Study of Antibiotic Spacer Design to Treat Infection After Hip Replacement

Overview

Infection remains one of the most difficult-to-treat complications of total hip arthroplasty. The gold standard treatment is two-stage removal of the prosthesis with later replacement of permanent implants.The first stage consists of removal of the infected arthroplasty components and the surrounding devitalized tissue, copious pulsed irrigation, and placement of a temporary antibiotic-impregnated cement spacer. This spacer is typically left in place six weeks, during which time the patient receives intravenous antibiotics. After the surgeon feels that the infection has been eradicated, or if a second debridement is required, a second operative procedure is performed. While the use of an antibiotic spacer is well accepted, whether the spacer should immobilize the hip (a so-called "static" spacer) or allow for range of motion (a so-called "articulating" spacer) is controversial. Proponents of static spacers argue that immobilization of the periarticular soft tissues aids in clearance of the infection and that these spacers are simpler to fashion intraoperatively. Proponents of articulating spacers argue that they improve hip function, prevent damage to the musculature surrounding the hip, allow easier reimplantation, improve hip function, and prevent dislocation following hip reimplantation. While good results have been described with both methods, comparative trials have been conflicting as to whether spacer design alters hip function, operative time, and dislocation rates. Equipoise exists within the literature, and no randomized clinical trial has been conducted to evaluate this issue. The purpose of this study is to compare articulating and static antibiotic-impregnated spacers for the treatment of chronic periprosthetic infection complicating total hip arthroplasty through a prospective, randomized clinical trial. The goals of this trial are to determine the effect of spacer design upon eradication of infection, hip function, ease of reimplantation, and dislocation rates. The investigators hypothesize that articulating spacers will provide shorter operative times at replantation while improving hip function and hip dislocation rates following hip reimplantation.

After diagnosis of infection and informed consent, patients will be taken to the operating room. After anesthetization, patients will be randomized to either an articulating spacer or static spacer. Randomization will be performed by prepared opaque envelopes administered by a nonparticipant in the study. After a complete debridement of devitalized tissue, explantation of infected components and any associated cement, either an articulating or static spacer will be placed. All spacers will be formed using 3.0 g of Vancomycin and 1.0 g of Tobramycin for each 40 g packet of cement. Articulating spacers will be formed of antibiotic-impregnated cement using the Stage One system (Biomet, Warsaw, IN) sized to fit the endosteal and acetabular bone defect. Static spacers will be hand-made with a rod of antibiotic-impregnated cement and cement beads of sufficient quantity to fill the acetabulum. Post-operatively, all patients will be made touch-down weight bearing protected with a walker or crutches. At the time of reimplantation, the joint will be aspirated and multiple cultures obtained along with intraoperative histopathological analysis to evaluate for persistent infection. Data collected preoperatively will include age, gender, laterality, etiology of hip degeneration, comorbidities, Harris Hip score, infecting organisms and Paprosky femoral and acetabular bone loss classification. The Harris Hip score has been used extensively in the study of revision hip arthroplasty and has been found to be reliable and valid and will be determined preoperatively and at all follow-up visits. Data collected at the time of implant removal and reimplantation will include operative time, blood loss, surgical approach, and need for an extended trochanteric osteotomy. Radiographs performed immediately following and just prior to reimplantation will be reviewed to determine if the spacer utilized has caused bone loss; bone loss to the cut bony surfaces will be confirmed intraoperatively. At each follow-up visits radiographic appearance, the Harris Hip Score, dislocation events, recurrence of infection, and the need for revision or reoperation of any kind on the hip will be determined. All portions of this study will be part of conventional care except for randomization and collection of the Harris Hip Score. Which type of spacer is used currently depends upon the judgment of the attending surgeons and both are used routinely. The primary outcome variable will be Harris Hip Score. A power analysis was conducted with the assistance of Dr. Mario Moric at Rush. Using the standard deviation of Harris Hip Scores from Hsieh and colleagues (2004) and Fehring and colleagues (1999), the largest previous studies reporting such data, Dr. Moric estimated 56 patients, 28 patients per group, would be needed to detect a clinically relevant difference of ten points. To account for attrition, our target total sample size will be 80 patients.