The Journal of Arthroplasty 29 (2014) 558–563

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Articulating Vs. Static Antibiotic Impregnated Spacers in Revision Total Knee Arthroplasty for Sepsis. A Systematic Review George N. Guild III, MD a, Baohua Wu, PhD b, Giles R. Scuderi, MD c, d a b c d

Insall Scott Kelly Institute for Orthopaedics and Sports Medicine, Lenox Hill Hospital Fellow, New York, New York Emory Department of Biostatistics, Department of Orthopaedic Surgery, Emory University, Atlanta, Georgia Insall Scott Kelly Institute for Orthopaedics and Sports Medicine, New York, New York Orthopedic Service Line, Northshore LIJ Health System, New York, New York

a r t i c l e

i n f o

Article history: Received 24 May 2013 Accepted 14 August 2013 Keywords: infection total knee arthroplasty two-stage exchange

a b s t r a c t Periprosthetic infection after total knee arthroplasty is a devastating complication, and two-stage exchange is the standard of care in North America. Articulating and static spacers have been developed to treat these infections but controversy exists over which method is superior. We performed a systematic review using MEDLINE and other literature search engines identifying 47 articles meeting inclusion criteria producing 2011 spacers for comparison. Articulating spacers had increased range of motion 100.1° vs. 82.9° (P b 0.003), lower re-infection rate 7.5% (P b 0.0031), facilitated re-implantation (P b 0.0011), and developed less bone loss (P b .0001) than did static spacers. This study answers several clinically relevant questions and provides useful information in guiding clinical decision making in treating periprosthetic infection. © 2014 Elsevier Inc. All rights reserved.

Infection is one of the most devastating complications after total knee arthroplasty with an incidence 1% to 2%, and is currently the leading cause for failure of total knee arthroplasty within 2 years of the index procedure [1]. Several strategies have been developed to treat infection after total knee arthroplasty including antibiotic suppression, irrigation and debridement, one-stage exchange, and two-stage exchange. Two-stage exchange remains the gold standard for treatment of infected knee arthroplasty in North America, and eradication rates exceed 90% in most series [2]. The original concept of two-stage exchange was developed by Insall whose methods evolved into the static spacer technique to prevent interim joint fibrosis [3,4]. Articulating spacers were later introduced to enhance functional status, maintain range of motion, and improve patient satisfaction [5]. Good clinical outcomes and low re-infection rates have been achieved with articulating spacers, but most reports are case studies in non-complex patients [6]. Controversy exists whether articulating spacers are effective in complex patients with bone loss, virulent organisms, and compromised hosts. Also, it not definitely known whether articulating spacers result in an increased final range of motion or facilitate re-implantation. Therefore, we performed a systematic review of the literature that compares the clinical effectiveness of articulating vs. static spacers with regard to out-

The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2013.08.013. Reprint requests: George N. Guild III, MD, 1007 Lexington Ave Apt. 2R, New York, NY 10021. 0883-5403/2903-0022$36.00/0 – see front matter © 2014 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.arth.2013.08.013

comes scores, range of motion, re-infection rates, re-implantation, bone loss, and complications.

Materials and Methods Search Strategy Extensive electronic searches were conducted with the aid of an experienced medical university librarian in October of 2012. We searched for two-stage exchange for infected total knee arthroplasty. The databases searched include MEDLINE, MEDLINE In-Process, EMBASE, BIOSIS, Clinicaltrials.gov, and Cochrane Database of Systematic Reviews. Full text searching of key surgical journals was also performed. Searches were not restricted by study design, publication year, or language, and conference proceedings and abstracts were included in the search. Reference lists of all included studies were scanned to identify additional relevant studies. Search terms included “infected total knee arthroplasty,” “surgery,” “two stage,” “articulating spacer,” “static spacer,” and “revision.” Excluded studies included those performed prior to 1988, studies not in English, two-stage exchanges performed without a spacer, early static spacer with inferior “hockey puck” techniques, review articles, non-clinical outcomes measures, and one-stage exchanges. The systematic search generated 523 abstracts from the above mentioned electronic sources. No additional abstracts meeting the inclusion criteria were identified with the previously described technique. A total of 47 studies met the inclusion criteria (Table 1). Data were extracted from these 47 studies.

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loss, as well as bone loss developed during interim spacer placement in each group.

Table 1 Study Characteristics.

Author Jaekel [7] Chiang [8] Park [9] Freeman [10] Hsu [11] Anderson [6] Pascale [12] Incavo [13] Villanueva [14] Van Thiel [15] Ocguder [16] Shen [17] Kalore [18] Gooding [19] Meek [20] Durbhakula [21] Hofmann [22] Pitto [23] Wan [24] Choi [25] Pietsch [26] Trezies [27] Macavoy [28] Huang [29] Hart [30] Haddad [31] Cuckler [32] Jamsen [33] Hofmann [5] Ha [34] Macheras [35] Fehring [36] Evans [37] Emerson [38] Johnson [39] Kotwal [40] Yoo [41] Hoad-Reddick [42] Hirsakawa [43] Goldman [44] Barrack [45] Booth [46] Lonner [47] Mont [48] Haleem [49] Kim [50] Kurd [51]

559

Level of Evidence

Age, Mean

III II III III III III IV III IV IV IV IV III IV IV IV IV IV IV III IV IV IV IV IV IV IV III IV IV IV IV IV III III III IV IV IV IV III IV IV III IV IV IV

69 71 60 64.9 64 68 61 71 66 70 64 68 72 67 67 70 64 65 66 58 68 68 69 68 68 70 65.7 64

Gender M:F 23:22 4:32

10:15 3:11 7:23 31:29 7:10 7:10 38:15 60:50 20:27 10:14 27:28 9:12 22:11 17:16 7:4 5:7 5:14 28:20 19:26 13:31 5:17 14:12 3:31

69 62 63

17:31

70 67 67 68.5 67

27:32 25:29 22:42

69 64 67

28:30

12:13 33:36 50:44 46:56

Spacer both both both both both mobile mobile mobile mobile mobile mobile mobile mobile mobile mobile mobile mobile mobile mobile both mobile mobile mobile mobile mobile mobile mobile both mobile mobile mobile both mobile both both static static static static static static static static static static static static

Follow-Up, Mean, Mo 41 29 58 54 12

35 20 31 39 108 41 33 74 24 24 43 28 28 52 48 48 63 12 31 30 145 27 24 45 27 29.4 54 56 61.9 90 36 25 56 63 83 48.6 35

No. of Spacers 35 45 36 76 28 25 14 11 30 60 17 17 53 110 47 24 55 21 33 47 33 11 13 21 48 45 44 30 26 12 34 55 31 48 115 37 4 38 55 64 28 25 53 69 96 96 96

Methodology, Level of Evidence Assessment, and Assessment of Risk Bias Two reviewers independently screened titles, abstracts, and full text papers for eligibility, extracted data via a standard form, and evaluated the methodological quality of the articles. Any disagreement between the two reviewers was resolved though consultation with a third reviewer. Studies were placed in either the static or articulating group. Study design, level of evidence, demographics, number of complex vs. non-complex patients, knee score outcomes measures, range of motion, exposure for re-implantation, infection eradication, bone loss analysis, and complications were all recorded. Studies were also stratified by level of evidence and the level of case complexity. The level of evidence was graded based on the classification introduced by Wright et al [52]. Complex cases were those that had multiple virulent organisms (MRSA, MRSE, VRE, gram negative infections, polymicrobial), draining sinus tracts, or those with significant pre-existing bone loss (AORI II or III). The complex data were then compared to noncomplex data to elucidate differences between static and mobile spacers in dealing with more difficult cases. Further data regarding bone loss was obtained that specifically looked at pre-existing bone

Statistical Analysis For the subsample of studies that reported each outcome, the mean average, range of averages, and weighted mean of the study sample size were calculated. Few studies reported standard deviations or standard errors precluding the prediction of inter-study variability by meta-analytic methods. For continuous data we made normaltheory assumptions and used one way analysis of variance (ANOVA) to compare continuous data. For categorical data the chi square and Fisher exact test were used for analysis. Results Patient and Study Characteristics A total of 1904 patients (2011 knees) undergoing a two-stage reimplantation for infected total knee arthroplasty were identified from the 47 studies (Table 1). There were 1087 spacers in the articulating group and 924 in the static group. Of the 47 studies, 25 evaluated only articulating spacers, 11 only static spacers, and 11 evaluated both articulating and static spacers. Of the 35 articles used to evaluate articulating spacers, there was 1 level II study, 11 level III studies, and 23 level IV studies (Table 1). Of the 22 articles used to evaluate static spacers there was 1 level II study, 12 level III studies, and 9 level IV studies (Table 1). The average age in the articulating group was 66.5 ± 0.6 (65.2–67.9) and the average age in the static group was 67.2 ± 0.8(65.4–69.0) (Table 1). The mean post-operative follow up was 66.5 ± 0.6 (65.2–67.9) months and 67.2 ± 0.8 (65.4–69.0) months in the articulating and static groups, respectively. The average BMI was 30.7 ± 1.0 (26.6–34.8) [7,24,26,33,38,39] for articulating spacers and 32.9 ± 1.3 (27.2–38.6) [7,33,39] for static spacers. In the 26 studies reporting gender in the articulating group, 45% of the patients were male. Of the 12 studies reporting gender in the static group, 45% of patients were also male. The average time of interim spacer placement in the articulating group was 17.2 ± 2.6 (10.8– 23.7) weeks, and 15.4 ± 3.9(5.8–24.9) weeks in the static group. To further analyze potential differences between the articulating and static spacer groups a sub-analysis was performed to determine the number of complex patients existing in each group. Patients were considered complex if they were culture positive for a virulent organism (MRSA, MRSE, VRE, gram negative, or polymicrobial), AORI grade II or III bone loss, or the presence of a draining sinus tract. 25 studies [5,6,8,9,11,13–16,19–21,23–25,28–32,34,35,37–39] with a total of 809 articulating spacers included data to extrapolate case complexity. 308 patients were considered complex with 38% complexity rate. Fifteen studies [8,9,11,25,38–42,44,46–49,51] with a total of 671 static spacers included data to extrapolate case complexity. 315 patients were considered complex with a 47% complexity rate. There was a statistically significant difference that static spacers were used in more complex patients (P b 0.0006). Clinical Outcomes HSS Score Five studies [6,9,22,26,31] with a total of 174 knees included preoperative HSS scores for articulating spacers. The average preoperative HSS score in the articulating group was 59.6 ± 4.8 (42–69). Nine studies [6,8,9,12,21,22,26,31,36] with a total of 265 knees included post-operative HSS scores for articulating spacers with an average of 84.9 ± 1.6(78.2–91.7). One study [9] with 22 static spacers included a pre-operative HSS score, which was 48.2. Six studies [8,9,36,43,44,46] included a post-operative HSS score using static spacers with a mean of 79.9 ± 1.8(72.1–87.8). There was no

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significant difference in the pre-operative HSS scores (P b 0.70) or post-operative HSS score (P b 0.12) between the articulating and static spacer groups.

rate. There was a statistically significant difference in favor of articulating spacers in the complex patient group for infection eradication (P b .0001).

KSS Score Twelve studies [5,7,15–17,23,29,32–35,39] with a total of 330 articulating included pre-operative KSS (function) scores with a mean of 46.8 ± 6.5(19.0–74.6). Sixteen studies [5,9–11,14–17,23,27,29,32– 35,39] included post-operative KSS (function) scores with a mean of 80.1 ± 6.0(3.7–156.4) in the articulating group. Four studies [7,33,39,49] with a total of 198 static spacers included pre-operative KSS (function) scores with a mean of 38.7 ± 8.6(1.8–75.5) in the static group. Eleven studies [9–11,33,39,41,44,45,48–50] with a total of 501 static spacers included post-operative KSS (function) scores with a mean of 77.2 ± 6.5(0–159.8). There was no statistically significant difference (P b 0.42) between the articulating and the static group with regard to the pre-operative KSS (function) scores. There was also no significant difference (P b 0.54) between the articulating and the static group with regard to post-operative KSS (function) scores.

Re-Implantation Twenty studies [5,8,9,11,13–17,19,21,22,24,25,28,29,31,32,34,36] with a total of 622 articulating spacers included data on reimplantation. There were 115 quadriceps snips, 1 VY quadriceps turndown, 9 tibial tubercle osteotomies, and 7 gastrocnemius flaps. One hundred forty eight patients (23.7%) required an extensile exposure or a rotational flap for soft tissue coverage. Seven studies [8,9,11,25,36,40,41,43] with a total of 203 static spacers included data on re-implantation. There were 19 quadriceps snips, 10 VY quadriceps turndowns, 27 tibial tubercle osteotomies, and 16 gastrocnemius flaps. 72 patients (35.4%) required an extensile exposure or a rotational flap for soft tissue coverage. There was a statistically significant difference in favor of articulating spacers for complexity of re-implantation (P b 0.0011). Bone Loss

Range of Motion In the articulating group, fourteen studies [5,11,15–17,19,20,23, 25,31,33,34,38,39] with a total of 468 knees included pre-operative range of motion data with a mean of 77.3° ± 2.6 (68.9°–85.8°). Twenty studies [5–9,11–14,16–18,22,23,28,29,32–34,37] with a total of 494 knees included interim articulating spacer range of motion data with a mean of 79.8° ± 2.2 (73.6°–86.0°). Twenty nine studies [5,6,8,9,11,13–23,25,28–39] included post-operative range of motion data with a mean of 100.1° ± 1.6(96.2°–103.9°). In the static group, 6 studies [11,25,38,39,45,49] included pre-operative range of motion data with a mean of 82.9° ± 4.2 (69.5°–96.2°). Eleven studies [7– 11,25,33,38,45,46,48,49] included data on interim static spacer range of motion with a mean of 1.8° ± 3.1 (0°–10.4°). Seventeen studies [8,9,11,25,33,36,38–41,43–46,48–50] included data on post-operative range of motion with a mean of 89.7° ± 2.1 (84.8–94.7). There was no statistically significant difference in the pre-operative motion between the two groups (P b 0.34). There was a statistically significant difference in favor of the articulating group with regard to interim spacer range of motion (P b 0.0001). It was also statistically significant that the articulating group had greater post-operative range of motion than the static group (P b 0.003). Infection Eradication Thirty-four studies in the articulating group evaluated their reinfection rates after two-stage exchange. Patients were labeled as being free of infection at their latest follow up appointment. These thirty-four studies produced 1065 knees with a mean re-infection rate of 7.5% ± 1.2 (4.7%–10.3%). Nineteen studies in the static group evaluated their re-infection rates producing 789 knees. The mean reinfection rate for the static group was 13.6% ± 1.4 (10.2%–16.9%). These data show a statistically significant difference in favor of articulating spacing achieving infection eradication (P b 0.0031). A sub-analysis was performed on complex case re-infection rates for both articulating and static spacer groups. Cases were considered complex in the presence of resistant organisms, bone loss, and draining sinus tracts, as detailed above. Twenty five studies [5,6,8,9,11,13–16,19–21,23–25,28–32,34,35,37–39] included data on complex re-infections for articulating spacers with a total of 308 patients. 26 of these patients were re-infected with the same or different organisms with an 8.4% re-infection rate. Fifteen studies [8,9,11,25,38–42,44,46–49,51] included data on complex re-infections for static spacers with a total of 315 patients. 89 of these patients were re-infected with same of different organism with a 28.2% re-infection

Pre-Existing Bone Loss Five studies [13,20,23,28,39] with a total of 126 articulating spacers included data on pre-existing bone loss encountered prior to implantation of the spacer. Ninety-nine (78.5%) patients had preexisting bone loss in the articulating group. The Anderson Orthopaedic Research Institution (AORI) classification of bone loss for these 126 patients is listed in Table 2. One study [39] with a total of 81 static spacers included data on pre-existing bone loss. Sixty five (80.2%) patients had pre-existing bone loss in the static group. The (AORI) classification of bone loss for these patients is listed in Table 2. There was no statistically significant difference between groups with regard to the existence of bone loss prior to implanting the anti-biotic spacer for all comers (P b 0.77). However, upon sub-analysis of the AORI classification of bone loss, static spacers were more frequently used when AORI type III bone loss was encountered on the femoral side (P b 0.0033). Bone Loss Development Eleven studies [6,9,11,12,15,20,23,28,30,34,38] with a total of 299 articulating spacers included data on bone loss development during the interim anti-biotic spacer placement. Ten (3.3%) patients in the articulating spacer group developed bone loss during its time period. Four studies [9,11,36,38] with a total of 78 static spacers included data on bone loss development during interim anti-biotic spacer placement. Thirty seven (47.4%) patients in the static group developed bone loss during its time period. Articulating spacers developed significantly less bone loss during their interim time period than did static spacers (P b 0.0001). Complications Thirty-five studies [5–39] with a total of 1087 articulating spacers included data on adverse events in the post-operative period. There

Table 2 Articulating and Static Spacers Placed With Pre-Existing Bone Loss. Variable AORI I Tibia AORI II Tibia AORI III Tibia AORI I Femur AORI II Femur AORI III Femur

Articulating (n = 126) % % % % % %

(n/N) (n/N) (n/N) (n/N) (n/N) (n/N)

45.2% 45.2% 9.5% 31.7% 54.0% 6.4%

(57/126) (57/126) (12/126) (40/126) (68/126) (8/126)

AORI: Anderson Orthopaedic Reseach Institute.

Static (n = 81) 37.0% 46.9% 16.1% 19.8% 60.5% 19.8%

(30/81) (38/81) (13/81) (16/81) (49/81) (16/81)

P Value 0.24 0.81 0.16 0.058 0.36 0.0033

G.N. Guild III et al. / The Journal of Arthroplasty 29 (2014) 558–563

were 173 (15.9%) complications during the treatment of patients in the articulating group utilizing a two-stage exchange for infection eradication. Twenty-two studies [7–11,25,33,36,38–51,53] with a total of 924 static spacers included data on adverse events in the postoperative period. There were 180 (19.5%) complications during the treatment of patients in the static group utilizing a two-stage exchange for infection eradication. There were statistically fewer adverse events in the articulating spacer group for complication of any type (P b 0.0362). Further analysis was performed on the type of complications observed with specific interest in mechanical complications of the spacers themselves, or a complication that was potentially contributed by the spacer. These complications are listed in Table 3. Sixty four (5.8%) complications that could potentially be attributed to the spacer occurred in the articulating group compared to 30 (3.2%) patients in the static group. There was no significant difference in this subset of complications between groups.

Discussion Infection continues to be a devastating complication in total knee arthroplasty and is the leading cause of failed total knee arthroplasty within two years of the index procedure [1]. The two-stage exchange is the current standard of care for treating infected total knee prostheses in North America with high rates of infection eradication [2]. However, significant controversy exists whether articulating or static spacers provide patients with improved outcomes. Current literature is comprised mostly of small series with level III and IV levels of evidence and a paucity of prospective randomized trials. These findings are consistent with the fact that the quality of research reporting in general orthopaedic journals lacks statistical rigor when assessing for compliance with CONSORT [53] and STROBE [54] guidelines. In this systematic review, the results of multiple studies were combined to ascertain outcomes in this cohort from the available published literature. We conducted thorough literature searches and applied current best practice for undertaking systematic reviews [55]. In general, a systematic review is dependent on several factors; was the search systematic and reproducible, was the methodological quality of the studies assessed and reported, and were the questions focused and clinically relevant? In this review, the literature search was systematic involving several databases and is reproducible using the search methodology listed above. The quality was assessed by classically utilized level of evidence rating [52]. Our focused questions were as follows: do articulating spacers provide increased post-operative range of motion and outcomes, do they provide adequate infection eradication rates, do they ease re-implantation, and can they be used effectively in more complex patients? Currently, articulating spacer use has gained popularity because it has the potential advantages of maintaining interim joint motion, preventing extensor mechanism shortening, facilitating re-implanta-

Table 3 Complications subluxation Spacer Dislocation arthrofibrosis Arthrodesis Extensor Lag Extensor Mechanism Failure Fractured Spacer Amputatation Periprosthetic Fracture Nerve Palsy Instability Total

Articulating Spacers

Static Spacer

4 8 7 3 3 3 5 5 3 3 20 64

1 0 1 13 4 2 5 3 0 1 0 30

561

tion, and improving post-operative function. The following descriptive review highlights important findings from the literature. Emerson et al [38] reported on the potential advantage of articulating spacers allowing for improved post-operative range of motion with articulating spacers achieving 107.8° of motion vs. 93.7° in the static group. Our systematic review echoes previous reports with the articulating spacers achieving an average of 100.1° of motion vs. 89.7° in the static group (P b 0.0030). We considered that the improved range of motion in the articulating group may have been due to a greater pre-operative range of motion; however the pre-operative motion for the articulating group was slightly less than the static group. It is also possible that static spacers were performed in patients with higher complexity. In our review, there were more static spacers placed for complex patients than articulating spacers. The fact that the complex patients had resistant organisms, bone loss, or draining sinus tracts cannot be ignored as a potential explanation for the lack of range of motion at final follow-up. In addition, the statistically significant decreased postoperative motion found in the static group may not result in clinically relevant patient satisfaction. Barrack et al [45], in a consecutive series of 125 patients described patient satisfaction outcomes after septic versus aseptic revision total knee arthroplasty. Despite the septic group having decreased final range of motion and inferior functional result, patient satisfaction was equivalent to the aseptic revision group. Unfortunately, we were unable to extract data that would have differentiated complex articulating spacer patients from complex static spacer patients with regard to range of motion. The articulating group did not have a paucity of complex patients, which was 37% in this systematic review. We therefore hypothesize that the statistically significant improved interim range of motion observed with articulating spacers allows for greater post-operative range of motion in most patients, however patients with increased case complexity may have decreased final range of motion compared to simple cases. The fact that there were no statistically significant difference in HSS scores or KSS scores between the articulating and static groups (P b 0.12 and P b 0.54) suggests that there is no functional difference in outcome between articulating and static spacers. However, in our analysis, articulating patients had greater range of motion, improved infection eradication rates, and less complex re-implantations. The HSS and KSS do extract data on functional outcomes, but are not specific enough to detect some of the above mentioned relevant outcome measures. Interestingly, when we looked at infection eradication rates for all comers, we found that the articulating spacers had statistically lower re-infection rates than did the static spacer group (P b .0031). Furthermore, when the case complexity was controlled for, the articulating group continued to show a significantly improved infection eradication rates compared to the static group (P b 0.0001). Although the results of the articulating spacer group show encouraging results the authors do not believe the improved eradication rate is solely based on the mechanical nature of the spacer itself, but rather a multitude of factors. For instance, the amount of antibiotics, the type of antibiotics, and type of bone cement showed significant inter-study variability. Even the methods to which the antibiotic spacers were fabricated including cement-on-cement, metal on poly, cement on poly, use of an intra-medullary rod, handmade, and pre-fabricated spacers had significant variance in both the articulating and static groups. Also, the case complexity was controlled for by giving those patients with resistant organisms, AORI type II and III bone loss, and draining sinus tracts a complex case designation. However, this methodology may not be specific enough to detect subtle difference in the host environment, such as MRSA/ MRSE vs. gram negative infections. Although this analysis does show superior results when articulating spacers were used to eradicate infection, even in complex cases, each patient must be evaluated individually taking into account multiple variables including organism resistance, bone loss, soft tissue envelope, and class of host.

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As mentioned above, articulating spacers are often used to facilitate implantation of the second stage of the two-stage exchange for sepsis [33]. We analyzed re-implantation after articulating and static spacer placement with regard to extensile exposure and need for rotational (gastrocnemius) flap for soft tissue coverage. The articulating group had significantly fewer extensile measures for exposure and rotational flaps in comparison to static spacer (P b 0.0011). We hypothesize that the interim range of motion provided for by articulating spacers does allow for improved soft tissue compliance, decreased extensor mechanism scarring, and facilitates second stage implantation. Once again, for this particular data point we were unable to extract information to differentiate the complexity of each case with regard to re-implantation. Therefore, reimplantations in the static group may have been performed in individuals with a more severely compromised soft tissue envelope. This could have potentially skewed the re-implantation data. A commonly cited justification for placement of a static spacer has been pre-existing bone loss. When we analyzed the data for existence of bone loss of any type, we found no statistical difference for static over articulating spacers being placed for the indication of bone loss (P b 0.77). However, when we categorized the bone loss based on the Anderson Orthopaedic Research Institute (AORI) classification of bone loss we found that static spacers were placed with significantly higher frequency for femoral bone loss than articulating spacers (P b 0.0033). These data however, may be flawed as only one study in the static spacer literature specifically addresses pre-existing bone loss, and only five studies in the articulating spacer literature. We also evaluated the bone loss incurred over the interim period each spacer type was implanted. Fehring et al [36] previously reported on the concerns of bone loss observed with static spacers and showed no bone loss with articulating spacers in their series. Our analysis confirms the work by Fehring and others with articulating spacers having significantly less bone loss than static spacers (P b 0.0001). There are several prevailing explanations for bone loss with static spacers including previously described bony invagination by the spacer itself, spacer migration, primitive nonstemmed spacers, and the tibial side of the spacer with poor bony coverage. Articulating spacers in general obtain greater bone coverage as may be achieved with standard modern prostheses. With greater bone coverage, the spacer distributes forces more evenly across the bone–spacer interface. Despite decreased bone loss observed in most studies with articulating spacers, concerns still exist with regard to mechanical complications resulting from the spacer itself. Previous literature has reported subluxation, instability, dislocation, and soft tissue envelope compromise secondary to spacer dislodgement [19]. Our analysis revealed that when examining complications of any type, the articulating group had significantly fewer adverse post-operative events (P b 0.0362). However, when examining complications directly related or potentially related to the articulating or static spacer there was no significant difference. This systematic review has several confounders including the inhomogenous data pool from which data were extracted. As mentioned above, there was no standardization between papers with regard to the methods in which spacers were fabricated, the anti-biotic type, the anti-biotic concentration, intra-venous antibiotics, the host classification, complex organisms, bone loss, and soft tissue envelope. In addition, the method of determining which patients are truly complex based on resistant organisms, bone loss, and draining sinus tracts may not be specific enough to detect differences between articulating and static spacer groups. Furthermore, there may be inadequate conduct or reporting in the literature itself as the majority of the analyzed studies are level III and IV levels of evidence. Also, a large proportion of the studies did not report measures of variability (SD) needed for meta-analysis of continuous data.

Despite the above mentioned confounders, this analysis does give insight into important clinically relevant questions regarding the superiority of one spacer technique over another with several statistically significant findings that have confirmed previous published data. This includes increased post-operative motion with articulating spacers, the ability of articulating spacers to be used even in complex patients with resistant organisms and bone loss, the paucity of bone loss observed with articulating spacers, and equivalent complication rates. Although this information is clinically useful, further high-level study to aid in the standardization of treatment for infected knee arthroplasty is needed. Examples of future study that would be clinically useful include: evaluation of a specific infecting organisms with specific treatment regimens, standardization of articulating spacers techniques (e.g. all metal on polyethylene, or all cement on cement), further studies on bone loss using an accepted classification scheme (AORI), systematic review of antibiotic dosing in cement and intravenously, and development of new techniques to treat the most complex patients with AORI III bone loss. References 1. Kurtz SM, Lau E, Watson H, et al. Economic burden of periprosthetic joint infection in the United States. J Arthroplasty 2012;27(8 Suppl):61. 2. Cui Q, Mihalko WM, Shields JS, et al. Antibiotic-impregnated cement spacers for the treatment of infection associated with total hip or knee arthroplasty. J Bone Joint Surg Am 2007;89(4):871. 3. Insall JN, Thompson FM, Brause BD. Two-stage reimplantation for the salvage of infected total knee arthroplasty. J Bone Joint Surg Am 1983;65(8):1087. 4. Borden LS, Gearen PF. Infected total knee arthroplasty. A protocol for management. J Arthroplasty 1987;2(1):27. 5. Hofmann AA, Kane KR, Tkach TK, et al. Treatment of infected total knee arthroplasty using an articulating spacer. Clin Orthop Relat Res 1995;321:45. 6. Anderson JA, Sculco PK, Heitkemper S, et al. An articulating spacer to treat and mobilize patients with infected total knee arthroplasty. J Arthroplasty 2009;24(4): 631. http://dx.doi.org/10.1016/j.arth.2008.04.003 [Epub ahead of print 2008 May 14]. 7. Jaekel DJ, Day JS, Klein GR, et al. Do dynamic cement-on-cement knee spacers provide better function and activity during two-stage exchange? Clin Orthop Relat Res 2012;470:2599. 8. Chiang E, Su Y, Chen T, et al. Comparison of articulating and static spacers regarding infection with resistant organisms in total knee arthroplasty. Acta Orthop 2011;82(4):460. 9. Park SJ, Song EK, Seon JK, et al. 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Articulating vs. Static antibiotic impregnated spacers in revision total knee arthroplasty for sepsis. A systematic review.

Periprosthetic infection after total knee arthroplasty is a devastating complication, and two-stage exchange is the standard of care in North America...
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