Percutaneous Anterior Internal Pelvic Fixator

A novel internal fixation method for open book injuries of the pubic symphysis- A biomechanical analysis

BACKGROUND

Pelvic fractures in adults are common injuries and account for up to 3.64% of all fractures. Usually, the treatment of open book injuries (Types B1.1 and B1.2 AO-Classification) is open reduction and plate stabilization using dynamic compression plates, with or without interlocking screws. These implants seem to enhance the outcome of such injuries, but also variety of complications occurs. To reduce complications and achieve appropriate reduction and stabilization, this study compared established stabilization techniques to a novel minimally invasive internal fixation method using an internal fixator system that is already being utilized for spinal fractures.

METHODS

This study was performed on 32 composite pelvises in a bilateral stance biomechanical model. The pelvises were variously stabilized with an internal fixator, a 4.5 mm dynamic compression plate and a 3.5 mm symphyseal locking dynamic compression plate. The contact area and loading forces were assessed by a sensor film inside the symphyseal gap.

FINDINGS

This study showed significantly greater reduction and loading capabilities of the internal fixator compared to the other implants (p < 0.05). There was also significantly greater contact area with the use of an internal fixator compared to the other implants (p < 0.05). The 3.5 mm interlocking plate showed significantly greater contact area compared to the 4.5 mm plate (p < 0.05).

INTERPRETATION

The internal fixator that is already proven in spinal surgery is biomechanically superior to conventional implants used in pelvic surgery. The contact area analysis furthermore showed a more physiological loading pattern, which can improve ligamentous healing in a clinical context.

Treatment of type B pelvic fracture using anterior subcutaneous internal fixator with triple pedicle screws: a new surgical technique

INTRODUCTION

To evaluate the clinical outcomes of anterior subcutaneous internal fixator using triple pedicle screws (ASIF/TPS) in the treatment of unstable type B pelvic fracture compared with open reduction internal fixation (ORIF).

MATERIALS AND METHODS

This was a retrospective cohort study of 26 patients with type B unstable fractures that underwent ASIF/TPS and 26 similar patients that underwent ORIF using plates and screws. Intraoperative blood loss, operating time, and post operation hospitalization duration were compared. Anteroposterior, inlet, and outlet X-rays and 3D computed tomography were obtained. Pain, numbness, sexual dysfunction, and activity were evaluated at every follow-up visit until the implants were removed. The Majeed score was used to assess the clinical and radiological outcomes.

RESULTS

Blood loss, operating time, and hospitalization duration were less (all P < 0.001) in the ASIF/TPS group compared with the ORIF group. The clinical and radiological outcomes of the ASIF/TPS group after a mean follow-up of 6 months were excellent and good in 80.8%, and moderate in 19.2%. In comparison, the results of the ORIF group were excellent and good in 65.4%, moderate in 29.0%, and poor in 5.6%. No patient experienced nonunion, delayed union, superficial infection, or deep surgical wound infection. No urethral injury or dysuria occurred in the ASIF/TPS group. Two patients had temporary lateral femoral cutaneous nerve numbness after operation. There were two superficial wound infections in the ORIF group.

CONCLUSIONS

The use of ASIF/TPS with triple pedicle screws could be a reasonable option for the treatment of type B unstable pelvic fractures.

Biomechanical characteristics of fixation methods for floating pubic symphysis

Background

Floating pubic symphysis (FPS) is a relatively rare injury caused by high-energy mechanisms. There are several fixation methods used to treat FPS, including external fixation, subcutaneous fixation, internal fixation, and percutaneous cannulated screw fixation. To choose the appropriate fixation, it is necessary to study the biomechanical performance of these different methods. The goal of this study was to compare the biomechanical characteristics of six methods by finite element analysis.

Methods

A three-dimensional finite element model of FPS was simulated. Six methods were used in the FPS model, including external fixation (Ext), subcutaneous rod fixation (Sub-rod), subcutaneous plate fixation (Sub-plate), superior pectineal plate fixation (Int-sup), infrapectineal plate fixation (Int-ifa), and cannulated screw fixation (Int-scr). Compressive and rotational loads were then applied in all models. Biomechanical characteristics that were recorded and analyzed included construct stiffness, micromotion of the fracture gaps, von Mises stress, and stress distribution.

Results

The construct stiffness of the anterior pelvic ring was decreased dramatically when FPS occurred. Compressive stiffness was restored by the three internal fixation and Sub-rod methods. Unfortunately, rotational stiffness was not restored satisfactorily by the six methods. For micromotion of the fracture gaps, the displacement was reduced significantly by the Int-sup and Int-ifa methods under compression. The internal fixation methods and Sub-plate method performed well under rotation. The maximum von Mises stress of the implants was not large. For the plate-screw system, the maximum von Mises stress occurred over the region of the fracture and plate-screw joints. The maximum von Mises stress appeared on the rod-screw and screw-bone interfaces for the rod-screw system.

Conclusions

The present study showed the biomechanical advantages of internal fixation methods for FPS from a finite element view. Superior stabilization of the anterior pelvic ring and fracture gaps was obtained by internal fixation. Subcutaneous fixation had satisfactory outcomes as well. Sub-rod fixation offered good anti-compression, while the Sub-plate fixation provided favorable anti-rotational capacity.