Preserved Proximal Femoral Bone Stock Volume in Total Hip Arthroplasty Significantly Reduces the Risk for Periprosthetic Fractures. A Novel Modelling Technique and Preliminary Clinical Results

Periprosthetic proximal femoral fractures (PPFFs) are one of the main causes for revi-sion after total hip arthroplasty (THA), and are associated with some already known patient-/surgical-/implant-related risk factors. Despite the established increased risk of single and double-wedge femoral implants, the highest incidence in our institution has been observed with the anatomical cementless femoral component Anatomic Benoist Girard (ABG) II. The cumulative probability of PPFFs rose from 2.1% at 1 year to 6.5% at 10 years post-implantation, prompting comprehensive and multidisciplinary analy-sis. A novel parameter of preserved proximal femoral bone stock volume around im-planted ABG II femoral stems (VPF) and the modelling technique for its evaluation on the standing anteroposterior (AP) hip radiographs were introduced and estimated for each hip. Study was designed according to the standard protocol for matched case-control research. In the preliminary analysis, 5 age-/sex-/implant size-/surgeon-matched stratums, each comprising a case and 2 matched controls, were included. To calculate VPF, a mathematical model was constructed by composing parts of rotational bodies and a prism, subject to geometrical parameters of the proximal fe-mur that were assessed from radiographs. The mean value of VPF in the group of cases was 141.6 ± 36.2 cm3 and significantly lower compared to the mean volume of 254.2 ± 33.8 cm3 in the control group (P < 0.01). Based on the preliminary results, the VPF seems crucial for the PPFFs prevention. However, the mechanism of its effect works as a ‘black box’. At this point, it can be hypothesized that insufficient bone stock from the implantation onwards interferes with adequate osseointegration by itself acutely and with increased stress shielding in the long term. The bone stock preservation should be emphasized and considered at all steps, starting from the preoperative planning. The novel parameter in THA, and the method for its evaluation were introduced and are further extensively analysed.