Fretting corrosion of the modular taper junction in total hip arthroplasty has been studied in several finite element (FE) investigations. In FE analyses, different parameters can be varied to study micromotions and contact pressures at the taper interface. However, to truly study taper wear, the simulation of micromotions and contact pressures in non-adaptive FE models is insufficient, as over time these can change due to interfacial changes caused by the wear process. In this study we developed an FE approach in which material removal during the wear process was simulated by adaptations to the taper geometry. The removal of material was validated against experiments simulating the clinical fretting wear process. Experimental test: An accelerated fretting screening test was developed that consistently reproduced fretting wear features observed in retrievals. Biomet Type-1 (4°) tapers and +9 mm offset adaptors were assembled with a 4 kN force (N=3). A custom head fixture was used to create an increased offset and torque. The stems were potted in accordance with ISO 7206–6:2013. The set-up was submerged in a 37°C PBS solution with a pH adjusted to 3 using HCL and NaCl concentration of 90gl−1. The components were cyclically loaded between 0.4 – 4 kN for 10 million cycles. After completion, the volumetric and linear wear was measured using a Talyrond-585 roundness measurement machine. FE model: This was created to match the experimental set up (Figure 1). Taper geometry and experimental material data were obtained from the manufacturer (Zimmer Biomet). The coefficient of friction of the studied combination of components was based on previous experiments (Introduction
Method
Fretting corrosion at the taper interface has been implicated as a possible cause of implant failure. Using Experimental test set-up: An accelerated wear test was developed that consistently reproduced fretting wear features observed in retrievals. Biomet stems with smooth 4° Type-1 tapers were combined with Ti6Al4V Magnum +9 mm adaptors using a 2 or 15 kN assembly force. The head was replaced with a custom head fixture to increase the offset and apply a torque at the taper interface. The stems were potted according to ISO 7206-6:2013. The set-up was submerged in a test medium containing PBS and 90gl-1 NaCl. The solution was pH adjusted to 3 using HCl and maintained at 37°C throughout the tests. For each assembly case, n=3 tests were cyclically loaded between 0.4–4 kN for 10 Million cycles. Volumetric wear measurements were performed using a Talyrond-365 roundness measurement machine. The FE model was created to replicate the experimental set up. Geometries and experimental material data were obtained from the manufacturer (Biomet). The same assembly forces of 2 and 15 kN were applied, and the same head fixture was used for similar offset and loading conditions. The 4 kN load was applied at the same angles in accordance with ISO 7206-6:2013. Micromotions and contact pressures were calculated, and based on these a wear score was determined by summation over all contact points.Introduction
Methods
Prosthetic joint infection (PJI) is a severe complication of prosthetic joint implantation, with an estimated incidence of 2.18%. Most frequently used treatment strategy for PJI is a two-stage revision procedure. However there are specific patients with a new or persisting infection after primary or revision surgery where further surgical treatment is not attractive. This may be because of medical or local surgical conditions, or patient's refusal to undergo (further) surgical therapy. For these patients suppressive antibiotic therapy (SAT) may be an alternative treatment. The aim of this study is to describe the clinical and radiological outcome of patients with a PJI of a hip arthroplasty, treated with SAT. Twenty-four patients with a hip arthroplasty treated with suppressive antibiotic therapy for PJI between January 1, 2008 and December 31, 2013 were included. All patients had a proven prosthetic joint infection, either by ≥2 intraoperative cultures or joint aspiration. SAT was defined as treatment with antibiotic therapy for more than three months. Most used antibiotics were doxycycline in 15 patients and cotrimoxazole in six patients. Patients were supposed to have a successful outcome when their prosthesis remained in situ and they had no relapse or new infection. Suppressive antibiotic therapy was considered successful in 15 (62.5%) patients with a mean follow-up of 20.6 months. Two patients (8.3%) had to stop the antibiotic therapy due to adverse effects. The mean duration of the SAT was 20.4 months (range 0.92–92.65 months). Mean modified Oxford hip score of the successfully treated patients at the latest follow up was 35 (range 16–49) and mean Harris hip score 71 (range 40–93). The mean visual analogue scale (VAS) was 16 (range 0–70) in rest, 32 (range 0–85) during exercise and 65 (range 10–100) for satisfaction. Of the 9 patients with an unsuccessful outcome, there was a radiological loosening of the cup in 4 patients. In the group of 15 patients that were considered successful, 2 patients had a radiological loosening of the cup and one patient loosening of the stem. Suppressive antibiotic therapy can be an attractive alternative treatment in selected patients with a prosthetic joint infection of a hip arthroplasty who cannot or will not undergo (further) surgical therapy. Further research with a larger number of patients is required. Also the optimal dosage and duration of suppressive antibiotic therapy and possible resistance to the antibiotic therapy is unknown.
Surgical site infections after total hip arthroplasty result in decreased quality of life, increased morbidity and increased health care cost. We hypothesized that the implementation of a bundle of care for total hip arthroplasty decreases the amount of surgical site infections. In this retrospective cohort study we investigated the implementation of this bundle in a University Medical Centre and its effect on perioperative surgical site infections after total hip arthroplasty and on incidence of hypothermia. In 2009 the bundle of care consisting of four elements was implemented in total hip arthroplasty in our hospital; (I) perioperative normothermia, (II) hair removal before surgery, (III) the use of preoperative antibiotic prophylaxis and (IV) discipline on the operation room measured by door movements. For this study we used data from January 2010 – October 2013. We measured all parameters prospectively including surgical site infections within 6 weeks postoperatively. In the study period a total of 585 patients received a primary total hip arthroplasty. Bundle compliance improved significantly in 3.5 years from 71.7% in 2010 to 91.6% in 2013. Postoperative hypothermia decreased from 10.5% to 8.4% (non-significant) and SSI rate from 0.9% to 0.0% (non-significant). Implementation of this bundle of care is possible in an academic tertiary referral center. A relatively cheap solution can increase patient safety in a surgical environment. Introduction of a bundle of care resulted in a non-significant reduction of hypothermia and rate of surgical site infections in total hip arthroplasty.
Local infiltration analgesia (LIA) is promoted as an effective treatment modality for pain control after total knee arthroplasty (TKA) (1). A mixture of drugs is used to provide a multimodal analgesic effect. Previous studies reported that the use of these drugs is safe. After we carefully implemented a LIA study protocol in our practice, concerns raised about patient safety with probably higher infection rates. This forced us to perform an interim analysis after the first 58 cases. 58 patients underwent a unilateral TKA with a standardised LIA protocol (2), which consisted of a mixture of ropivacaine, epinephrine, and triamcinolone acetonide. Complications, knee function and patient satisfaction scores were prospectively recorded during regular outpatient control. Four patients (6.9%) presented with signs of periprosthetic joint infection (PJI) within two months after surgery. Baseline characteristics were similar between the infected and non infected group. All infections were treated with debridement and retention, and antimicrobial treatment was started. One patient who suffered an infection died during followup. At two years followup all implants could be retained. Knee function and KSS score were acceptable for the patients who suffered PJI. There is no consensus on the combination of drugs used for LIA. The application of corticosteroids in LIA is reported to be safe (3), but arguable results about the injection of local corticosteroids around knee arthroplasty surgery in the past have raised suspicion in literature (4). Combined with our unacceptable high rate of PJI, we believe that the current body of evidence, with small heterogeneous series, does not support the safe use of corticosteroids in LIA.
This retrospective study evaluates the outcome of patients with a late infection of a cemented total hip arthroplasty (THA) treated with two-stage revision with retention of the original well-fixed femoral cement mantle. Operation reports of all two stage revision performed in our clinic between 2009 and 2013 were reviewed (249 patients). Patients in which femoral cement mantle was retained during surgery were included (10 patients). The average age at the first stage revision procedure was 61.5 years (range 38–80). The mean follow-up period was 26 months (range 5 to 54 months). Clinical, laboratory, and radiological outcomes were evaluated. Successful treatment of periprosthetic joint infection (PJI) was achieved in six out of 10 patients; four patients showed no signs of infection during follow-up. Two of these patients received three months of antibiotic treatment after second stage, because of positive cultures at second stage. The other two successfully treated patients showed recurrence of PJI one week after second stage. Debridement with retention of prosthesis (DAIR) was performed. Newly cultured microorganisms were successfully treated with 3 months of antibiotics. The other four patients were considered to be failures; in three patients, the femoral cement mantle was removed after the first stage due to recurrent infection. The other failure showed a recurrent PJI after second stage. Despite DAIR and three months of antibiotic treatment, this patient is treated with suppressive antibiotics until latest follow-up. Based on this study, results in managing an infected THA with cement-within-cement revision are disappointing. Therefore, more research is required to determine which patients are appropriate for cement-within-cement revision.
