A retrospective analysis was conducted on patients treated with staged revision for chronic hip PJI from January 2020 to December 2022. All data have been prospectively collected by our Istitutional Arthroplasty Register and retrospectively analyzed. The Institutional Review Board (IRB) approved this single center study (no. 007/2025). Written and informed consent was obtained from all the included participants. All procedures were conducted according to Declaration of Helsinki. All patients undergoing a two-stage hip revision with a specific articulating spacer (G21 - SpaceFlex Hip) coupled with a handmade acetabular spacer during the study period were enrolled. Patients revised with different kind of spacer or that were managed with interim Girdlestone procedure were excluded. PJI diagnosis was made according to the 2018 International Consensus Meeting (ICM) criteria [16]. Main demographic (age, sex, diagnosis, affected side, body mass index (BMI), comorbidities, smoke status, previous surgical procedures) and surgical data (surgical time, surgical approach, acetabular and femoral bone loss, stem and acetabular spacer size, time of the interstage period, the need of a lateral window at the first stage and final prosthetic implant type) were recorded. Patients were classified according to systemic host grade McPherson staging system [17]. Acetabular and femoral bone defects were classified radiographically before surgery and confirmed during surgery according to the classification of Paprosky et al. [18, 19].
Clinical and radiographic evaluation
Clinical and radiographic evaluation were scheduled as follows: before the first stage, 6 week after the first stage, one, three and six months after the second stage and once per year thereafter Clinical assessment included physical examination, the Visual Analogue Scale (VAS), the Harris Hip Score (HHS), and the Oxford Hip Score (OHS), and these were used to evaluate subjective and objective hip function. Radiographic analysis included LLD, FO, AO and GO measurements on the affected (spacer and post-reimplantation) and the contralateral side as well as osseointegration, loosening, radiolucent lines, osteolysis, stem subsidence, malposition, and heterotopic ossification after final prosthetic reimplantation. Heterotopic ossifications were classified according to Brooker grade [20]. Stem subsidence was defined as femoral stem distal migration greater than 2 mm seen on the last AP radiograph in comparison to the immediately postoperative imaging [21]. Radiolucency lines and osteolysis areas were reported and evaluated according to the Charnely-DeLee and Gruen method [22, 23] on the acetabular and femoral side, respectively. Radiographic analysis was performed on standard anteroposterior (AP) radiographs taken postoperatively with the patient in supine position and both legs in 15° internal rotation. The X-ray beam was centered on the symphysis pubis. All measurements were taken twice, at different time points, on digital AP radiographs of the pelvis by the same author (VM), who was not involved in index surgery. Recorded values were the average of the two measurements. Radiological distances (LLD, AO, FO and GO) were measured by using Carestream Imageview software. FO was defined as the perpendicular distance from the center of rotation of the femoral head to the anatomical femoral axis [24]. AO was defined as the perpendicular distance from the center of rotation of the femoral head to a line passing through the medial edge of the ipsilateral teardrop, perpendicular to the line through the inferior margins of the ischial tuberosities [25]. GO was defined as the sum of FO and AO [26]. Limb length (LL) was defined as the distance between the medial apex of the ipsilateral lesser trochanter and the line passing through the lower margins of the ischial tuberosity (Fig. 1).
We measured AO, LL and FO on both the operated and contralateral sides. Differences were defined as follows:
ΔGO = spacer GO – contralateral GO
ΔFO = spacer FO – contralateral FO
ΔAO = spacer AO – contralateral AO
LLD = spacer LL – contralateral LL
FO and AO were also assessed after reimplantation. Increase in offset measurements were expressed as positive values, while negative values defined offset reduction.
Complications were recorded during the interstage and post-reimplantation period. Radiographs were assessed by two orthopaedic fellows (EF, VP).
Surgical technique
All patients underwent a two-stage procedure for hip PJI via a posterolateral approach. Preoperative digital templating (Fig. 2) with spacer templates was routinely performed to estimate size and head dimensions, though final sizing was determined intraoperatively after broaching the femoral canal and assessing bone loss.
Scar tissue, sinus tracts, and abscesses were excised. In the first stage, the prosthesis was explanted and a G21 Spaceflex hip spacer (G21 S.r.l., Modena, Italy) was implanted. Before antibiotic administration, at least five microbiological samples were collected while prosthetic components were sent for sonication.
For stem extraction, an extended lateral cortical window was performed if needed. After final intraoperative confirmation of spacer size, the G21 Spaceflex spacer was intraoperatively molded. It consists of a titanium core coated with gentamicin-loaded cement. Available options include three sizes of stem (10, 13 and 15) three possible lengths (140, 170, 210 mm) and 4 head sizes (48, 52, 56 and 60 mm). Acetabular spacers were handmade intraoperatively by molding a cement cup 2 mm larger than the spacer head [27] (Fig. 3). Low-viscosity G3A cement (G21 S.r.l., Modena, Italy) was used for molding the spacer, while PALACOS G® gentamicin cement (Heraeus Medical GmbH, Hamburg, Germany) was used for fixing the devices. If needed, specific antibiotics were added to cement spacer according to preoperative microbiological data. Both acetabular and femoral spacers were loosely cemented to avoid excessive cement infiltration into cancellous bone. During reimplantation and after removal of the mobile antibiotic-loaded spacer, a new, accurate surgical debridement was performed. At least 5 intraoperative samples were collected, and spacer was sent for sonication. According to the size and shape of bone deficiency, the senior surgeon decided the best technique to address the bone defect and the final components.
Postoperative course
After first stage, partial weight-bearing with a walker or crutches started on the second post-operative day after removal of the surgical drain and was continued for the whole interstage period. Standard venous thromboembolism prophylaxis with enoxaparin and compression stockings was prescribed at least for 45 days. In agreement with the infectious disease team, a 6-weeks specific antibiotic course was administered (intravenous for 2 weeks and oral administration for 4 weeks if possible, according to microbiological data). After the second stage, physiotherapy started with mobilization on the first postoperative day. Ambulation was allowed with partial weight-bearing the second day after surgery. Standard venous thromboembolism prophylaxis with enoxaparin and compression stockings was prescribed at least for 35 days. An intravenous specific antibiotic course was administered until intraoperative microbiological results were attained and continued thereafter if necessary.
Statistical analysis
Continuous variables were reported as mean ± standard deviation (SD) and compared using paired or unpaired Student t test. Categorical variables were expressed as the number of cases and percentage and compared using chi-squared or Fisher’s exact tests. For all the analyzed data, a two-tailed, p value < 0.05 was considered statistically significant. For radiological parameters, interobserver reliability was evaluated with the Cohen’s kappa coefficient. We defined as re-operation any kind of surgery that involved the hip joint after the index procedure without removing the fixed prosthetic component. Conversely, revision was considered as any surgical procedure that required fixed component removal for any reason. Spacer revision was defined as any procedure performed on the affected hip during the interstage time. We defined septic recurrence as each new infection or positive culture at reimplantation with isolation of the original infecting organism. Statistical analysis was carried out with the XLSTAT and Excel statistical software.