Optimal configuration of a three-rod ortho-bridge system in the treatment of Vancouver type B1 periprosthetic femoral fractures: A finite element analysis

Abstract

Introduction and Aim

Periprosthetic femoral fractures (PFF) represent an increasing clinical and economic burden. This study aims to determine the optimal configuration of a bridge-combined internal fixation system in the treatment of Vancouver type B1 PFF, using finite element analysis.

Materials and methods

A three-rod ortho-bridge system (OBS) fixation model was used to evaluate the optimal configuration of four target parameters: position of the third rod; intersection angle between the proximal screws; connecting rod diameter; and number of screws used. Femoral displacement and the maximum von Mises stress of the OBS were used as the evaluation indices, to analyze the PFF and to determine the optimal use of an OBS. For each parameter, various candidate options were tested.

Results

Finite element analysis revealed that the rate of femoral displacement and the maximum von Mises stress of the OBS were at a minimum when there was a 35 mm downward movement of the third rod from the baseline. Therefore, the optimal position of third rod fixation was 35 mm below the fovea capitis of the femur. The optimal intersection angles between the proximal screws were found to be 71.92° or 84°. A 6 mm diameter connecting rod proved to be most effective. Configuration d, utilizing 7 screws, represented the most clinically appropriate screw number configuration, despite configuration f, utilizing 9 screws, eliciting the best evaluation indices.

Conclusion

An OBS used in the above-described configuration is well suited to the characteristics of PFF and provides an effective and reliable means for their treatment.

Introduction

As the proportion of elderly people in our populations increases, so too does the incidence of hip-related injuries, often caused by falls in osteoporotic patients. The field of surgical orthopedics has largely been able to adapt and meet the increasing demands of an aging population, particularly with regards to patents requiring total hip arthroplasty (THA). The number of patients needing THA is expected to increase dramatically, rising by 174% reaching 572,000 procedures by 2030 in the United States alone.¹ However, as the number of THAs increases, a surge in new developments of surgical technology and best practice is also expected. One of the key objectives of this progression, will be to improve the quality of life of THA patients, by preventing recurrent injuries in cases that require invasive surgical management, with considerable recovery and rehabilitation times. In recent years, there has been an increase in post-THA complications, including periprosthetic femoral fractures (PFF).² Abdel et al. reviewed 32,644 patients undergoing primary THA and reported an incidence of 1.7% for intraoperative femoral fractures, and a cumulative postoperative risk for PFF of 3.5%.³ Further, a prediction model has demonstrated that the number of PFF will increase by an average of 4.6% per decade from 2015 to 2060,⁴ representing a high clinical and economic burden for the orthopedic community to tackle.⁵

The treatment of PFF is complex in most cases, due to the need to use fixed femoral prostheses (Vancouver type B1) and the generally poor baseline physical condition of the patients.⁶ An accurate classification of the PFF is essential when planning the surgical management of the artificial hip, and the Vancouver classification is currently the most widely used.⁷ The Vancouver B1 fracture is a stable prosthetic fracture, without bone loss, that is treated with internal fixation as the main treatment of choice.8, 9, 10 Khan et al. reviewed 6,131 PFF patients and reported a high risk of morbidity, with a 5-year mortality rate reaching 60% in the highest risk group.¹¹

Fixation using plates is the standard treatment modality, which can be combined with ring ligation, and can achieve the desired surgical result.12, 13, 14, 15 The advantages of using a locking compression plate in the treatment of PFF are related to the direct surgical exposure and visualization of the reduction. Disadvantages include the need for soft tissue dissection and the difficulty in obtaining bicortical screw fixation, given the occlusion presented by the THA intramedullary prosthesis. Locking compression plates can also be combined with minimally invasive plate osteosynthesis and adequality maintain bone vitality.¹⁶ Some authors further suggest additional methods, such as allogeneic bone plates and a minimum of 10 cortices of fixation.17, 18, 19, 20 The most common complications of these existing internal fixation methods include fixation failure and nonunion, with hold incidence rates of 4.4% and 3.9% respectively.²¹

An ortho-bridge system (OBS) is a composite structure composed of fixed connecting blocks, fixed connecting rods, and screws (see Fig. 1). The connecting block variations allow for targeted use and include single-sided single-hole, single-sided double-hole, double-rod single-hole, double-rod double-hole, and special-shaped blocks suited to specific anatomical locations. The fixed connecting rods can have variable diameters, and the screws can be either locking or standard. The OBS design concept allows for individualization, diversification, and systematization of internal orthopedic fixation by surgeons, which introduces the advantages of patient-specific modeling, free combination, three-dimensional fixation and elastic fixation. In this study, we analyze the biomechanical properties of an OBS used in the treatment of PFF, in order to determine the optimal configuration for its use, via finite element analysis.