Introduction In recent years, there has been an increasing interest in custom triflange acetabular components (CTAC) for revision and oncological surgery. The aim of this study was to evaluate the surgical accuracy of positioning CTACs in patients receiving either total hip arthroplasty (THA) revision or tumor resection surgery, using a novel 3D analyzing technique. Method This retrospective cohort study included 35 patients (27 tumor and 8 THA revision cases), between February 2017 and March 2021. All patients received a CTAC. The planned and achieved implant position were assessed by means of a developed semi-automatic 3D-CT assessment method. The primary outcomes were the cup angles described as inclination, anteversion and cup rotation, and the translation of center of rotation (COR), pubic flange, ischial flange and ilium flange in three planes. Results The mean deviation, between planned and achieved, in inclination was 0.5° (SD: 3.9°), in anteversion 1.2° (SD: 6.1°) and in cup rotation 0.6° (SD: 3.2°). The mean deviation in COR in the sagittal plane was -0.8 mm (SD: 3.2), in the coronal plane -0.4 mm (SD: 6.3) and in the axial plane 0,6 mm (SD: 6,1). Translation of the ischial flange showed the largest aberration (median absolute value: 7.0 mm), followed by the pubic flange (6.4 mm) and the ilium flange (5.3 mm). Discussion A semi-automatic method to analyze the 3D position of CTAC was presented in this study. The results show good agreement between the planned and achieved implant position in patients receiving THA revision or tumor resection surgery. 89% of the components in this study were accurately positioned according to our criteria.

In the Netherlands about 36.000 total hip prostheses are implanted every year. Survival of these prostheses at 10 year follow-up is 90% in patients older than 70 years at the index operation. In younger patients these results decrease to about 80–85% at 10 years follow-up. The main cause of failure in total hip replacement is aseptic (mechanical) loosening which is caused by a biological response to wear products of the articulation of the joint. This foreign body reaction is associated with periprosthetic bone resorption and subsequent formation of periprosthetic fibrous (interface) tissue. As a result the implant is becoming increasingly loosened, causing debilitating pain on ambulation. At present, patients with loosened prostheses can only undergo revision surgery. This procedure is often extensive (3–5 hr surgery and over 1 liter of blood loss), due to the necessity of removing the prosthesis and all interface tissue; thereafter a new prosthesis is implanted. This revision surgery has a high complication rate in elderly patients with comorbidities (e.g. cardiovascular disease, diabetes etc), which can even result into death in a small percentage. Because of this high complication rate, this demanding procedure cannot be performed in patients with a poor general health, thus these patients remain with this debilitating pain. Therefore, we investigated the possibilities of an alternative minimally invasive refixation procedure that leaves the prosthesis in place, but relies on removing the periprosthetic interface membrane and replacing it with bone cement. Before the refixation procedure can be executed this way, an instrument to remove the interface tissue needs to be developed.