Infection remains a serious complication following arthroplasty. Despite the im- provement in surgical technique and implant design, the overall rate of infection ranges from about 0.5 – 1.4 % in total hip arthroplasty [12, 25].
The exact infection rate varies depending on localization, technique (cemented vs.
cementless), duration of follow-up and implant used (Table 1).
To understand the difficulties in treating periprosthetic infections, we have to focus on some microbiological concerns. Bacteria adherent to the surface of implants change their biological behaviour. They produce a biofilm, the so-called glycocalix [20], which creates a microenvironment protective against antibiotics and the host’s immune system (Fig. 1) [20, 33, 42]. Moreover, they reduce their metabolic activity and thus increase their generation times [4]. Because antibiotics act on growing bac- teria, the minimum inhibitory concentrations (MIC) are higher with bacteria which have reduced metabolic activity. Costerton et al. found an 800-fold increased MIC for Tobramycin in adhesive Pseudomonas aeruginosa compared to non-adhesive bacte- ria [11].
With antibiotics and the host immune system becoming ineffective against the adhering bacteria and no possibility to remove the bacteria from the implant surface, the replacement of a prosthesis is the only remedy in many cases.
For any treatment concept it is important that the microbiological cascade, includ- ing the biofilm production, is time-dependent. Hence, if the treatment starts early, before the planctonic bacteria become adhesive in large numbers and produce a pro- tective glycocalix, the best results can be achieved.
Table 1. Infection rate in total hip arthro- plasty
Technique Follow up (years)
Infection rate %
Year / reference
Cemented 5 0.2 (AB*) – 0.8 1997 / [18]
Cemented 10 0.4 (AB*) – 0.7 2003 / [17]
Screwed cup 10 4 1998 / [1]
Screwed cup 5 1.2 1998 / [15]
Screwed cup 6.3 0 2003 / [53]
Press-fit 9.1 0.76 1998 / [3]
Press-fit 9 1.4 2001 / [2]
Press-fit 10.3 1.1 2001 / [27] * antibiotic-loaded
cement
Fig. 1. Staphylococcus epidermidis adhesive on polyethylene (PE) (Photo: W. Mittel- meier, TU München)
Table 2. Revision concepts in infected arthroplasty
) Antibiotic treatment without surgery
) Debridement and irrigation with retention of the components ) One-stage revision
) Two-stage revision ) Multi-stage revision
The classification which correlates best with the microbiological process was pub- lished by Segawa et al [44] and Mont et al [39]. Early postoperative (acute) infection appears within the first four weeks after surgery, late chronic infection thereafter [39, 44]. Only in acute infection exists a realistic chance to eradicate the bacteria without removing or exchanging the implant. In chronic infection an exchange of the implant is mandatory.
However, the duration of infection is not the only parameter for the decision on a treatment concept. Age, comorbidity and immune response of the patient, sensitivity of the infecting bacteria and implant design [10] must be considered as well.
After taking all the details into account, the surgeon can decide which approach is the most promising. The different treatment options (Table 2) are described.
Revision Concepts
1. Antibiotic Treatment without Surgery
Conservative antibiotic therapy without an operative intervention should be restricted to patients which are not suitable for surgery because of their comorbidity or which disagree on a revision after informed consent. Cure from infection by con- servative treatment cannot be expected, but a controlled status quo can be achieved.
Prerequisite for antibiotic therapy is that bacteria have been identified and oral
antibiotics, according to the antibiogram, are available. To reduce the risk of inducing
resistance, a double therapy should be used. The combination of rifampicin and
shown by Tsukayama et al [46]. In addition, Crockarell et al could clearly show that debridement and lavage were only successful within 4 weeks after primary hip arthroplasty and if debridement is performed early after the onset of symptoms (within 6 to 14 days) [12]. In all cases of late chronic infection the treatment was doomed to fail, while in acute infection 72 % were successfully treated after one year.
However, after 6.7 years only 14 % were still free from infection [12]. In more recent trials success rates between 9 % [31], 32.6 % [45] and 35 % [14] in infected total knee arthroplasty were reported.
Radical debridement and lavage with retention of components should only be attempted in cases of early (acute) postoperative infection with a stable implant (Fig.
2). The surgical treatment is usually combined with IV antibiotics over 4 weeks fol- lowed by oral antibiotics for 6 weeks. Local antibiotics, like gentamicin-loaded colla- gen sheets can be used in addition [48]. If necessary, debridement can be repeated or a sequential therapy with Vacuum Assisted Closure (VAC) between two revisions per- formed [19].
Staphylococci have a high affinity to polyethylene (PE) components. In case of periprosthetic infection by these bacteria, exchange of PE components in combina- tion with debridement and lavage is suggested [5].
In case of progression of infection, a second revision with exchange of the implants becomes necessary.
Fig. 2. Debridement and irrigation by jet- lavage with retention of cup and stem and exchange of head and inlay in infected total hip arthroplasty
3. One-stage Revision
Bacteria adhesive to the components and protected by a biofilm cannot be removed from the surface by any mechanical, antiseptic or antibiotic approach. In conse- quence, a revision arthroplasty becomes necessary in late chronic infection. Debride- ment alone and retention of components were shown to fail in all cases of chronic infection [12].
In the early eighties Buchholz and coworkers published their experience in one stage total hip revisions. Surgery included excision of soft tissue, removal of the implant and cement, replacement with an appropriate prosthesis using antibiotic- loaded cement and systemic antibiotics. Overall success rate after ten years was 77 % in 583 patients [5]. Hanssen and Rand could show that the use of antibiotic-loaded cement in one stage revisions is significantly more successful than usual cement (suc- cess rate 83 % vs. 60 %) [25]. More recent studies showed a higher success rate in small series of 90.9 % [6], 91.7 [7] and 100 % [47]. In a literature review including 12 reports overall success was 83 % [34].
Advantages of a one-stage revision are lower morbidity (single surgery), shorter hospital stay, lower costs and better functional outcome. The price for these advan- tages is the risk of recurrent infection, if not all infected tissue and necrotic bone have been meticulously removed and the “bacterial race for the surface of the compo- nents” can start again.
Careful selection of patients is important for a one-stage revision: good immune response, no comorbidity, no draining sinuses and bacteria sensible to oral antibiot- ics are in favor of this approach.
4. Two-stage Revision
Late chronic periprosthetic infections account for about 70 % of the cases, as com- pared to less than 30 % for acute postoperative infections [52]. Elderly patients with concomitant diseases and a low immune response are those more often affected.
Moreover, infection generally starts long before the surgical treatment begins and draining sinuses exist over a long period.
With this difficult starting point, a one-stage revision is in our opinion too risky;
the two-stage revision should be preferred. Two-stage salvage consists of removal of implants and cement, placement of local antibiotics (Gentamicin PMMA beads [48]
or PMMA spacer), and appropriate intravenous antibiotic therapy followed by reim- plantation usually with antibiotic-impregnated cement (Fig. 3) [13]. Time interval between implant removal and delayed revision surgery varies between one to two months. Antibiotic therapy should be stopped two weeks before surgery and revision arthroplasty only performed if blood test (WBC, CRP), clinical examination and / or cultures of a hip aspiration are negative for infection [40]. In literature success rates of two stage revisions are reported between 80 % [24] and 92 % [22] in septic THA.
After removal of the implant soft tissue contracture, arthrofibrosis, instability of the extremity and thus immobility of the patient are feared complications. To avoid these problems spacers have been introduced to the two-stage revision concept [9].
First, block spacers made of PMMA and gentamicin were used. In addition to serv-
ing as a drug delivery system, the antibiotic-impregnated spacer block gave mechani-
a
Fig. 3. Two stage revision in infected total hip arthroplasty:
a Gentamicin PMMA beads after removal of the implant;
b and c Revision arthroplasty with a modular system
b c
cal stability to the joint [9]. Results were good with a recurrence rate of infection after revision TKA between 0 and 9 % [23, 26, 41, 49]. However, in some cases bone loss in the bone stock was observed [8]. This led to the frequent use of articulating spacers.
In infected THA spacers are either hand molded of bone cement [50], fabricated in a Teflon mould (Fig. 4) [43] or preformed (Fig. 5) [38]. Dislocation of hip spacers has been reported, often in combination with a loosening of the shaft at the femur [37].
This can be avoided if a small amount of additional cement is used for the fixation of
a b Fig. 4. Articulating,
antibiotic loaded, cement hip spacers.
Fabricated in a teflon mould (Biomet Deutschland, Berlin, Germany).
a b
Fig. 5. Articulating, antibiotic loaded, cement hip spacers, preformed (Spacer-G – Tecres Spa, Italy)
the spacer [21]. Results for the use of articulating spacers in two-stage revisions are shown in Table 3.
In two-stage hip revision for infection a comparison of the interim use of antibi-
otic-loaded PMMA beads and spacer prostheses in 128 cases was performed. Interest-
ingly, the recurrence of infection was not different in both groups (4.7 %). The use of
a spacer was associated with a higher hip score, a shorter hospital stay, a decrease in
0 10 20 30 40 50 60 70 80 90 100
positive cultures in %
1 2 3 4 5
revisions
operative time, less blood loss and less postoperative dislocations [29]. This supports the safety and efficacy of articulating spacers.
5. Multi-stage Revision
A multi-stage revision concept may be used in “worst case situations”, e.g. chronic infection caused by methicillin-resistant Staphylococcus aureus (MRSA) or Staphylo- coccus epidermidis (MRSE) [35] or an extensive system of draining sinus and abscesses. Surgical technique is equal to the two-stage revision concept, with the exception that between removal and reimplantation, surgical revisions with debride- ment and irrigation are performed [32]. During these “second” or “third” look sur- geries, the surgical site can be explored, debridement and irrigation repeated, speci- mens for microbiological examinations taken and the time point and technique of reimplantation planned. To secure drainage of the surgical site, Vacuum Assisted Clo- sure (VAC-therapy) should be used between the revisions [19].
In a trial (n = 30 patients) we could show that at every repetition of the debride- ment, less often bacteria were detected in the microbiological cultures (Fig. 6). In our opinion, the risk of a recurrent infection is minimized by the reduction of bacterial contamination of the surgical site before total hip re-implantation. Thus, not only in a “worst case situation”, where the bacterial contamination is extremely high, but also in a young patient with no comorbidity sequential debridement combined with
Fig. 6. Debridements and VAC-therapy after removal of the im- plants: positive bacte- rial cultures are reduc- ed by every repetitive debridement (n = 30)
VAC-therapy may be appropriate to reduce the risk of recurrent infection. If a patient is suitable for repeated surgeries (no concomitant diseases, good general health, low risk profile), we suggest a multi-stage revision concept to keep the risk of recurrent infection as low as possible.
Conclusion
Decision on a treatment concept in infected THA must be based first on the clinical situation of the patient, especially his age, comorbidity and immune response, second on the chronicity of infection and third on the sensitivity of the infecting bacteria.
All these factors have to be carefully considered and an individual therapy planned.
Conservative antibiotic therapy should be restricted to patients not suitable for surgery. Debridement and retention of components might be successful in an early acute infection in combination with a good immune response of the patient and bac- teria with low antibiotic resistance.
One-stage revision can be performed in early (acute) postoperative infection in a patient with no or little comorbidity.
Two-stage revision seems to become the standard procedure in chronic peripros- thetic infection with the use of an antibiotic-loaded spacer during the interval between removal and reimplantation.
Multi-stage revisions can be performed in “worst case situations” like chronic periprosthetic infection caused by methicillin-resistant Staphylococci or to reduce the risk of recurrent infection in patients suitable for repeated surgeries.
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