Prosthetic Hip Joint Infection: An Aluminium Mold for Intraoperative Production of Antibiotic-loaded Cement Hip Prostheses: 3 Cases Report

Introduction: To treat hip prosthetic infection, 2-stage revision, including removal and reimplantation, remains the standard treatment for prosthetic infection. Articulating cement spacer has been shown to provide better functional results after reimplantation. However, its cost as a manufactured product is not cheap and the choice of antibiotics is not flexible either. We designed an aluminium mold to make an antibiotic impregnated cement spacer, and replaced it between the first and the second stage. The current study was conducted to test their clinical efficacy. Case report: We report 3 cases of hip prosthetic infection treatment by using antibiotic impregnated cement spacer made by an aluminium mold. All patients presented to us in first 2-years postoperation and all had a deep infection. Three patients with infected total hip arthroplasties were treated with 2-stage revision using articulating spacers made by an aluminium mold and had a good result. Conclusion: Treating hip prosthetic infection with these articulating spacers eradicates infection effectively, improves the life quality before reimplantation and provides good final results without significant complications.


Introduction
Periprosthetic joint infection (PJI) is a truly devastating complication of total joint arthroplasty [1]. It adversely impacts the patient, by causing functional disability, increased morbidity and also mortality [2]. The management of PJI currently is far from optimal, often resulting in the need for prolonged hospitalization, administration of long term intravenous antibiotics, and the need for multiple surgical interventions [3]. The protracted course of treatment results in a massive financial burden on the treating institution and the health system on a national level. The incidence of PJI has been increasing steadily over the last decade, both in terms of the absolute number of cases, as well as the proportion of primary total hip and knee arthroplasties that succumb to infection [3,4]. The resistance profile of infecting organisms has also changed over the recent years with an increase in the number of surgical site infections and PJIs being caused by antibiotic resistant organisms [5,6]. While recurrence of PJI after treatment is not common, eradication rates as low as 16-37% has been shown with infection of certain organisms treated with less-aggressive strategies [7,8]. The extensive treatment required to appropriately treat a patient with PJI is significantly more expensive than that for aseptic loosening after primary total joint arthroplasty [3], and treating institutions are experiencing a decline in reimbursement along with the development of penalties for infection associated readmission.

Construction of the spacer mold
The mold was produced in a computerized CNC machine (DATRON Booth N-6021) and consists of 2 parts. It is made of high strength aluminium (AA7075 T6 3.4365; density 2.8 kg/dm 3 and tensile strength 520 560 Nm/mm 2 ) and coated by ANODE technique. Half of the coating penetrates into the base material, which results in an increase of 25 m, leading to a standard coating thickness of 50 m. The mold can be cleaned and sterilized for reuse ( Figure 1).

Case Report
Informed consent to publish the case report was obtained from the patients.

Case 1
The patient is a 59-year-old Vietnamese man. This patient has diabetes type 2 for 10 years; he was still on treatment with glucose level in control. In 2011, in the absence of previous traumas, he was diagnosed with bilateral femoral head avascular necrosis. Pain-killer treatment, corticosteroid therapy and nonsteroidal anti-infammatory drugs were performed in another medical Centre, in other Vietnamese region. Because of poor clinical improvement, he also underwent left hip arthroplasty. In 2013, he was operated with the right hip. 1 year after he developed PJI of the left hip with symptoms such as pain, swelling local, warmth and mild fever. He was hospitalized and debrided for 3 months. He was discharged after that and antibiotics treatment. On July 2016, he was in lot of pain on the same area with an abscess 3-5 cm. He was debrided in hospital X and transferred to Cho Ray hospital after 1 month in the unimproved infectious condition. He underwent debrided, serological tests, synovial fluid tests, antibiogramme and VAC drainage.

Case 2
The patient is a 50-year-old Vietnamese man. In 2009, in the absence of previous traumas, he was diagnosed with left femoral head avascular necrosis. Pain-killer treatment, corticosteroid therapy and non-steroidal anti-inflammatory drugs were performed in another hospital. Because of poor clinical improvement, he also underwent left hip arthroplasty in 2010. 1 year after he developed PJI of the left hip with symptoms, such as pain, swelling local and warmth. Antibiotic treatment and nonsteroidal anti-inflammatory drugs were performed. On February 2017, his clinical improvement was too bad with pus from drainage incision. He has been admitted to that hospital, and underwent debrided, VAC in three times. On May 2017 he underwent debrided again, removed the prosthesis, used PROSTALAC (made by hand) and then transferred to Cho Ray hospital in the unimproved infectious condition. At Cho Ray hospital, he underwent debrided to remove the PROSTALAC, serological tests, synovial fluid tests, antibiogramme and VAC drainage. After 3 times debridement and VAC drainage, he was impregnated with antibiotic-loaded cement spacer, which was made by aluminium mold and loaded: Imipenem 2 g, and Vancomycin 2 g (Synovial fluid tests result: Staphy-lococcus aureus, multiple antibiotic resistance). He was discharged after 2 weeks with the infection in control, dry wound. He keeps on using oral antibiotic treatment in 6 weeks ( Figure 5). Three weeks post operation, his wound was healing, and his serological tests results: WBC normal, ESR 1 h:58 mm, 2 h:84 mm, CRP: 34,2 mg/l. After 3 months, he checked up in Cho Ray hospital, his wound was healed, left leg function was good, and infectious condition was improved. Serological Tests: WBC: normal, ESR: normal, CRP: 5,5 mg/L ( Figure 6).
He also underwent left hip revision arthroplasty after 7 months.

Case 3
The patient is a 50 year old Vietnamese man. In 2015, this patient suffered from traffic accident (hit by train), then he admitted to hospital X with diagnosis: multi trauma; left renal injury grade II, epidural hematoma of left brain, fracture of the posterior wall of the left acetabulum, fracture of the left femoral head. He underwent 10 weeks in ICU. Because of good clinical improvement, he was transferred to orthopedic department. Then, he was operated for total hip replacement. After 3 weeks post-operation, patient has infection after hip replacement; at hospital X he was debrided with VAC (13 times). On January 2017, His infection are not reduced, patient was removed all component, used PROSTALAC (made by hand). After 1 month, the infection was not reduced, and then he was transferred to Cho Ray hospital.
At Cho Ray hospital, he underwent debridement 3 times and VAC drainage, and replaced an intra-operative production of antibioticloaded cement spacer, which combined 2 packs cement 40 g, 1,2 g Teicoplanin and 2 g Vancomycin (Synovial fluid tests result: Staphylococcus aureus, MRSA). After 2 weeks, he was discharged with healing wound. He also kept on using oral antibiotic treatment in 6 weeks (Figure 7).  He also underwent left hip revision arthroplasty after 6 months.

Discussion
To use an articulating, antibiotic-loaded PMMA cement spacer is a simple and fast molding method to fit all defects and allows early mobilization and efficient local antibiotic delivery [9,10]. PJI hard to treat, but results reported in the literature have shown improvement over time up to a cure rate of 90% [11,12]. Several major questions regarding two-stage revision remain unanswered, such as the optimal du-ration of intravenous antibiotic use and whether oral antibiotics should be used during the interim period and after final reconstruction, or the kind and amount of antibiotic to impregnate with cement. We chose the kind of antibiotics, such as heat-stable, powdered form and broad spectrum, and depended on antibiogramme.
Our results showed clearly the improved function between stages and we believe that a mobile hip allows easier second-stage operation and facilitates rehabilitation.
The commercially available molding system is the StageOne Hip Cement Spacer Molds (Biomet Orthopedics Inc., Warsaw, IN). This produces significantly better congruency of the articulating parts, with better stability. Because the molds are made of silicone, the surface of the spacers is not compressed during the hardening process. Also, these molds are only for single use, which is quite costly. We have developed a tapered aluminium mold for production of a custommade PMMA spacer during operation. The mold can be cleaned and sterilized for reuse.

Conclusion
The two stage revision hip arthroplasty protocol offers the greatest chance for eradication of infection. Although it has been the gold standard for the treatment of patients with chronic PJI, treating hip prosthetic infection with these articulating spacers eradicates infection effectively, improves the life quality before reimplantation and provides good final results without significant complications.