After institutional review board approval, this multicenter retrospective study examined all patients who had undergone cTHA and rTHA in which the acetabular component was revised with a novel titanium fully porous shell into which a new XLPE liner was cemented (Redapt Revision Hip System, Smith&Nephew, Memphis, TN, USA) between January 2016 to November 2018 at four large institutions (NYU Langone Orthopedic Hospital, NY, USA; Department of Orthopedic Surgery, Aurora Medical Center, Kenosha, WI, USA; Department of Trauma and Orthopaedics, University Hospital of Wales and University Hospital Llandough, Wales, UK; Adult Hip and Knee Reconstructive Surgery; London Health Sciences Centre - University Hospital, London, Canada) (Fig. 1). Fully porous shells with a cemented XLPE liner were used in the cases of acetabulum bone defects in complex primary (defined as primary THA in patients with compromised acetabular bone quality) and revision THAs.
Inclusion criteria for this study included: complex primary and revision THA and patients aged 18-years or older. Exclusion criteria included oncologic lesions in the affected hip joint and patients who were not involved in a postoperative follow-up imaging study.
Forty-eight patients were initially screened. Five patients were lost to follow-up and 3 did not complete a minimum follow-up time of 1 year. In total, 40 patients completed at least 1 year of follow-up and were included in this study. On average, patients were 71.42 (±9.97) years old and obese with a BMI of 30.36 (±6.88 kg/m2). Twenty-five (62.5%) were operated on the right side. The mean follow-up lasted 2.21 (±0.77) years. Against the Paprosky acetabular bone loss classification system, 1 patient was classified as type I (2.5%), 10 as type IIA (25.0%), 11 as type IIB (35.0%), 2 as type IIC (5%), 11 as type III (35.0%) and 2 as type IIIC (5.0%). Additional demographics are presented in Table 1.
Data search
The electronic medical records in four orthopedic centers were reviewed for demographic data, including age, gender, BMI, ASA scores, smoking status, laterality, indication for surgery, pre- and postoperative ambulatory status and Harris Hip Scores (HHS) scores [10], implants used, surgical complications, hospital length of stay and follow-up period. Additional parameters were documented, including inpatient complications, 90-day postoperative emergency department visits, 90-day postoperative readmissions and all re-revisions data. Acetabular bone loss was categorized according to Paprosky classification [11].
All patients were followed up prospectively for at least 1 year postoperatively. Pre- and postoperative hip stability was evaluated by the performing surgeon. Immediate postoperative anteroposterior and lateral hip radiographs were analyzed along with radiographs taken at three months, twelve months, and annually thereafter. All radiographs were assessed by two orthopedic surgeons who did not perform the surgery. The interface between the porous shell and the host bone was also assessed for initial and progressive radiolucency as well as areas of initial radiolucency that resolved with continued follow-up.
Shell fixation and osteointegration were assessed in relation to De Lee and Charnley zones as described by Moore et al. [12]. Three or more of the following signs would indicate radiological osteointegration: superolateral buttress formation, presence of an inferomedial buttress, medial stress shielding, radial trabeculae, and absence of radiolucent lines.
Surgical technique
After exposure, in the cases of revision THA, following removal of the failed acetabular component, granulation tissue was removed. The acetabulum was sequentially reamed using dedicated hemispherical reamers. Line-to-line or under reaming by 1 mm was performed based on surgeon's preference and intraoperative bone quality assessment. At this point, the bone stock was reassessed for the possible need of bone grafting to fill the cavitary defects. Trial components were used to assess coverage, impingement, and stability. The fully porous shell was impacted and when satisfactory orientation of the shell was achieved multiple screws were placed. An XLPE liner sized to fit the shell intra-diameter was cemented into the shell. The liner was then pressurized using the appropriately-sized liner impactor head until cement was cured, with any excess cement removed. The femoral stem stability and osteointegration were assessed intraoperatively and the stem was revised at surgeon’s discretion.
The fully porous revision hemispherical acetabular shell (Smith&Nephew, Memphis, TN, USA), was developed for use in revision cases. The fully porous shell is made from titanium alloy (Ti-6Al-4V) and has been shown to be biocompatible and structurally comparable to cancellous bone. To allow ingrowth, the shell has an inter-connected network of pores with a porosity of up to 80% in the near-surface regions, where the initial fixation will occur and the overall porosity is up to about 67%. Additionally, new variable-angle locking screws can be used to enhance implant stability and minimize micromotion after surgery (Figs. 2 and 3).
Statistical analysis
Descriptive statistics, including mean, average, range, and standard deviation, were presented for continuous variables. Survivorship was analyzed and presented graphically by using the Kaplan-Meier method. Log rank test was used to calculate P-values for the difference between groups. Outcomes and survivorship data were calculated by using time of latest follow-up. All statistical analyses were performed using IBM SPSS software (IBM-SPSS, version 26, Armonk, NY, USA).