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Corresponding author. Department of Orthopaedic Surgery, Cedars-Sinai Medical Center, 444 South San Vicente Boulevard, Suite 603, Los Angeles, CA 90048, USA. Tel.: +1 310 423 4566.
Although 2-stage exchange arthroplasty, consisting of temporary insertion of an antibiotic-impregnated cement spacer (AICS), is considered the standard of care for chronic periprosthetic joint infection (PJI) in total hip arthroplasty (THA), a consensus on the AICS design has not yet been established. Ceramic-on-polyethylene AICSs (Poly-AICS) are theorized to cause less pain and better function than cement-on-bone AICS (CemB-AICS) but use non-antibiotic-impregnated components that may harbor bacteria. This study evaluates the impact of spacer design on infection-free survivorship following THA reimplantation as well as pain and function during the interim AICS stage.
Methods
A retrospective review was performed of all cases of THA PJI treated with either Poly-AICS or CemB-AICS at a single high-volume academic center. Data were collected until the final follow-up after THA reimplantation with an average follow-up duration of 2.6 years. The primary outcome was infection-free survivorship after the final reimplantation. Secondary outcomes included postoperative pain scores, opioid use, time to ambulation, length of stay, complications, and discharge disposition.
Results
A total of 99 cases (67 CemB-AICS; 32 Poly-AICS) were included. There were no baseline differences between the 2 groups. There were no differences in infection-free survivorship after reimplantation in survivorship curve comparisons (P = .122) and no differences in postoperative inpatient pain scores, opioid use, length of stay, time to ambulation, complications, or discharge disposition during the AICS stage.
Conclusions
Patients with THA PJI treated with Poly-AICS did not have worse infection-related outcomes despite the use of non-antibiotic-impregnated components but also did not appear to have less pain or improved function during the early AICS stage.
]. While a 2-stage revision arthroplasty, involving temporary insertion of an antibiotic-impregnated cement spacer (AICS), is considered the standard of care for chronic hip PJI in the United States, a consensus on AICS design has not yet been established [
]. Nonarticulating AICSs do not provide a ball-and-socket articulation between the acetabulum and femur and generally consist of custom-made antibiotic-impregnated cement in the acetabulum, joint space, and/or femoral canal [
]. Articulating AICSs provide a ball-and-socket articulation between the acetabulum and femur and therefore have improved preservation of hip range of motion, limb length, offset, and soft-tissue tension [
]. Articulating AICSs have become more commonly used as they may improve function during the AICS stage, make the revision THA reimplantation technically easier, and allow faster rehabilitation [
Articulating AICSs are made in a broad range of designs, manufacturing techniques, and articulating surfaces, which may affect the durability of the polymethylmethacrylate cement, elution characteristics of the antibiotics, complications, and outcomes [
]. One common design is a cement-on-bone hemiarthroplasty AICS (CemB-AICS) created from sterile molds or prefabricated cement components, as shown in Figure 1 [
An increasingly common alternative is an AICS that has a metal or ceramic head on polyethylene articulation (Poly-AICS), as shown in Figure 2. These designs typically use a femoral stem cement mold fashioned from a sterile cast, a ceramic or metal head, and a polyethylene liner that is cemented into the acetabulum [
Two-stage revision total hip arthroplasty with a specific articulating antibiotic spacer design: reliable periprosthetic joint infection eradication and functional improvement.
]. Theoretically this design reduces pain and improves function during the spacer stage but carries the added cost of these components. A potential downside of nonantibiotic components, especially polyethylene, is the possibility of harboring bacteria since they have a higher affinity for bacterial biofilms [
There is a paucity of comparative studies of different AICS designs and none to our knowledge comparing different articulating AICS designs for the treatment of PJI after THAs. The purpose of the present study is to compare the CemB-AICS spacer design with the Poly-AICS design and evaluate their impact on infection-free survivorship following THA reimplantation as well as pain and function during the interim AICS stage. We hypothesized that patients treated with a CemB-AICS design would have better infection-free survival after second-stage reimplantation but would have more pain, greater opioid use, and worse function during the spacer stage than patients treated with a Poly-AICS design.
Material and methods
This study was a retrospective cohort study conducted at a single academic medical center from January 2008 to December 2018. The study was approved by the institutional review board. Inclusion criteria included all patients undergoing a 2-stage exchange arthroplasty for a chronic periprosthetic THA infection who were treated with either the CemB-AICS or Poly-AICS design. Chronic periprosthetic THA infection was determined according to the Musculoskeletal Infection Society criteria [
]. Exclusion criteria included AICS for native hip infection, AICS for hip-resurfacing infection, AICS for infected nonunion, history of previous AICS, history of girdlestone, proximal femur replacement, total femoral replacement, acetabular cage, acetabular triflange, history of oncologic resection around the hip, and patients with missing records. The decision to use a CemB-AICS vs a Poly-AICS was surgeon preference based on surgeon training and comfort in the preparation and implantation of each type of spacer.
Patient records were reviewed through their most recent follow-up. Data were collected on patient demographics, comorbidities, time from primary THA, history of revision, and history of hip surgery for infection. Additional data were collected on synovial fluid culture results (at the time of each surgery, including at the time of reimplantation), need for a repeat surgery after AICS other than THA reimplantation, rate of implantation, time to reimplantation, and infection-free survival after reimplantation. The latter was measured from the time of final reimplantation until the final follow-up. Infection-free survivorship was defined as lack of a recurrent periprosthetic infection per Musculoskeletal Infection Society criteria after the final replantation. Data were also collected from the inpatient stay following first-stage AICS implantation including inpatient daily opioid usage as measured by daily total morphine milliequivalents, average daily inpatient pain scores as measured by visual analog scale, length of stay, first day to ambulate, discharge disposition, and complications.
Data for continuous variables are shown as mean ± standard deviation and compared between groups using the Student's t-test. Categorical variables are shown as n (%) and compared between groups using a chi-square test. Infection-free survival differences between groups were compared using the Kaplan-Meier analysis, and patients were right censored for death, loss to follow-up, or infection free at the final follow-up at 3 years. P values < .05 were considered statistically significant. All analyses were carried out with SAS 9.4 (IBM, Cary, NC).
Results
A total of 236 patients were initially identified as having undergone a hip AICS within the 10-year study dates. A total of 99 patients, with 99 included hips, met the inclusion and exclusion criteria. Of these, 67 patients were treated with CemB-AICS and 32 patients were treated with a Poly-AICS. Baseline demographics and comorbidities did not differ between groups (Table 1).
Table 1Baseline patient demographics and comorbidities between patients treated with a CemB-AICS and those treated with a Poly-AICS.
There were no significant differences in the incidence of prior infection-related hip surgeries. The average time from a primary THA to an AICS surgery was 6.1 ± 6.0 years in the CemB-AICS group and 5.4 ± 5.1 years in the Poly-AICS group (P = .562). There was no statistical difference between the CemB-AICS group (45.9%) and the Poly-AICS group (50.0%) with regard to additional debridement, antibiotics, and implant retention procedures prior to undergoing a 2-stage exchange arthroplasty (P = .517). Furthermore, 48.5% of patients in the CemB-AICS group and 31.3% of patient in the Poly-AICS group had undergone at least 1 previous revision hip arthroplasty prior to the current exchange arthroplasty (P = .287).
The final synovial fluid culture results after AICS are presented in Table 2. The Poly-AICS group had a higher proportion of methicillin-sensitive Staphylococcus aureus (MSSA) infection (31.3% vs 13.4%; P = .035). Final cultures failed to identify an organism in 19.4% of the CemB-AICS group and 12.5% of the Poly-AICS group (P = .394).
Table 2Synovial fluid culture results after irrigation and debridement and first-stage insertion of an articulating antibiotic cement spacer between patients treated with a CemB-AICS and those treated with a Poly-AICS.
Before reimplantation, 17.9% of the CemB-AICS group and 18.8% of the Poly-AICS group underwent repeat irrigation and debridement for infection (P = .919). Additionally, 10.4% of the CemB-AICS group and 15.6% of the Poly-AICS group underwent another hip surgery unrelated to infection (P = .460), mostly for dislocation. During the spacer period, 11.9% of the CemB-AICS group and 12.5% of the Poly-AICS group experienced a dislocation (P = .936).
Of the 99 patients who received an articulating hip spacer, 89 ultimately underwent a second-stage hip reimplantation. Following the spacer period, 92.5% of the CemB-AICS group and 84.4% of the Poly-AICS group were deemed clear of infection and underwent second-stage revision THA reimplantation (P = .207). The average time to reimplantation was 16.1 ± 9.8 weeks in the CemB-AICS group and 17.0 ± 13.8 weeks in the Poly-AICS group (P = .727). There was 1 death prior to reimplantation in each group (P = .589).
Patients were followed up for an average of 2.6 years after reimplantation. Infection-free survival was compared between groups over time from reimplantation until the final follow-up or until a patient was diagnosed with recurrent deep PJI as presented in Figure 3. There was no significant difference between groups in infection-free survival over time (P = .122). A post-hoc analysis was conducted to adjust for group differences in the percentage of MSSA infection and did not show any significant difference between groups in survivorship with an adjusted hazard ratio (confidence interval) for CemB-AICS vs Poly-AICS of 3.03 (confidence interval 0.66, 13.85) (P = .152).
Figure 3Comparison of infection-free survival after second-stage total hip arthroplasty reimplantation between patients treated with a cement-on-bone articulating antibiotic cement spacer (CemB-AICS) and a ceramic-on-polyethylene articulating antibiotic cement spacer (Poly-AICS).
Secondary outcomes from the inpatient stay after the first-stage AICS procedure are presented in Table 3. Pain scores evaluated using the visual analog scale and opioid usage measured in morphine milliequivalents were similar in both groups. There was no difference in time to ambulation, length of stay between treatment groups, or rate of discharge to home. There were no significant differences between groups with respect to inpatient complications after the AICS procedure.
Table 3Inpatient outcomes after irrigation and debridement and first-stage insertion of an articulating antibiotic cement spacer between patients treated with a cement-on-bone articulating antibiotic cement spacer (CemB-AICS) and those treated with a ceramic-on-polyethylene articulating antibiotic cement spacer (Poly-AICS).
Outcome
CemB-AICS (N = 67)
Poly-AICS (N = 32)
P value
Length of stay (d)
7.5 ± 4.8
6.5 ± 4.2
.312
Total morphine milliequivalent POD 1
31.6 ± 24.0
25.2 ± 15.3
.212
Total morphine milliequivalent POD 2
33.1 ± 28.4
25.5 ± 14.1
.195
Total morphine milliequivalent POD 3
30.4 ± 26.2
23.9 ± 14.1
.239
Average VAS Pain POD 1
5.0 ± 1.7
5.3 ± 1.4
.445
Average VAS Pain POD 2
4.9 ± 1.9
4.7 ± 1.9
.685
Average VAS Pain POD 3
4.6 ± 1.8
4.6 ± 1.9
.942
First day of ambulation
POD 1
9 (14.1%)
7 (22.6%)
.688
POD 2
12 (18.8%)
4 (12.9%)
POD 3
9 (14.1%)
6 (19.4%)
POD 4
5 (7.8%)
3 (9.7%)
POD 5 or later
29 (45.3%)
11 (35.5%)
Discharge location
Home
32 (47.8%)
16 (50.0%)
.638
Nursing facility
30 (44.8%)
12 (37.5%)
Acute rehabilitation
5 (7.5%)
4 (12.5%)
POD, postoperative day; VAS, visual analog scale (0-10).
Continuous variables are presented as mean ± standard deviation and compared using the Student's t-test. Categorical variables are presented as n (%) and compared using the chi-square test. P < .05 was consisted statistically significant.
The present study is the first to our knowledge to compare 2 of the most common articulating AICS designs used to treat PJI in THAs. Our primary objective was to determine whether there was any difference in infection-free survival after the final reimplantation between patients treated with CemB-AICS and those treated with Poly-AICS. We initially hypothesized that patients treated with the CemB-AICS design, which does not have ceramic or polyethylene, would have a longer, on average, infection-free survival after second-stage reimplantation. This study did not find a significant difference in infection-free survival at 3 years. This is an important finding that suggests that both interim spacer options are acceptable treatment options for patients.
Furthermore, it brings into question whether there is a risk in using nonantibiotic components in antibiotic spacers, such as articulating AICSs which use ceramic heads and polyethylene liners. Retrieval studies of components explanted after THA PJI have shown that polyethylene liners have up to a 100% rate of positive cultures, suggesting a high rate of biofilm formation [
], which has led to the preferential use of ceramic heads for these articulating AICSs at our institution and in the present study. These components may harbor bacteria when used to treat PJI and reduce the efficacy of the AICS. The present study, however, does not show a decrease in efficacy in eradicating infection. Moreover, the survivability curve in Figure 3 shows a trend in favor of Poly-AICS.
A confounding variable in the present study is that surgeons may be using Poly-AICS spacers in settings of infection with less-virulent organisms since they may be less concerned about biofilms with these organisms. The incidence of MSSA infection was significantly higher in patients treated with Poly-AICS (31.3% vs 13.4%), but when adjusting our infection-free survival analysis, however, we were still unable to discern a significant difference between groups.
Our results are comparable to prior studies evaluating articulating AICSs. Hoffmann et al. described their experience of over 10 years using a design with polyethylene articulation in 27 patients, with eradication of infection and reimplantation in 96% of patients [
]. Complications were comparable to our series with a 15% dislocation rate. Tsung et al. have described their experience using a cemented polyethylene acetabular component and an antibiotic cement-coated femoral stem [
]. They showed infection-free survival of 84.2% at 6.7 years. A large proportion of their patients (44.7%) had sufficient function with their spacer that they declined hip reimplantation [
]. This level of function would give credence to improved function and less pain with polyethylene articulation. Jung et al. evaluated rates of complications in hip PJI patients similarly treated with a 2-stage revision [
]. Their series of 88 cases (82 cement-on-bone, 6 polyethylene articulation) report a 17% dislocation rate and 10.2% spacer fracture rate. The overall complication rate (surgical and medical) was 58.5%, higher than that in the current series [
The secondary goals of the study were to compare early postoperative pain levels, opioid usage, and function during the inpatient hospitalization after first-stage AICS procedures because the data were consistent and standardized allowing valid comparisons. Both groups had the same levels of pain and opioid usage out to the third postoperative day. Groups had similar lengths of stay, average time to ambulation, and discharge disposition. The study is limited to this inpatient stage, and differences after discharge were not able to be captured.
Considering equivalent efficacy between the 2 spacer types, cost becomes a more important issue. Spacers with noncement components are more expensive due to the cost of ceramic or metal heads and polyethylene liners. At our institution, after excluding the cost of the cement and the antibiotics, the cost of the CemB-AICS (sterile prefabricated molds) is approximately $2000. If made by hand using a bulb syringe, Steinman pin, and chest tube, the cost of CemB-AICS can be as low as $30. A Poly-AICS (femoral sterile prefabricated mold, ceramic head, and polyethylene liner) costs between $2500 and $4300 depending on manufacturer and pricing contracts. A clinically significant improvement in pain and function could possibly justify these greater costs. We could not evaluate pain and function during the outpatient part of the spacer implantation, and further studies comparing these 2 types of spacers with patient-reported outcomes are needed.
There are several limitations to the present study. First, the study is retrospective. PJI in THA is an inherently complex condition with a myriad of potentially confounding variables. We attempted to compensate for this by evaluating all hip AICSs over 10 years and using strict inclusion and exclusion criteria. Furthermore, the 2 groups were not different in terms of patient demographics or comorbidities. The only difference between treatment groups was in the incidence of MSSA infection in the Poly-AICS group, but we found no differences between groups after adjusting for this. Randomized controlled prospective studies on spacer design should be carried out. Another important limitation is that our assessment of pain and function is limited to the inpatient setting, and therefore, we did not evaluate pain or function levels after discharge. Such an assessment is necessary to truly evaluate the difference between AICS designs. Additionally, long-term follow-up of patients remains a limitation. While our average follow-up duration for both groups was greater than 2 years, further follow-up and larger cohorts are needed to strength the study.
Conclusions
In conclusion, patients with PJI in the THA treated with Poly-AICS had no significant differences in infection-free survival after second-stage reimplantation compared to patients treated with CemB-AICS. Furthermore, there were no significant differences in pain and function outcomes between these 2 AICS types in the inpatient setting after the first stage.
Funding
This study was partially supported by a grant from the Doren Family Foundation, Los Angeles, CA.
Conflicts of interest
S. S. Rajaee received research support from the Zimmer-Biomet Industry for a robotic TKA study. All other authors declare no potential conflicts of interest.
For full disclosure statements refer to https://doi.org/10.1016/j.artd.2022.10.002.
Two-stage revision total hip arthroplasty with a specific articulating antibiotic spacer design: reliable periprosthetic joint infection eradication and functional improvement.
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