Patients
This study was approved by the hospital ethics committee. In order to enroll patients reconstructed with the concept of iliac extended fixation, 102 consecutive patients who underwent revision THA with the use of porous metal augments at our institution from January 2014 to October 2016 were retrospectively reviewed. The inclusion criteria consisted of patients undergoing revision THA, acetabular reconstruction with a cementless hemispherical cup and porous metal augments, construction extending superiorly to more than 2 cm above the original upper acetabular rim, and minimal follow-up of 24 months. Of the initial 99 patients that were reviewed, 32 patients were deemed eligible based on the inclusion criteria and were therefore enrolled in this study. The other 72 patients were excluded because the augments did not extend over 2 cm above the original acetabular rim.
Trabecular metal augments made from tantalum (TM Augment; Zimmer, Warsaw, IN) or titanium (Restoration wedge augment; Stryker, Mahwah, NJ) were utilized to reconstruct the superior acetabular defects. There were twelve patients reconstructed with the EIEF technique, using a single buttress augment or combined with other augments, or a flying buttress using slope augments [12] (Table 1); twenty patients reconstructed with the IIEF technique, fourteen of whom using a single superior slope augment, and the other six with stacked superior slope augments (Table 2). Three patients received a combined application of augments from the two manufacturers, according to the concrete morphology of bone defects and suitable metal augments, and other patients received augments from a single manufacturer. Multiple holed revision cementless hemispherical cups (TM; Zimmer, Warsaw, IN) were inserted after insertion of augments with average diameter of 56 (range 44- 68) mm. Averagely 6.2(range 2-10) screws were used for each patient, among which 3(range 1-5) screws for the cup, and 3.3 (2-7) screws for augments. Thirteen (40.6%) patients received inferior screws into the ischial or ilium ramus. Eight (25.0%) patients received augments in the inferior anterior/posterior aspect. No autograft or allograft of bone was used in all patients.
Patients also underwent revision of the femoral component, including 17(53.1%) with a modular revision femoral stem (RM; Stryker, Mahwah, NJ), 7(21.9%) with a monoblock femoral stem (Wagnar; Zimmer, Warsaw, IN), and the other 5(15.6%) patients with only femoral head revision with a ceramic head lined by a titanium sleeve (TS; DePuy, Warsaw, IN).
The average patient age at the time of surgery was 57 years (range 38 - 78 years), the average body mass index (BMI) was 25.0 (range 18.7 - 33.7), and 13 (40.6 %) patients were female. On average, patients had 1.6 (range 1 - 5) previous hip operations. There were 21 patients (65.6%) revised for aseptic loosening, 6 (18.8%) for periprosthetic infection, 3 for recurrent dislocation (9.4 %), 1(3.1%) for severe acetabular side osteolysis without component loosening, and 1 (3.1%) for periprosthetic fracture. The preoperative Charlson comorbidity score was 0 in 26 (81.3%) patients, 1 in 4 (12.5%) patients, and 2 in 2 patients (6.3%). The average duration from first THA to surgery was 14 (range 0.5-31) years. The average number of previous surgeries for the index hip was 1.6 (range 1-5).
Surgical Technique
All the patients were cleared of infection at the time of index revision surgery. Patients revised for infection were treated with staged revision and sensitive antibiotics for 6 weeks, and the final revisions were not commenced until joint aspirations as well as ESR and CRP turned normal. Same protocol was followed for the patient with acute infection after revision. A posterior lateral approach was employed in all hips. The femoral head was removed after dislocation of the hip, and the femoral stem was removed if it was deemed loose or considered necessary for exposure, reconstruction, or if evidence of trunionosis was visible. The femoral stems in 7 (21.9%) hips were preserved with only the acetabular side revised. Extended trochanteric osteotomy was done in 6 (18.8%) hips because of difficulty in removing the femoral components.
The acetabular cups were then removed, and intraoperative tissues were sent to culture and pathology for detection of any possible residual infection. Fibrous tissue was then removed to fully expose the acetabulum and the bone defects. Patients with pelvic discontinuity were then treated with distraction technique by inserting a 3 mm pin into the ilium and ischium ramus, respectively, and then distracting the cranial and caudal fragments with a pliers holding the two pins, in order to stabilize the anterior and posterior column before preparation of augment and cup bony bed [21, 22].
The site, size, and shape of the bone defects were determined before reaming and preparing for insertion of the augment and metal shell. A hemispherical cup trial or reamer was positioned to a target level by aiming at the optimal COR and contact area of the bone bed. Augment trials were then used to determine the shape, size and position of the final metal augment.
Buttress and slope augments were implanted first and fixated with screws to the host bone, followed by a multiple holed, trabecular metal shell that was impacted and press fit to ensure primary stability of the whole cementless construct. For a slope augment, a tantalum augment (TM Augment; Zimmer, Warsaw, IN) was the first choice for use; if the available bone bed required more versatile screw fixation, a titanium augment (Restoration Wedge Augment; Stryker, Mahwah, NJ) was considered (Figures 1 and 2). Cement was placed between the augments and the augment-cup interface to unify these metal components into one solid unit. Multiple screws were then inserted through the porous metal shell. Polyethylene liners with a 10° high wall were used in 14 (43.8%) patients, and neutral polyethylene liners in the other half of patients. A 28 mm diameter Co-Cr-Mo alloy head was used in 2 (6.3%) patients, and 32 mm, 36 mm and 40 mm diameter ceramic heads in 18 (56.3%), 11 (34.4%) and 1 (3.1%) patients, respectively. There were no significant differences in the preoperative demographic factors between the EIEF and IIEF groups (Table. 4). The EIEF group had significantly higher preoperative vertical location of COR, and more screws used for augment fixation than the IIEF group (Table. 4).
Postoperatively, patients with IIEF were generally allowed to ambulate with touch-down weight bearing for the first 4 weeks, then encouraged to walk with partial weight bearing for another 8 weeks, which could be accelerated according to the intraoperative evaluation of reconstruct stability by the senior author (YXZ). Patients with EIEF were allowed to start touch-down weight bearing 2 weeks after surgery and for 6 weeks, and then partial weight bearing for another 4 weeks. By the 12th week, all patients were urged to walk with full weight bearing. Antibiotic prophylaxis with 2 grams of cefuroxime every 12 hours was initiated and then discontinued 48 hours post-operatively for aseptic cases. Antibiotics sensitive to the specific bacteria were used for second stage revision of infection cases according to previous antimicrobial susceptibility testing. Subcutaneous heparin and intermittent elastic compression were used as routine measures to prevent thromboembolic complications in the hospital, which was transitioned to low dose aspirin (100 mg per day) for 5 weeks after discharge.
Clinical Data
Patients were asked to revisit the hospital at 3 months, 6 months, 1 year, and then yearly after surgery. The Harris Hip Score (HHS) and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC, range 0-96 with higher score indicating worse outcome) were used for clinical evaluation. Clinical failure was defined as loosening or any complications requiring surgical removal of the cup. Patients also reported satisfaction based on an five-level subjective scale (very satisfied, satisfied, neutral, dissatisfied, or very dissatisfied), which was collected at the last follow-up[23].
Radiological Evaluation
Anteroposterior, lateral and Judet view radiographs of the bilateral hips were taken for all patients 1 week prior to the planned operation. Two surgeons (YH, HT) assessed the severity of the acetabular bone deficiency according to the preoperative radiographs on the basis of the Paprosky acetabular bone defect classification [24, 25]. Any discrepancies between the two surgeons were re-examined by the senior consultant surgeon (YXZ). There were 13 (40.6 %) patients classified as Paprosky type 3A, 19 (59.4%) as type 3B. Five (15.6 %) of the type 3B patients were assessed to have pelvic discontinuity.
Anteroposterior and lateral radiographs of the bilateral hips were taken for all patients immediately after the operation, as well as at 3, 6, and 12 months, and then annually thereafter, which is according to standard protocol at our hospital. Magnification was corrected by referring to the already known diameter of the femoral head. The height and the horizontal location of the center of rotation (COR) were determined by measuring the distance from COR to the inter-teardrop line and a vertical line passing the ipsilateral teardrop, respectively [12, 26]. Deviation of reconstructed COR was measured as the distance between postoperative COR and the anatomic COR mirrored from the normal contralateral hip to the revised side. In scenarios of abnormal contralateral hip, Ranawat triangle method was utilized instead to determine the anatomic COR, by calculating the acetabular height as 20% of pelvis height[27].
The radiographic abduction angle was assessed by calculating the angle between the inter-teardrop line and a line passing the longest axis of the cup’s projected ellipse rim. The radiographic anteversion angle was defined as the arcsin (short axis/long axis), as defined by Lewinnek et al [28].
The area surrounding the cup was divided into the 3 zones using the modified Delee-Charnley method, and zone 1 around the superior augments was further divided into two sub-zones 1A and 1B, with 1A in the superior lateral half and 1B in the inferior medial half of the bone-augment interface (Fig. 1-3). Radiolucent lines and osteointegration around the cup and augment were assessed to determine the stability of fixation of the acetabular components[29]. The acetabular cup was diagnosed as unstable if there was evidence of a continuous radiolucent line ≥ 1 mm wide around all the three acetabular zones, or if any progressive prosthesis displacement could be detected during follow-up. Fibrous stable was defined as evidence of a radiolucent line < 1 mm wide around two of the three acetabular zones, while bone ingrowth stability was defined as intimate contact between the bone bed and metal surfaces, but no radiolucent lines in two or three of all of the acetabular zones [29, 30]. The orientation of screws anchoring the augments were measured in reference to the inter-teardrop line, with screws pointing cephalad defined as positive values, and screws pointing caudally defined as negative values (Fig. 2B).
Statistical Analysis
The horizontal and vertical COR location data were compared between the preoperative and postoperative measurements and also between the studied and the contralateral hips using the student t test. All statistical analyses were performed using the SPSS statistical software package (version 15.0; IBM, Armonk, NY, USA), and the level of significance was set at P < .05 for a single comparison.