Elsevier

The Spine Journal

Volume 16, Issue 2, February 2016, Pages 226-232
The Spine Journal

Basic Science
Primary stability of three different iliosacral screw fixation techniques in osteoporotic cadaver specimens—a biomechanical investigation

https://doi.org/10.1016/j.spinee.2015.08.016Get rights and content

Abstract

Background

The incidence of osteoporotic and insufficiency fractures of the pelvic ring is increasing. Closed reduction and percutaneous fixation with cannulated sacroiliac screws is well-established in the operative treatment of osteoporotic posterior pelvic ring fractures. However, osteoporotic bone quality might lead to the risk of screw loosening. For this reason, cement augmentation of the iliosacral screws is more frequently performed and recommended.

Purpose

The aim of the present biomechanical study was to evaluate the primary stability of three methods of iliosacral screw fixation in human osteoporotic sacrum specimens.

Study Design/Setting

This study used methodical cadaver study.

Methods

A total of 15 fresh frozen human cadaveric specimens with osteoporosis were used (os sacrum). After matched pair randomization regarding bone quality (T-score), three operation technique groups were generated: screw fixation (cannulated screws) without cement augmentation (Group A); screw fixation with cement augmentation before screw placement (cannulated screws) (Group B); and screw fixation with perforated screws and cement augmentation after screw placement (Group C). In all specimens both sides of the os sacrum were used for operative treatment, resulting in a group size of 10 specimens per group. One operation technique was used on each side of the sacral bone to compare biomechanical properties in the same bone quality. Pull-out tests were performed with a rate of 6 mm/min. A load versus displacement curve was generated.

Results

Subgroup 1 (Group A vs. Group B): Screw fixation without cement augmentation: 594.4 N±463.7 and screw fixation with cement augmentation before screw placement: 1,020.8 N±333.3; values were significantly different (p=.025). Subgroup 2 (Group A vs. Group C): Screw fixation without cement augmentation: 641.8 N±242.0 and perforated screw fixation with cement augmentation after screw placement: 1,029.6 N±326.5; values were significantly different (p=.048). Subgroup 3 (Group B vs. Group C): Screw fixation with cement augmentation before screw placement: 804.0 N±515.3 and perforated screw fixation with cement augmentation after screw placement: 889.8 N±503.3; values were not significantly different (p=.472).

Conclusions

Regarding iliosacral screw fixation in osteoporotic bone, the primary stability of techniques involving cement augmentation is significantly higher compared with screw fixation without cement augmentation. Perforated screws with the same primary stability as that of conventional screw fixation in combination with cement augmentation might be a promising alternative in reducing complications of cement leakage. These biomechanical results have to be transferred into clinical practice and prove their clinical value.

Introduction

Pelvic ring fractures are comparatively rare [1], with an incidence of 0.3–8%, and typically result from high-energy trauma [2]. Because of increasing life expectancy, the incidence of osteoporotic and insufficiency fractures of the pelvic ring is increasing [3], [4], [5], [6]. Osteoporotic fractures of the pelvic ring differ substantially from high energy fractures regarding symptoms as well as treatment. Even the patient's own body weight can be sufficient to produce such a fracture [7]. An extreme reduction of bone mass and overstressing of the already weakened bone lead to insufficiency fractures [8]. Insufficiency fractures of the sacrum are already described by Lourie et al. in 1982 [9]. Closed reduction and percutaneous fixation with cannulated sacroiliac screws is a well-established therapy in the operative treatment of osteoporotic posterior pelvic ring fractures [10], [11], [12]. If elderly patients with sacral insufficiency fractures suffer from a high pain level, this minimal invasive procedure can help to both reduce pain and to recover mobility [13]. Even in unstable sacral fractures, iliosacral screw fixation is used and can be combined with lumbopelvic fixation to achieve a high biomechanical stability [14], [15], [16]. To attain even greater stability for the transverse component, lumbopelvic distraction osteosynthesis is combined with iliosacral screw osteosynthesis, resulting in a clinically sufficient multiplanar stability [16]. However, osteoporotic bone quality might lead to the risk of screw loosening [7]. For this reason, cement augmentation of the iliosacral screws is more frequently performed and recommended [11], [17], [18]. Cement augmentation is often performed before screw placement [3]. Wähnert et al. developed a new method with perforated screws, which allows the application of cement after screw placement [19] to reduce possible complications such as cement displacement resulting in nerve compression or embolization [13].

Section snippets

Aim of the study

The aim of the present biomechanical cadaver study was to evaluate the primary stability of three methods of iliosacral screw fixation in human osteoporotic sacrum specimens. Our goal was to compare axial pull-out failure in the following three techniques: screw fixation without cement application, screw fixation with cement application before screw insertion, and screw fixation with a modified, perforated screw and cement application after screw positioning.

Specimens

A total of 15 fresh frozen human cadaveric specimens were used (os sacrum). Only women donors (mean age 81.47±9.04 years) were selected, and bone density was measured in all specimens separately, which showed substantial osteoporosis (mean T-score −4.45±1.73). Osteoporosis was defined according to the World Health Organization (WHO) criteria—bone mineral density of more than 2.5 standard deviations below the mean of a young healthy reference population of the same gender (T-score). A

Pull-out force

The mean maximum pull-out force was 618.1 N±390.7 in Group A, 912.39 N±471.5 in Group B, and 959.7 N±453.2 in Group C (see Fig. 3).

The following pull-out forces were measured in subgroups that compared two different techniques in the same specimens with respect to bone quality:

Discussion

Increasing life expectancy in the last decades is leading to a higher incidence of osteoporotic as well as insufficiency fractures of the pelvic ring [3], [4]. Trauma mechanisms as well as the resulting treatment differ from other types of pelvic ring fractures. The most common mechanism of those fractures is a low impact trauma [2], leading to severe pain and dysfunction [20]. Whereas many elderly patients are still active and have high functional demands, other elderly patients already suffer

Conclusions

Our conclusions to screw stability in fixation techniques are based on a biomechanical evaluation. Regarding iliosacral screw fixation in osteoporotic bone, the primary stability of techniques using cement augmentation is significantly higher compared with screw fixation without cement augmentation. Perforated screws with the same primary stability as that of conventional screw fixation in combination with cement augmentation might be a promising alternative in reducing complications of cement

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    FDA device/drug status: Investigational (modified [six 2.0 mm perforations over the first 1/2 of the thread] self-cutting lag screws made of titanium [aap Biomatterials, Dieburg, GmbH]).

    Author disclosures: LO: Consulting (Vexim, B), Consulting (DFine, A). AM: Nothing to disclose. CB: Nothing to disclose. FD: Nothing to disclose. SR: Nothing to disclose. AK: Consulting (Vexim, B), Consulting (DFine, A).

    The disclosure key can be found on the Table of Contents and at www.TheSpineJournalOnline.com.

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