Lumbopelvic fixation with S2 alar-iliac screws for U-shaped sacral fractures

A biomechanical study on bilateral SAI annular fixation in the treatment of unilateral Denis Ⅱ sacral fractures

PURPOSE

To investigate the biomechanical properties of bilateral SAI annular internal fixation in the treatment of unilateral Denis type Ⅱ sacral vertical fracture, so as to provide a reference for clinical practice.

METHODS

The finite element approach was utilized to simulate the Denis type Ⅱ fracture of the right sacral (the entire fracture through the sacral foraminarum) as well as the fracture of the upper and lower ramus of the right pubic bone, which represents unilateral vertical instability of the pelvic ring. The posterior pelvic ring was fixed using three different methods: lumbopelvic fixation and S1 transsacral screw (LPF-S1), bilateral S1AI annular fixation and S2 transsacral screw (BS1AI-S2), bilateral S2AI annular fixation and S1 transsacral screw (BS2AI-S1), and the anterior pelvic ring was fixed with pubic ramus screws. Six different loading methods are used to simulate six conditions: standing, forward bending, left flexion, right flexion, left rotation and right rotation. The maximum Von Mises stress of the implant, the vertical displacement of the upper surface of the sacral, and the relative intrafragmentary displacement (RID) of the observation point on the anterior surface of the sacral were recorded and analyzed.

RESULTS

The maximum Von Mises stress of the implant in the three fixed models did not exceed the maximum yield stress of the titanium alloy under different motion conditions in the finite element model. The descending order from high to low was LPF-S1, BS1AI-S2, and BS2AI-S1. The RID of each observation point on the anterior surface of the sacral and the vertical displacement of the upper surface of the sacral were both lower in the BS2AI-S1 group than in the LPF-S1 group and the BS1AI-S2 group. In the standing, forward flexion, left flexion, right flexion, and left rotation conditions, the LSD test results indicated a statistically significant difference in the mean RID of observation points between the BS2AI-S1 and BS1AI-S2 groups (p < 0.05), but not in the LPF-S1 group. In the condition of right rotational motion, there was no statistically significant difference in the mean RID between the three groups (p > 0.05).

CONCLUSION

The biomechanical stability of the fixation of Denis type II sacral fractures was satisfactory in the LPF-S1, BS1AI-S2, and BS2AI-S1 groups, with the BS2AI-S1 group exhibiting the maximum level of stability. Bilateral SAI annular internal fixation is a viable alternative to the fixation of vertical sacral fractures, as it does not impair the lumbar spine's mobility and accomplishes satisfactory biomechanical stability.

Traumatic lumbosacral instability: part 2-indications and techniques for surgical management

Traumatic lumbosacral instability (TLSI) refers to a traumatic disruption of the axial skeleton at the level of the lumbosacral motion segment and/or sacrum, resulting in mechanical separation of the caudal spinal column from the posterior pelvic ring. Managing TLSI and its four underlying conditions poses unique challenges among spinal and pelvic injuries. This second part of a two-part series focuses on treatment strategies and decision making in TLSI, with an emphasis on surgical stabilization techniques. The primary objectives of this article are to: (1) elucidate factors influencing clinical decision-making, (2) synthesize current treatment options for the injury patterns underlying TLSI, and (3) briefly outline expected outcomes and complications.

Implantation of S1AIS has priority as a sacroiliac joint fixation technique

PURPOSE

The sacral alar-iliac screw (SAIS) fixation technique has evolved from spinopelvic fixation which originated from S2AIS to sacroiliac joint fixation, with more reports regarding its application of S2AIS than S1AIS. However, there is a lack of comparative evidence to determine which technique is superior for sacroiliac joint fixation. This study aimed to determine which of the screws was superior in terms of implantation safety and biomechanical stability for sacroiliac joint fixation.

METHODS

CT data of 80 normal pelvises were analyzed to measure the insertable range, trajectory lengths and widths of both S1AIS and S2AIS on 3D reconstruction models. Φ 6.5 mm and 8.0 mm screws were implanted on the left and right sides of fifty 3D printed pelvic models respectively to observe for breach of screw implantation. Ten synthetic pelvis models were used to simulate type C Tile injuries, and divided into 2 groups with an anterior plate and posterior fixation using one S1AIS or S2AIS on each side. The stiffness and maximum load of the plated and fixated models were measured under vertical loading.

RESULTS

The trajectory lengths and widths of the S1AIS and S2AIS were similar (p > 0.05) and there was no breach for Φ 6.5 mm SAIS. However, both the insertable range and trajectory length on the sacral side of S2AIS (234.56 ± 10.06 mm2, 40.97 ± 2.81 mm) were significantly less, and the breach rate of the posterior lateral cortex of the Φ 8.0 mm S2AIS (46%) was significantly higher than the S1AIS (307.55 ± 10.42 mm2, 42.16 ± 3.06 mm, and 2%, p < 0.05). The stiffness and maximum load of S2AIS were less than S1AIS but the difference was not statistically significant (p > 0.05).

CONCLUSION

S1AIS and S2AIS have similar screw trajectories and stability. However, S1AIS has a larger insertable range, less breach of the posterior lateral sacral cortex and longer trajectory length on the sacral side than S2AIS, which indicates S1AIS has higher implantation safety and a trend of better mechanical performance over S2AIS for sacroiliac joint fixation. Furthermore, S2AIS with an excessively large diameter should be used with caution for sacroiliac joint fixation.

[Translated article] Spinopelvic dissociation: Current concepts

INTRODUCTION

Spinopelvic dissociation is an uncommon injury, but, at the same time, very serious, since it can associate important complications with high morbidity and mortality. Its low frequency means that the experience of the specialists who have to deal with it is often very limited.

OBJECTIVE

To analyze the treatment indications based in classifications and surgery techniques.

METHOD

A search for scientific articles from high-impact journals was performed through international databases, such as Pubmed, Cochrane Library, Scopus, Science Direct and OVID.

CONCLUSIONS

The management of the injury we are analyzing represents a challenge. The diagnosis is carried out through a meticulous anamnesis and physical examination, supported by imaging tests, where tomography acquires special relevance. The treatment is fundamentally surgical, reserved the conservative option for a few cases. Triangular fixation is nowadays considered the treatment of choice.