplasty?Clin Orthop Relat Res. 2014; 472(1):162–168. doi:10.1007/s11999-013-3186-1 [CrossRef]
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Patient Demographics and Readmission and Revision Rates

CharacteristicGroupP

StandardCement Optimized
Age, mean (SD), y62.8 (9.7)64.9 (10.1).12
Height, mean (SD), cm170.0 (17.2)168.3 (20.4).50
Weight, mean (SD), kg94.7 (20.3)94.0 (20.4).79
Body mass index, mean (SD), kg/m232.6 (6.1)32.0 (6.1).50
American Society of Anesthesiologists score, mean (SD)2.43 (0.54)2.52 (0.52).36
Femur implant size, mean (SD), mm4.97 (1.4)5.16 (1.5).29
Tibia implant size, mean (SD), mm4.66 (1.5)4.99 (1.6).06
90-day readmission rate, No./Total No.1/88 (1.1%)4/170 (2.4%).67
30-day revision rate, No./Total No.0/88 (0%)2/170 (1.2%).78

Mixing and Cement Costs per Group

Cost/GroupMean (SD)P
Mixing costs.000001
  Standard group$31.30 ($45.11)
  Cement optimized group$10.99 ($27.83)
Cement costs
  Standard group$276.67 ($219.53)
  Cement optimized group$94.38 ($80.45)
Mixing and cement costs
  Standard group$309.97 ($217.03)
  Cement optimized group$105.37 ($88.03)

Cement Application

VariableGroup, No./Total No.P

StandardCement Optimized
Cases with 2 packs of cement83/86 (96.5%)126/170 (74.1%)<.01
Cases with 2 packs of cement, excluding implants ≥533/34 (97.1%)20/59 (33.9%)0
Cases with antibiotic cement13/86 (15.1%)14/170 (8.2%).09
Cases with vacuum mixing bowl or cement gun86/86 (100%)29/170 (17.1%)<.01

Cement Optimization per Surgeon

SurgeonGroup, No./Total No.P

StandardCement Optimized
1
  Cases with 2 packs of cement56/57 (98%)84/110 (76%)<.01
  Eligible casesa with 1 pack of cement0/17 (0%)22/35 (63%)<.01
  Cases with antibiotic cement12/57 (21%)7/110 (6%)<.01
2
  Cases with 2 packs of cement16/17 (94%)24/25 (96%)1
  Eligible casesa with 1 pack of cement0/6 (0%)0/7 (0%)
  Cases with antibiotic cement0/17 (0%)3/25 (12%).26
3
  Cases with 2 packs of cement11/12 (92%)18/35 (51%)<.01
  Eligible casesa with 1 pack of cement1/10 (10%)17/18 (94%)<.01
  Cases with antibiotic cement1/12 (8%)4/35 (11%)1
Authors

The authors are from the Department of Orthopaedic Surgery, University of Arkansas for Medical Sciences, Little Rock, Arkansas.

Drs Kee, Mears, and Edwards have no relevant financial relationships to disclose. Ms Bushmiaer holds stock in Stryker. Dr Barnes is a paid consultant for DJO, Zimmer, Medtronic, Health Trust, and Responsive Risk Solutions; receives royalties from DJO, Zimmer, and Medtronic; and holds stock in Responsive Risk Solutions.

Correspondence should be addressed to: James R. Kee, MD, Department of Orthopaedic Surgery, University of Arkansas for Medical Sciences, 4301 W Markham St, Slot 531, Little Rock, AR 72205 ( jkee@uams.edu).

Received: August 31, 2017
Accepted: April 23, 2018
Posted Online: July 27, 2018

10.3928/01477447-20180724-01

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