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Width of pubic symphysis relating to age and sex in Koreans

Introduction Diastasis of the pubic symphysis has been reported to occur in 13–16% of pelvic ring injuries. In Asians, there are only a few data showing the width of the pubic symphysis. The aim of this study is to see the width of pubic symphysis relating to age and sex in Koreans. Methods Width of pubic symphysis was measured in pelvis AP and pelvic CT of 784 peoples (392 males, 392 females). Results In supine AP, the width at the upper end was 4.8±2.5 mm (males; 3.46±1.38 mm, females; 4.04±2.76 mm). The width at the midpoint was 4.7±2.0 mm (males; 4.64±1.58 mm, females; 4.75±2.29 mm). The width at the lower end was 4.8±2.5 mm (males; 4.58±2.19 mm, females; 5.08±2.76 mm). In abducted AP, the width at the upper end was 3.8±2.9 mm (males; 3.65±1.50 mm, females; 3.97±3.85 mm). The width at the midpoint was 4.6±2.3 mm (males; 4.45±2.16 mm, females; 5.18±3.79 mm). The width at the lower end was 4.8±3.1 mm (males; 4.55±1.30 mm, females; 4.74±3.06 mm). In axial CT, the width at the anterior border was 15.0±6.2 mm (males; 14.50±6.62 mm, females; 16.44±6.22 mm). The width at the narrowest point was 3.1±1.5 mm (males; 3.19±1.53 mm, females; 3.09±1.50 mm). The width at the widest point was 4.1±1.6 mm (males; 4.27±1.60 mm, females; 4.00±1.50 mm). The width at the posterior border was 2.3±1.3 mm (males: 2.20±1.30 mm, females; 2.44±1.40 mm). Axial thickness was 27.1±5.3 mm (males; 29.48±4.60 mm, females; 24.70±4.82 mm). In coronal CT, the width at the upper end was 3.1±4.1 mm (males; 2.28±1.26 mm, females; 3.83±5.48 mm). The width at beginning of widening was 3.6±4.5 mm (males; 2.68±1.63 mm, females; 4.54±6.08 mm). The width at the lower end was 20.5±8.2 mm (males; 17.49±4.53 mm, females; 23.60±9.86 mm). Coronal thickness was 20.4±7.1 mm (males; 24.50±5.98 mm, females; 16.23±5.61 mm). In supine film, width significantly increased with age at the upper end (p=0.022) and midpoint (p< 0.001); however, it decreased at the lower end (p< 0.001). In abduction film, width at midpoint increased with age (p=0.003). Conclusion Pelvic malunion should be defined according to the population and age. These results could be a reference in assessing the quality of reduction after internal fixation of the patients with traumatic diastasis of the pubic symphysis. Supplementary Information The online version contains supplementary material available at 10.1186/s13018-021-02561-9.


Introduction
Diastasis of the pubic symphysis is one type of pelvic injury and has been reported to occur in 13-16% of pelvic ring injuries and occur following a high-velocity force such as road traffic accidents and particularly in those involving motorcyclists, horse riding, crush injuries, and falls from a height [1,2].
Techniques for managing traumatic diastasis of the pubic symphysis include bed rest, hip spica casting, pelvic slings, external fixation, and internal fixation [3].
The common hardware complications are infections, loosening, small particle disease/osteolysis, periprosthetic fracture, hardware fracture or dislocation, and recurrent disease, especially in patients with tumors [4]. Assessing the quality of reduction, fixation failure has been defined as either plate/screw loosening or breakage that resulted in a loss of postoperative reduction. Anatomically, the adductor longus and rectus abdominis are attached to the capsule and disk of the symphysis pubis which causes the pubic diastasis in injury [5]. The pelvic malunion has been defined as greater than 5-mm of displacement of the hemipelvis and pubic symphysis in a nonanatomic position, whether in a rotational or translational fashion [6].
Measuring adult cadavers, Loeschcke (1912) calculated mean joint widths to be 5 mm in men, 7.5 mm in nulliparous women, and 20 mm in multiparous women, but precise details of how these measurements were taken are lacking [7].
In Asians, however, there are only a few data showing the width of pubic symphysis [8,9]. Since the cartilage is removed in internal fixation, difficulties remain in assessing the quality of reduction after internal fixation of the patients with traumatic diastasis of the pubic symphysis.
We thought if we could show the changes in pubic symphysis width in distinct age-and gender-dependent plots, they could serve as standards of comparison to detect pathologic or posttraumatic changes in each age and sex group.
The aim of this study is to see the width of pubic symphysis relating to age and sex in Koreans.
The radiological images were obtained from an electronic image repository of Inha University Hospital, Incheon, Korea.

Standard process taking images
For Pelvis AP in abduction, both femurs were abducted 60 degree and knees were flexed to face each sole together in supine position. Position was held to have symmetrical obturator foramens and iliac crests. For coronal and axial CT of the pubic symphysis, subjects were laid in supine position with both anterior superior iliac spines in the same level. Coronal view includes from the 4th lumbar spine to the lesser trochanter of the femur. The DICOM files from the electronic image repository were used. Measurements were not performed in 504 samples of abduction AP, 286 of axial CT, and 8 of coronal CT.

Measuring methods
Two researchers measured the width of the pubic symphysis in pelvis AP and pelvis CT (Fig. 1).

Pelvic CT, axial view
Measured level: where anterior border and posterior border can be seen (S1 level) This study adhered to the principles outlined in the Declaration of Helsinki. Informed consent was obtained from all subjects or, if subjects are under 18, from a parent and/or legal guardian.
The independent two-sample t-test was used for comparisons between males and females. Simple linear regression analysis was used to evaluate linear correlations among age groups. P values < .05 were considered to indicate statistical significance. SPSS version 25 (IBM Corp., Armonk, NY, USA) was used for statistical analysis.

Length from anterior border to the narrowest point (LAN)
Mean LAN was 7.0±2.4 mm (Fig. 2). There was no significant difference between males (7.22±2.46 mm) and   Table 3). There were significant no differences among the age groups (p= 0.169) ( Table 4). There was no significant difference with aging (p=0.112) (Fig. 3).
Length from the beginning of widening to the lower end (LWL) Mean LWL was 5.0±2.9 mm (Fig. 2). LWL was significantly wider in males (5.91±3.03 mm) than females   Table 3). There were significant differences among the age groups (p=0.007) ( Table  4). There was no significant difference with aging (p= 0.805) (Fig. 3).

Comparison of pelvis AP and pelvis CT
Width of pubic symphysis at the upper end (WU) of supine film differed significantly from that of hip abduction film or coronal CT (p < 0.001). Coronal CT was lesser than supine film and hip abduction film. Width of pubic symphysis at the lower end (WL) of supine film differed significantly from that of hip abduction film or coronal CT (p< 0.001). Coronal CT was greater than supine film and hip abduction film.

Discussion
In supine pelvis AP, the width of pubic symphysis significantly increased with age at the upper end and midpoint (SWU: p=0.022, SWM: p< 0.001). However, the width of pubic symphysis significantly decreased with age at the lower end (SWL: p< 0.001). In hip abduction pelvis AP, the width of pubic symphysis at the midpoint (HWM) significantly increased with age (p=0.003).
In axial CT, the width of pubic symphysis at the anterior border (AWA) significantly decreased with age (p= 0.002). However, the width of pubic symphysis at the posterior border (AWP) did not change significantly with age (p=0.094). In coronal CT, like supine film, the width of pubic symphysis significantly increased with age at its entire length (upper end, CWU: p< 0.001; beginning of widening CWW: p=0.012; and lower end, CWL: p< 0.001). Also, the length from the upper end to the beginning of widening (LUW) significantly increased with age (p=0.039).
The pelvic malunion has been defined as greater than 5-mm of displacement of the hemipelvis and pubic symphysis in a nonanatomic position, whether in a rotational or translational fashion [6].
Since the width of pubic symphysis significantly increased with age at its entire length, we do think that pelvic malunion should be defined according to the population and age. The fixation failure is thought to be due to the intimate relationship between the adductor longus; rectus abdominis; and symphyseal cartilage, disk, and capsular tissues. The adductor longus and rectus abdominis are attached to the capsule and disk of the pubic symphysis. All adductor tendons are attached to the pubis [5].
A study invested structural organization of the mineralized cartilage of human pubic symphysis and found mineralization of cartilage is intermittent from 20 to 29 years, amount of gaps becomes less by 40-49 years and becomes intermittent again at the age of 70-79 years. In elderly and senile people, mineral plates of complex configuration appear in the interterritorial matrix and chondrocyte capsules; by the age of 87, there appear thick highly mineralized bundles of collagen fibers [10]. It is notable that in middle-age group, the amount of gap becomes less coincides well with our results (4.0±1.6 mm, lesser than 21-40 group or 61-100 group) (Supplement Table 1).
Mean widths determined by imaging studies of 130 non-pregnant women yielded 2.6 mm [11]. While 12.58±4.48 mm was measured at the most anterior part of the joint in women who had on average given birth to three children [12]. Alicioglu, in the single CT study, did not find any relationship between symphyseal width and parity or body mass index [12].
Comparing our X-ray data with Loeschcke, Caucasians (German) women have wider pubic symphysis than Korean women (p< 0.001). However, there was no significant difference between Caucasian men and Korean men (p=0.0951).
Comparing the bony pelvis of European American women (EA) and Korean women (Kor) from the literatures [13,14], European women have larger interspinous distance (EA: 104±9 mm, Kor: 94.0±7.2 mm, p< 0.001) and intertuberous distance (EA: 133.5±9.6 mm, Kor: 97.7± 10.1 mm, p< 0.001) than Koreans. From this, it is thought that the wider pubic symphysis in German women than Korean women is due to the larger pelvis size of Germans.
Comparing our CT data with Alicioglu [12], Koreans have a wider anterior border (p< 0.001) but, however, narrower posterior border (p< 0.001) than Turkish (Table 5). In this study, we could see that Koreans have a narrower pubic symphysis than Caucasians.
Recently, the elastic band has been used in the management of obstetric pubic symphyseal separation. Once the elastic band device was in place, on postpartum day 1, radiography showed a decrease of the pubic width from 41 to 12 mm. Use of an elastic band device was associated CT computed tomography, USG ultrasonography, P p value, each p value is compared with the present study, M male, F female, AWA width of pubic symphysis at the anterior border, AWP width of pubic symphysis at the posterior border, AWN width of pubic symphysis at the narrowest point with a reduction of the pubic width and pain associated after obstetric pubic symphysis separation [16]. Our present data can be a baseline to the evaluation of the effect of the management of pubic diastasis as obstetric separation.
In the present study, we did not analyze the inter-observer and intra-observer errors. However, two experienced researchers with such image assessment (two surgeons) were involved in order to reduce these errors [17]. We could not analyze the parity of the women (nulliparous or multiparous) included, and this is the limitation of the study.
Pelvic malunion should be defined according to the population and age. The results of this study can be a practical reference in assessing the quality of reduction after internal fixation of the patients with traumatic diastasis of the pubic symphysis. Further study is needed to introduce a new guideline for the pelvic diastasis according to age, sex, and population.
Additional file 1:. Supplemental Table 1. Comparison of age-related change of pubic symphysis.