Elsevier

Injury

Volume 48, Issue 7, July 2017, Pages 1714-1716
Injury

Technical Note
Defining the pubic symphysis angle with respect to the coronal plane — Clinical and biomechanical considerations

https://doi.org/10.1016/j.injury.2017.04.056Get rights and content

Abstract

Background

Fixation strength of constructs placed across the pubic symphysis after injury is dependent on screw length, maximisation of which requires knowledge of the bony anatomy. The aim of this study was to describe the ideal angle of drilling to achieve maximal safe screw placement within the pubic body. Furthermore, the influences of age and gender on the skeletal topography were investigated.

Methods

Three hundred CT scans of patients without pelvic injury were analysed to record the angle of the pubic body (APB) with respect to the coronal plane, and the depth of the pubic body (DPB) in the sagittal plane.

Results

Mean APB and DPB were 54.69° and 55.35 mm, respectively. Females had a significantly higher mean APB than males (57.29° vs. 52.41°; p < 0.001), whereas males had a significant larger mean DPB (59.13 mm vs. 51.03 mm; p < 0.001). Age had no effect on the mean APB. Mean width of the pubic body at the base was 9.38 mm.

Conclusion

The anatomy of this region is reliable in terms of angles and sizes; a drill angle of 55° with respect to the operating table will allow maximal screw length, which should be in the region of 55 mm. The mean width of the pubic body should allow for placement of a 3.5 or 4.5 mm diameter screw.

Introduction

Surgical management of pubic symphysis injuries has become the gold standard treatment for injuries with any rotational instability. Stabilisation of the anterior pelvic ring enhances overall pelvic stability and maintains reduction while permitting mobilisation of the patient [1]. Although external and internal fixation have been shown to achieve similar success in restoring anterior pelvic stability [2], [3], [4], internal fixation has clear advantages in regards of infection risk, patient comfort and acceptance; as a result it is more commonly employed. However, open reduction and internal fixation of the pubic symphysis is shown to be associated with significant rates of implant failure, 12–31%, and loss of reduction, 7–24% [5], [6], [7].

Despite the fact that late fixation failures are only infrequently clinically important [8], [9], there have been different methods discussed to improve fixation strength and prevent the deleterious effects of early loss of reduction. Still, conventional multi-hole plating of the pubic symphysis is the most widely used method and seems to be the most reliable [1], [10], [11], [12], [13].

Fixation strength of plates placed across the pubic symphysis is dependent on the rigidity of the plate and on screw purchase within the bone. Screw purchase, furthermore, is determined in part by screw geometry and bone density; in addition, screw length is one of the major factors effecting fixation strength that may be influenced by the surgeon [14], [15].

Because of the shape of the pubic symphysis and its limited exposure during surgery, maximisation of screw length requires knowledge of the bony anatomy. In addition, screw perforation beyond the cortex carries risks of damage to the surrounding structures, most notably the bladder or urethra. To our knowledge, the ideal screw direction has yet to be defined in terms of anatomy and biomechanics. The aim of this study was to describe the ideal angle of drilling to achieve maximum screw length and safe screw placement within the pubic body. Additionally, the effects of age and gender on the skeletal topography were investigated.

Section snippets

Patients and methods

A database with all pelvic CT scans of a tertiary hospital was reviewed, and 300 consecutive pelvic CT scans were identified, using only patients that had not presented with pelvic trauma.

Data were analysed on the sagittal CT slices to record the angle of the pubic body (APB) with respect to the coronal plane, and the depth of the pubic body (DPB) in the sagittal plane (Fig. 1). Also, we measured the width of the pubic body at the base, which was seen to be the thinnest part. These measurements

Results

Data from 300 CT scans were included into the study. Within this study population 140 (46.7%) were female and 160 (53.3%) male. Mean age was 66.71 ± 19.07 years (range 17–99).

The mean angle of the pubic body (APB) and depth of the pubic body (DPB) were 54.69° ± 6.23 and 55.35 mm ± 6.56, respectively. Females had a significantly higher mean APB of 57.29° ± 6.44 than males with 52.41° ±5.06 (p < 0.001)(Fig. 2), whereas males had a significant larger mean DPB (59.13 mm ± 5.86 vs. 51.03 mm ± 4.25; p < 0.001)(Fig. 3).

Discussion

Sufficient and safe screw placement is a challenge when fixing the pubic symphysis due to its limited exposure during surgery. In daily practise, some surgeons try to improve their aim by placing a finger alongside the posterior aspect of the symphysis to get an idea of its tilt. Alternatively, Kirchner wires may be placed anterior and posterior of the pubis. However, the oval section of the pubis in the sagittal plane may be misleading for both methods. Anticipation of an average ideal screw

Conclusion

In terms of angles and sizes the anatomy of the pubic symphysis is consistent across the age and sex spectrum. Drilling an angle of 55° with respect to the operating table will allow maximal screw length, which should be in the region of 55 mm.

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