The value of Gissane's angle in the population of central Serbia

Background / Aim. Determining the value of Gissane?s angle (GA) plays a role
 in diagnosis and prognosis of heel fractures, determining treatment methods
 and assessing the outcome of surgical treatment. Normal values of the GA
 vary in relation to ethnicity, age and gender of the examined group, which
 indicates its anthropometric significance. The aim of this study was to
 determine the range of normal GA values in the population of Central Serbia.
 Methods. GA was determined on lateral radiography of the foot of 145
 subjects, both sexes (67 women and 78 men), with subjects divided into 6 age
 groups. The patients included in the study did not have a calcaneus
 fracture. The obtained results were processed in the Graph Pad program. 
 Results: The average value of GA in Serbia was 110.8? ? 8.1, ranging from
 93? to 132.9?. The mean value of GA decreased with age, and no difference
 was observed between women and men, except in the youngest age group were
 women had higher GA values than men. Conclusion. The results of the study
 showed a wide range of normal GA values, as well as the existence of a
 difference in subjects of different age and sex.


Introduction
The calcaneus, the heel bone, is the largest tarsal bone, whose role is to provide stability and maintain a high degree of whole-body pressure 1 . All fractures of the calcaneus can be divided into extra-articular and intra-articular, totaling 2% of all bone fractures, as well as 75% of tarsal bone fractures 1,2 . Fractures occur most often due to a fall from a height, and in most cases in the younger adult population aged 21-45 3 . The morphometric dimensions of the calcaneus show ethnic heterogeneity and in addition may influence the plan of surgical treatment after injury 4 . Depending on the study, different normal values were reported: 95-105º, 96-152º, 100-130º, 120-145º 5 . The diagnosis of fractures is made on the basis of lateral and anteroposterior radiographs of the foot 6 . Radiographs of the foot provide accurate information about calcaneus morphology and angular relationships, and are therefore the method of choice in measuring the value of GA 7 . Imaging methods play a major role in the diagnosis of calcaneus fractures, so radiological measurement of Gissane angle values together with Bohler angle values is an important parameter both in the diagnosis and in the treatment and prognosis 8 . However, it should be emphasized that they cannot be used as an independent criterion when choosing a method of treatment and diagnosis, and that in addition to measuring calcaneal angles, it is necessary to determine the severity and location of fractures as well as dislocation of fragments, insight to which these angles do not provideError! Reference source not found. 9 . Gissane"s angle, (also known as critical angle, critical angle of Gissane) is named after Dr. William Gissane Images were analyzed from radiographies taken for medical indications. The population in which the calcaneus fracture was not present was included in the study. Also, the population under 10 years of age was not included, considering that the calcaneus completes its development after the tenth year of life. The values were measured by two observers, independently of each other, and the measurement was repeated after two weeks, in order to reduce the error.
Results are presented as mean ± standard deviation (SD). The obtained results were analyzed using Sigma Plot 12.0 (Systat Software) statistical program. As data had normal distribution and equal variance, as asserted by Shapiro-Wilk and equal variance tests, respectively, appropriate parametric test was used. Data were analyzed by the two-way analysis of variance (ANOVA) followed by Holm-Sidak posthoc, with factors "sex" and "age". Significance was accepted at p < 0.05.

Results
The Gissane"s angle was examined in 145 subjects, both sexes, divided into 6 age groups.
The mean GA value in the whole examined group was 110.3º ± 8.4, in the range from 93º to 132.9º. In the group of female subjects the measured angle averaged 110.9º ± 8.9 in the range from 93º to 132.9º, while in male subjects its value was on average 109.9º ± 8.1 while the range was from 93.8º to 132º. There was no statistically significant difference between males and females (p = 0.0213).
The GA value was also compared in different age groups. The youngest age group (respondents aged 10-20) had the highest mean value of the measured angle, which was expected due to the characteristics of the heel bone in the adolescent period. GA shows a tendency to decrease with age, and accordingly, the lowest values were observed in subjects older than 60 years. Differences between group mean values were shown between the 10-20 years and 21-30 years groups and all older groups ( Figure 2A).
Additionally, when age groups were separated by gender, a significant difference was found within the youngest group (10-20 years), with females having significantly larger angles (123.9º ± 6.5) compared with males (118.2º± 9.2), as shown in Figure 2B.

Discussion
On the lateral radiography of the foot, facies articularis anterior and posterior calcanei form a crucial angle or the Gissane"s angle. During the action of excessive axial compression forces, a calcaneus fracture occurs, when talus process acts as a "wedge", disrupts the bone between anterior and posterior articular surface12 12 of the calcaneus as well as underlying Ward neutral triangle leading to even bigger displacement or depression of fragments. All this leads to changes in values of Gissane and Böhler angles.
Since the calcaneus is the most vulnerable tarsal bone 8  Our study has shown a wide range of normal GA values, which coincides with previous research done on this topic [11][12][13] . The average value of GA in the examined population of obtained in the population of Serbia were lower than the values of most previously obtained results in various populations 5,8,9,12,14 . We did not observe significant differences among genders in GA values of the whole study group, similar to findings in previous studies done in Turkey, Saudi Arabia, Egypt and Brazil 5,11,12 . The radiological study conducted in Brazil did not show a statistically significant difference in the value of GA between the subjects of different sexes, as well as among subjects of different age groups, and the values that they reported (110.6º ± 11.9) were similar to those in our study 111 . The mean values of the measured angle in the Egyptian population were higher (122.9º ± 6.52) 12 . In Serbian population, clear differences in GA values were observed between the examined age groups. Unlike our research, where the highest GA values were measured in the youngest group (10-20 years), in Egyptian study highest value has been found in the age group of 41-50 years 12 . In the population of Egypt, the lowest values were measured in people aged 51-60 12 , while we observed a linear decline in GA values among the age groups, with lowest values measured in people older than 60.
We also analyzed data from two studies performed in India. In the first study, the value of GA was measured in the population of South India and it was on average lower (108.5º) than in Serbian population 8 . In another study, which involved subjects from all regions in India, average GA values were measured at 126.72º, thus higher than those in our study 33 .
Neither of these two studies found an association between the value of the measured angle and age or sex 3,8 .
A similar retrospective study was also conducted in South Korea using cadaveric calcaneus and digital goniometer for estimation of calcaneal angles. The mean value of GA was 114º ± 8.2, thus values were higher than in our study. In this study, a statistically significant difference was shown between the values obtained in the female population (112.5º ± 8.1) and the male population (117.7º ± 7.4) 14 . In our study, the difference between males and females was present only in the youngest age group, and it was oppositefemales had larger angles than males. GA of the population of Serbia is higher compared to the populations of Japan and Thailand where the mean GA value was 105.1° ± 7.5 15 . Similar mean GA values were obtained in a study conducted in Nigeria (116.29º ± 8.29), Turkey (115º ± 6.5) and Saudi Arabia (116.16º) 5,13,16 . None of these studies demonstrated a significant difference between the results obtained in males and females.
In studies conducted in Turkey and Saudi Arabia, the value of GA was measured on both lower extremities and no statistically significant difference between the left and right side was shown 5,13 .
The lowest GA values of all previously published research on this topic were reported among the population of Kwara, where a significant difference was also found in the values of the measured angle on the right and left foot (right foot: 63.94º ± 20.58; left foot: 80.23º ± 26.68) 17 . In this study, too, there was no difference between the sexes 17 Table 1.
When diagnosing a calcaneus fracture, it is important to know that GA values may be enlarged due to this injury 19 , whereby maintaining normal GA values is a good prognostic sign, therefore such patients are considered to have a better long-term outcome 20 .
Conservative treatment is usually recommended for extraarticular fractures, while intraarticular fractures should be treated surgically, where one of the goals is to return GA to the normal, pre-injury range 19 .
One of the study limitations is that the measurements were performed on one foot only. In available studies among Caucasians no significant difference was published comparing left and right feet calcaneal angles values. However, some authors recommend the use of lateral radiographies of the contralateral foot while planning operative procedures 3 .

Conclusion
The range of normal Gissane angle values varies in different populations, which was confirmed in this study as well. A statistically significant difference in GA in the Serbian population in relation to the age of the respondents was also shown. The results obtained  Asterisk marks significant differences in group mean values (p < 0.05; t-test); yyears.