Introduction

Periprosthetic infections occur in approximately 1% of patients, but are devastating [10, 36]. Chronic infections generally are managed with prosthesis revision. Options for surgical treatment include a single-stage procedure, in which the definitive revision implant is placed, and a two-stage revision, where mostly a temporary spacer is used [9]. A single procedure avoids the morbidity of repeat surgery, but at the cost of a higher risk of persistent or recurrent infection, even though success rates are reported between 75% and 100% for both concepts [10] (Table 1). However, two-stage septic revision surgery is still the gold standard [10].

Table 1 Studies of septic one- and two-stage revisions with clinical results using the Harriship score
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Severe acetabular defects, either at initial presentation or those that occur after joint débridement and removal of the infected cup, can preclude the use of a temporary acetabular spacer. Protrusio acetabuli and hip instability are serious complications that occur in some patients in those scenarios. Solutions for such a problem may be a temporary Girdlestone hip procedure, a provisional cage, an antibiotic-loaded cement shelf, a nonarticulating spacer, or a one-stage procedure with cages. In situations where a two-stage procedure is preferred on the femoral side (for example, cementless reimplantation of the femoral stem after a transfemoral approach, or a substantially sclerotic femoral canal precluding use of a cemented stem) and substantial acetabular defects are present, we have started to use an approach in which the acetabulum undergoes definitive reconstruction at the initial stage. After thorough débridement of joint and acetabular bone, the acetabular defect is bridged with a cage and a polyethylene cup is cemented in place. On the femoral side, a prosthetic stem with recognized poor fixation characteristics is cemented in place as a spacer [10, 12, 14]. The latter then is removed during the second stage of the revision and replaced with a cementless stem. This revision concept, which combines a one-stage revision of the acetabular component and a two-stage revision of the femoral component, to the best of our knowledge, has not been reported before.

We therefore asked (1) What proportion of patients treated with single-stage acetabular reconstruction as part of a two-stage revision for an infected THA remain free from infection at 2 or more years? (2) What are the Harris hip scores after the first stage and at 2 years or more after the definitive reimplantation?

Patients and Methods

Between June 2009 and June 2014, 225 patients with periprosthetic joint infections were treated. These patients consisted of 127 women and 98 men with a mean age of 68.3 ± 16 years, a mean BMI of 27 ± 3 kg/m2, and a median of the Charlson Comorbidity Index score of 0 (range, 0–2) [6]. Forty patients were treated with a one-stage procedure and 150 with a standard two-stage procedure. For the remaining 35 patients for whom a two-stage procedure was preferred on the femoral side (necessity of a transfemoral approach and/or substantial sclerotic femoral canal), and had an acetabular defect of Paprosky Types 2B, 2C, 3A, 3B [3], or pelvic discontinuity, (classified intraoperatively after removal of the infected cup), we used a combination of one-stage acetabular and two-stage femoral revision. These 35 patients were examined in a retrospective study that used a longitudinally maintained institutional database for hip scores and infection-related endpoints. The minimum followup was 2 years (42 ± 17 months; range, 24-84 months). No patients were lost to followup. One patient died 5 years after surgery from unrelated causes. The patient cohort consisted of 18 women and 17 men with a mean age of 70 ± 15 years, a mean BMI of 28 ± 3 kg/m2, and a median Charlson Comorbidity Index score of 0 (range, 0 – 2). The original diagnosis that led to the primary arthroplasty was osteoarthritis in 28 patients, femoral head fracture in two patients, femoral head necrosis in two patients, and rheumatoid arthritis in three patients. There were six cemented and 29 cementless acetabular cups and 10 cemented stems (three revision stems) and 25 cementless stems (eight revision stems). The lifespan of the primary implant was a median of 7 years (range, 0.2–24 years). In 13 patients a primary implant was involved, but there also were nine patients who already had undergone one revision operation. Six patients previously had undergone two revision operations, three patients had three operations, three patients had four operations, and one patient had five operations. Eleven of the patients who had more than two operations underwent septic revision surgery at other hospitals. The distribution of diagnoses and prior procedures were not different in the study group compared with the whole group of patients with periprosthetic joint infections during the same period.

Periprosthetic infection was diagnosed according to the criteria of the Musculoskeletal Infection Society [28]. Preoperative aspiration of the hip was performed; this is a standard procedure in our clinic before any revision of a hip prosthesis is done and bacteriologic cultivation of the aspirated fluid is assessed for 14 days according to Schäfer et al. [30]. Bacteriologic and histologic examinations according to the methods of Atkins et al. [1], Virolainen et al. [35], and Pandey et al. [26] of the membrane at the site of loosening, which was removed during the operation, were performed to confirm the original diagnosis. The most frequent microorganisms detected by these methods were Staphylococcus epidermidis and Propionibacterium acnes (Table 2); two causative organisms were identified in seven patients and three in three patients.

Table 2 The microorganisms identified as the cause of the periprosthetic infection
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The acetabular defects were classified intraoperatively according to the system reported by Bradford and Paprosky [3] as follows: 10 with Type 2B, seven with Type 2C, seven with Type 3A, seven with Type 3B, and four with pelvic discontinuities. The femoral defects present before removal of the stem were classified according to Paprosky et al. [27] as follows: two with Type 1, 11 with Type 2, 14 with Type 3A, five with Type 3B, and three with Type 4. The femoral component was removed via a transfemoral approach (27 times) when the cementless stem was fully integrated in the bone or the cement mantle was tightly embedded (Fig. 1A–B); this procedure resulted in Type 3A bone defects in all the patients with preexisting Type 1 defects and in six patients with preexisting Type 2 defects.

Fig. 1A–D
figure 1

(A) The radiograph shows the pelvis of a 67-year-old patient with an infected THA implant on the left side, with a well-osseointegrated acetabular cup and a stable distal cement plug of a cemented stem after two-stage revision 1 year before. (B) A radiograph of the left hip obtained after the first operation shows a Ganz ring and the Müller® low-profile cup on the acetabular side and the femoral spacer implanted via a transfemoral approach. (C) This radiograph of the patient’s pelvis obtained 2 weeks after the second operation shows the reimplanted femoral revision stem. (D) A radiograph obtained 2 years after the second operation shows osseointegration of the revision stem.

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The transfemoral approach was performed using a modified Wagner technique [11, 13, 14]. After removal of all implants and débridement, the cup was replaced as follows: 17 with a Ganz ring with a Müller® Low Profile Cup (Zimmer Biomet GmbH, Winterthur, Switzerland) (Fig. 1B), seven with a Burch-Schneider Reinforcement Cage with a Müller® Low Profile Cup (Zimmer Biomet GmbH), six with a Trabecular MetalTM Acetabular Revision System (TMARS) with augments and a revision cup (Zimmer Biomet GmbH), and five with a cup-and-cage system (Zimmer Biomet GmbH) (Table 3). For stems, we typically used obsolete monoblock implants that no longer are used for primary implantation. These stems are encased in antibiotic-containing cement and coated in the patient’s blood to facilitate easier removal. If a transfemoral approach had been used, the bony flap was closed immediately after the cement-covered stem had been inserted with double cerclage wires (1.5 mm diameter) and the excess cement removed from the flap. The two components of the spacer were connected by a metal head (Fig. 1B).

Table 3 Distribution of the devices used in the different acetabular defects
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According to the antibiotic susceptibility profile of the microorganisms, a specific mixture of antibiotics was recommended by our microbiologist (LF) for use in the cement of the cup, the femoral spacer, and in systemic treatment (Table 4). A maximum of 10% of the total cement powder amount was added as antibiotic to the industrially prepared Palacos® G (four times) (Heraeus Medical, Darmstadt, Germany) and Copal® cement (31 times) (Heraeus Medical); for example, 2 g vancomycin powder to the powder of 40 g Copal® cement. For 11 patients, the cement of the spacer contained two antibiotics and for 24 patients, the cement contained three antibiotics (Table 4). The parenteral antibiotic therapy was designed specifically for each patient by our microbiologist and was given for 2 weeks followed by individual oral administration of the antibiotic for 4 weeks (Table 4). Eleven patients received two antibiotics systemically, three received three antibiotics systemically, and one patient received four antibiotics systemically. Fourteen patients received two antibiotics orally.

Table 4 Local and systemic antibiotic therapy
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Six weeks after removal of the infected implant (if the C-reactive protein was decreased to a level below 20 mg/L [12, 15]), the femoral spacer was changed to a cementless standard stem in eight patients and a modular cementless revision stem (Revitan® curved; Zimmer GmbH, Winterthur, Switzerland) in 27 patients (Fig. 1C). After implantation of the new prosthetic components, the transfemoral approach was closed again using new 1.5-mm double cerclage wires in 26 patients and polyethylene cerclages in one patient (Fig. 1C–D).

During the reimplantation, at least five tissue samples were removed for bacteriologic examination and then the same parenteral antibiotic therapy was reinitiated as after the first stage. This was continued for 2 weeks and then changed to the appropriate oral administration of the antibiotic for 4 weeks. Rifampicin and ciprofloxacin were administered orally from the second day after both surgeries.

Postoperatively, we limited weightbearing to approximately 10 to 20 kg for 6 weeks. We increased this gradually to full weightbearing at 3 months postoperatively as described by others for other cementless revision stems [2, 32, 34].

All patients were examined before surgery and then at 3 months, 6 months, 9 months, 1 year, 18 months, and 2 years after surgery, and at the latest followup. Inflammatory parameters (C-reactive protein) also were followed. According to Masri et al. [24] and Zimmerli et al. [37], a patient could be judged infection-free at followup if he or she was free of clinical signs for infection (fever, local pain, redness, warmth, sinus tract infection) and had a C-reactive protein level less than 10 mg/L. The clinical outcome was evaluated by two of the authors (MS and DO) using the Harris hip score [16, 20].

The statistical analyses were conducted using SPSS for Windows Version 11.0 (SPSS Inc, Chicago, IL, USA). All subjects gave informed consent to participate in the study and the protocol was approved by the research ethics boards of the respective institutions.

Results

Thirty-four of 35 patients (97.2%; 95% CI, 85.4%–99.5%) were free of infection based on the criteria of Masri et al. [24] and Zimmerli et al. [37], at latest followup. There was a recurrence of infection in one patient 20 months after the second operation. This patient previously had three septic revision operations performed elsewhere, had infections with three different microorganisms (S epidermidis, Escherichia coli, and Proteus mirabilis), and had reinfection with S epidermidis and S lugdunensis. None of the samples taken during the second operation were positive for bacterial infection in any patients in this series.

The Harris hip score improved from 45 ± 20 (range, 5–82) points before surgery (35 patients) to 61 ± 13 (range, 20–74) with the spacer before the second operation (35 patients). All patients could walk pain-free with partial weightbearing. After the second operation, the Harris hip score increased steadily during the followup period: it was 65 ± 12 (range, 40–80) points at 3 months postoperative (35 patients), 68 ± 14 (range, 41–90) points 6 months postoperative (32 patients), 70 ± 15 (range, 46–92) points 9 months postoperative (31 patients), 74 ± 15 (range, 46–92) points 12 months postoperative (34 patients), 79 ± 16 (range, 48–94) points 18 months postoperative (32 patients), and 82 ± 16 (range, 59–98) points 24 months postoperative (35 patients).

Two patients experienced dislocations; one after the first stage and one after stem reimplantation; both patients were treated conservatively. One patient had deep vein thrombosis. No other complications occurred. Mean blood loss was 1390 ± 680 mL (range, 300–3600 mL) during the first operation and 1256 ± 612 mL (range, 400–3200 mL) during the second.

Discussion

Severe acetabular defects can preclude the use of a temporary acetabular spacer in two-stage revisions of periprosthetic infections of hip arthroplasties. To address this, we have started to combine a one-stage revision of the acetabular component and a two-stage revision of the femoral component in selected patients. To the best of our knowledge, this concept has not been reported before. We therefore sought to assess freedom from infection and Harris hip scores after the first stage and at 2 years after the definitive reimplantation. Ninety-seven percent of our patients were infection free and had a Harris hip score of 61 ± 13 points after the first operation and 82 ± 16 points 2 years after the second operation.

The study has limitations, however. One is the relatively low number of patients. This is the first description of the method to be published and therefore can be regarded as being equivalent to a pilot study. The promising results will have to be confirmed in additional studies with greater numbers of patients. Another limitation is the relatively short followup. However, we suggest that a minimum of 2 years is sufficient for questions posed by the current study because reinfection occurs only rarely after 2 years of reimplantation [21, 24, 33]. However, the observation period does not permit any assessment of the lifespan of the implants used in the study. Moreover, we acknowledge the possibility of bias in patient selection. In general, we prefer to use an uncemented femoral stem for all revisions, including those for sepsis. We performed single-stage femoral revisions in selected hips where a susceptible organism was identified before surgery, and where adequate bone stock was available for a cemented stem but inadequate bone stock on the acetabular side for a spacer. With respect to the acetabulum, we selected a one-stage procedure in the presence of defects classified as Paprosky Type 2B or higher, because of the high risk of dislocation of standard spacers. This approach was chosen before surgery if the defects could be classified as Paprosky Types 3A, 3B, or pelvic discontinuity preoperatively on radiographs and CT scans. If Paprosky Types 2B and 2C defects were found intraoperatively owing to the removal of well-fixed infected cups, and dislocation was likely, we opted for the one-stage procedure on the acetabular side. As such, we believe that any bias in selection is the use of this approach in more-difficult clinical settings.

We achieved a 97% success rate with this concept, comparable to the results with standard two-stage revision surgery with success rates of 90% or more and standard one-stage revision with success rates between 80 and 100% [4, 10, 12] (Table 1). Lange et al. [22] calculated, in a meta-analysis, a risk of reinfection of 10.4% for two-stage and 13.1% for one-stage septic revision.

After the first operation, all patients could walk pain free with partial weightbearing and attained a mean Harris hip score of 61. Although we did not explicitly set out to compare our approach with a Girdlestone resection arthroplasty, we note that it represents a potential alternative in settings where a temporary Girdlestone might be used, where segmental acetabular defects make a standard two-stage septic revision with a monoblock spacer impossible. The mean Harris hip scores after a Girdlestone procedure have been reported at approximately 50, which is not as good as the scores for our concept [23, 25, 29, 31]. Moreover, an implanted spacer is advantageous because the local release of antibiotics from the cement takes part in effective treatment of the infection and implantation of a prosthesis during the second stage is technically much easier than after a Girdlestone procedure [10, 15]. Spacers prepared in the same way as described in the current study release antibiotics, even after 6 weeks, in amounts that are greater than the minimal inhibitory concentration for the bacteria that are causing the infection of the prosthesis bed [15].

The Harris hip scores assessed at the end of the 2-year followup with a mean of 82 ± 16 points were similar to those reported in other studies with one-stage revisions with mean scores between 77 and 84 and two-stage septic revisions with scores between 73.4 and 84.3 (Table 1) [5, 7–9, 17–19]. Citak et al. [8] calculated, in a literature review of 1631 two-stage revisions, a mean Harris hip score of 84.3 using a surgeon-made articulating spacer and 81.8 with a preformed hip spacer.

Because only one of our patients experienced a dislocation after the first operation, we believe this concept is effective in preventing instability in patients with acetabular defects.

The results of this pilot study show that this concept is a promising therapeutic option for periprosthetic infections of the hip in which major acetabular defects render the typical articulating-spacer approach risky, and where a two-stage procedure is preferred for treating the infection and managing the femoral side.