Table 1 - Paprosky classification of acetabular bone loss – created according to Classifications In Brief - Paprosky Classification of Acetabular Bone Loss(19)
Defect
|
Tear drop
|
Superior dome
|
Anterior column
|
Posterior column
|
Bone bed
|
Type 1
|
Present
|
No migration
|
Intact
|
Intact
|
Mild (> 50% cancellous)
|
Type 2A
|
Intact
|
Mild migration
< 2 cm superior
|
Intact
|
Intact
|
Moderate (< 50% cancellous)
|
Type 2B
|
Intact
|
Mild migration
< 2 cm superolateral
|
Intact
|
Intact
|
Moderate (< 50% cancellous)
|
Type 2C
|
Moderate destruction
|
Mild migration
< 2 cm medial
|
Disrupted
|
Intact
|
Moderate (< 50% cancellous)
|
Type 3A
|
Moderate destruction
|
Severe migration
> 2 cm superolateral
|
Intact
|
Moderate lysis
|
Severe 10-2 o’clock loss (40% - 70% sclerotic)
|
Type 3B
|
Complete obliteration
|
Severe migration
> 2 cm superomedial
|
Disrupted
|
Severe lysis
|
Severe 9-5 o’clock loss
(30% sclerotic)
|
In the period from April 2016 to April 2018, 16 patients received treatment with aMace (© Materialise NV, Leuven, Belgium) CTACs for revision THA with concomitant acetabular type 3A or 3B bone defects (Table 1). Of these sixteen patients, nine agreed to be included and followed up in this trial. Four patients were treated at the hospital “Ordensklinikum Linz GmbH Barmherzige Schwestern”, and five patients were treated at the Orthopedic Hospital Gersthof. The reasons for revision surgery varied: seven patients received treatment because of aseptic loosening, and one patient each received treatment because of periprosthetic acetabular fracture and septic loosening. Before implantation, infection was excluded through preoperative intraarticular joint aspiration and evaluations of C-reactive protein (CRP) and white blood cell (WBC) count as well as clinical investigations. Additional intraoperative sonication of the dismantled implant and/or examination of five tissue samples verified correct preoperative diagnostics . Three of the nine surgeries were performed on the left hip and six on the right hip. All of the patients included were female, and the patients’ age at the time of surgery was between 42 and 85 years (mean 69.3). The mean body mass index was 29.2 kg/m2 (range: 19.8 - 42.1) (Table 2).
All patients who agreed to be included into this trial completed radiological and functional follow-up examinations (100%). While clinical follow-up comprised pre- and postoperative evaluation of Oxford hip score (OHS)(20) and Harris hip score (HHS)(21), radiological follow-up included preoperative CT scans and postoperative conventional X-rays. Pre- and postoperative images were compared for implant migration and to determine the correction of the offset. Offset-measurement comprised femoral (femoral axis to center of inlay), medial (center of pelvis to center of inlay) and ilioischial (ilioischial line to center of inlay) offset as well as center of rotation (inter-teardrop line to center of inlay) and was performed with TraumaCad (Brainlab AG, Munich, Germany).
The mean follow-up was 12.2 months (range: 10 - 18). Radiological investigation showed one patient with Paprosky type 3A and 8 patients with Paprosky type 3B acetabular defects (Table 2). The patients who completed follow-up were hospitalized for a mean of 21.9 days (± 6.3 SD).
Short-term follow-up was chosen due to the limited preexisting evidence and influence of the outcome on the applicability of the implant.
This study was approved by the ethics committee of the hospital “Ordensklinikum Linz GmbH Barmherzige Schwestern” (EKS 25/19). All patients provided informed consent.
Preoperative Evaluation and Planning
First, conventional X-rays in 2 planes (anterior-posterior and axial) were performed in the affected hip. Implant positioning and loosening and fractures were documented.
Then, a CT scan following a special protocol provided by the company was performed. A 3D model of the acetabulum and the pelvis was then virtually conducted, and bone defects and fracture lines were identified. While acetabular bone loss was quantified and classified into the Paprosky score, bone quality was evaluated for fixation of the screws (Figure 1)(11). An implant design based on the anatomical center of rotation, inclination, anteversion and bone preservation was proposed (Figure 2). The implant consisted of porous augmentation and the plate, which were built as one part. A titanium alloy was used for the triflanged acetabular cup and the defect filling trabecular augment (Ti6AI4V ELI). Screw length and direction as well as the diameter of the screws were chosen according to bone quality and remaining bone stock.
A preliminary planning report was provided to the surgeon and included instructions for preparation and reconstruction as well as a proposal for screw positioning and length. It was subsequently reviewed by the surgeon and updated to the surgeon’s suggestions via web meetings for improvement. Production started after a final check and confirmation of the final planning report. The listed time for planning and production was 5 weeks (1 and 4 weeks, respectively). The implant came with a trial implant, bone model and custom drill guides. All components were delivered nonsterile and had to be sterilized at the hospital facility. Instruments, screws and cup/liner components were provided by the hospital.
Surgical technique
Surgery was performed following a standard protocol. Antibiotics were administered preoperatively. Tissue samples for sonication and microbial evaluation were harvested intraoperatively. The procedure was performed in the supine position, and a transgluteal approach was used. For the preparation of proper implant insertion, bone removal and clearance of some bone fragments, according to the planning report, were sometimes necessary, and gaps were filled with morselized allograft bone material afterwards. After bone bed preparation, the trial model of the implant was placed into the acetabulum to confirm implant seating and fitting. Then, the implant was brought in together with a custom drill guide. After drilling, the screw length was confirmed and compared to the planned screw length. After fixation of the acetabular component, a standard or dual mobility cup/liner component was cemented in the implant. The maximum size was predefined by the planning report.
Postoperative protocol
Patients were mobilized immediately on the first postoperative day after drainage removal. Full weight bearing and full range of motion were allowed immediately after surgery in all patients.
Statistics
Statistical analyses were performed with IBM SPSS Statistics (Windows, 64 bit, version 23.0; IBM Corp., Armonk, NY, USA). Descriptive statistics were used to investigate patient characteristics. Pre- and postoperative OHS and HHS were compared using paired t-tests. Radiological differences between the treated side of the hip and the contralateral side were evaluated with descriptive statistics and paired t-tests. Statistical significance was reported as a p-value of ≤ 0.05. There were no missing data. Patients who did not complete the follow-up examinations were declared as lost to follow-up and were excluded from the final analysis.