Subsequent to the approval of the Institutional Review Board, we gathered the data using our institutional database. We retrospectively reviewed the data from 1272 patients (1366 hips) who underwent revision THA between January 2000 and January 2007. We defined an operation as revision THA when any part of the hip prosthesis, including the acetabular component (shell or cage), acetabular liner, femoral stem, and/or femoral head, was exchanged. Two-stage revision THA for infection was also included. Since the criteria for the diagnosis of infected hip replacement is evolving, the surgeons at our institution at any time use the contemporaneous criteria which are based on clinical presentation, imaging, serology, histopathology, bacteriology and recently sophisticated modalities such as PCR for questionable cases. For the current study periprosthetic infection was assumed to be the main cause of failure when the following criteria were present: abnormal serology, presence of sinus tract, evidence of purulence at surgery, and isolation of an organism from aspiration and/or intraoperative culture [5
]. There were 587 men (46%) and 685 women (54%). Six hundred twenty-one (45%) were left hips and 745 (55%) were right hips. Four patients underwent bilateral revision THA in one session. The mean age of the patients was 66 years (range, 24–94 years) and their average body mass index (BMI) was 28.2 kg/m2
(range, 16.1–53.8 kg/m2
). The diagnoses that resulted in index revision surgery included aseptic loosening in 694 (51%), instability in 203 (15%), wear in 190 (14%), infection in 112 (8%), periprosthetic fracture in 73 (5%), and miscellaneous in 94 (7%) hips (Fig. ). Of the miscellaneous cases, there was osteolysis in 37, component fracture in 24 (stem fracture in 19 and ceramic head fracture in five), limb length discrepancy in 28, and squeaking in 5 hips. Of the 694 hips with aseptic loosening, 307 (44%) had just loosening of the acetabular component, 249 (36%) had loosening of the femoral component alone, and 138 (20%) had loosening of both acetabular and femoral components. The minimum followup was 1 day (mean, 5.5 years; range, 1 day to 9 years). We tried to contact all the patients to find out whether they had reoperation or rerevision for any reason in another location. Of our cohort of 1272 patients, 65 (5%) were lost to followup: 53 patients had no accessible contact information and 12 were not willing to discuss their status. This was a chart review study and no patients were seen in followup specifically for the study.
This chart presents the rates of indications of index revision hip arthroplasty. Aseptic loosening is the major indication for revision THA.
Operations were carried out in the supine position through a direct lateral approach. During the revision surgery for 135 (10%) hips, trochanteric osteotomy and fixation were performed. Cementless fixation of both components was used in 1009 (74%) revisions, cemented fixation of both components was used in 339 (25%) revisions, and hybrid fixation (cemented fixation of one component and cementless fixation of the other component) was used in 18 (1%) revisions. During the revision surgery of 21 hips in the instability group, failure of the locking mechanism of the acetabular component was encountered. For 348 (25%) of 1366 revisions, bone graft was inserted in the femoral and/or acetabular side. In 69 hips, an acetabular cage was inserted. A 22-, 28-, 32-, or 36-mm head was used in all cases. Fifteen patients received a 22-mm head, 51 patients received a 28-mm head, 667 patients received a 32-mm, and 633 patients received a 36-mm head. Ceramic ball heads were used in 32 hips and cobalt-chrome ball heads were inserted in 1334 hips. In 83 cases, constrained liners were used. In 152 hips, a 10° or 20° lipped acetabular liner was inserted.
The regimen for thromboprophylaxis consisted of administration of warfarin on the day of surgery and continued for 6 weeks aiming for an international normalized ratio of 1.8 to 2.0. Patients were given intravenous first-generation cephalosporin or vancomycin for those with an allergy before the skin incision and for 24 h postoperatively. Patients were generally mobilized within 2 days after surgery under the supervision of a physiotherapist. On discharge, 556 (40.7%) of patients were sent home and 805 (58.9%) of them were sent to a rehabilitation facility. Five patients (0.3%) died during the hospital stay. Partial weightbearing with crutches continued for 6 weeks. Afterward the crutches were discarded and full weightbearing was permitted.
The patients were routinely followed clinically and radiographically at 6 weeks, 6 months, 2 years, and then every 2 years postoperatively. AP and lateral radiographs are assessed by the senior attending physician for signs of failures (loosening, infection, wear, etc.). Patients are followed until the time of failure or censorship (death or loss to followup).
We considered the date of rerevision or reoperation as the end point and the period from the index revision procedure to the end point as time to failure. Furthermore, we divided the failures into early and late groups based on the time to failure after the surgery. The failures that occurred less or more than 2 years after surgery were considered as early and late failures, respectively. Modes of failure were determined by the surgeon and then we categorized them into six groups, including aseptic loosening, instability, wear, infection, periprosthetic fracture, and miscellaneous. Since only one hip failed due to osteolysis we categorized it in the miscellaneous group. If multiple modes of failure were evident, we considered the predominant mechanism as noted by the surgeon on the operation note. For understanding the mode of failure, preoperative clinical and radiographic findings along with intraoperative findings such as status of the components and also culture results were reviewed.
We calculated standard descriptive statistics, including average, range, frequency, and proportions for gender, age, BMI, laterality, indication of index revision surgery, failure mechanisms, and time to failure. We used Kaplan–Meier survivorship analysis to estimate the probability of survival of the revision surgery from the time of the index revision to the end point (failure) [9
]. First we separated the cohort into septic and aseptic groups based on the indication of index revision surgery; then, we compared the survivorship of these two groups by using the log rank test. Second we separated the cohort into three groups: septic, instability, and the others, and again compared their survivorship by using the log rank test. All survivorship data were reported with 95% confidence intervals (CIs). We used SPSS®
15.0 (SPSS Inc, Chicago, IL) for statistical analysis.